Papers by Author: Xiao Hai Li

Abstract: Based on the topography of micro WEDM surface, lubricant retention, bearing capability, and sealing performance were evaluated by using the surface bearing index, lubricant retention index of core area, and lubricant retention index of valley bottom respectively. The results show that the micro WEDM surface with the characteristic of isotropy texture is beneficial to store lubricating oil, and the lubricant retention property is superior to that of the traditional machining surface.

Abstract: A new process of fabricating microstructures through micro electrochemical milling (micro EC milling) is proposed. The experiment equipment with a new type of ultra-short pulse supply was developed for micro EC milling. By controlling the movement track of simple micro tool electrode rotating at high speed on NC three-axis feed worktable, microstructures with high precision can be milled by micro-ECM under ultra-short pulse current. Micro EC milling can greatly improve the machining status in the tiny machining gap and thus make machining stable by simple rotary column electrode. The process of the NC generating micro-ECM integrating CAD/CAM technology is studied. G code for machining complex microstructures can be generated by the universal CAD/CAM of traditional milling based on UG software. Last, Microstructures with high precision were milled by this process, for example the micro trench with width of about 50μm.

Abstract: Water-lubricated thrust bearing is a key component of certain main pump motor. In this paper, the right structure of water-lubricated thrust graphite bearings is designed based on low viscosity hydrodynamic lubrication theory by combining the bearings running working condition, and the frictional accessory material is also determined by theoretical analysis and test. The factors influencing lubrication performances of water-lubricated thrust bearings are analyzed; the methods improving lubrication performances are put forward to guarantee that water-lubricated thrust graphite bearings have the good lubrication performances, good carrying capacity and longer work life.

Abstract: This paper describes a new method of die surface modification by ordinary Electrical Discharge Machining (EDM) tool. First, the principle of this method is studied. Secondly, the technology and characteristics of the die steel coating are discussed in detail based on lots of experiments, and the results show that the die steel characteristics are improved evidently by using EDM. At last, the technology is applied to the punch die initially, and it can be drawn that the life of the coated punch die is improved evidently compared with the non-coated punch die through the punching test.

Abstract: The five-axis linkage WEDM system with the rotate-swing-swing worktable accessories was developed to machine the ruled curved surface parts, and the component, motion parameters and motion laws of this system were analyzed. According to analytic geometry of space, the forming principle of ruled curved surface was analyzed, and the accordingly mathematics models of the five-axis linkage WEDM system were established, and the common functions were illustrated with examples. At last, the typical samples were machined in accordance with the mathematics models, the ideal machining results also prove the correctness of the mathematics models established, which widen the range of processing by WEDM, solve the difficult problem of space ruled curved surface parts.

Abstract: The research aims to develop an experimental equipment to carry out in depth research on micro electrochemical machining (micro-ECM). The mechanisms of ultra-short pulse current micro ECM are discussed. As a consequence, lower machining voltage, lower passivity electrolyte concentration, high frequency short pulse power supply and micro rotating tool electrode at high speed have been synthetically used to localize the dissolution area during micro-ECM. The machining gap can be kept at a very small value, and the better resolution of machined shape is achieved by using a novel designed electrode gap control system and the effective utilization of ECM for micromachining is fulfilled. The experiments on microstructure by micro-ECM milling on stainless steel plate are conducted. The micro structures milled on 304 stainless steel foil with 300μm thickness with high precision and high aspect ratio are achieved, and the width of micro beam is about 60μm.

Abstract: A new process of fabricating microstructures through micro electrochemical milling (micro EC milling) is proposed. By utilizing side wall of simple micro tool electrode rotating at high speed like micro mechanical milling and controlling the movement track on NC three-axis feed worktable, microstructures with high precision can be milled by micro-ECM under high-frequency short-pulse current. Micro EC milling can greatly improve the machining status in the tiny machining gap and thus make machining stable by simple rotary column electrode. The influence factors on the accuracy of micro-EC milling were investigated through process experiments, such as feed speed, machining voltage and kind of electrolyte. The process of the NC generating micro-ECM integrating CAD/CAM technology is studied. G code for machining complex microstructures can be generated by the universal CAD/CAM of traditional milling based on UG software. Last, Microstructures with complex shape were milled by this process, for example the micro bend beam with width of about 50μm, and its aspect ratio is about 6.

Abstract: This research work aims to explore the feasibility of applying electrochemical machining (ECM) to micromachining. An experimental setup for micro-ECM has been developed. Lower machining voltage, lower concentration of passivity electrolyte, high-frequency short-pulse power supply and micro tool electrode rotating at high speed have been synthetically adopted to localize the dissolution area in micro-ECM, so the machining gap can be kept at about 10 μm and the better resolution of machined shape is achieved. A micro-hole with 45μm diameter is drilled on the stainless steel foil with 100μm thickness. A new approach of fabricating microstructure by micro-ECM milling with a simple micro electrode is proposed, and the micro beam with width of about 50μm which has high precision is fabricated by micro-EC milling on the stainless steel foil (1Cr18Ni9Ti) with 300μm thickness. A mathematics model has been established, which can be used to simulate the process of shaping workpieces in the process of micro-ECM.

Abstract: Electrochemical machining (ECM) has been rarely applied in micromachining because the electric field is not localized. In order to explore the feasibility of applying ECM to micromachining at micro to meso-scale, an experimental setup with precision control over electrochemical micromachining (EMM) was developed, which is in fact a multifunctional machine tool. The micro tool electrodes for EMM can also be fabricated by micro electrical discharge machining (EDM) on the same machine tool. A high-frequency short-pulse micro-energy MOSFET power supply was designed. Lower machining voltage and lower concentration of passivity electrolyte are utilized together to localize dissolution area in EMM. A micro hole 45 ,m in diameter was drilled by EMM on stainless steel foil with 100 μm thickness. A new approach of fabricating microstructures by means of EMM milling using a simple micro tool electrode is proposed, and a shaped hole and a micro cantilever beam with high precision were acquired by EMM milling. The satisfactory process results indicate the potential capability of EMM for higher machining accuracy and smaller machining size.

Abstract: To perform several micro-machining on same machine tool, a micro machining equipment was researched and developed. The equipment adopts some high and new technologies. It is equipped with high precision XYZ stage, a spindle with high rotation accuracy and variable rotation speed, a granite worktable, a block electro discharge grinding unit for machining micro rod, a ultrasonic vibration unit for workpiece vibrating, a high frequency pulse power supply for micro-ECM and a video microscopic system with high enlargement factor. The equipment can perform micro electro discharge machining (EDM), micro electrochemical machining (ECM), micro ultrasonic machining (USM) as well as their combination. It can also machine 3D microstructures. A series of experiments were carried out. Using micro-EDM, micro rods with the diameter of less than 5µm were ground on block electrode, micro holes and 3D microstructures were obtained. Shaped holes were machined by using combination of micro-EDM and micro-USM. A micro hole with the diameter of 100µm was machined via micro-ECM.