MANUFACTURING SCIENCE S5ME -NITC-2016

Some basics - you had in FoundrySand casting.Sand casting.

Steps: » 1.Mechanical Drawing of the part» 2. Making pattern- about pattern material.» 3.Making cores- if needed» 4.Preparing drag and cope. (Setting the core, positioning etc.)» 5.Removal of pattern» 6Assembling cope and drag» 7.Pouring- factors, method, etc.» 8.Casting removed» 9.Trimming etc.» 10. READY FOR SHIPMENT

1.Mechanical Drawing of the part

2. Making pattern- about pattern material.

3.Making cores- if needed

4.Preparing drag and cope. (Setting the core, positioning etc.)

5.Removal of pattern

6Assembling cope and drag

7.Pouring- factors, method, etc.

8.Casting removed

9.Trimming etc.

10. READY FOR SHIPMENT

Some basics you had in Foundry

5b 6 8&9 10

3b 3c3a

CASTINGCASTING FUNDAMENTALS FUNDAMENTALS

Basically involves

i. Pouring molten metal into a mould patterned after the part to be made WITHOUT TURBULANCE , SERIES OF EVENTS TAKES PLACE

INFLUENCE SIZE, SHAPE, UNIFORMITY OF THE GRAINS FORMED, AND THUS THE OVERALL PROPERTIES.

• ii. Allow it to cool HEAT TRANSFER DURING SOLIDIFICATION

• iii. Remove from the mold INFLUENCE OF THE TYPE OF MOULD MATERIAL

• SIMILARITY WITH POURING CAKE MIX INTO A PAN SIMILARITY WITH POURING CAKE MIX INTO A PAN

POURING CAKE MIX INTO A PAN (MOULD) & BAKING IT *SELECT THE KIND AND SIZE OF PAN,

*CONTROL THE COMPOSITION OF THE MIX,

* CAREFULLY POUR THE MIX,

* SET THE PROPER BAKING TEMPERATURE,

* SET THE TIMER FOR PROPER BAKING TIME,

* LEAVE THE CAKE IN THE MOULD FOR A CERTAIN AMOUNT OF TIME BEFORE REMOVING.

(CASTING OF PLASTICS & CERAMICS - DIFFERENT)

Knowledge of certain fundamental relationships is essential to produce good quality economic

castings

This knowledge helps in establishing proper techniques for mould design and casting practice.

Castings must be free from defects, must meet the required strength, dimensional accuracy, surface

finish

Outline of production steps in a typical sand casting operation

- pattern making - Core making - Gating system

Moulding

Sand Mould

Melting Pouring casting Heat Treat Clean Inspect

Furnaces Solidification Shakeout Addl. Heat Treatment

Defects, pressure tightness, dimensions

ADVANTAGES OF CASTING PROCESS• Process is cheap• More suitable for mass production• Most suitable for manufacturing

complex/complicated/intricate shaped products.• Large parts weighing several tonnes and also small

components weighing a few grams can be cast. • No limitation on the size of component.• Directional properties absent in castings. Components with

uniform properties as well as with varying properties at different locations can be cast.

• By use of cores, saving in machining of holes achieved.• Internal stresses are relieved during solidification in many

types of castings.• Even some materials which cannot be made by other

processes made by casting: eg. Phosphor-Bronze.

DISADVANTAGES• Cast product properties inferior in many

cases when compared with other manufacturing processes.

• Elevated temperature working in castings, as material has to be melted.

• Thin section limitations exist.• For number of components very small,

casting not preferred.

SIGNIFICANT FACTORS-

•TYPE OF METAL,

•THERMAL PROPERTIES OF BOTH THE METAL AND MOULD,

• GEOMETRIC RELATIONSHIP BETWEEN THE VOLUME AND SURFACE AREA ,AND

•SHAPE OF MOULD.

• SOLIDIFICATION OF METALS

• AFTER POURING MOLTEN METAL INTO MOULD, SERIES OF EVENTS TAKES PLACE DURING SOLIDIFICATION AND COOLING TO AMBIENT TEMPERATURE.

• THESE EVENTS GREATLY INFLUENCE

THE SIZE, SHAPE, UNIFORMITY OF THE GRAINS FORMED, AND THUS THE OVERALLL PROPERTIES.

Volumetric variation from Liquid through Solidification and then to ambient temperature

The liquid Metal has a Volume "A”

It solidifies to solid with a new volume "B"

The solidified casting further contracts (shrinks) through the cooling process to Volume "C"

Three Stages of Contraction (Shrinkage)

COOLING CURVE For pure metal or compound

TEMPERATURE

TIME, log scale

Freezing begins Freezing ends

Liquid

SolidSolid

Cooling of Liquid

Cooling of solid

Latent heat of solidification

given off during

freezing-

At constant temperature

COOLING CURVE For Binary solid solutions

TEMPERATURE

TIME, log scale

Freezing with drop in temperature

And FOR ALLOYS:Alloys solidify over a range of temperaturesBegins when temp. drops below liquidous, completed when it reaches solidous.Within this temperature range, mushy or pasty state.

Inner zone can be extended throughout by adding a catalyst.- sodium, bismuth, tellurium, Mg (or by eliminating thermal gradient, i.e. eliminating convection. (Expts in space to see the effect of lack of gravity in eliminating convection)

(refresh dendritic growth- branches of tree, interlock, each dendrite develops uniform composition, etc)

The ambient temperature is always in a state of transition Minor variations in volumetric displacement are negligible,compared to the variations that occur from "A" to "B" and lastly to "C". A

STRUCTURE

FOR PURE METALSFOR PURE METALS:: At the mould walls, metal cools rapidly. Produces

solidified skin or shell (thickness depends on composition, mould temperature, mould size and shape etc)

• These of equiaxed structure.• Grains grow opposite to heat transfer through the mould• These are columnar grains• Driving force of the heat transfer is reduced away from

the mould walls and blocking at the axis prevents further growth

Solidified structures of metal - Solidified structures of metal - solidified in a square mouldsolidified in a square mould

(a). Pure metal(b). Solid solution(c). When thermal gradient is absent

within solidifying metal

Development of a preferred texture Development of a preferred texture - for pure metal at a cool mould wall. - for pure metal at a cool mould wall.

A chill zone close to the wall and then a columnar zone away from the mould.

Three basic types of cast structures-

(a). Columnar dendritic;

(b). equiaxed dendritic;

(c). equiaxed nondendritic

Size and distribution of the overall grain structure throughout a casting depends on rate & direction of heat flow

(Grain size influences strength, ductility, properties along different directions etc.)

CONVECTION- TEMPERATURE GRADIENTS DUE TO DIFFERNCES IN THE DENSITY OF MOLTEN METAL AT DIFFERENT TEMPERATURES WITHIN THE FLUID - STRONGLY EFFECTS THE GRAIN SIZE.

Outer chill zones do not occur in the absence of convectionOuter chill zones do not occur in the absence of convection

DIRECTIONAL SOLIDIFICATION

Atm.Pressure

Pouring basin

LIKE A PRESSURISED SYSTEM

MOULDING BOARDFLASKSHOWELDRAW SPIKERIDDLESLICKRAMMERLIFTERSTRIKE-OFF BARTROWELS GATE CUTTER BELLOWSSPRUE PINS VENT ROD …..

MOULDERS’TOOLS

AND EQUIPMENT

Making a Core; (a). Ramming Core Sand. (b). Drawing the core box

(c). Baking in an oven (d) Pasting the core halves

(e). Washing the core with refractory slurry

1. Make the pattern in pieces, prepare the core.

2. Position the drag half of pattern on mould board in the drag half of flask

3. Prepare the drag half of mould, roll drag over, apply parting sand, place the cope half of pattern and flask, ram and strike off excess sand

4. Separate flasks, remove patterns, cut sprue, set core in place, close flask

5. Now after clamping, ready fro pouring.

THREE BOX MOULDING PROCEDURE

LOAM MOULDING USING LOAM SAND

Design of Risers and Feeding of Castings• A simplified diagram by putting in

references to the equations (1, 2 & 4) there is no Equation 3, diagram not changed

• EQ(1) - Freeze Point Ratio (FPR)

FPR=X X = (Casting Surface/Casting Volume) /

(Riser Surface/Riser Volume)

• EQ(2) - Volume Ratio (VR) (Y Axis)

VR=Y=Riser Vol/Casting Vol*Note: The riser volume is the actual poured

volume

References - AFS Text Chapter 16; Chastain's Foundry manual Vol 2, Google

• EQ(4) - (Freeze Point Ratio) Steel

X=0.12/y-0.05 + 1.0**The constants are from experiments and are empirical

Volumes, Surface Areas, Castings and Risers...

There are relationships between all these items and values that will help in designing a complete mold that controls progressive solidification, and influences directional solidification to produce castings with minimal porosity and shrinkage defects.

This is by ensuring that the riser(s) are the

last to solidify.

4 points about the Riser/Casting Relationship

• 1 - Risers are attached to the heaviest sections of the casting

• 2 - Risers are the last to solidify

• 3 - A casting that has more than one heavy section requires at least one riser per heavy section

• 4 - Occasionally the thermal gradient is modified at the mold-metal interface by the introduction of a "Chill" that can better conduct the heat away from the casting and lower the solidification time for that section.

Gating / Runner Design• A look at the flow characteristics of the metal as it

enters the mold and how it fills the casting.

Of the flow characteristics fluidity/viscosity plays a role. Also,

velocity, gravitational acceleration & vortex, pressure zones, molten alloy aspiration from the mold and the momentum or kinetic energy of a fluid.

The demarcation point is

Re < 2000 is considered a Laminar Flow Re > 2000 is considered a Turbulent Flow

Objective is to maintain Re below 2000.

LAMINAR FLOW- REFERENCE

TURBULENT FLOW- REFERENCE

SEVERELY TURBULENT FLOW

Basic Components of a Gating System• The basic components of a gating system are: Pouring Basin, Sprue, Runners and Gates that feed the casting.

The metal flows through the system in this order.

Some simple diagrams to be familiar with are:

"Crucible-Mold Interface" is where the metal from the crucible first contacts the mold surface. This area is lower than the area where the Mouth of the Sprue is located.Metal flow will be less chaotic than pouring from the crucible down into the sprue."Dross-Dam" - to skim or hold back any dross from the crucible or what is accumulated through the act of pouring. As the lower portion fills and the metal is skimmed, the clean(er) metal will rise up to meet the opening of the sprue in a more controlled fashion.

Pouring Basin - This is the "Crucible -Mold Interface", A pouring cup and pouring basin are not equivalents, The pouring cup is simply a larger target when pouring out of the crucible, a Pouring Basin has several components that aid in creating a laminar flow of clean metal into the sprue.The basin acts as a point for the liquid metal to enter the gating system in a laminar fashion.

Sprue Placement and PartsThe sprue is the extension of the sprue mouth into the mold

The choke or narrowest point in the taper is the point that would sustain a "Head" or pressure of molten metal.

From the Pouring Basin, to reduce turbulence and promote Laminar Flow, the flow begins in a near vertical incline that is acted upon by gravity and with an accelerative gravity force

Fluids in free fall tend to distort from a columnar shape at their start into an intertwined series of flow lines that have a rotational vector or vortex effect (Clockwise in the northern hemi-sphere, and counter clockwise in the southern hemi-sphere).

• The rotational effect, though not a strong force, is causing the cork-screwing effect of the falling fluid.

• If allowed to act on the fluid over a great enough duration or free fall the centrifugal force will separate the flow into droplets.

• None of the above promotes Laminar flow, plus it aids the formation of dross and gas pick-up in the stream that is going to feed the casting.

The Gating System• The Gates (in this case)

accommodate a directional change in the fluid flow and deliver the metal to the Casting cavity.

• Again, the design objective is to promote laminar flow. The primary causes of turbulence are sharp corners, or un-proportioned gate/runner sizes.

• The two dashed blue areas when added together form a relationship to the Choke or base of the Sprue Area.

• The runner system is fed by the well and is the path to the gates.

• This path should be "Balanced" with the model of heating or AC ductwork serving as a good illustration. The Runner path should promote smooth laminar flow by a balanced volumetric flow, and avoiding sharp or abrupt changes in direction.

• The "Runner Extension" is a "Dead-End" that is placed after the last gate. The R-Ext acts as a cushion to absorb the forward momentum or kinetic energy of the fluid flow. The R-Ext also acts as a "Dross/Gas Trap" for any material generated and picked-up along the flow of the runner.

• An Ideal Runner is also proportioned such that it maintains a constant volumetric flow through virtually any cross-sectional area.

• The runner becomes proportionally shallower at the point where an in-gate creates an alternate path for the liquid flow.

The Runner System

Some dimensioning ratios from Chastain's Foundry Manual (no.2)

• 1- Choke or sprue base area is 1/5th the area of the well.• 2- The well depth is twice the runner depth.• 3- the Runner is positioned above the midpoint of the

well's depth

•By creating a sprue with a taper, the fluid is constrained to retain it's shape, reducing excessive surface area development (dross-forming property) and gas pick-up.

•The area below the sprue is the "Well". The well reduces the velocity of the fluid flow and acts as a reservoir for the runners and gates as they fill.

Formulae, Ratios and Design Equations

• What is covered so far is comprehensive, and intuitive on a conceptual level, but the math below hopefully offers some insight into quick approximations for simple designs, and more in-depth calculations for complex systems.

• Computerized Flow Analysis programs are used extensively in large Foundry operations.

• From basic concepts, designing on a state of the art system shall be attempted:

• Continuity Equation –

• This formula allows calculation of cross-sectional areas, relative to flow Velocity and Volumetric flow over unit time. This is with the assumption that the fluid flow is a liquid that does NOT compress (that applies to all molten metals).

Here, a flow passes through A1 (1" by 1", 1 sq") The passage narrows to a cross-sectional area A2 (.75" by .75", 0.5625 sq")

The passage expands to a cross-sectional area A3 (1" by 1", 1 sq").

Q= Rate of Flow (Constant - uncompressible)V=Velocity of flowA=Area (Cross-section)

If A1 and A2 are considered, the Area A2 is almost half of A1, thus the velocity at A2 has to be almost double of A1.

• The issue of sharp corners (both inner and outer) create turbulence, low & high pressure zones that promote aspiration of mold gases into the flow, and can draw mold material (sand) into the flow. None of this is good... By providing curved radius changes in direction the above effects are still at play but at a reduced level. Sharp angles impact the solidification process and may inhibit "Directional Solidification" with cross-sectional freezing.

