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

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

 

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

A: When the optical elements (such as processing lens, PR mirror or window, etc.) through which the laser beam of the laser cutting machine passes are stained, thermal lens effect will occur after the laser beam passes through, and the cutting surface will become rough as a result, and dross will appear. , And even burns.

When the processing quality of the laser cutting machine deteriorates, to determine whether it is affected by the thermal lens effect, first check whether the performance of the optical element changes with the irradiation time of the laser beam. At the beginning of processing, the optical element is still in a low temperature state, and as the processing progresses, the influence of the thermal lens effect will be manifested in the quality of the cut surface.

  • Reasons

Reflective optical elements (such as refraction mirrors) can be efficiently cooled directly from the back side, and reflective optical elements hardly have a hot mirror effect; while transmissive optical elements can only be cooled indirectly by cooling around them. Both surfaces of the optical element generate heat, so it is easy to produce thermal lens effect. Optical components will be thermally deformed when the temperature rises, the refractive index of the laser beam of the laser cutting machine will also change, and the condensing characteristics of the laser beam will also change accordingly.

  • Resolution method

Compare the cutting surface at the beginning and the end of the workpiece processed by the laser cutting machine. At the beginning of processing, because the laser beam is irradiated for a short time and the optical element is still in a low temperature state, the thermal lens effect is relatively small. At the end of the processing where the cutting time takes more than 10 seconds, because the optical element is irradiated by the laser beam for a long time, a thermal lens effect will occur, and the focus position and beam pattern will also change.

Once the focus position changes or the beam pattern changes, it will not automatically return to the original state during continuous irradiation processing. Comparing the cutting surface at the beginning and the end of processing, the quality at the end of processing becomes worse. It means that the thermal lens effect has occurred; if the quality of the two places is in the same degree of good condition, it means that the thermal lens effect has not occurred.

When laser cut stainless steel, to determine whether thermal lens effect has occurred, it is necessary to observe the dross conditions at the beginning and the end of the processing. If the amount of burrs at the processing place increases, it means that thermal lens effect may have occurred. In addition, in order to eliminate the directivity caused by other reasons such as the unevenness of the beam pattern or the tilt of the optical axis, it should be noted that the comparison must be performed on the same cutting surface (same processing direction).