The finite element modelling of machining of NST 37-2 steel

Abstract

NST 37-2 has vast applications in building construction and in machine components production in Nigeria, but the effects of induced residual stress in the material, optimum cutting parameters, efficient process planning, chip formation process and surface roughness of the machined products are some of the challenges faced in the industry. In this study, the finite element simulation of orthogonal cutting of NST 37-2 steel was carried out, and the effect of geometry on chip morphology, residual stress distribution, strain energy was investigated to address informed predictability on the material. Different rake angles of -15°, 0°, 15°, and 30° were adopted for the tool geometry. In each case, the chip formed was continuous due to the plastic nature of the material. At negative and 0 rake angles, there were narrow bands of heavily strained chip, and as the rake angle increased, the chip tended to narrow due to low adhesion in the tool-work-piece region and decreasing work for chip folding. Uniform deformation was also observed with positive rake angle simulations. Residual stress was found to increase with negative rake angle. However, with positive rake angle, residual stress led to an increase in tensile strength due to the shearing action of the cutting tool in the cutting direction on the material layers below the cut plane. Cutting and thrust forces were observed to decrease with increasing rake angles. Adiabatic shear bands with high temperatures and thermoplastic shear instability were observed in machining with negative rake angles. High temperatures were generated in the shear zone due to large amount of work done by deformation of work material in machining with negative rake tools. The shear zone temperatures were much less in machining with positive rake tools. Temperatures on the rake face reduced with increasing rake angles, but not as significantly as the temperatures in the primary shear zone.