Injection moulding is used to create many things: from packaging, bottle caps and automotive parts to pocket combs, one-piece chairs and mechanical parts. It is the most common modern method of manufacturing plastic parts and is ideal for producing high volumes of the same object.

But as is the case with any manufacturing process, things can go wrong. In Part 2 of this post, we take a look at the how you can overcome the four common injection-moulding defects we discussed in Part 1.

Flow lines

If the flow lines in your product are as a result of the moulding equipment, you should try the following: increase the nozzle diameter and temperature, increase the injection speed and pressure, raise the cylinder temperature and reduce the cushion or charging amount.

If the mould is the root of your problem, you should increase the mould temperature, providing a cold slug well. Increase the gate cross section surface and create more distance between the gates and the location of the mould.

To solve problems related to the materials, you should apply a surface lubricant.

Short shot

If your short shot challenges are as a result of the moulding equipment, you can try increasing the amount of material field. If the material field is still insufficient at maximum material feed capacity, you should change to a larger capacity machine. You should also try installing a screw with a back-flow check valve, increase the injection pressure and speed, raise the cylinder and nozzle temperature, and make sure there are no severed lines to the heater.

You should also look out for blockages in the nozzle. If the nozzle frequently clogs, raise the mould temperature or shorten the cycle time. If the mould is the issue, raise the mould temperature; increase the mould gas release, the gate cross section surface area and the moulded product thickness; and add ribs to the moulded product design to improve followability.

If the materials are causing the short shot, try using a low-viscosity high-flow material type and apply a surface lubricant.

Vacuum voids

To overcome vacuum voids caused by the moulding equipment, increase the injection pressure (including the secondary pressure), extend the injection time and lower the cylinder temperature setting.

To overcome challenges with the mould itself, you can change the product design so that the thickness is no greater than 6 mm. To enhance the strength, you can add several thick uniform reinforcement ribs to the product design. You should also try increasing the size of the fates, making the runners shorter and lowering the mould temperature to make it uniform.

For vacuum voids caused by the material, try using a highly viscous grade and dry the material thoroughly.

Warpage (warping)

If your warping is as a result of the moulding equipment, you can try the following: decrease the injection pressure, lower the cylinder temperature setting and lengthen the cooling time.

For the mould you can make the thickness of the moulded product uniform, eliminate the undercuts, change the gate locations and lower the mould temperature. You can also operate the knockout pins in a uniform fashion and provide multiple knockout pins.

For the very best in injection-moulding machinery that will last a lifetime, partner with Plastic&Chemical Trading today!

Resources –, plastictroubleshooter