Measures for Fiber Lasers to Deal with the Problem of Highly Reflective Materials
Ⅰ. What is a highly reflective material?
Generally speaking, high reflectivity refers to the fact that the resistivity of the processed material is small, the surface is relatively smooth, and the absorption rate of the near-infrared laser is low. During use, a large number of lasers are emitted. And because most of the laser usage scenarios are perpendicular to the material or a small amount of inclination, which causes the returning laser to re-enter the output head, and even part of the returning light is coupled into the energy-transmitting fiber, and is transmitted to the inside of the laser in the reverse direction along the fiber, making the core components inside the laser. sustained high temperature.
Ⅱ. Specific implementations for dealing with highly reflective materials
In the processing of highly reflective materials, once an excessively high return laser enters the laser, there will be a certain risk of damage to the cutting head or welding head and the laser itself. Especially for high-power fiber laser products, the return laser power is significantly higher than that of low-power laser products, and the risk of damage is also higher. When cutting high-reflection materials, when the material is not penetrated, there will be a high-power return light returning to the inside of the laser, damaging the laser. In view of the above problems, Raycus laser R&D personnel have designed a four-level anti-high reflection light protection design, and will add various return light monitoring functions to ensure real-time protection of the laser when abnormal processing occurs.
01 Four-level anti-high reflection light design
1). Optical cable output head anti-high reflection design
The QBH, QD and QP fiber output heads designed by Raycus can efficiently convert the uncontrollable return light into absorbable light and heat, and at the same time improve the heat absorption and heat dissipation capacity of the output head, so as to avoid the return light to the greatest extent. impact on internal components. For the laser processing system, the returning laser will first affect the output optical cable head, causing the output optical cable to heat up or even be damaged. In order to ensure the safety of the output optical cable, on the basis of the original design, we integrated a Stage return light stripping device, as shown in the figure. The anti-reflection design at the output end of the optical cable can strip most of the returning laser at the first time, reducing the damage to the internal optical structure of the laser. At the same time, combined with the water-cooling heat dissipation design, the stripped returning laser can be effectively absorbed to avoid its impact on the optical cable output head. produce thermal effects.
2). Two-stage anti-reflection design in the beam combining module
Multi-module high-power laser products are mainly based on the combination of multi-unit modules. When cutting high-reflection materials, after the return light passes through the first-level anti-reflection design at the optical cable, part of the light may still be reversely transmitted to the combined beam through the output optical cable. internal. Therefore, considering the safety and reliability of the optical devices and optical path design in the beam combination, a two-level anti-high-reflection protection design is added inside the beam combination. This design adopts a step-by-step step-by-step stripping of the returning laser to ensure the safety of the anti-high-reflection protection optical device, and at the same time reduce the impact of the returning laser on the laser optical path structure.
3). Anti-high reflection design in the unit module
Due to the presence of an optical resonator inside the unit module, once the low-power returning laser enters the unit module and is continuously amplified by the resonator, the optical stability of the laser will be seriously affected and the risk of laser damage will be increased. In order to further improve the stability and reliability of the laser during high-reverse cutting, combined with the optical path design inside the unit module, an anti-high-reflection device of the unit module is added to improve the reliability of the module.
02 Multiple high anti-software monitoring design
High-reflection software protection is mainly high-reflection monitoring protection, which means that when the laser is processing high-reflection materials, the strong retroreflection generated by the laser enters the laser optical system, causing instability of the laser operation or damage to the optical devices, and the laser operating state is adopted. monitoring or protection mechanisms.
Although the anti-high-reflection device can ensure that the laser can still work normally without damage within a certain return laser power threshold, there is still a risk of damage to the laser beyond this threshold. Therefore, in order to ensure that the laser can be protected in time when the return laser is too high , multiple high-reflection software protection designs are added to the multi-module high-power laser products:
1) High anti-reflection protection design of output optical cable
When the return optical power is high, part of the returned laser will return to the output optical fiber along the original optical path, and the other part will be directly incident on the front end of the output optical cable. We have integrated a number of detection functions including cable temperature monitoring, laser monitoring and return light monitoring in the output optical cable for real-time monitoring of the return laser. Once the returned laser power exceeds the range that the laser can bear, the laser will turn off the light in time and give an alarm to ensure that the laser will not be damaged, and at the same time, it can also remind the customer that there is an abnormality in the processing at this time.
2) Combined beam and optical module with high anti-reflection protection design
Considering that there are two types of return lasers: core laser and cladding laser, in addition to the high-reflection protection design for the output cable, we also added a high-reflection detection module inside the combined beam to detect the reverse transmission laser power, and Monitor the power of the returning laser in real time. This high-reflection detection module can detect not only the cladding laser, but also the core laser, which can effectively avoid the risk of laser damage caused by the core returning laser when only the cladding returning laser is detected. Once there is a high return laser inside the laser, the laser can also be turned off in time and an alarm can be issued to ensure the safety and reliability of the laser.
03 Cutting test
Due to the low laser absorption rate and high thermal conductivity of copper, the surface of copper has been in a mirror state, and a steady stream of laser light returns to the fiber output head, thereby verifying the anti-high reflection ability of the new fiber output head.
In fact, as long as it is properly operated, whether it is aluminum plate, brass, red copper and other high-reflection materials, Raycus laser can be controlled, efficient cutting, and good section effect. For the high-reflection abnormal processing test, it is to test the anti-high-reflection ability of the laser. By scribing the copper plate back and forth without penetrating the copper plate, the return light at this time is extremely high, and the laser can still be used normally, indicating that Raycus The laser has strong anti-high anti-reflection ability.
It can be seen from the above high-reflection test that during the cutting process, the high-reflection monitoring signal can be transmitted to the display screen in real time. In the abnormal processing state, a high inverse signal can be monitored, and its signal is within the laser threshold. When the high reflection exceeds a certain threshold, the machine alarm will be triggered to remind the staff to check whether the operation is wrong.
Ⅲ. For cutting highly reflective materials, professional engineers give the following suggestions:
(1) When cutting brass, copper and other materials, the speed should be conservative, leave some space, and do not be too extreme.
(2) Red copper must be cut with oxygen, not with nitrogen or air.
When the following problems occur, please stop and check immediately.
(1) The lower protective lens is contaminated.
(2) Cut high reflective material perforation without penetration.
(3) When cutting high reflective materials, the perforation penetrated, but the cutting did not cut through.