Q: What is the thermal lens effect of laser cutting machine processing? How to tell?

A: When there is stain on the optical component (such as processing lens, PR mirror or window) transmitted by the laser beam of the laser cutting machine, the thermal lens effect will occur after the laser beam is transmitted, the cutting surface will become rough, and the slag will appear. There may even be a burn.
When the processing quality of the laser cutting machine becomes poor, if it is judged whether it is affected by the thermal lens effect, it is first necessary to check whether the performance of the optical element changes with the irradiation time of the laser beam. At the beginning of processing, the optical components are still in a low temperature state, and as the processing progresses, the effect of the thermal lens effect is manifested from the quality of the cut surface.

The reason

Reflective optical elements (such as refractors) can efficiently cool directly from the back side, and reflective optics can hardly produce a thermo-mirror effect; while transmissive optical elements can only be indirectly cooled by cooling around them. The two faces of the optical component in turn generate heat, so it is easy to produce a thermal lens effect. The optical element undergoes thermal deformation when the temperature rises, and the refractive index of the laser beam of the laser cutter changes, and the condensing characteristics of the laser beam also change.

Resolution method

Compare the cut surface at the beginning and end of the workpiece being a machine by the laser cutter. At the beginning of the processing. Since the laser beam irradiation time is short, the optical element is still in a low temperature state. So the influence of the thermal lens effect is relatively small. In the case where the cutting time requires more than 10 s at the end of the processing, since the optical element is irradiating with the laser beam for a long time, the thermal lens effect occurs, and the focus position and the beam mode also change.
Once the focus position changes or the beam mode changes. It does not automatically return to the original state during continuous illumination processing. The cutting surface at the beginning of the machining and the end of the machining are comparing. And the quality at the end of the machining is deteriorat. It indicates that the thermal lens effect has occurred; if the two masses are all in the same good state, then the thermal lens effect does not occur.
When the laser cutting machine processes the stainless steel material and judges. Whether the thermal lens effect has occurred. It is necessary to observe the drossing condition at the beginning and the end of the machining. If the amount of burrs at the machining station increases, it indicates that the thermal lens effect may occur. In addition. In order to eliminate the directionality caused by other reasons. Such as the unevenness of the beam mode or the inclination of the optical axis. It should notes that the comparison of the same cutting faces (the same machining direction). Must performing at the time of comparison.