3 Injection Molding Defects and How to Fix Them

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Injection molding is a manufacturing process that’s been around for quite some time. For many products, it’s the cheapest, fastest, and easiest way to produce thousands or millions of identical pieces. Injection molding machine operators have a lot of control over how well their machine operates and whether or not defects are produced. Defects in injection molded parts typically fall into different categories. Let’s have a look at some of them.

Runner Marks

A result of fluid leaks during the injection process causes striations on the surface of the plastic, which are almost always vertical because those are the points where metal touched metal for as long as possible before seeping out. The easiest way to fix runner marks is to remove the part from the injection molding machine, sand, and polish. If you can find a leak in the runner system, this fix should take care of it as well.

Gate Defects

This is a defect that occurs in either a gate or a mold half that’s caused by power fluctuations or speed fluctuation during the injection process, causing raised surface defects. Gate defects are much less obvious than runner marks because they don’t have a definite border and normally just appear as “white spots” on top of black plastic.  If you’re lucky, they’re white spots; if you’re unlucky, they’re brown spots (orange). A gate defect can be easily removed by washing it off with acetone and polishing the plastic with a soft cloth.

A String of Plastic Sticking Out

An injection molded part can have a string of plastic sticking out from a plastic line in the mold. Usually, these are the result of white plastic being poured into the mold too quickly or too far into the cavity, causing it to stick out of the mold. This is most common with small injection molded parts where it’s easy to fix by just taking them out, washing off any excess white plastic, and re-inserting them back into the machine. These are usually pretty easy fixes, but if you want to avoid potential difficulties with your machine, it’s a good practice to also control temperature and speed so these problems don’t occur.

Connekt, LLC, is operational in Grass Valley and Auburn, providing mechanical and engineering design services, custom injection molding, custom plastic parts, finite element analysis, and consulting services, and various other offerings. You can reach out to us for your engineering and design needs.

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