Key Issues Of Electrochemical Mechanical Machining With Non-uniform Mechanical Effect

Roller bearing is a widely applicable basic element, which plays important roles in mechanical equipments. The machining quality of bearing raceway and roller has a large influence on the performance, life, reliability etc. With the advantages in high processing efficiency and good surface quality, electrochemical mechanical machining (ECMM) becomes an attractive machining method. The paper proposes a new machining method called electrochemical mechanical machining with non-uniform mechanical effect, providing a new way to solve the forming and finishing problem at the same time. In the developed ECMM processes, the passive film on the anode surface was non-uniformly removed by the non-uniform mechanical effect, further controlling the ECMM effect and realizing the forming and finishing processes of workpieces at the same time.The passive film generated by electrochemical machining is the main cause of forming precision in ECMM. The paper focus on passivation characteristics, passive film impedance, capacitive properties, and the effect of electrochemical parameters on passive film topography, the effect of non-uniform mechanical effect on the removal of passive film, and mechanism of the ECMM with non-uniform mechanical effect. The main works are as follows:Electrochemical characteristics of GCrl5are tested using the PARSTAT2273electrochemistry workstation. The polarization curve shows that GCrl5exhibits activation dissolution stage and passivation stage in NaCl solution. The polarization curves in NaNO3and NaClO3solution are similar, both having stable activation, transition, passivation and over-passivation stages. In the passivation stage, macroscopic passive film didn’t appear in sample surfaces. However, the black passive film was formed in the over-passivation stage in the NaNO3solution which is a suitable electrolyte for the ECMM. The experimental analysis of electrochemical impedance spectroscopy and capacitive reactance of materials in different passive potential show that stable and semi-conducting passive film was present on the sample surfaces in the passivation stage. The passive film has a double-deck structure composed of the inner low-valent metallic oxide and outer high-valent metallic oxide.Based on the analysis of the electrochemical machining action processes, the morphology, element composition, and thickness of the passive film under different electrochemical processing parameter were detected via special equipment such as SEM. The results show that current density is the main effect of microscopic structure of passive film. Proper current density produces uniform and compact passive film while high current density forms loose, nubby and flocculent passive film. Machining time and inter-electrode gap have a slight effect on passive film structure. The higher ampere density and longer machining time produce more thick passive film. The C element content in passive film decides the black color. Passive film mainly consists of metallic oxide.The current efficiency and removal quantity of GCr15in NaN03solution were studied. The results show current efficiency of material in the solution increases with the increasing current density. The whole process presents piecewise function relation. Removal quantity under different processing parameter shows that current density is the main influential factor.The passive film removal laws of non-uniform mechanical effect were studied. Firstly, the grinding passive film process of grains was modeled. Then, experiments were done to study the relationship between grinding parameters and stability and sensibility of removal of passive film. At last, the relevance between grinding parameters and removal quantity was analyzed by gray correlation theory. The results demonstrate that the removal quantity of passive film increases with the increasing of grains size, grinding velocity, grinding pressure and grinding time. The removal quantity of passive film is sensitive to grinding velocity and grinding time, normally sensitive to pressure, and stable to grains size because of the low hardness of passive film. The removal quantity has a high correlation with grinding pressure and grains size, and a low correlation with grinding time.At last, machining experiments of the ECMM with non-uniform mechanical effect are done. Surface roughness and removal quantity serve as evaluation parameters of machining effect, and the surface quality and forming precision are also taken into consideration. Least squares support vector machines practice and predict the experimental results. The results display that the prediction error of surface quality eM and eR are5.20%and5.77%, respectively. The remove prediction error eM and eR are8.42%and9.88%, respectively. The prediction results of ECMM parameters, such as current density, grinding pressure, machining time, velocity and grains size, are stable and errors are under15%. A bright finish surface with certain convexity is produced in3min. Surface quality is largely improved with surface roughness Ra decreased from0.087μm to0.023μm and roundness error RoNt from0.93μm to0.39μm.