Zinc alloys are very versatile and can be cast and processed in a variety of ways. The alloy choice depends on the type of process being used, which also depends on other various characteristics of the component such as annual volume and part complexity. The following videos give the basics of varioius casting processes that are commonly used to make zinc components.
Die casting is the most efficient process for high volume precision castings. This process produces castings with the highest tolerances, strength as well as having the highest production rates. Although initial tooling costs are high because premium grade H13 tooling is used, extremely high volumes can be achieved. Typically, tooling can last up to a million shots in zinc, which is 10X longer than what is typically achieved in Aluminum alloys.
Die casting should be considered for components requiring a production run of at least 10,000 pieces. 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. ZAMAK die casting alloys, ZA-8 and EZAC can be cast 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 and associated alloys should always be considered first due to their faster cycle times, lower energy costs, and overall lower processsing costs.
ZA12 is typically conisdered as the main alloy choice for permanent mold applications, although all ZA alloys can be cast in this process. Traditionally, this process has been done using steel or cast iron molds, but due to zinc's low attack rate, graphite molds can be used instead. Graphite tooling is far more economical than steel tooling and still offers high tolerances and a smooth surface finish which can reduce machining operations.
Permanent mold casting is a competitive alternative to die casting when lower annual volumes are required. This near net shape process is well suited for medium production runs of 500-15,000 pieces per year.
Sand Casting is used for very low volume production runs, typically up to 500 pieces per year. All the ZA alloys are suitable for sand casting; however, ZA-12 is the most popular due its combination of castability and strength. 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.
Other casting methods include spin casting, continuous casting, investmentment casting and slush casting. Each of these processes have unique advantages, and can use a variety of zinc alloys depending on the process.
Hot Chamber Die Casting Process
Cold Chamber Die Casting Process