Die casting is the process of injecting molten metal into a mold to form a strong, resistant and durable product. Many different shapes, sizes and forms are made from the die casting process, which requires a complex and comprehensive design plan.
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Part designers and casters must work closely together at all stages of development, especially initial stages, to ensure the accuracy of the finished metal product. Most die cast parts have a uniform wall thickness, cores of a simple shape and may be hollow, solid, round, cylindrical, flat or complex. Die casting is mostly done in high volumes, offers a high degree of accuracy and repeatability and has the ability to produce identical products. Many different metals and alloys may be used, including steel, aluminum, zinc, magnesium, brass, copper and lead. The aerospace, automotive, commercial product manufacturing, industrial machinery, construction and electronics industries use die cast products like doorknobs, motor and pump casings, wheels, parking meters and computer housings. Parts may be as simple as a handle or as complex as transmission housing for cars. They generally weigh up to 55 pounds and may have holes, threading, external undercuts or projections.
There are four types of molds used during die casting. Single cavity molds are made for a single part; multiple cavity dies have many of the same molds and produce multiple identical parts at once; unit cavity dies have the molds of different parts, which are usually part of the same finished product; finally, combination dies produce several different parts for an assembly. The dies are made of alloy tool steel and are often brushed with lubricant to ease the ejection process. A die caster is composed of two die halves - one that stays in place and another that is able to open and close. For complex designs, many molds have removable slides to make projections and undercuts, or cores, which make holes in the part. Often it is less expensive and easier to simply drill holes as a secondary process. Very large castings are rare, as they can struggle with porosity problems when air bubbles are entrapped below the metal surface. However, this can be overcome by using a vacuum pump. Thin and uniform walls are recommended in order to prevent uneven cooling issues and trapped gases. If the part has corners, they all must be radiused to avoid stress concentration. A draft allowance between 0.25º and 0.75º per side helps to cut down on deformation when releasing the part from the mold.
