Laser cutting is a thermal cutting process. With the help of a laser beam, the material, which is blown away downwards immediately after its formation with a gas stream, melts or vaporizes.
Solid-state laser compared to CO₂ laser
There are different versions of focused high-power lasers that are used in laser beam cutting. The most frequently used are the CO₂ laser (a gas laser) or the fiber laser (solid-state laser). The CO₂ laser is the more established cutting technology and has been used successfully for many decades. For some years now, however, the gas laser has been increasingly competing with the fiber laser. This special form of solid-state laser is particularly convincing due to its high efficiency compared to the well-known cutting system. The Nd:YAG laser, which like the fiber laser belongs to the group of solid-state lasers, is also becoming increasingly important in laser cutting. However, it is mainly used for micro-drilling and welding.
Compared to CO₂ lasers (carbon dioxide lasers), fiber lasers have significantly lower operating and maintenance costs. Thanks to the most modern and sophisticated technologies, they are at least on par with established lasers in terms of precision with different material thicknesses. However, the fiber laser is being used more and more frequently in laser cutting technology and is competing with the CO₂ laser. Compared to the still dominant CO₂ lasers, solid-state fiber lasers score with a number of strengths – first and foremost with the cost factor. Thanks to modern and sophisticated technologies, even supposed weaknesses can be eliminated. This makes the fiber laser a more than attractive alternative to the existing system.
The CO₂ lasers belong to the group of gas lasers and are also called carbon dioxide lasers or carbon dioxide lasers. They are based on a carbon dioxide gas mixture, which is electrically excited. CO₂ lasers score with a very good cutting quality and are mainly used for metallic materials but also for non-metallic materials like wood, textiles, plastics, foils, acrylic, glass, paper and leather. In contrast to fiber lasers, carbon dioxide lasers can also be used to process even thicker stainless steel sheets with good cutting quality – even at high feeding speeds. The CO₂ laser is the established laser type that has been used for decades and enables high quality with a wide range of material thicknesses. The disadvantage is the comparatively high operating and maintenance costs for the laser gases as well as for consumables working in the laser source. The efficiency is around 10 percent.
The fiber laser, which is a special form of solid-state laser, is on the advance. It scores with its cost-effectiveness, low operating costs and long service life of the wear parts. Thanks to a beam wavelength that is ten times shorter than that of the CO₂ laser, the fiber laser is also suitable for cutting materials that are otherwise difficult or impossible for the CO₂ laser to cut, especially non-ferrous metals (NF metals). For higher material thicknesses, a variable focus diameter is necessary to compete with the cutting quality of the carbon dioxide laser. The laser sources are also highly effective and consume significantly less input current for the same power. The so-called socket efficiency of the fiber laser is about 30 percent.
Like fiber lasers, Nd:YAG lasers are solid-state lasers and are also known as crystal lasers or vanadate lasers. Nd:YAG laser is the abbreviation for neodymium-doped yttrium-aluminum-garnet laser. A YAG crystal is used as host crystal. This technology is used less for laser cutting, but rather for engraving, welding and micro-drilling. Metals, metals with coatings and plastics are processed with this solid-state laser. In contrast to fiber lasers, however, this cutting technology has a high wearing of pump diodes. In addition, the lifetime of the neodymium-doped YAG crystal is shorter than that of the fiber laser.
A laser consists of three basic parts:
- Energy source
- Laser medium
The energy source, also called pump or pump source, has the task of "pumping" energy into the system. This creates a population inversion. The source can be electrical, but also light, heat or even another laser. Sufficient energy must be transferred into the laser medium to achieve population inversion – this means that the number of particles in the excited state must be higher than the number of particles in the ground state. The light of the laser is produced by spontaneous emissium in the excited laser medium and is amplified by stimulated emission. The resonator consists of two curved mirrors, one of which is partially transparent. Radiation originating from spontaneous emission and having the correct wavelength, phase and direction is reflected back and forth between them. Part of the radiation escapes as a focused laser beam through the partially transparent mirror and the other part is reflected back for further amplification.
