THERMOPLASTIC COMPOSITES | INNOVATION
types, both of which are widely used in the global automotive industry, to make it possible to indi- vidually evaluate for each component which machine type and technology enables the most efficient and cost-effective production process. One area of development in which Engel has
recently been involved is precise software control of IR ovens. IR heating technology has become established as the standard in the processing of thermoplastic composite materials. It makes it possible to heat flat thermoplastic sheets of up to about 3 mm thickness within the cycle times characteristic for injection moulding processing. The focus is on process control. On the one hand, it is important that the heating process is fast, and on the other hand, the material must not be overheat- ed. It is also important to achieve excellent tem- perature homogeneity. Simultaneous processing of blanks with different thicknesses is a particular challenge. In the established one-step process for the production of thermoplastic composite compo- nents, the materials in the form of plate-shaped blanks are located in magazines. They are removed from the magazines by a robot and conveyed to an IR oven. After heating, the now malleable compos- ite material is picked up again by the robot and deposited in the mould of the injection moulding machine. It is reshaped and reconsolidated by the mould closing movement; immediately afterwards, detailed geometries are added by injection moulding. After completing the cooling phase, which is required above all for the injection mould- ed areas, the ready-to-fit composite part is removed from the mould. One of the most important advantages of thermoplastic composites is that the cycle time for producing a technical component is only 40-80s. A thermoset composite solution would require at least a few minutes for this. IR ovens might be set up to provide optimum
Above: Engel has supplied the Fraunhofer pilot plant centre in Germany with two machines for lightweight construction development. (From the left) Claus Wilde, Managing Director of Engel Deutschland, Prof. Peter Michel, Head of the Polymer Applications Business Unit at the Fraunhofer IMWS and responsible for polymer processing at the Fraunhofer PAZ, and Franz Füreder, Vice President Automotive at Engel Austria
temperature homogeneity for a specific operating point, for example, when it is loaded with 70% of the nominal payload area in the form of a rectan- gle. However, since the real operating point usually deviates significantly, this is not meaningful. A system with a very good basic characteristic in terms of thermal homogeneity is more useful. The software of the Engel IR ovens is therefore capable of optimally controlling a large variety of operating states and influencing variables, which enables excellent thermal homogeneity over a wide range of applications. Precise control of the IR heating process is an essential part of process control in the manufacture of thermoplastic composite parts. In Engel system solutions, the IR oven control is therefore integrat- ed into the injection moulding machine control unit. This allows the process parameters and measured values of the IR oven to be documented along with the production data from the injection moulding process.
Due to the multitude of possible causes for thermal inhomogeneities, each control zone has a different heating characteristic in practical applications. In the case of a control zone that reaches its temperature setpoint early at full
radiator power, the radiator power must be reduced early in the heating phase. Automatic reciprocal optimisa- tion and coordination of the control
zones means that the radiator power of all affected control zones is continuously adjusted to keep the
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Left: Three thermoplastic sheets of different thickness are heated in two IR ovens in the production of a door structural part
January/February 2022 | INJECTION WORLD 17
IMAGE: ENGEL
IMAGE: FRAUNHOFER IMWS
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