Research On High-Speed Milling Of Zirconia Ceramics

Zirconia ceramic which was fully sintered has been widely used in the field of aerospace,aviation,mechanical manufacturing,biomedicine due to its good performance such as heat resistance,wear resistance,corrosion resistance etc.Howerver it also has hard and brittle properties which lead to low processing efficiency,serious tool wear and poor surface quality with traditional milling methods.To improve machining efficiency,manufacturing quality and the tool life,and lay the foundation for practical milling process,basic research work in high-speed milling zirconia ceramics is conducted with machining experiments in this paper.The main work in this paper is as follows:(1)Research on the mechanism of high-speed milling zirconiaIt’s discovered by milling experiments that the topography of finished surface and shape of chip in low-speed milling zirconia show more brittle features while more ductile features in high-speed milling zirconia,and several t-Zr O2 were rmed to m-Zr O2.The mechanism of brittle milling and ductile milling were investigated with theoretical analysis and finite element method.The formation mechanism of serrated chips was analyzed.According to the finished surface morphology,the critical cutting thickness of brittle-ductile transition was determined to be about 1.6μm,which was raised about 1μm than in low-speed milling.Thus larger feed rate,radial cutting depth and axial cutting depth can be employed to obtain high machining efficiency in high-speed milling zirconia.(2)Research on the cutting force in high-speed milling zirconiaThe milling force signal was acquired to analyze the characteristics of the time domain and the frequency domain.The effects of spindle speed,feed rate,radial depth of cut and axial depth of cut were analyzed.The results show that there is no vibration chatter in high-speed milling zirconia.With the increase of spindle speed and the decline of feed rate,radial depth of cut and axial depth of cut,radial and tangential forces decreased.The prediction model based on PSO algorithms and BP neural network which has a maximal error of 6.22% was proposed.(3)Research on the workpiece temperature and thermal stress in high-speed milling zirconiaThe theoretical model and finite element model of workpiece temperature were established based on heat source method.The temperature measuring experiments were conducted in milling zirconia.The milling force removed the noise was used to calculated the frictional heat flux between the flank of the cutting tool and the machined surface of the workpiece.The heat transfer ratio of cutting heat incoming into ceramics was determined to be about 5.2% with finite element method.Then the workpiece temperature and thermal stress were calculated to analyze the effects of spindle speed,feed rate,radial depth of cut and axial depth of cut.It’s found that the highest workpiece temperature and maximum thermal stress decreased with the decline of spindle speed,radial depth of cut and axial depth of cut and the increase of feed rate.(4)Research on the tool wear in high-speed milling zirconiaTool wear experiments were conducted with PCD tools under the low spindle speed(n=2000rpm ae=0.1mm ap=3mm vf=60mm/min)and high spindle speed(n=14000rpm ae=0.1mm ap=3mm vf=60mm/min).It’s found that the tool life was only 44 minutes in low-speed milling zirconia,while 908 minutes which was 20.6 times in high-speed milling zirconia.This shows that the tool life can be greatly improved in high-speed milling zirconia.The tool wear mechanism were found to be in the form of grain shedding caused by abrasive wear,tool tipping and graphitization wear by scanning electron microscope and energy dispersive spectrometer.The effect of tool wear on correlation dimension of cutting force was also analysed.(5)Research on the surface integrity in high-speed milling zirconiaSurface roughnesses experiments and surface residual stress were conducted.The experimental result indicated that the surface roughness was under Ra0.4μm in high-speed milling zirconia and residual stress was compressive stress which decreased with the increase of spindle speed.The effects of spindle speed,feed rate,radial depth of cut and axial depth of cut on surface roughnesses were inbestigated.The formation mechanism of residual stress were also analysed.