Simulation And Experimental Study Of The Bubble Influence On ECM Process

Electrochemical machining(ECM)technology is used to remove the metal material by the principle of electrochemical dissolution.ECM process is influenced by a wide variety of physical parameters such as electric field,flow filed,chemical reaction temperature and so on.It is difficult to establish a accurate theoretical model.The ECM simulation has been widely used,which plays an important role in improving machining accuracy and predicting machining process.Cathodic hydrogen evolution reaction accured in the ECM process,the existence of large number of bubbles effect the electric field and result in uneven distribution of current density on the electrode surface,thus affecting the removal rate of anode material.Especially the micro ECM in hydrostatic condition,bubbles in the machining gap is not easy to be discharged,its influence can not be ignored.However,the average diameter of the bubble is only about 25?m,and it is more difficult to monitor the bubble in the machining gap.On the basis of the principle of flow field theory,this paper has studied the formation mechanism of hydrogen in the machining gap.In this paper,the influence of bubbles on the ECM process is studied by means of simulation.(1)Summarized the process of hydrogen bubble growth through.The generation of hydrogen molecules speed depends on the cathodic current density.Bubble nucleation and growing rate depend on the hydrogen molecule concentration in the electrolyte.Bubble growth is always accompanied by diffusion mass transfer,convective mass transfer and inter-phase mass transfer.The mass transfer rate is determined by mass transfer coefficient.(2)Bubble observation experiment.Bubble formation and motion process was shot by high speed camera under different current.For every image,we used image processing method to extract the effective bubble characteristics.Then statistics the number of hydrogen bubbles and calculated their diameters.The results show that the current value is an important factor to affect the bubble size.(3)The simulation model is established.Using the component transport model to simulate the diffusion of hydrogen molecules,the VOF model is used to track the movement of the gas liquid interface.According to the bubble images,we studied the effects of single and multiple bubbles on the anode surface current density.The result show that the closer distance between bubble and anode,more effects on the anode surface current density distribution.The influence of bubble number is small.(4)The gas liquid two phase flow model was established.This paper adopted the population balance model(PBM)and Euler model,with entrance conditions for gas bubble diameter distribution obtained by experiment,to simulate the fl ow field distribution of velocity and pressure in machining gap.The results show that hydrogen is easily trapped in the vortex in the vicinity of the cathode.