Friday, 27 January 2017

Understanding The Plastic Injection Molding Process

By Ann Foster


Injection molding basically refers manufacture processes that capture the heating and melting of plastic granules before being strained through mold cavities. The technique is generally used in the manufacture of parts made of plastic. Nevertheless, through plastic injection molding, the manufacture of these products is made possible. Such products normally are variant in application, size and complexity. The process nonetheless utilizes raw plastics passed through machines and molds.

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.

The injection molding cycle is usually very short lasting between 2 seconds to 2 minutes, and the cycle consists of four stages. The first stage is known as clamping. Before injecting the material into a mold, you must close the two halves securely using a clamping unit.

In injection phases, the halves are clipped on machines and slid onto each other. The clamping component is motorized hydraulically to push the cast halves to combine and also applying pressure to ascertain that they remain firmly locked as materials are infused.

The second stage is injection, where the raw plastics are often in form of pellets is continuously put in the molding machine and advanced to the foam by the unit. At this stage the material is usually melted by pressure and heat. The molten material is quickly injected into the mold as the pressure buildup packs and holds the material. The injected amount of material is usually known as a shot. The time taken in this stage may be difficult to calculate but can be estimated by the volume of the shot, injecting pressure, and injecting power.

The third phase is cooling. Here molten materials contained in molds are left to cool as they gain contact with the internal mold surfaces. They then solidify and take the desired shapes. Nonetheless, some shrinking can happen as the cooling takes place, although packing of materials at this point usually allows for addition of material into the molds that reduces any visible shrinkages.

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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