The main laser cutting processes include 1. vapor cutting, 2. melting cutting, 3. oxidation cutting, and 4. controlled fracture cutting.
Using a high energy density laser beam to heat the workpiece, the temperature rises rapidly, reaching the boiling point of the material in a very short period, and the material begins to vaporize, forming vapor. These vapors are ejected at a large rate, and a kerf is formed in the material while the vapors are ejected. Some of the material then vaporizes and disappears as vapor. Some of the material is blown away as ejecta from the bottom of the cut by the auxiliary gas stream. The heat of vaporization of the material is generally very high, so a high power and power density are required for laser vapor cutting.
Laser vapor cutting is mostly used for the cutting of very thin metallic materials and non-metallic materials (e.g. paper, cloth, wood, plastic, and rubber).
When laser melting cutting, the laser is used to heat the metal material to melt, and then non-oxidizing gases (Ar, He, N, etc.) are sprayed through the nozzle coaxial with the beam, and the additional airflow coaxial with the beam takes away the molten material around the hole. As the workpiece moves, the small hole is synchronized across in the cutting direction to form a slit. Depending on the strong pressure of the gas, the liquid metal is expelled, and a slit is formed.
The laser beam continues along the front of this slit, and the molten material is continuously or pulsatingly blown away from the slit.
Laser melting cutting does not require the metal to be completely vaporized. Laser melting is mainly used to cut materials that are not easily oxidized or reactive metals, such as stainless steel, titanium, aluminum, and their alloys.
3. Oxidation cutting
Melting cutting generally uses inert gas; if replaced by oxygen or other reactive gases, the material is ignited under the irradiation of the laser beam, and oxygen to produce a violent chemical reaction and another heat source, known as oxidation cutting.
The principle of oxidation cutting is similar to that of oxyacetylene cutting. It uses the laser as a pre-heating heat source and an active gas such as oxygen as the cutting gas. The gas is blown out acts on the one hand with the cutting metal and an oxidation reaction takes place, giving off a large amount of oxidation heat; on the other hand, the molten oxides and melts are blown out of the reaction zone and a kerf is formed in the metal. Due to the large amount of heat generated by the oxidation reaction during the cutting process, the energy required for laser oxygen cutting is only 1/2 of that required for melt cutting, while the cutting speed is far greater than that of laser vapor cutting and melting cutting.
Laser oxygen cutting is mainly used for carbon steel, titanium steel and heat-treated steel, and other easily oxidized metal materials.
4. Controlled fracture cutting
For brittle materials susceptible to thermal damage, a high-speed, controlled cut-off by heating the laser beam is called controlled fracture cutting. The main elements of this cutting process are: the laser beam heats a small area of brittle material, causing a large thermal gradient and severe mechanical deformation in the area, leading to the formation of cracks in the material. The laser beam can guide the creation of cracks in any desired direction as long as a balanced heating gradient is maintained.
Controlled fracture uses the vertical temperature distribution created when the laser scribes a groove to create local thermal stresses in the brittle material, causing the material to break along the small groove.