Sometimes, the alloy that shows the best properties on paper may have production characteristics that make it less desirable on an overall basis than other eligible alloys. The foundry is in the best position to advise on such factors as availability, relative ingot costs, production costs and reproducibility of results. When this is coordinated with the designer’s knowledge of service requirements, such as strength, hardness, corrosion resistance, impact strength and machinability, the best possible selection will result.
Because of this coordination, changes from the initial design may be indicated to improve design efficiency and/or lower production costs. For instance, a casting with sound design from other standpoints may have a size or shape conducive to distortion in heat treating, which could be minimized through design changes.
Production and service requirements have a large bearing on the casting method, as do the size and shape of the part. For example, castings required in large numbers must be made either by the permanent mold, diecasting or automated sand casting processes, provided the size and design features of the casting and available alloys are suitable.
Once the casting method is determined, the alloy choice is narrowed (because not all alloys can be used with all casting methods). The next considerations are the service requirements. If high strength is required, heat-treatable alloys must be used. Alloy choice can be narrowed further when remaining requirements, such as pressure tightness, corrosion resistance and machinability, are considered.
In some instances, it may be required to maximize one certain property—for example, highest possible yield strength. This limits the alloy and heat treatment choices, as well as the casting method, to one or two choices. In addition, compromises will have to be made on the other requirements, such as ductility.
So, the design for manufacturing is important for a good aluminum casting part.