Most plastic injection mouldings that are produced today are still compromised when compared to what they could be in terms of a fully optimised product.
Just take one example of the fact that most part geometry – even though it is created in modern 3D CAD systems – has wall thicknesses that are round figure dimensions such as 3mm, 2.5mm or 2mm etc. This indicates that the wall thickness decision is based on nothing more than……?? Well, it is certainly not based on the minimum that could be moulded or the minimum that the physical performance requires; but if it was, it would reduce costs enormously.
What happens if the polymer supplier calls to say that the price of ‘Polywarpylene’ is increasing by 5% next week? Major discussions would ensue between supplier and customer; because such an increase is, “… totally unacceptable!!!”
So what if I tell you that most injection moulded parts could easily be 20% cheaper and you would not notice? Well, consider a 3mm thick part – designed to a nice comfortable round figure based on the fact the last part that was similar in design was 3mm and worked well.
Why not make it 2.7mm thick?? That’s 10% less polymer (puts the row over a 5% price increase into perspective!) But more than a wall thickness reduction – 2.7mm will cool around 12% – 15% faster than 3mm. So, whichever way you slice the ratio of plastic to production cost, the new thinner parts will be at least 20% cheaper.
When was the last time someone offered you a cost reduction like this?? Probably never.
Now if you are an astute supplier you can probably double your profits with this technique. How? Well, the price you are getting for your products now has been greatly influenced by your competitors. You won the business by beating them – read that as ‘undercutting them’. The net result is that if you are making 5% on sales you are doing well – but let’s suppose you are. By reducing the wall thickness and consequentially the production time you can increase this margin to at least 20%. Give half to your customer as a cost down and keep the remaining 10%, thereby doubling your profitability.
“OK that’s all very well but the parts won’t be as strong “, you say. Strictly speaking, you are correct – but what is the strength requirement. I can guarantee that if the product had been optimised for strength based upon the design load cases then the wall thicknesses would not be expressed in nice round numbers. That fact is a good giveaway. Very few parts are ever subjected to development through the application of stress analysis (yet we have been designing bridges, planes, ships and cars using these technologies for decades). Why? Because it is so difficult to determine the load cases for the moulded part’s life performance; and that is mostly because we have not done a lot of stress analyses on plastic parts!
Optimisation of product design means using the least amount of material that will enable the product to perform its fit and function requirement without failure during warranty.
You don’t get optimum parts by plucking wall thickness values out of thin air!