Casting

Casting 

Manufacturing Processes 

© 2011 Su-Jin Kim GNU 



Associate Professor Su-Jin Kim 

School of Mechanical Engineering 

Gyeongsang National University

Outline 

1. Casting Physics 

2. Sand Casting 

3. Investment Casting 

4. Die Casting 

5. Cost/Quality 



© 2011 Su-Jin Kim GNU


• Casting is a manufacturing process by which a liquid 

material is poured into a mold, 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 is Versatile 

• Many types of metals 

• Rapid production 

• 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 


Fluid flow of mold filling 

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

→ cavity →open riser 

Bernoulli’s equation 

p 

h 

g 

Velocity of the molten metal leaving the gate 




2 

v 

Constant 

2g 

h = elevation 

p = pressure at elevation 

v = velocity of the liquid 

ρ = density of the fluid 

v 

c 2gh

Fluid flow of mold filling 

• Reynolds number, Re 

Re 

• Ordinary gating system: Re = 2,000 ~ 20,000 mixture of 

laminar and turbulent flow 




vD 

 

v = velocity of the liquid 

D = diameter of the channel 

ρ = density 

n = viscosity of the liquid.

Heat transfer 

• Heat flow depends on casting material and the mold 

and process parameters. 

• Temperature distribution in the mold-liquid metal 

interface is shown below. 




Solidification time 

• Solidification time is a function of the volume of a 

casting and surface area (Chvorinov’s rule). 

• Effects of mold geometry and elapsed time on skin 

thickness and its shape are show. 




Volume 

Solidifica tion time C 

Surface Area 

n 

C = constant 

n = 2 if Sand casting 

n = 1 if Die casting

Shrinkage 

• Shrinkage in casting causes dimensional changes and 

sometimes cracking 




Expendable Mold Casting Processes 

1. Sand casting 

2. Shell mold casting 

3. Plaster mold casting 

4. Investment casting (lost wax casting) 

5. Lost foam casting 




Sand casting 

• Use expendable sand molds 

• Low cost 

• Small quantity production 

• Complex entire parts at one time 

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

• Green (moist) sand has almost no part weight limit 

• Dry sand has a part mass limit of 2,500 kg 

• The sand is bonded together using clays, chemical 

binders, or oils. 




Sand casting 




Sand casting 




http://www.youtube.com/watch?v=rgL2Jn5mk1A

Shell mold casting 

• 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. 




Plaster(석고) mold casting 

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

• Accurate, good surface and low melting point alloy 



http://www.youtube.com/watch?v=xPSI1wUOBnk&p=9B6D9EAE75875D9D 


Investment casting 

(lost wax 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. 




SME: http://www.youtube.com/watch?v=PIneaDTZ16g


(lost wax casting) 

• Wax pattern Mold Pouring 



Coin: http://www.youtube.com/watch?v=4Yvm6fUXf1U 

Aerospace: http://www.youtube.com/watch?v=f7FXtnXVqzY 


Lost foam casting 

• Pattern is made of polystyrene form which evaporates 

with molten metal to form a cavity for the casting. 




Non-expendable Mold Casting 

Process 

1. Permanent-mold casting 

2. Die casting 

3. Centrifugal casting 

4. Continuous casting 




Permanent mold casting 

• The molten metal is poured into a metal mold. 




Die casting 

The molten metal is forced into 

the die cavity by high pressure. 




http://www.youtube.com/watch?v=1AgDGLNE6Es SME 90s

Die casting 

• Can be automated for large production runs. 

• Strength-to-weight ratio of die-cast parts increases with 

decreasing wall thickness. 

• Good surface finish and dimensional accuracy. 

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




Centrifugal casting 

• Molten metal is solidify in rotating mold. 

• It uses centrifugal force to form cylindrical parts. 




Centrifugal force = mv 2 /r 

Gravitational force = mg 

http://www.youtube.com/watch?v=SUtAamMr4Vs

Continuous casting 

• Developed for casting metal slab or strip continuously at 

low cost. 




