Estudo do contato entre material da peça e superfície de folga da ferramenta de usinagem

Abstract

It is known that micro machining operations are very susceptible to excessive shear forces and vibrations which may be damaging the tool and the workpiece. In this case it is necessary development and improvement of methodologies to understand and optimize the models implemented mechanisms for material removal in micro scale. The main objective of this work is to analyze the contact between the machined surface of the workpiece and the clearance surface during micro machining , and verify the effect of parameters and cutting conditions in the contact length , elastic recovery of the workpiece and the residual cutting forces proposing a mathematical model for its prediction. This analysis were machined AISI 1045, cast iron GH - 190 , 1000 series aluminum and aluminum 3030 , in operation simulation of orthogonal cutting and turning cylindrical external tools HSS and carbide coated . It is the effect of cutting parameters : speed, undeformed chip thickness , rounding radius of the tool and clearance angle of the tool in the machining force components and specific cutting pressure. For each operation was obtained residual shearing force and the minimum undeformed chip thickness using the method of extrapolation to zero. Samples were obtained from tests of quick -stop for metallographic analysis and microhardness. The results obtained with the methods used for turning showed that the residual forces ranging from 57 N to 83 N , the specific pressure between the cutting 2,593 N/mm2 and 3,306 N/mm2 , suggesting that the chips begin to form undisturbed over the range of thicknesses of 6 μm to 10 μm . The orthogonal cutting simulation , suggested a variation of the residual forces between 19 N and 31 N , specific cutting pressure between 997 N/mm2 and 1,045 N/mm2 and chip formation undisturbed for thicknesses over the range of 6 μm to 10 μm. For both materials analyzed, smaller undeformed thicknesses provided significant increase in specific cutting pressure, suggesting the existence of a redundant plastic work resulting from plowing and sliding part off the loose surface of the tool, whose deformation requires an additional expenditure of energy, which overcome that produced in the removal of material. Smaller undeformed thicknesses of the chip provided a relative percentage of contact area attributed to loose surface over 60% of the total contact area during cutting process, reducing significantly with the increase of the same one, which reached minimum values over 20%, realizing then the great influence of contact on the loose surface with the variation of the undeformed thickness of the chip. The mathematical model for predicting the cutting forces in orthogonal cutting simulation showed an average relative error of the order of 10 %, and turning on the order of 18%.