Research On Key Technologies Of Micromachine For Electrochemical Micromachining (ECMM) With Nanosecond Pulse Voltage

Electrochemical micromachining (ECMM) is a promising micromachining technology, since it offers several advantages which include absence of machining forces and residual stresses, no tool wear, good surface finish, adaptability to various processes, and ability to machine complex 3D micro features with the material removal/addition unit at the atomic scale (0.1nm or even smaller).To realize ECMM, the foremost thing is to prevent the stray erosion caused by the distributing electric field in the conventional ECM, which means the localization of electrochemical reaction should be improved. Motion platforms (linear stages and rotation stages) with high accuracy and resolution in an ECMM machine tool are needed as well to meet the requirements for micromachining. Based on the application of ultrashort voltage pulses to the localized electrochemical reactions, this study is aimed at developing an ECMM setup to achieve nanosecond voltage pulses ECMM and focuses on several key issues of electrochemical micromachine.the theory of ultrashort voltage pulses ECMM are summarized from the basic principle of electrochemistry and the related literature, which explains the principles for the micrometer and submicrometer machining by using ultrashort voltage pulses in ECMM. The equivalent electric circuit of electrochemical polarization is formed, and mathematical models describing the forming laws of ECMM are established. Simulations on the ECMM are carried out.An electrochemical machining system is developed. The elements of the machine setup are descirbed in detail, which includes the drive of the nanometer accuracy and resolution, power supply, machining chamber, microscope, etc. The control strategy and hardware and software for the control system are presented as well. A circuit enabling the transformation of the voltages between the cathode and anode is specially designed to solve the problems encountered in direct sampling of the ultrashort voltage pulses because of their very high equivalent frequencies. Thus autoidentification and controlling of machining is achieved.This dissertation proposes a novel concept of rotary flexural bearing that is based on the motion principles of elastic flexures to provide rotational oscillations of one complete revolution, therefore the repeatablility of the rotary motions guided by this type of bearing is expected to be very high (atomic scale), thus the error motions with extremely high accuracy (nanometer or less) can be obtained. The bearing is also characterized by smooth motions, no mechanical wear and no lubrication requirements, no gaps or interfaces, in addition to its compactness. The overall conceptual design of the bearing is presented. A design analysis on the various aspects of the bearing is provided, including material selection, stress analysis and calculations (such as nonlinear finite element analysis, static and fatigue strength designs), motion error analysis and error reduction strategy, parametric design, etc. A prototype bearing is presented. The machining route of the bearing tube is proposed from the analysis of the fabrication characteristics. Low speed Wire EDM (LSWEDM) is chosen as the machining method of the flexural bearing. Technical measures to reduce the residual stresses and strengthen the stiffness (especially the torsional stiffness) of the bearing tube are adopted. Dimensional accuracy of±5μm is obtained over the 150μm thickness for the bearing flexures and a variation of less than 3μm is achieved for the flexures of opposing sides, and surface roughness Ra of 0.3μm is obtained for the flexures of the entire bearing. The assembly methodology focuses on the reduction of radial motion error caused by the tilt angle between axes of the inner bearing tube and the outer bearing tube due to the"error enlargement effect". A special assembly measure is suggested to confine the location of the both ends of the inner bearing tube, thus preventing the"error enlargement effect"from happening. The basic principle for component selection or designing of the spindle system is presented. The vibration characteristics of the bearing is theoretically analysed and experimentally measured. Several techniques concerning the micro spindle motion error measurements are discussed and compared to provide useful references for future use of motion error estimation or motion error compensation.On-the-machine tool-making methods are overviewed. Micro cylindrical electrodes with diameterφ20μm or less are obtained by using the electrochemical fabrication method with constant current density; The basic methods and key operating steps towards successful ECMM machining of micro features in stainless steel (SS) using nanometer voltage pulses are discussed, which is important to further unveil the machining mechanisms of ECMM and to lay foundation for future practical application of ECMM machine tool.