As you probably know, here at Toolcraft we have longstanding experience of designing plastic parts for the injection moulding process. This month, we want to share some design tips with you.

Draft angles

In injection moulding, you'll always need to keep the draft angle in mind, especially if you're designing a product with a textured surface. Basically, the rougher the surface, the larger your draft angle will have to be, otherwise the texture will prevent the part from coming out of the mould easily, or the part may be damaged. View the table to the right for an indication of the required draft angles for surface texture.

Thin features

If you need a very thin or delicate feature, it's probably best to have some models of your design made first. If the SLA/SLS model doesn't show up your feature adequately, it is unlikely that you'll get a better result with the plastic moulding process. Increase the size or thickness of the feature and have some more models done to ensure the feature reproduces correctly, before investing in an injection moulding tool.

Thick features

Here's a nice & simple rule: the 2/3 rule. If you need a boss or rib on an injection moulded product, the width of the boss shouldn't be more than 2/3 of the thickness of underlying wall. Otherwise, you'll get sinking of the plastic material underneath the feature. A way to get around this problem is to core out thick areas.

Tolerances

Don't specify too many areas that will need a tight tolerance. It's very difficult to achieve them consistently and unless you really need them, they'll prolong the design & modelling process, drive the price of your product up unneccesarily and perhaps even make it impossible to design.

It's also not practical to specify the same tolerance across all types of mouldings & materials, due to the vast range of materials available. As a guide, BS7010:1988 is a list of achievable tolerances for each material, available from the BSI website. Toolcraft far exceed the BSI tolerances through correct tool design & optimisation !

We hope these short tips will be useful to you. Have a look at our help pages for more injection moulding design tips, including advice on plastic moulding material selection, SLA or SLS processes and more. And if you're ready to make use of our design expertise to benefit your own projects, contact us.

With best wishes,

Sonja van Leeuwen, Marketing Coordinator
Toolcraft Plastics (Swindon) Ltd, Tel: 01793-641040