Let us introduce the mechanism of scribing with the example of glass cutting.
Scribing is a processing method that utilizes the physical properties of brittle materials.
Through accurate control, a fine flaw (crack) is generated and propagated, which enables high-precision and high-quality cutting.
What is glass?
Quartz is a mineral made from crystallized silicon dioxide (Silica/SiO2), which is the main component in the commonly used glass. It is idiomorphically crystallized to a hexagonal columnar shape without distortion in many cases. Quartz is characterized by its high chemical resistance and high transmission of light in a wide range (from vacuum ultraviolet to infrared region).
- Glass has a non-crystalline amorphous structure. A non-crystalline amorphous structure appears when liquid is solidified by rapid cooling. Unlike crystals, it is isotropic and does not have a regular atomic arrangement.
- The features of glass include (1) transparency, (2) high moldability, (3) high degree of freedom of composition and physical properties, and (4) thermal and chemical stability. Taking advantage of the high degree of freedom of composition, various types of glass are made by fusing glass with materials other than silicon dioxide.
Soda-lime glass made with sodium (Na) and calcium (Ca) is inexpensive and can be easily processed and molded. Therefore, it is used in many glass products such as glass bottles. Non-alkali glass made with boron (B) instead of Na has a small dimensional change on being heated and cooled, and shows a high elastic modulus. Because of this feature, this type of glass is used for panels.
Two-stage process of crack propagation in scribing.
In scribing, the crack is propagated in the following two stages.
In the first stage, the crack is propagated when it is under the load of a scribing wheel. At this stage, the cut surface caused by the crack is called “rib mark” because it resembles the appearance of “ribs” owing to the effect of the tip shape of the wheel.
In the second stage, after the wheel has passed through, the crack is propagated again by residual stress.