Spanende Verfahren zur Mikrostrukturierung
Final Report Abstract
In this report correlations for the high quality machining of micro dimples are presented. Small cutting speeds, negative rake angles as well as rounded cutting edges encourage ploughing effects which result in chipping and contour deviations. Due to a larger chip compression ratio, the lateral material flow ahead of the cutfing edge towards the free edges is increased, leading to larger burr dimensions. Besides the material properties, a major parameter influencing the burr dimensions is the effective tool cutting edge angle. Due to a smaller material volume and a stronger material deflection small tool cutting edge angles work against burr formation, due to a shear localisation at the free edges. If small effective tool cutting edge angles cannot be realised, burr formation can be avoided by use of positive inclination angles. Besides S235JR steel, materials used for cylinder liners were examined, and their interactions with micro structuring were analysed. The material GJS400 shows a ductile material separation which is comparable to the one of steel. For thermally sprayed FeMo50 coatings, maierial separation is caused by cohesive failure in the boundary areas of the sprayed lamella. Moreover a process strategy for load-specific machining of micro dimples into the inner surfaces of cylindrical components was developed and analysed. By systematic variation of the process variables, their influence on the arrangement and geometry of micro dimples when machining inner surfaces of cylindrical components was described, and process limits were identified. Tool geometries so far used with plane surfaces can be transferred lo process strategies for machining cylindrical surfaces. In process design, it must however be considered that for up- and downmilling certain process parameter combinations lead to a considerable distortion of the respective tool trajectory. Respectively, this goes along with a stretching or compression of the cut. In both cases however, the effective clearance angle is considerably reduced which cannot be neglected. Within the scope of this joint research project, the methods developed and experiences made were applied for machining a large number of cylinder liners, the tribological potential of which is described. Besides load-specific micro structuring, also hybrid cylinder liners were created. Here no interactions of micro structuring with the cylinder liners, pre-machined by different manufacturing methods, could be observed. In order to compensate deviations in form and position, an elastic micro structuring tool resting against the component's surface to be machined, was developed and characterised concerning its performance characteristics. With the help of this tool system, deviations in form and position can be compensated about 97 %, thus providing a basis to transfer micro structuring with its narrow tolerances to conventional machine tools and processes and to become an integral part of them.
