Laser cutting

How laser cutting works?

September 25, 2020

Sheet metal cutting is the most common laser cutting application undertaken by industries today. Such cutting is achieved mainly through laser vaporization, laser melting or flame cutting. The method chosen depends on the material to be cut, type of cut required, available power and processing requirements. One may wonder how a laser helps in cutting in the first place.

In a typical laser cutting set-up, the magic takes place between the laser resonator and the tip of the nozzle. The laser comes to life in the laser resonator/generator. In the case of CO2 lasers, this happens in a special gas medium and in fiber lasers, in a solid-state medium (a bank of diodes).

From there on, the laser beam goes places. In a CO2 laser, the beam is guided with the help of a system of mirrors within the resonator that helps the beam gain intensity. Once the beam exits the resonator, it is sped along its path with another set of cooling mirrors before it arrives at the cutting head. Meanwhile, the beam in the fiber laser bounces along the fiber optic cable until it reaches the head.

The functioning mechanisms of both types of lasers in the cutting head are the same. The laser beam is focused with the help of a special lens/curved mirror in the cutting head. It is concentrated on a very small area through the center of the cutting head. The concentration of energy at intense levels results in the heating, melting or vaporization of the metal workpiece. Simultaneously, the assist gas is blasted onto the area through a nozzle built into the cutting head.

Stages of laser cutting and parameters that affect the cut quality

The stages of laser cutting are beam generation, beam focusing, heating and melting of the working area and beam movement. The final quality of the laser cut that emerges from these stages depends on the following: 

Material parameters: The type of material, as well as its shape, thickness and thermal properties, influences the quality of the laser cut. The surface characteristics of the material also impact the cut. Further, the presence of dirt, scale, sand and even paint deflects the gas flow. In addition, the reflectivity of the material also needs to be considered. 

Beam parameters: The laser beam’s power, along with its intensity, quality, polarization and wavelength, affects the outcome. When the laser power parameter is set right, it ensures that the material is cut as required, while generating little to no “melt.” Higher the laser power, lower the processing time.  

Process parameters: These consist largely of those parameters that can be adjusted to arrive at the required cut quality. These include the focal length and the focal position of the lens, cutting speed, nozzle diameter and/or alignment, the distance from the workpiece, the choice of continuous beam or pulsed beam, and the choice of assist gas and its pressure setting. It must be noted here that an unclean focusing lens can lead to it heating up and being deformed and damaged in extreme cases. Lens deformation shifts the focal position. Thereby, burrs may form, and surface roughness may develop. Exact focus-point positioning of the lens is critical for good results. 

Assist gas

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The type of assist/process gas used and the pressure of this gas are major factors that affect the quality of the cut. So what exactly is the role of the assist gas?

Primarily, the gas assists in the laser cutting process by blowing away any build-up of molten material during the cut. Nitrogen, oxygen and air are the assist gases generally used in laser cutting. Of these, nitrogen is by far the most popular assist gas owing to its inertness. Therefore, nitrogen also serves to purge the laser beam’s path.

As you’ll find in this post, assist gases do a whole lot more than just blow away the build-up accumulated during the laser cutting process. If you are looking to set up your laser-cutting enterprise or to step up your existing operations, explore Pneumatech’s range of nitrogen generators. Or get in touch with us right away. Call at +49 (0)2841 788 480 or e-mail to support-eu@pneumatech.com.