Research on Key Techniques of Through-mask Electrochemical Machining of Array Structure on Metal Materials

Author:Wang Guo Qian

Supervisor:zhu zuo li han song


Degree Year:2018





With the development of science and technology,metal array structure has been used more and more in the fields of aerospace,electronics,energy,materials science and so on.This kind of structure is often characterized by large number of characteristic structures,dense arrangement and high processing precision.In addition,most of the processing objects are hard alloy materials,such as high temperature alloy,titanium alloy and intermetallic compound,and most of them are thin-walled parts.After processing,no recast layers,no cracks and no deformation are required,which proposes a great challenge to manufacturing technology.Through-mask electrochemical machining(TMECM)is used to limit the processing area by prefabricated mask,and the efficient processing of metal array structure can be realized.Aiming at the technology of TMECM for metal array structure,this paper has carried out research in multiaspect,such as the analysis of electric field and flow field,the proposal of key technology and the research of machining experiment.The main contents are as follows:(1)To carry out the analysis of electric field theory in TMECM,the reasonable mathematical model of anodic dissolution is established.On the different mask structures,the anode current density distribution and the forming process of anode are analyzed by numerical simulation dduring TMECM.The results indicate that there is a significant effect of mask aspect ratio on the anode forming process template.When the mask aspect ratio AR<0.8,section morphology change process of anode is“convex→flat→circular arc concave pit”,and when the mask aspect ratio AR≥0.8,the section morphology change process of anode is“flat→circular arc concave pit”.On the other hand,the greater the aspect ratio of t the mask has the higher corrosion rate of the anode.Therefore,according to the different characteristics of the array structure,the different mask structure of the depth and width ratio can be selected.(2)Double sided cathode-mask electrochemical machining technology and tapered mask hole electrochemical machining technology are put forward to solve the taper problem of array hole structure in TMECM.Among them,double-sided cathode-mask electrochemical machining technology is using cathode-mask to improve perforation efficiency,and double side symmetric processing can significantly reduce the sidewall taper of holes.On the other hand,the tapered mask hole can increase the flow field in the mask hole by increasing the opening angle of the msk hole,and improves the discharge of the electrolytic products in the processing area,so as to improve the stability of the TMECM and reduce the taper of the hole.Through the flow field simulation and machining experiment,it is found that when the opening angle of the mask hole is 140°,the flow velocity in the template hole is higher and the electrolyte flow state is more smoothly.The taper,roundness and the surface quality of the fabricated holes have been obviously improved.(3)The flow field in TMECM of large-area hole array is analyzed and solved.First,the theoretical and experimental analysis of the flow around the compressed cylinder have been conducted during TMECM.The relationship between the transverse spacing L1,the vertical spacing L2 and the diameter D of the compressed cylinder is obtained in TMECM.When the compressed cylinder satisfing L1≤3D,L2≥3D,the electrolyte flow rate can guarantee the quantity and uniformity in the processing area.In subsequent processing experiments,it is also confirmed that a reasonable compressed cylinder arrangement can ensure the processing consistency while ensuring the close fitting of template and workpiece.Secondly,the serpentine flow channel is put forward for TMECM.By distinguishingly designing the serpentine flow channel,the machining area of TMECM can be increased,and the uniformity of the electrolyte flow velocity is achieved in the processing area.Then,in the optimized flow field,the electrical conductivity distribution in the serpentine channel is calculated theoretically in DC machining and pulse machining.It is found that the electrical conductivity difference in pulse machining is very small,and this conclusion is confirmed in subsequent experimental processing.The aperture deviation of the group hole structure is less than 0.05 mm and the roundness error is less than15μm when a large area of hole array are processed in the serpentine flow channel with pulse power supply.(4)In view of the semi-circular profile microgroove array structure required for fiber reinforced composites,the theory and experimental study are carried out in TMECM.By analyzing the structural characteristics of semi-circular microgrooved profile,the forming process of the microgroove are simulated in different mask structures.On the base of the simulated results,the aspect ratio of the mask structure and the material of mask are determined.According to the exposure and development test of dry film,the dry film exposure time of the microgroove structure is optimized to be 2.5 s and the development time is 180 s.On this basis,the microgroove mask is prepared.At the same time,an optimization scheme for the flow field of microgroove mask for electrochemical machining is put forward,which significantly improves the flow rate of electrolyte in microgrooves and improves the consistency of flow velocity in microgrooves.According to the optimization scheme,the design and preparation of special fixture are carried out,and the orthogonal test of micro TMECM is conducted in the fixture.The optimized experimental parameters are obtained for TMECM:voltage of 15 V,pulse frequency of 400 Hz,20%duty cycle,the electrolyte temperature of 45℃.The optimization parameters are applied in the fabrication of microgroove array structure by TMECM.The experimental results show that the radius deviation of the cross section of the microgroove is 4.47μm,and the maximum roundness error is 8.63μm,which can meet the design requirements of the cross-section of the microgroove array.(5)A variety of typical metal array structure electrochemical machining experiments have been carried out,including air-duct damping sleeve in the aeroengine and molybdenum grid structure in RF broadband coating equipment.The machining process has confirmed the electrochemical machining technology of various parts.Through the test of processing results,we can use the TMECM technology to realize the metal array.