During hard cutting process there is severe thermodynamic coupling effect between cutting tool and workpiece, which causes quenching effect on finished surfaces under certain conditions. However, material phase transf...During hard cutting process there is severe thermodynamic coupling effect between cutting tool and workpiece, which causes quenching effect on finished surfaces under certain conditions. However, material phase transformation mechanism of heat treatment in cutting process is different from the one in traditional process, which leads to changes of the formation mechanism of damaged layer on machined workpiece surface. This paper researches on the generation mechanism of damaged layer on machined surface in the process of PCBN tool hard cutting hardened steel Cr12MoV. Rules of temperature change on machined surface and subsurface are got by means of finite element simulation. In phase transformation temperature experiments rapid transformation instrument is employed, and the effect of quenching under cutting conditions on generation of damaged layer is revealed. Based on that, the phase transformation points of temperature under cutting conditions are determined. By experiment, the effects of cutting speed and tool wear on white layer thickness in damaged layer are revealed. The temperature distribution law of third deformation zone is got by establishing the numerical prediction model, and thickness of white layer in damaged layer is predicted, taking the tool wear effect into consideration. The experimental results show that the model prediction is accurate, and the establishment of prediction model provides a reference for wise selection of parameters in precise hard cutting process. For the machining process with high demanding on surface integrity, the generation of damaged layer on machined surface can be controlled precisely by using the prediction model.展开更多
The characteristic of metallographic structure of the SnSb alloy moulds is that hard particles are distributed on the soft metal matrix. Great difference of the hard particles and the soft metal matrix’hardness makes...The characteristic of metallographic structure of the SnSb alloy moulds is that hard particles are distributed on the soft metal matrix. Great difference of the hard particles and the soft metal matrix’hardness makes moulds’polishing become difficult. When a rigid grindstone is used to polish the surface of the SnSb alloy mould, the hard abrasives fall off and are embed in the soft matrix of SnSb alloy and while the process, the grinding chips are able to block the gap on the grindstone surface and enable the grindstone to blunt, which brings about the polished area on the surface of the mould is seriously squeezed and deformed and the crystal lattice of SnSb alloys is seriously distorted, and the work hardening takes place. At the same time, the rigid grindstone is easy to scratch the surface of the SnSb alloy mould. Owing to the above reasons, it is difficult to reduce surface roughness and improve the surface quality of SnSb alloy moulds. Taking use of the CAD/CAM technique and the complex processing of combining electrolyzing polishing and mechanical polishing with the magnetic force, mould’s polishing automation is realized on the numerical control machine tool. This complex processing is finished under a comprehensive action as the following: 1. Electrolyzing polishing action Under the electric field, the electrolyte between the elastic grind wheel and the mould is ionized, which electrolyzes the metal of the mould’s surface. The electrolyzing speed of convex peak on the mould’s surface is faster than that of concave valley, which levels the mould’s surface. 2. Mechanical Polishing action During electrolyzing, a dense passive film of low hardness is formed on the mould’s surface. While polishing, soft grinding wheel scraps the passive film on the conven peak easily, and the new metal surface is exposed, then, a new passive film is formed again, going round and round, the conven peak on the mould’s surface is leveled quickly. 3. Magnetic force action The charged particles in electric field will be acted by the Lorentz force in magnetic field. The field plays a stirring part on electrolyte and reduces electrochemical polarization and concentration polarization, and accelerates the electrochemical reaction. The complex polishing process is not only of high efficiency, but also of good surface quality and provides a good effective method for the non-ferrous metal polishing. When the mould is polished, a speed-raising tool system is used and it can increase the grinding wheel spindle’s speed up to five times. This paper describes the SnSb alloy moulds’polishing steps, grinding wheel speed-raising tool system, polishing principle and the results.展开更多
Ultra-precision diamond machining with piezoelectric-assisted fast tool servo (FTS) was used to produce various free-form surfaces.A low cost,rapid and large area fabrication of uniform hydrophobic surface at room tem...Ultra-precision diamond machining with piezoelectric-assisted fast tool servo (FTS) was used to produce various free-form surfaces.A low cost,rapid and large area fabrication of uniform hydrophobic surface at room temperature which transfers the FTS fabricated sinusoidal grid surface to the flat film with UV-moulding process was described.A piezoelectric-assisted FTS with high band width of 2 kHz,travel range up to 16 μm and the compact mechanism structure was designed for the sinusoidal grid surface machining and the dynamic performance testing of FTS was described in detail.Machining results indicate that the dimensions of sinusoidal grid change with the variation of the FTS machining condition.Wetting properties of UV-moulded surface were evaluated,the best contact angle was measured to be 120.5° on the sinusoidal grid surface with profile wavelength of 350 μm and peak-to-valley amplitude of about 16 μm.展开更多
