In laser cutting machines, several key technologies must mastere. And solved for parts with high cutting precision or large thickness. Focus position control 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 create 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  also relate 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 cutting material.

How to cut a good sample with a laser cutter？

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 focus, the spot size is proportional to the focal length of the lens. After the beam is focuse 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 shortcoming is that the depth of focus is very short and the adjustment margin adjust. Small, generally suitable for high-speed cutting of thin materials. Since the telephoto long 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 particularly important to ensure cutting quality. Due to the high 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 a constant relative position of the focus to the workpiece throughout the cutting process is an important condition for obtaining a stable 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 proper position, the slit is small, the efficiency is high, and the cutting speed can obtain a good cutting result. In most applications, the beam focus is adjuste just below the nozzle. The distance between the nozzle and the surface of the workpiece is generally about 1.5 mm.

In the laser application process, there are often problems such as focusing. And there are three convenient ways to determine the focus position:

(1) Printing method: The cutting head is move from top to bottom. And laser beam printing is performing on the plastic plate, and the smaller diameter is the focus.

(2) Inclined plate method: The plastic plate obliquely placed at an angle to. The vertical axis is horizontally pull to find the smaller portion of the laser beam as the focus.
(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 larger.