Laser Cutting Theory
In order to understand what makes a laser suitable for cutting, one must distinguish its unique features in comparison to ordinary light.
Conventional light produces waves which radiate out in all directions to fill up and illuminate a wide area. The energy intensity rapidly decreases as one moves away from the source, just as the sun’s intensity diminishes when it finally reaches the earth.
The laser on the other hand provides a stream of collimated, coherent light waves which give it exceptional intensity and direction ability. Lacking the dispersion of conventional light, a laser can be easily projected as a beam over relatively long distances while maintaining nearly all of its useful power output.
The use of lasers for cutting can be thought of in the same way as that of focusing sunlight with a magnifying glass to produce a concentrated source of heat energy. While this method only results in a few burned holes in paper, it gives us an illustration that light is indeed a source of energy with potential material processing capabilities.
A laser can be used for cutting by exposing material to the intense heat energy developed by its beam. If that heat input to the material is greater than that material’s ability to reflect, conduct, or disperse the added energy, it will cause a sudden rise in temperature of the material at that point. If the temperature rise is substantial enough, the input heat is capable of initializing a hole by vaporizing the material. The linear movement of this intense heat energy with respect to the material provides cutting action.
In most cases the “raw” (unfocused) beam of even high power (multi-kilowatt) industrial lasers has inadequate energy to do much more than slowly heat a surface. Therefore, the beam is directed through a focusing lens. This allows the energy to be concentrated into a spot of less than 0.25 mm thus producing power densities of over a million watts per centimeter squared, capable of vaporizing many materials.
While intense heat is capable of vaporising material, the control of that heat is essential in determining quality. The key performance features of a laser are those beam characteristics that affect the resultant power density as it is directed onto the workpiece.