There are several key technologies that must be mastered and solved in a laser cutting machine in order to cut parts with high precision or thickness. Focal spot position control is one of them. One of the advantages of laser cutting is the high energy density of the beam, so the focal spot diameter is as small as possible to create a narrow slit. Because the focusing lens has a small depth of focus, the focal spot diameter will also be small. For high quality cuts, the effective depth of focus is also related to the lens diameter and the material being cut. Therefore, it is important to control the position of the focal spot relative to the surface of the material being cut.

  Since the laser power density has a great influence on the cutting speed, the choice of lens focal length is an important issue. After the laser beam is focused, the spot size is proportional to the focal length of the lens. After the beam is focused by a short focal length lens, the spot size is small and the power density at the focal point is high, which is favorable for material cutting. However, the disadvantage is that the depth of focus is very short and the adjustment margin is adjusted. The small size is generally suitable for high-speed cutting of thin materials. Since the telephoto long lens has a wide depth of focus, it is suitable for cutting thick workpieces as long as it has sufficient power density.

  After determining which focal length lens to use, the relative position of the focal point with respect to the surface of the workpiece is particularly important to ensure cut quality. Due to the high power density at the focal point, in most cases the focal point position during cutting is only at or slightly below the surface of the workpiece. Ensuring a constant relative position of the focal point to the workpiece throughout the entire cutting process is important for consistent cut quality. Sometimes, poor cooling causes the lens to be heated and results in a change in focus, which requires timely adjustment of the focus position.

  When the focal point is located in the proper position, the slit is small, the efficiency is high, and the cutting speed can obtain good cutting results. In most operational applications, the beam focus is adjusted below the nozzle. The distance between the nozzle and the workpiece surface is usually about 1.5 mm.

  In the laser application process, there are often problems such as focus, there are three convenient methods to determine the focus position:

  (1) Printing method: The cutting head is moved from top to bottom and the laser beam is printed on a plastic plate, with the smaller diameter being the focal point.

  (2) Tilted plate method: The plastic plate placed at an angle to the vertical axis is pulled horizontally to find a smaller portion of the laser beam as the focal point.

  (3) Blue Spark Method: Remove the nozzle, blow air, and pulse the laser on the stainless steel plate so that the cutting head moves from top to bottom until the blue spark becomes larger.