Factors that affect plastic injection moulding quality

There are a number of factors that can affect the quality of plastic injection mouldings. Here’s a short list of some of the key considerations together with details on how Skar works to ensure the highest quality of production is maintained.

Mould tool design

Tool design is a crucial part of the injection moulding process because the way a product is injection moulded will have implications for its strength, quality and durability. For example, designing a tool where the cooling process can be intelligently managed can reduce distortion in the final product and keep manufacturing tolerances tight.

Ensuring a product is designed-for-manufacture and procuring the best possible injection mould tool can make all the difference to product quality, manufacturing speed, unit cost and productivity. It is why Skar Precision Mouldings provides design support and project management of the injection mould design process on behalf of customers.

Product wall thickness

Product wall thickness is a key consideration when designing products for plastic injection moulding. Thicker walls offer more strength but there is also a higher likelihood they may suffer from warping as the cooling process takes longer and there shall be more shrinkage.

Typically, engineers and designers look to minimise wall thickness for injection moulding for a number of reasons: thinner parts require less material, reducing material costs; they cool quicker, shortening the moulding cycle and reducing unit costs; and they weigh less, potentially reducing shipping costs.

The minimum wall thickness for injection moulding is dictated by the strength and the structural requirements of the product or component.

Behaviour of product over time

When designing a product or component, it is imperative to consider what it will go through on a day-to-day basis, as this will affect how long it will last. Factors to bear in mind when starting a project include:

• Creep – when a plastic is stressed over time and will not return to its original shape.
• Fatigue – when a repeated strain can result in the failure of a component.
• Wear – the gradual erosion of a material which has been subject to friction over time.
• Weathering – long-term exposure to weather conditions that affect the colour and material properties of the plastics.

At Skar we have a detailed knowledge of plastic polymers and specialist materials and can advise on which would work best for a particular application. We can also process specialist high performance injection moulding materials such as chemical resistant plastics, flame retardant plastics, and high strength plastics.

Shrinkage

Shrinkage is an inevitable part of the injection moulding process, which occurs because of the difference in density and volume between plastic in its molten state and plastic in its solid state. As a part cools in the mould and contracts, it must be controlled to avoid warping and control shrinking.

At Skar we use techniques like water cooling the parts coming out of the mould, packing the plastic into the mould at particularly high pressure or controlling the cooling time to reduce the effect of the shrinkage.