material selection | DFM
Table 1: Savings resulting from value engineering analysis of a water meter part produced in brass, POM and reinforced PA6,6
Volume/Year Material Volume/part )
35,000 35,000
35,000
Brass POM
PA6,6
(cm3 281 281
208
Density (g/cm3
)
8.4 1.4
1.14
weight/ part (g)
2360.4 393.4
237.12 weight/
35k pcs (t) 82,614.00 13,769.00
8,299.20
PA reinforced with 30% glass fibre it was possible to reduce the overall wall thickness and, due to the new material’s characteristics, reduce the cooling time. The higher raw material price of the glass reinforced polyamide meant there was very little cost saving from the alternative material option. However, the savings in cycle time (-18%) were significant and estimated to amount to about €45,000 a year. The faster cycle time meant it was also possible to
reduce the total tooling requirement. Eliminating the need for an additional four-cavity mould resulted in an estimated additional cost saving of around €68k in this project.
The DFM stage of any product development pro-
gramme is also the appropriate time to carry out some value engineering calculations to determine if the mechanical properties, visual quality and other properties resulting from the incorporation of costly additives such as fire retardants in the material selection are in line with the overall project goals. Recently, AST was involved in just such a value engineering project for a water metering component. The client wanted to replace a part originally cast in brass and capable of withstanding a water pressure up to 12 bars. The main goal of the project was to reduce the component cost while maintaining similar mechani- cal properties, such as dimensional stability and resistance to water absorption.
Figure 2: The thick wall
sections in this POM water
meter compo- nent design required a
cycle time of around 120s. Switching to
reinforced PA presented big
cost reduction opportunities.
50 INJECTION WORLD | October 2012
Price/ kg (€)
3.50 € Design Comment original design 2.50 € 35% material saving
Material Costs (€)
289,149.00 €
1.80 € POM version of original 24,784.20 € optimised design
20,748.00 € Switching from brass to an injection moulded POM
(Figure 2) but retaining a similar wall thickness to the original part not only reduced the material cost significantly, but was also able to meet the high mechanical requirements. However, by introducing a water resistant, glass reinforced PA6,6 into the analysis it was possible to develop a component design with a much thinner overall wall thickness and increased overall strength. Analysis of this thinner component design in PA6,6
showed the cycle time could be reduced from 120s (for the POM part) down to 50s. The overall savings achievable by using the new PA component compared to
the POM version was calculated to amount to around €45,000 a year. The main bulk of this saving was accounted for by the faster cycle time, resulting predominantly from the shorter cooling times required for the thinner wall thickness. The full breakdown of the cost savings for the two
alternative polymer-based components against the the cost for the original brass design are shown in Table 1. It should be noted, however, that the weight savings in the plastic designs also provided a further and quite significant saving on shipping charges. Experience shows that material selection can have a huge influence on part cost and production economics. Companies that take an intelligent approach to resin selection will realise valuable capital and production cost savings, speed their time-to-market, and produce parts that perform better.
About the author: André Eichhorn is general manager of Germany-based AST Technology. This is the second instalment in a series of articles presenting a step-by-step discussion of the Design for Manufacturing (DFM) process. If you missed the first instalment in this series you can view it here. Part three, which will be published in the next edition of Injection World, will look at optimisation of part structure. ❙
www.ast-tech.de
AST Technology will also be exhibiting at the Fakuma trade fair in Friedrichshafen in Germany later this month. You can find the company in Hall A1, Stand 1302.
www.injectionworld.com
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