Casting

Manufacturing Processes

© Su-Jin Kim GNU

Manufacturing Processes

Casting (주조)

Professor Su-Jin Kim

School of Mechanical Engineering

Gyeongsang National University

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Outline

1. Casting Physics

2. Sand Casting

3. Investment Casting

4. Die Casting

5. Gravity casting

6. Cost/Quality

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Casting

• Casting(주조) is a manufacturing process by which a liquid material(용융금속) is poured into a mold(주형), which contains a hollow cavity of the desired shape, and then allowed to solidify.

• First casting: 4000 B.C.

• Bronze, iron age, light metal age?

http://www.youtube.com/watch?v=yXVLbzI3xTE Engine block 5min

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Casting

Casting is Versatile

• Many types of metals

• Wide range of shapes and sizes

• Complex parts as an integral unit

Disadvantage

• Poor dimensional accuracy and surface quality

http://www.youtube.com/watch?v=mx1qteRUYwI Sand, Investment, Lost form SME 6:16

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Cast structure (주조조직) of alloying

• Solidification begins when temperature drops below the liquidus(액상점), TL, and complete when solidus(고상점), TS, called freezing range(응고범위)

• For normal cooling cored dendrites(유심구조 수지성장) are formed. Surface has a higher concentration of alloying elements.

110

0

1200

1300

20 40 (wt% Ni)

(ºC)

Liquid, L

Solid, α

L+α

40

% 35

%

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Fluid flow (유동) of mold filling

Gravity casting: pouring cup→sprue →well →runner →riser → cavity →open riser

Bernoulli’s equation

Velocity of the molten metal leaving the gate

Constant 2

2

g

v

g

ph

h = elevation

p = pressure at elevation

v = velocity of the liquid

ρ = density of the fluid

ghcv 2

Core

(sand)

Vent Pouring basin (cup)

Open riser

Cope

Drag

Mold

cavity

Runner Well

Sand

Gate

Parting

line

Sprue

Flask Flask Blind

riser

©정하림GNU

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Fluid flow of mold filling

• Reynolds number, Re

• Ordinary gating system: Re = 2,000 ~ 20,000 mixture of laminar and turbulent flow

vDRe

v = velocity of the liquid

D = diameter of the channel

ρ = density

n = viscosity of the liquid.

Casting

Manufacturing Processes

© Su-Jin Kim GNU

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Heat transfer (열전달)

• Heat flow (열유동) depends on casting material and the mold and process parameters.

• Temperature distribution (온도분포) in the mold-liquid metal interface is shown below.

Distance

Tem

pera

ture

Room

temperature

Melting

point

Air Mold Solid Liquid

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Solidification time

• Solidification time (응고시간) is a function of the volume of a casting and surface area (Chvorinov’s rule).

• Ex) Sand casting

n

C

Area Surface

Volumetion timeSolidifica

C = constant

n = 2 if Sand casting

n = 1 if Die casting

4

4

.5

2 2

2

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Shrinkage

• Shrinkage (수축) in casting causes dimensional changes and sometimes cracking.

• Thermal expansion Metals

주물재료

Contraction

수축률(%)

Aluminum 7.1

Zinc 6.5

White iron 4.0-5.5

Copper 4.9

Brass(70-30) 4.5

Magnesium 4.2

dTldl

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Expendable Mold Casting Process (소모성 주형 주조 공정)

1. Sand casting

2. Investment casting (lost wax casting)

3. Lost foam casting

4. Shell mold casting

5. Plaster mold casting

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Sand Casting (사형주조)

Create pattern Place flask(box) over the pattern plate Fill flask with sand and remove pattern Pouring molten metal into mold Shakeout mold and cutoff gating system

http://www.youtube.com/watch?v=rgL2Jn5mk1A Sand Casting (4 min)

Pattern Sand mold Product Pouring

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Sand Casting

• Use expendable sand molds

• Low production rate(1–20 pieces/hour-mold)

• Low cost, Recycle sand

• Small quantity production

• Complex entire parts at one time

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Investment Casting (정밀주조)

Investment casting = lost wax casting

Injecting wax patterns Pattern assembly tree Slurry coating Sand coating Wax pattern melt out by heat Pouring molten metal Shakeout

https://youtu.be/6u4lwdIPefM (8 min)

Wax pattern assembly Pouring metal into shell mold

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Investment casting

• A wax pattern is coated by ceramic slurry that hardens into the mold.

• One pattern creates one part, which increases production time and labor costs.

• Complex geometries, good surface and high melting point alloy.

Aluminum Investment Casting : http://www.youtube.com/watch?v=f7FXtnXVqzY

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Lost foam casting (소실모형주조)

• Polystyrene patterns evaporate with molten metal to form a cavity for the casting.

Molding (금형) Patterns

Compact in sand

Coating

Casting Shakeout Manhole cover

© samhwacast.com

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Shell mold casting (셸주조)

• Fine sand mixed with a resin is heated by the pattern and hardened into a shell around the pattern

• Can produce castings with close dimensional tolerances, good surface finish and low cost.

https://youtu.be/28_I7Bdz4yY Shell mold casting

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Plaster mold casting (석고주형 주조)

• Plaster is mixed with water and poured over the pattern.

