At the beginning of the development process, the first step was to construct base bodies from ceramic material with heating structures made of copper. In a second step, steel base bodies were then used which were coated homogeneously with insulating layers of Al2O3, afterwards heating structures were added. Both the insulation layers and the copper layer were deposited by the physical vapor deposition process. During the development process, heating structures with different layer thicknesses and designs were created at the Fraunhofer IST. It was found that significantly higher heating output levels could be achieved with the more complex meander design. The figure above shows a first micro-sized injection mold with a heating structure of this kind. A new structuring process was developed for production, consisting of a combination of photolithography, laser structuring and wet chemical etching.
Verifying the functional capability of the heating structures
In order to verify the functional capability of the heating structures, they were provided with electrical contacts at the Kunststoff-Zentrum in Leipzig gGmbH (KUZ) and power applied to them in a test rig. Here a high dynamic in the heating rates was obtained as a function of the resistance achieved, depending on the design of the heating structure. Accordingly, a temperature increase of 100 K from a temperature level of 373 K to 473 K was, for example, possible within a second at an output of approx. 120 W (energization with a protective extra-low voltage of 30 V). In a second test set-up it was also possible to carry out successful long-term tests with the aforementioned parameters involving around 60,000 test cycles. No damage to the layer was detected, even after the long-term tests. This indicated general suitability for the first utilization of heating layers under exposure to injection molding stresses.
In the next step the Fraunhofer IST, in collaboration with the Kunststoff-Zentrum in Leipzig gGmbH (KUZ), aims to provide the heating structures with a final abrasion-protection coating and to investigate the long-term stability of the structures. As part of the “R & D funding of non-profit external research institutions in eastern Germany (INNO-KOM-OST) – Market-oriented research and development module (MF)“ this project will continue to be supported by the Federal Ministry of Economics and Technology (BMWi).