Laser Cutting header
Laser cutting is continuously evolving and is progressing towards applications demanding great quality, on an ever increasing range of thicknesses and cost savings sought even when processing batches containing a higher number of pieces.
Thanks to the increased ability to focus laser beams, it is possible to achieve tight, parallel cut edges, a much reduced thermally altered zone, limited heat distortion, the capacity to operate on complex profiles and with tiny bends of the rays (also sharp edges).
In practice laser cutting produces finished pieces that do not require any further manipulation (e.g. drilling) or finishing (e.g. emery-polishing etc).
The term Laser is an acronym for “Light Amplification Stimulation Emission of Radiation”. A medium is excited to enable it to emit a coherent and monochromatic source of light (single wavelength).
The laser beam can be focused, concentrating a high power density onto one single spot so that it reaches extremely high temperatures, in a short space of time; temperatures which are often higher than the vaporisation temperatureof the various materials involved.
The most common types of cutting laser are:
1) the CO2 laser which uses a gas lasing medium and is available in output power levels of up to 40Kw.
2) the Nd YAG laser : which uses a crystal lasing medium and is available in output power levels up to 5Kw.
3) the Fibre laser, using the “core” of an optical fibre doped with ytterbium (Yb) as an active gain medium which is subsequently pumped by lamp diodes. Fibre lasers today reach output power levels of up to 50 Kw.
Laser cutting is a process which in a just few years has gained huge market share, being used today to cut various metallic and non-metallic materials in a wide range of thicknesses (carbon steels up to 30 mm, stainless steel up to 20 mm, light alloys up to 20 mm, but also Plexiglas up to 30mm, wood etc) and in a wide range of applications:
Gases are of major importance in this technology, performing three different roles:
1. Shielding gases the optical course: have the job of keeping the optical course free from dust and contaminants. Atmospheric air is not always the best choice for this application. Hydrocarbon residues, even in well filtered air, and humidity can become deposited on the mirrors along the optical course, absorbing energy with consequent, and at times irreparable, damage and variations in the working environment. SIAD recommends Laser Nitrogen from its Laserstar range for these applications.
2. Lasing Gases: For CO2 source lasers (the most widely used laser in this application), lasing gases contribute to the execution of the process. To obtain the stable power, over time, required for mechanical work it is necessary to use the correct gas mixtures made up principally of:
- Carbon dioxide: the most important gas, in the lasing gas mixture, in that it gives rise to the laser effect;
- Nitrogen creates the environment which enables high power density levels to be reached with the laser light generated;
- Helium enables efficient dissipation of the heat generated by the incoming electric power in the mixture.
3. Assist Gases: play a major role both in the execution of the process and in the quality of the finish. Metal cutting is carried out using two different techniques: Oxyfuel combustion and fusion cutting each using its specific assist gas.
Oxyfuel combustion is used to work carbon steels and construction alloy steels. This technique uses oxygen which favours the exothermic reaction with the metal, making it possible to reach faster work speeds and protects the lens from the spatter and vapours produced. The purity of the oxygen, in this case, plays a pivotal role in the cutting of mild steel or steel with a low carbon content. It has been demonstrated how, if one goes from a purity level equivalent to 99.5% to a level equivalent to 99.98% it is possible to increase cutting speeds by up to 20%.
Thanks to close working relationships with the manufacturers of laser plants, SIAD has developed HIGH SPEED OXYGEN, a gas with a purity level of 99.999% and with particularly low Argon content to enable superior quality levels and high speeds to be attained