Manufacturing Processes Casting (주조) Associate Professor Su-Jin Kim School of Mechanical Engineering Gyeongsang National University 1

Outline Casting Physics Sand Casting Investment Casting Die Casting Cost/Quality

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 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

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. Solidification begins when temperature drops below the liquidus(액상점), TL, and complete when solidus(고상점), TS. Freezing range(응고범위) Columnar dentrite(주상 수지상정) For high cooling rates, structure becomes finer with smaller dendrite arm spacing. For higher cooling rates structures developed are amorphous. The developed structures and grain size influence the properties of the casting. When alloy cooled slowly dendrite develops a uniform composition. For normal cooling cored dendrites(유심구조 수지성장) are formed, which have a surface composition that is different from that a their centers. Surface has a higher concentration of alloying elements. Segregation(편석)

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 Core (sand) Vent Pouring basin (cup) Open riser Cope Drag Mold cavity Runner Well Sand Gate Parting line Sprue Flask Blind riser h = elevation p = pressure at elevation v = velocity of the liquid ρ = density of the fluid ©정하림GNU

Fluid flow of mold filling Reynolds number, Re Ordinary gating system: Re = 2,000 ~ 20,000 mixture of laminar and turbulent flow v = velocity of the liquid D = diameter of the channel ρ = density n = viscosity of the liquid.

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 Temperature Room temperature Melting point Air Mold Solid Liquid

Solidification time Solidification time (응고시간) is a function of the volume of a casting and surface area (Chvorinov’s rule). Ex) Sand casting C = constant n = 2 if Sand casting n = 1 if Die casting 4 2 .5 2 2 4

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