The next time you brush your teeth in the morning, take a good look at the lid of the toothpaste tube. This component, like many others that we use and which surrounds us in our everyday lives, has been derived from a process called injection moulding. Sounds and looks simple, doesn’t it, and in a way it is, however there is a lot that can go wrong in the process, leading to problems with the components etc. and subsequently incurring financial losses and environmental consequences.
Injection moulding is a manufacturing process used to inject a molten 'plastic' material into a mould, producing a solid plastic part, once it has been allowed to cool. The fundamentals of it are simplistic but there is a lot more to it than this, which consequently makes the intricacies of the process extremely complex. The materials being used for both the mould and part must be carefully considered at the design stage. For example, injection mould tools made of steel which are much more durable for production, are a lot more expensive to produce than those from aluminium, so if mistakes are made and the parts don’t fit or work as intended, then not only has a lot of time been lost, but costly materials too are wasted.
During the component and mould tool design and development stage there is a lot to consider, such as the option of creating one tool for just one part or perhaps splitting it into its associated/mating component parts. This too is a balance between manufacturing a cost effective product or risking it not working at all. Another solution which is often on the cards at this part of the production cycle, is to design a mould tool that is slightly too small in terms of the number of components that can be moulded at once. If there are subsequent production problems then perhaps rather than throwing it away and starting again from scratch, it could possibly be 're-purposed' and adapted for the desired outcome or even utilised for a different component arrangement.
As a design engineering company serving clients in this area, we appreciate that there is great skill and expertise involved during the design phase. The mould itself is not a hollow shell, but a vessel which contains a complex pathway of gates, sub gates and runners, all of which facilitate the movement of the molten material throughout the mould cavity. An improperly designed cavity can result with the molten material not flowing into all the areas that it is required to fill. The mould closure system is another important part of the tool design. The position of these mould interlocks on the tool also has to be carefully considered as holds the mould in place during the process, suppressing any movement.
Materials used during the injection moulding process can vary depending on the end use and overall cost effectiveness of production. It is not unheard of though for some unseen problem to occur resulting with some shrinkage or warpage in the final component. So you see, in precision engineering, there is a very fine line in the injection moulding process between something working and lasting the lifetime required of the part, and that which is defunct over a short period of time.
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