The Study of Glass Cutting Based on the Micro-Crack Control Chao Huang 1,a, Jimin Chen 1,b, Jianwen Yuan 1,c

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1 Key Engineering Materials Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland The Study of Glass Cutting Based on the Micro-Crack Control Chao Huang 1,a, Jimin Chen 1,b, Jianwen Yuan 1,c 1 Institute of Laser Engineering, Beijing University of Technology, Beijing ,China a huangchao@ s.bjut.edu.cn, b jimin@bjut.edu.cn, c l @qq.com Keywords: Laser; Glass Cutting; Ansys; Irregular-Curve Cutting; Slant Cutting; Stress Field Abstract: A 532nm Diode-Pumped green laser was used to cut glass with the Micro-Crack control. The Micro-Crack was the micron-sized round-like crack caused by laser in the glass and the line-crack around the round-like crack. This paper researched the generation of the Micro-Crack and discussed how to control it, then researched the stress field in the glass during the cutting by finite element analysis. Propose a new method about the glass cutting which had advantages of low power, low heat effect, irregular-curve cutting and slant cutting. Introduction With the rapid development of laser cutting technology, it has been applied in sweeping areas. It has unique advantages in the field of glass cutting. Traditional methods of glass cutting are based on scoring and snapping in which a diamond blade tool was used for scribing, which weakens the glass surface and then breaking was done by applying the mechanical force [1]. This method was relatively simple, but it results in the weakening of glass edges and generation of residual stresses [2]. The use of a laser for cutting brittle materials was first proposed by Lumley [2] in the 1870s. His cutting process, using controlled fracture technique with a CO 2 laser, was limited to a glass thickness of 1mm. This was because the optical penetration depth of CO2 laser of wavelength l=10.6 µm was in the range of a few microns for most glass materials [3].To solve this problem, the Nd-YAG and diode lasers are used. Unlike CO 2 laser, they provide higher optical penetration depth and hence offering the possibility of cutting glass with higher thickness [3]. In controlled fracture technique.tsai and Liou [4] divided the cutting process into three stages in 2003 In the first stage, fracture was initiating because of the tensile stresses. And the crack grows stably in the second stage. In the third stage, crack extends unstable due to complete control of tensile stresses. Dekker and Zonneveld [5] proposed a method similar to controlled fracture technique for cutting glass. They made a small scratch at the start of the cut, which helped in initiating the crack and leads to the separation of the glass. They called it thermally induced fracture. However, the fracture propagation was difficult to control and the substrate was always separated along an unexpected path when the glass substrate was cut by a defocused laser beam alone [6]. To solve this problem, in Verheyen s study, a scoring wheel was employed to generate a micro crack along the cutting path on a glass surface [7]. A defocused laser beam followed the movement of the scoring wheel to drive the fracture completely through the glass thickness. A rotation chisel was used to scribe the glass plate surface in Ikeda s study [8], and a CO2 laser followed behind the chisel. Tsai [9] replaced the mechanical tools to a focused Nd:YAG laser to scribe a groove on the ceramic substrate and applied another defocused CO 2 laser followed it to induce thermal stress to separate the substrate along the laser moving path. In Junke Jiao s study a focused CO2-laser beam was used to scribe a straight line on the substrate, and a defocused CO2-laser beam was used to irradiate on the scribing line to generate a tensile stress and separate the substrate [6]. However, the whole cutting process was complicated, and the laser power was high. In other way, the cutting profile in the method above all can only vertically to the glass surface [see fig.1]. And the crack was difficult to control in the irregular-curve cutting. In this study, the new glass cutting method based on the micro-carck control was proposed. In this method, the laser power for cutting could be greatly reduced to less than 1W, and it could realize the slant cutting (the cutting section don t perpendicular to the glass surface) [see fig.1] and the Irregular-Curve Cutting. Besides, in the course of cutting, the heat effect was low. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-08/04/16,23:08:08)

