Laser Cutting Process
Basically, metal laser cutting is effected by locally heating the material at the focal point of the focused laser beam above its melting point. The resulting molten material is ejected either by a coaxial gas jet or the induced vapor pressure, thus forming the cut kerf. The cut geometry, cycle time, system technology and, above all, the material composition are the crucial factors for the decision which laser source to chose.
Laser Fusion Cutting
In the case of higher alloyed steel and aluminum, an inert gas (nitrogen, argon) is typically used as a cutting gas. This process is solely depending on the energy of the laser beam. The required laser power is therefore higher than that for laser flame cutting. Laser fusion cutting affords oxygen-free cut edges, which is particularly important when welding is the next process step after cutting. Today, laser fusion cutting is used industrially for material thickness of up to 15 mm.
There are three different cutting processes:
- Fusion cutting
- Flame cutting
- Sublimation cutting
In principle, both high power CO2 and solid-state lasers are suited for this kind of applications. Providing higher average power, CO2 lasers are an excellent option for the separation of thicker cross sections.
Laser Flame Cutting
For low-alloyed steel in particular, oxygen is typically used as a cutting gas. This process, known as laser flame cutting, receives additional energy from the exothermic reaction of the material, which is heated above the ignition temperature. The required laser power is therefore lower than for laser fusion cutting. Today, laser flame cutting is used in industry for material thicknesses of up to 25 mm.
Here, too, both high power CO2 and solid-state lasers are applied. Providing higher average power, CO2 lasers are an excellent option for the separation of thicker cross sections.
Laser Sublimation Cutting
In sublimation cutting the material is molten by the absorbed laser energy until it partially evaporates. since the resulting steam is pressurized, material removal is effected by ejection from the open cut against the beam impact direction. This requires significantly higher power densities is simultaneously associated with much slower speeds than the two cutting processes mentioned above.
Since the cutting depth in a single-pass is typically in the range of some 10 microns, thicker materials are separated by the so-called multi-pass process. Commonly, material thicknesses that can be cut economically do not exceed 1 mm.
Here, mostly solid-state lasers are employed for metals, ceramics, or diamond and CO2lasers are applied for ceramics and plastics. Pure sublimation cutting processes, that means the direct transition from solid to gas state, are applied for cutting of wood and PMMA.
Materials
Besides the already named materials and applications the laser cuts also ceramic, graphite, nonferrous metals such as titanium and brass, leather, abrasive paper and many more materials. Many plastics, wood and paper can only be cut with the CO2 laser as they are too transparent for the solid-state lasers. Metals can be cut with the CO2 laser as well as with the solid-state laser.
|