• The image is just a representation

• By proportioning the gating system, a more uniform flow is promoted with near equal volumes of metal entering the mold from all points. In an un-proportioned system the furthest gates would feed the most metal, while the gates closest to the sprue would feed the least.

(this is counter to what one initially thinks).

DIRECTIONAL SOLIDIFICATION-

GATING RATIO is-

Areas of Choke : Runner : Gate(s)

• The base of the Sprue and Choke are the same.

• The ratios between the cross-sectional Area can be grouped into either Pressurized or Unpressurized.

• Pressurized: A system where the gate and runner cross-sectional areas are either equal or less than the choke cross-sectional area.

Pressurized - is a system where the gate and runner cross-sectional areas are either equal or less than the choke cross-sectional area;A1= Choke = 1 unitA2 = 1st Runner c/s Area = 0.75 unitA3 = 2nd Runner c/s Area = 0.66 unitA4 = 1st Gate = 0.33 unitA5 = 2nd Gate = 0.33 unit

Unpressurized - The key distinction is that the Runner must have a c/s area greater than the Choke, and it would appear that the Gate(s) would equal or be larger than the Runner(s).

Common Ratios are;1 : 2 : 4; 1 : 3 : 31 : 4 : 4; 1 : 4 : 6

• Areas A2 & A3 do not get added as they are positioned in line with each other and flow is successive between the points and not simultaneous.

• Areas A4 & A5 are added together as flow does pass through these points simultaneously.

• This would resolve to a pressurized flow of

1 : 0.75 : 0.66

A1= Choke = 1

A2 = 1st Runner c/s Area = 0.75 A3 = 2nd Runner c/s Area = 0.66 A4 = 1st Gate = 0.33A5 = 2nd Gate = 0.33

Pressurized

Unpressurized:• The key distinction is that the Runner must have

a cross sectional area greater than the Choke, and it would appear that the Gate(s) would equal or be larger than the Runner(s).

• Common Ratio's noted in Chastian's Vol 2 are:• 1 : 2 : 4• 1 : 3 : 3• 1 : 4 : 4• 1 : 4 : 6

• An exception is noted in Chastain with a 1 : 8 : 6 ratio to promote dross capture in the runner system of Aero-Space castings.

• The Continuity Equation is simplified with the use of ratios as the velocity is inversely proportional between any 2 adjacent ratio values. ie H : L equates to an increase in velocity while a L : H equates to a drop in velocity.

• Laminar Flow is harder to control at a high velocity than a relatively lower velocity.

• Chastain's Vol 2 has much more mathematical expressions and calculations.

PURE METALSPURE METALS-

Have clearly defined melting/freezing point, solidifies at a constant temperature.

Eg: Al - 6600C, Fe - 15370C,

and W- 34100C.

Solidified structures of metal - Solidified structures of metal - solidified in a square mouldsolidified in a square mould

(a). Pure metal(b). Solid solution(c). When thermal gradient is absent

within solidifying metal

Development of a preferred texture Development of a preferred texture - at a cool mould wall. - at a cool mould wall.

A chill zone close to the wall and then a columnar zone away from the mould.

Three basic types of cast structures-

(a). Columnar dendritic;

(b). equiaxed dendritic;

(c). equiaxed nondendritic

STRUCTURE FOR PURE METALSFOR PURE METALS:: At the mould walls, metal cools rapidly. Produces

solidified skin or shell (thickness depends on composition, mould temperature, mould size and shape etc)

• These are of equiaxed structure.• Grains grow opposite to heat transfer through the mould• These are columnar grains• Driving force of the heat transfer is reduced away from

the mould walls and blocking at the axis prevents further growth

Size and distribution of the overall grain structure throughout a casting depends on rate & direction of heat flow

(Grain size influences strength, ductility, properties along different directions etc.)

CONVECTION- TEMPERATURE GRADIENTS DUE TO DIFFERNCES IN THE DENSITY OF MOLTEN METAL AT DIFFERENT TEMPERATURES WITHIN THE FLUID - STRONGLY EFFECTS THE GRAIN SIZE.

Outer chill zones do not occur in the absence of convectionOuter chill zones do not occur in the absence of convection

FOR ALLOYS:• Alloys solidify over a range of temperatures• Begins when temp. drops below liquidous, completed

when it reaches solidous.• Within this temperature range, mushy or pasty state

(Structure as in figure)• Inner zone can be extended throughout by adding a

catalyst.- sodium, bismuth, tellurium, Mg (or by eliminating thermal gradient, i.e. eliminating

convection. (Expts in space to see the effect of lack of gravity in eliminating convection)

(refresh dendritic growth- branches of tree, interlock, each dendrite develops uniform composition, etc)

SOLIDIFICATION TIMESOLIDIFICATION TIME

During solidification, thin solidified skin begins to form at the cool mould walls.

Thickness increases with time.For flat mould walls thickness time (time doubled, thickness by 1.414)

CHVORINOV’S RULE solidification time (t) is a function of volume of the casting and its surface area t = C ( volume/ surface area )2

C is a constant [depends on mould material, metal properties including latent heat, temperature]

A large sphere solidifies and cools at a much slower rate than a small diameter sphere. (Eg- potatoes, one big and other small)

Volume cube of diameter of sphere,

surface area square of diameter

Solidification time for various shapesSolidification time for various shapes::

Eg: Three pieces cast with the SAME volume, but different shapes. (i)Sphere, (ii)Cube, (iii)Cylinder with height = diameter. Which piece solidifies the fastest?Solution: Solidification time = C (volume/surface area)2

Let volume = unity. As volume is same, t = C/ surface area2.

Cylinder: V = πr2h = 2 π r3; ie, r = (1/2 π) 1/3

A = 2 πr2 + 2πrh = 6 πr2 = 5.54. Then, t cube = 0.028C ; t cylinder = 0.033C ; t sphere= 0.043CMetal poured to cube shaped mould solidifies the fastest.

Sphere: V= 4/3 (π r3); i.e. r = (3/4 π)1/3

A= 4 π r2 = 4 π (3/4 π)1/3 = 4.84Cube: V = a3; ie a = 1; A = 6 a2 = 6.

SHRINKAGE AND POROSITYSHRINKAGE AND POROSITY

METALS SHRINK(CONTRACT) DURING SOLIDIFICATION

- CAUSES DIMENSIONAL CHANGES

LEADING TO CENTRE LINE SHRINKAGE, POROSITY, CRACKING TOO

SHRINKAGE DUE TO:(1).CONTRACTION OF

MOLTEN METAL AS IT COOLS PRIOR TO SOLIDIFICATION

(2) CONTRACTION OF SOLIDIFYING METAL,

LATENT HEAT OF FUSION

(3) CONTRACTION OF SOLIDIFIED METAL

DURING DROP TO AMBIENT TEMP

OUT OF THESE, LARGEST SHRINKAGE DURING OUT OF THESE, LARGEST SHRINKAGE DURING COOLING OF CASTINGCOOLING OF CASTING (ITEM 3) eg:pure metal

SOLIDIFICATION CONTRACTION FOR VARIOUS METALSSOLIDIFICATION CONTRACTION FOR VARIOUS METALS

METAL Volumetric Solidification Contraction Al 6.6 Grey cast Iron Expansion 2.5 Carbon Steel 2.5 to 3 Copper 4.9Magnesium 4.2 Zinc 6.5

• POROSITY DUE TO SHRINKAGE OF GASES

AND METAL TOO. RELATED TO DUCTILITY AND SURFACE FINISH(DUCTILITY V/S POROSITY CURVES FOR

DIFFERENT METALS) - ELIMINATION BY VARIOUS MEANS(ADEQUATE SUPPLY OF LIQUID METAL, USE OF

CHILLS, NARROWING MUSHY ZONE- CASTING SUBJECTED TO ISOSTATIC PRESSING

POROSITY BY GASESPOROSITY BY GASES

LIQUID METALS HAVE HIGH SOLUBILITY FOR GASESDISSOLVED GASES EXPELLED FROM SOLUTION DURING SOLIDIFICATION(Hydrogen, Nitrogen mainly)ACCUMULATE IN REGIONS OF EXISTING POROSITY ORCAUSE MICROPOROSITY IN CASTING- TO BE CONTROLLED

Effect of microporosity on the ductility of quenched and tempered cast steel – Porosity affects the ‘pressure tightness’ of

cast pressure vesselD

Porosity(%)

Elongation

Reduction of area

0 5 10 15

FLOW OF MOLTEN METAL IN MOULDSFLOW OF MOLTEN METAL IN MOULDSImportant: pouring basin, mould cavity & riser

GATING SYSTEM Design -fluid flow, heat transfer, influence of temperature gradient,

FLUID FLOWWithout turbulence

or with minimized turbulence

HEAT FLOW INFLUENCED BY MANY FACTORS

FLUIDITY-A characteristic related to viscosity.TEST OF FLUIDITY - USING A SPIRAL MOULD.Fluidity Index

TEST FOR FLUIDITY

USING A SPIRAL MOULD.

FLUIDITY INDEX IS THE LENGTH OF THE SOLIDIFIED METAL IN THE SPIRAL PASSAGE. GREATER THE LENGTH, GREATER THE FLUIDITY INDEX.

PATTERNPATTERN

• Model of a casting constructed such that it forms an impression in moulding sand

PATTERNPATTERN• 1st step- Prepare model (pattern) Differs from the casting Differences Pattern Allowances.

• To compensate for metal shrinkage, • Provide sufficient metal for machining• Easiness in moulding

• As Shrinkage allowance, Draft allowance, Finishing allowance, Distortion or camber allowance,

Shaking or rapping allowance

MATERIALMATERIAL1. WOOD.2. METAL Al, CI, Brass, 3. For special casting processes, Polystyrene which leaves mould as gas when heated also used. Types- many

Simple-Identical patterns; Complex, intricate- with number of pieces. Single or loose piece; Split; gated; Match Plate; Sweep; Segmental; Skeleton(frame, ribbed), skell; Boxed Up; Odd shaped etc. Sketches--

MaterialMaterial1. WOOD.(+) Cheap, easily available, light, easiness in surfacing, preserving (by shellac coating), workable, ease in joining, fabrication

(-) Moisture effects, wear by sand abrasion, warp during forming, not for rough use . Must be properly dried/ seasoned, free from knots, straight grainedEgs. Burma teak, pine wood, mahogany, Sal, Deodar, Shisham, Walnut, Apple tree

2. METAL: For durability, strengthEgs: Al alloys, Brass, Mg alloys, Steel, cast Iron for

mass production(first, wooden pattern is made, then cast in the metal)Type of material depends on shape, size, number of

castings required, method of moulding etc.

TYPES OF PATTERNS

1. SINGLE PIECE PATTERN.

2. SPLIT PATTERN (TWO PIECE )

2. a, THREE PIECE SPLIT PATTERN

3. LOOSE PIECE PATTERNN

4. COPE AND DRAG PATTERN

• COPE AND DRAG PARTS OF THE PATTERN MOUNTED ON SEPARATE PLATES.

• COPE HALF AND DRAG HALF MADE BY WORKING ON DIFFERENT MOULDING MACHINES.

• THIS REDUCES THE SEPARATE COPE AND DRAG PLATE PREPARATION.

• GENERALLY FOR HIGH SPEED MECHANISED MOULDING.

5. MATCH PLATE PATTERN – Pattern generally of metal and plate making

parting line metal/wood.

6. FOLLOW BOARD PATTERN. For thin sections.

THIN PATTERN

7. GATED PATTERN - Gating system is a part of the pattern.

8. SWEEP PATTERN – For large size castings in small numbers. Template of

wood attached to a sweep used.

9. SEGMENTAL PATTERN – For rings, wheel rims, large size gears.

10. SKELETON PATTERN.- Stickle board used to scrape the excess sand. Eg. Oil pipes, water pipes, pipe bends, boxes, valve bodies etc.

Stickle board

11. SHELL PATTERN

12. BUILT UP PATTERN – Also called lagged up patterns- For barrels, pipes,

columns etc

13. LEFT AND RIGHT PATTERN – For parts to be made in pairs. Eg: legs of sewing machine, wood working lathe, garden benches, J hangers for shafts, brackets for luggage racks etc.

• Type of pattern depends on: • Shape and size of casting, • number of castings required, • method of moulding employed, • easiness or difficulties of the moulding

operations, • other factors peculiar to the casting.

CHARACTERISTICS OF PATTERN MATERIALS

CHARACTERISTIC RATING

WOOD AL STEEL PLASTIC CAST IRON

MACHINABILITY E G F G G WEAR RESISTANCE P G E F ESTRENGTH E G E G GWEIGHT E G P G PREPAIRABILITY E P G F GRESISTANCE TO:• CORROSION (by water) E E P E P• SWELLING P E E E E

E- Excellent; G- Good; F-fair, P- Poor

Functions of pattern

• Moulding the Gating system;• Establishing a parting Line,• Making Cores, • Minimising casting Defects,• Providing Economy in moulding• Others, as needed

MOULDING SAND• Granular particles from the breakdown of rocks by frost, wind, heat and water currents

• Complex Composition in different places

• At bottom and banks of rivers• - mainly silica (86 to 90%); Alumina (4% to 8 %); Iron oxide (2 to 5%) with oxides of Ti, Mn, Ca. etc.

NATURAL SAND , called Green sand. Only water as binder; can maintain water for long time

SYNTHETIC SAND.- (1)GREEN and (2)DRY types (1) Artificial sand by mixing clay free sand, binder(water and bentonite) Contains New silica sand 25%; Old sand 70%; bentonite 1.5%;moisture 3% to 3.5%

(2) New 15%; Old 84%; bentonite and moisture 0.5 % each

DRY SAND- for moulding large castings. Moulds of green sand dried and baked with venting done. Add- cow dung, horse manure etc.LOAM SAND- mixture of clay and sand milled with water to thin plastic paste. Mould made on soft bricks. The mould dried very slowly before cast. For large regular shapes-

drums, chemical pans etc.FACING SAND- used directly with surface of pattern; comes in contact with molten metal; must have high strength, refractoriness.Silica sand and clay without used sand- plumbago powder, Ceylon lead, or graphite used. Layer of 20 to 30 mm thick--- about 10% to 15% of whole mould sand

BACKING SAND- old used moulding sand called floor sand black in colour. Used to fill mould at back of facing layer. Weak in bonding strengthSYSTEM SAND- used in machine moulding to fill whole of flask. Strength, premealibility and refractoriness highPARTING SAND- used for separating boxes from adhering, free from clayCORE SAND- for making cores. Silica sand with core oil (linseed oil, rosin, light mineral oil, binders etc)SPECIALISED SANDS - like CO2 sand, Shell sand, etc for special applicationsMould washers- slurry of fine ceramic grains applied on mould surface to minimize fusing

About MOULDING SAND

1. NATURAL SAND2. SYNTHETIC SAND.- GREEN and DRY3. DRY SAND4. LOAM SAND5. FACING SAND6. BACKING SAND7. SYSTEM SAND8. PARTING SAND9. CORE SAND10. SPECIALISED SANDS11. Mould washers

ADV - Acid Demand ValueDefined as the property of a sand or additive to affect the cure process as a function of the materials acidity or basicity on the pH scale.

