Lasers have been used for cutting and welding thin metal sheets for 30 years, locally heating the material by focusing the beam. This method is flexible and economical, and it shines in many industrial applications. In fact, glass has a lower heat transfer than metal, so the laser should be able to be applied to the cutting of glass.
In fact, some companies began developing complete systems as early as the 1970s, when they used CO2 lasers with kilowatt output power levels. However, because of the high power level, the glass has a thermal influence that cannot be ignored, so that the local material is melted, so the laser cutting technology at that time is difficult to ensure a neat and smooth cutting edge. In many applications, it is still necessary to polish the cutting edge. At the same time, the price of CO2 lasers at the time was very expensive and daunting.
Recently, some engineers and scholars have discovered a glass cutting method that uses a lower power laser to separate the glass without causing thermal effects such as melting on the glass. This method is complicated and involves a lot of detail techniques. The basic principle is to use the laser induced stress to "separate" the glass. During the period, thanks to the development and maturity of the sealed-off CO2 laser technology, laser-cut glass technology is more economical and practical.
In our study, a CO2 laser with an average output of 150 W (Coherent's K-150) was used to form an elliptical focus point on the glass surface by focusing the optical path. The focus of the ellipse ensures that the laser energy is in the cutting line. Uniform and optimized distribution of the sides. The glass strongly absorbs the 10.6 micron laser, so almost all of the laser energy is absorbed by the 15 micron absorber layer on the glass surface, moving the laser spot relative to the glass surface to form the desired cutting line. Choose the right moving speed to ensure that there is enough laser heat to create a localized stress pattern (set cut line) on the glass without melting the glass.
Another key component in laser cutting is the quenching gas (water) nozzle. As the laser spot moves, the quenching gas (water) nozzle blows cold air (water) onto the glass surface to rapidly quench the heated area, and the glass will follow A fracture occurs in the direction in which the stress is greatest, thereby separating the glass in a set direction.
It should be noted that in order to induce cracking of the glass, it is necessary to first mechanically draw a slight initial crack at the starting point of the cutting line.
Selecting different processing parameters such as laser power and spot scanning speed, the stress-induced fracture depth can reach 100 micrometers to several millimeters, which means that the laser can be used to cut glass with a depth of 100 micrometers to several millimeters in one step.
Because this process relies on thermo-induced mechanical stress, the depth of fracture and the cutting speed are related to the expansion coefficient of the material itself. In general, the glass suitable for laser cutting should have a coefficient of expansion of at least 3.2x10-6K-1. Fortunately, most ordinary glass meets this requirement.
This new approach has several important advantages over traditional mechanical cutting methods. First of all, this is a dry, one-step process. The edges are smooth and tidy and do not require subsequent cleaning and sanding. Moreover, the laser-induced separation process produces high-strength, naturally tempered edges with no micro-cracks. Using this method, unpredictable cracks and breaks are avoided, the defective rate is reduced, and the yield is increased.
Qualitatively describe the dynamic difference between three different cuts on a 1.5 mm thick piece of glass. The edges of the glass cut are clean without lobes and cracks and do not require subsequent processing. Because the laser is a non-contact tool, there is no wear problem with the tool, which guarantees consistent, uniform cutting thickness and edge quality. For comparison, 3(b) shows the edge of the cut using a metal wheel, and it can be seen that there are various residual tension components along the cut line. 3(c) is the result of diamond wheel cutting, and many tiny cracks can be seen. For many applications, the cutting edge needs to be sharpened.
In order to quantitatively evaluate the edge quality, according to ISO 3274, the edge of the laser cut should be measured using a Stylus profilometer. Authoritative measurements show an average roughness (Ra) of less than 0.5 microns. Edge strength Because of the excellent edge quality and the natural tempering effect during heating/quenching, the edge strength of laser cutting is very high. The Otto-Schott-Insititut Institute of Jena has been independently tested according to the DIN 5230011 parameters and the relevant data has been published. With this new method, the edge strength is increased by about 30% compared to the polished sample after mechanical processing.
There are three factors that limit the cutting speed: the thickness of the glass, the coefficient of thermal expansion of the material, and the output power of the laser. In this test, we cut a glass of a = 7.2 x 10-6 and a thickness of 1.1 mm using a CO2 laser with a power output of 150 W, and cut it at a speed of 500 mm/sec. In comparison, a hard metal wheel cuts the same thickness of the same glass up to 1500 mm/sec. However, even in speed-conscious applications, this difference will be offset by the economic and quality advantages of laser cutting. At the same time, we believe that further process optimization and cutting with higher output power lasers can easily increase processing speed by two to three times.
Since the crack is a trace drawn exactly along the laser beam, the laser-induced separation can cut out a very precise curve pattern.
In fact, the experiments we have done also prove that laser cutting can continuously and accurately complete the set pattern, regardless of the line or curve, with repeatability up to +50μm. So the laser can perform precise cutting of curves and 3D graphics.
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