Peiman Mosaddegh, Ph.D. Department of Mechanical Engineering · Peiman Mosaddegh –Manufacturing...

Peiman Mosaddegh – Manufacturing Process

Department of Mechanical Engineering



اصول ریخته گریPeiman Mosaddegh, Ph.D.

Department of Mechanical EngineeringIsfahan University of Technology

Spring 2020



PROCESSES

Mental Map

Material

Removal

Material

Transformation

Material

Addition

Bulk

Deform.

Casting

Processes

Polymer

Processes

AdhesionJoining Rapid Prototyping

Machining

Processes

Integration Interpretation Quality

•QFD •GD & T •Metrology

•SPC

•Push / Pull

•Lean Mfg.

•Turning

•Milling

•Drilling

•Grinding

•Sand

casting

•Diecast

•Investment

•other

•Forging

•Rolling

•Extrusion

•Drawing

Sheet

Metal

•Bending

•Stamping

•Blanking

•Punching

•Extrusion

•Inj. Molding

•Blow molding

•Rotomold,etc.

•Composites

•Welding

•Brazing

•SLA

•SLS

•3D

Printing

•other

DESIGN INDUSTRIAL

Time

Design for X Process Planning

MANUFACTURING

2



• Heat Transfer

• Liquid Metal Flow

Casting Fundamentals

• Solidification (Phase Change)

• Shrinkage/Part Removal

Casting Basics

3



Turbine Blades

Example Products

Casting Basics

4



Ornamental - jewelry, statues

Example Products

Casting Basics

5



Engine Block

Example Products

Insert engine block photo

Casting Basics

6



• Large range of sizes possible

Advantages

• Complex shapes possible

• High volume parts

• Difficult to process materials

• Near Net Shape products

• Wide range of materials

Casting Basics

7



• Lower toughness, ductility & strength

Disadvantages

• Higher porosity

• Relatively poor surface finish

• Relatively poor dimensional accuracy

(shrinkage)

• Environmental and Workplace safety

Casting Basics

8



• Made of sand, plaster, ceramic, metal

The Mold

• Imparts final shape (oversized)

• Open or Closed mold

• Permanent or Expendable

Casting Basics

9



- Pouring basin accepts

molten metal from ladle

- Sprue carries metal to

runner(s)

- The part itself is formed

in the cavity (the cavity is

formed via a pattern)

Kalpakjian, S., Manufacturing Engineering & Technology, 1992, p. 286

Sand Casting

- Runners carry metal to

cavity where it enters

through the gate

Typical Sand Cast Part (untrimmed)

(Open Riser)

Casting Terminology

10



- Risers supply extra

molten material to the

part as it shrinks &

control back pressure


Sand Casting

- Vents allow gases to

escape from the mold

Typical Sand Mold

Note: want part to

solidify before riser

Casting Terminology

11



Melting Process (Pure Metal)

Q m c h ctot p o fg ps melt l pour melt [ ( ) ( )]T T T T

Total heat required:

isothermal

melting

heat solid to melt

point

heat liquid to

pour temp.

Te

mp

era

ture

Tm

Time

Pouring

Temp.

(lower bound)

Superheat

Heat of fusion

Casting –Phase Change Process

12



Rate of Pour

Fast enough to...

- fill entire mold before solidification

- make process cost effective.

But not so fast that... - turbulent flow causes erosion

or entrainment of air

Re 2,000 μ

ρVDRe

Casting – Liquid Metal Flow

- Avoid high pour rates & sudden

changes in direction or cross-section

13



Flow in Sprue

Governing equations (conservation of energy):

hv

hv

g g1

1

2

1 22

2

22 2

P

FP

F1 2

Bernoulli Equation yields...

For free falling,

frictionless flow...

hv

hv

g g1

1

2

22

2

2 2 Therefore...

v

1

hh2

h1

P P1 2 F F1 2 0&

P2 =P1

P1 =atm.

v2

14



Flow in Sprue

Governing equations:

v gh v2 1 12

Specifying h2 = 0 & v1 = 0

By continuity... v v1 1A A 2 2

A A2 1Therefore...

v1=0

hh2 =0

h1

P2 =P1

P1

=atm.

v2 > v1

i.e., fluid stream narrows as it falls

need tapered sprue

= Q

15



Fluidity

Measure of the capability of a molten metal to flow and

fill the mold before freezing

Affected by:

- viscosity (temp dependent)

- surface tension (oxide films)

- pouring rate & temperature

- metal composition (shorter freezing range, higher Fluidity)

- heat transfer

Measured qualitatively by spiral or channel flow test

16



Solidification Process (Pure Metal)

Q m c h ctot p fg pl pour melt s melt

[ ( ) ( )]T T T T

Basically the reverse of the heating process

isothermal

solidificationcool to melt point isothermal

freezing

cool solid to

ambient

cool liquid

to freezing

Te

mp

era

ture

Tm

Time

Pouring

Temp.

