With the advancement of glass technology in recent times, glass has become one of the most important engineering materials in architectural, medical, automotive, flat panel display, and electronics applications. Desired shape and size of the glass can only be achieved through accurate and precise cutting technique. Laser technology has an advantage over traditional cutting processes for glass due to good quality, surface finish, and high speed of operation. This paper provides a review of all the laser glass cutting techniques discovered in recent work and forms a comparison framework, in particular, their limitations and their current status which would facilitate prospective research and future development.

Laser glass cutting techniques—A review

In laser cleaving of brittle materials using controlled fracture technique, thermal stresses are used to induce a crack and the material is separated along the cutting path by extending this crack. In this study, a glass sheet is stressed thermally using a 808–940 nm diode laser radiation. One of the problems in laser cutting of glass with controlled fracture technique is the cut deviation at the leading and the trailing edges of the glass sheet. In order to avoid this damage it is necessary to understand the stress distributions which control crack propagation. A study is conducted here to analyse the cut deviation problem of glass by examining the stress fields during diode laser cutting of soda-lime glass sheets. Optical microscope photographs of the breaking surface are obtained to examine the surface quality and cut path deviation while the latter is explained from the results of the stress fields which are obtained from a finite element simulation.

Effect of thermal stresses on chip-free diode laser cutting of glass

Cutting glass substrates with dual-laser beams

As a volumetric heat source, YAG laser can penetrate through the glass, and has many advantages in cutting of glass with controlled fracture compared with CO2 laser cutting of glass. This work lays great emphasis on studying the technique of YAG laser cutting of multi-layer glasses. This paper indicates the experiments of YAG laser cutting of two-layer and four-layer soda-lime glasses with controlled fracture. Optical microscope photographs of the separation surface are obtained to examine the surface quality. The impact of laser power, scanning speed and laser beam size on the cutting quality is studied and the optimum processing parameters are presented in the paper. A theoretical model of a thermal laser shock method for separation of two-layer glasses is developed, and the fracture propagation mechanism is studied by examining the temperature and stress fields using finite element software ANSYS. In YAG laser cutting of multi-layer glasses, the temperature distribution is uniform across the thickness of the glass and the fracture propagates from the top and bottom surface to middle so that better separation surface quality can be acquired and multi-layer glasses can be cut simultaneously.

YAG laser cutting soda-lime glass with controlled fracture and volumetric heat absorption

The study investigates the use of CO2 laser to induce glass strip peeling off to form microchannels on soda lime gass substrate. The strip peeling exhibits a strong dependence on the energy deposition rate on the glass surface. In spite of the vast difference in the combination of laser power and scanning speed, when the ratio of the two makes the energy deposition rate in the range 3.0-6.0 J/(cm2 s), the temperature rising inside glass will be above the strain point and reach the softening region of the glass. As a result, glass strip peeling is able to occur and form microchannels with dimensions of 20-40 μm in depth and 200-280 μm in width on the glass surface. Beyond this range, higher energy depsotion rate would lead to surface melting associated with solidification cracks and lower energy deposition rate causes the generation of fragment cracks.

Investigation on CO2 laser irradiation inducing glass strip peeling for microchannel formation

A CO 2 laser with a line-shape beam was used to cleave a soda-lime glass substrate at various beam-rotation angles to the cutting direction. The stress distribution on the glass substrate cleaved by the laser beam has been analyzed in this study. An uncoupled thermal-elastic analysis was achieved by the ABAQUS software based on the finite element method. The numerical results show that the stress field of the fracture is caused by a complex stress state and the cleavages are significantly affected by the heat diffusion and beam rotation angle. At the rotation angle of zero degree to the cleaving direction, the phenomena of the chip formation have been found due to a large temperature gradient at the cleaving depth of the glass substrate.

Characterization of the laser cleaving on glass sheets with a line-shape laser beam

Aqueous solutions of atactic poly(N-isopropylacrylamide) (a-PNIPAM) undergo complex phase transitions at 20–33 °C. In this temperature range, the a-PNIPAM solution exhibits a phase behavior of lower critical solution temperature at the binodal temperature (Tb) and physical gel formation at the gel temperature (Tgel). On slow heating of the one-phase solution containing linear a-PNIPAM chains, branched chains are gradually developed to proceed with the physical gelation before phase separation considering that Tgel < Tb. Thus, the phase separation temperature determined from the conventional approaches, either by turbidity to derive the Tb or by scattering to derive the spindal temperature (Ts) from the Ornstein–Zernike analysis, is strictly the transition temperature associated with the a-PNIPAM hydrogel (or highly branched chains newly developed at elevated temperatures), rather than the initial a-PNIPAM solution prepared. Herein, the spinodal temperatures of a-PNIPAM hydrogels (Ts,gel) of various concentrations were determined from rheological measurements at a heating rate of 0.2 °C/min. Analyses of the temperature dependence of loss modulus G″ and storage modulus G′ give rise to the Ts,gel, based on the Fredrickson–Larson–Ajji–Choplin mean field theory. In addition, the specific temperature (T1) above which the one-phase solution starts to dramatically form the aggregated structure (e.g., branched chains) was also derived from the onset temperature of G′ increase; this is because as solution temperature approaches the spinodal point, the concentration fluctuations become significant, which is manifested with the elastic response to enhance G′ at T > T1. Depending on the solution concentration, the measured Ts,gel is approximately 5–10 °C higher than the derived T1. On the other hand, Ts,gel is independent of solution concentration to be constant at 32.8 °C. A phase diagram of the a-PNIPAM/H2O mixture is thoroughly constructed together with the previous data of Tgel and Tb.

/pdf/physical-gels-of-atactic-poly-n-isopropylacrylamide-in-water-3qtabwo0.pdf

Yu Zan Wang

Papers

Characterization of the laser cleaving on glass sheets with a line-shape laser beam

Physical Gels of Atactic Poly(N-isopropylacrylamide) in Water: Rheological Properties and As-Derived Spinodal Temperature