Georg Kaufmann Formenbau: First Dolphin two-component mould in operation at K 2007

Rotary injection mould combines soft-touch with rigidity

Now effectively ready for service in mass production, the first injection mould for the Dolphin process could be seen in operation at K 2007. This process combines the injection moulding and foaming operations in one production cell and is used for the low-cost production of passenger compartment armrests featuring high rigidity and soft-touch feel (Photo). One of the key functions in this process is performed by the two-component rotary mould developed and built by Georg Kaufmann Formenbau AG (www.gktool.ch). Its most important feature are the vertical flash faces, which are spring-loaded and capable of several millimetres´ movement. They ensure that no melt can escape from the cavities when the mould performs the necessary slight opening stroke for generating the soft-touch foam. The mould was installed in an Engel twoplaten injection moulding machine equipped with an additional injection unit on the moving platen and a rotary table for the centre plate arranged to move in unison with the moving platen as the mould performs its opening and closing movements.

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The two stations of the rotary mould each have two cavities. Station 1 is for the injection moulding of the left and right armrest substrate in a glass fibrereinforced PBT/ASA blend. The centre plate of the mould then rotates though an angle of 180°, thus positioning the moulded substrate structures in Station 2. Here the foam for the soft-touch effect is produced with the aid of the Mucell process. To this end, the substrates in the closed mould are overmoulded with a gas-laden thermoplastic elastomer (TPE), which is injected into the cavities so as to fill them volumetrically. During a short cooling phase, a solid, textured skin forms against the cavity walls. The mould then opens by approx. 3 mm with absolutely controlled parallelism, while its vertical flash faces, which are incorporated in the mould like slide bars and are backed by powerful springs, prevent any egress of melt from the mould. This expansion phase initiates the foaming process and allows a permanently flexible layer of TPE foam to form beneath the solid skin. It goes without saying that the parts position in the mould is so shaped that the foam is at its thickest in the comfort zone and the radii of the armrest. The chemical affinity of the materials ensures a very good bond between the substrate and the foam.

Besides this one particular application, the Dolphin process has enormous potential for many vehicle interior components. Typical examples are dashboard panels and trim components for lorries and buses. For such applications, the desired combination of high durability and "feel appeal" was hitherto possible only at considerably greater cost.

Georg Kaufmann Formenbau AG, Busslingen, Switzerland

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