Injection Molded PP Plastic Part Warp – How To Fix It

PP is one of the most commonly seen soft plastics on the market.

It is applied to a variety of industries including packaging,automotive industry, like Step Pads, and other household products. Though for its wide use, PP is meanwhile is a very flexible, soft material with a relatively low melting point. Because of all these factorers, PP plastic molded part is most liable to get warped under heat,which becomes an annoying headache in daily production.

How to solve the warp on PP plastic parts? According to HS’s over 20 years of practical experience, there are basiclly 3 ways.

Improve design

In product design, use reinforced ribs with appropriate size wherever possible. For large area of surface, design it as micro-arc shape with equal wall thickness to reduce the internal stress.

Improve processing parameter

Most warp in plastic injection molded part is caused by uneven stress. There are only 4 primary plastic processing variables in the injection molding process – cavity pressure, melt temperature, fill rate, and cooling rate. All of them can contribute to injection molded part warp but the cooling rate of the plastic in the mold is by far the most important. The general rule is the plastic that cools the slowest shrinks the most.

Use reinforced PP

Use glass fiber reinforced PP instead of PP. This process can effectively strengthen the rigidity of the PP plastic injection part. Adding glass fiber is a common and mature method. But the shortcomings of this method are also obvious, high viscosity of plastic,poor flow, floating fiber on the surface of parts, part surface not being shinny enough . In this case, we have to solve the issues by adjusting molding process.

Posterior surface finishing

Alumininizing the surface of the plastic part and the chromium plating can improve the rigidity and the surface hardness of the part as well

In short, different ways could be adopted to solve the warp issues depending on specific PP plastic parts. At HS Mold, we have used polypropylene in a number of applications across a range of industries,including our ability to CNC machine polypropylene plastic parts for prototype development.

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