Papers by Author: Li Li

Abstract: Micro milling process is more favorite than other processes for its unique advantages in ultra-precision machining of miniature components with intricate three-dimensional geometrical feature made of various materials. Aiming at micro milling applications, a three-axis desktop milling machine tool with linear motors and nano-meter linear scales has been introduced. Natural granite is used as the frame material and air-bearing cylinders are used for z-axis gravity balancing. Finite element method is applied to the design and optimization of the machine structures. The designed machine adopts linear motors and 5nm resolution linear scale using an open control architecture. The workspace is 100mm×100mm×100mm and the overall size is 610mm×650mm×630mm. Experimental evaluations show the sub-micron machining feasibility of the introduced machine.

Abstract: Electrochemical micro-machining (EMM) has become one of the main machining methods for production of miniaturized parts and components. Utilizing the developed EMM set-up, the effects of ultrasonic wave frequency on characteristics of localized dissolution and accuracy of micro-hole in EMM are investigated and evaluated. The experiment results demonstrate that the accuracy of micro-hole and characteristics of localized dissolution can become better with the increase of ultrasonic wave frequency. The accuracy of micro-hole machined by 26KHZ can improve about 30% than that by 16KHZ. Moreover, the ability of localized dissolution by 26KHZ can be increased about 27%-30%.

Abstract: This paper presents an experimental investigation of the machining characteristics of IN718 nickel-based super alloy in wire electrical discharge machining (WEDM) process. During experiments, parameters of discharge current and pulse on time were changed to explore the effect on various aspects of the surface characteristic. Scanning electron microscopy (SEM), surface roughness and micro hardness tests were performed. Experimental results reveal that the surface roughness will increase with the increasing of current and pulse duration. Micro hardness tests show there is no hard phenomenon.

Abstract: In order to improve the corrosion resistance of sintered NdFeB magnet, experiments are done by the new process which involves ultrasonic electroforming Ni–P alloys. The influence of ultrasonic on electroforming Ni–P alloy on NdFeB was studied by using microscope, adhesion test and NaCl solution immersion test.The results showed that the Ni–P alloy deposit on NdFeB is rough and has poor adhesion without ultrasonic agitation; However, the Ni–P alloy deposit on NdFeB with ultrasonic agitation has the following advantages: uniform and smooth deposit grains, strong adhesion and good corrosion resistance.

Abstract: In this study, the machining parameters of electrical discharge machining (EDM) are varied to study the effects of electrical discharge energy on material removal rate and surface roughness of NdFeB magnet. Moreover, the micro-cracks on the machined surface induced by EDM are also examined. The experimental results reveal that the MRR increases with the electrical discharge energy. The surface cracks on the machined surface are more serious when the discharge energy is higher. Thus, using EDM process to machine sintered NdFeB magnet depends on setting the machining parameters to prevent surface crack.

Abstract: A new kind of ultrasonic machining is proposed for sintered NdFeB permanent magnet. Experiments were carried out on self-made equipment. Test results showed that the MRR would increase with the amplitude of tool, static load and the size of abrasive grain at certain range. This kind of ultrasonic machining is a suitable method for machining NdFeB material.

Abstract: Electrochemical micro-machining (EMM) appears to be very promising as a future micro-machining technique, since in many areas of applications, it offers many advantages, which include excellent machining precision and control, high machining rate, perfect surface quality and a wide range of materials that can be machined, regardless of their strength and toughness. In the paper, a new style EMM equipment for micro-holes is presented. Double vertical column style structure is chosen as the main mechanical structure of the equipment, which has the advantage of excellent structure rigidity, compact framework dimension as well as good maneuverability and maintainability. In order to verify the reliability of this EMM equipment, some measurement works including static measurements, assembling interferences checking and kinematics simulation have been done. Furthermore, the low-speed kinematics characteristics of the developed EMM equipment are concentrated. The kinematics simulation results indicate that the developed EMM equipment can satisfy the requirements for low-speed motion and anti-interference characteristics of EMM process.

Abstract: This paper presents an experimental investigation of the machining characteristics of sintered NdFeB permanent magnet using a combination process of electro-discharge machining (EDM) with ultrasonic machining (USM). Concentration of abrasive in the dielectric fluid is changed to explore its effect on the material removal rate (MRR). MRR of EDM /USM, conventional EDM are compared, machined surface characteristics are also compared between them. It is concluded that the combination EDM/USM process can increase the MRR and decrease the thickness of the recast layer. In the combination process, an appropriate abrasive concentration can improve its machining efficiency.

Abstract: In this study, the electrical discharge machining (EDM) of sintered NdFeB magnet was investigated. The surface characteristics were studied in terms of machining parameters. Correlation between the surface roughness, hardness, recast layer and the machining parameter were analyzed. Results show that an excellent machined finish can be obtained by setting the machine parameters at low pulse energy. Low pulse energy reduces the frequency of bursts of dielectric fluid and melt expulsions.

Abstract: Sintered NdFeB permanent magnet is widely used in many areas because of its excellent magnet property. In this study, the machining parameters of electrical discharge machining (EDM) are varied to study the effects of electrical discharge energy on material removal rate and surface roughness of NdFeB magnet. Moreover, the micro-cracks on the machined surface induced by EDM are also examined. The experimental results reveal that the MRR increases with the electrical discharge energy. The number of surface cracks on the machined surface increases with the enhancement of discharge energy Thus, using EDM process to machine sintered NdFeB magnet depends on setting the machining parameters to prevent surface crack.