How can fiber lasers solve the problem of high reflective metal?

Some metals have high reflectivity, such materials are difficult to been cut by fiber laser cutting machine. As a best cutting tools, how can metal laser cutter solve this problem? Here are the solutions for our metal laser cutting machine.

What is high reflective metal?

High reflectivity metal refers to the low resistivity of the processing material, the smooth surface, and the low absorption rate of the near-infrared laser. As shown in the figure, it is the absorption coefficient of common metal elements, which leads to a large number of the laser beam reflected, and because most lasers source are used perpendicular to the material or at a slight inclination. As a result, the returning laser beam re-enters the laser cutter output head, and even part of the returning laser beam is coupled into the energy-transmitting fiber source, and is transmitted reversely along the fiber to the inside of the laser, causing the core components inside the laser source to continue to be at high temperature, damaging the fiber laser source and affecting the service life of the laser cutting machine.

Which metals are high reflectivity?

Aluminum, brass and copper, sliver, titanium. All of these metals have high reflectivity and require the use of a specialist reflective absorption protective device allowing them to be processed on a fibre laser cutting process.

How does the fiber laser cutting machine solve the problem of high reflection?

When cutting high-reflection metal materials such as aluminum, copper, and titanium, once the excessively high return laser beam enters the laser source, there will be a certain risk of damage to the cutting head of the laser cutting machine and the laser itself, especially for high-power fiber lasers products, the return laser power will be significantly higher than that of low-power laser cutting machine, and the risk of damage is also higher. When cutting metals with high reflectivity, when the material is not penetrated, there will be a higher power return light returning to the inside of the laser source, damaging the laser source. Raycus laser R&D personnel have designed a four-level anti-high-reflection light protection design in response to the above problems. At the same time, various return beam monitoring functions will be added to ensure real-time protection of the laser when abnormal processing occurs.

01 Four-Grade design in laser cutter for Anti-high reflection beam

Optical cable output head anti-high reflection design

The QBH, QD and QP series fiber output heads designed by Raycus laser can efficiently convert the uncontrollable return laser beam into light and heat that can be absorbed, and at the same time enhance the output head’s ability to absorb and dissipate heat, thus being able to avoid the impact of return laser beam on the internal components of the fiber laser cutting machine to the greatest extent. For the laser processing system, the return laser beam will firstly affect the output laser cutter optical cable head, making the laser cutting machine output optical cable at risk of heating or even damage. In order to ensure the safety of the output optical cable, based on the original design, we have integrated a level of return laser beam stripping device inside the laser cutting machine output optical cable, as shown in the figure. The anti-reflective design of the output cable can strip most of the return laser at the first time, reducing the damage to the internal optical structure of the laser.

Also combined with water-cooled heat dissipation design, the stripped return fiber laser beam is effectively absorbed to avoid its thermal impact on the optical cable output head.

Two-stage anti-reflection design in laser beam combining module of fiber cleaver

The multi-module high-power laser fiber cutting machine is mainly based on the combination of multi-unit modules. When cutting high-reflection metal 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 fiber laser cutter output optical cable. Therefore, considering the safety and reliability of the optical devices and optical path design in the fiber cutting machine bundle, a two-level anti-high-reflection protection design is added inside the bundle, as shown in the figure. While anti-protecting the safety of optical devices, it also reduces the impact of the returning laser on the laser light path structure of the cutting machine.

Anti-high reflection design in the cutter unit module

Since there is an optical resonator inside the unit module of the fiber cutting machine, once the low-power returning laser source and enters the unit module and is continuously amplified by the resonator, it will seriously affect the optical stability of the cutting machine laser and increase the risk of laser damage. In order to further improve the stability and reliability of the laser of the laser cutting machine during high anti-reflection cutting, combined with the optical path design inside the cutting machine unit module, the anti-high-reflection device of the cutting machine unit module is added to improve the reliability of the module, as shown in the figure.

02 Multiple monitoring design

The high-reflection software protection of the laser cutting machine mainly provides monitoring and protection for the high-reflection cutting process. It means that when the laser of the cutting machine is processing high-reflection materials, the strong retro reflection generated by the cutting machine enters the optical system of the laser of the cutting machine, resulting in unstable laser operation or The damage of the optical device is adopted to monitor or protect the operating status of the laser.

Although the anti-reflection device of the laser cutting machine can ensure that the laser can still work normally without damage within a certain return laser power threshold, the laser of the cutting machine will still have the risk of damage after this threshold is exceeded. Therefore, in order to ensure that the return laser can be protected in time, and multiple high-reflection software protection designs are added to the multi-module high-power laser cutting product:

High anti-reflection protection design of output optical cable in laser cutter

When the return optical power of the cutting machine 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 of the cutting machine. In the research of function integration technology, we have integrated a number of detection functions including cable temperature monitoring, laser monitoring and return light monitoring in the output optical cable of the laser cutting machine, which are used for real-time monitoring of the returning laser during the cutting process. Once the returned laser power exceeds the range that the laser can bear, the laser of the fiber cutting machine will turn off the light in time and give an alarm to ensure that the laser will not be damaged.

Combined beam and optical module high anti-reflection protection design

Considering that the return laser of the fiber laser cutting machine has two types of core laser and cladding laser, in addition to the high-reflection protection design of the cutting machine for the output optical cable, we also add a high-reflection detection module inside the cutting machine bundle to detect the laser power which is transmitted in the reverse direction for detection, and the power of the laser returned by the fiber cutting machine is monitored in real time. This high-reflection detection module can not only detect the cladding laser of the cutting machine, but also the core laser of the laser cutter, which can effectively avoid the risk of laser damage caused by the return laser of the core when only the cladding return 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 high-reflection resistance of the new fiber output head.

Experiments have shown that, 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 through the high-reflection test that the high-reflection monitoring signal can be transmitted to the display screen in real time during the cutting process. In the abnormal processing state, a high inverse signal can be detected, and the 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.

For cutting highly reflective materials, listen to the advice of process engineers:

(1) When the fiber cutting machine cuts brass, copper and other materials, the speed should be conservative, 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 protective mirror under the fiber cutting machine is polluted.
(2) The perforation of cutting high reflective material does not penetrate.
(3) When cutting high reflective materials, the perforation penetrated, but the cutting did not cut through.