MOULDING SAND- PROPERTIES

• Green Strength- Adequate strength after mixing, and plasticity for handling

• Dry Strength- After pouring molten metal, adjacent surface loses water content. Dries. Dry sand must have enough strength to resist erosion

• Hot Strength- Strength at elevated temperature after evaporation of moisture

• Permeability- Permeable or porous to permit gases to escape. Ability of sand moulds to allow the escape of gases

• Thermal stability- Rapid expansion of sand surface at mould-metal interface. May crack. Results in defect called SCAB

• Refractoriness- Ability of sand to withstand high temperature

• Flowability- Ability to flow & fill narrow portions around pattern

• Surface finish- Ability to produce good surface finish in casting

• Collapsibility- Allow easy removal of casting from mould• Reclamation- Should be reusable and reclaimable

FURNACES Proper selection depends on:• Composition and melting point of alloy to be cast• Control of atmospheric contamination• Capacity and rate of melting required• Environmental considerations- noise, pollution• Power supply, availability, cost of fuels• Economic considerations-initial cost, operating cost,

maintenance cost etc.CUPOLAS (> 50 T, VERTICAL, HIGH RATES) ELECTRIC FURNACESINDUCTION FURNACES

FOUNDRIES• From Latin word- fundere (meaning melting & pouring)

• Pattern & Mould making- automated, computer integrated facilities- CAD/CAM

• Melting, controlling composition & impurities, pouring- Use of conveyors, automated handling, shakeout,

cleaning, heat treatment, inspection, etc.

CRUCIBLE FURNACE

OIL FIRED FURNACE

CUPOLA

* CHARGE PASSES DOWNWARDS UNDER GRAVITY* MEETS FLOW OF HOT GASES MOVING UPWARDS* CONTINUOUS IN OPERATION

.Vertical steel shell, lined with fire bricks..Base on four steel columns.Hinged doors in the base plate to remove residue at the end of melt..Air blast through tuyeres (number on size).Through charging door, coke, pig iron, scrap & lime stone charged..Cold & Hot blast cupolas.

TOWER FURNACE

TO MELT ALUMINIUM & alloys

3 main sections- charging elevator, melting unit, holding furnace (Cylindrical rotary unit).

Automatic controls

Grate above burners supports solid charge

Molten charge runs down

REVERBERATORY FURNACE Small units (50kg) for melting non ferrous metals, large (about 25T) 10 T capacity to melt iron AIR FURNACE:One type of RB- to melt cast iron for roll mill rolls, malleable castings, 15 T capacity – Charge out of contact with fuel, less sulphur absorbed, long melting time enables control of composition, large size scrap handled.Lump coal, pulverised fuel, oil used to fire. Solid coal burnt in a grate

TYPICAL DIRECT ARC FURNACE

A TYPICAL DIRECT

The Sand Casting Process The most commonly used Casting Process, in the entire

Casting Industry.

• Concept: The top and the bottom of the mold form the flask. "holds the whole thing together." The cope and the drag.

• An impression device, in the middle of the flask assembly, called the pattern.

• The sand around the pattern is called the, holding medium. • These are the basic, universal casting components, which can

be applied to all Casting and Molding Processes.• The mold maker uses the pattern to make the impression in

the holding medium, the sand, then sets the pattern aside, closes the cope and drag, to complete the flask, and forms the mold, fills that void with a molten material; which could be almost anything.

Continuous Casting

Figure 1

Casting a component

Middle support for a bike rack on public trains.

• Material:535 aluminum.• Process: Sand casting.• Casting Supplier: Dent

Manufacturing, Inc., Northampton, Pennsylvania.

• This 2-lb casting replaced four stainless steel fittings, eliminating the need for several nut and bolt assemblies.

• The 8.5 x 7.5 x 3.5-in. component is designed to hold 1.25-in. steel pipe handrails on a bike rack.

• The foundry polishes and clear anodizes the casting for a long-lasting finish, which provides a cleaner appearance when compared to the previous assembly.

• The casting eliminates the need for multiple parts, reducing manufacturing time and overall cost.

Air scoop that directs air flow for an agricultural combine.

Material:80-55-06 ductile iron.• Process:Sand casting.• Casting Supplier: Neenah Foundry

Co., Neenah, Wisconsin.• Originally manufactured as a

stamping and weldment, this 25-lb component was converted to a ductile iron casting at a 40% cost reduction. Pictured is the casting (r) and the previous stamping/weldment (l).

• The cast component, which measures 210 x 60 x 620 mm, afforded the customer a simpler design, eliminating the need for capital resources and manpower for extensive stamping and welding equipment.

Torque arm bracket for the after-market automotive industry.

• Material:80-55-06 ductile iron.• Process: Sand casting.• Casting Supplier: Farrar Corp.,

Norwich, Kansas.• Converted from a fabricated steel

assembly, the casting saved the customer $49/part due to reduced grinding and no assembly time for the component (previously 8-10 hours per bracket).

• Fully machined by the foundry, the casting achieves tighter dimensional tolerances than the fabrication and has experienced zero returns due to failure in the field.

• Using rapid prototyping, the foundry was able to deliver sample parts for approval within one week from design delivery.

SHELL MOULDING-DEVELOPED IN 1940s

• THERMOSETTING RESINS USED AS BINDERS

• PHENOL FORMALDEHYDE(3% BY WT.OF SAND)

• 15% HEXAMETHYLENE TETRAMINE ADDED TO GIVE THERMOSETTING PROPERTY

• RESIN SETS AT ABOUT 2500 C (1750 C- 3700 C)• SHELL OF 4 to 9 MM FORMS • SHELL MOULDING MACHINES

USED• PATTERN MADE OF METAL• MOUNTED ON MATCH PLATES

WITH GUIDE PINS

• PATTERN HEATED TO 2500 C• CLEANED WITH COMPRESSED

AIR, PETROLEUM SPIRIT APPLIED

• PATTERN INVERTED, PLACED IN DUMP BOX CONTAINING SAND MIX , LOCKED

• DUMP BOX INVERTED, KEPT FOR A FEW MINUTES, (1-3 MINS) SHELL FORMS

• RE-INVERTED, SHELL FORMED IS TRIMMED, REMOVED USING GUIDE PIN EJECTION,

• ANOTHER HALF ASSEMBLED, READY FOR POURING

SHELL MOULDING - SEQUENCES

CARBON-DI OXIDE PROCESS(SILICATE BONDED SAND PROCESS)

• FIRST IN 1950s• MIXTURE OF SAND AND 1.5% TO 6 %

SODIUM SILICATE (AS BINDER)• MIXTURE PACKED AROUND THE

PATTERN, HARDENED BY BLOWING CO2

• DEVELOPED FURTHER BY ADDING OTHER CHEMICALS AS BINDERS

• MAINLY TO MAKE CORES-AS USE IS IN ELEVATED TEMPERATURE APPLICATION

Na2O SiO2 + H2O +CO2 Na2CO3 + (SiO2 +H2O) (Silica Gel)

Formation of Silica Gel gives strength to the moulds

+ Points:• Drying not necessary• Immediately ready for pouring• Very high strength achieved• Dimensional accuracy very good- Points- Collapsibility poor, can be improved by additives- Na2O SiO2 attacks and spoils wooden pattern

Funnel

CO2 Moulding

DIE CASTING

GRAVITY SEMI PERMANENT MOULDOR PERMANENT MOULD COLD CHAMBER HOT CHAMBER (HEATING CHAMBER) OUTSIDE THE MACHINE INTEGRAL WITH THE MACHINE

PERMANENT MOULD OR GRAVITY DIE CASTING *METALLIC MOULDS USED *TWO HALVES OF DIES- ONE FIXED, ONE MOVABLE

•VERY CLOSE TOLERANCE CASTINGS, MORE STRENGTH, LESS POROUS

•-BETTER SURFACE FINISH COMPARED TO SAND CASTING

•-SURFACE FREE FROM SAND & DENSITY HEAVY

ONLY FOR SMALL AND MEDIUM SIZE CASTINGS

FOR NON FERROUS, MAINLY

LARGE QUANTITY, BUT IDENTICAL PIECES ONLY

PERMANENT MOULD OR GRAVITY DIE CASTING *METALLIC MOULDS USED - MOULD TO WITHSTAND TEMPERATURE

*NO EXTERNAL PRESSURE APPLIED,

*HYDROSTATIC PRESSURE BY RISERING

*LAMP BLACK/CORE OIL APPLIED TO DIE SURFACES FOR EASY REMOVAL

*FAST CONDUCTION, RAPID COOLING

*TWO HALVES OF DIES- ONE FIXED, ONE MOVABLE NITC

• +POINTS • - VERY CLOSE TOLERANCE CASTINGS, • MORE STRENGTH, LESS POROUS• - BETTER SURFACE FINISH COMPARED TO • SAND CASTING• - SURFACE FREE FROM SAND• - DENSITY HEAVY• - MORE DIMENSIONAL ACCURACY - 0.06 TO 0.3 MM• - DIES LESS COSTLY THAN PRESSURE DIE CASTING DIES• - GOOD FOR PRESSURE TIGHT VESSELS• - LESS COOLING CRACKS• - LESS SKILL • - GOOD FOR LARGE QUANTITIES

- POINTS

ONLY FOR SMALL AND MEDIUM SIZE CASTINGS FOR NON FERROUS, MAINLY LARGE QUANTITY, BUT IDENTICAL PIECES ONLY POOR ELONGATION STRESS AND SURFACE HARDNESS DEFECTS OBSERVED CASTING TO BE WITHDRAWN CAREFULLY FROM DIES

A TYPICAL DIE

ECCENTRIC CLAMPING

MOULD / DIE HALFVENT HOLE POURING

MOULD CAVITY

SEMIPERMANENT DIECASTING

• DIE PRESSURE AT 20 TO 20,000 ATM

• PRESSURE FILL SOLIDIFICATION

• FOR NONFERROUS METALS

• FOR INTRICATE SHAPES

• CLOSE TOLERANCES POSSIBLE

• FOR MASS PRODUCTION, >10,000

FOR SEMI AND PRESSURE DIE CASTING SET UPS, THE FOLLOWING FACTORS A MUSTA MUST

1. A GOOD DIE SET MECHANISM

2. MEANS FOR FORCING METAL

3. DEVICE TO KEEP DIE HALFS PRESSED

4. ARRANGEMENT FOR AUTOMATIC REMOVAL OF CORES- IF ANY

5. EJECTOR PINSNITC

TWO TYPES OF PRESSURE DIE CASTING COLD CHAMBER- HEATING CHAMBER OUTSIDE THE MACHINE - FOR Al, Mg, Cu, AND HIGH MELTING ALLOYS HOT CHAMBER- HEATING INTEGRAL WITH THE HANDLING GOOSE NECK MECHANISMS WIDELY USED FOR LOW MELTING ALLOYS- Zn, Pb, Etc.ALSO VACUUM DIE CASTING MACHINES- SPACE

BETWEEN THE DIES AND PASSAGE VACUUMISED BEFOR POURING-

SUBMERGED PLUNGE TYPE, DIRECT AIR DIE CASTING MACHINES

D.A.D.C. MACHINE – showing two positions of pot

ANOTHER TYPE OF D.A.D.C. MACHINE

SQUEEZE CASTING• DEVELOPED IN 1960’S (also called liquid forging)• SOLIDIFICATION OF MOLTEN METAL UNDER HIGH

PRESSURE (pressure application when liquid partially solidifies 70 to 140 MPa)

• A COMBINATION OF CASTING & FORGING• DIE, PUNCH, EJECTOR PIN • PUNCH KEEPS ENTRAPPED GASES IN SOLUTION, RAPID

COOLING DUE TO HIGH PRESSURE DIE- METAL INTERFACE

• PARTS OF NEAR-NET SHAPE MADE, COMPLEX AND FINE SURFACE DETAILS OBTAINED. No riser needed

• FOR FERROUS & NON FERROUS• AUTOMOTIVE WHEELS, SHORT BARRELED CANNONS

VACUUM DIE CASTING MACHINES

• SOME AIR ENTRAPPED IN ORDINARY DIE CASTING MACHINES• THIS PRODUCES BLOW HOLES• IN VACUUM DIE CASTING TYPE, VACUUM PUMP CREATES VACUUM

IN DIE CAVITY, A SEAL CUTS OFF THE PIPE CONNECTION AFTER EVACUATING

• THIS PREVENTS FLOW OF METAL FROM DIE TO VACUUM PIPE• FLOW OF MOLTEN QUICK AND AUTOMATIC

• FINISHES:• ALL DIE CASTINGS SUSCEPTIBLE TO CORROSION, HENCE

SUBJECTED TO FINISHING OPERATIONS OR PLATING

DESIGN CONSIDERATIONS• USE OF RIBS, HUBS, BOSSES MUST BE TO REDUCE WEIGHT,

STRENGTHEN THE PART, IMPROVE THE APPEARANCE• THICK SECTIONS MAKE DIE HOTTER AND THUS LESSEN

DIE LIFE• LARGE SECTIONS TO BE COOLED MAY CAUSE POROSITY• EXCESSIVE SECTIONAL CHANGES TO BE AVOIDED• AVOID UNDERCUTS• FILLETS DESIRABLE OVER SHARP EDGES• DRAFTS NEEDED ON ALL CASTINGS• EJECTOR PINS AT BACK TO AVOID VISIBILITY OF MARKS• FLASH NECESSARY , TO BE REMOVED LATER BY

TRIMMING

DIE MATERIALS

CASTING ALLOYS DIE MATERIAL

TIN, LEAD ALLOY CAST STEEL WITHOUT HEAT TREATMENT

ZINC, Al HEAT TREATED LOW ALLOY STEEL

COPPER BASE ALLOYS

HEAT TREATED SPECIAL ALLOY STEEL

DIE CASTING ALLOYS• MAINLY NON-FERROUS CASTINGS WITH

PROPERTIES COMPARABLE WITH FORGINGS

ZINC ALLOYS:- WIDELY USED ( 70%)- Al 4.1%; Cu MAX 1%, Mg 0.4%; BALANCE ZINC

• -- PERMITS LONGER DIE LIFE, SINCE TEMP. IS LOW• GOOD STRENGTH, Tensile Strength: 300 Kg/cm2

• VERY GOOD FLUIDITY, THUS THIN SECTIONS POSSIBLE• USESUSES: AUTOMOBILES, OIL BURNERS, FRIDGES, RADIO, TV

COMPONENTS, MACHINE TOOLS, OFFICE MACHINERIES

ALUMINIUM ALLOYS:

• BY COLD CHAMBER PROCESS-• Cu 3 to 3.5%, Si 5 to 11 %, BALANCE Al.• LIGHTEST ALLOYS, GOOD CORROSION

RESISTANCE, FINE GRAINED STRUCTURE DUE TO CHILLING EFFECT

• Tensile Strength: 1250 to 2500 Kg/cm2

• GOOD MACHINABILITY, SURFACE FINISH• USESUSES: MACHINE PARTS, AUTOMOTIVE,

HOUSE HOLD APPLIANCES ETC.

