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Scottish Plastics and Rubber Association Scottish Plastics and Rubber Association

Stepping Beyond Conventional Design Guidelines

Eric Henry, Autodesk (right) with Kenneth McIntosh, SPRA Vice-President

Kenny McIntosh, SPRA Vice President, welcomed SPRA members and non-members to the February SPRA meeting, sponsored by Rosti UK Ltd and held at their plant in Larkhall, for the topic “Beyond Conventional Practices for Injection Moulding Design” and a guided tour of the Rosti facilities. An experimental video link to Edinburgh Napier University provided students, who were unable to travel to Lakhall, the opportunity of participating in the meeting.
When the original speaker, Andrew Blemings was unable to travel from China, Eric Henry, Simulation Technical Sales for Autodesk Europe, kindly stepped in at the last minute to talk on the original theme.

Eric provided a very informative and interesting presentation, detailing the benefits to both the moulder and the end manufacturer, with the main focus on designing in quality and functionality to a range of components prior to tool manufacture.

design guidelines for injection moulding
He started with some design guidelines to be followed to reduce various moulding defects that can be eradicated at the design stage.

Eric then went on to describe the “3 Islands of Automation” that can lead to a problematic and inefficient product development and increased costs for all parties. Traditionally designing for injection moulding has been carried out in isolated pockets of activity.

3 Islands of Automation
The product designer carries out the initial component design and passes the results to the tool designer who then passes the tool to the moulder, who often has to cope with problems which could have been addressed in the earlier stages. This model tends to miss opportunities for part and process optimisation and often leads to being late to market.

The question was then posed – “Why simulate?” - because many in the design sector will still use the more traditional design and prototype template.
Below is a comparison detailing the cost benefits over the traditional route versus the simulation route.

One of the main misconceptions you will hear is “has this part been Moldflowed?” Eric explained that to gain the greatest benefit from Moldflow, it must be integrated at the start of the product design phase and not an add-on because a problem has been encountered.

Eric then went on to provide the audience with case studies that detailed how a simple design error can cause major mechanical failure. One example was an electrical connector casing that shattered under load (see below). This was caused by excessive shear stress during filling.

On analysis the excessive shear stress was found to be caused by poor gate design. The gate was redesigned and the excessive shear stress was eradicated. The shear stress calculation cannot be carried out without the use of Moldflow.
On summary Eric stressed the need to gain and maintain a competitive edge and in both terms of cost and quality our product development process needs to evolve to include simulation at the outset.

Rosti UK Ltd, Larkhall, with the recently installed wind turbine
Report by Chris Clark, SPRA Young Member Representative, March 2013

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