Efficient milling and cutting of borosilicate glasses through a thin flowing water film with a picosecond laser

Abstract

Direct laser ablation allows high-quality processing, precision, and cutting of complex shapes. Unfortunately, this technology is usually not considered as the primary candidate for cutting and milling of glasses due to low processing speeds. Thus, laser-based rear side drilling and crack generation techniques are chosen instead. However, we report on the milling and cutting of borosilicate glass plates with high average power and high pulse repetition rate picosecond laser. We optimised laser processing parameters for the efficient direct material ablation and employed water-assisted ablation to improve the ablation efficiency and the cutting speed of borosilicate glasses. The laser process was realised through a thin flowing water film, which was formed by spraying water mist on the surface of the workpiece. Firstly, we characterised thin water film parameters, such as film thickness, flow velocity, and defined a working area with constant processing conditions. Next, we optimised laser processing parameters for both processing environments: ablation through the thin water film and in air. Under optimal parameters, ablation through the thin water film was much more effective, increasing the cutting speed of 420 μm thick glass plates nearly ten times – from 0.52 to 5 mm/s. Furthermore, the morphology of the cuts was improved as well: cut wall roughness and edge chipping were reduced, spatter deposition was avoided in the vicinity of the cut. We investigated the milling of 130 to 1700 μm wide and 50 to 500 μm deep grooves with a maximum depth-to-width ratio of 3.8. Findings revealed that the ablation efficiency increase provided by the water layer did not depend on the depth or the width of the groove and remained constant. Therefore, it became possible to predict the ablation efficiency through the thin water film by knowing the ablation efficiency in air and an absolute ablation efficiency difference between two processing environments. • Efficient borosilicate glass milling and cutting in the air and through the water film was conducted with a picosecond laser. • Optimal laser fluence for efficient glass ablation was 40% higher than in air. • An absolute change in ablation efficiency between two environments did not depend on the transverse dimensions of the groove. • Water film improved ablation efficiency significantly, resulting in nearly 10 times higher cutting speed than in air.