Microholes are the key structure of core components in aerospace, precision instruments, and other fields. Both the machining accuracy and surface quality play a key role in the performance of the components. Titanium alloy has good high specific strength, excellent corrosion resistance, and super fracture toughness and fatigue properties, but its poor thermal conductivity, toughness, and large friction coefficient, result in the processing of titanium alloy deep small holes being more difficult. This paper proposes Laser and Shaped Tube Electrochemical Machining (Laser-STEM), which utilizes the total internal reflection to guide the laser to the machining zone. In Laser-STEM, the laser-induced local temperature rise of the electrolyte and direct processing could benefit the removal process of electrochemical machining of titanium alloy. Experiments were carried out using a liquid-core fiber-optic tube electrode with an electrolyte of 12.5% sodium nitrate solution while processing micro holes on Ti-6Al-4V titanium alloy. The effect of pulse voltage, laser power, and feeding rate on the machining accuracy of deep small-hole in titanium alloy was experimentally studied. With the increase in laser power, the machining gap increased by 34.74% and the side gap decreased by 24.13%. The experimental results show that the laser can improve the electrochemical machining accuracy. The experimental results showed that a deep hole without a recast layer of 1.5 mm in diameter and 50 mm in depth could be obtained in the Ti-6Al-4V workpiece at a processing voltage of 20 V, a laser power of 5 W and a feed rate of 1.2 mm/min. This paper verified the feasibility of processing deep and small holes in titanium alloy by combining laser and electrochemical machining, and provided a new solution for the high-efficiency processing of deep small holes and surface structures of titanium alloy.
Aiming at the issues of low machining efficiency and difficulty in keeping consistency of machining accuracy of micro array holes with high surface quality. This paper proposed a laser and in-situ electrolytic machining technology for processing array holes, which utilized the advantages of high laser machining efficiency and good surface quality electrochemical machining (ECM). Firstly, laser was used to perform high-efficiency drilling of prefabricated micro array holes on workpieces that was covered with insulating layer, and then the recast layer and taper of prefabricated holes were removed by ECM. To verify the feasibility of the proposed method, laser prefabricated of the array holes with the diameter of 0.8 mm and the in-situ electrolytic recast layer removal were carried out on the Inconel 718 workpiece. Influences of laser scanning speed, defocusing distance, scanning times and insulating plate thickness on the taper of prefabricated hole were investigated experimentally. The optimized laser processing parameters were as follows: scanning speed 60 mm/s, defocusing distance 1.5 mm, scanning times 50, and insulating plate thickness 0.4mm. Results of in-situ ECM showed that the recast layer on the surface of the laser processed holes could be removed, indicating that the laser and in-situ ECM could achieve high efficiency and high precision machining of micro array holes without recast layer.
Laser and shaped tube electrochemical machining (Laser-STEM) has been proposed to process small holes with high efficiency and surface quality. In Laser-STEM the laser energy is transmitted to the machining zone with high efficiency by total internal reflection confined in the inner hole of the tool electrode. Coupling between the laser and the tool electrode is of importance to guarantee the stability and accuracy of the Laser-STEM process. The previous studied focuses the laser beam to the entrance of the tool electrode utilizing a focusing lens. However, the method was easily affected by the focal length, spot size, and installation error, which would influence laser coupling stability and transmission efficiency. This paper focuses on the research of a novel laser coupling method based on the conical optical guide to improve the coupling robustness. Mathematical model of the laser propagation through the conical guide has been derived. The maximum coupling angle of the conical guide with different sizes was obtained. The effect of laserliquid- core fiber tool electrode coupling error on laser energy coupling efficiency is investigated by optical simulation, and the feasibility of conical light-guiding devices for efficient conduction of laser energy was verified experimentally. Results showed that the conical optical guide could improve the laser axial incidence range by about 3 times, the radial range by 2 times, and the angular coupling range by 1.9 times, with the laser coupling efficiency of 90%. The introduction of the conical guide remarkably improved the coupling efficiency and stability of the laser and tool electrode, which is of great significance for improving the stability of Laser-STEM.
With the increasing application of titanium alloys (Ti-6Al-4V) in aero engineering, great challenges have been posed to improve the surface quality and machining accuracy of titanium alloy. Titanium alloy is difficult to be processed. The existing processes suffer from thermal damage or low-efficiency. In this paper, laser and shaped tube electrochemical machining (Laser-STEM) has been employ to process titanium alloy, in which both the laser beam and electrolyte jet are guided to the machining zone through the inner hole of a specially designed tubular electrode. The processing characteristics of TC4 titanium under different processing voltages, laser power, and feeding rates were experimentally studied, while using sodium nitrate as the electrolyte. Influences of key process parameters on the machining profile size and surface roughness was explored. Results showed that the deep and narrow grooves with a good surface profile can be obtained under the voltage of about 20 V, laser power of 3 W, and electrode feeding rate of 1.8 mm/min. Finally, the rectangular wave slot with an average width of 1.6 mm and depth of 0.759 mm was machined by a layer-by-layer laser and electrochemical machining method. The feasibility of laser and shaped tube electrochemical hybrid machining of TC4 titanium alloy with high precision and efficiency has been verified, which laid a foundation for the application of this process in aerospace manufacturing.
The machining stability and electrode feeding rate in the shaped tube electrochemical machining (STEM) process was limited by the formation of central residual. Laser-STEM combined the advantages of STEM and water-guided laser machining to enhance the materials removal rate (MRR) and precision, to some extent. In this study, a retracted hybrid tubular electrode was applied to make the MRR between the different machining regions homoplasy. Simulation results showed that the electric current density distribution homogeneity could be improved with the inner low-refractive layer retracted, and got an increase of 38% with a retracted length deg of 2 mm. W-shaped residual in the central machining area could be removed. When the retracted length deg increased from 0 mm to 2 mm, the laser coupling efficiency exceeded 74.5%. Hence, the retracted hybrid tubular electrode could act as both the tool electrode and optical waveguide in the Laser-STEM process. Experiment results confirm the simulation results and showed a significant improvement in machining efficiency and precision by utilizing the retracted hybrid tubular electrode. With the retracted length deg rising from 0 mm to 1.5 mm, the residual height showed a reduction of 72.6% in the STEM process. In the Laser-STEM process, the residual height decreased by 53.8% and 111% with the laser power of 6 W and 10 W, respectively.
This paper proposed a new high-surface-quality and high-precision small hole processing technique by using laser and electrochemical hybrid machining (LECM) based on internal total reflection (ITR). During LECM via ITR the laser beam could be transferred to the large depth with a small attenuation machining area as the tube electrode feeds into the inner workpiece. The mechanisms of LECM via ITR has been clarified. The ITR through the tube electrode is also studied, in mathematical and simulation manner. Additionally, with the developed experimental setup, the feasibility of LECM via ITR has been proved. Experimental results demonstrated that the side gap could be decreased by laser assistance in LECM, and the side gap has been decreased by 25%.
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