Experimental Study On Formation Process And Geometric Characterization Of Serrated Chip

At present,high-speed cutting technology has become the main method of processing difficult-to-machine materials in manufacturing industry.High-speed cutting technology has the advantages of high processing efficiency,but it also produces the serrated chip whose formation process,formation mechanism and deformation measurement index are different from the traditional banded chip.The formation of serrated chip is often accompanied by the high frequency fluctuation of cutting force,which causes the high frequency vibration of cutting process and affects the machining accuracy,surface quality and tool wear and breakage.In this paper,the formation process and micro-geometric characterization of serrated chip were studied and analyzed by the method of experimental investigation.The main work of this paper is as follows :(1)Taking titanium alloy as the research object,a large number of root samples of serrated chip were obtained through root cutting test.After metallographic treatment of root samples,high quality root metallographic images were obtained.The formation process of serrated chip was analyzed based on metallographic deformation of root,and the formation process model was established.The results show that the serrated chip formation process can be divided into the accumulation of shear extrusion deformation and formation of initial shear plane,the separation stage of free surface of serrated element and free surface of cutting layer,serrated unit overall shear slip in the first and second deformation zone.The cracks inside the adiabatic shear band and at the surface of the cutting layer are generated during the overall shear slip stage of the serrated unit,and the formation of cracks is not the incentive for adiabatic shear instability of serrated chips.(2)The variation of geometric characterization of serrated chip and cutting performance index with cutting parameters were studied by orthogonal experiment.The results show that with the increase of feed rate,the tooth pitch and serrated degree increase while the serrated frequency decreases.With the increase of cutting speed,the serrated degree and serrated frequency increase,while the tooth pitch decreases.The back-feeding amount has little effect on the geometric characterization of chips.The tooth top angle and tooth bottom angle change little with cutting parameters.The dynamic component of cutting force and surface roughness increases with the increase of feed rate and back-feeding amount,and decreases with the increase of cutting speed.The unit cutting force decreases with the increase of feed rate and back-feeding amount,and increases with the increase of cutting speed.The static component of cutting force increases with the increase of three cutting parameters.At the same time,through the analysis of the above test results,the rationality of the serrated chip formation process and the model proposed in this paper is verified.(3)Taking the cutting parameters as the bridge,the correlation between the geometric characterization of serrated chip and the cutting performance index was explored.The results show that the dynamic component of cutting force has the strongest correlation with the serrated degree;the correlation with serrated frequency is the second,and both are negatively correlated under the corresponding feed rate and cutting speed.The static component of cutting force has the strongest correlation with tooth pitch;the correlation with the tooth base angle is the second,and both are negatively correlated under the corresponding feed rate and cutting speed.The correlation between unit cutting force and tooth pitch is the strongest,and both are negatively correlated under the corresponding feed rate and cutting speed.The correlation between surface roughness and serrated frequency is the strongest,and both are negatively correlated under the corresponding feed rate and cutting speed.