Introduction in injection moudling


Injection molding is a manufacturing process of shaping plastic resins, thermoplastic, also known as thermo softening  and thermosetting plastic materials. These materials are polymers that liquefy when exposed to heat and freeze, turning into a crystallized state when sufficiently cooled down.

The process begins by feeding the materials into a heated container, stirred and forcefully pressed into a cavity where it forms after cooling and hardening to the shape of the mould. Another form of process is by pouring through a vessel the granulated material into a heated barrel by gravity. The granules are pushed forward by screw type plunger, also called the ram injector, and pushed through the cylinder into a heated orifice where it melts. The force of the plunger presses the melted materials through a nozzle that is attached to the mold, entering into a cavity where it solidifies in the cold as soon as it is filled up. It is always maintained at a cold temperature allowing the molten plastic to solidify. The mold becomes a part of the machine as it receives the melted plastic and eventually forms the shape of the tool. They are pressed by hydraulic or mechanical forces. The force is calculated as the injection pressure times the total surface area of the cavity. This is achieved by the operation of the injection molding machine.

To get the color desired for the finished molds, colorants are also fed into the injection molding machines directly after the hopper. Some imperfections could be noticed after the molding process like burnt parts which could be caused by a high temperature setting. If the parts have traces of warping, it could be caused by uneven surface temperature of the molds or uneven thickness of the molds. Bubbles may be caused by gas presence in the surface or resin decomposition will produce surface imperfections. Insufficient resin shots can cause incomplete filling of cavities.

Polymers are great scientific creations. Shaping them is a higher scientific breakthrough that can be achieved by Injection molding.