Compared to traditional cutting processes such as oxy-acetylene and plasma cutting, laser cutting offers high speeds, narrow kerfs, small heat-affected zones, excellent edge perpendicularity, and smooth cut surfaces. It is compatible with a wide range of materials, including carbon steel, stainless steel, alloy steel, wood, plastic, rubber, fabric, quartz, ceramics, glass, and composite materials. Driven by rapid market economic growth and constant technological innovation, laser cutting technology has found widespread application in sectors such as automotive manufacturing, machinery, electric power, hardware, and electrical appliances. In recent years, the technology has advanced at an unprecedented pace, growing at an annual rate of 15%–20% globally; in my country, the growth rate has exceeded 25% annually since 1985. However, a significant gap remains between my country's overall laser cutting capabilities and those of leading nations, indicating vast prospects for development and immense potential for application within the domestic market.
During the laser cutting process, the beam is focused by a lens within the cutting head-which is mounted on the Z-axis-into a tiny focal point, generating high power density at that spot. The heat input from the beam far exceeds the heat lost through reflection, conduction, or diffusion, rapidly heating the material to its melting and vaporization temperatures. Simultaneously, a high-speed gas stream (delivered coaxially or non-coaxially) blows away the molten and vaporized material, creating a cut aperture. As the focal point moves relative to the material, this aperture extends into a continuous, narrow kerf, thereby completing the cutting process.
Currently, the external optical path of laser cutting machines predominantly utilizes a "flying optics" system. The beam emitted by the laser generator travels via mirrors 1, 2, and 3 to the focusing lens on the cutting head, forming a focused spot on the material surface. Mirror 1 is fixed to the machine body; mirror 2 moves along the X-axis with the crossbeam; and mirror 3 moves along the Y-axis with the Z-axis assembly. As illustrated, the length of the optical path constantly changes during the cutting process as the crossbeam moves along the X-axis and the Z-axis assembly moves along the Y-axis. Currently, due to factors such as manufacturing costs, laser beams emitted by commercial laser generators possess a certain divergence angle, resulting in a "conical" shape. When the height of this "cone" changes-effectively altering the optical path length of the laser cutting machine-the cross-sectional area of the beam at the surface of the focusing lens changes accordingly. Furthermore, light exhibits wave-like properties, making diffraction inevitable; diffraction causes the beam to expand laterally during propagation. This phenomenon is inherent to all optical systems and dictates their theoretical performance limits. Due to the "conical" nature of Gaussian beams and the effects of diffraction, the beam diameter at the lens surface fluctuates as the optical path length changes. This leads to variations in focal spot size and depth of focus, although the impact on the focal position itself is minimal. If the focal spot size and depth of focus fluctuate during continuous processing, it inevitably has a significant impact on the results-for instance, causing inconsistent kerf widths, or leading to incomplete cuts or material ablation when using the same cutting power.
