Design for casting
Mufaddal Rasheed 
Explore the important considerations when designing for casting for design engineers
Casting - A manufacturing process in which liquid metal, is poured into a mold containing a hollow cavity of the desired shape and then allowed to solidify. This process is widely used to create complex shapes that would be difficult or uneconomical to make through other methods
Three most common types of casting
- Sand casting It involves creating a mold from a mixture of sand and a binding agent, into which molten metal is poured
- Die Casting : Die casting involves forcing molten metal under high pressure into a mold cavity, usually made of high-quality steel. It is commonly used for high-volume production of small to medium-sized parts
- Investment casting : Investment casting, also known as lost-wax casting, involves creating a wax model of the final product, coating it with a ceramic material to form a mold, and then melting away the wax to leave a hollow ceramic shell. Investment casting, also known as lost-wax casting, involves creating a wax model of the final product, coating it with a ceramic material to form a mold, and then melting away the wax to leave a hollow ceramic shell.
Sand casting process flow:
Key considerations when designing for casting
- Selection of Materials : Different metals and alloys have varying casting properties, including melting points, fluidity, shrinkage rates, and solidification characteristics.
- Geometry : Complex geometries can lead to defects and increased costs. Simplifying the design where possible can enhance castability. Avoiding sharp corners, intricate details, and deep cavities, using generous radii and fillets to allow for smoother flow of molten metal
- Uniform Wall thickness : Important for Even cooling and solidification, minimizing the risk of warping, shrinkage, and other defects.
- Draft angles : For the easy removal of the cast part from the mold, draft angles are necessary . typical draft angle ranges from 1 to 3 degrees depending on the complexity of the part.
- Shrinkage allowance: When metal melts it shrinks hence allowance has to be given in the mold for shrinkage. This factor also has to be considered in design.
- Usage of Cores : Cores are used when a cavity is required in the final part. The core blocks liquid flow in certain areas hence creating cavities / holes there. Such cores have to be designed very carefully and their placement affects the design .
Design practices
Its always better to have smooth transitions in changes in sections rather than abrupt changes.
Accumulation of molten metal in one area results in localized hot spots .
In the below example, the cooling of metal will be slower at the corner.
Design modified for casting example:
Added fillets, draft angles and uniform cross section.
Categories: : DFM