Quality and flexural strength of laser-cut glass: classical top-down ablation versus water-assisted and bottom-up machining

Abstract

The growing applicability of glass materials drives the development of novel processing methods, which usually lack comprehensive comparison to conventional or state-of-art ones. That is especially delicate for assessing the flexural strength of glass, which is highly dependent on many factors. This paper compares the traditional top-down laser ablation methods in the air to those assisted with a flowing water film using picosecond pulses. Furthermore, the bottom-up cutting method using picosecond and nanosecond pulses is investigated as well. The cutting quality, sidewall roughness, subsurface damage and the four-point bending strength of 1 mm-thick soda-lime glass are evaluated. The flexural strength of top-down cut samples is highly reduced due to heat accumulation-induced cracks, strictly orientated along the sidewall. The subsurface crack propagation can be reduced using water-assisted processing, leading to the highest flexural strength among investigated techniques. Although bottom-up cut samples have lower flexural strength than water-assisted, bottom-up technology allows us to achieve higher cutting speed, taper-less sidewalls, and better quality on the rear side surface and is preferable for thick glass processing.

Efficient Water-Assisted Glass Cutting with 355 nm Picosecond Laser Pulses

“…A rougher sidewall could indicate the presence of larger defects which negatively affect the strength of glass strips [ 17 ]. For this reason, we studied the roughness of laser-cut sidewalls produced in ambient air and water at preselected hatch values (optimal, ridge-free and intermediate).…”

“…Improved glass cooling in water avoided cut sidewall quality degradation related to heat accumulation, showing a consistent surface roughness irrespective of the hatch value. The roughness was higher than in ambient air due to increased mechanical forces acting on the glass wall during the laser ablation (collapse of cavitation bubbles, confined plasma generated shockwaves), which led to a more mechanical glass erosion and porous-looking cut wall surface [ 16 , 17 , 57 ].…”

“…In order to utilise full laser potential at optimal material processing conditions, one must either increase the laser beam spot size at the expense of machining accuracy or increase the laser pulse repetition rate to maintain optimal fluence levels. Unfortunately, excessive heat would accumulate in either case and ultimately lead to fractures and destruction of the brittle material even for ultrashort pulses [ 16 , 17 ].…”

Femtosecond Laser Cutting of 110–550 µm Thickness Borosilicate Glass in Ambient Air and Water

“…A comprehensive comparison of multiple laser-based glass-cutting techniques was conducted by Dudutis et al [ 19 , 36 ]. They compared glass cutting via the bottom-up technique with direct laser ablation in ambient air and water [ 36 ] and stealth dicing [ 19 ]. In both studies, 1 mm thick soda–lime glass plates were used as the samples.…”

“…Furthermore, glass samples cut in water via direct ablation had the highest flexural strength (134 MPa at the front and 131 MPa at the back) compared to other investigated laser-cutting techniques. However, cutting of 1 mm thick soda–lime glass via direct laser ablation was notably slower (0.19 mm/s in ambient air and 0.34 mm/s in water) than the stealth dicing with Bessel beams (100 mm/s) and bottom-up cutting (0.74 mm/s) using 1064 nm wavelength ps pulses [ 19 , 36 ]. The use of 532 nm wavelength nanosecond pulses for the bottom-up cutting increased the glass-cutting speed up to 9 mm/s [ 19 ], but the strength of laser-cut glass remained higher when cutting was conducted in water via direct laser ablation.…”