Laser has been applied in teaching, military as well as industrial production. Laser cutting machine is one of the applications. It can be used in both metal and non-metal cutting, Melting surface material by laser beam. This article will discuss the work theory of
laser cutting machine.
Introduction on the work theory of laser cutting machine.
Laser cutting machine adopts the energy released on the time when
laser beam irradiate metal surface. The metal is melt by laser and sinter is blow away by gas. Because laser power is highly focused, only a very little heat effects the other part of metal plate and causes a little or no deformation. Laser can cut any complex shape precisely, which needs no further processing.
Laser source is generally CO2 laser beam with operating power of 500～5000W. The power is even lower than that of many household electric heater, and because of lenses and reflectors, laser beams are focused in a very small bit of area. Highly focused energy heat the area quickly and makes the metal plate melted.
Laser cutting machine can cut stainless steal of thickness less than 16mm; when adding oxygen in laser beam, the cutting thickness is 8～10mm but it will generate a thin oxidation film in the cut surface. The maximum thickness is 16mm which leads to larger cutting deviation on the size of components.
Since the advent of laser, numerous laser products have been developed, such as laser printer, laser cosmetic instrument, laser marker, laser cutting machine etc. Due to its late start in China, the laser technology in China is greatly behind the developed countries. Although Chinese manufacturers can produce plenty of laser products, some key parts such as laser tube, driving motor, galvanometer and focus lens are imported products. This leads to an increase on cost thus an increase on consumer's payment.
In recent years, domestic research and production of laser products become closer to advanced overseas products with the progress of laser technology in China. Some aspects are even superior to products abroad, which has a leading role in market because of the advantages of price. Overseas products have absolute predominance in precision machining for its quality on stability and endurance.
Work theory of laser cutting machine
Laser tube is the core part of laser cutting machine. So, below is an introduction of the most popular laser tube. CO2 laser tube.
Laser tube is composed of hard glasses, so it is fragile. It adopts layer of sleeve construction with discharge tube in the most inside layer. However, the diameter of discharge tube is thicker than laser tube, diffraction between the thickness of discharge tube and the size of flare is in direct ratio; the length of tube is in proportion to output power of discharge tube. Laser tube generates a large quantity of heat in the operation of laser cutting machine, which influences the normal work. So cold water machine is needed to cool laser tube, ensuring constant temperature for successful running.
Cutting features of laser cutting machine
Advantages of laser cutting:
One — high efficiency
Laser cutting machine is always connected to several numerically-controlled rotary tables to achieve numerical controlled cutting. It only needs to change the NC program to adjust to components of different shapes, which can make 2D cutting as well as 3D cutting.
Two — high speed
When cutting low carbon steel sheets of 2mm thickness, the speed of 1200W laser cutting is 600cmmin; when it is 5mm thick polypropylene resin plate, the cutting speed is 1200cmmin. The material needs no clamping fix in laser cutting process.
Three — high quality cutting
Laser cutting features thin kerf. The two sides of kerf are parallel and the kerf is vertical to the surface. The cutting precision can reach to ±0.05mm. The cutting surface is clean and nice, with roughness of tens of microns. The cut components can even come into use directly without further machining. After laser cutting, the heat effected area is very small and material near to kerf has not been affected, making little deformation, high cutting precicion and perfect geometrical shape.
Four — non-contact cutting
Laser cutting is non-contact cutting, which means no tool wear problem. When processing different shapes, there is no need to change tools, the only way is to alter the output parameter of laser. The whole laser cutting process features low noise, little vibration and little pollution.
Five — various cutting material
Compared to oxyacetylene cutting and plasma cutting, laser cutting can be applied on more materials, including metal and non-metal, metal matrix and non-metallic matrix composite, leather, wood as well as fibers.
Cutting methods of laser cutting machine
Vaporization cutting
It means that
vaporization is the main way to remove the processed material. In the process of vaporization cutting, workpiece surface is heated to vaporization temperature quickly by focused laser beams, forming High pressure steam and spraying outward at supersonic speeds. In the meantime, a hole is formed in the laser active area and laser beams reflex several times in the hole to increase the absorption of laser by material.
When high-pressure vapors spray outward, the melted materials are blown away in the kerf till the workpiece is finally cut. Vaporization cutting needs very high power density, which is eighth power of ten watt above per square centimeter. It is usually applied in low flash point materials and refractory materials.
Reaction Fusion Cutting
When assistant airflow not only blows the melted materials from the kerf but also has thermal reaction with the workpiece, this is the so-called reaction fusion cutting. Gases that can have reaction with workpiece are oxygen or mixture gases containing oxygen. When the surface temperature of workpiece reach to ignition temperature, strong combustion heat release occurs to improve the laser cutting ability.
Combustion heat release of low carbon steel and stainless steel is 60%. And it is about 90% for reactive metals like titanium.
Compared to vaporization cutting and general fusion cutting, reaction fusion cutting need less laser power density. However, reaction fusion cutting may effect the performance of worpiece since the combustion reaction can lead to chemical reaction on materials.
Fusion Cutting
When adding a assistant airflow system coaxial with laser to blow the melted materials away from kerf, this kind of cutting is fusion cutting. In fusion cutting, workpiece needn't to be heated to vaporization temperature so the required laser power density is reduced greatly.
Laser Scribing
It is mainly used in semiconductor materials, in which laser of high power density make a shallow groove in the semiconductor materials of the workpiece and then makes it crack through mechanistic or vibratory methods. The quality is valued by the surface fragments and size of heat affect area.
Cold Chipping
It is a new processing method, which is put forward along with ultraviolet band superpower excimer laser appeared in recent years. The basic theory is that energy of ultraviolet photons is similar to binding energy of many organic materials; this high-energy photons are used to impact bond organic materials thus make it crack, achieving purpose of cutting. This new technology has promising application future, especially in electron industry.
Thermal Stress Cutting
Mechanism of thermal stress cutting is that laser beams heat an area of fragile material to produce evident temperature gradient. The high surface temperature makes expansion and inner lower temperature hinders expansion, forming pulling stress in the surface and radial crushing stress inside. When the two stresses exceed fracture limit strength of the workpiece, crackle appears. And then the workpiece is broken along the normal direction of the crack. It is suitable for glasses and ceramics.
Conclusion:
laser cutting machine is a cutting technology of melting and gasifying surface material through focused energy generated by the use of laser specialties and focused lens. It features good cutting quality, high speed, various cutting material and high efficiency.