2 Key Engineering Materials Vols Glass Surface Glass Surface Cutting Surface Cutting Surface Fig.1 The diagram of perpendicular cutting The diagram of slant cutting The key step of this method was using the laser to create a series of micro-crack in the glass. These crack constitute the cutting section. Then applied force on the glass, the glass would be fractured from the cutting section, the cutting was finished. Fig.2 The diagram of cutting section The diagram of the glass fracture The Mechanism Analysis of Glass Cutting The injury mechanism of glass by laser. The micro-crack control cutting method was based on the thought of differential. The traditional cutting section was divided into a lot of little section. The laser focus on the point in the glass, the high energy made the glass broke, create a round-like crack which the average size about 10 µm. The glass was the hard and brittle materials. So the crack would be spread under the inner stress and create several line-crack around. When the laser with high power density focused on the point in the K9 glass, there would be a variety of changes in the glass. Such as temperature rise, melt, gasify, plasma spraying and so on [10]. The ultra white glass used for test was 5mm thick, and the transmissivity was 92.1%. The laser used for test was 532nm green Nd:YAG laser. It s repetition rate was 1.81KHz, the pulse width was 55µs, the beam diameter was 10µm and the average power was 0.78W. With these data, we can know that the power density in the point which the laser focus on was 6.19*10 5 W/cm 2, so the glass was molten at that time[1]. Fig.3 was the morphology of two micro-crack. The crack consists of three parts. The round-like area in the middle of the crack was produced by glass melt. The melt cause the changes of stress distribution and because of the discontinuity of material, there are several radial line crack around the round-like crack. Fig.3 The crack morphology

3 1410 Micro-Nano Technology XIV The formation of cutting section. The cutting section was constituted by micro-crack. The Fig.4 was the model diagram of the micro-crack. The white points in the fig.4 are the location where the laser focus on successively. Fig.4 is the cutting section morphology in the glass. The black area was the round-like cracks and the line crack. The stress superposition on the white area was more serious, so it was the important part of the cutting section. The fracture strength threshold of the glass reaches its minimum at the cutting section (The value was determined by the micro-crack density and the laser power). So when the force applied, the cutting section would be broke first. Simulation and Analysis Fig.4 The model diagram of the micro-crack The cutting section morphology anterior to the glass broke Modeling and laser loading. The model was the cuboid with 0.3mm long, 0.2mm wide and 0.04mm high. The element type was Solid70 and the parameters of the glass set according to the Table 1. The central area where the laser would be load on should be meshing further as 3 grade. Fig.5 was the ANSYS simulation model. Table 1 The thermal physics and mechanics parameters of glass material Density [g/cm 3 ] Fuse point [K] Elastic moduli [Gpa] Poisson ratio Thermal Tensile rupture strength capacity [Mpa] [J/g K] Heat conductivity [W/m K] Thermal coefficient of expansion [10-6 /K] For the simulation of the temperature, Load the laser on the surface of the model as the heat flux. The Eq. 1 was the function of the laser heat flux. The QC was the laser power density. It s value was 6.19*10 9 W/m 2. The xcenter and ycenter was the coordinate value of the location where the laser load on. And the rb was the spot radius. Hflux=QC*exp{-2*[(x-xcenter) 2 +(y-ycenter) 2 ]/(rb 2 )}. (1) At the first step, load the laser on and set the KBC as 1. The time was set to 55µs.At the second step, delete the laser load, and the time was set to 495µs. The third step duplicated the first step to load the laser on the new place. Repeat this process until the loading was completed. After the cutting section was crated, the mechanical force and the DOF should be loading. Before the loading, convert the element type to Solid185 first. The location of the force and the DOF as was shown in the fig. 5.

4 Key Engineering Materials Vols Fig.5 The simulation model The location of the force and the DOF Temperature and stress analysis. Analysed the temperature after each step and killed the elements whose temperature higher than 1693K. Fig.6 was the model after elements killed. We can see that use the finite elements analysis software to analyse the glass had its special advantages. Because the glass was one kind of hard-brittle material, so when it was broke, the tiny section would be created. And the tiny section was corresponding to the ANSYS elements. Therefore, the simulate would be more real if the element size was rational. Fig.6 The model after elements killed Fig.7 The thermal stress distribution of signal point To research the single micro-crack, analysed the thermal stress in the process of single point. Our main concern was the thermal stress distribution[see fig.7]. We can see that the thermal stress was spread from the center to the edge, and the strength decreased gradually. In circumferential direction the stress distribution was alternant in strong and weak. It was consistent with the fig.3 basically. But there was a defect in the simulation the glass material wasn t symmetrical perfectly. Fig.8 is the stress distribution after loading the mechanical force. The blue circular region was the Micro-Crack created by laser. This area was not influenced by the stress, because it had been killed during the temperature analysis. The tensile stress was biggest near the Micro-Crack, and in the rear of the Micro-Crack, the stress was weakened. So the effect of the crack was just like the fire belt. Fig.8 The stress distribution after loading the mechanical force

