As the preferred material for the hot-end structural components of aero-engines, nickel-based superalloys present significant challenges for the preparation of high-quality film cooling holes due to their inherent high hardness and strength. Water-guided laser processing technology has shown considerable potential in the fabrication of film cooling holes, but its engineering application is limited by the coordination between processing quality and efficiency. To address this issue, this study employed a multi-focus water-light coupling mode to achieve efficient coupling of a 1064 nm high-power laser with a stable water jet. In addition, a multi-pass annular cutting drilling strategy from the inside out was introduced, and the effects of laser single-pulse energy, scanning speed, and pulse frequency on the micro-hole surface morphology and geometric accuracy were investigated using the control variable method. Based on this, micro-holes prepared under optimized process parameters were analysed and verified using scanning electron microscopy and energy dispersive spectroscopy. The results indicate that single-pulse energy is the key parameter for achieving through micro-holes. By appropriately increasing the scanning speed and pulse frequency, melt deposition and thermal accumulation effects can be effectively mitigated, thereby improving the surface morphology and machining accuracy of the micro-holes. Specifically, when the single-pulse energy is set to 0.8 mJ, the scanning speed to 25 mm/s, and the pulse frequency to 300 kHz, high-quality micro-holes with an entrance diameter of 820 μm and a taper of 0.32℃ can be fabricated in about 60 seconds. The microstructure and elemental distribution of the micro-holes confirm that water-guided laser processing exhibits excellent performance in reducing recast layers, minimizing the heat-affected zone, and maintaining hole wall smoothness.
Keywords: water-guided laser; nickel-based alloy; film cooling holes; multi-pass annular cutting; processing mechanismAs the preferred material for the hot-end structural components of aero-engines, nickel-based superalloys present significant challenges for the preparation of high-quality film cooling holes due to their inherent high hardness and strength. Water-guided laser processing technology has shown considerable potential in the fabrication of film cooling holes, but its engineering application is limited by the coordination between processing quality and efficiency. To address this issue, this study employed a multi-focus water-light coupling mode to achieve efficient coupling of a 1064 nm high-power laser with a stable water jet. In addition, a multi-pass annular cutting drilling strategy from the inside out was introduced, and the effects of laser single-pulse energy, scanning speed, and pulse frequency on the micro-hole surface morphology and geometric accuracy were investigated using the control variable method. Based on this, micro-holes prepared under optimized process parameters were analysed and verified using scanning electron microscopy and energy dispersive spectroscopy. The results indicate that single-pulse energy is the key parameter for achieving through micro-holes. By appropriately increasing the scanning speed and pulse frequency, melt deposition and thermal accumulation effects can be effectively mitigated, thereby improving the surface morphology and machining accuracy of the micro-holes. Specifically, when the single-pulse energy is set to 0.8 mJ, the scanning speed to 25 mm/s, and the pulse frequency to 300 kHz, high-quality micro-holes with an entrance diameter of 820 μm and a taper of 0.32℃ can be fabricated in about 60 seconds. The microstructure and elemental distribution of the micro-holes confirm that water-guided laser processing exhibits excellent performance in reducing recast layers, minimizing the heat-affected zone, and maintaining hole wall smoothness.
Keywords: water-guided laser; nickel-based alloy; film cooling holes; multi-pass annular cutting; processing mechanism
This study explores the use of 1064 nm wavelength water-guided laser for annular drilling of Inconel 718. It elucidates the mechanisms by which key process parameters such as single pulse energy, scanning speed, and pulse frequency affect the morphology and geometric accuracy of micro-holes. Based on these findings, the optimal approach for achieving high-efficiency and high-precision drilling is determined. The main conclusions are summarised as follows: (1) Adopting a "from inside to outside" multi-pass annular water-guided laser drilling strategy can enhance the scouring effect of the water jet on molten material, reducing the heat-affected zone and residual molten material at the micro-hole entrance surface. (2) When processing Inconel 718 micro-holes with a 1064 nm wavelength water-guided laser, the optimal combination of process parameters is: single pulse energy 0.8 mJ, scanning speed 20 mm/s, and laser pulse frequency 300 kHz. Under this parameter configuration, high-quality micro-holes can be produced with an entrance diameter of 822.7 µm, circularity of 0.9893, taper of 0.32℃, and surface roughness Sa less than 9.58 µm. (3) Based on the sectional morphology characteristics of micro-holes processed by water-guided laser, the surface of the micro-hole can be divided into four distinct regions: resolidification zone, protrusion zone, depression zone, and fracture zone. The resolidification zone and fracture zone respectively represent the unique morphology at the entrance and exit of the micro-hole. The protrusion zone and depression zone are distributed along the entire micro-hole wall, and their formation mechanism is closely related to the photothermal effect and rapid heating and cooling characteristics during the water-guided laser processing. (4) Observations of the micro-hole entrance, exit, and hole wall profile reveal that water-guided laser processing exhibits excellent performance in reducing the recast layer and heat-affected zone and maintaining hole wall cleanliness. This technology effectively mitigates the thermal effects and oxidation damage associated with conventional long-pulse laser processing, thereby achieving high-quality and high-efficiency machining of Inconel 718.