COPPER BASED ALLOYS:

• Cu 57 to 81%;Zn 15 to 40%; SMALL QUANTITIES OF Si, Pb, Sn

• VERY HIGH TENSILE STRENGTH: 3700 to 6700Kg/cm2;

• GOOD CORROSION RESISTANCE; WEAR RESISTANCE

• LOW FLUIDITY, HENCE REDUCED DIE LIFE• USESUSES; ELECTRICAL MACHINERY PARTS,

SMALLGEARS, MARINE, AUTOMOTIVE AND AIR CRAFT FITTINGS, HARDWARES

MAGNESIUM BASED ALLOYS:• LIGHTEST IN DIE CASTING, PRODUCTION COST SLIGHTLY

HIGH, Al: 9%; Zn: 0.5%; Mn: 0.5%; Si: 0.5%, Cu:0.3%; REMAINING Mg.

• USESUSES: IN AIRCRAFT INDUSTRY, MOTOR & ISTRUMENT PARTS, PORTABLE TOOLS, HOUSE HOLD APPLIANCES

LEAD & TIN BASED ALLOYS; • Lead base: 80% Pb & ; Tin base 75% tin, antimony, copper • LIMITED APPLICATIONS. LIMITED APPLICATIONS. LIGHT DUTY BEARINGS, BATTERY

PARTS, X-RAY SHIELDS, LOW COST JEWELLERY, NON-CORROSIVE APPLICATIONS

V-Process 1. Pattern (with vent holes) is placed on hollow carrier plate.2. A heater softens the .003" to .007" plastic film. Plastic has good elasticity and high plastic deformation ratio.3. Softened film drapes over the pattern with 300 to 600 mm Hg vacuum acting through the pattern vents to draw it tightly around pattern.4. Flask is placed on the film-coated pattern. Flask walls are also a vacuum chamber with outlet shown.5. Flask is filled with fine, dry unbonded sand. Slight vibration compacts sand to maximum bulk density.6. Sprue cup is formed and the mold surface leveled. The back of the mold is covered with unheated plastic film.7. Vacuum is applied to flask. Atmospheric pressure then hardens the sand. When the vacuum is released on the pattern carrier plate, the mold strips easily.8. Cope and drag assembly form a plastic-lined cavity. During pouring, molds are kept under vacuum.9. After cooling, the vacuum is released and free-flowing sand drops away leaving a clean casting, with no sand lumps. Sand is cooled for reuse.

Benefits Of Using The V-Process:

• Very Smooth Surface Finish • 125-150 RMS is the norm. Cast surface of 200 or better, based on The Aluminum Association

of America STD AA-C5-E18. • Excellent Dimensional Accuracy • Typically +/-.010 up to 1 inch plus +/-.002 per additional inch. Certain details can be held

closer. • +/-.010 across the parting line. • Cored areas may require additional tolerances. • Zero Draft • Eliminates the need for machining off draft to provide clearance for mating parts and

assembly. • Provides consistent wall thickness for weight reduction and aesthetic appeal. • Allows for simple fixturing for machining and inspection.

• Pattern construction becomes more accurate and efficient. • Total tolerance range becomes more accurate and efficient. • Geometry/tolerance of part is at its simplest form. Draft does not use up

tolerance. • Design/drafting is less complex. Calculations and depictions related to draft are

eliminated. • Thin Wall Sections • Walls as low as .100 in some applications are possible. • Excellent Reproduction Of Details • Very small features and lettering are possible. • Consistent Quality • All molding is semi-automatic. Variable "human factor" has been reduced. • Superior Machining • Sound metal and no hidden sand in the castings means fewer setups, reduced

scrap and longer tool life. • Low Tooling Costs

• All patterns are made from epoxy, machined plastics, SLA or LDM. There is no need to retool for production quantities.

• Unlimited Pattern Life • Patterns are protected by plastic film during each sand molding cycle. • Easy Revisions To Patterns • No metal tooling to weld or mill. Great for prototypes. • Short-Run Production Capability • Excellent for short-run production while waiting for hard tooling. The V-

PROCESS method can outproduce traditional prototype methods such as plaster or investment castings.

• Fast Turnaround

• From placement of order to sample casting in as little as two to four weeks.

• Known for several hundred years.

• But its evolution into a sophisticated production method for other than simple shapes has taken place only in this century.

• Today, very high quality castings of considerable complexity are produced using this technique.

CENTRIFUGAL CASTING

AN OVERVIEW

• To make a centrifugal casting, molten metal is poured into a spinning mold.

• The mold may be oriented horizontally or vertically, depending on the casting's aspect ratio.

• Short, square products are cast vertically while long tubular shapes are cast horizontally. In either case, centrifugal force holds the molten metal against the mold wall until it solidifies.

• Carefully weighed charges ensure that just enough metal freezes in the mold to yield the desired wall thickness.

• In some cases, dissimilar alloys can be cast sequentially to produce a composite structure.

CENTRIFUGAL CASTINGTRUE- C.I. PIPES, LINERS, BUSHES, CYLINDER BARRELS ETC.SEMI- CENTRE CORE FOR INNER SURFACE- SHAPE BY MOULD AND CORE, MAINLY NOT BY CENRTRIFUGAL ACTION- Eg:FLYWHEELSPRESSURE OR CENTRIFUGAL CASTING- ALSO TERMED AS CENTRIFUGINGFOR NON SYMMETRICAL SHAPES MOULD WITH ANY SHAPE PLACED AT CERTAIN DISTANCE FROM AXIS

• SEMI- • CENTRE CORE FOR INNER SURFACE- SHAPE BY MOULD AND CORE, MAINLY NOT BY CENRTRIFUGAL ACTION- Eg:FLYWHEELS • SPEED OF ROTATION- 60 TO 70 TIMES GRAVITY FOR HORIZONTAL

AND INCLINED TYPES ABOVE 100 FOR VERTICAL TYPES.

CENTRIFUGING PROPERTIES OF CASTING DEPEND ON

DISTANCE FROM AXIS

SQUEEZE CASTINGDIE, PUNCH, EJECTOR PIN

PARTS OF NEAR-NET SHAPE MADE, COMPLEX AND FINE

SURFACE DETAILS OBTAINED

FOR FERROUS & NON FERROUS

CENTRIFUGAL CASTING• + points:• Denser structure, cleaner, foreign elements

segregated (inner surface)• Mass production with less rejection• Runners, risers, cores avoided• Improved mechanical properties• Closer dimensions possible, less machining• Thinner sections possible• Any metal can be cast

- points:

- Only for cylindrical and annular parts with limited range of sizes

- High initial cost- Skilled labour needed- Too high speed leads to surface cracks- (high

stresses in the mould )

• For copper alloy castings, moulds are usually made from carbon steel coated with a suitable refractory mold wash.

• Molds can be costly if ordered to custom dimensions, but the larger centrifugal foundries maintain sizeable stocks of molds in diameters ranging from a few centimetres to several metres.

• The inherent quality of centrifugal castings is based on the fact that most nonmetallic impurities in castings are less dense than the metal itself. Centrifugal force causes impurities (dross, oxides) to concentrate at the casting's inner surface. This is usually machined away, leaving only clean metal in the finished product.

• Because freezing is rapid and completely directional, centrifugal castings are inherently sound and pressure tight.

• Mechanical properties can be somewhat higher than those of statically cast products.

• Centrifugal castings are made in sizes ranging from approximately 50 mm to 4 m in diameter and from a few inches to many yards in length.

• Size limitations, if any, are likely as not based on the foundry's melt shop capacity.

• Simple-shaped centrifugal castings are used for items such as pipe flanges and valve components, while complex shapes can be cast by using cores and shaped molds.

• Pressure-retaining centrifugal castings have been found to be mechanically equivalent to more costly forgings and extrusions.

PRODUCTS• Material:Gray iron.• Process: Centrifugal casting.• This 84-lb brake drum is produced by casting gray

iron centrifugally into a steel shell. This shell acts as a protective jacket, resulting in superior drum strength and allowing for the removal of iron in the drum band and mounting areas normally required in a full cast brake drum.

• Through concerted efforts between the foundry, machine shop and engineering/testing resources, 6 lb were removed from the brake drum while providing the same performance, balance and reliability as the standard drum. With the weight optimized at 84 lb, the drums are ideal for weight sensitive applications such as refrigerated trailers, tankers and bulk haulers.

• Utilizing these drums on an 18-wheel tractor/trailer application can provide up to 224 lb of weight savings.

Brake drum for commercial highway Class 8 trucks and trailers.

Commercial products made by centrifugal casting

• Belt buckles, battery lug nuts, lock parts, "pot metal" gears and machine parts, bushings, medallions, figurines, souvenirs, memorial coins and plaques, toy and model parts, concrete expansion fasteners, hardware such as drawer pulls and knobs, handles, decorative wall switch plates etc. etc.

INTRODUCTION • Investment casting, often called lost wax casting, is

regarded as a precision casting process to fabricate near-net-shaped metal parts from almost any alloy. Although its history lies to a great extent in the production of art, the most common use of investment casting in more recent history has been the production of components requiring complex, often thin-wall castings. A complete description of the process is complex. But, the sequential steps of the investment casting process are as below, with emphasis on casting from rapid prototyping patterns.

Fig: 1- Investment casting process NITC

• The investment casting process begins with fabrication of a sacrificial pattern with the same basic geometrical shape as the finished cast part

• Patterns are normally made of investment casting wax that

is injected into a metal wax injection die. Fabricating the injection die is a costlier process and can require several months of lead time.

• Once a wax pattern is produced, it is assembled with other wax components to form a metal delivery system, called the gate and runner system. The entire wax assembly is then dipped in a ceramic slurry, covered with a sand stucco, and allowed to dry. The dipping and stuccoing process is repeated until a shell of ~6-8 mm (1/4-3/8 in) is applied.

Fig. 2- Investment casting process - dewaxing NITC

• Once the ceramic has dried, the entire assembly is placed in a steam autoclave to remove most of the wax.

• After autoclaving, the remaining amount of wax that soaked

into the ceramic shell is burned out in a furnace. At this point, all of the residual pattern and gating material is removed, and the ceramic mold remains.

• The mold is then preheated to a specific temperature and filled with molten metal, creating the metal casting. Once the casting has cooled sufficiently, the mold shell is chipped away from the casting.

• Next, the gates and runners are cut from the casting, and final post-processing (sandblasting, machining) is done to finish the casting.

(The CAD solid model, the shell, and the pattern produced in the QuickCast process is schematically shown)

Fig. 3. Investment casting process –Preheating and pouring

INVESTMENT CASTINGAlso called LOST WAX PROCESS- used during 4000-3000 BC

• Die for casting wax pattern made with allowances for wax and metal.

• Pattern and gating systems made of wax (bee wax, aera wax, paraffin) or plastic (polystyrene) by injecting -in molten condition - into the metal die

• PRECOATING- The pattern dipped in a slurry of refractory material (fine 325 mesh silica &binders, water, ethyl silicate, acids), and sprinkled with silica sand

• This pattern with initial coating dried, coated repeatedly to increase thickness

• The one piece mould is dried• DEWAXING- Inverted and

heated to 900C -1750 C for 12 hours

• Wax melts. Can be reclaimed and reused.

• Mould fired to 6500C-10500C for about 4 hours

• POURING- Metal poured, allowed to solidify

• Mould broken, casting taken out

INVESTMENT CASTING- SEQUENCES

Plus and Minus points

• Very good dimensional accuracy

• No or very little finishing • Intricate and thin shapes

possible• About 40 kg parts cast• Both for ferrous and

nonferrous alloys• Suited for mechanization

• Careful handling needed,as the patterns are not strong.

• Close control of process needed

• Labour and material costs high, but high melting point alloys cast with good surface finish & close tolerances.

• Eg: gears, cams, valves, ratchets, turbine blades, electrical & electronic components etc.

CAD solid model (top), SLS polycarbonate pattern (left), A356 aluminum casting (right).

• The major impact rapid prototyping processes have had on investment casting is their ability to make high-quality patterns (Fig. 5) without the cost and lead times associated with fabricating injection mold dies.

• In addition, a pattern can be fabricated directly from a design engineer's computer-aided design (CAD) solid model. Now it is possible to fabricate a complex pattern in a matter of hours and provide a casting in a matter of days.

• Investment casting is usually required for fabricating complex shapes where other manufacturing processes are too costly and time-consuming.

• Another advantage of rapid prototyping casting is the low cost of producing castings in small lot sizes.

1. Vacuum Vessel for the power generation industry

• Material:Inconel 625 • Process: Investment • Casting Supplier:

Bescast, Inc., Willoughby, Ohio

Vacuum Vessel for the power generation industryMaterial:Inconel 625

• Process: Investment Casting• The 5-lb casting is one-tenth scale of the vacuum vessel

for the National Compact Stellarator Experiment (NCSX) being developed by the Princeton Plasma Laboratory and the Oak Ridge National Laboratory as the next generation of fusion experiment. The scale model was investment cast to determine the feasibility of using a casting for a vacuum vessel with complex geometry.

• To meet the rush timeline (with the help of buycastings.com), SLS rapid prototyping techniques were employed to make the complicated wax patterns from a CAD/STL file in 2 weeks. Solidification modeling predicted the potential “hot spots” and ways to optimize the pour parameters.

