The distance between the laser focus point and the material to be cut must be adjusted before any sheet is cut off.
Focus point is important to laser cutting quality. Different focus point positions often result in different levels of fineness in the cross-section of the cut material, different bottom slagging and even failure to cut the material.
Depending on the workpiece and the material to be cut, the choice of focus point position for the laser cutting machine will vary.
So how do you make the right choice?
1. Zero Focus Cutting
Zero focus cutting means that the cutting focal point is on the workpiece surface, in this case, the cutting surface close to the focal point is relatively smooth, while the lower surface away from the cutting focal point appears rough.
This is mainly used when cutting thin sheets with continuous lasers and when cutting foil layers with pulsed lasers using peak power vaporization.
2. Positive focus cutting
Positive focus cutting means cutting with the focal point on top of the workpiece, positioning the focal point above the material being cut.
For carbon steel oxygen cutting, it is suitable for a positive focus.
The bottom of the workpiece has a larger cutting width than the upper surface, which is conducive to slag removal and facilitates the oxygen reaching the bottom of the workpiece to participate in the full oxidation reaction.
Within a certain focus range, the larger the positive focus point, the larger the spot size on the surface of the plate, the better the preheating and heat supplement around the slit, the smoother and brighter the cutting surface of carbon steel.
3. Negative focus cutting
Negative focus cutting means the cutting focus is inside the workpiece.
This mode, due to the focal point away from the cutting surface, the cutting width is relatively larger than the cutting point in the workpiece surface, while the need for cutting airflow needs to be large and temperature to be sufficient.
Cutting stainless steel is suitable for negative focal point cutting, with uniform cutting surface pattern and good cross-section.
Perforation of the plate before cutting, due to a certain height of perforation, perforation uses a negative focal point, which can ensure that the location of the perforation spot size is minimum, energy density is maximum.
The choice of a positive or negative focal point for laser cutting is not determined by the material of the metals (stainless steel, carbon steel), but by the cutting method (oxidation cutting, fusion cutting).
The different workpieces processed by the laser cutting machine require the use of different focal patterns.
Due to different types of cutting head focus position and different ways of adjustment, users can choose the appropriate focus cutting method according to the different effects of positive and negative focus in cutting stainless steel and carbon steel, combined with their own processing needs to give greater play to the performance advantages of the laser cutting machine.
Except choose correct focus point, it’s also necessary to do a proper inspection of the machine before cutting. It will ensure to cut high-quality sheets and promise the normal operation of the laser cutting machine. In the next article, we will introduce some measurments to do proper inspection.
