Thermoforming and injection molding in one single mold
Making its début at K2010, the world’s No.1 plastics and rubber trade fair, in Düsseldorf (October 27 until November 3)
will be a combined thermoforming and injection mold developed by Georg Kaufmann Formenbau AG, Busslingen/Switzerland.
This so-called organo sheet mold will be demonstrated by KraussMaffei Technologies GmbH in fully automatic operation on a CX 300-1400 IMC. The mold is used for the production of a lightweight structural component. This dynamically loaded component for a passenger car is produced from organo sheet-a glass fiber reinforced semi-finished thermoplastic composite-and stiffened with molded-on ribs. The organo sheet is first thermoformed in the mold and then, in the same mold, provided with the molded-on stiffening ribs.
This innovative combination of thermoforming and injection molding 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 mold 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 mold with absolute, reproducible accuracy. The mold closing operation commences with the advance stroke of a female mold insert, which presses the organo sheet onto the male mold half and holds it there. The actual thermoforming operation now takes place: the sheet is drawn over the male mold 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 molded 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 mold remains in its closed position at the end of the thermoforming process. The melt for the molded-on stiffening ribs, consisting of a glass fiber 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 molded 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 K2010. 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 mold, for example, Kaufmann was already commencing the mold trials in its own pilot facility.
This combined thermoforming and injection mold 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 molding-to-shape of the structural component and they are necessary to make these operations better understandable for future applications. Further organo sheet molds 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.
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