Laser Cutting Theory
LASER CUTTING VARIABLES
An important asset of laser cutting is the high level of control which is available over the variables affecting the process. The cut can be tailored to meet the exact requirements of the job and the results can be readily duplicated. The principle variable parameters are:
- Focusing Lens
- Focal Point Position
- Assist Gas
Since speed is a function of available power density, the choice of the focusing lens has a great impact on the resulting cut quality. Imaging of lasers beams is usually accomplished with transmissive lenses of focal lengths ranging from 2.5 to 10 inches. Because the focused spot size is proportional to the focal length, the power density that is produced is proportional to the square of that length. Short focal length lenses give very high energy densities, but are limited in their application due to a shallow working depth. They are appropriate for use with thin materials and in high speed operations where the material can be held within the limited depth of field. Longer focal length lenses have lower power densities but are able to maintain those densities over a much broader range and therefore can be used for thicker cross sections of materials given that they have enough energy initially.
Focal Point Position
During the laser cutting process, the focal point of the lens should be consistently positioned in order to provide the best cutting results. In most cases, the focal point is positioned at or slightly below the surface of the material. Above or below this point the power density will taper off until it is insufficient to produce an effective cut. Cutting systems that employ short focal length lenses must ensure constant monitoring of the lens-to-workpiece distance.