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Find out more about the common processing issues in the injection moulding process then use the links provided to contact and acquire quotes from the leading UK companies that can help you.
The primary considerations when looking to either prevent moulding issues at the pre-production stage or to find the root cause of a quality concern are:
These can all influence the quality of a moulded component, sometimes in combination.
To get help and advice from PlastikCity partners that specialise in troubleshooting & process optimisation, please visit here.
Below are some common moulding process issues, their most common causes and some possible solutions.
The tool cavity is not completely filled with plastic. Areas that are furthest from a plastic injection point, or where the material flow is restricted, are the most susceptible to this issue.
This is usually a combination of:
Possible solutions to short shot issues
1. Modification of the component design
2. Modification of the injection mould tool
3. Modifying the moulding process
Sink marks and voids are caused by the natural shrinkage of plastic materials during the cooling process within the mould tool. Different material types will shrink by differing amounts.
Whereas a sink mark is a visible depressed area on the outer surface of a moulding, a void is hidden within the wall section of the product.
In some respects, a void is more of an issue, as it is not easy to detect and can cause an inherent weakness.
An area of the moulding is discoloured, or material is degraded by excessive heat or corrosive gasses.
Burning is usually caused by caustic gases released by certain polymer grades being trapped within a mould tool. Venting of the tool allows this gas to escape.
If the material is not kept within the confines of a mould cavity, it will solidify as a thin layer (flash) that may need to be removed. Flashing most commonly occurs where tool faces meet, or around items such as ejector pins that require a small clearance to operate without sticking.
The surface of the product has lighter coloured lines or swirls that spread out from the material injection point.
1. Injection mould tool design
2. Modification of the moulding process
3. Material preparation or choice
Once a product is removed from the mould tool and is no longer supported, it loses its shape.
1. Component design
2. Tool design
3. Modification to the moulding process
Weld lines are an indication of where two or more material flow paths have converged and combined. Flow marks are a visible indication of where the hot material flow has come into contact with the cooler surface of the mould tool. As well as being cosmetically problematic, both issues can result in structural weaknesses.
In the case of weld lines, the material has cooled to the point that it won’t fully mesh together. This may be because the distance from the material injection point is too long.
Flow marks are typically caused by:
1. Mould tool design
2. Modification to the moulding process