Research On Micro-hole ECDM Machining Technology Of Single Crystal Material For Aero-engine

The single crystal superalloy is prepared by directional solidification process.Its transverse grain boundaries perpendicular to the stress axis are eliminated,reducing the application of low melting point elements that can be used to strengthen the grain boundaries,improving the high temperature resistance.Single crystal superalloy is mainly used for the preparation of aero engine turbine blades and other components.A large number of micro-hole structures are distributed in aero-engine key components,in particular,in the aero engine turbine blades.The processing requirements of the film cooling holes are without burr,no micro-cracks,no recast layer,thus they can not be achieved by using the traditional processing methods.Electrochemical discharge drilling(ECDD)combines the discharge machining and electrochemical machining and possesses the advantages of both technologies,it can achieve the processing of single crystal materials and other materials difficult to machine.The method is expected to achieve the requirements of the film hole processing.In this paper,in order to improve the quality of electrochemical discharge machining of single crystal material,a large number of experimental analyses and researches are carried out.The main studies and contributions in this paper are as followings:(1)The researches on the single crystal material DD6 were carried out to optimize the electrical parameters and working fluid concentration of single crystal ECDD and explore the effect of hybrid machining on organizational structure of single crystal.The basic experiments were carried out,the effect on the hybrid machining performance of single crystal material was analyzed by obs erving the morphology of single crystal DD6 micro holes,cross section taper and wall recast layer.(2)In order to improve the processing quality of single crystal micro holes,the influence of the flow stability on the micro-hole surface quality during processing was studied.The processing mode of constant flow was proposed and the metering pump circulation system was established to improve the flow stability during processing.Experiments were carried out to investigate the effect of flow on the micro hole diameter,processing efficiency,electrode loss,and the removal effect of recast layer.(3)In order to remove the residual recast layer at the exit of the hole,the methods of tube electrode feeding pause and the conductive contrast layer were used.The hybrid machining experiments with different feeding pause times on single crystal were carried out to study the effect of feeding pause times on the removal of recast layer.At the same time,the processing efficiency,the morphology,the diameter and the waveforms of voltage and current during the processing were analyzed.The preparation of different conductive materials has been tried and the conductivity and fluidity of the conductive materials have been investigated.Experiments show that the graphite conductive paste has good filling and removal performance in turbine blades with complicated internal structure,which is helpful for the effective removal of the recast layer at the exit of single crystal micro holes by ECDD.