Thermal effect analysis and improvement of fiber laser cutting, marking and welding machine

After a long period of continuous laser irradiation, optical transmission type components will undergo thermal deformation due to the increase in temperature, causing changes in the refractive index of transmission optical components and the reflection direction of reflection optical components. The thermal lens effect will change the position of laser focusing, thereby affecting the application effect.

For pulse fiber optic equipment, after the laser is output from the isolator of the laser, it mainly passes through the red light combining lens, galvanometer, and f - theta; Due to the more pronounced thermal lens effect of transmissive optical components, the analysis of field lenses mainly focuses on red light combining lenses, lasers, and field lenses.

The influence of thermal lens effect

When the thermal lens effect is generated, the optical components expand under thermal action, the focusing ability becomes stronger, the focused spot size becomes smaller, and the focal length and focal depth become shorter. These phenomena can lead to unstable marking and seriously affect the marking effect. Through several typical applications of pulsed fiber lasers, we analyzed the impact of the thermal lens effect.

1. Aluminum oxide blackening:

When the thermal lens effect occurs, the focal length becomes shorter, the energy density on the material surface decreases, and aluminum oxide cannot turn black. In severe cases, the blackness effects at the center and edges are inconsistent.

2. Metal deep carving:

Metal depth generally uses a field lens with a shorter focal length (depth of focus). When high-power depth is used, the energy density of the material rapidly decreases due to the effect of the thermal lens, making the metal carving not deep enough. Because the center of the optical element is larger than the edge, the center is shallow and the depth around it varies.

3. Thin slice cutting:

According to different materials, pulsed fiber laser cutting plates usually use two methods, single slow or multiple, which will undergo thermal expansion and cooling shrinkage in a very short time (<1s). Therefore, the starting position of cutting can be cut, and other positions cannot cut materials.

4. Welding of metal foil:

For high-power pulsed fiber laser welding of metal sheets, the thermal lens effect can lead to inconsistent weld size and insufficient tensile force.

Improvement of thermal lens effect

The higher the power, the higher the reflective material, the faster the thermal expansion of optical components, and the more pronounced the thermal lens. Improving thermal lenses can be approached from three aspects: laser, field lens, and red light lens

1. Laser:

Regularly clean the laser protection lens of the output head of the laser to avoid impurity contamination, and use quartz material to reduce the thermal expansion coefficient of the optical lens of the collimator.

2. Field Mirror:

Using medium to high power (100W) pulsed fiber lasers, it is recommended to use composite or quartz materials for the field mirror; The protective mirror of the field lens should be regularly inspected and cleaned to avoid contamination or damage from impurities.