A laser cutting machine focuses the laser emitted from the laser into a high-power laser beam through an optical path system. The laser beam irradiates the surface of the workpiece, causing it to reach the melting or boiling point, while the high-pressure gas coaxial with the beam blows away the melted or vaporized metal. What are the main optical compensation measures for laser cutting machines?

Precision laser cutting machine

1. Beam collimation using a beam expander

The waist diameter of a beam is inversely proportional to the far-field divergence angle. The larger the waist diameter, the smaller the far-field divergence angle. At present, beam expanders are mainly divided into two types: refractive and reflective, and their principle is equivalent to an inverted telescope.

The main function is to reduce the far-field divergence angle by increasing the waist diameter of the beam, thereby improving the instability of the focus size and depth caused by changes in the length of the optical path. Currently, there is not much research on beam collimation in China, with most of it focusing on refractive and reflective methods.

The design, processing, and adjustment of refractive beam expanders are relatively easy, but due to the lens's tendency to deform due to excessive temperature rise, refractive beam expanders are only suitable for collimating low-power laser beams. For high-power beam collimation such as laser cutting machines, reflective beam expanders are generally used.

However, the curvature radius of the reflective beam expander is difficult to determine through analytical methods and can only be obtained through numerical fitting, making it difficult to design, manufacture, and adjust. Therefore, the method of collimating the beam with a beam expander is used to compensate for the optical path of the flying optical system of the laser cutting machine, with minimal effect.

2. Using variable curvature radius lenses (VRM)

By adjusting the output flow rate of the variable pump to change the water pressure in the water tank inside the VRM lens, the curvature radius of the focusing lens can be changed, thereby changing the parameter f in the focusing equation. Variable curvature radius lenses can dynamically adjust the characteristic parameters of the beam when the length of the optical path changes, to maintain the stability of the focal radius and depth.

The VRM system has a complex structure, high cost, and requires closed-loop control. Some technologically advanced products abroad have already adopted this optical path compensation measure. However, the current domestic technological level makes it difficult to achieve the expected usage effect.

3. Equal optical path system directly driven by servo motor

Compared with the two optical path compensation measures mentioned above, equal optical path has the advantages of simple structure, low cost, and easy adjustment, which can ensure that the spot area on the focusing lens remains unchanged during continuous processing; At the same time, it can also change the size of the focus radius and depth during cutting according to different cutting process requirements.

At present, there is not much research on equal optical path in China. For example, Yang Xiaodong from Tianjin University of Urban Construction proposed three mechanism design schemes for optical path length compensation system, and analyzed and compared them from the perspective of the mechanism. The proposed method has certain guiding significance for the design of laser cutting machine flying optical path.

Using mechanisms to achieve optical path compensation will result in the structural size of the equipment being too large, while increasing the complexity of the equipment and making installation and adjustment difficult. With the increasing maturity of servo control technology, using servo motors to directly drive optical path devices has the advantages of simple structure and convenient adjustment, making it an economical and practical optical path compensation method