Numerical multiscale modelling and optimization of cooling concepts in gear skiving

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The project aims in modelling the lubrication and cooling with resulting chip formation in power skiving, a kinematically complex and inaccessible machining process for gears. The cutting conditions vary along the cutting edge and during the process. The resulting multi-part chips repeatedly disrupt the process by adhesion to workpiece or tool surfaces or they get caught between workpiece and clearance face. This results in effects like squeezed chips, which lead to surface defects and tool wear. Only a model of the chip formation under the influence of the cooling lubricant enables understanding the occurrence of these defects. Dominant factors for chip formation are process parameters and the cooling lubricants effect between chip and rake face. In practice, the optimisation of the lubricants application is experience-based. A model-based process optimization requires considering the lubricants application and distribution, as well as the influences on the friction between chip and rake face and of course the effects on chip formation and chip flow. However, the entire process is too complex to be reproduced in a single model. Therefore, a simulation is to be created in which a flow model is coupled with a chip formation model and a friction model. The aim of the second funding phase is to transfer the developed coupled simulation methods of the orthogonal bonded cut to the complex power skiving process using compressed air and oil flood cooling. The complex mechanisms that lead to squeezed chips are considered on a multiscale level in the sub-areas of tribology, chip formation and fluid flow. Chip formation is modelled by means of an FEM simulation. The cooling lubrication concept is modelled using the VOF and SPH methods and the friction between tool and workpiece is investigated with molecular dynamic and quantum chemical simulations taking into account the cooling lubricant, which affects chip formation and adhesion to the tool. The first step is the transfer of the simulation models of the individual sub-areas to the skiving process and subsequently their coupling for a holistic view of the process and the complex interactions of the considered scale areas. This simulative mapping of the influence of the effect of the differently considered cooling lubrication strategies lays the foundation for describing the main effect mechanisms that lead to chip squeezes. In the third phase of the project, based on the generated understanding of the development of chip squeezes, suitable cooling lubrication strategies are to be developed with reference to the main mechanisms of the investigated scales and can be used in the future for the setting of a stable, advantageous chip formation and thus to better surfaces and longer tool life.