• The foundry employed a vacuum-assist casting method to cast the Inconel 625 air melt alloy with a consistent wall thickness of 0.1 in. The entire vessel is assembled by welding three equal segments cast by the foundry.

2.Cam clamp used to secure ambulance gurnees.

• Material: Stainless steel.

• Process: Investment casting.

• Casting Supplier: Independent Steel Castings Co., Inc., New Buffalo, Michigan.

Cam clamp used to secure ambulance gurnees.Material:Stainless steel.

• The casting design requires intricate angles and surface profiles—the dimensional integrity of the profile angles have to be held to ±0.005 in./linear in. tolerances while helix and spiracle angles move both horizontally and vertically.

• The foundry redesigned the component to remove material from the rear casting section for weight reduction. In addition, the founry designed in a tapered bore for mounting a bearing during assembly.

• The casting requires slotting at the top and bottom to align mating components. Holes at the top and bottom are cast-in and sized as ready-to-tap.

3. Mounting bracket for medical centrifuge.

• Material:CF3M stainless steel.

• Casting Supplier: Vestshell, Inc., Montreal, Quebec, Canada.

Mounting bracket for medical centrifuge.Material:CF3M stainless steel.

Process: Investment casting.

• This casting provides balanced, vibration-free support to a centrifuge that turns at more than 1000 RPM.

• Originally designed as a machined weldment, investment casting reduced costs by 450% and provided this precision component with dimensional repeatability and high-strength qualities.

• To date, the customer has received 800 parts without encountering casting-related defects.

4. Duck bill for White Cap, L.L.C. to seal caps on food jars.

• Material:316L stainless steel.

• Casting Supplier: Northern Precision Casting Co., Lake Geneva, Wisconsin.

Duck bill for White Cap, L.L.C. to seal caps on food jars.Material:316L stainless steel.

• Casting Supplier: Northern Precision Casting Co., Lake Geneva, Wisconsin.

• Originally constructed as a three-piece stamping/weldment, the 3.9-oz, 3.44 x 3.15 x 1.49-in. new casting design offers lighter weight (29% reduction), a one-piece construction, increased strength and a smooth sanitary finish (an important requirement for the food service industry).

• The conversion to casting from a multi-piece weldment resulted in a 70% cost savings for the customer.

• To accommodate the thin sections of the component, the foundry designed a unique gating and tooling system that uses wedge gates and gating into the top of the component to ensure against porosity.

5. Fan Frame Hub

• Material: Titanium. • Process: Investment

casting. • Casting Supplier:

Precision Castparts Corp. (PCC), Portland, Oregon.

A fan frame hub for General Electric’s CF-6-80C engine for Boeing’s 747, 767 and MD-11 aircraft.

Material:Titanium.• Process: Investment casting.

• This single 52-in. titanium investment casting replaced 88 stainless steel parts (from five vendors) that were previously machined and welded together.

• The casting, which supports the front fan section of the engine and ties it to the compressor section, provides improved strength and dimensional control in addition to a 55% weight reduction.

• Conversion to a metal casting allowed GE to include several unique details including bosses, flanges and a 2-in. larger overall diameter.

This single 52-in. titanium investment casting replaced 88 stainless steel parts (from five vendors) that were previously machined and welded together.

The casting, which supports the front fan section of the engine and ties it to the compressor section, provides improved strength and dimensional control in addition to a 55% weight reduction.

Conversion to a metal casting allowed GE to include several unique details including

bosses, flanges and a 2-in. larger overall diameter.

6. Racing car upright

• Material: Titanium 6246.

• Casting Supplier: Coastcast Corp., Rancho Dominguez, California.

Normally manufactured via machining or welding, four of these one-piece cast components were manufactured via rapid prototyping and investment casting from design to delivery in 8 weeks.

Using rapid prototyping with the investment casting process eliminated an up-to-$50,000 tooling cost for these components.

manufacture the components, they don’t require any rework during use. The cast titanium provided the same strength—but at a reduced weight—as 17-4PH steel (the other material considered). In addition, with no welds required to

7. Housing actuator for an engine for Hamilton Sundstrand.

• Material: A203 aluminum alloy.

• Casting Supplier: Cabiran, Ltd., Kibbutz Cabri, Israel.

With wall thickness to 0.12 in., this casting requires moderate strength, good stability and resistance to stress-corrosion cracking to 600F (316C).

This casting exhibits mechanical properties at room temperature of 32-ksi tensile strength, 24-ksi yield strength and 1.5% elongation, while maintaining a 16-ksi tensile strength and 4% elongation at 600F.

The component's as-cast surface finish meets the customer's requirements, and the invest casting process reduced the customer's finishing and machining costs.

SEMI-PERMANENT MOLD CASTING

Semi-permanent mold is a casting process - producing Aluminum alloy castings - using re-usable metal molds and sand cores to

form internal passages within the casting. Molds are typically arranged in two halves - the sand cores being put into place before the two halves are placed together. The molten metal flows into the mold cavity and surrounds the sand core while filling the mold cavity. When the casting is removed from the mold the sand core is removed

from the casting leaving an internal passage in the casting.

The re-usable metal molds are used time and again, but the sand cores have to be replaced each time the product is cast, hence the term semi-permanent molding.

Semi-permanent molding affords a very high precision quality to the

casting at a reduced price compared to the sand casting processes.

8. Aluminum composite alloy

• Material: 359/SiC/20p aluminum composite alloy.

• Process:Semi-permanentmold casting.

• Casting Supplier: Eck Industries,Inc., Manitowoc, Wisconsin.

The brake rotor was converted to an aluminum metal matrix composite (MMC) alloy casting at a 50% weight reduction, with the same casting yield and without a loss in performance.

In terms of mechanical properties, the aluminum MMC brake rotor’s modulus and its wear rate in application are the same as

cast iron.

9. Bucket chain link for a conveyor system

• Material:C95410 nickel aluminum bronze.

• Process:Permanent mold casting.

• Casting Supplier: Piad Precision Casting Corp., Greensburg, Pennsylvania.

PERMANENT MOLD CASTINGPRODUCTS

• Material:C95410 nickel aluminum bronze.

• Process: Permanent mold casting.

• Casting Supplier: Piad Precision Casting Corp., Greensburg, Pennsylvania.

10. BUCKET CHAIN

Previously made from two steel stampings welded together with two tube sections and subsequently tin-plated for corrosion resistance (r), this bronze cast component (l) now is a one-piece permanent mold casting.

The cast component (l) exhibits good corrosion resistance (without plating or

11. Manual Trip

• Material:Copper aluminum bronze alloy.

• CastingSupplier: Piad Precision Casting Corp., Greensburg, Pennsylvannia.

Originally manufactured by fabricating and welding 7 components, pressing in a steel spring pin, and adding a zinc chromate coating for corrosion protection, this part was converted to a single permanent mold casting with a cast-in stainless steel pin.

By casting in the pin, the foundry reduced the component's cost by eliminating the reaming and pressing operations.

The foundry's alloy provides the necessary corrosion resistance to the component, thus

eliminating the zinc-chromate coating previously required.

12. Felsted Division/Furon’s foot pedal control lever.

• Material: Zamak 3. • Process: Diecasting. • Casting Supplier:

CrecoCast, Seville, Ohio.

The lever originally was designed as a steel sand component with machining operations to size the shaft, pivot hubs and cable connection holes.

The die cast component combined two levers (for 2- and 3-in. cable travel) and provided connecting holes for different cable travel lengths.

The redesign held the required hole diameter tolerance of ±0.001 in. and the hub diameter

tolerance of +0.002, -0.001 in. while eliminating a lever and machining

requirements. This reduced component cost by 91%.

13. Instrument panel frame for the Cadillac DeVille.

• Material: AZ91 magnesium alloy.

• Process: Diecasting. • Casting Supplier:

Intermet Corp’s Hannibal Plant, Hannibal, Missouri.

Originally manufactured as a steel stamping, this component was redesigned into a two-piece die casting to better control tolerances and to fit the end-user’s mounting requirements. The design also allows more flexibility for future vehicle platform changes.

The 15-lb cast component reduced the part’s original weight by 45 lb while reducing tool-building time, delivery cost and lead time.

The foundry assembles the frame before delivery to the end-user for installation.

14. Valve spacers for Warren Rupp’s Sandpiper II air-actuated pumps.

• Material: ZA-8 zinc alloy.

• Process: Diecasting. • Casting Supplier:

CrecoCast, Seville, Ohio.

Previously machined from stainless steel bars, the valve spacers now are hot chamber die cast at net shape, eliminating secondary machining.

In addition to the cost reductions achieved by casting, Warren Rupp’s designers were

able to maximize air flow with the cast spacers by designing for fit and function without the restrictions of machining from

bar stock.

NO BAKE CASTING The No-Bake Sand

Casting process consists of sand molds created using a wood, metal or plastic pattern. Sand is mixed with a urethane

binder and deposited into a box containing the

pattern (and all necessary formers and inserts) for

pouring. Filling a wood mold with sand

PRODUCTS 15. TENSIONER PULLEY

Material: Gray iron

Process: Nobake sand

Casting Supplier: Wellsville Foundry, Wellsville, Ohio

This 175-lb component is used as a brake that puts tension on a 4 ft. wide roll of rubber feeding into a tire press.

Converted from a steel fabrication (two ring burn-outs with spokes), the

foundry provided the end-user with a 50% cost savings.

Previously made from two steel stampings welded together with two tube sections and subsequently tin-plated for corrosion resistance (r), this bronze cast component (l) now is a one-piece permanent mold casting.

The cast component (l) exhibits good corrosion resistance (without plating or painting), 50 ksi yield strength and 95 ksi tensile strength.

By converting this part to a copper-based permanent mold casting, the

16. Suspension crossmember

• Material:B356 aluminum alloy.

• Casting Supplier: CMI-Precision Mold, Inc., Bristol, Indiana.

This 26-lb safety-critical component was redesigned to an aluminum casting from a steel weldment, resulting in a 14-lb weight reduction.

The casting’s dimensional tolerances are held to 0.5 mm across the length of the part, a threefold reduction over the previous design.

The casting’s mechanical properties include 44 ksi ultimate strength, 32 ksi yield strength and 10.4 x 106 psi Young’s modulus.

17. Bracket for a piston cooling system

• Material:953 aluminum bronze.

• Process:Permanentmold casting.

• Casting Supplier: Aurora Metals, L.L.C. (Hiler Industries), Montgomery, Illinois.

This 0.8-lb component was converted to permanent mold casting to eliminate the leaks inherent in the previous manufacturing method. In addition, the conversion realized a cost savings by reducing man-hours and eliminating heat treatment as permanent mold casting achieves the required mechanical properties.

Permanent mold casting allows a stainless steel tube insert to be cast directly into the bracket.

Green Sand Casting

18. Cleaning Brush

• Material: 65-45-12 ductile iron.

• Process:Green sand casting.

• Casting Supplier: Smith Foundry Co., Minneapolis

Previously manufactured as a four-piece weldment, this component was redesigned as a single casting at a $3/casting, $72,000/year savings to the customer.

The weldment experienced failure and breakage under heavy shock loading. The conversion to cast ductile iron eliminated the field failure and also incorporated the three holes in each blade as-cast to eliminate post-process drilling.

19. Carrier component

• Material: Steel • Process:Green sand • Casting Supplier: The

Falk Corp., Milwaukee, Wisconsin

Converted from a fabrication, this component design was the result of foundry and end-user engineering collaboration.

The casting design (especially its volume) was optimized through casting process modeling, resulting in weight and cost savings for the component.

The casting meets all necessary mechanical properties while fitting in the same application envelope as the previous fabrication.

20. Powerhead for a pallet truck.

• Material: A356-T6 aluminum.

• Process:Green sand molding.

• Casting Supplier: Wisconsin Aluminum Foundry Co., Inc., Manitowoc, Wis.

This single-piece casting replaced a 21-piece weldment. The casting eliminated the need for extensive and complicated fixturing of the weldment. The cast component also allowed for the addition of features for accessory mounting points that would have been difficult to accomplish as a weldment.

The largest benefit of the casting is the increased throughput of the parent product, resulting in savings in purchasing, receiving,

stocking, distribution, fabrication and assembly. With the conversion, there was a 15% reduction in assembly time, 18% cost

reduction per part and a 45% weight reduction.

Lost foam process The Lost Foam Casting process originated in

1958 when H. F. Shroyer was granted a patent for this cavityless casting method, using a

polystyrene foam pattern imbedded in traditional green sand. The polystyrene foam pattern left in the sand is decomposed by the molten metal.

The molten metal replaces the foam pattern, precisely duplicating all of the features of the

pattern. Like investment casting (Lost Wax), a pattern must be produced for every casting

made. The Evapcast Division of Advanced Cast Products began producing lost foam castings in

1987, after three years of research and development.

21. Center ring for a fall protection system

• Material: Manganese bronze.

• Process: Lost foam casting.

• Casting Supplier: Irish Foundry and Manufacturing, Inc., Seattle, Washington.

Redesigned to a lost foam component, the 1-lb casting provided a 70% cost savings to the customer due to reduced machining and production time.

Cast in high-tensile manganese bronze, the component must withstand 5000 lb of pressure in application.

The casting incorporates thin to thick to thin wall designs without defects, a detail made easier in lost foam casting.

22. Lifeline horizontal slide for safety equipment.

• Material: Manganese bronze.

• Process: Lost foam casting.

• Casting Supplier: Irish Foundry & Manufacturing, Inc., Seattle.

By redesigning this 2-lb, 4 x 3-in.-diameter component as a two lost-foam castings with a near-net-shape, the foundry was able to reduce grinding time by 80% (because risers are eliminated as well as the riser contacts that must be ground) and eliminate machining.

The redesign to lost foam resulted in higher aesthetic qualities, including rounded edges

and smooth passageways.

CASTING TECHNIQUES FOR SINGLE CRYSTAL GROWING (S.C.G.)

• POLYCRYSTALLINE- ANISOTROPY• SINGLE CRYSTAL- PROPERTIES SAME IN

ALL DIRECTIONS• CASTING OF GAS TURBINE BLADES BY

S.C.G.

CASTING TECHNIQUES FOR SINGLE CRYSTAL GROWING (S.C.G.)

CONVENTIONAL USE OF CERAMIC MOULD

GRAINS WITH THE ABSENCE OF THERMAL GRADIENT

DIRECTIONAL SOLIDIFICATION PROCESS CERAMIC MOULD PREHEATED.

MOULD SUPPORTED BY WATER COOLED CHILL PLATES.