Casting Phase Change - Solidification

17



Solidification Process (Pure Metal)

Pure Metal Solidification…

Material is strongest in

direction parallel to grain

- starts at mold surface

- works its way to center

- is normal to surface

- is opposite direction

of heat flow

Pure MetalAlloy Nucleating Agent

Chill zone

Columnar zone

Equiaxed structure

Cast structure of metals

Solidified in square mold


Rapid Cooling

Fine equiaxed grains

18



Solidification Process (Alloy)


Example: Ferrous Alloys

Cast Iron- Fe +…

• 2.11% to 4.5% Carbon

• 1% to 3.5% Silica

1 2 3 4

1

2

3

4

Steels

Grey cast

iron

White cast

iron

% S

ilico

n

% Carbon

- Gray (flakes)

- White (Fe3C)

- Nodular (spherical)

- Malleable (Ann. Wht.)

- Cast Steels (hi temp)

Types:

19



Solidification Process (Alloy)

Solidifies in stages

isothermal

solidificati

oncool to melt

point freezing

solid cooling

liquid cooling

Tem

pe

ratu

re

Time

Pouring

Temp.

Te

mp

era

ture

Liquid Solution

L & S

Solidus

Liquidus

Solid Solution

CuNi % Copper

20



Solidification Process

(Alloy)

Alloy Solidification…

Material strength depends on

location and direction

(Anisotropic)


- starts at mold surface

- works its way to center

- equiaxed center zone

Pure Metal Alloy Nucleating Agent

Equiaxed zoneChill zone

Columnar zone

Equiaxed structure

Micro &

Macro-scopic

variation


21




Liquid

Solid

Te

mp

era

ture

TL

Alloying Element %

Liquid

Mushy Zone

Solid

TS

S + L

Mold

WallSolid

Liquid

L + S

Distance


Liquid

Dendrites

22




Effect of Cooling Rate on Structure…

- Faster = finer, more equiaxed grains

- Slower = coarser, more columnar grains

- Very fast results in amorphous structure (no grain structure)


Smaller grain size =

- higher strength & ductility

- Less (micro) porosity

- Less tendency of cracking during solidification (hot tears)

23



Controlling Solidification

“Chills” - heat sinks used to control

cooling & solidification process


- usually same material as

casting

- internal or external

- placed in regions where

there is larger volume of metal

- Used to prevent porosity or

voids due to shrinkage


24



Kalpakjian, S., Manufacturing Engineering & Technology, 1992, p. 290, 291

Note: internal angles thin, external angles thick

Air LiquidSolidMold

Te

mp

era

ture

Tmelt

T at metal-mold

interface

T at mold-air

interface

Distance

Ambient


“Chills” - heat sinks used to control

cooling & solidification process

- usually same material as

casting

- internal or external

- placed in regions where

there is larger volume of metal

- Used to prevent porosity or

voids due to shrinkage

25



Solidification

ST V

As

Chvorinov’s Rule uses power law relation...

For a given Volume, part with larger

surface area will cool faster...

26



Solidification

ST V

As

Chvorinov’s Rule uses power law relation...

For a given Volume, part with larger

surface area will cool faster...

(where n 2)

Constant C is function of casting material, mold material

& temperature i.e., C = f(k,h,T)

n

A

VCST m


27



Casting Defects


28



Casting Processes

Sand Molding

- Green

- Skin dried sand

- fully dried sand

- cold cured sand

Shell Molding

- Resin

Plaster Mold

Permanent

Mold Casting

Die Casting

Metal Graphite

Investment

Casting

Expendable

Mold(مصرفی)

Permanent

Mold(دایمی)

Permanent

Pattern

Expendable

Pattern

Process Classification

Centrifugal

Casting

29

Composite

Mold(کامپوزیتی)



