Sodium-lime glass YAG laser cutting technology using crack control method

As a brittle material, glass has a uniform texture, good transparency, smooth surface and corrosion resistance. Therefore, it has been widely used in scientific research and industrial and agricultural production. Especially in recent years, with the rapid development of the IT industry, high-tech electronic products such as liquid crystal displays and plasma displays have emerged, and the requirements for the quality of glass products are getting higher and higher.

The traditional method is to use a diamond or hard metal wheel to scribe on the surface of the glass, and then mechanically break it, which easily leads to splashing of the cutting powder, irregular cutting edges, generation of micro cracks and even glass breakage. The surface quality of the cutting edge is very good. Poor, often requires secondary processing and may affect the strength and function of the glass. Cutting the glass with laser can avoid these problems, and also has the advantages of narrow slit, good verticality of the slit edge, smooth cut surface without burr, and small heat affected zone.

1 Principle of laser-cut glass The method of laser-cutting glass can be divided into two principles in principle: one is melting (evaporation) cutting method, and the other is crack control method. The melt cutting method has a poor cutting effect, and it is easy to form hot cracks in the slit section, so that the strength of the material is greatly reduced, and the re-condensation due to laser ablation may contaminate the substrate. The crack control method has the advantages of straight slit, no broken shoulder, no microcrack.

The glass laser cutting using the crack control method is to use a laser to heat the surface of the glass, so that the temperature at the heated portion is sharply increased, and a large compressive stress is generated in the glass. As the laser moves, the heated glass is convected under air. Cooling produces residual tensile stress, and if the stress exceeds the breaking strength of the glass, the crack expands to break.

The stress is: length.

There are two typical forms of glass absorption of laser light: one is the surface absorption form and the other is the body absorption form. It can be seen that when the wavelength is above 5 pm, the absorption rate of light by glass is very high, and the CO2 laser with a wavelength of 10.6 pm is easily absorbed on the surface of the glass.

Therefore, when the glass is cut by the CO2 laser, the crack spreads from the surface, the quality of the slit is poor, the thickness of the cut glass is limited, and the multilayer glass cannot be cut, and the crack is not well controlled during cutting. The YAG laser with a wavelength of 1064 nm can penetrate the glass. The absorption of laser energy by the glass is a form of bulk absorption. The cracking of the glass is uniform and transparent. The YAG laser cutting glass method based on bulk absorption can not only obtain better cutting quality. Moreover, it can cut multi-layer glass, laminated glass and glass tube, complete cutting at one time, without secondary processing, and can draw any curve in addition to straight line cutting.

2 Test apparatus and method 2.1 The test apparatus fiber output maximum power 300W, laser focal spot diameter 0.6mm. The specimen was observed by 2400x optical microscope and scanning electron microscope. The plate soda lime glass size was 70 mm x 50 mm x 2.5 mm and the test apparatus was as shown.

2.2 Test Methods Laser power, laser scanning speed and laser spot size are the three most important factors affecting the quality of glass cutting. The laser power required to determine the optimum cutting quality for different spot diameters and scanning speeds is determined by a single factor test method that changes the spot diameter, laser scanning speed, and laser power. According to the test results, the influence of three parameters on the cutting quality and the relationship between them were analyzed. The test parameters are as shown in Table 1. Test parameters 3 test results and analysis of bookmark3 3.1 laser cutting and mechanical cutting glass cutting quality, as shown, It can be seen that the slits obtained by cutting the soda-lime glass with YAG laser are straight, without broken shoulders and without micro-cracks, while the cuts obtained by mechanically cutting the soda-lime glass plate have obvious broken shoulders and the slits are not straight. There is also a crush layer on the surface (as shown in (d)), and there is a broken shoulder in the crushed layer, which seriously affects the cutting quality. It can be seen from the surface roughness of the slit shown that the surface roughness of the glass cut by YAG laser is 2.9 nm; the surface roughness of the glass cut by mechanical scribing is 26.5 nm, and the YAG laser cutting method has obvious quality compared with the mechanical cutting method. Advantage.

