Plastic parts can be designed in many different varieties. But these all share the same basic principles that make a big difference with your final product. Understanding some of these can save your project a lot of time and effort.

Use an experienced Plastic Injection Moulding provider

Plastic injection moulding for blog on tips for designing plastic parts

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It might seem like an obvious point, but an experienced plastic injection molding operator will help you avoid many classic mistakes made with part designs. A simple example is the placements of the gates – this is where the molten plastic will be injected into the mold. How the plastic flows and cools determines many of the properties of the part, such as seams and weak spots. Experience can dictate the best designs for your mold that will also compliment the process you wish to use.

Anticipate slight taper or draft

Plastic objects need to cool before they come out of the mold, which will result in slight shrinkage. Ideally, the product should slide out easily. But if the sides are completely straight, this is far less likely to happen and you may have to force the part out, risking damage to the part as it scrapes due to friction. Adding a very slight taper to the external sides of the part fixes this problem. It’s a very simple idea, yet hugely effective and a fundamental principle of injection molding design.

Maintain uniform thickness when possible

Sink marks, which is where flat surfaces instead curve inwards – as if the plastic wall as sunken in – is a common problem with plastic molding. This happens because the different areas in the part didn’t cool uniformly. It’s mainly a question of space and time: areas that need more plastic will take longer to fill and cool, raising the risk that they will deform as the rest of the part cools faster. The way to avoid this is to try and keep the main walls’ thicknesses as uniform as possible.

Avoid hard corners

Picture showing flow of plastic on corners for blog on tips on designing plastic parts

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As molten plastic moves into the mold, it will attempt to fill every nook and cranny. But hard and sharp corners are much more difficult to fill. This can cause turbulence in that area, leading to poor fills and other shape problems. Professional designers thus prefer to use slightly rounded corners: these help the plastic flow more comfortably into the corner, filling it uniformly.

Know your materials

Know what type of plastic you want to use or what your options are. Different plastics have different properties, such as their viscosity (how well they flow when heated) and their cooling rate. This can be further altered by additives. The material you use will have a lot to do with the purpose of the part – for example, you may want UV resistance. Bt this can impact other properties and how the plastic responds to different designs. It is quite possible to have a mold made that will not work with the intended material, so do your homework to ensure you get a happy harmony.