Before cutting any sheet, the distance between the laser focus and the cutting material must be adjusted. Different focal points often lead to varying degrees of delicacy in the cutting material section, different slag hanging at the bottom, and even inability to cut the material; The selection of the focal point position of the laser cutting machine varies depending on the workpiece and material being cut. So how to choose it correctly?
Definition of focal point position: The distance from the focal point to the upper surface of the cutting workpiece. The focal point position above the workpiece is generally referred to as the positive focal point, and the focal point position below the workpiece is generally referred to as the negative focal point.
Meaning of focal point position: Changing the focal point position refers to changing the size of the light spot on the surface and inside of the board, increasing the focal length, thickening the light spot, and widening the cutting seam, thereby affecting the heating area, cutting seam size, and slag removal ability.
How to correctly select the focus position during laser cutting process
Positive focus cutting
The cutting focus is on the workpiece, and the focus is positioned above the cutting material.
For carbon steel oxygen cutting, it is suitable to use a positive focus. The bottom of the workpiece has a larger cutting amplitude than the upper surface, which is conducive to slag removal and oxygen reaching the bottom of the workpiece to participate in sufficient oxidation reactions. Within a certain focal range, the larger the positive focal point, the larger the size of the light spot on the surface of the plate, the more sufficient preheating and heat supplementation around the cutting seam, and the smoother and brighter the carbon steel cutting surface.
For the pulse cutting of stainless steel thick plates using a ten thousand watt laser, using a positive focus ensures stable cutting, facilitates slag removal, and is not prone to blue light reflection;
Effect of Chuangxin Laser 12000 W Laser on Positive Focus Cutting of Carbon Steel
Negative focus cutting
That is, the cutting focus is inside the workpiece. In this mode, as the focus is far from the cutting surface, the cutting amplitude is relatively larger than that of the cutting point on the workpiece surface, and the required cutting airflow is larger and the temperature is sufficient.
When cutting stainless steel, it is suitable to use negative focus cutting, with uniform cutting surface texture and good cross-section.
Before cutting, the perforation of the sheet metal has a certain height, and the perforation adopts a negative focus, which can ensure the minimum size of the perforation spot and the maximum energy density. The deeper the perforation position, the larger the negative focus.
How to correctly select the focus position during laser cutting process
Effect of Negative Focus Cutting of Stainless Steel by Chuangxin Laser 6000W Laser
Zero focus cutting
The cutting focus is on the surface of the workpiece, and the cutting surface close to the focus is generally relatively smooth, while the lower surface far from the cutting focus appears rough. This situation is mainly used for continuous laser cutting of thin plates and pulse laser peak power vaporization cutting of metal foil layers.
Effect of Zero Focus Cutting of Carbon Steel Thin Plate by Chuangxin Laser 2000W Laser
The choice of the focus for laser cutting is not determined by the material of the cutting plate (stainless steel, carbon steel), but by the cutting method (oxidation cutting, melting cutting).
Laser cutting machines need to use different focus modes for processing different workpieces. Due to the different focus positions and adjustment methods of different types of cutting heads, users can choose the appropriate focus cutting method based on the different effects of positive and negative focus points when cutting stainless steel and carbon steel, combined with their own processing needs, in order to better utilize the performance advantages of laser cutting machines!