Cutting the cost of design

Designers can slash the cost of their designs by using plastics intelligently. Lou Reade reports

Designer furniture, injection mould tools and golf: last month’s ‘Designing in Plastics’ Design Day had it all. More than 70 delegates crowded into Buckingham House (part of New Hall, Cambridge) to hear how plastics can lead to cost-saving and value-creation.
For Craig Norrey, technical programmes manager at DuPont, there are many reasons for switching a design to plastics, including weight reduction, functional integration and improving system or part performance.
“But if cost saving isn’t one of them, it isn’t going to happen,” he said.
An important way that plastics can cut cost is by reducing manufacturing cost. Norrey focused on an aspect of this that is often overlooked: wall thickness. While it is usually seen as a way of reducing material usage, it plays a critical manufacturing role because it determines the cooling cycle of a plastic part. Norrey compared the time taken to cool 2mm and 4.5mm thick parts. The relative cooling times would be 25 seconds against 60 seconds, which could more than double daily part production.
John Brenchley, product manager at polymer distributor Distrupol, pointed out that material cost is not the only factor to consider when looking for savings. A material’s density is commonly ignored, but if chosen correctly can lead to substantial savings. Potential alternatives to polycarbonate (density of 1.2, and used to make CDs and baby bottles) include: PMMA (density 1.11) and clear ABS (density 1.10). These would give 8-9% more parts for the same amount of material.
He cited the example of a pen barrel made from clear ABS. The customer was looking for cost savings and eventually got them by using Zylar 631, a styrenic co-polymer from Ineos. Cycle time was cut by 20%, leading to overall savings of 13%.

Fast furniture
Martin Kirk, of Materialise UK, gave an overview of additive layer manufacturing (ALM) techniques, which builds up products layer by layer. A rapid prototyping machine has no restrictions on part production. Materialise, a rapid prototyping bureau, has moved into rapid production by spinning off a company that uses such techniques to produce designer furniture.
It has used machines from companies such as EOS to produce complex products in a ‘single shot’ – such as the One Shot stool that is made from 50-micron particles of polyamide (nylon). The stool consists of a number of hinged parts, which bend automatically into a self-supporting structure.
Holloid managing director Julian van Wyngaarden explained how delegates should select an injection moulding partner. His ‘interrogation list’ included:
· Can they advise and select a range of quality materials?
· Do they have robust QC systems?
· Can they apply test & measurement?
· Do they have modern machinery?
He also pointed out the importance of tool design, which is often one step away from a design engineer’s capability.
“Poor tool design can cause problems,” he said. “A toolmaker is not usually experienced in moulding, so it’s essential for a moulder to control tool design.”

Showers and golf
The event’s independent speakers explained how plastics had been beneficial in their own products. Steve May-Russell, of design consultancy Smallfry, highlighted examples where plastics had added value – including a shower head that fits over hot and cold taps. By mixing the water under normal pressure, then pressing a trigger to mix the streams, he said the manufacturer was able to double the price compared to the existing design. Similarly, John Greaves used a selection of plastics to design a new type of powered golf trolley – which retailed at less than £200. Plastics were crucial in bringing the price down.

Tom Shelley

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