Before cutting down any plate, the distance between the laser focal point and the cutting material must be adjusted. Different focal point positions often lead to different degrees of fineness of the cutting material section, different hanging slag at the bottom, or even the inability to cut off the material; different cutting workpieces, different materials, laser cutting machine focal point position selection will also be different, so how to choose the correct choice?
The Focal point position refers to the distance from the focal point to the upper surface of the cutting workpiece. A focal point position above the workpiece is generally referred to as a positive focal point, and a focal point position below the workpiece is generally referred to as a negative focal point.
Changing the position of the focal point means changing the size of the light spot on the surface and inside the plate. A larger focal length makes a thicker light spot and wider kerf, which affects the heating area, the size of the kerf and the slag removal capacity.
Exact Focus Cutting
The cutting focal point is above the workpiece, positioning the focal point above the material being cut. For carbon steel oxygen cutting, it is suitable to use a positive focal point, the bottom of the workpiece than the upper surface cutting width is larger, conducive to slagging, conducive to oxygen to reach the bottom of the workpiece to participate in the full oxidation reaction. Within a certain focus range, the larger the positive focus, the larger the spot size on the surface of the plate, the more adequate preheating and heat replenishment around the cut, the smoother and brighter the carbon steel cutting surface. For 10,000 watt laser pulse cutting stainless steel thick plate, the use of positive focus, cutting stability, conducive to slagging and not easy to anti-blue light.
Negative Focus Point Cutting
The cutting focal point is inside the workpiece. In this mode, as the focal point is far away from the cutting surface, the cutting width is relatively larger than the cutting point on the surface of the workpiece, while the cutting airflow is required to be large and the temperature is sufficient. When cutting stainless steel, it is suitable for negative focal point cutting, the cutting surface pattern is uniform and the section is better. Before cutting the plate perforation, due to the perforation has a certain height, perforation using negative focus, can ensure that the perforation position spot size minimum, the maximum energy density, and the deeper the perforation position, the greater the negative focus.
Zero Focus Point Cutting
The cutting focal point is on the surface of the workpiece and this type of cutting generally has a relatively smooth surface close to the focal point, while the lower surface away from the cutting focal point appears rough. This is mainly used for cutting thin plates with continuous lasers and for cutting metal foil layers by means of high peak power vaporisation with pulsed lasers.
|Cutting Methods||Cutting Plates||Focus|
|Melting Cutting||Stainless Steel Nitrogen/Air Cutting||Negative focus(Above 10,000 watts laser pulse method cutting thick stainless steel with positive focus, below 10,000 watts cutting thick Stainless steel with negative focus)|
|Carbon Steel Nitrogen/Air Cutting||Negative focus|
|Aluminium and Brass Nitrogen||Negative focus|
|Oxidation Cutting||Oxygen Cutting of Carbon Steel||Positive Focus|
|Negative focus is used for all piercings before cutting|
In summary, laser cutting machine processing different workpieces need to correspond to the use of different focus modes, due to different types of cutting head focus position and adjustment methods, the user can be based on the positive and negative focus in cutting stainless steel, carbon steel, different effects, combined with their own processing needs, to choose the appropriate focus cutting mode, in order to give greater play to the performance advantages of laser cutting machine!