Laser Cutting Technology Parameters And Performance Indicators

Laser Cutting Technology 

Parameters And Performance Indicators

Laser cutting technology must be familiar to everyone. Laser cutting technology is a processing method that uses a high-energy-density laser beam to accurately cut materials. It is widely used in the processing of metal and non-metal materials. The most common laser cutting equipment is laser cutting machines.

Laser cutting machines use the cutting principle of lasers. The core of laser cutting is the laser beam generated by a high-power laser. Through a reflector and lens system, especially a focusing lens, the beam is focused into a very small spot, usually with a diameter of only tens of microns to hundreds of microns, thereby forming a very high energy density on the surface of the processed material.

Under the irradiation of high-energy-density lasers, the surface of the material quickly heats up to thousands to tens of thousands of degrees Celsius, causing the material to melt, vaporize or burn instantly. For metal materials, there may also be an oxidation reaction.

In the laser cutting process, high-pressure auxiliary gases (such as oxygen, nitrogen, argon or compressed air, etc.) are often used in combination. On the one hand, they help blow away the molten or vaporized materials, and on the other hand, they protect the cutting area, reduce the heat-affected zone, and improve the cutting quality and speed.

The main process parameters of laser cutting are cutting laser power, incision width, cutting speed and gas flow rate. Other factors, such as laser beam quality, lens focal length, defocus and nozzle, also have a great influence on laser cutting.

(1) Laser power

For material properties, if the surface reflectivity of the material is high, then when the laser irradiates the surface of the material, more energy will be reflected back instead of being absorbed by the material for cutting. Therefore, in order to ensure sufficient energy for cutting, the laser power needs to be increased. Similarly, if the thermal conductivity of the material is good, the heat generated by the laser irradiation will be quickly conducted inside the material, making it difficult for the temperature of the cutting area to rise to a level sufficient for cutting. In this case, the laser power also needs to be increased to improve the cutting efficiency. In addition, cutting materials with high melting points also requires larger laser power and power density. This is because materials with high melting points require more energy to melt or vaporize them, thereby achieving the purpose of cutting.

(2) Cutting speed

Under certain power conditions, when the plate thickness increases, the laser beam needs to penetrate deeper material layers to complete the cutting. Studies have shown that the relationship between cutting speed and cut surface roughness is not a simple linear relationship, but shows a U-shaped change trend. This means that for materials of different plate thicknesses and different cutting gas pressure conditions, there is an optimal cutting speed point. When cutting at this speed, the roughness value of the cut surface can be minimized, that is, the cut is the smoothest. Generally speaking, the faster the cutting speed, the greater the power required.

(3) Gas pressure (gas flow)

During the melting cutting process, the laser beam heats the material to the melting temperature. At this time, the gas blown away the liquid metal to form an incision. The gas pressure must be large enough to effectively remove the molten metal and ensure the continuity of the cutting and the clarity of the incision. The gas flow rate is also related to the nozzle form. Different nozzle forms have different effects on the distribution and flow characteristics of the gas, so the applicable gas flow rate will also be different. When selecting the nozzle and setting the gas flow rate, it is necessary to match and optimize according to the specific cutting requirements and material properties.

(4) Beam quality, lens focal length and defocus

The beam mode output by the laser is crucial to the cutting effect. The fundamental transverse mode (TEM00 mode) beam is considered to be the most ideal beam mode in laser cutting because of its small beam diameter and concentrated energy. Experimental studies have shown that the incision width is almost equal to the laser spot diameter in non-oxygen-assisted cutting. The spot size is proportional to the focal length of the focusing lens, that is, the longer the focal length, the larger the spot; the shorter the focal length, the smaller the spot. However, although a short focal length lens can obtain a smaller spot, its focal depth is also reduced accordingly. The smaller the focal depth, the stricter the distance requirement from the workpiece surface to the lens. The defocus value has a great influence on the cutting speed and cutting depth, and must remain unchanged during the cutting process. Generally, the defocus value is a negative value, that is, the focus position is placed at a certain point below the cutting plate surface.

(5) Nozzle

The nozzle is an important component that affects the quality and efficiency of laser cutting. Laser cutting generally uses a coaxial (airflow and optical axis concentric) nozzle, and the nozzle outlet diameter should be selected according to the plate thickness. In addition, the distance from the nozzle to the workpiece surface also has a great influence on the cutting quality. In order to ensure the stability of the cutting process, this distance must be kept constant.

