Steel, stainless, injection mold material

The injection mol ding process eliminates the restriction of straight-sided components required when parts are ejected from a die, and offers opportunities for external undercuts and threads. A wide variety of alloys can be processed, including alloy steels and stainless steels. Material properties of injection molded parts are available (32). 

Materials used in the mold must resist corrosion. This makes stainless steel and copper alloys the materials of choice for water injection molds. The mold is designed with an overflow to provide positive control material flow at the opposite end of the cavity. When the main cavity has been filled, the valve to the overflow is opened and the injection of the secondary material takes place. At this point in the cycle, a gas (typically nitrogen) might be injected to core out the hollow feature and force the displaced plastic into the overflow. If a gas is used, then water injection follows. If not, water injection only occurs. Following water injection, another gas or even plain air is used to discharge the water from the part. 

Injection molds are machined from a variety of tool steels and then hardened or in some cases plated with chromium, nickel, or proprietary materials. Large molds use prehardened tool steels because they cannot be hardened after machining. 124 Stainless steel is employed for some smaller molds, particularly those used for optical and medical parts and for corrosion resistance. Since they provide better heat transfer and, thus, shorter molding cycles, materials such as beryllium copper are used as inserts in critical areas. Injection molds are usually cooled or heated with water, although oil or electric heater cartridges are employed for high-mold temperatures. Mold-temperature controllers pump water into the manifolds and then into cooling fine machine into the molds. 

Molds must be made from an extremely durable material if they are to survive the large forces associated with injection molding over prolonged production mns. Hardened stainless steel is normally used, but more exotic materials... 

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