Study On Machined Surface Topography For Large Pitch Thread In Turning

Large pitch thread plays an important role in the working performance of heavy-duty press as the key component transfer pressure and movement.The machined surface topography of large pitch thread directly determines its working performance.The thread parts are usually machined by turning,however,this kind of large pitch thread belongs to non-standard parts,and the tool cutting edge and the its shape have poor retention in the turning process because of large size,large pitch,long axial length,large machining allowance,and groove width and depth.The cutting vibration and wear seriously affect the wear resistance,the sealing property and the service life of thread,and even to destroy the consistency of the machined surface topography of thread.So,designing the reasonable process scheme and enhancing the consistency of machined surface topography of large pitch thread have great significance.This paper originates from the application technology research and development program of Heilongjiang province project "high quality efficient thread cutting technology"(GC13A404)and the National Natural Science Foundation "based on the generalized dynamic space gives high vibration cutting tool wear mechanism"(51575148);In order to improve the machined surface morphology of large pitch thread and to achieve its consistency,the machined surface morphology of large pitch thread and its consistency are studied according to the present situation of the production process of large pitch thread workpiece.Based on the characteristics of axial layering turning of large pitch thread,through establishing the movement trajectory equation of cutting edge analyzing contact relationship between the cutting tool and workpiece,then work angle between the left and right cutting edges are ensured and the machined surface morphology experimental plans of turning large pitch thread come forward.Combined with the structure characteristics of large external thread pitch,detection method of machined surface topography is proposed.According to the machined surface of super depth of field test results and micro contour detection results of the left and right thread surfaces,distribution characteristics along the axial direction of machined surface morphology can be quantitatively described by using the distribution curve of surface asperity and surface roughness.According to the fact that the machined surface quality of large type thread parts have difficulty on-machine measurement,the cutting edge wear and the effect of tool vibration on machining surface topography are studied.Under considering the tool wear and the vibration,the simulation model for machining surface topography of large pitch thread is established.By the tool and workpiece vibration signals and the cutting edge wear data obtaining from the experiment,the machining surface topography of large pitch thread is simulated,thereby proving the validity of simulation model using the simulation examples and experimental results.Firstly,based on the tool wear and the result of vibration experiment,according to the machined surface topography simulation of turning large pitch thread,the characteristics are analyzed,which belong to the machined surface topographies of left and right surfaces change with the increase of cutting times.Furthermore,the influence of tool wear and vibration to machined surface topography is judged by the distribution uniformity of machined surface topography and the similarity of different surface topographies in left and right thread surfaces,in addition,the best cutting times and cutting strokes of left and right cutting edges are obtained.Finally,according to the simulation behavior sequences of machined surface topographies in axial distribution and the absolute correlation degree,the distribution consistency belonging to the machined surface topographies of left and right surfaces is characterized and evaluated,the tool wear,the vibration characteristics and the service life which satisfies the high quality requirement of machined surface topography are identified.The above methods provide the basis of effectively controlling the tool wear and vibration.According to the turning process requirement of large pitch thread and using the trial cutting experimental result and the simulation model of machined surface topography,the feasible region of process design variables are determined by the simulation and evaluation of the tool wear and the effect of vibration on machined surface topography.Aiming at enhancing the distribution consistency of the machined surface topographies of left and right thread surfaces,the design method of finish machining process for turning large pitch thread is proposed.Finally,the turning experiment is carried out and the distribution consistency of the machined surface topography is analyzed and judged.The results show that the machined surface topography and its distribution consistency can be improved by adopting this method.