Cafeteria Seating gets a Ruggedized Re-design

When a market leader in educational seating approached us to assess proposed design developments and optimise the design of one of their ABS plastic products, we needed to apply some lateral thinking. The ABS plastic seats were cracking around the mounting post and concern was raised as to whether different methodologies for attaching the seats to the metal posts was causing the cracking, or increasing the likelihood of cracking occurring. There is a saying that you should "never under-estimate the ingenuity of stupidity", but when designing for the education market we needed to think more along the lines of "never under-estimate the ingenuity of abuse a youngster can apply to your design". Our starting point was to look at the range of sizes and weights of users, as teachers may use the seats as well as students. We then considered what a 'reasonable level of abuse' was to apply to the seat surface and decided that a person standing on the edge of the seat was a foreseeable event. Using finite element analysis software we prepared computer models of three seat designs and evaluated the resulting stress plots to determine percentage improvement in the different design stages. The second developmental design from the client was 14% stronger than their initial design. Our 'optimised design' was able to minimise the amount of additional material required and also reduced the modifications needed to the seat moulds. The 'optimised design' was 36% stronger than the client's second design and 55% stronger than the initial design, which in real terms means it would need a person weighing 232Kg sitting on our design to break it. Though the different methods for seat attachment in the USA and Europe did not cause the cracking, we were able to prove that in the USA, they were applying almost 100 times the necessary force into the seat attachment bolt.

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