Research On Key Technique Of Electrochemical Drilling Of Multiple Small Holes

Electrochemical drilling (ECD) is a versatile process for drilling small holes in hard-to-machine metals. The ECD process has been applied in aerospace industries as well as automotive industry to machine coolant channels on aircraft turbine blades, combustion chambers, and apertures on extrusion die mold, etc. In this dissertation, some key technologies in electrochemical drilling multiple small holes are studied.A mornitoring and control system for ECD has been developed by the author, in which the machining current is real-time monitored as the feedback signal to control the machining process with different control scheme. The threshold current method is adopted to ensure short circuit protection and stray current attack control in the hole shape.Fundermantal research on ECD process is carried out systematically. Insulation of electrodes is achieved by electrostatic spraying process with polyethylene terephthalate (PET) powder. Electric field simulation of the side gap shows that the current distribution varies remarkably with the size of insulation layer shape, and appropriate thickness of insulating layer leads to an improvement in hole accuracy and machining stability. Flow model of the electrolyte along the machining gap is also established, based on which, the influence of machining parameters on the current is analyzed theoretically. The experiments were conducted subsequently to show that the machining accuracy and stability were influenced by the process parameters such as insulation thickness, tool feed rate, and electrolyte pressure.In order to improve machining stability of ECD, an electrochemical drilling method with electrolyte extraction has been proposed. Flow distributions along the machining gap with different electrolyte flow pattern indicate that reverse flow using electrolyte extraction distributes the pressure more uniformly and hence leads to a more stable machining process. Machining characteristics of electrolyte extraction are investigated experimentally. To minimize the radial overcut of machined hole by electrochemical machining with electrolyte extraction, the orthogonal design is used to optimize process parameters such as initial machining gap, voltage, tool feed rate, and electrolyte concentration. Good results have been obtained in the experiments with optimized parameters.A method of electrochemical machining of inclined holes using wedge shaped electrode tubes is also developed. Flow simulation of the machining area with and without the wedged tip at different machining inclination angle indicates that uniformity of electrolyte flow distribution along the initial machining gap decreased sharply with machining inclination angle increasing. In the case of using wedged electrode, the flow distributes more evenly comparing to normal electrode. Wedged electrode proved its usefulness to enhance the ECD accuracy through the decrease and elimination of sparking and striated dissolution.In the last section of this dissertation, a series of research on electrolyte manofild simulation and optimization are carried out. Process stability and machining accuracy of ECD on multiple holes were affected by the size of electrolyte manifolds. Flow of the electrolyte along the manifold was modeled to analyze the main parametesrs affecting the uniformity of the electrolyte distribution. Machining tests with electrode arrays were carried out to obtain the optimal manifold structure which suits the electrochemical drilling of multiple holes. With optimized manifold structure, array holes with good uniformity and stability have been machined, short circuit was diminished during the machining process.