Study On Ultrasonic Assisted Splitting And Its Micro-mechanism For Connecting Rod

Connecting-rod fracture splitting technology is the most advanced production technology of connecting rod at present.Through the brittle fracture in the big end hole of the connecting rod,the fracture surface is a natural cross-section,and the three-dimensional concave convex structure of the cross-section is used to locate the connecting rod body and cap.At present,the research of splitting technology is mainly focused on fracture splitting process and materials,and there are still many defects,such as connecting-rod big end hole out of round,slag falling from fracture surface,crack deviation and so on.In order to improve the above defects,expand the application range of connecting rod materials and reduce the requirements for process parameters,this paper studies the ultrasonic-assisted splitting technology of connecting rod with quenched and tempered 45 steel as the connecting rod material,simulates and analyzes the effects of amplitude,frequency,groove depth,flare angle and curvature radius on stress nephogram,strain and splitting force,and tests and analyzes the effects of amplitude on splitting force and deformation,ductile-brittle transition and dislocation changes.Find out the general rule of the influence of different parameters on splitting,so as to better control the splitting quality of connecting rod.The research work and achievements have been listed:(1)The effect of amplitude,frequency,groove depth,flare angle and radius of curvature on parameters such as strain and splitting force were studied by ABAQUS finite element simulation.The main conclusions: Compared with the frequency,the amplitude has a greater influence on the splitting process of the connecting rod;When the amplitude is 15?m and the frequency is 20 kHz,the strain and splitting force are the least,which is more suitable for splitting connecting rod;With the increase of groove depth,the fracture time of connecting rod decreases,and the strain and splitting force decrease;The influence of flare angle on splitting is rather complicated,not a single linear relationship;The stress concentration of 30° specimen is the most obvious,the fracture is the first,and the strain and splitting stress are the least,whichis beneficial to the splitting of connecting rod;The smaller the curvature radius is,the smaller the plastic deformation is.(2)The effect of amplitude on splitting force and deformation was studied by ultrasonic-assisted splitting experiment.The main conclusions: When the ultrasonic amplitude increases from 0?m to 15?m and then to 30?m,the splitting force and the displacement of the tensile mechanism required decrease first and then increase;At15?m,the splitting force and the deformation of the sample are the least.(3)The effect of amplitude on the ductile-brittle transition was studied by scanning electron microscopy.The main conclusions: There is a threshold value near the amplitude 15?m,when the amplitude is lower than this threshold value,ultrasonic vibration plays a main role in splitting,and its low amplitude "softening" and high amplitude "hardening" are in accordance with the experimental results;When the amplitude is higher than this threshold value,the thermal effect caused by ultrasound is prominent,leading to the continuous improvement of fracture plasticity;At 15?m,the fracture surface is flat without necking,and the fracture is the most brittle.(4)The effect of amplitude on dislocation changes was studied by XRD and TEM analysis.The main conclusions: When the amplitude increases from 0?m to 6?m,the dislocation density decreases,the dislocation lines decrease at the depth of 2 mm,and the direction of dislocation movement becomes less obvious;When the amplitude increases from 6?m to 15?m,the dislocation density of fracture increases,and dislocation tangle and grain fracture trace appear;When the amplitude increases from15?m to 30?m,the dislocation density decreases,and the dislocation slip path appears;The increase of amplitude will lead to the decrease of dislocation density first,then increase and then decrease,and the fracture plasticity will first increase and then decrease,and then increase.The effect of amplitude on dislocation will lead to the change of fracture surface;There is a threshold near the amplitude 15?m,and the minimum splitting force and deformation can be guaranteed when the amplitude is the threshold,and the fracture is brittle and smooth.