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233. The Industrial Science of Injection Molding

Science of polymers was an amazing invention and further their shaping was a blast. The most common method of shaping plastic resins is called plastic molding. It is accomplished by large machines called injection molding machines. The process was first designed in the 1930s and was originally based on metal die casting deigns. It has many advantages over alternative manufacturing methods which include: Minimal losses from the scrap; Recycling; Nominal finishing requirements.

Plastic resins are injected with force. The science of transforming plastic resins into useful things through the process called Injection Molding had made an incredible impact on industry and on our daily lives. The designs could be summed up into following guidelines:

(1) To minimize sinking, warping, residual stresses and improve mold fill and cycle times you can use uniform wall thickness throughout the part.

(2) Use least thickness compliant with your design requirements. It ensures cooling, short cycle times and minimum shot weight.

(3) Designs should make easy withdrawal from the mold by providing draft in the direction of mold opening or closing

(4) Use generous radius at all corners with minimum of one material thickness

(5) You can use ribs or gussets to improve stiffness in bending

It is to be noted that injection molding is a process of some complex calculations. Every different resin has a shrinkage value which has to be accurately determined. Or else the final product might be incorrectly sized or may contain flaws. So this can be compensated by filling mold with resin and holding it under pressure and then adding more resin to compensate for contraction.

The process can be used with variety of plastic resins and the popular charts include: polypropylene, polyethylene and ABS. Every resin holds its own set of advantages and disadvantages so it has to be chosen as per their characteristics desire.