Comparison of Processes

Casting versatility leads to further savings.

Die Casting

Die casting is the most efficient process for high volume precision casting, producing the best tolerances and rapid production rates, but having high initial tooling costs.

Die casting should be considered for components requiring a production run of at least 10,000 pieces. All tolerances depend on part size and complexity; however, tolerances of ±0.001" are common. Hot chamber die casting cycle rates range from roughly 150 parts per hour for large components to over 2,000 per hour for small ones.

The ZAMAK die casting alloys and ZA-8 can be used in a "hot chamber" die casting machine, while ZA-12 and ZA-27 must be "cold chamber" die cast like the aluminum alloys. The hot chamber process offers faster cycle times, resulting in lower production costs.

Due to the low melting temperature of zinc die casting alloys, dies for zinc parts last longer; often 3-4 times longer than the same dies when used for casting aluminum alloys.

Permanent Mold Casting

ZA-8 and ZA-12 are generally considered for permanent mold applications. Permanent mold casting has traditionally been done using steel or cast iron molds, but is now also performed in graphite molds. Permanent mold casting often competes with sand casting by providing tighter tolerances and a smoother surface finish which can reduce machining operations. Permanent mold casting is a competitive alternative to die casting when lower annual volumes are required.

Ferrous permanent molds designed for aluminum alloys are generally suitable for casting zinc alloys. However, due to the superior casting fluidity of zinc, thinner sections can be cast. This process is well suited for medium production runs of 500-10,000 pieces. Ferrous permanent mold casting has great flexibility in terms of part size, ranging from ounces up to 100 lbs.

Graphite permanent mold casting offers some distinct advantages over metal tooling. Improved tolerances, lower tooling costs, and a superior surface finish are all benefits of the graphite mold process. Drawbacks are limited component size, complexity and coring.

Sand Casting

All the ZA alloys are suitable for sand casting; however, ZA-12 is the most popular. Sand casting offers the greatest design flexibility in terms of size, complexity and quantity requirements. Tooling costs are generally low; and, therefore, facilitating low volume production. However, surface smoothness and tolerance capabilities are limited, usually requiring machining.

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