In laser cutting, also known as laser beam cutting or CNC laser cutting, the focused laser beam is absorbed at the cutting front and thus generates a melt and metal vapour which is blown away downwards by a gas stream immediately after it is generated. A cutting gap remains, which can take on any contours depending on the feed direction of the laser beam.
Components processed with laser
Advantages and disadvantages of the fiber laser
The decisive advantage of fiber lasers is obvious: With this solid-state laser, up to half the costs for operation and maintenance of the CNC laser cutting system can be saved. This fact is of course significant for the increasing popularity of this technology. Not only does this cutting technology require no gases for beam paths, but the laser sources are also highly effective: the nominal power of a 4 kW fiber laser (with a cooling device) is about 18 kW compared to 57 kW for a 4 kW-CO₂ laser. Several maintenance costs of a carbon dioxide laser are also eliminated: the costs that depend on the life cycle of the discharge tubes or on the turbine in the cooling circuit of the laser gases or the vacuum pump. These account for an enormous part of the comparatively high maintenance costs of the CO₂ laser.
There are, however, other physical characteristics that are advantageous to the fiber laser: Thanks to a beam wavelength that is ten times shorter, fiber lasers can achieve a smaller beam diameter (i.e. a higher energy density) at the center of the cutting head – thus thin material can be cut faster than with the CO₂ laser. However, the thicker the material, the more this characteristic becomes a disadvantage due to the very thin kerf and a resulting risk of kerf filling with the discharge material (slag).
It is therefore necessary to have a larger focus diameter for cutting thicker materials. In the interest of industrial use, the laser cutting head should be able to change the focus diameter automatically – without the intervention of operating personnel, e.g. by manually changing lenses. In order to meet the versatile requirements of the market – i.e. to enable cutting over the entire material thickness range – MicroStep uses laser cutting heads from leading manufacturers such as Highyag, Precitec and Thermacut, tailored to the customers' needs, for maximum productivity in 2D cutting and bevel cutting of sheet metal, pipes or profiles. Due to the possible fully automatic control of focus position and focus diameter in combination with fast focus movements on the material, materials up to 25 mm thickness and more can be processed with a single fiber laser, depending on the laser source. The cutting heads do not require changing the ocular lens – only the cleaning of the protective glass is part of the operator's tasks.
The quality of fiber laser technology has improved considerably in recent years. Today, modern fiber lasers can cut mild steel up to a thickness of more than 25 mm, stainless steel up to 15 mm, aluminum up to 15 mm, brass up to 8 mm and copper up to 6 mm – and all this with very good quality.
Laser cutting technology has undergone enormous development in recent years. It is still used mainly in the smaller and smallest thickness range. The cutting range in modern laser cutting is between 0.5 and 30 mm, depending on the material and the power of the beam source, with optimum environmental variables.
Where is laser cutting used?
Due to the highly focused laser radiation and the high traverse speed, the thermal input into the material is limited to a narrowly defined area. This means that the components do not deform as much during laser cutting, which results in very high precision.
Laser cutting is mainly used in the automotive industry, in precision engineering, the semiconductor industry or by manufacturers of optical instruments. This cutting technology is used in all industrial sectors dealing with metalworking and cutting technology in general. The materials to be processed range from rubber to diamond stone. This cutting technology is mainly used for steel sheets of all types and grades, for stainless steel sheets and for non-ferrous metals such as aluminium and brass. Other suitable materials for laser cutting are titanium, plexiglass or acrylic glass, wood or bronze.
Laser cutting technology is predestined for use on a CNC cutting system. Modern laser cutting systems combine the advantages of the laser with the possibility of multifunctional processing on a CNC machine. Today's CNC lasers offer a wide range of configuration options for processing sheet metal, pipes and profiles. Thus cutting, drilling, tapping, countersinking, marking or bevel cutting – for example for weld edge preparation – is possible on one cutting machine.