TYPICAL

TYPICAL SURFACE

MATERIALS FINISH SHAPE DIMENSIONAL

PROCESS CAST MINIMUM MAXIMUM (Ra mm) POROSITY*

COMPLEXITY*

ACCURACY*

MINIMUM MAXIMUM

Sand All 0.05 No Limit 5 - 25 4 1 - 2 3 3 No Limit

Shell All 0.05 100+ 1 - 3 4 2 - 3 2 2 ---

Evaporative

PatternAll 0.05 No Limit 5 - 20 4 1 2 2 No Limit

PlasterNonferrous

(Al, Mg, Zn, Cu)0.05 50+ 1 - 2 3 1 - 2 2 1 ---

InvestmentAll

(High Melting Point)0.005 100+ 1 - 3 3 1 1 1 75

Permanent

MoldAll 0.50 300 2 - 3 2 - 3 3 - 4 1 2 50

DieNonferrous

(Al, Mg, Zn, Cu)< 0.05 50 1 - 2 1 - 2 3 - 4 1 0.5 12

Centrifugal All --- 5000+ 2 - 10 1 - 2 3 - 4 3 2 100

* Relative Rating: 1 best, 5 worst

SECTION

THICKNESS (mm)WEIGHT (kg)


Characteristics of Casting Processes

Casting Processes

30



Courtesy of efunda.com

Allowances for Select Cast Metals

31

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.

ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Production Steps in Sand-Casting

Figure 11.2 Outline of production steps in a typical sand-casting operation.



Sand Mold

Figure 11.3 Schematic illustration of a sand mold, showing various features.



Pattern Plate

Figure 11.4 A typical metal match-plate pattern used in sand casting.



Design for Ease of Removal from Mold

Figure 11.5 Taper on patterns for ease of removal from the sand mold



Sand Cores

Figure 11.6 Examples of sand cores showing core prints and chaplets to support cores.



Sequence of

Operations for

Sand-Casting

Figure 11.8 Schematic illustration of the sequence of operations for sand casting. (a) A

mechanical drawing of the part is used to generate a design for the pattern. Considerations such

as part shrinkage and draft must be built into the drawing. (b-c) Patterns have been mounted on

plates equipped with pins for alignment. Note the presence of core prints designed to hold the core

in place. (d-e) Core boxes produce core halves, which are pasted together. The cores will be

used to produce the hollow area of the part shown in (a). (f) The cope half of the mold is

assembled by securing the cope pattern plate to the flask with aligning pins and attaching inserts to

form the sprue and risers. Continued on next slide.



Sequence of

Operations for

Sand-Casting,

Con’t.

(g) The flask is rammed with sand and rthe plate and inserts are removed. (h) The drag half is

produced in a similar manner with the pattern inserted. A bottom board is placed below the drag

and aligned with pins. (i) The pattern , flask, and bottom board are inverted; and the pattern is

withdrawn, leaving the appropriate imprint. (j) The core is set in place within the drag cavity. (k)

The mold is closed by placing the cope on top of the drag and securing the assembly with pins.

The flasks the are subjected to pressure to counteract buoyant forces in the liquid, which might lift

the cope. (l) After the metal solidifies, the casting is removed from the mold. (m) The sprue and

risers are cut off and recycled, and the casting is cleaned, inspected, and heat treated (when

necessary). Source: Courtesy of Steel Founder’s Society of America




Sand Casting Molds Jolt Type Mold Making Machine

Note: grain size determines surface finish

Casting Processes – Expendable Molds

Green Sand

- relatively weak

- mix of sand, water & clay

- inexpensive

- inner mold surfaces dried

Skin Dried Sand

- slightly stronger

- slightly more expensive

- organic binders (phenolics)

39



Green Sand


Sand Casting Molds

- relatively weak

- mix of sand water & clay

- inexpensive

- inner mold surfaces dried

Skin Dried Sand

- slightly stronger

- slightly more expensive

Jolting & Squeezing

- organic binders (phenolics)


40



Fully Dried Sand


Sand Casting Molds

- even stronger

more expensive

Cold Cured Sand

Squeeze Head Mold Making

Flat Head Profile Head

Equalizing Pistons

Flexible

Diaphragm

- oven baked

better dim. control

- add chemical binders to

increase strength

(furan, alkyds)

41




Sand Casting Molds

Vertical Flaskless Molding

Fully Dried Sand

- even stronger

- more expensive

- add chemical binders to

- increase strength

- (furan, alkyds)

Cold Cured Sand

- oven baked

- better dim. control

42




Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Vertical Flaskless Molding

Figure 11.7 Vertical flaskless molding. (a) Sand is squeezed between two

halves of the pattern. (b) Assembled molds pass along an assembly line

for pouring. (c) A photograph of a vertical flaskless molding line. Source:

Courtesy of American Foundry Society.

