The Rotary Combined Ultrasonic And ECM Device And Experiment Study

The material removal principle of Electrochemical Machining (ECM) is based on the anode electrochemical dissolution. As all the metal material can be processed by the technology with high speed, good surface quality with no loss of electrode, ECM is widely used in three-dimensional surface, cavity, shaped holes, micro- deep holes and so on.Ultrasonic machining is a non-traditional technology impacting the abrasive between tool and the work piece by the ultrasonic frequency vibration of the tool head to remove the material, and the surface of the work piece is generally broken and removed by the strike action of abrasives and ultrasonic cavitations. Not only is it suitable for the machining of the non-metallic materials such as glass, ceramics, semiconductor wafers and so on, but also suitable for the machining of hard and brittle metal material such as the carbide, hardened steel and so on.It is a long time for the research of the electrochemical machining and ultrasonic machining, they have gradually become mature and practical machining methods applied in military industry and civil industry abroad. However, for the specific part with the processing condition and requirements, there are some drawbacks and limitation for both of them. The single method can not effectively complete the removal of the material, and require the improvement based on the original processing methods-a combination of processing method utilized a variety of energy to improve the processing efficient, better dimensional accuracy, shaped accuracy and surface integrity is produced. In this context, the combination of the ultrasonic frequency vibration and electrochemical machining called ultrasonic combined ECM technology (UECM) is proposed. The anode passivation formed in the ECM on the surface of work piece is damaged by the high frequency vibration of the cathode and ultrasonic cavitations, which kept the ECM going on. The discharging of the products of ECM and the updating of electrolyte are accelerated. The machining speed, the machining locality, machining accuracy and surface quality are improved by the application of the vibration of cathode. In this paper, some studies of the UECM are done as follow:1) Considering the passive film generated in ECM, the difficulty for electrolyte entering the processing area and products of ECM excluding, the overall scheme of rotary ultrasonic combined ECM is proposed. The test device have X, Y, and Z translation based on a small vertical milling machine body. The work platform made from the marble with PO -level precision and the electrolyte box are designed. The metal filler is inlayed in the marble work platform. In order to seal, the electrolyte box and work platform are connected by the screws. The Gugao motion control system with the current collecting and short circuit protection devices is developed.2) It is difficulty for the electrolyte to enter the processing area and for products of ECM to exclude the processing area in the micro-deep holes machining by ECM, thus, the spray style of electrolyte is adopted in this paper. There are two options for this:the traditional full-wavelength vibration system and the half-wavelength vibration system based on the principle of local resonant vibration are designed based on ultrasound theory, finite element theory. Two kinds of the ultrasonic vibration system are developed based on the optimization design model of the finite element software AN SYS. Comparative results show that the half-wavelength resonance vibration system has the advantages of a small volume, small rotary damping, high rotary precision and the tool system does not affect the frequency of the vibration system. The technical parameters of the designed rotary ultrasonic vibration system are frequency of 20±1 kHz, the amplitude of 40-80μm, rotary precision of 0.02mm.3) In order to determine the problem of the insulation of the stainless steel capillary in the micro-deep hole machining by RUECM with the nonlinear electrolyte of sodium nitrate, the single factor experiments were carried for the voltage, the initial end gap, feed rate, rotary speed and the electrolyte pressure. The results showed that the taper of the machined holes are large with the non-insulated cathode. The effects of the parameters to the taper were gained by the analyzing the collected machining current and experimental results. It is not suitable for the machining stability with the large feed rate and small initial end gap. With large electrolyte pressure, there are anti-splash electrolytes, the jitter of cathode and high temperature, which caused the unstable processing, stray corrosion on the work piece surface and the uncontrollable temperature in the RUECM. Finally the corrosion-resistant submersible pump with the pressure 0.5MPa is adopted.4) The experiments of the small holes machined by the device are carried out. The single-factor experiments, factorial experiments and response surface experiments are carried out for the processing parameters of machining voltage, initial machining gap, feed rate, speed of rotation and cathode bare length. The response of the side gap, the material removal rate (MMR) and the actual volume electrochemical equivalent are gained by the analyzing of single factor experiments, which provided a reference for the parameters level selecting in the future experiments. By factorial experimentas not only analyzed the significant effects of various factors and interaction on the side gap, MMR, but also got the positive or negative effects of the parameters to these responses. The multivariate regression models of the side gap and MMR were developed with the relative error 8.18% and 8.82% respectively comparing the experimental results. As there were some squared terms in the regression model of the side gap, the fully quadratic regression model of the side gap and the best optimization parameters were gained by the response surface experiments, and the relative error of the side gap is about 4.96% and the prediction accuracy of the side gap of regression model is improved.5) The taper of the holes and the machining stability are studied. The results show that for a given depth hole, the most effective way to decrease the taper is to increase the feed depth with the other conditions contained, and the increasing value is equal to the sum of cathode bare length and the initial machining gap when value of the taper reach to the best. The nesting processing appeared in the RUECM with the hollow tube cathode and a small boss is deformed at the centre of holes causing speaks and other phenomenas, which hindered the RUECM. It was effectively to remove the small boss with the "cross" auxiliary cathode and the machining stability and feed rate were improved, which is the foundation for the studying of RUECM in micro small machining and application. The experiment of micro deep holes was carried with the diameter 4.007mm and depth 67.5mm with the stability current in the paper. The contrast experiments by the RUECM and RECM showed that it is helpful to update the electrolyte, exclude the products of ECM and improve the surface quality in the RUECM.6) The gas-liquid two-phase flow model is established based on the theory of fluid dynamics for the simulation of cathode rotation and the cathode vibration respectively in the ANSYS CFX, and the effects of the rotation and vibration of cathode were qualitively analyzed. With the rotation of cathode, the distribution of electrolyte velocity was uniform and the bubbles rose from the work piece surface. A portion of bubbles leaved from the processing zone, and the other aggregated at the bottom of the cathode. It was helpful for the bubbles leaving from the work piece surface with the lower rotary speed, which led to the increasing of the dissolution of anode. With the increasing of the rotary speed, there were more and more bubbles at the bottom of the cathode, which led to the conductivity of the electrolyte decreasing and the dissolution rate of anode decreasing. It was helpful for the decreasing the side gap of hole. The vibration of cathode induced the cyclical fluctuations in the machining zone and the bubbles had the up and down movement, which accelerated the bubbles leaving from the work piece surface and discharged along the side gap. With the amplitude increasing, the gathered bubbles increased at the bottom of hole, which led to the gas volume fraction increased and the dissolution rate of anode decrease. With the bigger end gap, the discharge rate of bubbles was larger and the stability was improved. When the frequency was higher, a larger number of bubbles were gathered at the bottom of holes, which decreased the axial MMR in the RUECM.The cyclical changing of the position of cathode led to the end gap changed between the big end gap and small end gap in the ECM, the local dissolution of anode and precision of machined hole was improved.7) Simulation machining Research was carried out based on finite element simulation. By two-dimensional and three-dimensional simulation machining studies show that three-dimensional simulation process not only improves the prediction accuracy, but also shows different moments of the processing surface, which provide guidance for RUECM.