All casting processes have their design limitations, and the permanent mold aluminum casting process is no exception. Though none of the following guidelines are etched in stone and nearly any part can be cast, following these guidelines closely will result in a part that is more easily manufactured, cost effective and trouble free.
Minimum draft for full permanent mold is typically 3 degrees. Less draft can be attained through creative part orientation in the mold, metal core pulls, collapsible metal cores, or sand cores. In addition to the standard methods of minimizing draft, Watry has designed and built a specialty casting machine that can produce certain types of casting with near 0 internal draft in full permanent mold. Generous draft minimizes mold maintenance and premature mold wear.
Minimum wall section is dependent on casting alloy, metallurgical quality, complexity of design, and required surface finish. Under ideal conditions the minimum wall section can be as low as .115″-.120″. Heavy casting sections isolated from the parting line of the mold should be avoided whenever possible.
Sharp corners are to be avoided. Radii should be as generous as the part design will allow. Whenever possible internal and external radii should be sized to maintain uniform wall section around corners.
Lettering should be raised whenever possible. Depressed letters should be avoided, as they increase initial mold cost and are subject to premature wear and damage. Minimum letter size for raised letters is 1/8″ with 1/4″ preferred. Minimum letter size for depressed letters is 3/16″ with 5/16″ preferred.
Casting surface finish is expressed in microinches. Typical permanent mold casting finish is between 200 and 420 microinches. Again, casting design plays a large role in a foundry’s ability to maintain a predictable and consistent finish. Smoother than typical microfinishes require additional, more frequent mold prepping and increase casting cost.Contact Watry Now