Study On Micro Removal Mechanism And Surface Properties Of Material In Ultrasonic Elliptical Vibration Cutting

β Titanium alloy has become a representative medical bone material due to its excellent properties(high strength,high toughness,wear resistance,etc.)and characteristics similar to the elastic modulus of human bones.There are problems of high cutting temperature and large cutting force in traditional titanium alloy machining.Moreover,traditional cutting cannot produce micro textures that meet the needs of medical applications,limiting the application ofβ titanium alloy.Ultrasonic elliptical vibration cutting(UEVC)technology can effectively reduce cutting temperature and cutting force by utilizing its characteristics such as "toolworkpiece periodic separation" and "micro removal".Compared with shot peening and laser processing,it has unique advantages in processing microtextured surfaces.Therefore,this topic is oriented towards β titanium alloy,aiming at ultrasonic elliptical vibration cutting technology,and studying the micro removal mechanism of materials.In order to provide theoretical guidance for micro texture processing of β titanium alloy,the main research contents are as follows:First,the theoretical part of ultrasonic elliptical vibration cutting is analyzed and modeled.Construct kinematic model of UEVC and decompose cutting process,elaborate characteristics of UEVC micro-removal and periodic separation;Multi-period elliptic trajectory with different parameters is generated by MATLAB software.The transient front and rear angles of cutting process are modeled and calculated analytically.It is found that the transient rake angle at any time with phase difference of 135° is larger than that with phase difference of 45° and 90°.Construct the mechanical model of cutting area and elaborate the law of mechanical change during cutting process.Construct the UEVC micro-removal model and the chip characteristic model,and find that the UEVC process can form two types of chip shape: continuous and broken.Then,establish finite element simulation model of ultrasonic elliptical vibration cutting.The elliptical vibration cutting process under different trajectories and cutting parameters is simulated and analyzed.The micro-removal of material during cutting is extracted in stages.It is found that there is a "press-shear-pull" transition in the micro-removal process of materials.The chip formation process under different cutting parameters is analyzed.It is found that single-cycle material removal plays a decisive role in chip shape.The surface morphology characteristics of workpiece under different cutting paths were obtained.It is found that there is a "secondary cutting" feature in the cutting cycle when the phase difference is 45° and 90°.When the phase difference is 135°,the tool has an ironing effect on the chip separation position.Then,UEVC experiments are carried out and the cutting force and cutting temperature data are extracted.The Force-Heat variation law of cutting process is explored with simulation analysis.The machined surface and chips of the material were observed by scanning electron microscope(SEM)to obtain the micro-morphology of the machined surface and chips.The formation mechanism of surface defects in UEVC processing was explored and the material micro-removal mechanism under different processing conditions was revealed.The microstructures of machined surfaces were also examined.Phase transformation and grain refinement were found on the machined surface of UEVC.Phase transformation and grain refinement are the most obvious phenomena when the feed rate is 100μm/r.Finally,the surface properties of UEVC are explored.It is found that the surface microhardness of the machined material has been improved to some extent.When the feed rate is 40μm/r,the increase of microhardness is the most obvious,reaching 416.84 HV.With the decrease of feed and the increase of cutting speed,the roughness of machined surface of material tends to decrease.The stress distribution of material surface layer is mainly compressive stress.The depth of the plastic strain layer on the surface of the material is about10μm.Higher cutting speed and bi-directional amplitude will result in higher plastic strain level of material surface.The friction coefficient tends to decrease with the increase of feed.Abrasive wear is the main wear mode on the machined surface of UEVC.Adhesive wear is the main wear mode on unprocessed surfaces.