Designing for injection moulding

Rutland Plastics answers some of the most commonly asked questions about using injection moulding.

Q) Why should I consider injection moulding? A) The two main reasons are weight and cost reduction. For example, material selection and good product design can produce a moulded part that can replace a metal equivalent. Plastics also provide for a wider variety of shapes and colours. Q) How do I start designing for injection moulding? A) The best starting point is the end use requirements. These fall into functional, aesthetic and manufacturing related. Are any special strength characteristics required? When considering loading, for example, it is vital to be clear on the type of load, the rate at which the load may be applied, duration and frequency. The same approach can be applied to environmental factors such as exposure to very high or low temperatures, chemicals and UV light. Q) Isn't injection moulding just for large numbers of parts? A) Not necessarily. Although mould tools are relatively expensive alternative manufacturing methods may result in much higher part prices than an injection moulded part. Also, a number of parts can be combined in a single injection moulding so reducing or eliminating assembly. Q) Is there a limit on wall section? A) General guidelines for wall sections are 0.5mm – 5mm but do not be misled into thinking these are hard and fast rules. There are occasions where thick sections are necessary and Rutland Plastics has moulded parts with sections in excess of 100mm. Gas Assisted Moulding can be used to hollow out thick sections so producing a very strong box section effect. Q) How do I know what polymer is best? A) Again, this depends on the end use requirements. Strength can be provided by part design, material or a combination of both. Depending upon the part and type of strength required it may be better to use a more expensive material in a part with thinner sections and fewer ribs than a cheaper material where the reverse is true.