Fundamental Research On Electrochemical Trepanning Of Diffuserand Application

Aero engine technology is known as the pearl of modern industry crown,and the development of aeroengine represents the industry base and technology levelof a country.The manufacture technology of aero engine components has been the research hotpoint in mechanical engineering,for their high requirement of machining quality and accuracy.With the improvement of aeroengine performance,integral components,combining blades with disk together and made of hard-to-cut material,have been widely used in recent years.Applications of integral components,such as integral diffuser,result in higher challenges faced to the processing technology.Different from other machining processes,electrochemical machining(ECM)provides a new method to remove material by electrochemical dissolution.ECM can be used to machining hard-to-cut material regardless of its mechanical property,without recast layer and cutting stress existing on the manufactured work-piece.ECM also has the advantages,such as high efficiency and lowtool cost.Because of these properties,ECM process has becomeone of the key technologies to manufacture blades of diffuser.Electrochemical trepanning is a specific form of ECM process,which is usually used as the finish machining of straight blades or the rough machining of twisted blades.In this paper,studies concentrating on problems of flow field optimization,stray corrosion control,electrode design and machine tool develop have been conducted.The application of electrochemical trepanning was finally conducted on process of an integral diffuser of a new turboshaft engine.The major contents of the dissertation are as follows:(1)The flow field optimization of electrochemical trepanning based on forward flow mode was investigated.To solve the problems such as high flow resistance and divergency,a method for enhancing forward flow field by optimizing the cathode structure was presented in this paper.By adjusting the width of internal hall,the radius of cathode tip,and the insulation coating of cathode block,the property of flow field is improved.The experiments were carried out,and results showed that stability and effiency of machining process were improved.(2)A new lateral flow mode was proposed to process the blades by ECM.Comparative study of flow field simulation of both forward and lateral flow mode was carried out,results showed that,the uniformity of electrolyte flow in processing zone was enhanced,and the electrolyte flow in non-processing zone was weakened in lateral flow mode.Comparative study of experiments was also carried out,results showed that flow marks at the hub surface was eliminated,as well as the machining quality of blade was improved in lateral flow mode.(3)The method for restricting the stray corrosion by a picgraphic insulation sleeve was investigated.The electrochemical trepanning proscee based on lateral flow mode was simulated,and the protruding length of picgraphic insulation sleeve was optimized.With the help of the picgraphic insulation sleeve,the side gap is controlled to a small size,which is beneficial for limiting the affected region of stray current and improving the surface quality of blade.(4)A new method of cathode design oriented to the entire profile of blade was proposed.In this paper,the forming regularity of electrochemical trepanning was investigated,and programe for calculating the cathode profile by desired blade shape was built utilizing the Finite Element Method(FEM).By this method,the cathode design cycle is shortend and the machining accuracy is improved.(5)A machine tool for electrochemical trepanning was developed.The machine tool was designed with double working platforms to fabricate an aero engine diffuser,which has both radial blades and axial blades.(6)Application of electrochemical trepanning was conducted.Based on the preliminary study,an integral diffuser of the new turboshaft engine was manufactured.The electrochemical trepanning technology was successfully used to fabricate large scale blades,and the process cycle was shorted by a large scale compared with traditional cutting process.