5 1412 Micro-Nano Technology XIV Experiment The glass used in the experiments was ultra white glass with 5mm thick and the transmissivity was 92.1%. Another glass was soda-lime glass with 1.1mm thick. The laser was 532nm diode-pumped green laser. Its parameters had been introduced in this paper. Fig.9 is the sample of glass cutting including the sample of perpendicular cutting, slant cutting and Irregular-Curve Cutting. Fig.9 The sample of glass cutting We realize the control to the size of Micro-Crack by regulating the laser power and the number of the Micro-crack in per square millimeter.the size of the Micro-Crack was one of the main factors to the roughness of the cutting section.table 2 was the roughness report of the cutting section by LSCM. The conditions of the test was as following: the pump current of the laser was 39A, the number of the Micro-crack in per square millimeter was 101, the speed of the cutting was 1500 point per second. Table 2 The roughness report of the cutting section by LSCM Conclusion The laser was focused on the position in the glass to create a micron level crack. A series of Micro-Crack formed a cutting profile, so the glass was cut off. This method could realize the perpendicular cutting, slant cutting and Irregular-Curve Cutting. And the roughness was at the micron grade. The average power of laser for cutting was lower than 1W. In the slant cutting, the angle between the cutting profile and the glass surface was 90 ~125. During the cutting, the time of laser action was short, and the position where the laser focused on was not continuous. So the heat affection was reduced greatly. Currently the maximum thickness of glass we can cut was 11mm. There was a lot of phenomenon during the process need to research further. And the roughness, cutting speed need to be improved. In addition, according to the character of this method, maybe it was more suitable for ultra-thin glass cutting. This was next focus of research.

6 Key Engineering Materials Vols References Reference an article: [1] Salman Nisar, M.A. Sheikh, Lin Li, Shakeel Safdar, The effect of material thickness, laser power and cutting speed on cut path deviation in high-power diode laser chip-free cutting of glass, Optics & Laser Technology. 42 (2010) [2] R.M. Lumley, Controlled separation of brittle materials using a laser[j], Ceramic Bulletin. 1969, 48: [3] Tonshoff HK, Ostendorf A, Kulik C, Hesener H, Haupt O, Final Glass Products in One Processing Step by the means of Laser Radiation. In: Proceedings of the 22 nd International Congress on Applications of Lasers and Electro-Optics, ICALEO. Jackonville, FL, USA: Laser Institute of America; 2003,pp [4] Tsai CH, Liou CS, Fracture mechanism of laser cutting with controlled fracture, Transactions of the ASME. Journal of Manufacturing Science and Engineering 2003;125: [5] Dekker JN, Zonneveld MH, Thermal Severing. The Cutting of Brittle Materials by Thermally Induced Fracture. In: Advances in Fracture Research. In: Proceedings of the 7th International Conference on Fracture. Houston, TX USA: Pergamon; 1989,pp [6] Junke Jiao, Xinbing Wang, Cutting glass substrates with dual-laser beams. Optics and Lasers in Engineering 47 (2009) [7] Verheyen W, Raes A, Coopmans JP, Lambert JL. Glass cutting, US Patent 1976; No [8] M. Ikeda, T. Shibata, E. Makino, Y. Takahashi, A. Ono, F. Matsumoto, Study on laser breaking of glass plate (1streport) generation and growth of vertical cracks by scribing. J Precis Eng (Japan), 62 (1996), pp [9] C.H. Tsai, H.W. Chen, Laser cutting of thick ceramic substrate by controlled fracture technique. J Mater Process Technol, 136 (2003), pp [10] Yao Guoling. The Research on Mechanism of Dual-wavelength Short-pulse Laser Induced Damage on K9 Glass [D]. : Changchun University of Science and Technology,2011. [11] M.A.Finucane, I.Black. CO2 laser cutting of stained glass[j]. The International Journal of Advanced Manufacturing Technology. 1996,12(1):47-59 [12] Egidijus Vanagas, Jouji Kawai, Kazutaka G.Nakamura. Glass cutting by femtosecond pulsed irradiation[j].society of Photo- Optical Instrumentation Engineers.2004,3(2) :

7 Micro-Nano Technology XIV / The Study of Glass Cutting Based on the Micro-Crack Control / DOI References [11] M.A. Finucane, I. Black. CO2 laser cutting of stained glass[j]. The International Journal of Advanced Manufacturing Technology. 1996, 12(1): /BF