AFTER POURING, ASSEMBLY LOWERED

CRYSTALS GROW AT CHILL PLATE SURFACE UPWARD. COLUMNAR GRAINS FORM

CONVENTIONAL

• USE OF CERAMIC MOULDGRAINS- AS WITH THE ABSENCE OF THERMAL

GRADIENTPRESENCE OF GRAIN BOUNDARIES- MAKES

STRUCTURE SUSCEPTIBLE TO CREEP AND CRACKING ALONG BOUNDARIES

DIRECTIONAL SOLIDIFICATION PROCESS, (1960’s)

CERAMIC MOULD PREHEATED. MOULD SUPPORTED BY WATER COOLED CHILL

PLATES.AFTER POURING, ASSEMBLY LOWERED CRYSTALS GROW AT CHILL PLATE SURFACE

UPWARD. COLUMNAR GRAINS FORMBLADE DIRECTIONALLY SOLIDIFIED WITH

LONGITUDINAL- NOT TRANSVERSE- GRAIN BOUNDARIES. THUS STRONGER

SINGLE CRYSTAL BLADES, (1967),MOULD HAS CONSTRICTION IN THE SHAPE OF CORK

SCREWTHIS CROSS SECTION ALLOWS ONLY ONE CRYSTAL

TO FIT THROUGHWITH THE LOWERING, SINGLE CRYSTAL GROWS

UPWARD THROUGH CONSTRICTIONSTRICT CONTROL OF MOVEMENT NEEDEDTHERE IS LACK OF GRAIN BOUNDARIES, MAKES

RESISTANT TO CREEP AND THERMAL SHOCK.--EXPENSIVE

SINGLE CRYSTAL GROWING (S.C.G.)• FOR SEMICONDUCTOR INDUSTRY

• CRYSTAL PULLING METHOD- CZOCHRALSKI PROCESSCZOCHRALSKI PROCESS• SEED CRYSTAL DIPPED INTO THE MOLTEN

METAL, PULLED SLOWLY, (AT 10 m/ s), WITH ROTATION

• LIQUID METAL SOLIDIFIES ON THE SEED AND CRYSTAL STRUCTURE CONTINUED THROUGHOUT

FLOATING –ZONE METHOD

• POLYCRYSTALLINE ROD (SILICON)- ALLOWED ALLOWED TO REST ON A SINGLE CRYSTALTO REST ON A SINGLE CRYSTAL

• INDUCTION COIL HEATS THE PIECES• COIL MOVED UPWARD SLOWLY (20 m/ s) • SINGLE CRYSTAL GROWS UPWARD WITH

ORIENTATION MAINTAINED• THIN WAFERS CUT FROM ROD, CLEANED,

POLISHED• USE IN MICROELECTRONIC DEVICES

PLASTER MOULD CASTING• For casting silver, gold, Al, Mg, Cu, and alloys of brass and

bronze.• Plaster of Paris (Gypsum) (CaSo4.nH2O) used for cope and drag

moulding• A Slurry of 100 parts metal casting plaster and 160 parts water

used. • Plaster added to water and not water to plaster. To prevent cracks,

20-30% talc added to plaster. Lime and cement to control expansion• Stirred slowly to form cream Poured carefully over a match plate

pattern (of metal)• Mould vibrated to allow plaster to fill all cavities. • Initial setting at room temperature(setting time reduced by either

heating or by use of terra-alba/ magnesium oxide)• Pattern removed• Cope and drag dried in ovens at 200- 425 C(about 20 hours)• Mould sections assembled

+ points • Dimensional accuracy 0.008 t0 0.01 mm per mm• Excellent surface finish as no sand used.. No further

machining or grinding• Non ferrous thin sectioned intricate castings made.

- points• Limited to non ferrous castings.(sulphur in gypsum

reacts with ferrous metals at high temperatures)• Very low permeability as metal moulds used. Moulds

not permanent, destroyed when castings removed.

FROZEN MERCURY MOULDING (MERCAST PROCESS)

• Frozen Mercury used for producing precision castings• Metal mould prepared to the shape with gates and sprue holes• Placed in cold bath and filled with acetone (to act as lubricant)• Mercury poured into it, freezes at –20 C, after a few minutes

(10mins)• Mercury Pattern removed and dipped in cold ceramic slurry

bath. • A shell of 3 mm is built up. Mercury is melted and removed at

room temperature.• Shell dried and heated at high temperature to form hard

permeable shape.• Shell placed in flask- surrounded by sand-, preheated and

filled with metal. • Solidified castings removed.

• For both ferrous and non ferrous castings.(melting temperature upto 16500C)

• Very accurate details obtained in intricate shapes• Excellent surface finish, machining and cleaning

costs minimum.• Accuracy of 0.002 mm per mm obtained.

• But, casting process costly.• Casting cost high.

23.An ice cutter used in an industrial ice machine.Material:316 stainless steel.

• Converted from a stainless steel fabrication consisting of 4 stampings, bar stack and a form rolled base, this one-piece casting has an enhanced overall efficiency and performance.

• The conversion to casting reduced the customer's annual cost by more than $100,000, eliminated extensive straightening operations due to warping in the welding process, and reduced the component's high scrap.

• The finished cast component is supplied by the foundry after being completely machined to print specifications and solution-annealed.

24.Racing car upright for Minardi Formula 1.Material:Titanium 6246.

• Normally manufactured via machining or welding, four of these one-piece cast components were manufactured via rapid prototyping and investment casting from design to delivery in 8 weeks.

• Using rapid prototyping with the investment casting process eliminated an up-to-$50,000 tooling cost for these components.

• The cast titanium provided the same strength—but at a reduced weight—as 17-4PH steel (the other material considered). In addition, with no welds required to manufacture the components, they don’t require any rework during use.

25. Housing actuator for an engine for Hamilton Sundstrand.

Material:A203 aluminum alloy.

• With wall thickness to 0.12 in., this casting requires moderate strength, good stability and resistance to stress-corrosion cracking to 600F (316C).

• This casting exhibits mechanical properties at room temperature of 32-ksi tensile strength, 24-ksi yield strength and 1.5% elongation, while maintaining a 16-ksi tensile strength and 4% elongation at 600F.

• The component's as-cast surface finish meets the customer's requirements, and the invest casting process reduced the customer's finishing and machining costs.

26. Spacer component for an aerospace radar system.

Material:17-4PH steel.• Process: Investment casting.

• Converted from a weldment, the cast design reduced component weight and machining time required.

• The 1-lb component is cast near-net-shape with zero draft and webbed walls.

27. A laser chassis (housing) for an Israeli Aircraft Industries night targeting system.Material:A357 aluminum alloy.

• Process: Investment (lost wax) casting.

• Previously machined from A6061 aluminum wrought alloy, the component was redesigned for investment casting at a cost savings of $25,000/part.

• The casting achieves mechanical properties of 41 ksi tensile strength, 31 ksi yield strength and 3% elongation in areas up to 2.5 mm thick and 38 ksi tensile strength, 28 ksi yield strength and 5% elongation in areas over 2.5 mm thick.

DESIGN CONSIDERATIONSCAREFUL CONTROL OF LARGE NUMBER OF

VARIABLES NEEDED- • CHARACTERISTICS OF METALS & ALLOYS

CAST• METHOD OF CASTING• MOULD AND DIE MATERIALS• MOULD DESIGN• PROCESS PARAMETERS- POURING,

TEMPERATURE, • GATING SYSTEM• RATE OF COOLING Etc.Etc.

• Poor casting practices, lack of control of process variables- DEFECTIVE CASTINGS

• TO AVOID DEFECTS-• Basic economic factors relevant to casting

operations to be studied.• General guidelines applied for all types of castings

to be studied.

CORNERS, ANGLES AND SECTION THICKNESS• Sharp corners, angles, fillets to be avoided Cause cracking and tearing during solidification• Fillet radii selection to ensure proper liquid metal flow-

3mm to 25 mm. Too large- volume large & rate of cooling less• Location with largest circle inscribed critical. Cooling rate less shrinkage cavities & porosities result- Called HOT SPOTS

• LARGE FLAT AREAS TO BE AVOIDED- WARPING DUE TO TEMPERATURE GRADIENTS

• ALLOWANCES FOR SHRINKAGE TO BE PROVIDED• PARTING LINE TO BE ALONG A FLAT PLANE- GOOD AT CORNERS OR EDGES OF CASTING• DRAFT TO BE PROVIDED• PERMISSIBLE TOLERANCES TO BE USED• MACHINING ALLOWANCES TO BE MADE• RESIDUAL STRESSES TO BE AVOIDED

ALL THESE FOR EXPENDABLE MOULD CASTINGS.

• DESIGN MODIFICATIONS TO AVOID DEFECTS-

• AVOID SHARP CORNERS • MAINTAIN UNIFORM CROSS SECTIONS• AVOID SHRINKAGE CAVITIES• USE CHILLS TO INCREASE THE RATE OF COOLING• STAGGER INTERSECTING REGIONS FOR UNIFORM CROSS SECTIONS• REDESIGN BY MAKING PARTING LINE STRAIGHT• AVOID THE USE OF CORES, IF POSSIBLE• MAINTAIN SECTION THICKNESS UNIFORMITY BY REDESIGNING (in die cast products)

PROPERTIES AND TYPICAL APPLICATIONS OF

CAST IRONS, NON FERROUS ALLOYS etc. Tables shall be supplied

General Cost Characteristics of Casting Processes

PROCESS COST PRODUCTION RATE (pc/hr)

DIE EQUIPMENT LABOUR

SAND L L L-M <20SHELL L-M M-H L-M <50PLASTER L-M M M-H <10INVESTMENT M-H L-M H <1000PERMANENT MOULD

M M L-M <60

DIE H H L-M <200CENTRIFUGAL M H L-M <50 NITC

THIXOTROPIC DIE CASTING

Some of the die-cast joints used in the Insight's aluminum body are made using a newly developed casting technology invented by Honda engineers, called Thixotropic Die Casting.

Thixotropic Die Casting uses aluminum alloy that has been heated to a semi-solid condition, instead of the molten, liquid state normally used in die casting.

Pieces made with molten aluminum must be more highly processed and refined before casting.

However, Thixotropic Die Casting requires less energy for smelting (an important consideration since aluminum is more expensive than steel), and owes much of its strength to the controlled formation of discrete aluminum crystals within the metal casting.

Thixotropic casting involves vibratory casting of highly thixotropic slips of very high solids loadings that are fluid only under vibration, using porous or nonporous molds.

It is quite different from other conventional and new methods for solid casting ceramics, including vibroforming, vibraforming, in situ flocculation, direct coagulation casting, and gel casting. This is demonstrated in Table 1.

Casting Method and Major Features Differentiating Properties of Thixotropic Casting

Vibroforming – Requires a cement for setting

Cement is not required for setting

Vibraforming – Requires excess counter ions and centrifugation for settling

Addition of organic deflocculant/binder and vibration are the only necessary steps

In situ flocculation – requires the addition of urea and heating to control the pH to the isoelectric point

No urea additions, heating, control of pH, or attainment of the isoelectric point are required

Injection moulding – required large quantities (15-30wt%) of entraining polymer and pressurized mould feeding

Only traces (<1%) of binder are needed and no pressure needed for filling of moulds

Direct coagulation casting – requires control of the pH through an enzyme catalysed decomposition reaction

No enzyme additions or control of pH are required

Gel casting – requires use of a neurotoxin to cause polymeric gelling

No polymer additive or polymerization are required

Table 1. Thixotropic casting in comparison with the alternatives.

Thixotropic casting is a little-known derivative of solid slip casting, having reportedly been used in the refractories industry in the early 1970's. Since then, the refractories industry has since largely embraced low-cement and ultra-low-cement castables. It is also a suitable process for forming ceramic matrix composites and metal-ceramic functionally gradient materials. Thixotropic casting involves vibratory casting of highly thixotropic slips of very high solids loadings that are fluid only under vibration, using porous or nonporous molds. It is quite different from other conventional and new methods for solid casting ceramics, including vibroforming, vibraforming, in situ flocculation, direct coagulation casting, and gel casting. (This is demonstrated in Table 1)

Continuous Casting

Figure 1

Ejector Pump

The ejector pump is a type of vacuum pump. Gas is removed from a container by passing steam or water at a high velocity through a chamber that is connected to the container. The mixing chamber contains both the gas from the container and the steam or water. At the inlet port, the ejector pump is connected to the container that is being evacuated. NITC

• Melting

• For both ferrous and non ferrous castings.(melting temperature upto 16500C)

• Very accurate details obtained in intricate shapes• Excellent surface finish, machining and cleaning

costs minimum.• Accuracy of 0.002 mm per mm obtained.

• But, casting process costly.• Casting cost high.

• PRODUCTION OF ALLOY WHEELS• METHOD OF PRODUCTION; COUNTER

PRESSURE DIE CASTING• • The manufacturing process commences

with the smelting of pure aluminium ingots in a 5-ton basin type furnace.

• The furnace is a dry sole type furnace whose function is to smelt the primary raw material, and reprocess alloy scraps consisting of:- wheels used in destructive testing by the quality control department, and the risers and gates removed from the wheels following the casting process. From the dry sole furnace, the molten aluminium is transferred to the alloy induction furnaces via a feed channel to enable the mixing and smelting of the elements required in the preparation of the alloy – AlSi 7.

• A spectrometer equipped quality control laboratory is used during the process of alloy preparation to ensure the composition of the alloy meets the required specification during this stage of the preparation process. Spectrometer analysis sampling is also applied randomly to finished wheels.

• Molten alloy is transferred to holding furnaces for eventual transfer to the casting machines. After the molten alloy has been tested for conformance to specifications, it is transported to the alloy treatment station where the alloy is submitted to three procedures performed by an automatic process control system. The treatment unit introduces salts into the molten alloy using a high-speed spinner, where the alloy purification is assisted by the use of nitrogen gas jets. The three procedures to which the molten alloy is submitted are:-

Degassing Refining Modifying

These processes are intrinsic to the removal of all undesirable impurities in the molten alloy. The automation of these processes improves the product quality control, production rates and importantly minimizes wastage by reducing the possibilities of rejection of the finished product. Following the procedures to ensure that the molten alloy conforms to precise specification, it is transported in holding furnaces to the low pressure casting machines. These furnaces are designed to produce casting by employing pressurised air within a range of 0.3 – 1.0 atm., the pressurization being monitored and varied by a computerized process control system according to flow requirements NITC

Computerized process technology automatically controls the casting process, and then, at the end of the 4.5 minute casting cycle, cools and ejects the wheel onto a catcher arm designed for this purpose.