(c)



Strength – maintain shape & resist erosion

Measures of Sand Quality

Permeability – allow gases to escape

Thermal Stability – ability to resist heat of molten metal

Collapsibility – tendency to “give” during shrinkage &

removal

Reusability – use of the sand in multiple molds


44



Shell Casting

- Improved dimensional

accuracy & finish

- Sand with TS binder coated

onto heated pattern halves

- Resulting shells

assembled for casting

- Allows for more complex

shapes

- Smaller parts but higher

precision (gears, camshafts)

Groover, M., Fundamentals of Modern Manufacturing, 1996, p. 267

Shell Sand with Binder


45



Ceramic Mold Casting

- Similar to sand shell

casting

- Ceramic used to coat

pattern

- Used with higher melt

point materials (steel)

Standard mold with ceramic

insert for smooth surface finish

http://manoirusa.com


46



Plaster Mold Casting

- Plaster used to coat pattern

(which is later removed)

- Used with lower melt (<2200F)

point materials (Al, Mg, Cu)

www.metalbot.com

Parts made using Plaster Molds

- Throughput limited by mold

making process


- Good surface finish & detailed

geometry possible

- Mold is lower permeability

(pour under vacuum or pressure)

- Re-usable pattern made from

Al, brass, TS plastics

47



Lost Foam Casting

- Intricate geometry possible

- “Evaporative” pattern of

foam or Polystyren

- mold built around pattern

(pattern can be assembled

from multiple pieces)

- Pattern evaporates during

filling (fill rate depends on rate

of evaporation)



- Example Parts: Cylinder heads,

crankshafts, engine blocks (auto applications)

48



Investment Casting


- Expensive - low thruput

- Coat wax or PS pattern

with ceramic slurry

- Bake to solidify slurry &

melt pattern

- High precision parts

(gears, cams, valves)

- Small to medium parts

(1 – 100 Kg)


49



www.metalbot.com


Investment Casting

- Expensive - low thruput

- Coat wax or PS pattern

with ceramic slurry

- Bake to solidify slurry &

melt pattern

- High precision parts

(gears, cams, valves)

- Small to medium parts

(1 – 100 Kg)

50



- Molds machined from

metal or graphite

- High production rate

- Mold interior protected

with refractory coating

- Part removal a concern

(ejector pins)

- High volume parts

- Good surface finish &

dimensional accuracy


mold preheated

Casting Processes – Permanent Mold

Permanent Molds

51



Slush Casting

- Allow metal to partially

solidify

- Pour out remaining

material

- Used to create hollow

parts (ornaments)



52



Pressure Casting (or Vacuum Casting)

- Permanent mold placed

over reservoir of molten

metal

- Pressure used to force

molten metal into mold

- Reduces porosity


(Approx 15 psi)


53



Die Casting

- Precision small parts

- Injection molding

using molten metal

-High pressure injection

(20 – 70 MPa)

- High production rates

-Lower melt point metals

(Al & Mg alloys)

- ExpensiveKalpakjian, S., Manufacturing Engineering & Technology, 1992, p. 331

Types of Dies

Die Casting

Machine

1,000 - 50,000 psi


54



Hot-Chamber Die-Casting

Figure 11.17 Schematic illustration of the hot-chamber die-casting process.



Cold-Chamber Die-Casting

Figure 11.18 Schematic illustration of the cold-chamber die-casting process.

These machines are large compared to the size of the casting, because high

forces are required to keep the two halves of the dies closed under pressure.



True Centrifugal Casting

- Axis of rotation horizontal

or vertical

- Molten metal poured

into rotating mold

- Hollow parts produced - Rotational speed critical


F = mv2/R


57



True Centrifugal Casting

Horizontal Machine

Vertical Machine


58



Semi-centrifugal Casting

- Center of casting

typically machined away

- Similar to centrifugal

casting

- Axisymmetric parts

- Run at approx. 15 g



- Solid, not hollow parts

produced

59



Questions????

Peiman Mosaddegh, Ph.D. Department of Mechanical Engineering · Peiman Mosaddegh –Manufacturing...

Documents

Transcript of Peiman Mosaddegh, Ph.D. Department of Mechanical Engineering · Peiman Mosaddegh –Manufacturing...