Things to Consider when Making Plastic Parts for Injection Molding

Things to Consider when Making Plastic Parts for Injection Molding

There are several ways you can create large quantities of plastic parts in the industry. One of the most effective processes used is injection moulding, a complex process where liquid plastic is injected into a metal mould, cooled and ejected before it is connected to its other half to create a complete product.

Before you begin the injection moulding process, you need to understand a few things about it. Here are some great time-saving things to consider when working in plastic manufacturing.


Radiused edges make it easier to eject your parts. Used along with draft and other techniques, they can also save you money and reduce the chances of your part cracking under stress. When you use radii, make sure you accommodate them by balancing out the wall thickness on the corresponding side.

Solid or Shell

When a part is made from solid plastic, it is more at risk of shrinking or warping when it’s cooled. Rather than creating a solid part, you can make a shell. This reduces the chances of distortion and saves you money on materials.


Draft angles make it easier to eject the plastic part from the mould. They help reduce friction when you remove it from the metal, which can damage the part. They can be used either on the outside or on the inside of the part. For every inch of thickness within the wall, you should add 1 degree of angle in the draft.

Joining Parts

Most of the time, injection moulding is used for several parts of one complete whole. The parts are joined together by using a range of tools, including mounting bosses, screws and snap hooks. The type of connection you choose depends on several factors, including all the elements mentioned in this article.

Division Line

The dividing line is where you connect the two sides of a part together. Almost always this leads a visible line on the finished product, but if you’re clever with your design you can effectively hide them by placing them at an edge.

Sink Marks

When a section of the surface plastic appears to have sunk down into the component, it causes sink marks. This can happen because of several reasons, including the varying thickness of the walls, improper radii and sharp edges in the design.

Support Ribs

These are constructed inside the walls of the component. Also called gussets, they can be used to provide extra support where there is an internal right-angled corner, or when the size of the part in relation to the thickness of its walls risks it becoming weak and breaking.


You want to avoid undercuts wherever you can, as they can cause problems with ejection which can lead to damaged or broken parts, and they will also make your production more expensive. However, sometimes your part will require undercuts, in the form of parts inside the mould which move, but if you can avoid them, do.

Ejector Pins

These are used, of course, to help eject your part from its mould. They can, however, leave undesirable imprints on your part if not positioned correctly, so keep this in mind when choosing where they go.

There are lots of things to be aware of when making plastic parts; we hope you’ve found our brief overview helpful for saving time and money.

Category Business

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