Holding furnaces contain between 500-750kg of molten alloy - sufficient for up to approx. 4 hours of casting operations. When the holding furnace is exhausted it is exchanged for a full replacement furnace using the transfer shuttle - illustrated above - without interruption to the casting process.

Hydraulic systems control many of the unit’s operating movements, and, due to high operating temperatures many measures have to be taken to enable minimization of risk and reduction of maintenance of these systems. For example, it is necessary for all hydraulic systems to employ fire resistant fluids thereby eliminating fire risk. Likewise, all hydraulic hoses have to be metal covered and insulated against accidental splashes of molten metal.

The operators of the Counter Pressure Casting Machines perform an initial visual quality control as the wheels are ejected from each unit and palleted ready for transport to the Riser cutting department.At this first stage in the machining process following casting, the removal of the gates and risers is carried out by automated machines designed for this purpose – with a cycle time of 50 seconds per wheel. The CNC riser-cutting unit performs the following operations

Pre-boring of the central hole of the wheel • · Removal of the channel burrs corresponding to the surface joints on the Die’s

moving parts • · Trimming upper and lower edges of the wheel • The working cycle of the Riser cutting unit is completely automated to improve both

quality control and production rate per machine. All waste products are collected for recycling at the foundry. The machine operations are performed under a suction hood to remove aluminium dust and particulates from the environment in proximity to this unit.

• Customarily, after the machining processes have been completed on the newly cast wheels, the wheels are passed to the quality control unit for examination under a variety of non-destructive and destructive tests. Batch sampling of the wheels may involve taking a 1-2mm scrape taken using a lathe, and running a spectrometer analysis of the resulting alloy sample.

• X-Ray analysis machine in Quality control department• Non-destructive testing is undertaken using radiography processes. It is common practice for

the VM customers to include within their contractual requirements testing volumes and timescales (i.e. before or after machining). The X-ray control equipment can be pre-set with information from up to 1000 wheel designs, and wheels can be inspected on a wide variety of positions / angles (normally 20 position variants).

• The wheel manipulator for handling the wheels during the inspection cycle has 5 fully computerized axes and a roller conveyor automatically provides loading/unloading of the machine with the wheels for inspection.

• The X-Ray unit takes 2 wheels at a time - one in process of inspection cycle, and a second wheel in a ‘holding’ position. As the testing machine completes the automated inspection cycle, it simultaneously ejects the inspected wheel, puts the second wheel into position for inspection and draws another wheel into the ‘holding’ position. Thus the performance inspection cycle is enhanced to its maximum possibility. During an inspection, the operator monitors the x-ray image on a viewing console and has the possibility of magnifying the image or ‘replaying’ the process to precisely identify any casting defect exposed by this machine.

• The next stage of the quality control process is undertaken on Geometrical control benches where the physical dimensions of the wheels are compared with the specification standard using pantographs and micrometers.

• The semi- finished product, having been submitted to various machining and quality control procedures are passed to the finishing dept. which - dependent upon client specification - either submits the wheels through an automated paint shop - or polishing line where a bright lacquer finish has been specified.

• The finished wheels are then palleted and wrapped in polyethylene film - ready for transfer to a wheel/tyre assembly plant - prior to final shipment to the production lines of the VM customer

• The pallet/box wrapping equipment consists of a motorized wrapping machine – allowing pallets to be placed on a rotating turntable, and providing film wrapping through this rotation with a fixed unit holding the polyethylene roll.

• The finished wheels are stored on pallets/boxes until shipping. • COUNTER PRESSURE DIE CASTING MACHINES• The casting machines have evolved over 25 years of development and manufacturing

experience of counter-pressure & low pressure casting machines. • Simplicity of design, operating convenience and ease of maintenance are the core

attributes that produce highest levels of egonomics and safety. • The above principles are well emphasised by the rugged vertical tie-bar construction

incorporating an integral holding furnace. • The well tried and proven technical solutions provide stability, accuracy in guiding and

controlling the precision of the moving parts, and include essential rigidity, operational dependability and longevity of the machines.

• All machines are designed to withstand heavy-duty service in foundries operating continuous 24 hour cycles.

CASTING DEFECTS

SURFACE

METALLIC PROJECTION (4)DEFECTIVE SURFACE (11)CHANGE IN DIMENSION- WARPINCOMPLETE CASTING MISRUN, RUNOUTCAVITY- BLOWHOLES, SHRINKAGE PINHOLESDISCONTINUITY

HOT CRACKCOLD SHUT, COLD CRACK

SUBSURFACE

SUBSURFACE CAVITYINCLUSIONSDISCONTINUITY

Casting Defects• Metal casters try to produce perfect castings.• A few castings, however, are completely free of

defects. • Modern foundries have sophisticated inspection

equipment which can detect small differences in size and a wide variety of external and even internal defects. For example, slight shrinkage on the back of a decorative wall plaque is acceptable whereas similar shrinkage on a position cannot be tolerated.

• No matter what the intended use, however, the goal of modern foundries is zero defects in all castings

• Scrap castings cause much concern.

• In industry, scrap results in smaller profits for the company and ultimately affects individual wages.

• Scrap meetings are held daily. Managers of all the major departments attend these meetings. They gather castings that have been identified as scrap by inspector. The defect is circled with chalk. An effort is made to analyze the cause of the defect, and the manager whose department was responsible for it is directed to take corrective action to eliminate that specific defect in future castings.

• There are so many variables in the production of a metal casting that the cause is often a combination of several factors rather than a single one.

• All pertinent data related to the production of the casting (sand and core properties, pouring temperature) must be known in order to identify the defect correctly.

• After the defect is identified attempt should be to eliminate the defect by taking appropriate corrective action.

CASTING DEFECTSSURFACE

METALLIC PROJECTION –• Swell, Crush, Mould Drop, Fillet Vein

• DEFECTIVE SURFACE –• Erosion Scab, Fusion, Expansion Scab, Rat tails,

Buckle, Seams, Gas Runs, Fillet Scab, Rough Surface, Slag Inclusion, Elephant Skin

• CHANGE IN DIMENSION- • Warped casting• INCOMPLETE CASTING- • Misrun, Run out• CAVITY- • Blow Holes, Shrinkage cavity, Pinholes• DISCONTINUITY-• Hot6 Cracking, Cold Shut, Cold Cracking

SUBSURFACESUBSURFACE CAVITY- Blow Holes, Pin Holes, ShrinkagePorosity, Internal Shrinkage,

SevereRoughness

INCLUSIONS- Gas Inclusions, Slag, Blow Holes

DISCONTINUITY- Cold Shuts

Repairability

FINS OR FLASH ON CASTINGS -AsMetallic Projections

• Joint flash or fins. Flat projection of irregular thickness, often with lacy edges, perpendicular to one of the faces of the casting. It occurs along the joint or parting line of the mold, at a core print, or wherever two elements of the mold intersect.

• Possible Causes• Clearance between two elements of the mold or between

mold and core; • Poorly fit mold joint. • Remedies• Care in pattern making, molding and core making; • Control of their dimensions; • Care in core setting and mold assembly; • Sealing of joints where possible.

• Flask was disturbed while investment was setting. • Base was removed too soon. • Flask was allowed to partially dry before dewaxing. • Incorrect dewaxing or a furnace malfunction. • Flask burned out and allowed to cool below (260oC) before

casting reheating, flask allowed to cool between dewax and placement in preheated oven.

• Flask was improperly handled or dropped. • Speed was set too high on centrifugal casting machine. • Patterns were placed on one plane. The should be staggered

on top rack. • Incorrect water powder ratio was used. • Not enough investment was placed over the patterns. • Flask was placed too close to heat source in burnout oven. • Flasks were not held at low burnout temperature long

enough.

DEFECTS IN CASTINGS- CAN BE ELIMINATED/MINIMISED BY PROPER DESIGN, MOLD PREPARATION, PROPER

POURING.

DEFECTS IN CASTINGS- AS HOT TEARS - DUE TO CONSTRAINTS IN LOCATIONS, CASTINGS

CANNOT SHRINK FREELY

Cavities

• Blowholes, pinholes. Smooth-walled cavities, essentially spherical, often not contacting the external casting surface (blowholes). The largest cavities are most often isolated; the smallest (pinholes) appear in groups of varying dimensions.

• The interior walls of blowholes and pinholes can be shiny, more or less oxidized or, in the case of cast iron, can be covered with a thin layer of graphite. The defect can appear in all regions of the casting.

• Possible Causes

• Because of gas entrapped in the metal during the course of solidification:

• Excessive gas content in metal bath (charge materials, melting method, atmosphere, etc.); Dissolved gases are released during solidification.

• In steel and cast irons: formation of carbon monoxide by the reaction of carbon and oxygen, presents as a gas or in oxide form. Blowholes from carbon monoxide may increase in size by diffusion of hydrogen or, less often, nitrogen.

• Excessive moisture in molds or cores.• Core binders which liberate large amounts of gas.• Excessive amounts of additives containing hydrocarbons.• Blacking and washes which tend to liberate too much gas. • Insufficient evacuation of air and gas from the mold cavity; -

insufficient mold and core permeability. • Entrainment of air due to turbulence in the runner system.

• Remedies• Make adequate provision for evacuation of air

and gas from the mold cavity• Increase permeability of mold and cores • Avoid improper gating systems• Assure adequate baking of dry sand molds• Control moisture levels in green sand molding

• Reduce amounts of binders and additives used or change to other types; -use blackings and washes, which provide a reducing atmosphere; -keep the spree filled and reduce pouring height

• Increase static pressure by enlarging runner height.

Discontinuities

• Hot cracking. A crack often scarcely visible because the casting in general has not separated into fragments. The fracture surfaces may be discolored because of oxidation. The design of the casting is such that the crack would not be expected to result from constraints during cooling.

• Possible Causes• Damage to the casting while hot due to rough handling or excessive

temperature at shakeout.

• Remedies• Care in shakeout and in handling the casting while it is still hot; • Sufficient cooling of the casting in the mold; • For metallic molds; delay knockout, assure mold alignment, use

ejector pins

Defective Surface

• Flow marks. On the surfaces of otherwise sound castings, the defect appears as lines which trace the flow of the streams of liquid metal.

• • Possible Causes• Oxide films which lodge at the surface, partially marking the

paths of metal flow through the mold.

• Remedies• Increase mold temperature; • Lower the pouring temperature; • Modify gate size and location (for permanent molding by

gravity or low pressure); • Tilt the mold during pouring; • In die casting: vapor blast or sand blast mold surfaces which

are perpendicular, or nearly perpendicular, to the mold parting line.

Incomplete Casting

• Poured short. The upper portion of the casting is missing. The edges adjacent to the missing section are slightly rounded, all other contours conform to the pattern. The spree, risers and lateral vents are filled only to the same height above the parting line, as is the casting (contrary to what is observed in the case of defect).

• Possible Causes• Insufficient quantity of liquid metal in the ladle; • Premature interruption of pouring due to workman’s error.

• Remedies• Have sufficient metal in the ladle to fill the mold; • Check the gating system; • Instruct pouring crew and supervise pouring practice.

Incorrect Dimensions or Shape• Distorted casting. Inadequate thickness, extending

over large areas of the cope or drag surfaces at the time the mold is rammed.

• Possible Causes• Rigidity of the pattern or pattern plate is not sufficient to

withstand the ramming pressure applied to the sand. The result is an elastic deformation of the pattern and a corresponding, permanent deformation of the mold cavity. In diagnosing the condition, the compare the surfaces of the pattern with those of the mold itself.

• Remedy• Assure adequate rigidity of patterns and pattern plates,

especially when squeeze pressures are being increased.

Inclusions or Structural Anomalies

• Metallic Inclusions. Metallic or intermetallic inclusions of various sizes which are distinctly different in structure and color from the base material, and most especially different in properties. These defects most often appear after machining.

• Possible Causes• Combinations formed as intermetallics between the melt and metallic impurities

(foreign impurities); • Charge materials or alloy additions which have not completely dissolved in the

melt; • Exposed core wires or rods; • During solidification, insoluble intermetallic compounds form and segregate,

concentrating in the residual liquid.

• Remedies• Assure that charge materials are clean; eliminate foreign metals; • Use small pieces of alloying material and master alloys in making up the charge; • Be sure that the bath is hot enough when making the additions; • Do not make addition too near to the time of pouring; • For nonferrous alloys, protect cast iron crucibles with a suitable wash coating

• INCLUSIONS (FOREIGN PARTICLES) IN CASTINGS

• Patterns were improperly sprued to wax base or tree or not filleted, causing investment to break at sharp corners during casting.

• Flask was not sufficiently cured before placing into burnout oven. • Improper dewaxing cycle was used. • Flask was not cleaned from prior cast. • Loose investment in sprue hole. • Molten metal contains excess flux or foreign oxides. • Crucible disintegrating or poorly fluxed. • Improperly dried graphite crucible. • Investment was not mixed properly or long enough. • Contaminants in wax pattern. • Flask was not held at low burnout temperature long enough. • Flask was placed too close to heat source in burnout oven.

• POROSITY• Pattern is improperly sprued. Sprues may be

too thin, too long or not attached in the proper location, causing shrinkage porosity.

• Not enough metal reservoir to eliminate shrinkage porosity.

• Metal contains gas. • Mold is too hot. • Too much moisture in the flux. • Too much remelt being used. Always use at

least 50% new metal. • Metal is overheated. • Poor mold burnout.

• ROUGH CASTINGS• A poor quality pattern • Flask was not sufficiently cured before

placing into burnout oven. • Flask was held in steam dewax too long. • Metal, flask or both were too hot. • Patterns were improperly sprued. • Flask was placed too close to heat source

in burnout oven.

• BUBBLES OR NODULES ON CASTINGS

• Vacuum pump is leaking air. • Vacuum pump has water in the oil. • Vacuum pump is low on oil. • Investment not mixed properly or long

enough. • Invested flasks were not vibrated during

vacuum cycle. • Vacuum extended past working time.

• SPALLING (an area of the mold wall flakes into the mold cavity)

• Flask was placed into a furnace at low temperature (below 150oC) for an extended period.

• Flask was placed too close to the source of heat.

• Sharp corners are struck by metal at high centrifugal velocities.

• Improper burnout cycle was used.

• NON-FILL OR INCOMPLETE CASTINGS• Metal was too cold when cast. • Mold was too cold when cast. • The burnout was not complete. • Pattern was improperly sprued, creating

turbulence when casting in a centrifugal casting machine.

