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Die Casting

Castings vs Forging Comparison Chart

castings vs forging comparison chart

Die casting uses metal as the mold as opposed to using sand. The diversity of design is limited to pattern allowable in utilization of metal. The metal is injected into the mold under high pressure. This results in a more uniform part, generally good surface finish and good dimensional accuracy. For many parts, post-machining can be totally eliminated, or require only very light machining to bring dimensions to size. Expansion and contraction is held to a minimum with this procedure. Die-casting can be done using a cold chamber or hot chamber process.

Die Casting

Die Cast / Aluminum / w/chemical film finish/
Small aircraft starter housing

 

 

Cold Chamber Process– The molten metal is ladled into the cold chamber for each shot. There is less time exposure of the melt to the plunger walls or the plunger. This is particularly useful for metals such as Aluminum, and Copper (and its alloys) that alloy easily with Iron at the higher temperatures.

Hot Chamber Process– The pressure chamber is connected to the die cavity which is immersed permanently in the molten metal. The inlet port of the pressurizing cylinder is uncovered as the plunger moves to the open (unpressurized) position. This allows a new charge of molten metal to fill the cavity and thus can fill the cavity faster than the cold chamber process. The hot chamber process is used for metals of low melting point and high fluidity such as tin, zinc, and lead that tend not to alloy easily with steel at their melt temperatures.

Die casting molds (called dies in the industry) tend to be more expensive for short run production, as they are made from hardened steel, and the cycle time for building these tend to be longer. Ata production run of 1000 or more, Die Casting produces a lower per part cost. Of course, the break-even point depends on the complexity of the part.

Aluminum, Zinc and Copper alloys are the materials predominantly used in die-casting. On the other hand, pure Aluminum is rarely cast due to high shrinkage, and susceptibility to hot cracking. It is alloyed with Silicon, which increases melt fluidity, reduces machinability. Copper is another alloying element, which increases hardness, reduces ductility, and reduces corrosion resistance. Ferrous metals such as iron and steel cannot be die-cast.

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