A new technology makes it possible to use enveloped CO2 lasers to create sharp, high-quality markings directly on glass. This is a technology that can replace expensive solid-state lasers and traditional glass marking methods (25W CO2 lasers Meet most of the requirements for marking on glass). The CO2 laser marks the glass by breaking the glass surface, so that a certain amount of cracks on the glass is allowed, but excessive cracks will result in unclear marks, potentially weakened material strength, and more seriously make the substrate become loose. Accurately controlling the amount of cracking in the marking process can avoid these problems.
There are three methods that can be used to control the type and amount of cracks generated on the glass surface: the first method uses multiple laser radiation; the second method is to use discrete points to form a ring crack; the third method is to produce a cracked surface crack. Using a single laser irradiation produces a sharp-edged visible mark on the glass, but the direction of the crack and stress pattern will extend perpendicular to the direction of laser movement. Shortly or even several days after marking, these cracks perpendicular to the moving direction of the laser will form new cracks, extend to the area near the original mark to form debris, and thus affect the clarity of the mark. With multiple laser radiation, the areas adjacent to the marked area are heated by heat conduction so that these areas form a stress gradient, reducing the possibility of secondary breakage. This method is very effective in marking soda-lime glass and borosilicate glass. One laser radiation is more effective in marking silica glass and quartz glass because the expansion coefficient of these two materials is very low.
The second method uses a series of circular cracks to form text, bar codes, square or rectangular codes, and other shape code patterns. The glass generates low-density annular cracks through heating and cooling cycles. When the glass is heated, it expands and squeezes the surrounding material. When the temperature rises to the softening point of the glass, the glass rapidly expands to form a dome of the low-density material on the convex glass surface. After heating, the glass shrinks to the initial surface position, but this relaxation time is the time for the entire low density to form, making it unable to return to the initial position before the softening temperature.
Three different marking methods were used to mark the glass with a CO2 laser, ie, multiple passes of the laser; discrete points formed a ring-shaped crack and a cracked surface crack.
Since the spot energy is Gaussian, the temperature at the center of the spot is high. When this high temperature zone returns to near the initial position, the center of the annular crack is formed in this zone. A stable annular crack is formed at the junction between the low density formation region and the standard density region. This method is suitable for marking ordinary optical materials and tempered glass, chemically-reinforced glass, or ordinary soda-lime float glass.
The third method also uses the same heating and cooling process, both to change the surface of a particular volume of glass. However, the size of the spot used in the third method is relatively large, and the boundary between the two density regions is not as clear as the ring crack method. Marks produced by this method are not immediately visible, requiring slight pressurization before starting to produce lattice cracks along the laser marking area. The text, graphics, and various codes are formed using the resulting chipless fringe pattern. Because this method requires a pure surface, clear marks can be printed with high-quality automotive glass.