Laser cutting of industrial materials

(1) Laser cutting of metal materials

Almost all metal materials have high reflectivity to infrared light at room temperature. For example, the absorption rate of 10.6μm carbon dioxide laser is only 0.5%~10%. However, when the power density exceeds the focused beam of , the surface can begin to melt in microseconds. The absorption rate of most molten metals will rise sharply, generally up to 60%~80%. Therefore, carbon dioxide lasers have been successfully used in many metal cutting practices.

The maximum thickness of carbon steel plates that can be cut by modern laser cutting systems has exceeded 20mm. The cutting seam of carbon steel plates can be controlled within a satisfactory width range by oxygen-assisted melting cutting method, and the cutting seam of thin steel plates can be as narrow as about 0.1mm. Laser cutting is an effective processing method for stainless steel plates. It can control the heat-affected zone within a very small range, thereby maintaining its corrosion resistance. Most alloy structural steels and alloy tool steels can obtain good cutting edge quality by laser cutting.

Aluminum and aluminum alloys cannot be cut with oxygen-assisted melting. A melting cutting mechanism must be used. Aluminum laser cutting requires a very high power density to overcome its high reflectivity to 10.6μm wavelength lasers. 1. 06μm wavelength YAG laser beams can greatly improve the cutting quality and speed of aluminum laser cutting due to their high absorption rate.

Titanium and titanium alloys commonly used in the aircraft manufacturing industry have intense chemical reactions when oxygen is used as an auxiliary gas, and the cutting speed is fast, but it is easy to form an oxide layer on the cutting edge, and even cause overburning.

It is safer to use inert gas as an auxiliary gas to ensure cutting quality. Most nickel-based alloys can also be cut with oxygen-assisted melting. Copper and copper alloys have too high a reflectivity and basically cannot be cut with 10.6μm carbon dioxide lasers.

(2) Laser cutting of non-metallic materials

The 10.6μm CO2 laser beam is easily absorbed by non-metallic materials. Its low reflectivity and evaporation temperature allow almost all of the absorbed light energy to enter the material, and instantly cause vaporization to form holes, entering a virtuous cycle of the cutting process. Plastics, rubber, wood, paper products, leather, natural fabrics and other organic materials can be cut by laser. However, the thickness of wood must be limited. The thickness of wood boards is within 75mm, and the thickness of laminates and wood chip boards is about 25mm. Among inorganic materials, quartz and ceramics can be cut by laser. The latter should be cut with controlled fracture and high power should not be used. Glass and stone are generally not suitable for laser cutting.

Other materials that are difficult to process by conventional methods, such as composite materials and cemented carbides, can be cut by laser, but reasonable cutting mechanisms and process parameters must be selected through experiments.

In the actual application of laser cutting technology, improving cutting efficiency, improving cutting quality and reducing cutting costs are one of the things we often need to consider.

Improving laser cutting technology to improve production efficiency, cutting quality and reduce costs can be done from the following aspects:

1. With the advancement of laser technology, the use of higher-power lasers (such as 10,000-watt lasers) can significantly increase cutting speeds, while reducing heat-affected zones and material deformation, making cutting more efficient and better quality, especially for cutting thicker materials.

2. Reasonably adjust parameters such as laser power, cutting speed, auxiliary gas type and pressure, and the distance between the nozzle and the material, and make detailed settings based on specific materials and cutting requirements. Find the optimal parameter combination through multiple tests to improve cutting efficiency and quality.

3. Through the automatic focusing system, the laser focus position is automatically adjusted according to the material thickness and type to ensure cutting accuracy.

4. Reduce non-cutting time and improve overall operating efficiency by quickly moving the cutting head to the next cutting starting point.

5. Automatically detect material edges and tilt angles, automatically adjust the cutting path, and reduce material waste and preprocessing time.

6. Use CNC software to simulate cutting, plan the simplest cutting path, reduce empty strokes, and improve material utilization and cutting speed.

7. Regularly maintain and service the laser cutting machine, such as replacing wearing parts, cleaning optical components, calibrating equipment, etc., to ensure long-term stable operation of the equipment and maintain optimal cutting performance.

8. Keep the working environment of the laser cutting machine clean, with appropriate temperature and moderate humidity to avoid the impact of dust and excessive humidity on the equipment and cutting effect.

9. Use more advanced CNC control systems and software to improve control accuracy and response speed, and support more complex cutting tasks.

10. Continue to pay attention to new developments in laser technology, such as more efficient laser sources, more advanced optical systems, intelligent software algorithms, etc., to continuously improve cutting capabilities.