“Mind the gap”, I’m sure you’ve all heard this familiar automated announcement when using the London Underground. The design of some stations present an unsafe gap between the platform and train and therefore to make passengers take extra care with embarking and disembarking, this message can be heard each time a train arrives. In engineering, we too have to be mindful of the gap, which can be equally disastrous, especially when dealing with injection moulded parts.
It is a truth universally acknowledged that during the manufacturing process there will be acceptable degrees of variation to the CAD design model. These imperfections are very slight changes to the size of a component, so small that to the naked eye you wouldn’t really be able to tell the difference. But in product design, and particularly the injection moulding process, a mechanical design engineer has to take into consideration the tolerance of the tooling parts being used and design a part so that any deviation in size means it will still fit together, during the assembly process. Tolerance Analysis is the process which aids engineers and helps them to do just this.
Designing a mould tool that doesn’t take into consideration the tolerances could easily mean it doesn’t work or fit as it should, and most certainly, if it is too small, will result with it having to be thrown away and the design process restarted. Not only having a negative impact on hitting project deadlines, but budgets too. So you see, we engineers have to be very mindful of the gap too!
