Chip Free Surface Research Articles

Application of Computational Machining Method to Discontinuous Chip Formation

A finite element modeling is developed to simulate and visualize the discontinuous chip formation in the orthogonal cutting of 60 percent Cu-40 percent Zn brasses. A ductile fracture criterion expressed as a function of strain, strain rate and hydrostatic pressure is applied to the crack growth from the tool tip to the chip free surface in the segmentation of discontinuous chips. Chip shape and the inclination of fracture surface produced in computational machining are in good agreement with those in actual machining. The visualization of the computational machining processes clarifies the mechanism of discontinuous chip formation. The influences of chip segmentation upon the residual stress and strain in the machined layer are also clarified quantitatively.

せん断形切りくず生成の有限要素法シミュレーション

A finite element modelling is proposed for simulating the discontinuous chip formation of 60% Cu-40% Zn brass. In the modelling geometrical nonlinearity and the reduction of constraint of incompressibility in the large deformation of finite elements are taken into account. The initiation and growth of ductile cracks from cutting edge to chip free surface during chip segmentation are directly introduced into the finite element model using an appropriate fracture criterion, which is determined in terms of strain, strain rate and hydro-static pressure. Chip segments, which are periodically formed in the simulation, are in good agreement with those experimentally obtained both in configuration and deformed grid. Variation of velocity, stress, strain, strain rate calculated during a chip segmentation make clear the mechanism of discontinuous chip formation. Normal and frictional stresses on the rake face calculated are found to be almost uniform over the tool-chip contact length.