Grooving of Metals by High-Intensity Focused Ultrasound-Assisted Water-Confined Laser Micromachining

Abstract

Laser grooving (i.e., the production of surface grooves through laser machining) has several advantages and many current or potential industrial applications. However, conventional laser grooving in air may often suffer from quality defects such as debris depositions. A new machining process, with the name “ultrasound-assisted water-confined laser micromachining” (UWLM), was previously proposed by the corresponding author. In UWLM, in situ ultrasound is applied during laser machining of a water-immersed workpiece surface region to improve the machining quality and/or efficiency. If the ultrasound is applied using a high-intensity focused ultrasound (HIFU) transducer, the process can be called “HIFU-based UWLM.” Despite previous investigations on UWLM, to the authors' best knowledge, experimental studies on surface grooving using a HIFU-based UWLM process have been rarely reported in any paper. Such a study has been presented in this paper (for the first time in a paper to the authors' best knowledge). In this work, surface grooves are produced through the ablation of a moving workpiece immersed in water by laser pulses fired at a pulse repetition rate of 1 kHz or 3 kHz. Each laser pulse is followed by a focused ultrasound pulse (from a HIFU transducer) that reaches the workpiece surface approximately 30 µs later. The laser spot on the workpiece surface is approximately at the same location as the geometrical focal point of the HIFU transducer. Under the conditions investigated, it has been found that typically the grooves produced by the HIFU-based UWLM process appear much cleaner and have much smaller amounts of debris particles and recast material than those produced by laser ablation in air, and they typically have much larger depths than those by laser ablation in water without ultrasound. Some related fundamental physical mechanisms have been discussed. The study suggests that the HIFU-based UWLM process has a great potential to provide a new surface grooving technology with competitive performance.