engleski

Dynamic instability of the hard turning process

Purpose: Purpose of this paper is consideration of dynamic behavior of the hard turning process. There are several indicators which could confirm assumption of turning instability (depth of cutting, high ratio of forces Fc/Fp, small tool nose radius, and non-uniform stress distribution over tool/workpiece contact). Lead edge angle and passive force Fp are strongly depend on depth of cutting in hard turning what additionally increase instability. Design/methodology/approach: Numerical calculation and experimental tests have been done to evaluate the rate of cutting instability while using and comparing different process monitoring sensors, and acquisition techniques based on PC platform. Findings: It was found that high chip thickness alteration occur because of cutting depth vary for a value of some 60 % and even more if Fp force signal is analyzing when machine tool has inadequate stiffness. Research limitations/implications: Results and findings presented in this paper are qualitative and might be slightly different in other cutting condition (e.g. if wiper inserts are used). Also there are no experiences with coated workpieces or with workpiece material with low deformation energy. Practical implications: Assuming that a hard turning is a semi finishing or finishing process, surface finish is of big relevance. Surface roughness is a consequence of both cutting instability and of tool/workpiece loading condition. Results of test indicates an optimal cutting depth for final pass when minimum surface roughness can be achieved what can be valuable for cutting regime determination. Furthermore, more effective use of the machine tool performances might be achieved. Originality/value: Originality of the paper is in analysis of sources of turning instability (variable depth of cutting combined with side edge angle and tool nose radius) which lead primary to condition where Fp sensing data does not fit to the normal distribution and secondary to cyclic push-offs of the edge. Keywords: Machining ; Mechanical properties ; Dynamic properties ; Depth of cutting

machining; mechanical properties; dynamic properties; depth of cutting

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