| GCr15SiMn is a high-quality high carbon chromium bearing steel material.It is widely used in aerospace,automotive industry,precision instruments,robots and other fields because of its comprehensive excellent mechanical properties such as high strength,high hardness,good toughness and good wear resistance.Due to the increase of silicon and manganese elements in GCr15 SiMn,the performance of the material has been greatly improved,especially the improvement of strength,which further expands its application in rolling bearings,but also makes its cutting performance worse,resulting in poor surface quality of machined workpieces,which seriously affects the fatigue service life of rolling bearings.It is one of the effective ways of anti-fatigue manufacturing technology to use various new processing methods to expect parts with high anti-fatigue effect.Ultrasonic vibration-assisted machining is very suitable for the machining of some hard and brittle materials due to its characteristics,and has unique advantages in improving the surface machining quality of parts,reducing cutting force,cutting temperature,and tool wear.In this paper,the Ultrasonic vibration-assisted grinding(UVAG)is applied to the processing of GCr15 SiMn bearing steel materials,and the research is carried out on the three-dimensional surface morphology,grinding force,surface roughness and residual stress of the workpiece.The main research contents and conclusions include:(1)Based on the characteristic parameters of the grinding wheel,a mathematical model was established to characterize the topography of the grinding wheel.By analyzing the trajectory of abrasive particles,the formation mechanism of the grinding surface under ultrasonic conditions was studied,and the trajectory equation of any abrasive particle on the surface of the grinding wheel was established.Then,based on the geometric mapping relationship between the grinding wheel surface and the workpiece surface,the theoretical mathematical model of the UVAG surface was established,and the simulation of the grinding wheel surface and the surface topography of the workpiece was realized by MATLAB software.Finally,the simulated surface topography and the measured surface topography of two different grinding methods were compared and analyzed.The results showed that the basic characteristics of the simulated surface and the simulated surface are highly similar.The grooves of the ordinary grinding(OG)surface are parallel to each other along the feed direction,and the grooves are deep,while the grooves of the ultrasonic grinding surface are relatively curved,and the grooves are shallow and wide.In addition,the surface of the ground workpiece was observed by scanning electron microscope,and it was found that there was serious tearing on the OG surface,while the surface after UVAG was relatively smooth without tearing phenomenon.(2)The wear form of single abrasive particle was studied,and the causes of different abrasive particle wear were explored.In addition,based on the continuous wear of abrasive particles in the machining process and the dynamic change of the number of abrasive particles in the grinding area,a new dynamic grinding force model of UVAG was established,and the model was verified by grinding GCr15 SiMn steel.An UVAG system with the tool as a vibration carrier was developed and an experimental platform was built to grind GCr15 SiMn bearing steel.Orthogonal and single factor experiments were used to explore the influence degree and variation law of different processing parameters on grinding force.The results showed that the established grinding force model can effectively predict the grinding force.The grinding force shows an upward trend with the increase of grinding depth and feed speed,and a downward trend with the increase of the spindle speed.With the increase of ultrasonic amplitude,it first decreased and then increased.Under the same processing parameters,when the ultrasonic amplitude is 4 μm,the grinding force of UVAG reaches the minimum value.Compared with OG,it is found that the radial and tangential grinding forces under ultrasonic condition are reduced by about 27.8% and32% respectively.(3)Based on the surface micro-geometry and the physical and mechanical properties of the surface layer,the surface machining quality of the workpiece was studied.The effects of different machining parameters on the surface roughness and residual stress were investigated through single factor experiments.The results showed that the surface roughness increases with the increase of grinding depth and feed speed,and decreases with the increase of grinding wheel speed and ultrasonic amplitude;The surface residual compressive stress decreases with the increase of grinding depth and spindle speed,and increases with the increase of ultrasonic amplitude.Under the same processing parameters,when the ultrasonic amplitude is 6 μm,the surface roughness and residual stress reach the minimum and maximum values respectively.Compared with OG,the surface roughness under ultrasonic conditions is reduced by about 27%and the residual compressive stress on the grinding surface is increased by more than13.5%. |
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