Saturday, January 28, 2017

The Plastic Injection Molding Process

By Ann Foster


Basically, injection molding is a manufacturing process which involves heating the plastic granules and then forcing the melted plastic through a mold cavity. This process is the one commonly used in production of plastic parts. However, with plastic injection molding, various products are produced. These products usually vary complexity, sizes, and application. This process, however, requires a machine, a mold, as well as raw plastic materials.

Normally, the raw plastic materials are first converted into molten states by the machine before being infused into the mold for cooling and solidification. In Cobourg, ON, the technique produces plastic parts that are thin-walled and are put to different uses such as plastic cases. The cases are usually used to seal various products including household appliances, consumer electronics, power tools and automotive dashboards. Other products that are also produced include open containers such as buckets.

Injection molding cycle generally is a four stage short process that lasts for about 2 seconds and two minutes. The initial stage is referred to as clamping. Prior to injection of materials into the molds, one ought to ensure that the two halves are securely closed with clamping units.

At the injection phase, one of the halves is clipped to machines as the remaining half is slid onto it. The clamping unit normally is powered hydraulically and pushes together the mold halves and at the same time exerting some force that ensures the mold remains securely closed as the material is injected.

The next phase entails infusion raw plastic pellet continuously into the molding apparatus. In this phase, raw materials are melted using continuous application of heat and pressure. The melted materials are then imparted into the casts where additional pressure build-up holds and compacts them. The quantity of imparted material is called a shot. The interval or time duration that the phase lasts is generally hard to ascertain. However, estimations are generally gained by relying on the injection power, injection pressure as well as quantity of shot.

The third stage is known as cooling, where the molten material in the mold starts to cool after getting into contact with the inner mold surfaces. As the molten material cools, it solidifies taking the shape of the desired part. Nevertheless, some shrinkage may occur during cooling, but packing the material at this stage makes it possible for additional material to get into the mold thereby reducing the visible shrinkage.

The final stage is the ejection stage. This takes place after enough time has passed and the cooled parts can, therefore, be ejected by the ejection system from the mold. Once the mold is opened, a certain mechanism is used to remove the part from the mold. Normally, force is applied in ejecting the part since the part shrinks and sticks to the foam during cooling. To facilitate the ejection process, a mold release agent may be used and sprayed on mold cavity surfaces before injecting the material.

When the cycle is completed, post-processing is normally done. This is since the materials contained in molds channels normally solidify as they cool and remain stuck attached on these parts. Nevertheless, the extra material and any flash that may have occurred needs to be trimmed off.




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