Papers by Author: Feng Jun Chen

Abstract: Magnetic characteristics of three magnetic polishing fluids such as magnetic fluid (MF), magnetorheological fluid (MRF), and magnetic compound fluid (MCF) under magnetic field are experimentally investigated and analyzed. Their magnetic cluster structures under action of magnet field are observed, and their magnetic cluster models are established. Magnetic flied assisted polishing experiments for tungsten carbide are developed used these three kinds of magnetic fluids, material removal and surface roughness are respectively measured. At last, the machining characteristic of three magnetic fluids are contrasted and discussed according to experimental results.

Abstract: According to the principle of optical design, two kinds of 2 Mega-pixel cell phone camera lenses are proposed. One is made up of three plastic (3P) lenses; the other is made up of two plastic lenses and one glass (2P1G) lens. The shapes of all lenses are aspheric. By comparison, the overall length of 2P1G lens is much less than that of 3P lens. Furthermore, in FOV the former is 5 degrees larger than the latter. At the same time, in distortion of the maximum field angle, the former is much less. The other aberrations of 2P1G lens are almost same to those of 3P lens. Therefore, in cell phone camera lens design, it’s recommended to adopt one aspheric glass lens to improve the performance and compactness though the cost will become a little higher due to the introduction of aspheric glass lens. However, the cost of aspheric glass lens could be reduced tremendously by a new cost-effective manufacturing method  compression molding technology.

Abstract: With the rapid development of opto-electronics communications, optics, aerospace and other industries, ultra-precision aspheric glass lenses are widely used in middle/high-grade optical opponent because of its high resolution and imaging quality. To achieve ultra-precision molding pressing of micro-lens, ultra-precision mold must be fabricated firstly. In this paper, some key new technologies were proposed for fabricating ultra-precision mold of small-size aspheric optical lens. A method of finite element simulation was employed to predict mould pressing process of the glass lens for correcting molds and improving the formation efficiency. An ultra-precision inclined-axis grinding and error compensation technology was also used to improve form accuracy of micro lens mold.

Abstract: This paper reports a systematic investigation of a nozzle-type ELID grinding characteristics of cemented carbides. Two groups of experimental scheme were carried on by using fine grain cast iron diamond wheel and nozzle-type ELID grinding apparatus. The grinding forces were measured by a dynamometer and the ground surfaces were characterized using scanning electron microscopy (SEM) and atomic force microscope (AFM). The influences of electrolytic and grinding parameters on grinding force were discussed. The material removal mode and micro-morphology characteristics were also analyzed.

Abstract: Glass lens molding is an effective approach to produce precision micro aspheric glass lens at high efficiency. In this paper, a new two-step isothermal glass molding process was proposed. The mechanisms of new molding process were analyzed. Finite element simulation was conducted to analyze the key factors such as the pressing load, die damage, molding time and residual stress of lens during the traditional molding and the two-step isothermal molding. The results showed that the two-step isothermal glass lens molding process may decrease residual stress and improve stress and strain distribution. Furthermore, prolong the service life of die.

Abstract: This paper reported an experimental study on ultra-precision grinding for micro aspherical lens mould. One-point grinding mode and inclined axis grinding mode are employed and investigated in grinding process. Grinding test of a micro-lens mould using form error compensation technique is conducted. The experimental results show that ground micro aspheric mould surfaces with form (PV) around 0.122 µm and a roughness (Ra) less than 2 nm is achieved successfully.

Abstract: Silicon is widely used as the most important substrate material in integrated circuit and micro electronic devices field. Electrolytic in-process dressing (ELID) grinding technique is an effective grinding process especially for machining hard and brittle material. In this paper, using super fine abrasive wheel, sets of ELID cross grinding experiment were conducted for investigating the influences of various grinding conditions including grain sizes, rotation speeds of grinding wheel, rotation speeds of workpiece and ELID conditions on surface roughness during grinding silicon wafers. Surface roughness characteristics of fine ELID cross grinding for silicon wafers were discussed. In an optimized condition, surface roughness of 2.2 nm in Ra can be achieved by using #20000 wheel.

Abstract: ELID (electrolytic in-process dressing) grinding was proposed by one of the authors for automatic dressing the grinding wheel while performing grinding for a long time. It offers a high effective way and has been widely used for grinding hard and brittle optical materials. However, those surfaces produced by fixed abrasive grinding are characterized by considerable sub-surface damage, micro-crack. Magneto-rheological finishing (MRF) is a novel precision finishing process for deterministic form correction and polishing of optical materials by utilizing magneto-rheological fluid. In this paper, an ultra-precision synergistic finishing process integrated MRF and ELID grinding is proposed for shorten total finishing time and improve finishing quality. A lot of nano-precision experiments have been carried out to grind and finish some optical materials such as silicon, silicon carbide, etc. ELID grinding is employed to obtain high efficiency and high surface quality, and then, MRF is employed to improve further surface roughness and form accuracy. In general, form accuracy of ~ λ/20 nm peak-to-valley (P-V) and surface roughness less than 10 Angstrom are produced in high efficiency.

Abstract: In this paper, a new mathematical model and grinding method of ball-end milling cutter are proposed, based on the orthogonal spiral cutting edge curve. The movements of grinding wheel and ball-end milling cutter are presented while grinding rake face. In order to grind conveniently and avoid interference, a conical wheel is also designed and employed to grind the rake face of ball-end milling cutter on a grinder. In order to improve the machining characteristics of ball-end milling cutter, the model of rake face with equal rake angle is established. The software of ball-end milling cutter is developed to design and optimize different shapes of rake face. Furthermore, the simulation analysis on rake face with equal rake angle is carried out to confirm the validation of the mathematical models.

Abstract: This paper proposed a viewpoint to explain why vibration assistance may increase material removal rate (MRR) in vibration-assisted magnetic abrasive finishing process. A series of experiments on vibration-assisted finishing have been carried out. On the basis of these experiments, the finishing characteristics are represented summarily. It was shown that the increase in material rate is mainly due to an increase in material removal per unit working distance.