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DFM | material selection Intelligent material


selection can have a big impact on the cost of a


product and is an essential step in any good DFM


project. André Eichhorn explains why


Effective material selection essential for good design


Selecting the correct material for production of a specifi c injection moulded part can be a challenging task that requires in-depth knowledge of the huge range of injection moulding resins that are available on the market today. It also requires a sound understand- ing of the part’s requirements. Before any intelligent material selection can be


attempted, all product-related characteristics and costs need to be identifi ed and carefully taken into considera- tion. Therefore, it is important to fi rst work closely with the developer of the product, who will have the best understanding of what the requirements are with regard to critical aspects such as part geometry, shape and loading, as well as what the environmental infl uences will be when the product is in use. If an incorrect material selection is made, it does not


matter how good the part design may be as the end result will potentially be an unreliable product that is liable to in-service failure. If such problems arise after the mould tool has been built, fi nancial cost can rise dramatically. A change of material at this stage in the development process will very often require rebuilding all or part of the tool, as the new material will have a different shrinkage rate, or need different gating arrangements or venting requirements. For reasons of speed, is not uncommon for a material to be selected based on prior experience – specifying a resin that was used successfully in the past on a similar product or assembly. Of course that may not have been the best choice then, but even if it was it may not be any longer. Materials manufacturers continually improve their products so it is always worth talking to your resin supplier to fi nd out if there is a new


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material or grade available that will suit the new application better. An improved material formulation could lead to a big improvement in the quality and performance of the fi nal part, as well as helping to reduce production costs. Materials with lower density will help to make the


fi nal products lighter. By introducing reinforcement such as glass fi bre, component properties such as strength will be improved and part dimensions poten- tially reduced. In this way, it may be possible to optimise the design to make a lighter and more robust compo- nent.


Figure 1 shows a simple but high volume cover part that was intended initially to be moulded in ABS. Around 14m parts were required annually. The key driver in this project was to reduce the cycle time by decreasing the overall wall thickness, while keeping the mechanical strength at the same level.


By changing the material from the original ABS to a


Figure 1: Selection of a more rigid resin for this housing application enabled the part to be reduced in thickness, cutting cycle time and cost


October 2012 | INJECTION WORLD 49


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