Lightweight structures, the future technology – Thermoforming and injection moulding in one single mould

This dynamically loaded component for a passenger car is produced from organo sheet – a glass fibre reinforced semifinished thermoplastic composite – and stiffened with moulded-on ribs. The organo sheet is first thermoformed in the mould and then, in the same mould, provided with the moulded-on stiffening ribs.

This innovative combination of thermoforming and injection moulding processes requires a production system in which the individual process stages are exactly coordinated and synchronized with each other. This is where the organo sheet mould plays an essential role in terms of both product quality and process reliability. For the first stage of the process – the thermoforming of the organo sheet – the cut-to-size sheet, which has been preheated and is therefore very soft and unstable, must first be positioned in the mould with absolute, reproducible accuracy. The mould closing operation commences with the advance stroke of a female mould insert, which presses the organo sheet onto the male mould half and holds it there. The actual thermoforming operation now takes place: the sheet is drawn over the male mould half and its peripheral edge is held in place by means of clamping strips that are shaped three-dimensionally so as to match the contours of the moulded part. These clamping strips must be set with extreme precision in order to allow the hot organo sheet to flow freely without sustaining any damage or deterioration.

The mould remains in its closed position at the end of the thermoforming process. The melt for the moulded-on stiffening ribs, consisting of a glass fibre reinforced polymer, is injected via three injection nozzles and bonds completely with the organo sheet. The melt flow-ways ensure in addition that those parts of the structural component that could not be filled during the thermoforming operation are now fully moulded to shape.

All told, as many as six companies and organizations were involved in this future-oriented, technology-bridging project, the results of which are now to be presented at K 2010. Despite the complexity of this involvement, the project was realized within the very short period of only six months. Within three months of receiving the initial component specifications for the design of the mould, for example, Kaufmann was already commencing the mould trials in its own pilot facility.

This combined thermoforming and injection mould for the processing of organo sheet is equipped with more than a dozen sensors for pressure and temperature measurement. They serve not only to monitor the flow of the organo sheet during the thermoforming operation, the injection of the polymer melt and the complete moulding-to-shape of the structural component and they are necessary to make these operations better understandable for future applications. Further organo sheet moulds will likewise be equipped with – albeit considerably fewer – sensors, as they are absolutely indispensable when it comes to process monitoring and quality documentation in applications involving the production of safety-relevant parts.

Innovation through partnership
This project demonstrates quite impressively how it is possible for even a project involving many partners to be realized quickly and successfully all the way through to series production. Involved in this technology-bridging project, besides KraussMaffei Technologies GmbH and Kaufmann, were Jacob Composite GmbH, Audi AG, Lanxess Deutschland GmbH and Bond-Laminates GmbH.

In addition, when it came to optimizing the processing sequences in the mould, specific know-how in the fields of temperature control, hot runner technology and measuring technology was contributed respectively by the following firms: gwk Gesellschaft Wärme Kältetechnik mbH, Incoe Europe and Kistler Instrumente AG.

Further information:
Roger Kaufmann, Georg Kaufmann Formenbau AG
Rugghölzli 3, CH-5453 Busslingen/Switzerland
Phone: +41 (0) 56/485 65 60, Fax: +41 (0) 56/496 54 00
E-Mail: r.kaufmann@gktool.ch

Editorial contact and voucher copies:
Dr. Diether Burkhardt, KONSENS Public Relations GmbH & Co. KG,
Hans-Kudlich-Straße 25, D-64823 Groß-Umstadt
Phone: +49 (0) 60 78/93 63-0, Fax: +49 (0) 60 78/93 63-20
E-Mail: mail@konsens.de