3.2 Influence of laser parameters on cutting quality 3.2.1 Influence of laser power on cutting quality For a certain spot size and cutting speed, there is always the best laser power value to make the crack propagation most stable, and the obtained glass incision is the most straight and quality. the best. Below this value, the glass does not crack or begin to crack, and only a short crack is suddenly exploded at the end of the glass along the laser sweeping trajectory, and the crack is not straight (as shown). Above this value, cracks appear on the upper and lower surfaces of the glass, and then cracks in the middle, resulting in the notch being concave and convex, and the greater the energy, the worse the quality of the incision, and even the glass bursts with a certain kinetic energy, and the slit produces a glass broken shoulder. . The reason is summarized as the residual tensile stress generated by the laser energy absorbed by the glass is less than the crack propagation strength when the laser power is too low, so the crack does not extend along the laser trajectory; and when the laser power is too high, the temperature inside the glass The field temperature is very high, and the upper and lower surfaces of the glass are rapidly cooled under natural convection conditions due to direct contact with the air, generating a large enough tensile stress to cause the crack to expand, and the middle portion is slow to generate a slow tensile stress, so the crack propagation lags behind. The upper and lower surfaces, such uneven cracking, result in a low quality of the glass cut.

3.2.2 Influence of laser scanning speed on cutting quality The higher the laser scanning speed, the higher the laser power required to cut the glass, and it is approximately linearly proportional. However, the laser scanning speed cannot be increased without increasing the laser power, because when the laser scanning speed is increased to a certain value, the crack propagation speed is unstable, resulting in a decrease in the quality of the slit. During the test, it was found that when the laser scanning speed was increased to 15 mm/s, the crack suddenly accelerated and expanded, resulting in unevenness of the glass cut and poor quality.

3.2.3 Effect of laser spot size on cutting quality The larger the laser spot, the higher the laser power required to cut the glass. Generally, the cutting glass uses a larger spot to reduce the temperature field and thereby reduce the ablation and melting of the glass, thereby realizing glass laser cutting based on the crack control method. During the test, it was found that when the laser spot diameter is less than 1.0mm, melt cutting will occur; when it is larger than 1.0mm, glass laser cutting based on crack control method can be realized, and it is obvious that there is no ablation and melting on the upper and lower surfaces of the glass incision, and the quality is very high. Ok (as shown). The velocity increases substantially linearly, and as the diameter of the laser spot increases, the slope of the curve also increases.

3.3 Multilayer glass, glass tube and curved track cutting YAG laser can be used to cut multiple layers of glass and laminated glass (as shown). When the multi-layer glass is cut, the quality of the undercut glass is better than that of the upper glass, because the lower glass absorbs less laser energy than the upper glass and does not cause ablation melting. In addition, the YAG laser can also cut curves and tubular glass (as shown) with good cut quality.

(a) Optical micrograph of the glass cut on the lower surface of the upper surface (b) 3.2.4 Optimal cutting parameters The optimal cutting parameters of the YAG laser-cut flat soda lime glass can be obtained by adjusting the parameters such as laser power, scanning speed and spot size. (as shown). It can be seen from the figure that the laser power is scanned with the laser. 4 The glass is in the form of bulk absorption of the YAG laser. The crack is transparently cracked throughout the thickness of the glass. The YAG laser cut glass is straight, smooth, free of burrs and microcracks. Laser power, laser spot size, and laser scanning speed are important parameters that affect cutting quality.

For a certain spot size and cutting speed, there is always the best laser power value to make the crack propagation most stable, and the obtained glass cut is the most straight and the best quality. There is an upper limit to the laser scanning speed. When the scanning speed is too high, the crack will be unstable and the cutting quality will be affected. The quality of the upper and lower surfaces of the slit can be improved by selecting a larger spot.

In order to ensure the best cutting quality, the laser power should increase with the laser scanning speed and spot size. Relatively certain laser scanning speed and spot size, there is always the best laser power value to optimize the quality of the glass cut. (Continued to page 520) The ideal sintering temperature is 1 320t. Adding a small amount of FeMn is beneficial to the improvement of density and mechanical properties. After 300MPaCIP, 1320t sintering and 1250t/120MPa HIP treatment, the elastic modulus of 3% FeMn+AISI316L sample, The yield strength, tensile strength and elongation reached 209.5 GPa, 306 MPa, 656.45 MPa and 53.1%, respectively, which were comparable to those of the annealed AISI 316L dense material.

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