Application And Fundamental Research Of Multiple Holes By Electrochemical Machining Using Mask

Structures of multiple micro-holes are applied widely in the field of aviation, space, electronics, instrument, textile, printing, medical, and automobile, such as optical fiber connector, spinneret, electron microscopic grating, micro-nozzle, filter screen, cooling holes in jet turbine and printed circuit boards. Various techniques have been developed to produce multiple micro-holes in different ways such as mechanical drilling, laser beam machining (LBM), electrical discharge machining (EDM), through mask electrochemical micromachining (TMEMM) and electron beam machining (EBM). Each of methods has its inherent disadvantages for machined micro-holes in sheet metal. Mechanical drilling presents several problems related to internal stress and a burr. LBM has the advantage of high machining efficiency, and but it causes the formation of heat-affected zones and microcracks on the workpiece. The tool electrode wear takes place during the EDM process. TMEMM involves many working procedure.A novel processing method, electrochemical machining (ECM) using mask, is presented in order to manufacture multiple micro-holes in sheet metal at the same time. The thesis would provide a new idea for the fabrication of multiple holes.Basic researches have been carried out, and tube for air coolant in guide vane of a new aeroengine is machined by the technique. This dissertation consists of six sections. The main contents are as follows:(1) The ECM using mask is proposed. According to theories of electrochemical anodic dissolution, the mask pattern will be transferred to the workpiece in an electrolytic cell. During the machining process, the stencil mask is closely clung to the surface of the workpiece rather than bonded to the workpiece. The proposed microstructure fabrication technique offers some unique advantages over other technology such as electric field distribution and the fashion of electrolyte flow, simple and easy implementation and low cost.(2) On the basis of analyzing the characteristics of the proposed technology, the experimental system has been set up which consists of mask fabrication unit, electrolyte circulating system, electrode holder and power supply. The microstructures with multiple micro-holes are fabricated fast and efficiently which fulfills the requirements of the actual processing.(3) Based on the theories of electric field, three models of electric field in interelectrode gap are built respectively. Finite Element Method is used to solve the model, and analysis of current density distribution on the workpiece surface is carried out. For better understanding the process, the dissolving process is analyzed and numerical simulation is verified experimentally. The three machining mode are observed comparatively, and the best mode, (ECM using a dual cathode), is selected out. The current density distribution is possibly influenced by the following parameters: thickness of the copper sheet, thickness of insulation layer, hole diameter, hole space and applied voltage. In this thesis, the influences of five parameters on the machining accuracy are discussed during EMM using a dual cathode.(4) An electrolyte flow mode, active distributary mode, was proposed. An incompressible flow field mode describing the distribution of electrolyte flow in the interelectrode gap is developed and verified at positive flow or side stream. A new electrolyte flow mode is named as the beam positive flow which is established and analyzed. Compared with the traditional positive flow, the flow mode overcomes low velocity in the center of processing zone results in a uniform distribution of electrolyte flow. The results show that the side stream mode of active distributary improves the holes diameter consistency and machining accuracy contracted to the side stream mode of passive ditributary. A two-dimensional incompressible flow field mode of serpentine channel is carried out, and microstructure with good uniformity of diameters is obtained.(5) According to characteristics of ECM using mask, two process methods were presented to improve the machining accuracy. The effects of auxiliary anode and mask wall angle on the machining accuracy are discussed. The holes taper is decreased by using the auxiliary anode. The process analysis and experiment results show that mask wall angle has great influence on the eroded workpiece surface topography. The holes diameter consistency is greatly improved, and the holes taper are reduced with the mask wall angle increasing.6) ECM using a dual cathode and the active distributary mode of flow field are applied in the development of a certain tube for air coolant in guide vane of an aeroengine. Because the requirement of high machining accuracy, no burr, low cost and mass production of the tube for air coolant, it was difficult to be machined by other technology. The results revealed that the machining accuracy could be improved to 0.06mm with the technology.