Research On The Key Technology Of High Performance Structural Parts By Pulse Electroforming With Microbeads-Adaptive-Assisted-Grinding

Electroforming is a process of depositing metal on the surface of a conductive cathode core using electrochemical principles.Traditional electroforming techniques are affected by factors such as hydrogen evolution and impurities,which can easily produce defects such as pinholes,burrs or nodules,affecting the quality and performance of the deposition layer.Using microbeads friction-assisted technology that using microbeads to grind and impact on the surface of the cathode can effectively remove these defects.However,when using the cathode vertical rotation device for electroforming processing and manufacturing,the microbeads are influenced by their own gravitational potential energy and tend to accumulate at the bottom of the anode basket.As the thickness of the deposition layer increases,a large number of microbeads squeeze each other to produce excessive pressure on the surface of the cathode,resulting in excessive internal stress in the cathode deposition layer,which affects the performance of the deposition layer.At the same time,the accumulation density of microbeads is much greater than the density of electroforming fluid,which makes the movement ability of microbeads weaker or even unable to be disturbed,resulting in excessive friction between the cathode and microbeads,which eventually forms dents and grooves defects on the surface of the deposition layer,affecting the surface quality and performance of the deposition layer.In order to solve the above problems,this paper proposes a microbeads-adaptive-assistedgrinding technology,in which a flexible support medium with elasticity is added between the inner wall of the anode basket and the cathode.And this paper choses the high-density sponge as the flexible support medium.Ceramic microbeads are then added between the flexible medium and the cathode.When the thickness of the deposition layer increases continuously,the flexible medium will be compressed,which provides a buffer space for the extrusion of the microbeads and the growth of the deposition layer and reduces the excessive pressure generated by the microbeads on the surface of the deposition layer.At the same time,by supporting the grinding of the microbeads on the cathode surface with a flexible medium,the friction of the microbeads can be kept stable.So the defects such as dents and grooves can be avoided,thus improving the quality and performance of the deposition layer.Meanwhile,the use of flexible medium can greatly reduce the amount of microbeads used,and control the electroforming process and improve the quality of the deposition layer.In addition,the combination of pulse electroforming technology and microbeads-adaptive-assisted-grinding technology plays a better role in refining the grain,and the nanocrystalline nickel structure is obtained through the experiments.In this paper,theoretical modeling and analysis are carried out based on the microbeadsadaptive-assisted-grinding technology,and an electroforming nickel experimental device is developed and built independently.Firstly,the basic control experimental of the key technology of microbeads-adaptive-assisted-grinding electroforming is carried out.The experimental results show that compared with traditional free microbeads-assisted-grinding electroforming,the deposition layer obtained by microbeads-adaptive-assisted-grinding is free of defects such as pinholes,burrs or nodules,has fine and dense and uniformly distributed grains.And the surface of the deposition layer is flat and smooth without the defects such as dents and grooves.And the surface brightness is higher,the microhardness is increased by about 1.1 times and the surface roughness is reduced by about 35%.Secondly,the influence factors on the performance of pulse electroforming nickel with microbeads-adaptive-assisted-grinding are researched by experiments.It is carried out to investigate the effects of changes in the average current density,duty cycle,pulse frequency and cathode speed on the surface quality and mechanical and physical properties of the nickel deposition layer through SEM,microhardness,surface roughness,XRD and cross-sectional metallographic morphology of the deposition layer.The experimental results show as follows.(1)Below the limit current density,increasing the average current density can refine grains,reduce the microhardness,improve the surface roughness of the nickel deposition layer,reduce the intensity difference of the crystal anisotropy.So the uniformity and the compactness of the deposition layer is better.When the average current density is 3 A/dm~2,the minimum grain size is 29.33 nm.However,when the limiting current density is exceeded by the average current density,the grinding effect of the microbeads is weakened and the coarse crystallisation effect of the current is stronger.So the grain size of the deposition layer is larger and the number is less.And it decreases the microhardness and increases the surface roughness and the intensity difference of the crystal anisotropy,so the uniformity of the deposition layer is poor.(2)As the duty cycle continues to increase,the grain size becomes larger,the columnar crystal is obvious.And it decreases the microhardness,increases the surface roughness and the intensity difference of crystal anisotropy,so the distribution of the deposition layer is not uniform.When the duty cycle is 20%,the quality and performance of the deposition layer is optimal,with a microhardness value of 437.6 HV,a surface roughness value of 0.057 μm and a grain size of27.57 nm.(3)As the pulse frequency continues to increase,the grain size becomes smaller and more numerous,the columnar crystals are reduced.It increases the microhardness,decreases the surface roughness and the intensity difference of crystal anisotropy,so the grain distribution of the deposition layer is relatively more uniform.When the pulse frequency is 2000 Hz,the quality and performance of the deposition layer is optimal,with a microhardness value of 458.8 HV,a surface roughness value of 0.05 μm and a grain size of 24.86 nm.(4)When the cathode rotational speed is 5 r/min,the grinding effect of the microbeads is weakened,so the grain size is larger and the number is less,the columnar crystals are obvious,the microhardness is lower,the surface roughness is higher,and the(200)crystal shows an obvious preferred orientation.When the rotational speed is 10 r/min,the grinding effect of the microbeads is strong,so grain size of the deposition layer is only 22.83 nm,the microhardness increases to 461.9 HV,and the surface roughness decreases to 0.045 μm.When the rotational speed is 20 r/min and 30 r/min,the rapid speed increases the friction between the cathode and the microbeads,so the surface of the deposition layer is relatively smoother.