Lasers were first used for cutting back in the 1970s. In modern industrial production, laser cutting is more widely used for processing materials such as sheet metal, plastics, glass, ceramics, semiconductors, textiles, wood and paper.
When a focused laser beam shines on a workpiece, the irradiated area heats up dramatically to melt or vaporize the material. Once the laser beam penetrates the workpiece, the cutting process begins: the laser beam moves along a contour line while melting the material. The molten material is usually blown away from the kerf by a jet of air, leaving a narrow slit between the cut part and the plate holder that is almost as wide as the focused laser beam.
Flame cutting
Flame cutting is a standard process used when cutting mild steel, using oxygen as the cutting gas. Oxygen is pressurized to up to 6 bar and blown into the kerf. There, the heated metal reacts with the oxygen: combustion and oxidation begin. The chemical reaction releases a large amount of energy (up to five times the energy of the laser) which assists the laser beam in cutting.
Melt cutting
Melt cutting is another standard process used when cutting metals. It can also be used to cut other fusible materials, such as ceramics.
Nitrogen or argon gas is used as the cutting gas, and a gas pressure of 2 to 20 bar is blown through the kerf. Argon and nitrogen are inert gases, which means that they do not react with the molten metal in the kerf, but simply blow it away towards the bottom. At the same time, the inert gases protect the cut edge from air oxidation.
Compressed air cutting
Compressed air can also be used to cut thin plates. Air pressurized to 5-6 bar is sufficient to blow away the molten metal in the cut. Since nearly 80% of the air is nitrogen, compressed air cutting is basically a melt cutting.
Plasma-assisted cutting
If the parameters are properly selected, a plasma cloud will appear in the plasma-assisted melt cutting kerf. The plasma cloud consists of ionized metal vapor and ionized cutting gas. The plasma cloud absorbs the energy of the CO2 laser and converts it into the workpiece so that more energy is coupled to the workpiece and the material will melt faster, resulting in a faster cutting speed. Therefore, this cutting process is also called high speed plasma cutting.
The plasma cloud is in fact transparent with respect to solid-state lasers, so plasma-assisted melting cutting is only possible with CO2 lasers.
Gasification Cutting
Vaporization cutting vaporizes the material, minimizing the impact of thermal effects on the surrounding material. This can be achieved by using a continuous CO2 laser to vaporize low-heat, high-absorption materials, such as thin plastic films and non-melting materials such as wood, paper, and foam.
Ultrashort pulsed lasers allow this technology to be applied to other materials. The free electrons in the metal absorb the laser and heat up dramatically. The laser pulse does not react with the molten particles and plasma, the material sublimates directly and there is no time for the energy to be transferred to the surrounding material in the form of heat. Picosecond pulses ablate the material with no visible thermal effect, no melting and no burr formation.
Parameters: Adjustment of the process
Many parameters affect the laser cutting process, some of which depend on the technical properties of the laser and machine tool, while others are variable.
Polarization
Polarization indicates what percentage of the laser light is converted. Typical polarization is usually around 90%. This is sufficient for high quality cutting.
Focus Diameter
The focal diameter affects the width of the cut and can be changed by changing the focal length of the focusing lens. A smaller focal diameter means a narrower kerf.
Focus position
The focal point position determines the beam diameter and power density on the surface of the workpiece as well as the shape of the kerf.
Laser Power
The laser power should be matched to the type of processing, material type and thickness. The power must be high enough that the power density on the workpiece exceeds the processing threshold.