基金Supported by National Natural Science Foundation of China (Grant Nos.51105119,51235003)
文摘During hard cutting process there is severe thermodynamic coupling effect between cutting tool and workpiece, which causes quenching effect on finished surfaces under certain conditions. However, material phase transformation mechanism of heat treatment in cutting process is different from the one in traditional process, which leads to changes of the formation mechanism of damaged layer on machined workpiece surface. This paper researches on the generation mechanism of damaged layer on machined surface in the process of PCBN tool hard cutting hardened steel Cr12MoV. Rules of temperature change on machined surface and subsurface are got by means of finite element simulation. In phase transformation temperature experiments rapid transformation instrument is employed, and the effect of quenching under cutting conditions on generation of damaged layer is revealed. Based on that, the phase transformation points of temperature under cutting conditions are determined. By experiment, the effects of cutting speed and tool wear on white layer thickness in damaged layer are revealed. The temperature distribution law of third deformation zone is got by establishing the numerical prediction model, and thickness of white layer in damaged layer is predicted, taking the tool wear effect into consideration. The experimental results show that the model prediction is accurate, and the establishment of prediction model provides a reference for wise selection of parameters in precise hard cutting process. For the machining process with high demanding on surface integrity, the generation of damaged layer on machined surface can be controlled precisely by using the prediction model.
文摘The characteristic of metallographic structure of the SnSb alloy moulds is that hard particles are distributed on the soft metal matrix. Great difference of the hard particles and the soft metal matrix’hardness makes moulds’polishing become difficult. When a rigid grindstone is used to polish the surface of the SnSb alloy mould, the hard abrasives fall off and are embed in the soft matrix of SnSb alloy and while the process, the grinding chips are able to block the gap on the grindstone surface and enable the grindstone to blunt, which brings about the polished area on the surface of the mould is seriously squeezed and deformed and the crystal lattice of SnSb alloys is seriously distorted, and the work hardening takes place. At the same time, the rigid grindstone is easy to scratch the surface of the SnSb alloy mould. Owing to the above reasons, it is difficult to reduce surface roughness and improve the surface quality of SnSb alloy moulds. Taking use of the CAD/CAM technique and the complex processing of combining electrolyzing polishing and mechanical polishing with the magnetic force, mould’s polishing automation is realized on the numerical control machine tool. This complex processing is finished under a comprehensive action as the following: 1. Electrolyzing polishing action Under the electric field, the electrolyte between the elastic grind wheel and the mould is ionized, which electrolyzes the metal of the mould’s surface. The electrolyzing speed of convex peak on the mould’s surface is faster than that of concave valley, which levels the mould’s surface. 2. Mechanical Polishing action During electrolyzing, a dense passive film of low hardness is formed on the mould’s surface. While polishing, soft grinding wheel scraps the passive film on the conven peak easily, and the new metal surface is exposed, then, a new passive film is formed again, going round and round, the conven peak on the mould’s surface is leveled quickly. 3. Magnetic force action The charged particles in electric field will be acted by the Lorentz force in magnetic field. The field plays a stirring part on electrolyte and reduces electrochemical polarization and concentration polarization, and accelerates the electrochemical reaction. The complex polishing process is not only of high efficiency, but also of good surface quality and provides a good effective method for the non-ferrous metal polishing. When the mould is polished, a speed-raising tool system is used and it can increase the grinding wheel spindle’s speed up to five times. This paper describes the SnSb alloy moulds’polishing steps, grinding wheel speed-raising tool system, polishing principle and the results.
基金supported by NCRC(National Core Research Center)program of the Ministry of Education,Science and Technology(2010-0008-277)"Development of next generation multi-functional machining systems for eco/bio components" project of ministry of knowledge economy
文摘Ultra-precision diamond machining with piezoelectric-assisted fast tool servo (FTS) was used to produce various free-form surfaces.A low cost,rapid and large area fabrication of uniform hydrophobic surface at room temperature which transfers the FTS fabricated sinusoidal grid surface to the flat film with UV-moulding process was described.A piezoelectric-assisted FTS with high band width of 2 kHz,travel range up to 16 μm and the compact mechanism structure was designed for the sinusoidal grid surface machining and the dynamic performance testing of FTS was described in detail.Machining results indicate that the dimensions of sinusoidal grid change with the variation of the FTS machining condition.Wetting properties of UV-moulded surface were evaluated,the best contact angle was measured to be 120.5° on the sinusoidal grid surface with profile wavelength of 350 μm and peak-to-valley amplitude of about 16 μm.
