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Analyzing how to control the cutting quality of laser cutting machines

 Many companies are very concerned about how to use laser cutting machines to process high-quality workpieces? Now let's talk about how to control the cutting quality of a laser cutting machine. Summarize several factors that affect cutting quality: cutting speed, focal position, auxiliary gas, laser output power, and workpiece characteristics! Let's analyze them one by one for everyone:

1, The influence of cutting speed on cutting quality

For a given laser power density and material, the cutting speed follows an empirical formula. As long as it is above the threshold, the cutting speed of the material is proportional to the laser power density, that is, increasing the power density can improve the cutting speed. The power density referred to here is not only related to the laser output power, but also to the beam quality mode. In addition, the characteristics of the beam focusing system, namely the size of the focused spot, also have a significant impact on laser cutting.

The cutting speed is inversely proportional to the density (specific gravity) and thickness of the material being cut. When other parameters remain constant, the factors that increase cutting speed are: increasing power (within a certain range, such as 500-2000W); Improve beam modes (such as from high-order modes to low order modes up to TEM00); Reduce the size of the focused spot (such as using a short focal length lens for focusing); Cutting materials with low initial evaporation energy (such as plastics, organic glass, etc.); Cutting low-density materials (such as white pine wood, etc.); Cutting thin materials.

Especially for metal materials, while keeping other process variables constant, the laser cutting speed can have a relatively adjustable range while still maintaining satisfactory cutting quality. This adjustment range appears slightly wider when cutting thin metals than thick ones. Sometimes, slow cutting speed can also cause the discharge of hot melt material to burn the surface of the mouth, making the cut surface very rough.

2,  The Influence of Focus Position Adjustment on Cutting Quality

Due to the significant impact of laser power density on cutting speed, the selection of lens focal length is an important issue. The size of the focused laser beam spot is proportional to the focal length of the lens. After being focused by a short focal length lens, the spot size is very small, and the power density at the focal point is high, which is beneficial for material cutting; But its disadvantage is that the depth of focus is very short, the adjustment margin is small, and it is generally more suitable for high-speed cutting of thin materials. Due to the wide focal depth of telephoto lenses, as long as they have sufficient power density, they are more suitable for cutting thick workpieces.

After determining which focal length lens to use, the relative position between the focal point and the workpiece surface is particularly important for ensuring cutting quality. Due to the high power density at the focal point, in most cases, the focal position is just on the surface of the workpiece or slightly below the surface during cutting. Ensuring a constant relative position between the focus and the workpiece throughout the entire cutting process is an important condition for obtaining stable cutting quality. Sometimes, poor cooling during lens operation can cause changes in focal length due to heating, which requires timely adjustment of the focal position.

When the focus is in the optimal position, the cutting seam is smaller and the efficiency is higher, and the optimal cutting speed can achieve better cutting results.

In most applications, the beam focus is adjusted to just below the nozzle. The distance between the nozzle and the workpiece surface is generally around 1.5mm.

3,  The influence of auxiliary gas pressure on cutting quality

In general, material cutting requires the use of auxiliary gases, which mainly involve the type and pressure of auxiliary gases. Usually, auxiliary gas is sprayed coaxially with the laser beam to protect the lens from contamination and blow away the slag at the bottom of the cutting area. For non-metallic and partially metallic materials, use compressed air or inert gas to process melted and evaporated materials while suppressing excessive combustion in the cutting area.

For most metal laser cutting, active gas (as long as it is O2) is used to form an exothermic oxidation reaction with the hot metal, which can increase the cutting speed by 1/3 to 1/2 of the additional heat.

Under the premise of ensuring the auxiliary gas, the gas pressure is an extremely important factor. When cutting thin materials at high speed, a higher gas pressure is required to prevent slag from sticking to the back of the incision (hot slag sticking to the workpiece can also damage the cutting edge). When the material thickness increases or the cutting speed is slow, the gas pressure should be appropriately reduced. In order to prevent plastic edge frosting, it is also better to cut with a lower gas pressure.

Laser cutting practice has shown that when the auxiliary gas is oxygen, its purity has a significant impact on cutting quality. A 2% decrease in oxygen purity will reduce cutting speed by 50% and lead to a significant deterioration in incision quality.

4, The influence of laser output power on cutting quality

For continuous wave output lasers, the laser power and mode quality have a significant impact on cutting. In practical operation, higher power is often set to achieve higher cutting speed or to cut thicker materials. But the beam mode (the distribution of beam energy in cross-section) sometimes becomes more important, and when the output power is increased, the mode often deteriorates slightly. It is often observed that higher power density and better cutting quality are achieved at the focal point under conditions of less than high power. During the entire effective working life of the laser, the mode is not consistent. The condition of optical components, subtle changes in the mixed gas during laser operation, and fluctuations in flow rate can all affect the mode mechanism.

In summary, although the factors affecting laser cutting are complex, cutting speed, focal position, auxiliary gas pressure, laser power, and mode structure are four important variables. During the cutting process, if it is found that the cutting quality has significantly deteriorated, the factors discussed above should be checked first and adjusted in a timely manner