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Hochpräzisionsbearbeitungszentrum

Subject Area Production Technology
Term Funded in 2014
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 264354707
 
Final Report Year 2019

Final Report Abstract

The focus regarding the use of the high-precision machining center lies in research activities aimed at generating functional surfaces by means of machining processes. Within the frame-work of the MERGE Cluster of Excellence, hybrid joints consisting of an aluminum alloy and a thermoplastic fiber-reinforced composite material were produced by ultrasonic joining. To in-crease the share of load transfer carried by the fibers, micro-pins were generated on the alumi-num-alloy component, initially using end mills and subsequently circular saw blades. This ena-bled an increase in the shear tensile strength of the joint to more than seven times that of un-structured joining partners. One focus within the Collaborative Research Centre HALS was the finishing of particle-reinforced aluminum matrix composites by milling, with the objective of de-liberately generating surface properties suitable for dynamically loaded stress-boundary surfac-es. During face milling, surfaces largely free of imperfections and with roughness values for Rz well below 1 µm were produced using milling tools equipped with monocrystalline diamond. In addition, depending on the tool geometry, compressive residual stresses in the matrix alloy of up to approximately 250 MPa were achieved in the near-surface layer. To increase the static coeffi-cient of friction in longitudinal press-fit connections, micro-structures are designed and pro-duced by turn-milling on the planar surfaces of specimens made of quenched and tempered steel 42CrMo4. By using tools with an almost pointed cutting-edge corner, specimen surfaces could be micro-structured in such a way that the static coefficient of friction, in combination with an unstructured counter body, increased to more than 0.6. This corresponds to approximately three times the value achieved with a pairing of two unstructured specimens. One challenge in the adherent deposition of CVD diamond on steel materials is the difference in thermal expan-sion coefficients, which leads to high compressive residual stresses in the diamond during cool-ing of the coated substrate. These stresses are to be reduced, among other measures, by target-ed micro-structuring of the substrate surface. For this purpose, milling is carried out with super-imposed ultrasonic vibration in the direction of the passive force. The experimental results show that adequate micro-structuring can be realized using this method and that CVD diamond layers with greater coating thickness can be deposited on steel substrates with good adhesion. Beyond the generation of functional surfaces, the large-scale research instrument was used for the manufacture of precision components for various experimental setups, specimens, and tools for the forming of bipolar plate components with structural dimensions down to the micrometer range. A further research topic is the integration and use of additional sensors for monitoring the process and the machine.

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