• Accurate, good surface and low melting point alloy

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Permanent Mold Casting Process (영구주형 주조)

1. Die casting

2. Gravity casting

3. Centrifugal casting

4. Continuous casting

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Die Casting (다이캐스팅)

The molten metal is forced into the die cavity by high pressure.

Ejector platen

(moves)

Ejector

die half

Ejector

box

Ladle

Stationary

die half

Shot

sleeve Plunger

rod

Metal sleeve Cover disk

Closing cylinder

Pouring hole

Plunger

Plunger rod

Shot

sleeve

©갈창우

https://youtu.be/0XkDK46rwvQ Die casting

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Die Casting

• Fast (30 ~ 60 s/part) automatic process for mass production (0.1 million parts/mold).

• Good surface finish and dimensional accuracy.

• Strength-to-weight ratio increases with decreasing wall thickness. Small voids decrease strength.

• It is used for aluminium, magnesium and copper alloys.

https://youtu.be/iSyBsdJkQu8 Die Casting Process

https://youtu.be/h2A7oUMeLmM Machine

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Die Casting

Aluminum Furnace

Die Casting factory

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Gravity Tilt Casting (금형중력주조)

• Gravity casting = Gravity die casting = Gravity tilt casting

• Molten aluminum flows slowly into mold by gravity force.

• The mechanical properties, tolerance and surface finish are better than sand casting. Thick aluminum parts.

Gravity casting: https://youtu.be/IaSY6feXk7A

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Centrifugal casting (원심주조)

• Molten metal is solidify in rotating mold.

• It uses centrifugal force to form cylindrical parts.

Centrifugal force = mv2/r

Gravitational force = mg

https://youtu.be/ZxVA-htTunU : Centrifugal Casting (2min)

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Continuous casting (연속주조)

• Developed for casting metal slab or strip continuously at low cost.

Strip casting Continuous casting

slab strip

hot rolling

Continuous Casting https://youtu.be/d-72gc6I-_E

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Casting process comparison (비교)

Process Advantages Disadvantages

Sand Casting Almost any metal is cast; Small to large parts; Low tooling cost

Low dimensional accuracy & surface quality

Investment Cast Good dimensional accuracy and surface finish; Complex shape, fine detail; Ferrous and non-ferrous metals

Costs are higher than Sand, Permanent Mold or Plaster process Castings

Die Casting Excellent dimensional tolerances and surface finish; Parts require a minimal post machining; High production rate

High die cost; Part size limited; Limited to nonferrous metals

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Cost of casting (비용)

Sand casting: Finishing costs can be high

Process Tooling & Equipment

Direct labor Material utilization

Sand Casting Low High Low

Investment Cast

Moderate & Low High

Low

Die Casting High Low High

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Quality of Casting (품질)

Process Tolerance (mm)

Mechanical Property Surface finish

Sand Casting 0.7~2.0 Material property is poor

Generally have a rough grainy surface

Investment Cast

0.08~0.2 Mechanical property and microstructure depends on the method

Good to excellent surface detail possible due to fine slurry

Die Casting 0.02~0.06 Good mechanical property and microstructure due to high pressure

Excellent surface detail

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Rate of Casting (생산성)

Development time is also depending on the size and complexity.

Production rate is depending on the cooling time.

Process Development time

(weeks)

Production rate

Sand Casting 2~10 OO min, t~(V/A)2

Investment Cast

5~16 OO min, t~(V/A)2

Die Casting 12~20 OO s, t~(V/A)1

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Economics of Casting (경재성)

• Cost of equipment per casting decreases as number of parts increases.

100 101 102 103 104 105 106

Number of pieces

Cost

per

pie

ces

1 2

3

4 5

6

7

8

9

Sand

casting

Investment

casting

Die casting

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Defects (주조결함)

• Dimensional Accuracy, Surface finish

• Porosity : a void in the casting

• Shrinkage cavity(void) : internal vacancy

• Slag or sand inclusion

• Surface blowholes or pinholes

• Crack

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Design for Casting (설계)

• Draft angle : is required to extract pattern from mold. Sand 3~5˚, Invest 0~3˚ , Die 1~2˚

• Control shrinkage : Add padding and riser to feed metal reduced as transitions from liquid to solid state.

• Junction design: Fillets to distribute strains stress. Uniform section to remove shrinkage cavity.

• Datum point(plane) for post machining.

Uniform section Padding, Riser Draft angle

Casting

Manufacturing Processes

© Su-Jin Kim GNU

Casting CAE

• : http://www.anycastsoftware.com

• 제조업: http://www.jejoup.kr

Casting

Manufacturing Processes

© Su-Jin Kim GNU

References

• POSCO: http://www.posco.com

• http://www.dhcasting.co.kr

• http://www.edaehan.co.kr

• http://www.taechangpi.co.kr

• http://www.donglimms.co.kr

• http://www.yeonghwa.co.kr

• http://www.himet.co.kr

• Casting: http://www.custompartnet.com