The Fives Stages Of Plastic Injection Molding

Injection molding is a process that is used when plastic parts need to be fabricated. There are several products that are manufactured with the injection molding technique and each varies in their sizes, applications and complexity. Usually, this process requires injection molding machines, raw plastic materials as well as molds. The plastic is melted down into this machine and then injected into a mold, where it is left to cool and eventually solidify into the final product. The process for injection molding is relatively short, on average taking between two seconds and two minutes. Lets take a moment to discuss the four stages that are involved in this process.

Custom Plastic Parts Can Be Simple or Complex |

Plastic Injection Molding: Initial Stages

Stage 1: Clamping
Before anything is injected into a mold, both halves of the mold have to be clamped together in order to ensure they are securely closed. Each half is fixed to the injection molding machine and one of the halves is allowed to slide. The clamping unit, which is hydraulically powered, then pushes both of the mold halves together and gives off enough force to keep the mold securely fastened while the material is being injected. How much time this process takes is completely dependent upon the size of the machine; larger machines exert greater force and will require much more time.

Custom injection molding is also based on the quantity as well as materials used in the molding process. 


Stage 2: Injection
In the injection stage, plastic pellets are fed into the machine and the injection unit pushes them towards the mold. During this time, the pellets are melted down by the pressure and heat. This molten material is then quickly injected into the mold which causes a buildup of pressure which, in turn, packs and holds all of the material. The amount of material that is being injected is called a 'shot'. Its very difficult to accurately calculate the injection time because of the complex and ever-changing flow of molten plastic into the molds. However, time can usually be estimated by each shot volume and the injection pressure and power.

Custom Plastic Parts: The Desired Shape and Quantity

Stage 3: Cooling
As the molten plastic inside the mold makes contact with the surfaces of the interior mold, it starts to cool down. As it begins to cool, it solidifies into the desired shape. Shrinkage may take place during this phase, however, packing of material during injection allows additional material to make its way into the mold and this helps to reduce the amount of shrinkage. The mold is not opened until the appropriate amount of cooling time has passed. The time it takes for cooling can be estimated from the part's maximum wall thickness as well as various thermodynamic properties of the plastic itself. After the custom plastic parts have cooled, then any excess material is trimmed off.

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