Papers by Author: Fei Hu Zhang

Abstract: Ultra-precision fly cutting machines have long been the hardest one to compliant and induce great focus of researchers. In this paper, a surface topography model is proposed to predict the surface generation in an ultra-precision fly cutting machine. The building of surface topography model is based on the trace of the tool tip. With the 3D surface profile simulations of workpieces, several influencing factors of surface topography, especially the factors related to micro waviness error, are studied.

Abstract: Ductile removal behavior of hard and brittle material in the process of machining has always been a sticking topic. A series of nanoscratch tests of K9 glass were conducted with Berkovich probe on nanoindenter XP to investigate the ductile removal process, material deformation and crack damage. It was found that the scratches surface was free from crack damage in the range of the selected scratching parameters and excellent machinability of K9 glass was obtained. The observation also showed that the stable chips were distributed on the sides of the scratches and the deformation of chips was much larger than that obtained in the conventional machining. Meanwhile, a pile-up phenomenon was obvious and the residual depth of scratches was decreased with the increasing of scratch velocity under the same normal load condition.

Abstract: Metal bonded diamond grinding wheels are very important for precision grinding operations of hard and brittle materials especially like ceramics or cemented carbides. But the trueing and dressing problem has affected its wide use. In this paper, a new EDD (Electrical discharge dressing) device was developed for the dressing of metal bonded diamond arc grinding wheels. The EDD experiments were carried out with the new dressing device. The influence of dressing parameters on the dressing efficiency and precision was studied. Experimental results shown that the increase of pulse period and duty period helped improve the dressing efficiency in a certain range. The higher electrical parameters could get better dressing efficiency. The detection results revealed that the error of the arc profile after EDD could reach to around 3μm. mazhaokai2014

Abstract: Silicon carbide ceramics with its excellent physical and mechanical properties have become the preferred material for space large diameter mirror. Diamond wheel grinding is the main way of SiC ceramics forming processing. Subsurface cracks is generated due to the high hardness and brittleness of the material after grinding. In order to remove the impact of cracks, poishing processing with very low efficiency is applied, so it is significant to control the depth of silicon carbide ceramic grinding subsurface cracks and shorten the processing cycle.In this paper grinding experiment of SiC ceramic is conducted. The method of cross-section polishing combined with scanning electron microscope observation is used to research grinding subsurface cracks. The depth of broken surface layer and the maximum depth of sub-surface cracks were proposed to evaluate the grinding subsurface cracks. The result show broken surface layer depth and the maximum depth of sub-surface cracks increase with the decreasement of spindle speed, and increasement of feed rate and grinding depth.

Abstract: Silicon carbide ceramics with its excellent physical and mechanical properties have become the preferred material of space large diameter mirror. But because of its higher hardness, diamond wheel would appear some wear form and wear rate in the mechanical processing process, wear form is an important factor to effect surface and subsurface quality, wear rate effects the surface shape accuracy, so the research on the laws of wear rate of grinding wheel has an important role in grinding. But, because of the particularity of wheel structure, wheel wear form and wear rate changes with time going, which limits the wheel wear research. By the grinding process experiment, the author found the relationship between diamond grinding block wear rate and wheel feeding, and got the laws of wear rate with time. With the laws of wear rate, we can predict the surface accuracy and guide the compensation of wheel feeding.

Abstract: The components of spindle system are key components in ultra precision machine tool. According to the characteristics of the machining process of vertical hydrostatic spindle system for ultra-precision fly cutting machine, the mass- stiffness model of the spindle system is established. This paper describes a system for the analysis of the spindle system under the action of external shocks. The use of the state space method is discussed and an example is given. The influence law of vibration frequency is obtained for the various mass and stiffness value of the spindle system components.

Abstract: In order to improve the positioning resolution of the tool adapter on ultra-precision machine tool for KDP crystals, this paper presents a new piezo tool actuator. First, a new flexible membrane structure is designed after considering the characteristics of the machine tool for KDP crystals. Then, its detailed structural dimension is determined by finite element method. Finally, the piezo tool actuator is machined based on designs and its performance data is obtained by experiments. Experimental results indicate that its positioning resolution is superior to 0.5μm and its stroke reaches 4.7μm, which can meet the requirements of ultra-precision machine tool for KDP crystals.

Abstract: In this work, optical K9 glass surface has been flattened by nanoparticle colloid jet machining, which is an ultra-smooth surface processing technique utilizing surface chemical effect between work surface atoms and nanoparticles in alkaline colloid to remove the uppermost surface atoms. The surface removal process of nanoparticle colloid jet machining has been investigated through K9 glass polish experiments. And the characterizations of ultra-smooth K9 glass surface polished by nanoparticle colloid jet machining have also been studied in this paper. Surface profiler and atomic force microscopy (AFM) are used to observe the surface microscopic morphological characteristics of K9 glass sample before and after polishing by nanoparticle colloid jet machining. The measurement results of processed surface prove that the primary scratches on the original surface have been completely wiped off by nanoparticle colloid jet machining and the roughness of the K9 glass surface has been improved to be less than 1 nm (Rq). Autocovariance (ACF) is investigated along a cross section of the K9 glass surface to determine the dominant spatial frequencies. The ACF curves show that the surface morphology of K9 glass processed by nanoparticle colloid jet machining is completely different from the preprocessed surface. The final K9 glass surface has been flattened by nanoparticle colloid jet machining. The microscopic morphological profile of the final K9 glass surface becomes increasingly smooth and eventually close to a flat state.

Abstract: This paper provides the transfer matrix method to analysis the natural frequency of the vertical spindle using on ultra-precision fly cutting machine tool. Several transfer matrix equations of the typical units of the spindle had been established when considering the effects of the gyroscopic torque as the rotor has a large inertial tensor. And then the natural frequencies and each modal shape of the spindle rotor system were calculated using the transfer matrix model. Also, the modal experimental test had been taken out. The theoretical results from the transfer matrix model are very close to the test results, and the accuracy and the effective of the model was proved.

Abstract: In this paper, experiments are conducted to study the characters of Ultrasonic Assisted Grinding (UAG) and Conventional Grinding (CG), diamond grinding wheel is used in experiments, grinding forces and surface roughness are measured in both UAG and CG. The effects of different parameters on grinding force, surface roughness and force ratio are discussed. The results show that the grinding force and surface roughness in UAG is smaller than those in CG. The force ratio in UAG is lower than that in CG, which reveals that the grinding wheel has a good wear-resistant property in UAG process.