Research On Micro-EDM And Its Superhydrophobic Property Of Beryllium Copper Alloy

Micro-gyroscope is the new direction for the development of gyroscopes because of its small size,impact resistance and low cost.There are important practical significances for carrying out the research and product development of strategic micro-gyroscopes.The development of high precision gyroscopes requires the micro-parts with high precision and quality.The influences of size effect and surface effect on the motion characteristics of the moving parts are more and more significant when the size of the micro-parts reduces.Therefore,the manufacture of micro-parts is not only strict in size,but also in surface property,such as anti-corrosion,fluid drag reduction and lubrication.The stable operation of the micro-gyroscope requires microfluidic channel with high surface quality,and the mate structures with high dimensional accuracy and their surfaces with fluid drag reduction.In this dissertation,micro-EDM technology is used to machine micro-holes and 3D micro-structures on beryllium copper alloy which has special properties.And the superhydrophobic property of the surface machined by micro-EDM is also studied.During micro holes-machined by EDM,the cycling velocity of working fluid decreases with the increase of depth ratio,which leads to the discharge debris accumulated in the processing area effecting the stability of the process.In this dissertation,the effects of different working fluid on the high aspect ratio micro-holes machined by micro-EDM on beryllium copper alloy are studied.A new method was proposed to machine high aspect ratio micro-holes on beryllium copper alloy with deionized water as the working fluid.And the micro-holes with aspect ratio of 23.26 at the holes' diameter of 215 ?m are realized.Experimental analysis shows that both EDM and ECM in this process simultaneously.The quality of the end surface and the wall of the micro-holes are poor because of the stray-current corrosion.The shield electrode is used to protected the end surface of micro-holes by transferring the stray-current corrosion form the end surface of micro-holes to the surface of the shield electrode.In situ powder mixed EDM is proposed to improve surface quality of micro-holes.The average surface roughness decreases from Ra 2.65?m to Ra 0.92?m when the boron carbide powders with particle sizes of 3.5-6?m are mixed in working fluid.3D micro-structures are difficult to be machined by EDM due to the electrode wear,especially the micro-structure with curved surface morphology.The effects of EDM layered milling and EDM forming on the micro-ball sockets are studied in this dissertation.The results show that the shape precision and surface quality of micro-ball sockets machined by EDM layered milling are poor because of the long milling path and large electrode wear,which is difficult to meet the performance requirements of the mate parts of the micro-gyroscope.However,the mothed is universal significance for the common ball socket machined by EDM.For preparation of the mate ball sockets in micro-gyroscopes,steels balls with matching relationship are proposed as the electrode in EDM forming.The clamping device based on magnetic adsorption is proposed to clamp the spherical electrode rapidly,which resolves the problem of repeatable positioning accuracy,when the ball sockets are machined by EDM forming.The characteristic of electrode wear and its effects on the machining quality are studied by experiment.The spherical electrode clamped rapidly with high accuracy and mate ball sockets with high accuracy are realized.The superhydrophobic property of the material surface is not only related to the surface energy,but also the micro-topography of material surface.The special material removal method of EDM brings about micro-bulges and micro-craters coexisted on the surface with similar micro-structures.The relationship between the surface morphology of micro-EDM and superhydrophobicity is preliminarily built based on the analysis of surface characteristics machined by micro-EDM and the wetting state of beryllium copper alloy surface.The effects of micro-EDM parameters on surface morphology are studied.The relationship is verified by comparing the theoretical with the actual value of the contact angles.Based on the micro-structures on the surface machined by micro-EDM,flame deposition method is proposed to construct nano-structures on the surface to realize the superhydrophobicity which depends on the micro-/nanohierarchical structures.The method of oil penetration and drying is put forward to improve the stability of the nanostructure based on the capillary force on the aggregation of particles when the liquid evaporates.The experiments show that oil treatment improves the superhydrophobic performance and enhances the surface corrosion resistance,mechanical shock resistance and drag reduction.Compared with the smooth surface of beryllium copper alloy,the inhibition efficiency of corrosion current density and charge transfer resistance can reach 98.77% and 99.38%,respectively.The method for batch preparation of the superhydrophobic surface based on micro-EDM was proposed,which can be extended to various metallic materials.