• Centrifugal casting machine had too high revolution per minute.

• GROWTH-LIKE ROUGH CASTING THAT RESISTS REMOVAL IN PICKLING SOLUTION

• Burnout temperature too high. • Mold temperature was too high when

casting. • Metal temperature was too high when

casting.

• SHINY CASTINGS• Carbon residue was left in the mold,

creating a reducing condition on the surface.

AVERAGE SURFACE ROUGHNESS VALUES BY VARIOUS PROCESSES

DESIGN CONSIDERATIONS

CAREFUL CONTROL OF LARGE NUMBER OF VARIABLES NEEDED-

• CHARACTERISTICS OF METALS & ALLOYS CAST

• METHOD OF CASTING• MOULD AND DIE MATERIALS• MOULD DESIGN• PROCESS PARAMETERS- POURING,

TEMPERATURE, • GATING SYSTEM• RATE OF COOLING Etc.Etc.

• Poor casting practices, lack of control of process variables- DEFECTIVE CASTINGS

• TO AVOID DEFECTS-• Basic economic factors relevant to casting operations to

be studied.• General guidelines applied for all types of castings to be

studied.

DESIGN CONSIDERATIONS

CORNERS, ANGLES AND SECTION THICKNESS• Sharp corners, angles, fillets to be avoided Cause cracking and tearing during solidification• Fillet radii selection to ensure proper liquid metal flow-

3mm to 25 mm. Too large- volume large & rate of cooling less• Location with largest circle inscribed critical. Cooling rate less shrinkage cavities & porosities result- Called HOT SPOTS

DESIGN MODIFICATIONS TO AVOID DEFECTS-

• AVOID SHARP CORNERS • MAINTAIN UNIFORM CROSS SECTIONS• AVOID SHRINKAGE CAVITIES• USE CHILLS TO INCREASE THE RATE OF COOLING• STAGGER INTERSECTING REGIONS FOR UNIFORM CROSS SECTIONS• REDESIGN BY MAKING PARTING LINE STRAIGHT• AVOID THE USE OF CORES, IF POSSIBLE• MAINTAIN SECTION THICKNESS UNIFORMITY BY REDESIGNING (in die cast products)

• LARGE FLAT AREAS TO BE AVOIDED- WARPING DUE TO TEMPERATURE GRADIENTS

• ALLOWANCES FOR SHRINKAGE TO BE PROVIDED• PARTING LINE TO BE ALONG A FLAT PLANE- GOOD AT CORNERS OR EDGES OF CASTING• DRAFT TO BE PROVIDED• PERMISSIBLE TOLERANCES TO BE USED• MACHINING ALLOWANCES TO BE MADE• RESIDUAL STRESSES TO BE AVOIDED

ALL THESE FOR EXPENDABLE MOULD CASTINGS.

DESIGN MODIFICATIONS TO AVOID DEFECTS- AVOID SHARP CORNERS TO REDUCE STRESS

CONCENTRATIONSNITC

DESIGN MODIFICATIONS TO AVOID DEFECTS- MAINTAIN UNIFORM CROSS SECTIONS TO AVOID HOT

SPOTS AND SHRINKAGE CAVITIES

GOOD DESIGN PRACTICE NITC

STAGGERING OF INTERSECTING REGIONS

DESIGN MODIFICATIONS TO AVOID DEFECTS- SECTION THICKNESS UNIFORMITY MAINTAINED

THROUGHOUT PARTNITC

DESIGN MODIFICATIONS TO AVOID DEFECTS

DESIGN MODIFICATIONS TO AVOID DEFECTS- USE OF METAL PADDING (CHILLS)

TO INCREASE RATE OF COOLING NITC

MAKING PARTING LINE STRAIGHT NITC

DESIGN MODIFICATIONS TO AVOID DEFECTS-IN DESIGN

INSPECTION OF CASTINGS• SEVERAL METHODS• VISUAL• OPTICAL• - FOR SURFACE DEFECTS• SUBSURFACE AND

INTERNAL DEFECTS THROUGH

NDTs & DTs

• PRESSURE TIGHTNESS OF VALVES BY SEALING THE OPENING AND PRESSURISING WITH WATER

EXERCISE

PROPERTIES AND TYPICAL APPLICATIONS OF

CAST IRONS, NON FERROUS ALLOYS etc. Tables shall be supplied

General Cost Characteristics of Casting Processes

PROCESS COST PRODUCTION RATE (pc/hr)

DIE EQUIPMENT LABOUR

SAND L L L-M <20SHELL L-M M-H L-M <50PLASTER L-M M M-H <10INVESTMENT M-H L-M H <1000PERMANENT MOULD

M M L-M <60

DIE H H L-M <200CENTRIFUGAL M H L-M <50 NITC

Steel Shaping: Hot Rolling and Continuous Casting Continuous casting (right, red arrows) is a method of

working steel that conveys the metal from its molten state to blooms, ingots, or slabs. The white-hot metal is poured into open-ended moulds and continues on through rollers cooled by water.

A series of guide rollers further shapes the steel into the desired form. However, hot rolling (left, blue arrows) is still the primary means of milling steel. This process begins with preshaped steel slabs, which are reheated in a soaking pit. The steel passes through a series of mills: the blooming mill, the roughing mill, and the finishing mill, which make it progressively thinner. Finally, the steel is wound into coils and transported elsewhere for further processing.

Ejector Pump

The ejector pump is a type of vacuum pump. Gas is removed from a container by passing steam or water at a high velocity through a chamber that is connected to the container. The mixing chamber contains both the gas from the container and the steam or water. At the inlet port, the ejector pump is connected to the container that is being evacuated. NITC

Cast PartsN

• Foundry Networks IPv6 Solutions for the New InternetFoundry continues to address the ongoing challenges faced by service provider and enterprise customers alike with industry-leading, hardware-based 10GbE and Gigabit Ethernet Layer 3 switches and routers for IPv4. Foundry Networks proven IronWare operating system (IronWareOS), now delivers a rich IPv6 feature set that allows customers to begin their migration path to IPv6. Foundry’s IPv6 implementation maintains many of the basic attributes of IPv4 while offering new capabilities and increased flexibility, and addressing key challenges inherent to IPV4 such as growth, quality of service and security. Features designed to provide smooth migration and support of dual-routing environments, are among them.

MeltingN

• June 2004 International

Conference

MERCAST PROCESS

New Installation Mercury Castings

Increases Quality, Repeatability With Shot Control System To successfully compete in today’s die casting industry, a firm must know its niche and be efficient. Mercury Castings, a division of Mercury Marine, casts more than two million pounds of aluminum a month for outboard engine components and other custom OEM applications. Located in Fond du Lac, Wisconsin, Mercury Castings started casting custom components for OEMs in the mid 1990s. Today, this business has grown to more than 20% of its total

aluminium castings production.

• Using the experience they’ve gained over the years, the company focuses on making big parts, ranging from 5-30 kg, where their technical expertise and production methods give them an advantage with OEM customers.

• Given the size and volume of parts, repeatability and

scrap reduction are critical factors for cost-effective production.

• Another major goal is the reduction of microporosity to produce higher quality parts.

• An important component of the process Mercury Castings uses to achieve these goals is the installation of a Sure-Trak shot control system on 24 of its die casting machines. The control system is a real time, all digital, closed loop shot control system produced by Visi-Trak Worldwide, L.L.C., Valley View, Ohio. The first retrofit with the control system at Mercury Castings was made in 1993 when a shot controller, integrated with a new HPM shotend, was installed on a 2500-ton die casting system. Nine more installations soon followed in the next few years. These were followed by further installations on 900- and 1200-ton die casting systems.

• Retrofitting the shot controllers has allowed us to convert older machines to a full closed loop system at a fraction of the cost of a new shot end, said Mark Potratz, senior process engineer at Mercury.

• They enable us to do a number of things, such as reduce air entrapment during the slow shot phase and control constant acceleration.

• Production benefits include reducing the scrap rate by up to 2% and decreasing microporosity by as much as 50% for certain parts.

•Equally important, repeatability of the casting process has improved significantly.

•As castings become more complex, the demand on the machine to be more repeatable increases,

•With the shot control system, we put in the process parameters and the machine monitors the shot. If we fall outside the parameters, we get a light or alarm. We’ve gotten to the point that if the light comes on, the casting is scrapped or set aside for X-ray evaluation.

• While different settings in the control system might be programmed depending on the part, a typical casting might use a closed loop motion block to slow the shot cylinder as the die is nearly full. The shot controller would slow the speed from 200 IPS to 100 IPS over a distance of 3 in. to begin reducing the kinetic force of the shot cylinder as impact approaches. Then, there would be a final open loop closing of the throttling valve at a fixed position to dampen the impact even further.

• Mercury Castings uses industry formulas and calculations to determine settings, as well as information that they have learned from their own experience.

• One example involves the ramping of certain areas in the shot. When this occurs, velocity increases and stepped velocity increases. The shot control velocity profile can be programmed in up to six separate motion blocks, and four electronic limit switch settings are available for initiating vacuum, start of intensification and follow through.

• Using the shot profile display, Mercury Castings can tune the deceleration of the shot end to the force that the clamp end can hold closed, allowing flash reduction and leading to more stability in the biscuit size.

• Reducing flash helps extend tool life and improves productivity because the operator can run one shot after another without extensive clean up.

Very little training is required to use the shot control system. The critical process settings can be password protected to prevent individual operators from changing defined parameters. This can be an important quality control advantage in a multi-shift operation. Experience in using the control systems also has made it easier to analyze and justify the cost benefits. Initial calculations, based on anticipated savings, have been verified now with historical data. Installation costs for retrofitting the shot control system also have declined for Mercury Castings because initial engineering costs have been eliminated for repeat applications.

• The Sure-Trak shot control system is a real-time, all digital, closed-loop system to increase die-casting quality. Mercury Castings has seen success in reducing air entrapment during the slow shot phase on a variety of parts, including these outboard engine covers

www.moderncasting.com/info

• Largest Vertically Parted Mold Machine Built for Denmark.

• DISA Group (with U.S. headquarters in Oswego, Illinois) received a contract for the delivery of a jumbo-sized DISA 280B vertical green sand molding system.

• Molds measure 850 x 1200 mm, making it the largest vertically parted green sand molding system ever produced.

• This new jumbo-sized molding system provides a space-saving, high-capacity and high-quality alternative to conventional horizontal molding lines. N

• It works on the vertically parted molding principle of blowing green sand into the mold chamber, which is subsequently squeezed into flaskless molds. In the inaugural installation, the DISA 280B is replacing a horizontal green sand molding line of a similar flask/box size. The foundry is making the switch from its existing horizontal molding arrangement to the large-scale vertically parted machine to gain competitiveness through productivity gains and enhanced casting quality. These improvements are fundamental to the foundry’s success in its market sector.

The contract includes the design and changeover of existing horizontal patterns to a vertical

orientation. This assures that the foundry will be able to continue to use more than 98% of its

existing patterns. The foundry expects to begin production without any compatibility problems as

the new line takes the same position of the existing mold line on the foundry floor.

The MM Casting Process

Design Considerations – Metal Specifications – Tooling – Machining –

Supply of Design Information – Inspection / Quality Assurance

Case Studies - Automobile Telephone Chassis - Cassette Slide

Ratchet - Casting for Satellite TV - Clamp - Computer Data Backup System - Gauge Body - Hand Held Breathalyzer - Light Shield - Regulator Valve - Roller Carrier Slide - Small Metal Connectors - Switch Gear - Twister

MM-Micro Metalsmiths in the field of Investment casting

The MM casting process – Precision investment casting process

The aim of this guide is to enable the designer to take advantage The aim of this guide is to enable the designer to take advantage of the technical and commercial benefits offered by the MM of the technical and commercial benefits offered by the MM

casting process. Also included in the guide are design ideas and casting process. Also included in the guide are design ideas and considerations to help and stimulate the design processconsiderations to help and stimulate the design process. .

T Micro Metalsmiths continues to develop its process so as to meet ever more exacting market challenges.

For over thirty years Micro Metalsmiths has refined its techniques for excellence in the production of copper

and aluminium alloy investment castings.

Micro Metalsmiths has combined its impressive investment casting technology with best practice CNC machining, so allowing many of the constraints placed

on engineering design to be overcome.

All this is carried out within a BSI accredited ISO 9001 Quality System.

TWhy use the MM casting process

•Reduce overall costs by Designing for Manufacture: simplify an assembly by combining a number of parts: eliminate joining processes: reduce the part count whilst improving the integrity of the finished product.

•Reduce time to market through use of Rapid Prototyping technology and obtain casting, machining, assembly and packaging from one source. Finished metal parts are deliverable from concept in less than four weeks.

•Design flexibility, with quick modifications to tooling that costs 90% less than for a pressure die casting, whilst maintaining economic batch quantities of up to 500,000 parts per annum.

What the MM casting process can deliver: • High quality finish, detail and specification. Thin

walls as fine as 0.2 mm, typically 1-3 mm. • Light weight components, weighing as little as 1g

can be produced using techniques to minimise material usage whilst retaining component integrity.

• Maximum size of 190 mm x 160 mm x 160 mm. A length of 250 mm is possible providing no other dimension exceeds 100mm.

• Complex detail on internal and external features. • Superfine surfaces with 0.8 micrometres being the

“as cast” finish. • Zero draft angles

PROCESS FLOW CHART• RECEIPT OF ORDER• (REVIEW)• ARE THE TERMS ACCEPTED? NO COMMUNICATE-

NEGOTIATE• YES• PREPARE WORK ORDER• WORK ORDER TO Q.C, INSPECTION, PLANNING, METHODS,

PRODUCTION AND DESPATCH

PRODUCTION PLANMETHOD DRAWING, QA DATA, PATTERN PLAN MOULDINGWORK ORDER, CORE MAKING, HEAT CONFORMATION MELTING AND POURING FOR THESE, LAB TEST REPORTS

KNOCK OUTSTAGE ISPECTION- NOT OK, REJECT

OK, SHOT BLASTING, GAS CUTTING/ARC CUTTING ASTM STANDARDS

HEAT TREATMENTROUGH FETTLING, FINISH FETTLING,

INSPECTION

• NDT- CUSTOMER REPORT, NOT OK, WELDING & RECTIFICATION

• WELDING LOG SHEET RE-INSPECTION, NOT OK-

REJECT• MACHINE - IF REQUIRED• STRESS RELIEF• HYDRAULIC TESTS Etc.• TEST CERTIFICATE DESPATCH

DOCUMENTS, PACKING, Etc. Etc.