Titanium alloys have ultra-high specific strength and excellent high-temperature corrosion resistance and are widely used in manufacturing key components in the aerospace industry. Many issues arise during the mechanical processing of titanium alloy materials, including serious tool wear, residual stress, burns, and adhesion. Consequently, the reliability and yield of the current processes are relatively low, and the cost is high. Synchronous nanosecond laser-assisted electrochemical machining has been proposed for environment-friendly, efficient, and precise machining of the Ti-6Al-4V titanium alloy. This method takes advantage of the high efficiency and local temperature rise of laser processing and the good surface quality of electrochemical machining (ECM). Experimental studies were conducted to determine the effects of key process parameters, such as electrolysis voltage, laser power, and feeding rate. The results revealed that a electrolysis voltage of 20 V, laser power of 3-5 W, and feeding rate of 1.8 mm/min were preferred for high-efficiency and high-precision machining of Ti-6Al-4V titanium alloy. The method of “high→low laser power” was proposed to obtain high-precision and efficient machining using laser-assisted ECM.

We use self-designed and developed special equipment for experimental research (Fig.2). The processing object is Ti-6Al-4V titanium alloy sheet with a specimen size of 50 mm×50 mm×5 mm and a polished surface. The tool tube electrodes with an inner diameter of 0.53 mm and an outer diameter of 1.20 mm was used in experiment. In order to ensure that the electrolyte flow state was laminar flow and achieve high laser coupling efficiency, the electrolyte flow was set to 100 mL/min. Before the processing test, Ti-6Al-4V specimens were cleaned sequentially for 15 min in acetone and absolute ethanol by ultrasonic cleaning, and then dried with a hair dryer. Sodium nitrate (NaNO₃) solution with mass fraction of 12.5% at room temperature (24 ℃) was adopted as electrolyte. By controlling the relative movement of the workpiece and the tool electrode, the short-circuit current real-time detection method is used to set the initial machining gap between the tool tube electrode and the workpiece. In the actual machining, there is a short circuit phenomenon when the machining gap is 0.1 mm, and there is no obvious machining when the gap is too large, so the initial gap is selected as 0.2 mm. Each group of tests is done three times, after the test, the sample is cleaned with absolute ethanol and deionized water in turn, dried with a hair dryer. Laser confocal microscope (VK-X200K, KEYENCE) and scanning electron microscope (Scanning Electron Microscopy, SEM, S5000, Hitachi) were used to measure the surface morphology and contour of processing, mainly including the groove width, groove depth and bottom surface roughness. Finally, the data is processed to obtain various charts to analyze.

To investigate the effects of electrolysis voltage, laser power, and feeding rate on the machining performance of Ti-6Al-4V titanium alloy, single-layer synchronous nanosecond laser-assisted ECM experiments were performed. At electrolysis voltages lower than 18 V, the surface color of the workpiece was yellow-brown, and the main surface component was a yellow passivation film structure of TiO₃ formed without laser assistance (Fig. 3). The electrochemical machining process stability of the titanium alloy was relatively poor without laser assistance. In contrast, the surface processing quality of the microgrooves was better, and the machining contour accuracy was higher with laser assistance. A small amount of white substance formed inside the microgrooves as a result of the electrolytically activated TiO₂. Thus, the stability of the ECM can be increased by laser assistance. With a laser power of 3 W, the end-face gap material was removed via laser-assisted electrochemical machining, and the processing area at the bottom of the microgroove was flat (Fig. 5). With a laser power of 6 W, the laser center processing area was larger than that of electrochemical machining, and a deep groove was formed in the center of the workpiece processing area. When the feeding rate was less than 1 mm/min (Fig. 7), a microgroove was formed at the center of the machining area. The stray current corrosion and taper of the groove side were significant. When the feeding rate was greater than 1.5 mm/min, the bottom surface of the groove was relatively flat. Furthermore, increasing the feeding rate decreases the depth of the microgroove. A novel processing mode (Fig. 9) with a high laser power followed by a low laser power was also proposed. Using the control strategy, the average groove width was decreased, and the bottom of the groove was smoothened. It was demonstrated that using a high laser power first and then low laser power processing mode could not only improve the localization of processing but also effectively reduce the roughness of the bottom surface of the microgroove.

The laser-assisted ECM was used to achieve precise and efficient machining of the microgrooves on Ti-6Al-4V titanium alloy material using a self-designed experimental apparatus. Laser-assisted ECM can achieve three-dimensional machining of Ti-6Al-4V titanium alloy using a passive salt solution and low electrolysis voltage at room temperature. A laser power of 3 W, low electrolysis voltage, and feeding rate of 1.8 mm/min were preferred for the efficient and precise machining of titanium alloy materials. A gradient laser power (5 W→3 W) was applied to enhance both machining efficiency and accuracy. A rectangular table and a deep and narrow groove with a width of 1583.12 μm and a depth of 3724.63 μm were processed using the optimized machining parameters.