Plastic Injection Moulding

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Plastic injection molding process involves the use of plastic, or polymer. The granular polymer is fed into a heated barrel. It is also further melted and mixed in the barrel by the rotation process of a screw type plunger, as heat is generated by the friction between polymer granules when the screw is rotating.

The melted plastic is then forced into a mold cavity with the required final shape through a nozzle by the screw rotation action. The mold is relatively cold which may have cooling channels run through it. This causes the molten polymer solidifies almost as soon as the mold cavity is filled. The solidified part with the final required shape is then ejected out when the mold open again. It will be further cooled down by the ambient air.

Material: Polymer

There are many types of polymer used in injection molding, depends on what kind of properties is needed. Basically it can be classified into 2 categories:

Thermoplastic and THERMOSTAT

Below is a list of most common polymer used in plastic injection molding:

1. PC

2. PC-ABS

3. ABS

4. POM

5. HIPS

Machine

Plastic injection machine is used to hold the mold in place and to melt the plastic and inject it into the mold cavity.

Injection machine is classified by it tonnage. Tonnage is the clamping force that the machine use to clamp the mold during injection molding process. It can be ranged from less than 10ton to 5000 tons, depend on part size and material used.

Another variety of injection machine is whether it is single injection machine or double injection machine. For double injection machine, it will have 2 set of screw plunger, hoppers and nozzles.

Plastic Injection Defect

In plastic injection molding, there are many common defect due to the process constraint and material properties.

Common defects are:

Sink mark, short mold, wrap, silver streak, flow mark, flashes, weld line etc..

With better injection machine, material, skill and better parts design, such defect can be overcome quite easily nowadays.

Product

Plastic product are widely used in electronic, automobile, machinery, equipment, telecommunication products etc. Around 80% of these products are made from injection molding process. Plastic product can be produced in large quantity with relatively low cost, these are 2 of it’s main advantages compare to other processes. With the help of slider, internal lifter etc, most of the 2D or 3D product can be molded using injection molding machine without any difficulty. Product produced using injection molding has high precision, high level of complexity, good surface finishing, consistency, high production and relatively low cost which cannot be achieved using other type of production technology.

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Source by Wong Jun Xiang