Die Casting is a custom manufacturing process that produces engineered metal parts by injecting molten metal under very high pressure into reusable molds, called “dies,” made from premium tool steel. The dies can be designed to cast very complex shapes and sharply defined product features with a high degree of accuracy and repeatability, often with no post-casting machining required to meet part specifications. Smooth surfaces can be produced as-cast, as well as various textured surfaces. Die castings are suitable for a range of cosmetic finishes to match other mated parts or add extra durability in use. High-pressure die casting, is capable of producing net, or near-net-shape castings of high integrity and dimensional precision— at very high cycle speeds. A complete die-casting cycle can vary from less than one second for small components weighing less than an ounce to no more than a minute or two for a casting of several pounds. The process’s advantages make die casting the most efficient technology available for producing a wide range of commercial, industrial, and consumer products in durable, rigid metal. Chicago White Metal produces die castings from Aluminum, Magnesium, and Zinc alloys.
Die castings offer many of the qualities of gravity-cast parts: the rigidity, look and feel of solid metal; excellent strength characteristics; sound-damping properties; inherent EMI shielding for electronic applications; part serviceability; and, as with all castings, they are 100% recyclable. Unique to the advanced die casting process, die castings can be rapidly and consistently produced to close tolerances, often eliminating all machining. Sand castings require a new sand mold with each casting or gate of castings. The permanent mold gravity process uses iron or steel molds but is far slower and less precise than die casting. High-tech die casting can produce the highest quality surface finishes at the lowest part cost, and offers the best overall value provided there is enough volume to justify the higher tooling cost.
High-pressure casting and high-pressure die casting are terms used in Europe and other countries outside of the U.S. for what is referred to in the U.S. simply as the die casting process. The terms low-pressure die casting and gravity die casting are terms used outside the U.S. for what in the U.S. is called low-pressure permanent mold and gravity permanent mold casting. Although they each use metal dies, because of the lower pressures involved, they are restricted to heavier section parts, resulting in higher costs because of the less efficient use of the alloys and the longer cycle time.
The casting industry generally has applied the word “miniature” to minuscule zinc die castings produced at high volume and low cost using specialized hot-chamber machines. These high-speed die casting machines (often called 4-slide or Techmire machines) yield castings that are virtually flash-free. Parts can be cast in Zinc #2, #3, #5, and #7, and higher-strength ZA-8 alloy, with minimal draft and very close tolerances. Miniature zinc die castings typically require no die trimming or other post-casting operations. Small zinc die castings can be produced using multiple-cavity dies on larger, conventional die casting machines. However, 4-slide equipment is the optimum method for casting net-shape flash-free, very small zinc alloy parts at the lowest part cost with minimum die investment. Miniature zinc die casting can produce parts with tolerances as tight as +/- .001″ and walls as thin as 0.020″, in parts weighing up to .75 lbs.
Squeeze casting is a specialized high-pressure casting process that, through the use of very large gates and hydraulic pressure, can cast liquid metal with a minimum of turbulence or gas entrapment. The result is a porosity-free, heat-treatable component with thick walls capable of surviving the critical functional testing essential for structural automotive parts. Production costs will be higher than conventional high-pressure die casting, but squeeze-cast parts have replaced permanent mold, forgings, and iron castings in high-strength applications. Most production to date has been made with aluminum alloys. CWM does not offer squeeze casting, and the number of casters utilizing squeeze-casting machines is relatively limited.
The semi-solid metal casting process (SSM) uses a special cast billet, which is then cut into heated slugs and introduced into the shot chamber of specialized casting machines. The uniform, globular semi-solid microstructure of the heated slugs provides flow characteristics capable of filling the casting die under high pressure: gas entrapment is substantially eliminated, and solidification shrinkage is reduced. Early qualification of parts for structural automotive applications has been successful. The process can cast thinner walls than squeeze casting and has proven suitable for use with aluminum and magnesium alloys. However, production costs are higher than for conventional high-pressure die castings. CWM does not offer semi-solid metal casting, and the number of casters utilizing the SSM casting process still needs to be increased.
Thixomolding uses chipped metal that is fed into a heated barrel and utilizes a screw to turn the chips into a semi-solid material that is then injected into the die. The added cost of the chipped material and the increased cost of machinery, including frequent maintenance and replacement of the screw, typically result in higher-cost for parts that can often be produced just as effectively via CWM’s conventional high-pressure die casting technology. CWM does not offer Thixomolding, and the number of producers utilizing Thixomolding machines is still limited.