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What is Injection Molding...
Injection molding is one of several plastics forming processes available and is one of the most widely used worldwide with over 50,000 molding machines sold annually. The process involves taking plastic resin in the form of pellets, melting them via heat and pressure, and injecting the molten material into a mold being held closed under high pressure.
Once the plastic has cooled, which generally happens rapidly, the mold is opened and the parts are removed. This process is nearly always done in an automatic mode to allow high volume production.
One of the major advantages of injection molding is the ability to produce many parts at the same time and this is done by having more than one cavity in the mold. Molds can range from 1 cavity up to 228 or more. The process, while quite simple on the surface, has many components that must function well together.
This is where it all starts. As stated, the raw material that begins the process is often called “resin”. This resin is in the form of round pellets or small tubular pieces which range in size from 1mm in diameter to around 4 mm in length. The material is shipped to the injection molding company in small bags, large drums, large boxes, or in some cases via truck or train rail car.
The resin is transported to a hopper on the molding machine or it is sent directly into the feed throat (see Melt Preparation).
Certain materials have a tendency to absorb moisture and are referred to as hygroscopic. If this moisture is not removed prior to the molding process, it will cause problems with the molding and lead to poor quality parts. For these hygroscopic materials, a drying process is required which entails heating the resin to a temperature below its melting point for a period of 2-6 hours.
Once the material is dry, it is then fed into a loading hopper or directly into the feed throat of the machine.
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Injection Molding Links
Following, in this column, are helpful links and resources relating to Injection Molding. If you have any suggestions to add here, please email the