Research On Key Techniques Of Shaped Tube Electrochemical Machining

Multiple holes of0.3mm to2mm in diameter,104to105in quantity, diverse cross-sectiongeometries and at divergent oblique angels to the normal direction of the surface in the range of0°to75°, are well applied in key components of aircraft engine. These holes in difficult-to-cut materials arerequired with no micro cracks or recast layers and bring much serious challenge to modern drillingtechnologies. Considerable attention has been paid to reliably producing these fine holes of highefficiency and surface integrity all over the world.Shaped tube electrochemical machining (STEM) removes material by controlled anodicdissolution in an electrolytic cell and produces the workpiece into designed hole shapes via a shapedtube electrode. Inherent characteristics of STED, such as good surface integrity, absence of tool wearand metallurgical defects, suited simultaneously drilling of numerous small holes in difficult-to-cutmaterials, enable itself to be a promising and low-cost process for yielding these holes. Thedissertation focuses on key issues of shaped tube electrochemical machining.(1) The electrochemical drilling technique applying a potential difference between an auxiliaryelectrode and the anode is proposed. An electric model for this drilling process is established toanalysis the current distribution in the machining gap. Simulation and experimental results indicatethat, when the tube electrode is excessively feed, a proper potential difference could diminish the straycurrent attack on the hole exit, lower the sensibility of the exit accuracy to excessive feeding depthand enhance the machining accuracy of multiple holes.(2) Pulsating electrolyte flow is introduced to the electrochemical machining process. Amulti-physics model coupling of electric, heat and transport of diluted species was established tocalculate the effects of pulsating flow on electrochemical machining via the finite element method andthe moving mesh method. Both the simulation and experiments verified that using optimal pulsatingparameters, the heat transfer, the material removal rate, the machining gap uniformity and surfaceroughness are improved. Moreover, optimal pulsating flow in deep hole drilling could enhance theprocess stability, the machining accuracy as well as the maximum machining depth.(3) The insulation coating with good durability is prepared. A computational method based onthe elastic mechanics and interface mechanics is proposed to estimate the distribution of theinterfacial stresses between the insulation coating and metal electrode substrate. Moreover, anelectrode tip structure is presented to reduce the interfacial stress and enhance the coating durability. And the coating adhesion to the electrode substrate is enhanced via the optimized surface rougheningtreatment.(4) An electrochemical drilling system is developed. A three dimensional moving platform ofgantry structure as well as a follow sealing structure is designed to modify the unreliable sealingperformance of the traditional machine. A precise numerical-controlled turntable is designed for themachining of typical components with planar arrayed holes. Moreover, a computer system isdeveloped to control the hardware and software devices of the electrochemical drilling system, whichcould monitor the machining process and recognize the abnormal process status.(5) Electrochemical drilling of multiple holes in typical structures is experimentally processed. Aspecialized tool was designed to fix the row electrode tubes for electrochemical drilling. Withoptimized process parameters, multiple holes in a planar array of8×35, a floating tile simulator withmultiple holes in an arc array of8×27, a trapped vortex combustor simulator with multiple obliqueholes in a planar array of9×90and at an oblique angle of45°, a flow deflector simulator withmultiple oblique holes in a planar array of5×90and at oblique angles of10°,30°and55°, weresuccessfully machined.