Laser cutting machines must master and solve several key technologies for parts with high cutting precision or large thickness. Focus position control technology is one of them. One of the advantages of laser cutting is that the energy density of the beam is high, so the focal spot diameter is as small as possible to produce a narrow slit. Because the focal depth of the focusing lens is smaller, the focal spot diameter is smaller. For high quality cutting, the effective depth of focus is also related to the lens diameter and the material being cut. It is therefore important to control the position of the focus relative to the surface of the material being cut. How to cut high-quality products with a cutting machine?
Since the laser power density has a great influence on the cutting speed, the selection of the lens focal length is an important issue. The size of the spot after focusing is proportional to the focal length of the lens. After the beam is focused by the short focal length lens, the spot size is small, and the power density at the focus is high, which is good for material cutting. However, its disadvantage is that the depth of focus is short and the adjustment margin is small. Generally suitable for high-speed cutting of thin materials. Since the long focal length lens has a wide focal depth, 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 focus to the surface of the workpiece is especially important to ensure the quality of the cut. Due to the highest power density at the focus, in most cases, the focus position at the time of cutting is just at the surface of the workpiece, or slightly below the surface. Ensuring that the focus is relatively constant relative to the workpiece throughout the cutting process is an important condition for achieving consistent cutting quality. Sometimes, the lens is heated due to poor cooling and causes a change in focal length, which requires timely adjustment of the focus position.
When the focus is in the best position, the kerf is the smallest and the most efficient, and the best cutting speed can get the best cutting result. In most applications, the beam focus is adjusted just below the nozzle. The distance between the nozzle and the surface of the workpiece is generally about 1.5 mm.
Laser cutting machines often encounter problems such as focusing during laser application. There are three convenient ways to determine the focus position:
(1) Printing method: the cutting head is moved from top to bottom, and laser beam printing is performed on the plastic plate, and the smallest diameter is the focus.
(2) Inclined plate method: The plastic plate obliquely placed at an angle to the vertical axis is horizontally pulled, and the minimum point of the laser beam is focused.
(3) Blue spark method: remove the nozzle, blow the air, and pulse the laser on the stainless steel plate to move the cutting head from top to bottom until the blue spark is at the maximum focus.