Continuous casting 

slab 

strip 

Strip casting 

hot rolling 

http://www.posco.com/homepage/docs/eng/html/company/product/s91c5010010c.html

Casting process comparison 

Process Advantages Disadvantages 

Sand Casting 

Plaster Cast 

Investment Cast 

Die Casting 




Almost any metal is cast; Small to 

large parts; Low tooling cost 

Good dimensional accuracy and 

surface finish ; Fine details including 

thinner walls; Large parts cost less to 

cast than by Investment process 

Good dimensional accuracy and 

surface finish; Complex shape, fine 

detail; Ferrous and non-ferrous 

metals 

Excellent dimensional tolerances and 

surface finish; Parts require a minimal 

post machining; High production rate 

Low dimensional accuracy & 

surface quality 

More costly than Sand or 

Permanent Mold-Casting 

Limited to nonferrous metals 

Costs are higher than Sand, 

Permanent Mold or Plaster 

process Castings 

High die cost; Part size limited; 

Limited to nonferrous metals

Design for Casting 

• Corner X 

• Uniform section 

• Draft direction 




Cost of casting 

Sand casting 

• Tooling and equipment costs are low 

• Direct labor costs are high 

• Material utilization is low 

• Finishing costs can be high 


• Tooling costs are moderate depending on the complexity 

• Equipment costs are low 

• Direct labor costs are high 

• Material costs are low 

Die casting 

• Tooling and equipment costs are high 

• Direct labor costs are low to moderate 

• Material utilization is high 




Quality of Casting 

Sand casting 

• Tolerance (0.7~2 mm) and defects are affected by shrinkage 

• Material property is inherently poor 

• Generally have a rough grainy surface 


• Tolerance (0.08~0.2 mm) 

• Mechanical property and microstructure depends on the method 

• Good to excellent surface detail possible due to fine slurry 

Die casting 

• Tolerance (0.02~0.6 mm) 

• Good mechanical property and microstructure due to high pressure 

• Excellent surface detail 




Rate of Casting 

Sand casting 

• Development time is 2~10 weeks 

• Production rate is depending on the cooling time : t~(V/A) 2 


• Development time is 5~16 weeks depending on the complexity 


Die casting 

• Development time is 12~20 weeks 





Economics of Casting 

• Cost of equipment per casting decreases as number of 

parts cast increases. 

• When demand is small cost per casting increases, more 

economical to manufacture. 




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 




Solidification of metals 

• Pure metals have defined melting points and 

solidification takes place at a constant temperature. 

• Alloys solidify over a range of temperatures. 




Phase diagrams 

• A phase diagram or equilibrium diagram shows the 

relationships among temperature, composition and 

phases present in an alloy system. 




The iron-carbon system 

• Iron-carbon binary system is represented by the ironiron 

carbide phase diagram. 

• Ferrite, Austenite, Cementite 




Microstructure 

• Metals solidified in square mold 

a) Pure metals: equiaxed grain on skin, columner grain 

solidified in a square mold. 

b) Solid-solution alloys: equiaxed grain inner zone 

c) Heterogeious nucleation of grains 




Microstructure 

• When alloy cooled slowly dendrite develops. 

• Three basic types of cast structures. 




Columnar dendritic Equiaxed dendritic Equiaxed nondendritic

Ceramic-mold casting 

• A ceramic slurry is poured over the wooden pattern. 

• After hardening, The ceramic mold is removed, dried, 

and baked in an oven. 

• Ceramic mold is suitable for casting high melting point 

metals like as steels. 

Wooden pattern 




Ceramic mold 

Mold is baked

Vacuum casting 

• Alternative to investment, shell-mold and green-sand 

casting. 

• Can be automated and production costs are similar to 

green-sand casting. 




Squeeze casting 

• The combination of casting and forging.

Casting

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