The rapid development of China aerospace, microelectronics, and medical industries has led to the emergence of materials characterized by their high hardness, brittleness, and anisotropic properties. These materials, which include single-crystal substances, metals, and composites, are susceptible to subsurface damage and geometric inaccuracy during machining. This poses stringent challenges to modern processing technologies in terms of precision control and surface integrity preservation. Currently, the widely adopted industrial processing technologies primarily fall into three categories: mechanical machining, electrical discharge machining (EDM), and laser processing. Traditional mechanical machining dominates large-scale mold manufacturing due to its cost-effectiveness and mature technology. However, its “hard-contact” processing mechanism induces strong interactive forces between tools and workpieces, frequently causing material edge chipping and abnormal tool wear. While EDM can overcome material conductivity limitations, its low processing efficiency, coupled with electrode wear and dielectric fluid contamination, exacerbates operational costs and environmental burdens. Conventional laser processing suffers from heat accumulation effects during operation, potentially generating heat-affected zones (HAZ) and micro-burrs at processed edges, which critically compromise component service performance. To address these limitations, water-jet guided laser (WJGL) machining technology establishes a hybrid processing system integrating nanosecond lasers and high-pressure water jets.

The operational principle of water-jet guided laser machining involves precisely controlling the laser beam incident angle to remain below the critical angle for total reflection within the water jet. This total internal reflection transmission mechanism completely confines the laser beam within a 50?100 μm diameter water jet, simultaneously achieving material removal and cooling in the machining zone. Fundamentally, the mechanical stress, thermal damage, and environmental pollution inherent to conventional processing methods are eliminated.

This paper focuses on investigating the critical factors influencing WJGL machining performance and highlighting its advantages in precision manufacturing applications. First, an in-depth analysis of the fundamental principles and the material removal mechanisms of WJGL machining is conducted. Subsequently, the key factors influencing machining quality are systematically examined from three perspectives: water-jet characteristics, laser parameters, and system stability. Finally, the superior capabilities of WJGL machining technology are comprehensively summarized, including enhanced machining efficiency, sub-micron precision, high aspect ratios, and multi-axis processing flexibility. Based on current research advancements, a prospective analysis is provided to outline the optimization strategies for future developments in WJGL precision machining technology, aiming to further expand its industrial applicability.

This paper systematically elaborates on the critical factors influencing processing quality and the latest technological advancements in water- jet guided laser machining. The water-jet guided laser system consists of a nanosecond laser, a high-pressure water circulation system, a water-laser coupling device, and a motion platform system (Fig. 1). Numerical simulations reveal that the material removal process primarily involves alternating cycles of laser thermal effects and water jet cooling (Fig. 5). Key influencing factors include water jet stability length, laser parameters, and mechanical system/motion platform performance. The stability of water jets is determined by the structure of the nozzle (Fig. 7), the diameter of the nozzle, and the flow velocity (Fig. 8). Furthermore, the processing quality is significantly influenced by the laser parameters. Ultraviolet (355 nm), green (532 nm), and infrared (1064 nm) lasers exhibit distinct water absorption coefficients (all below 10?1 cm?1), requiring wavelength optimization based on material properties (Fig. 9). Reducing duty cycle to 2% enables precise control of heat-affected zone (HAZ) thickness below 5 μm (Fig. 10). Adjusting single-pulse energy density within specific ranges ensures machining depth while effectively suppressing recast layer formation (Fig. 11). The high-pressure water circulation system, equipped with accumulators and triple-stage precision filtration (particle size of <1 μm), guarantees water jet purity, while the five-degree-of-freedom motion platform achieves efficient laser-water jet coupling (Fig. 12). Optimized tool paths combined with appropriately reduced scanning speeds simultaneously enhance processing efficiency and surface quality (Fig. 13). Compared with conventional techniques, water-jet guided laser processing demonstrates superior advantages for metals, semiconductors, and composites: narrower kerf widths (Fig. 15), higher aspect ratios (Fig. 16), and enhanced complex geometry fabrication capability (Fig. 17), and meeting high-precision component manufacturing requirements (Fig. 14).

This paper systematically analyses the laser-material interaction mechanisms and the process parameter influencing patterns in water-jet guided laser processing. However, significant differences exist in the interactions between water-jet guided lasers and various materials, and the processing mechanisms remain incomplete, requiring further exploration. To better understand the processing mechanisms and optimize the techniques, potential future development directions for the water-jet guided laser machining technology include:

1) Advancement and optimization of equipment technology. Developing high-precision real-time monitoring systems to track laser energy, water jet parameters, and material thermophysical states during processing. Integrated with advanced feedback control technologies, these systems will enable dynamic process adjustments to ensure stable machining quality and precision, adapting to diverse materials and processing requirements.

2) Multidisciplinary collaborative research. Future studies will emphasize cross-disciplinary integration, combining theoretical and experimental approaches from physics, materials science, fluid dynamics, and optics to investigate water-jet guided laser mechanisms across materials. By establishing more precise physical models, researchers aim to elucidate the transmission, absorption, and conversion processes of laser energy within water jets as well as material thermophysical responses, thereby providing theoretical foundations for process optimization.