engleski

Turning conditions of Ck 45 steel with alternate hardness zones

Purpose of this paper is investigation of dynamic impacts on cutting edge during machining of locally hardened steel. Alteration of hardness on a single workpiece is a source of impact on tool which could lead to breakage of cutting tool and workpiece surface damage in turning. Influence of material properties (primary hardness) is important when workpiece is locally induction hardened and part of material is soft annealed. Methodology: Experimental tests of cutting outputs have been done on specimens after induction hardening to evaluate the rate of variation of cutting forces, surface roughness and chip formation because of hardness alteration. Measured data of main cutting force were analyzed in frequency and time domain. Findings: It was found that chip formation condition, chip thickness and chip shape depends on cutting forces alteration in transition areas in the range of 10 to 15%. Much higher alteration of force signal is recorded when machining is performed with low depth of cutting value as a result of backlash in system. Mean value of cutting force correlates with depth of cutting, and roughness correlates oppositely to the hardness. Research implications: Results and findings presented in this paper are qualitative and might be slightly different in other cutting condition (e.g. other heat treatable steels or other hardening techniques or other single cutting point processes). There is evident force value alteration in the transition (hard to soft state) zone. Practical implications: Surface roughness is a consequence of both cutting impacts and of tool/workpiece loading condition. Originality: Originality of the paper is in analysis of stability of turning of heat treatable steel influenced with alternate workpiece hardness. It was recorded edge loading shock when overcoming from hard to soft machining. It is recorded and analyzed self-exited vibration. A new type of chips: horseshoe-type was found.

Manufacturing and processing; Machining; Mechanical properties; Dynamic properties; Depth of cutting

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