Sand casting: Cope and Drag, Mold Cavity, Pattern, Pouring Cup, Sprue, Runner, Gate, Risers, Vents, Cores and Important considerations for casting

Sand casting: Cope and Drag, Mold Cavity, Pattern, Pouring Cup, Sprue, Runner, Gate, Risers, Vents, Cores and Important considerations for casting Sand casting uses natural or synthetic sand (lake sand) which is mostly a refractory material called silica (SiO2). The sand grains must be small enough so that it can be packed densely; however, the … Read more

Casting methods

Casting methods Metal casting process begins by creating a mold, which is the ‘reverse’ shape of the part we need. The mold is made from a refractory material, for example, sand. The metal is heated in an oven until it melts, and the molten metal is poured into the mould cavity. The liquid takes the … Read more

Shell-mold casting

Shell-mold casting Shell-mold casting yields better surface quality and tolerances. The process is described as follows: – The 2-piece pattern is made of metal (e.g. aluminum or steel), it is heated to between 175°C-370°C, and coated with a lubricant, e.g. silicone spray. – Each heated half-pattern is covered with a mixture of sand and a … Read more

Expendable-pattern casting (lost foam process)

Expendable-pattern casting (lost foam process) The pattern used in this process is made from polystyrene (this is the light, white packaging material which is used to pack electronics inside the boxes). Polystyrene foam is 95% air bubbles, and the material itself evaporates when the liquid metal is poured on it. The pattern itself is made … Read more

Shrinkage Allowance

 Shrinkage Allowance As the casting cools, the metal shrinks. For common cast metals, a 1% shrinkage allowance is designed in all linear dimensions (namely, the design is scaled p by approx 1%). Since the solidification front, i.e. the surface at the boundary of the solidified and the liquid metals, travels from the surface of the … Read more

Parting line

 Parting line The parting line is the boundary where the cope, drag and the part meet.  If the surface of the cope and drag are planar, then the parting line is the outline of the cross-section of the part along that plane.  You can easily see the parting line for many cast and molded parts … Read more

Drafts and tapers

Drafts and tapers allowance It is not good for a casting to have surfaces whose normal is perpendicular to the direction along which the part will be ejected from the mold.  This can cause the part to stick in the mold and forceful ejection will cause damage to the part (and mold, if the mold … Read more

Casting design and quality

Casting design and quality Several factors affect the quality/performance of cast parts – therefore the design of parts that must be produced by casting, as well as the design of casting molds and dies, must account for these. You may think of these as design guidelines, and their scientific basis lies in the analysis – … Read more