Research on Shaped Tube Electrochemical Machining of Holes/Grooves
Author:Wang Xin Di
Supervisor:qu ning song
Shaped-tube electrochemical machining(STEM)is a branch of electrochemical machining(ECM).In this technique,a hollow metallic tube is used as both the electrolyte nozzle and the cathode.The workpiece material is removed through electrochemical dissolution.Other than the common advantages of ECM,such as good surface quality,disregard of the hardness of the material,no cutting force,STEM is also known for the high localizion and flexibility.After applying an insulating layer on the outter wall of the tube,deep-small holes can be fabricated efficiently.By controlling the movement of the nozzle and the machining parameters,grooves can be produced.In this paper,endeavors are made to improve the machining quality and machining ability of STEM.(1)In electrochemical drilling using neutral electrolytes,the insolubale products in the machining area will inhabit the refreshment of electrolyte,leading to the deterioration of the machining quality and stability.To alleviate this situation,a method of electrochemical drilling with constant electrolyte flow is proposed.The experimental results show that compared with electrochemical drilling with constant electrolyte pressure,the feed rate,hole quality and machining stability are improved notablely when constant electrolyte flow is applied.(2)In jet electrochemical groove milling,the low current densities in the edge area are responsible for the stray corrosion on the groove edge and the decreased localization.To reduce the stray corrosion on the edge,the jet reflection shape is adjusted.The interrelation between the machining parameters,jet reflection shape and edge condition is investigated,based on which,grooves with sharp edges are produced successfully.In addition,electrochemical milling with multiple-passes is applied to obtain grooves with both sharp edges and good surface quality and deep grooves with sharp edges.(3)To investigate the possibility of applying STEM as a post process of laser rapid forming(LRF),the electrochemical behaviors of as-deposited LRFed Inconel 718 alloy are studied.Based on the special microstructure of LRFed alloy,the influence of surface orientation and laser power on the polarization behavior,electrochemical impedance and current efficiency is investigated.Results show that within the selected range,differences in the surface orientation and laser power hardly produce any notable influences.However,the surface topography after dissolution exhibits anisotropy.In the vertical surfaces,layer band structure is distinguished,which will influence the surface quality.Further research shows that the height of the layer band structure and the Ra value of the machined surface decrease with the increase of current density.(4)Based on the investigation of the electrochemical behavior of as-deposited LRFed Inconel 718 alloy,STEM is applied.It is found that in hole drilling process,layer bands are bound to appear on the sidewall,and the surface quality would be inferior.As for electrochemicla milling the evaluation criterion of the surface flatness is established.It is confirmed that constant-voltage and small gaps are beneficial for the smoothing of the rough surface.After parameter optimization,plane machining is conducted on the vertical surface through STEM.The unevenness of the surface is decreased significantly.