Experimental Study On Micro Electrochemical Milling By Rotational Cathode Tools

Micro-electromechanical Systems (MEMS) attract more and more attention due to their small volume, light weight, less material usage and low energy consumption. Product minimization becomes available and minimized products are being widely used in industries and our daily life with the development of micro machining technology. Micro electrochemical machining (micro ECM) is based on electrochemical dissolution to remove metallic materials. Compared with micro mechanical milling, micro electrical discharge machining (micro EDM), micro ultrasonic machining (micro USM) and laser beam machining (LBM), micro ECM has many advantages, such as no tool wear, absence of stress/burr, smooth surfaces, regardless of material hardness and strength. Thus micro ECM has been widely used in the aviation, space, automobile, biomedical industries.Recently, micro ECM has made great progress in machining efficiency and accuracy. However, following problems exist in micro ECM:First, fine pulse power supply is widely used in micro ECM due to machining accuracy. However, the direct-current (DC) power supply is over pulse power supply in machining efficiency and process control. There is little research on micro ECM using direct-current power supply with low voltage, which is suitable in micro ECM. It is necessary to investigate the influence of machining parameters on machining accuracy, the tool feed control, the short circuit during machining and the electrolytic product. Second, micro ECM with ultra-short voltage pulses is widely used in micro hole drilling. However, few reports were found on the investigation on complex structures machined by micro ECM using rotational cathode tools. To improve machining accuracy, the influence of electrode rotation, parameters of power supply, electrode feed rate, flow rate of electrolyte, span of tool path has to be studied.In this study, a set of numerical control (NC) program has been designed for micro ECM based on NI Lab VIEW software, including the functions of online electrode fabrication, tool setting, micro drilling and three dimensional milling.Extensive experiments are carried out, attempting to solve problems mentioned above. Experimental results indicate that the electrode rotation in micro hole drilling with direct-current voltage can reduce the hole entrance machining gap and taper angle of micro hole. The machining time is shortened significantly as well. While the tool rotational rates have little influence on the hole exit machining gap. It was found that the flow condition in narrow machining gap of micro ECM has been improved significantly when the electrode rotates, resulting in evenly distribution of electrolytic products, increase of machining efficiency and decrease of the machining gap; In micro electrochemical milling, the tool rotational rate, machining voltage, pulse on time, pulse period and feed rate have regular effects on the machining gap, while the electrolyte flow rate has no significant effect on the gap. In micro electrochemical milling, the best tool path span is1/2-2/3of the tool diameter. When tool paths with angle of0°and90°are used alternatively, the flatness of side surfaces in micro features is improved significantly. Finally, a complex micro structure in200μmx200μm cavity was machined. The maximum machining error is within3.6μm.