Metal castings are extremely important to the global economy and are used in 90% of all finished manufactured products. As an important segment of the larger metal casting industry, the die casting industry produces over one-third of all metal castings.
Die casting entails forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mold. Most die castings are made from non-ferrous metals, the most common being zinc, aluminum and magnesium.
Why Zinc Castings?
For countless decorative and functional applications no other material and process can match the properties and economics of zinc die casting.
Zinc casting alloys are stronger than reinforced molded polymers and zinc’s hardness, self lubricating properties, dimensional stability and high modulus make it suitable for working mechanical parts, such as gears and pinions, that would be less durable if molded from polymers. Zinc’s excellent thermal and electrical conductivity, as well as precise casting tolerances, make it an ideal material choice for heat sinks, electrical components and applications requiring electromagnetic shielding. Zinc can be cast at moderate temperatures thus providing significant energy and processing savings over other metals and engineering alloys.
Zinc castings also accept a broad assortment of finishes allowing almost any desired aesthetic characteristic and coating durability to be achieved. For example, zinc castings can be made to look like solid gold, weathered brass, stainless steel, and even leather And, because of zinc’s density, cast zinc parts provide a feel of substance and durability that simply cannot be matched by plastic components.
Key Advantages of Zinc Casting Alloys include:
Virtually any casting process can be used with zinc alloys to satisfy virtually any quantity and quality requirement. Precision, high-volume die casting is the most popular casting process. Zinc alloys can also be economically gravity cast for lower volumes using sand, permanent mold, graphite mold and plaster casting technology.
Zinc alloys are castable to closer tolerances than other metals or molded plastics, therefore presenting the opportunity to reduce or eliminate machining. “Net Shape” or “Zero Machining” manufacturing is a major advantage of zinc casting.
Strength & Ductility:
Zinc alloys offer high strengths (to 60,000 psi) and superior elongation for strong designs and formability for bending, crimping and riveting operations.
Few materials provide the strength and toughness of zinc alloys. Impact resistance is significantly higher than cast aluminium alloys, plastics, and grey cast iron.
Zinc alloys have the rigidity of metals with modulus of elasticity characteristics equivalent to other die castable materials. Stiffness properties are, therefore, far superior to engineering plastics.
Zinc alloys are non-sparking and suitable for hazardous location applications such as coal mines, tankers and refineries.
Bushing and wear inserts in component designs can often be eliminated because of zinc’s excellent bearing properties. For example, zinc alloys have outperformed bronze in heavy duty industrial applications.
Zinc castings are readily polished, plated, painted, chromated or anodized for decorative and/or functional service.
Thin Wall Castability:
High casting fluidity, regardless of casting process, allows for thinner wall sections to be cast in zinc compared to other metal.
Fast, trouble-free machining characteristics of zinc materials minimize tool wear and machining costs.
Low Energy Costs:
Because of their low melting temperature, zinc alloys require less energy to melt and cast versus other engineering alloys.
Long Tool Life:
Low casting temperatures result in less thermal shock and, therefore, extended life for die casting tools. For example, tooling life can be more than 10 times that of aluminum dies.
Clean and Recyclable:
Zinc alloys are among the cleanest melting materials available. Zinc metal is non-toxic, and scrap items are a reusable resource which are efficiently recycled.
The Zinc Alloys
There are two basic families of zinc casting alloys: ZAMAK alloys and ZA alloys. Zamak alloys contain approximately 4% aluminum and provide excellent die castability and good strength. The majority of zinc die castings are made from Zamak alloys. ZA alloys contain higher amounts of aluminum and offer superior strength.
From bathroom fixtures and door and window hardware to office equipment and tools as well as automotive and countless electronic components, zinc castings are truly everywhere and positively impact our lives on a daily basis.