Innovative Plastics technologies from KraussMaffei

It was developed by KraussMaffei in a collaboration with Elastogran GmbH and Mues Products & Moulds GmbH. X-Form has been designed for applications which currently use metal-rubber composites. Possible applications include covers for housings with integrated seals or engine mountings. The process uses a new thermoplastic polyurethane (TPU) called Elastollan, made by Elastogran, that crosslinks to TPU-X during cooling. Crosslinking takes place in an injection moulding compounder where the crosslinking agent is mixed evenly with the TPU melt. The mix is then supplied, via a shot-pot, to the discontinuous injection process.

As a practical illustration of the process, KraussMaffei and its partners designed a roll restrictor, a component used in machine mountings or in the running gear of a car or truck.

At the K2007, the company demonstrated an injection moulding compounder cell producing this multicomponent part. The roll restrictor is made of two materials: the body and collar are made of Ultramid CR, a glassfibre-reinforced plastic from BASF. Between the body and the collar is a damping element made of TPU-X. An elastic seal around the component is also made of TPU-X.

The most strikingly innovative aspect of the production process is the cycle time; a finished part is produced every 60 seconds. This is achieved by producing each part in three work phases that take place simultaneously in the manufacturing cell. The fourth phase is demoulding by a linear robot. The damping element in the roll restrictor has a wall thickness of 15 mm to be capable of absorbing strong vibrations. Material this thick would normally need a longer cooling time and therefore a longer cycle time. Using a turntable mould and a smart process, the cooling time can be kept to a minimum. The body and the collar are first injection moulded from polyamide. The mould turns 90 degrees and TPU-X is injected between collar and body in a star shape.

Another 90-degree turn and the gaps are filled with more TPU-X. Finally, in the fourth phase, the part is removed while the mould is closed. Compared with conventional elastomer processing, cycle time here is reduced by a factor of four to six.

Nonetheless X-Form is in many respects a conventional 2C thermoplastic injection moulding process. The mould need not be designed with the hot and cold zones, normally required when working with rubber/thermoplastic composites. This makes process control far easier.