The four processes of classic die casting, sometimes referred to as high-pressure die casting, are die preparation, filling, ejection, and shakeout. These four steps serve as the foundation for all other die casting variations. Spraying lubricant into the mold cavity helps to prepare the dies. The lubricant aids in the removal of the casting as well as in regulating the temperature of the die. The dies are subsequently sealed and high pressure—between 10 and 175 megapascals (1,500 and 25,400 psi—molten metal is pumped into the dies. The pressure is kept up until the casting solidifies after the mould cavity has been filled. After that, the dies are opened, and the ejector pins eject the shot—which differs from castings since a die might have numerous chambers that produce multiple castings per shot. The next step of the shakeout is to separate the shot from the junk, which consists of the gate, runners, sprues, and flash. A customized trim die in a power press or hydraulic press is frequently used for this. Sawing and grinding are additional techniques for shaking out. If gates are thin and easily broken, tumbling shots is a less time-consuming option; gates must then be separated from final pieces. Remelting this scrap allows for recycling.The yield is somewhere around 67%.
The fast fill of the die caused by the high-pressure injection is necessary so that the whole cavity fills before the casting solidifies. Discontinuities are prevented in this way, even when the design calls for thin, challenging-to-fill parts. This causes the issue of air entrapment because there is little time for the air to escape when the mold is quickly filled. Even with a highly refined process, there will still be some porosity in the core of the casting. This issue is reduced by incorporating vents along the separating lines.
To create features that are not easily castable, the majority of die casters also execute various auxiliary processes, such as drilling a hole, polishing, plating, buffing, or painting.
Excellent dimensional precision, typically 0.1 mm for the first 2.5 cm (0.004 inch for the first inch) and 0.02 mm for each subsequent centimeter (0.002 inch for each subsequent inch), depending on the casting material.
Smooth cast surfaces (0.04-0.10 thou rms or Ra 1-2.5 micrometers).
Comparatively to sand and permanent mould casting, thinner walls (about 0.75 mm or 0.030 in) can be cast.
Threaded inserts, heating elements, and high-strength bearing surfaces are examples of inserts that can be cast in.
Reduces or stops using secondary machining processes.
Rapid rates of output.
Reaching a tensile strength of 415 megapascals (60 ksi) for casting.
Unlike permanent molds, sand castings, and other varieties, the length of the die casting fluid is unaffected by the range of solidification.
Due to the smoother surface of die castings, corrosion rates are lower than those for sand castings.
Die casting's primary drawback is its extremely high capital expense. In comparison to most other casting techniques, both the necessary casting equipment and the dies and associated components are relatively expensive. Therefore, a high production volume is required to make die casting a financially viable technique. Other drawbacks include:
The procedure is just for metals with high fluidity. Fluidity failure can result in higher scrap rates, and die casting has significant scrap costs.
Questions of repeatability are particularly crucial when it comes to die casting because there are numerous elements involved.
Prior to 2018, casting weights could only be between 30 grams (1 oz) and 10 kilograms (20 lb), however starting in 2018, shots up to 80 kilograms (180 lb) are now feasible.
The final casting produced by the typical die casting process contains a modest percentage of porosity. Due to the expansion of the gas in the pores caused by heat, which results in microcracks inside the part and surface exfoliation, this inhibits any heat treating or welding. Some businesses have, however, discovered techniques to lessen the part's porosity, enabling only limited welding and heat treating.Die casting is thus limited to portions in which softness is acceptable, which is a related drawback. Parts that require tempering and hardening (either through hardening or case hardening) are not cast in dies.