Fig. 1. Principle of WJGL machining technology

Fig. 2. Schematic diagrams of conventional laser and WJGL machining. (a) Conventional laser machining; (b) WJGL machining

Fig. 3. Schematic diagram of WJGL machining system^[22]

Fig. 4. Schematic diagrams of the formation of vena-contraction and nozzle structure. (a) Formation process of vena-contraction; (b) cylindrical nozzle; (c) cone nozzle; (d) cone-up nozzle; (e) cone-down nozzle

Fig. 5. Flow field characteristics and structural form of multi-channel coupling devices. (a) Comparison of turbulent flow velocity and kinetic energy distribution under different numbers of flow channels^[30]; (b) schematic structure of the multi-flow channel coupling device^[31]; (c) streamline distribution in the double-side inlet coupling cavity^[32]

Fig. 6. Water-jet formation and transport process. (a) Water-jet structure^[33]; (b) water-jet transport state without gas-assistance^[34]; (c) water-jet transport state with gas-assistance^[34]

Fig. 7. Improvement of machining performance by auxiliary gases. (a) Liquid-fluidized film structure^[35]; (b) improving machining quality^[36]; (c) improving machining efficiency^[37]

Fig. 8. Absorption properties of water jets on laser and thermal effect of laser. (a) Absorption rate of water on different wavelengths of laser at the same temperature^[38]; (b) pulse energy of different wavelengths of laser^[40]; (c) temperature distribution of the water jet under the thermal effect of laser^[41]

Fig. 9. Optical path shaping optimization techniques. (a) Tunable oscillating cavity laser^[44]; (b) schematic of a diffraction-free beam lens^[45]; (c) schematic of a multifocal lens^[46]

Fig. 10. Light distribution in the water-jet and the position of laser‒water coupling. (a) Light distribution in the water jet^[48]; (b) relative position error of laser‒water coupling^[49]; (c) laser‒water coupling form under longitudinal error change^［49］; (d) a schematic diagram of a long-pulse Nd∶YAG solid-state laser with a symmetrical plano‒plano cavity configuration^[50]; (e) an off-axis optical system with double lenses^[51]

Fig. 11. Laser energy distribution under coupled energy beam. (a) Laser ablation under different numbers of pulses^[52]; (b) laser spot distribution after longitudinal error transformation^[53]; (c) coupling effect in a water jet^[54]

Fig. 12. Applications of WJGL machining technology to conventional metallic materials. (a) Effect of hole-making process parameters on hole morphology and machining quality of 304 stainless steel^[57]; (b) WJGL cleaning of epoxy resin coating on 304 stainless steel surface^[58]; (c) WJGL surface peening of TC4 titanium alloy for improving cycle fatigue life^[59]

Fig. 13. Applications of WJGL machining technology for high-temperature alloys. (a) Comparison of WJGL and EDM hole-making results for CMSX-4 alloy^[60]; (b) comparison of WJGL and LBM cross-section for commonly used alloys^[61]; (c) cross-section crystallographic orientation after WJGL hole-making for DD6 high-temperature alloy^[62]; (d) WJGL multistep helical hole-making method for DD91 high-temperature alloy^[63]; (e) WJGL sacrificial layer method to optimize the quality of hole-making for GH4169 high-temperature alloy^[64]; (f) response surface methodology to predict the depth of WJGL grooves in Inconel 718 high-temperature alloy and optimize the process parameters^[66]; (g) WJGL preparation of polygonal closed grooves on the surface of Inconel 718 high-temperature alloy^[67]

Fig. 14. WJGL machining technology applications for semiconductors. (a) WJGL scribing results for GaN^[68]; (b) conventional laser versus WJGL grooving results for single-crystal Si^[69]; (c) fluid volume method for predicting single-crystal Si WJGL grooving depths^[70]; (d) the effect of scanning speed on machining quality during single-crystal Si WJGL grooving^[71]; (e) WJGL grooving process parameters (laser power, laser repetition frequency, number of passes, and cutting speed) optimization for single-crystal Si^[72]; (f) WJGL preparation of grooves with large depth-to-diameter ratios for single-crystal Si^[73]; (g) WJGL grooving machining parameters for SiC^[74]; (h) WJGL surface modification for single-crystal Si to increase hydrophilicity^[75]

Fig. 15. Applications of WJGL machining technology for carbon fiber reinforced resin (CFRP). (a) Comparison of WJGL and traditional laser beam machining (LBM) results^[76]; (b) optimization of WJGL processing parameters: minimized heat-affected zone width and improved machining efficiency^[77]; (c) machining of 6 mm-thick CFRP with high-power WJGL^[78]; (d) optimization of high-power WJGL machining parameters using response surface methodology^[79]

Fig. 16. Applications of WJGL machining technology in metal-matrix and ceramic-matrix composites. (a) Comparison of drilling between WJGL and traditional laser in SiC-reinforced Al-matrix composites^[80]; (b) comparison of drilling between WJGL and femtosecond laser in SiC/SiC composites^[81]; (c) preparation of high-aspect-ratio slot structures of SiC/SiC composites via WJGL^[82]; (d) suppression of water-jet sputtering during WJGL processing of C_f/SiC composites^[84]; (e) optimization of WJGL machining parameters for SiC_f/SiC composites using neural networks^[85]