Fundamental Experiment Research On Electrochemical Grinding For Titanium Alloys

Because of high strength ratio, high-temperature resistance and corrosion resistance, titanium alloys are ideal materials in such industries as aviation, aerospace, marine, petroleum, and chemical. However titanium alloys are materials difficult to machine. There are the shortcomings of rapid tool wear, high processing temperature, serious surface hardening and residual stress when machining it mechanically, and it is difficult to ensure the integrity of the workpiece surface. When electrochemical machining titanium alloys, it’s prone to cause the phenomenon of stray current corrosion and hydrogen embrittlement.As a combined process technology of electrochemical machining and mechanical grinding, electrochemical grinding(ECG) was developed rapidly in1960s. The removal of material in ECG mainly depends on the electrolytic dissolution, and the grinding wheel is used to cutting the passivation film adsorbed on the metal. The workpieces machined by electrochemical grinding have integrated surface characteristics. Titanium alloys have a good peculiarity of self-passivation. In the process of electrochemical machining for titanium alloys, the surface of workpiece is prone to produce a layer of oxide passivation film which has properties of extremely high resistance and high compactness. The hardness of passivation film is far lower than the base metal. The destruction of the passivation film and the restoration of base-metal’s chemical activity depend on the activity of electrolytes. When using the method of electrochemical grinding to machine titanium alloys, the passivation film is removed under the action of mechanical scraping. This method can take the advantage of the characteristics of high precision of grinding and high efficiency, no tool wear and no contact pressure of electrochemical machining. It can ensure the dimensional accuracy of parts and the integrity of the surface. So we can solve the problem of hard machinability of titanium alloys through the method of electrochemical grinding.In this paper, the material properties and present processing status of titanium alloys are described, and both of the research status and basic theories of ECG are summarized. A method using conductive grinding wheel as a cathode of ECG to machine titanium alloys is proposed. The anodic polarization curves of titanium alloys TC18in different electrolytes are measures by electrochemical method, and the passivation properties of titanium alloys TC18are analyzed and studied. All of these provide’a theoretical basis for the electrolytes in electrochemical grinding titanium alloys. The electrochemical grinding system is designed and built, including the function planning, the design of main structure and control system. The technological rules of electrochemical grinding titanium alloys are studied by the method of single factor experiment. The conductive grinding wheel and processing parameters are selected, and the workpiece clamping tool is designed. In the single factor experiment, the influencing factor of surface roughness and material removal are discussed, such as machining voltage, feed rate, electrolyte flow rate and cut depth.