Peter's Processing and Manufacturing Blog

Common Injection Molding Defects that Newbie Molders Should Avoid

According to experts, the quality of an injection moulding process is critical to a company's success in the plastic industry. The reason is that a quality moulding process eliminates the possibility of product defects which would otherwise cost the business clients and sales. If you are new to injection moulding, maintaining high levels of expertise is one way you can prevent propagation of defects. However, it is only possible if you understand the most common faults, their causes, and how to avoid them. This article offers a good starting point for newbie injection moulders.

Air pockets

When air bubbles get trapped in a plastic mould during injection moulding, the finished product will have vacuum voids. If the voids are large enough, they create weak points on the product, making it susceptible to breakage. Usually, the air pockets form when some air remains during the moulding process. It is generally as a result of the application of low pressure on the mould. Enough pressure should be applied to the mould to remove trapped air to avoid air pockets in moulded products,

Colour Streaking

The goal of injection moulding process is to meet customer specifications, which includes colour. Therefore, if you notice pigment inconsistencies on a mould, then it could be as a result of residual tones from a previous moulding cycle. All parts of an injection moulding machine should be cleaned thoroughly to prevent product discolouration. For complete removal of colour specs, a purging compound is recommended to leave the mould clean for another run. 

Sink Marks

There are times when the internal part of an injection moulding product cools faster than the outside parts. When it happens, a section on the outside might get sucked in, forming a dent which is referred to as a sink mark. However, it is a defect that is entirely avoidable. One way to avoid sink marks is to ensure mould components have relatively thin walls to allow uniform cooling on both sides of a product.


When you notice peeling on the surface of a plastic product, it is referred to as flaking. Such peeling on a product is as a result of contamination of moulding materials that cause poor bonding. When flaking appears on a prototype, it is critical that you investigate possible contamination causes and arrest the issue immediately. It can be achieved through careful handling of moulding materials such as resin pellets.

About Me

Peter's Processing and Manufacturing Blog

Hello, my name Peter and this is my processing and manufacturing blog. I live in Melbourne with my wife and our two kids. I have always been interested processing and manufacturing. Have you ever wandered around a supermarket or shopping centre and looked at all the goods on display? Many people never stop to think about how the goods go from being raw materials to sitting on the shelves of shops. I decided to find out. I spent 7 weeks at my uncles processing and manufacturing plant. It was the best time of my life. I decided to start this blog to pass on what I have learnt.



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