How to avoid injection moulding issues

Injection moulding issues can cause as many problems for customers as they can for manufacturers

There are a number of important factors that must be considered to ensure every component is of consistently high quality. Typically, plastic injection moulding accuracy is within 0.005 inches, making it one of the most reliable processes to produce parts with.

However, the temperamental nature of the process means that defects can be common with less experienced manufacturers.

Below are common problems that plastic injection moulding manufacturers encounter and the steps they take to ensure that their components maintain their high standards.

Creating an accurate mould

The creation of a bespoke mould for plastic components is a highly skilled task. It is imperative that the mould is perfect to resolve manufacturability and tooling issues that could potentially cause component defects such as air traps, voids, warpage, shrinkage, blemishes and weaknesses within the component structure.

Traditionally, this process relied on the skill and experience of a toolmaster. As a result, there was always an element of trial and error before the mould was perfected. Delays in this process adding time and cost to the injection moulding process.

Tooling and prototyping software has reduced the risk associated with mould development. Toolmakers are now able to digitally simulate moulds and the printing process, and so can be confident that a mould will be fit for purpose before it is created. This in turn reduces the production process, enabling manufacturers to deliver components to customers in a shorter time.

Avoiding burn marks

Burn marks are discolourations on the surface of the components. In addition to the aesthetic issues associated with the marks, burns can also result in degraded plastic. Burn marks can be caused by air that is trapped within the moulding machine that becomes overheated, or by a build up of resin within the mould that also can also overheat.

To avoid burn marks, manufacturers can decrease the speed at which the resin is injected. This reduces the chance of air becoming trapped. Alternatively, manufacturers can introduce vents or degassing systems that will remove trapped air. A final option is to reduce the temperature to which the plastic is heated to.

Preventing flow marks

Flow marks are wavy lines that appear on the component. They are normally the result of resin cooling too quickly within the moulding machine, or the position of the gate (the opening that allows the molten plastic to be injected into the cavity of the mould) needing relocation.

This issue can typically be resolved by increasing the speed and pressure that the liquid plastic is injected into the mould. This will help the plastic fill the mould in a more uniform manner, which will result in more consistent cooling throughout the mould. However, in severe cases, the mould needs to be redesigned to change the position of the gate to stop the molten plastic changing direction suddenly. By working with a skilled manufacturer, you’ll be able to avoid these problems and get consistent, high-quality parts.