LASER CUTTING has been the major application for industrial lasers in manufacturing for the last 30 years. It is a well-established process that offers many advantages and benefits over traditional cutting methods. Laser cutting is typically high speed, repeatable and reliable, producing a very narrow and clean kerf (cut width) in a wide variety of material types and thickness. It is a process that can easily be automated by integration into flexible programmable machine tools or robots.

Cutting lasers typically are CO₂ or Nd:YAG, available in power levels ranging to 6 kW. Cutting occurs when the focused laser beam comes in contact with material, vaporizes and/or melts the material. The melted material is expelled by means of a process assist gas, typically oxygen, nitrogen or argon, through the backside of the material. The assist gas is directed into the cutting area via a nozzle. Oxygen is used for low pressure cutting (100 psi) but can leave a minimal oxidization on the cut edges. High pressure cutting (up to 400 psi) uses inert gases such as nitrogen or argon and will leave the cut edge free of oxidization.

Lasers are the ideal tool for cutting carbon, stainless and zinc coated steel, as well as super alloys. In addition, more difficult materials can be cut with lasers, such as titanium and aluminum. The laser can cut materials that have been coated with enamel, porcelain or ceramic without damage to the outer coating.

The laser is capable of cutting to very tight tolerances thanks to the temporal and power stability of the laser beam. Parts are free of distortion because laser cutting requires no physical contact between the work piece and a cutting tool. There is little or no distortion from heat and the heat affected zone is minimal. In addition, the laser has a kerf as small as 0.005" (0.125 mm). By varying the cutting speed, power, focus spot size, focus position and assist gas pressure, characteristics of the cut such as kerf, taper, and surface finish, can be controlled to complement the material type. Dross (burr) from laser cutting is minimal with most materials.

Laser cutting is extremely repeatable when compared to traditional processing methods. The tool does not change size or wear when optimum parameters are established for an application - the laser will perform continuously. The laser can be integrated to multiple axis machine tools controlled by programmable CNCs that are capable of processing complex 2D and 3D parts. These systems (machine tool and laser) are extremely flexible - operators can change from one part to another in as little time as it takes for the CNC's computer to load a new program. Laser cutting saves set-up and cycle time and, therefore, money. Tooling and associated costs are all but eliminated. Easily programmed beam motion, combined with the narrow kerf, allows programmers to "nest" parts, reducing waste or scrap material remaining after processing.

Power or average power is determined by the pulse frequency and pulse energies selected. Most axial flow CO₂ lasers can be operated in both a pulse mode or continuous wave. Transverse flow CO₂ lasers can operate only in continuous wave, but can be modulated by use of a beam chopper. Nd:YAG lasers historically have operated in either a pulsed mode or continuous wave, but not both. The newest design of CW:YAG does have enhanced pulse capability. The typical operating range for cutting with a CW CO₂ laser is 100 to 5000 watts. In the pulsed mode, lower average powers can cut metal due to higher (peak instantaneous) powers. The power ranges for cutting metal in the pulsed mode range from less than 100 watts to 2000 watts (for CO₂ lasers). Cutting with Nd:YAG pulsed lasers is done with power of less than 100 watts to over 400 watts. When operating in the pulsed mode, the laser parameters to be selected are pulse length, pulse frequency, and pulse energy.

Pulse length is selected to optimize the quality of the cut surface. Shorter pulse lengths (<0.75 msec) are used to produce intricate cutting in thin metals. Shorter pulse lengths may limit the maximum energy achievable in a single pulse. Longer pulse lengths (up to 2 msec) provide greater pulse energies, allowing thicker metals to be cut. Similar pulse lengths are used for both CO₂ and Nd:YAG lasers.

Pulse frequency is adjusted to give the maximum cutting speed for the quality required. In general, higher frequencies are used to cut thinner metals. For CO₂ lasers, higher frequency ranges from 200 to 2000 Hz. In Nd:YAG lasers, higher frequencies range from 30 to 100 Hz. Lower frequencies are used when cutting thicker metal sections.

Pulse energy needed in cutting is related to material thickness. As metal thickness increases, greater pulse energy is required. CO₂ lasers deliver maximum pulse energies up to 2 joules at longer pulse lengths and lower pulse frequencies. Nd:YAG lasers can produce much higher pulse energies, up to 80 joules, with pulse frequency limited by the maximum average power rating of the laser.

Lens choice is based on metal thickness, composition, and quality requirements. Unfocused beam diameter is an important consideration in lens selection. The following guidelines are useful with beam diameters from 0.5" to 1". For CO₂ lasers, a general rule is a 2.5" focal length lens is most often used for metals up to 0.25". A 5" focal length is most often used for metals from 0.2" to 0.625" and a 7.5" or 10" lens is most often used for materials greater than 0.5". Some metals, such as aluminum, require a larger kerf width for acceptable quality. Wider kerf widths are obtained by using longer focal length lenses. Typical focal length lenses for Nd:YAG lasers range from 4" f.l. for metals below 0.125" to 6" f.l. to 10" f.l. for metals up to 1". Above 1" thick metals require even longer focal lengths.

A gas jet is a device that provides a coaxial, columnar flow of gas through the cut slot to remove molten metal. The gas used can be oxygen, inert gas, or air, depending on material type and quality requirements. Oxygen is most commonly used for cutting steels. When an oxide-free surface is desired, an inert gas, such as helium, is used. Gas pressures for oxygen range from 15 to 50 psi while inert and air pressures range from 30 to 90 psi. Typical nozzle orifices range from 0.030" to 0.100". Nozzle stand-off varies up to 0.06" for CO₂ lasers and up to 0.200" for Nd:YAG lasers. Nozzle stand-off and gas pressure can have a tremendous effect on cut quality.

Using a CO₂ laser, a clean cut (oxide-free and dross free) can be achieved in thin sections of metals such as stainless steel, aluminum or titanium, using inert coaxial gas with minimum nozzle stand-off.