| Because of high strength,high hardness and other properties of high hardness materials,the cutting edge of PCBN tool should be treated with T-land negative chamfering to increase the strength of the cutting edge and prolong the service life of the toolin hard cutting.However,on the other hand,when the cutting edge structure of circular arc with chamfer is cutting at a large negative front angle,it increases the extrusion effect on the cutting material which causes the cutting area to produce larger cutting deformation,and makes the chip flow out of prone to accumulation and obstruction.These results lead to larger cutting heat and force field,aggravate the wear and tear of the tool,reduce the quality of the cutting surface.Therefore,the hard cutting efficiency and the working performance of the machined parts are seriously restricted.So,based on the idea of coordinating chip flow and improving the state of cutting zone,the spatial curved enhanced edge PCBN tool with gradient chamfer is designed.The experimental study on the hard cutting performance of the designed tools is carried out for hardened steel materials.Based on the cutting state analysis of the cutting edge region and the problems existing in the cutting process of PCNB tool with uniform chamfered edge,the design of the enhanced edge of the PCBN tool is carried out according to the idea of coordinated chip flow.According to the method of face grinding,an approximate grinding trajectory planning scheme is proposed,and a mathematical model of grinding trajectory is established.The grinding process is simulated by using 3D software.The simulation edge curve is extracted by matlab and compared with the theoretical edge line.The process parameters are optimized to achieve the precision preparation of the enhanced edgeshape.A method for detecting the defect of cutting edge,the width and angle of chamfer is presented,and the accuracy of edge preparation is evaluated quantitatively.Based on PCBN tools with the near cosine enhanced edge,the near sine enhanced edge and the uniform chamfered edge,the contrast test of cutting hardened steel GCr15 is designed.The effects of cutting parameters and cutting edge structure on cutting force,chip morphology and tool wear are studied.Using high speed camera to capture chip flow state and combining chip macro and micro morphology,the evolution process of chip macro and micro morphology is analyzed.The mechanism of chip generation,crimp and outflow of enhanced edge structure is revealed.In order to further coordinate chip flow and enhanced the structure of tools,a design scheme of adding enhanced structure on rake face is proposed.The method of combining 3D precision laser machining technology and sand blasting surface treatment is introduced to fabricate three-dimensional enhanced structure on rake face.A comparative experiment is carried out on the cutting performance of the tool with near cosine enhanced edge and the tool with enhanced structure of double inclined walls.It was found thatthe tool with double oblique walls had good ability to guide chip flow and reduce the impact.The formation mechanism of white layer machined by the tool with double oblique walls under different cutting conditions is studied.The change rules of surface morphology and residual stress with tool wear and cutting speed are obtained.Finally,the dynamic characteristics of PCBN tools with different chamfering edge structures are studied experimentally,and the influence of cutting parameters on the cutting vibration characteristics of the tool with enhanced edge is obtained.The dynamic modeling and amplitude solution of cutting chatter system for the tool with enhanced edge are studied,and the obtained amplitude is introduced into the prediction model of surface roughness.On this basis,the optimization model with the goal of surface quality and material removal rate is established,and the multi-objective optimization of cutting parameters based on improved genetic algorithm is realized. |
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