Search

forming tool coating. Most of the forming tools are made of steel, so that especially the coatability of steel by a polycrystalline diamond coating would rise the range of fields of application. The polycrystalline CVD-diamond coatings are deposited by a laser induced plasma CVD process, without a vacuum chamber. Various surface microstructures were investigated regarding their influence on the residual stresses to prevent a flaking of the coating: on the one hand, deterministic structures generated by ultrasonic vibration assisted milling (UVAM) and on the other hand, stochastic structures manufactured by blasting and polishing processes. For the UVAM, a surface prediction tool was used to design the surface microstructure beforehand. All steel substrates (material no. 1.2379) were coated in one batch by high-power impulse magnetron sputtering with a chromium nitride coating with a thickness of 2.4 μm. The specimens were analysed by laser microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Raman spectroscopy. None of the microstructures investigated in this study was able to prevent delamination of the coating entirely. It could be shown that a roughness higher than Sa 0.1μm supports the interlocking between coating and surface as well as that sharp peaks inhibit a homogenous diamond coating deposition.

Micro forming can be used for a highly efficient manufacturing of small parts like screws or caps. Because of the small dimensions of the structures, high stresses and forming forces occur, especially in the case of micro bulk forming. In addition, the influence of friction is significantly higher compared to macro forming processes. A typical example of small structures are micro channels. An approach for the reduction of the necessary forming force to obtain lower loads on the tool consists in a vibration-assisted micro forming process. As vibration source, a piezo power module is placed directly in the force axis of the forming press. For the investigations, micro channels with a depth of more than 300 μm and a width of 300 μm are formed into 1.5 mm thick AlMg4.5Mn0.7 aluminium alloy sheets. The focus of the research lies in the influence of the process parameters like frequency and oscillation amplitude onto the material flow and the achieved channel depths. To investigate a possible influence on the friction conditions due to the vibration assistance, different lubrication conditions are applied. First results show a channel depth increase of 12 % compared to samples formed without vibration assistance.

Tribological conditions between workpiece and tool have a major impact onto forming processes. Besides lubrication, temperature, and material, they are mainly influenced by the tool surface characteristics, especially by its topography, which is a result of finishing technology. Thereby formed lubricant pockets are of prime importance for the tribosystem due to its ability to separate the tribopartners by storing lubricant. The influence of four different tool finishing processes and their according surface topographies onto frictional behaviour have been investigated and quantified by the barrel compression test, in dry and lubricated tribosystems. The tool steel surfaces were stochastically microstructured by grinding and spark erosion as well as deterministic structured with micro calottes, applied by jet electrochemical machining and compared to a polished reference tool. The allocation of open and closed lubricant pockets over tool surfaces before and after the forming process was analysed by a self-made MATLAB tool.