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The insert and outsert technique has long proved to be highly effective in the injection moulding of metal/plastic sandwich parts for small electrical appliances.
Christian Karl Siebenwurst Modell- und Formenbau GmbH & Co. KG, Dietfurt/Germany, recently transferred the basic idea of this process technique to the production of large parts for the automotive industry.
(Published on October-November 2005 – JEC Magazine #20)
Siebenwurst built a hybrid injection mould to produce the fitting frame for the fro n t - end module of the Audi A4. A bracket of formed and punched sheet steel is placed into the injection mould and encapsulated with polyamide re i n f o rc e d with 30 wt% glass fibre. The steel bracket gives this cost-, weight- and function-optimised fitting frame a torsional and bending stre n g t h that is otherwise unachievable for the same weight, even using a long glass- fibre- re i n f o rced plastic. The encapsulation of large areas of the steel bracket with plastic provides the functional integration and design f reedom that vehicle manufacture r s demand for such parts today.
Major design challenges
The manufacturers of “white goods” (washing machines, tumble dryers and dishwashers), rail-bound and commercial vehicles, and motorbikes also use or need hybrid moulds for parts that combine functionality and rigidity. When designing and constructing such a hybrid mould, the mould-maker has to overcome major challenges. Precise matching of the steel-bracket forming and punching tool to the injection mould demands particular care, as the bracket has to be inserted into the injection mould reliably and accurately, and in a fully automated process. The injection mould must be carefully designed so that the steel bracket will not cause any wear during the long service life.
Another consideration is that, while the bracket contour is precisely defined by the cutting die, the formed areas of the bracket may exhibit cert a i n tolerances due to differing spring-back behaviour of the steel.
Siebenwurst has decades of experience with cutting dies and injection moulds, p roviding a single source for the design and construction of the tools and moulds needed for this type of project. The single source helps to minimise tool-matching time and costs; placing the overall responsibility in the hands of a mould-maker simplifies the coordination and monitoring of the project for the client.