Modelling and simulation of mechanical cutting

Sammanfattning: The commercial success of a new product is influenced by the time to market. Shorter product lead-times are of importance in a competitive market.This can be achieved only if the product development process can be realised in a relatively small time period. New cutting inserts are developed by a time consuming trial and error process guided by empirical knowledge of the mechanical cutting process. One of the state-of-the-art efforts in manufacturing engineering is the finite element simulation of the mechanical cutting process. These computational models would have great value in increasing the understanding of the cutting process and in reducing the number of experiments which traditionally are used for tool design, process selection, machinability evaluation, and chip breakage investigations. This thesis focuses on the development of a finite element model for the cutting process, which can predict chip formation, cutting forces, temperature and pressure distribution on the tool-chip interface and the residual stresses of the work piece. The work is concentrated to handle the large and localised deformations, chip formation and contact and friction. Two basically different modelling approaches have been used for the chip separation, geometrical and physical model. The physical model has been found to be more suitable to simulate the chip formation. The geometrical model is based on the separation of a pre-defined crack path at a certain limit of stresses. In the physical model the chip formation occurs through the plastic deformation of the elements. The excessive element distortion is handled by frequently updating the finite element mesh, using the advance front technique for generation of quadrilateral elements. The adaptive meshing is managed using the error measures based on the stress gradients in the finite element mesh and also the plastic work rate at each element. The automatic control of the mesh quality is managed by using the distortion metric. The implemented combined penalty-barrier contact algorithm has been found to be efficient in conjunction with the adaptive remeshing. The effect of previous cutting on chip formation and the surface residual stresses has been studied. The chip formation is not affected much. There is only a minor influence from the residual stress on the surface from the first cutting on the second pass chip formation. Thus, it is deemed to be sufficient to simulate only the first pass. The influence of the cutting speed and feed on the residual stresses has been computed and verified by the experiments. It is shown that the state of residual stresses in the work piece increases with the cutting speed.