Papers by Author: Ren Ke Kang

Abstract: Grinding force is an important indicator related to processing efficiency and residual strength in the progress of grinding SiC. With the method of ultrasonic assisted grinding (UAG), this paper studied the influence of four parameters on grinding force based on orthogonal experiment, namely vibration amplitude, depth of grinding, feed rate and spindle speed. A series of results with high efficiency and low grinding force were obtained. A regression empirical model under the condition of UAG was established and verified. It was also proved that ultrasonic vibration was conducive to improve the ground surface quality of workpiece.

Abstract: The origin of drilling force in drilling with twist drill is quite complicated owning to the complex shape of the drill bit cutting edges. In this paper, the drilling experiments both with and without the ultrasonic were designed and conducted on aluminum alloy with pre-drilled hole. The drilling force was tested and the different effects between the cutting edges of the twist drill on the drilling force were analyzed under various drilling parameters including the spindle speed, feed rate and vibration amplitude. The drilling force of conventional drilling (CD) and ultrasonic assisted drilling (UAD) was characterized and the roles of the ultrasonic vibration in drilling were discussed.

Abstract: Machining the aircraft skin, using CNC milling to replace the traditional chemical milling, is a trend owning to the great pollution of the chemical milling to the environment. Based on the instantaneous rigidity force hypothesis, a milling force model for mirror milling of aircraft skin was proposed, which was validated by the milling force measurement during mirror milling experiments. A FEM model was established to calculate the deformation of the aluminum plate in mirror milling. The effects of the supporting position on the deformation was analyzed.

Abstract: Ultra-precision grinding is widely used in machining of the hard and brittle materials due to its high surface accuracy and machining efficiency. However, grinding inevitably brings about surface and subsurface damage that needs to be removed by the polishing processes. This study investigated the surface and subsurface integrity of glass-ceramics induced by ultra-precision grinding. The characteristics of surface roughness, surface topography and subsurface damage depth of ground glass-ceramics with diamond grinding wheels with different grain sizes were presented and compared. Discussion was also provided to explore corresponding reasons of surface and subsurface integrity induced by diamond grinding wheels with different grain sizes.

Abstract: Titanium alloy has been widely used in aeronautics and astronautics industry owing to its unique combinations of properties. The unique physical and chemical properties of titanium alloy make it a typical difficult-to-machine material. The elevated temperatures at the machining zones may cause thermal damage, residual stress and micro-structural changes in the surface layer of titanium alloy during grinding. In this study, grinding experiments were performed on the titanium alloy, and the grinding temperature was experimentally tested with the grindable thermocouples. The effects of the grinding parameters on the grinding temperature were analyzed. The grinding temperature rises with the increase of grinding speed and grinding depth.

Abstract: Responding to the demand on the ultra-precision equipment for machining monocrystalline silicon, sapphire, zirconia ceramics and other large-size functional crystal substrates in the microelectronics and optoelectronics manufacturing, this study analyzes the current state-of-the-art of polishing technologies and the technical challenges to achieving high surface quality substrates. In this study, a planetary double-sided polishing machine is designed to solve the problem between achieving high polishing quality and efficiency. The machine is characterized by process stability, large polishing pressure and high polishing speed, etc. which is verified by polishing zirconia substrates with satisfactory results: material removal rate of 5 μm/h and the surface roughness Ra of 1 nm.

Abstract: In order to improve the efficiency and reduce the cost of sapphire crystal machined by loose abrasive lapping, the fixed-abrasive diamond grinding tools for sapphire grinding were investigated in this paper. Four vitrified-resin composite bond diamond grinding tools with different grain sizes (40μm, 20μm, 7μm, 2.5μm) were developed. The grinding experiments were performed with the developed diamond grinding tools and the grinding performance of four grinding tools were evaluated by comparing the surface roughness and the material removal rate (MRR) of sapphire. The experiment results show that with the increase in grain size, both the MRR and the surface roughness increase. A high-efficiency and high-quality ultra-precision grinding process using diamond grinding tools with different grain sizes was proposed.

Abstract: Diamond is widely used in the fields of precise and ultraprecise machining because of its superlative characters. Due to high hardness and great brittleness of diamond, the grinding of diamond needs a kind of high effective and stable polishing method. Dynamic friction polishing (DFP) is deemed to be an innovative method by means of a synergistic reaction of mechanical effect and chemical change. The condition of high pressure and high temperature puts forward a high requirement for mechanical property of the grinding wheel in DFP, other than that, the graphitization of diamond catalyzed by catalytic metal is also a focus of research. In this paper, the transition metals with unpaired d electrons were selected as polishing materials, and powder metallurgy technique was used to prepare alloy grinding wheel for polishing diamond by dynamic friction polishing.

Abstract: This paper presents the results of an experimental investigation on molar ratios of MgO/ MgCl₂ affecting the hardness of magnesia grinding wheels, which is one of the most important properties. Magnesite grinding blocks of different ratios of MgO/MgCl₂ were prepared. The surface Rockwell hardness of which was tested under the same curing conditions. By an integrated assessment of the experimental studies of hardness and component, it is recognized that the molar ratios of MgO/MgCl₂ can significantly affect the properties of magnesia grinding wheels. With the increase of MgO/MgCl₂ molar ratio, hardness of the specimens increases. Scanning electron microscopy (SEM) studies on grinding blocks of different ratios indicated that micro needle shaped crystal structure of phase 5 are mainly responsible for hardness development. Finally the optimal recipe was selected in consideration of the characteristics of the silicon mechanical chemical grinding (MCG), which was verified to be effective by the following grinding experiment.

Abstract: Lapping is widely applied to hole surface finishing. However, for small holes of high hardness material, low efficiency and unstable hole surface quality of traditional lapping cannot be ignored. In this paper, the ultrasonic transducer and horn–tool were designed by the analytical method and the finite element method (FEM). An equipment of ultrasonic lapping for small holes was developed. Vibration performance tests of developed equipment were conducted by using microscope and laser displacement sensor. The result showed that the amplitude of ultrasonic lapping equipment can meet manufacturing demand. The machining performance of the developed ultrasonic lapping equipment was also investigated by comparing the surface quality and material removal rate with traditional lapping. The result showed that the higher material removal rate and better hole surface quality can be obtained by ultrasonic lapping.