Research On The Mechanism And Technology Of Vibration-assisted Abrasive Flow For Precision Polishing Of Circular Tubes

Abrasive flow machining is based on the fluid abrasive as the abrasive tool,relying on the abrasive particles in the fluid abrasive to microcut the surface materials of the workpiece.It has high profiling and processing accessibility and was suitable for polishing the surface of parts with micro size and complex shape.Vibration-assisted abrasive flow machining is a new processing method based on the AFM process,which can improve the polishing performance of the conventional AFM process.High-frequency vibration can change the movement of abrasive phase and the distribution characteristics of flow field.The effect of abrasive particles on the wall surface of workpiece was enhanced,and the material removal amount of the abrasive particles and the surface quality of workpiece after processing were improved.The abrasive particles flow along the same direction to cut the workpiece and the single texture was formed on the workpiece surface after machining in conventional AFM process.In vibration-assisted abrasive flow machining,the new relative motion was produced between the abrasive particles and workpiece surface,and the abrasive particles cut the workpiece material in a compound motion mode.The surface roughness and surface morphology of the workpiece were changed significantly after processing.In this paper,the rheological properties of viscoelastic fluid abrasives,the effect of vibration on fluid abrasives in the process of vibration-assisted abrasives flow machining,the motion characteristics of abrasive phase,the material removal of abrasive phase and the surface quality after machining were theoretically analyzed and experimentally studied.The main research work was as follows:(1)The composition and properties of viscoelastic fluid abrasives were analyzed.The constitutive equation of fluid abrasives was characterized based on the power law fluid equation.The flow model of the fluid abrasive in the circular tube flow passage was established.The pressure field and velocity field distribution of flow field in the flow passage were obtained.According to the capillary method,a test device for measuring the rheological parameters of viscoelastic abrasive was built.The viscosity coefficient,non-Newtonian index and the first normal stress difference coefficient of fluid abrasive were measured.The effects of carrier viscosity,abrasive particle mass fraction and abrasive particle size on rheological parameters of fluid abrasive were analyzed.(2)The vibration assisted abrasive flow machining system for circular tube and nozzle was designed based on hard and soft fluid abrasive.The effect of vibration on fluid abrasive was analyzed.The fluid abrasive was regarded as a solid-liquid two-phase fluid and its fluid-solid interaction was analyzed.The force and motion of a single abrasive particle in the flow field were obtained.The hard ball model was used to analyze the impact between abrasive particles and abrasive particles and between abrasive particles and workpiece wall surface.The material removal process of the abrasive particles on the wall surface was analyzed and the motion characteristics of the abrasive particles were obtained.(3)The material removal mode of abrasive phase in fluid abrasive was analyzed.The cutting depth model of abrasive particles was established according to Rayleigh distribution function.The abrasive particle was regarded as a regular octahedron shape and the critical state,contact state and non-contact state of regular octahedral abrasive particles were analyzed.The edge flow layer of fluid abrasive was defined and the number of abrasive particles involved in cutting in the flow passage of the tube was calculated.The material removal effect of a single abrasive particle was analyzed,and the indentation length,indentation depth and the vertical projection area of the indentation on the flow direction were obtained.The change of abrasive particle cutting path in vibration-assisted abrasive flow machining was analyzed and the material removal model for vibration-assisted abrasive flow machining was established.The material removal experiments of hole in vibration-assisted abrasive flow machining were carried out to analyze the effects of ultrasonic vibration and fluid abrasive parameters on material removal.(4)The effect of abrasive particles on the surface profile of workpiece was analyzed and the position of any abrasive cutting edge and the surface profile peak of workpiece in the spatial coordinate system were obtained.The conditions under which abrasive particles did not overlap and the effective height of surface profile peaks removed by fluid abrasive were analyzed.The height change of the surface contour peak after abrasive cutting was obtained and the height removal model of the surface contour peak was established.The surface morphology of the workpiece after vibration assisted abrasive flow machining was analyzed.The mathematical model of spiral scratches on the inner surface of tube was established.The screw pitch,screw angle and track length of spiral scratches were obtained.The surface quality tests of vibration assisted abrasive flow machining tube were carried out.The effects of fluid abrasive parameters,workpiece materials,fluid abrasive velocity and vibration on surface roughness were analyzed.The surface morphology of the machined tube was observed and the effectiveness of vibration-assisted abrasive flow machining to improve surface quality was verified.The results show that the cutting effect of abrasive phase in fluid abrasive was enhanced by vibration compared with conventional abrasive flow machining.The cavitation effect of soft fluid abrasive was produced and the material removal and processing efficiency of abrasive flow machining were improved.Moreover,the cutting path of abrasive particles and the scratch morphology of workpiece surface were changed by vibration.The surface morphology of workpiece surface was changed.The change rate of workpiece surface roughness and surface quality were improved.The material removal amount was increased and the cutting effect of fluid abrasive was enhanced with the increase of abrasive particle mass fraction and abrasive particle size in vibration-assisted abrasive flow machining.When the carrier viscosity and abrasive particle mass fraction was increased and the abrasive particle particle size was decreased,the change rate of workpiece surface roughness was increased and the value of surface roughness after machining was lower.