Some Basic Knowledge Of Laser Cutting
As early as the 1970s, lasers were first used for cutting. In modern industrial production, laser cutting is more widely used in sheet metal, plastic, glass, ceramics, semiconductors, textiles, wood and paper materials processing.
Laser cutting
When the focused laser beam shines on the workpiece, the illuminated area will heat up sharply to melt or vaporize the material. Once the laser beam penetrates the workpiece, the cutting process begins: the laser beam moves along the contours while melting the material. A jet stream is usually used to blow the melt away from the cut, leaving a narrow gap almost as wide as the focused laser beam between the cut section and the frame.
Flame cutting
Flame cutting is a standard process for cutting low carbon steel, using oxygen as the cutting gas. Oxygen is pressurized up to 6bar and blown into the incision. There, the heated metal reacts with oxygen: it begins to burn and oxidize. The chemical reaction releases a large amount of energy (up to five times the energy of the laser) to assist the laser beam in cutting.
Fusion cutting
Melting cutting is another standard process used when cutting metal. It can also be used to cut other fusible materials, such as ceramics.
Nitrogen or argon gas is used as the cutting gas, and the gas pressure of 2 to 20bar is blown through the incision. Argon and nitrogen are inert gases, which means they do not react with the molten metal in the cut, simply blowing it away towards the bottom. At the same time, the inert gas can protect the cutting edge from air oxidation.
Compressed air cutting
Compressed air can also be used to cut sheet metal. Air pressurization to 5 to 6bar is sufficient to blow away molten metal in the incision. Since nearly 80% of the air is nitrogen, compressed air cutting is basically melting cutting.
Plasma assisted cutting
If the parameters are selected properly, plasma clouds will appear in the plasma-assisted melting cutting incision. The plasma cloud consists of ionized metal vapor and ionized cutting gas. The plasma cloud absorbs the energy of the CO2 laser and converts it into the workpiece, allowing more energy to be coupled to the workpiece, and the material to melt faster, resulting in faster cutting. Therefore, this cutting process is also called high-speed plasma cutting.
Plasma clouds are actually transparent relative to solid lasers, so plasma-assisted melting cutting can only be done with CO2 lasers.
Gasification cutting
Gasification cutting vaporizes the material and minimizes the thermal effect on the surrounding material. This can be achieved by using continuous CO2 lasers to process materials with low heat evaporation and high absorption, such as thin plastic films and non-melting materials such as wood, paper and foam.
Ultrashort pulsed lasers allow the technique to be applied to other materials. The free electrons in the metal absorb the laser and heat up violently. The laser pulses do not react with the molten particles and plasma, and the material sublimates directly, leaving no time to transfer energy in the form of heat to the surrounding material. There is no obvious thermal effect when the picosecond pulse ablates the material, no melting and burr formation.
Parameters: Adjust the process
Many parameters affect the laser cutting process, some of which depend on the technical performance of the laser and the machine tool, while others are variable.
Degree of polarization
The degree of polarization indicates what percentage of the laser light has been converted. The typical degree of polarization is around 90%. This is sufficient for a high-quality cut.
Focal diameter
The focal diameter affects the width of the incision and can be changed by changing the focal length of the focusing mirror. A smaller focal diameter means a narrower incision.
Focus position
The focus position determines the beam diameter and power density on the workpiece surface as well as the shape of the incision.
Laser power
The laser power should be matched with the type of processing, the type of material and the thickness. The power must be high enough that the power density on the workpiece exceeds the machining threshold.
Working mode
The continuous mode is mainly used to cut standard profiles of machined materials in millimeter to centimeter sizes. In order to melt the perforation or produce a precise profile, a low-frequency pulsed laser is used.
Cutting speed
Laser power and cutting speed must match each other. Cutting too fast or too slow will result in increased roughness and burr formation.
Nozzle diameter
The diameter of the nozzle determines the flow rate and shape of the gas flowing out of the nozzle. The thicker the material, the larger the diameter of the gas jet, and correspondingly, the diameter of the nozzle opening should also be increased.
Gas purity and pressure
Oxygen and nitrogen are often used as cutting gases. The purity and pressure of the gas affect the cutting effect.
When oxygen flame cutting is used, the purity of the gas needs to reach 99.95%. The thicker the steel plate, the lower the gas pressure used.
When using nitrogen melt cutting, the gas purity needs to reach 99.995% (ideally 99.999%), and higher air pressure is required when melting and cutting thick steel plates.
Technical parameter list
In the early stage of laser cutting, users must determine the setting of processing parameters by themselves through test runs. Mature machining parameters are now stored in the control unit of the cutting system. For each material type and thickness, there are corresponding data. The technical data sheet makes it possible to operate laser cutting equipment smoothly even for people who are not familiar with this technology.
Laser cutting quality evaluation factors
There are many criteria for determining the quality of laser cut edges. Criteria such as burr form, depression, grain can be judged by the naked eye; Perpendicularity, roughness and incision width are measured by special instruments. Material deposition, corrosion, heat-affected areas and deformation are also important factors in measuring the quality of laser cutting.
Broad prospect
The continuous success of laser cutting is difficult to achieve with most other processing methods. This trend continues today. In the future, the application prospect of laser cutting will be more and more broad.