WHAT IS DIE CASTING?
Die casting process
The basic die casting process consists of injecting molten metal under high pressure into a steel mold called a die. Die casting machines are typically rated in clamping tons equal to the amount of pressure they can exert on the die. Machine sizes range from 200 tons to 5,000 tons. Regardless of their size, the only fundamental difference in die casting machines is the method used to inject molten metal into a die. The two methods are hot chamber or cold chamber. A complete die casting cycle can vary from less than one second for small components weighing less than an ounce, to two-to-three minutes for a casting of several pounds, making die casting the fastest technique available for producing precise non-ferrous metal parts.
Die construction
Dies, or die casting tooling, are made of alloy tool steels in at least two sections, the fixed die half, or cover half, and the ejector die half, to permit removal of castings. There are four types of dies:
Single cavity to produce one component
Multiple cavity to produce a number of identical parts
Combination die to produce several different parts for an assembly
Unit die to produce different parts at one time
From a design point of view, it is best to design parts with uniform wall thicknesses and cores of simple shapes. Heavy sections cause cooling problems, trapped gases causing porosity. All corners should be radiused generously to avoid stress concentration. Draft allowance should be provided to all for releasing the parts – these are typically 0.25º to 0.75º per side depending on the material.
Die Casting Advantages
Die casting is an efficient, economical process offering a broader range of shapes and components than any other manufacturing technique. Parts have a longer service life when compared to plastic, and may be designed to complement the visual appeal of the surrounding part. Designers can gain a number of advantages and benefits by specifying die cast parts.
High-speed production – Die casting provides complex shapes within closer tolerances than many other mass production processes. Little or no machining is required, and thousands of identical castings can be produced before additional tooling is required.
Dimensional accuracy and stability – Die casting produces parts that are durable and dimensionally stable, while maintaining close tolerances.
Strength and weight – Die cast parts are stronger than plastic injection moldings having the same dimensions. Thin-wall castings are stronger and lighter than those possible with other casting methods. Plus, because die castings do not consist of separate parts welded or fastened together, the strength is that of the alloy rather than the joining process.
Multiple finishing techniques – Die cast parts can be produced with smooth or textured surfaces, and they are easily plated or finished with a minimum of surface preparation.
Simplified Assembly – Die castings provide integral fastening elements, such as bosses and studs. Holes can be cored and made to tap drill sizes, or external threads can be cast.
From a design point of view, it is best to design parts with uniform wall thicknesses and cores of simple shapes. Heavy sections cause cooling problems, trapped gases causing porosity. All corners should be radiused generously to avoid stress concentration. Draft allowance should be provided to all for releasing the parts-these are typically 0.25º to 0.75º per side depending on the material.
