What Defects Should You Watch Out for in the Injection Moulding Process? All You Need to Know

As with any other process, the injection moulding process also comes with its share of flaws, defects, and pitfalls. After all, the process of injection moulding can be quite complex, involving more than a few steps and parts, and it is undoubtedly important to make sure that all these parts and cycles are moving and functioning well.Injection Moulding ProcessBut sometimes, even with the most careful and meticulous attention to detail and precision, defects are unavoidable. Here, then, is your guide to some defects and flaws in the injection moulding process (either in the actual mould or the actual process) which can ultimately affect the production of various parts and components.

Burn marks

Another name for marks caused by burns is dieseling, and it can also be referred to as air burns or gas burns. These are often characterised by brownish or blackish coloured burnt sections in points where air becomes trapped or on the parts located furthest from the gate. The common cause for this would be a lack of venting for the tool or injection speeds which are too high.

Burrs or flashes

This defect is often seen as extra materials in a thin layer which exceed the customary geometry of the part. One main reason for this is that the mould may be overflowing or over packed, or the tool has a damaged parting line. It could also be caused by injection speeds which are too high or even dirt and other contaminants located on the tool surface.


Since the injection moulding process deals with heat and the melting of plastic, a defect known as blistering can occur. Blistering occurs when there is a layered or raised area on the part’s surface. One common cause of blistering is when the material or tool is too hot, which is frequently caused by a cooling deficiency in the heater or the tool.

Flowing Lines Or Marks

This type of defect is characterised by a series of wavering patterns, marks, or lines on the part. A typical cause for this defect is an injection speed which is not fast enough, or too slow. Since the speed is not fast enough, the resin would cool down during the injection cycle, resulting in a series of wavering lines or patterns.

Colour Streaking

Another common defect in the plastic moulding process is colour streaking, characterised by a change in colour of a certain area in the part or component. A reason for this could be that the batch has been improperly mixed. Another reason for this defect could be the residue of preceding coloured materials left in the nozzle or valve.

Particulates and other contaminants embedded into the part

As the phrase implies, this is typically seen as particulates or contaminants which become embedded into the component or part which are foreign in origin. This defect is often caused by various foreign particles on the surface of the tool, debris on the machinery’s barrel, or too much heat which burns the plastic material before injection.

Injection moulding experts like www.dataplastics.co.uk know all too well about the flaws and defects to be avoided in the injection moulding process. And with the right expertise and knowledge, you can lessen the risk of these defects from occurring.


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