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Tianhong Classroom | Interpretation of Common Process Parameters of Laser Welding
- Categories:Product analysis
- Author:Tianhong laser
- Origin:Tianhong laser
- Time of issue:2021-03-10 12:42
- Views:
(Summary description)Laser welding is one of the important aspects of the application of laser processing technology, and it is a welding technology that has attracted much attention and has great development prospects in the 21st century. Compared with traditional welding methods, laser welding has many advantages, such as higher welding quality and faster efficiency. At present, laser welding technology has been widely used in manufacturing, powder metallurgy, automobile industry, electronics industry, biomedicine and other fields.
Tianhong Classroom | Interpretation of Common Process Parameters of Laser Welding
(Summary description)Laser welding is one of the important aspects of the application of laser processing technology, and it is a welding technology that has attracted much attention and has great development prospects in the 21st century. Compared with traditional welding methods, laser welding has many advantages, such as higher welding quality and faster efficiency. At present, laser welding technology has been widely used in manufacturing, powder metallurgy, automobile industry, electronics industry, biomedicine and other fields.
- Categories:Product analysis
- Author:Tianhong laser
- Origin:Tianhong laser
- Time of issue:2021-03-10 12:42
- Views:
Information
Laser welding is one of the important aspects of the application of laser processing technology, and it is a welding technology that has attracted much attention and has great development prospects in the 21st century. Compared with traditional welding methods, laser welding has many advantages, such as higher welding quality and faster efficiency. At present, laser welding technology has been widely used in manufacturing, powder metallurgy, automobile industry, electronics industry, biomedicine and other fields.
Laser welding principle
Laser welding belongs to fusion welding, using laser beam as the welding heat source. The welding principle is: the active medium is excited by a specific method to make it oscillate back and forth in the resonant cavity, and then converted into a beam of stimulated radiation. When the beam and the workpiece are in contact with each other , its energy is absorbed by the workpiece, and welding can be performed when the temperature reaches the melting point of the material.
According to the formation mechanism of welding pool, laser welding has two basic welding mechanisms: heat conduction welding and deep penetration (small hole) welding. The heat generated during heat conduction welding diffuses to the inside of the workpiece through heat transfer, melting the surface of the weld seam, and basically does not produce vaporization. It is often used for welding low-speed thin-walled components. Deep penetration welding vaporizes the material and forms a large amount of plasma. Due to the high heat, small holes will appear at the front of the molten pool. Deep penetration welding can completely penetrate the workpiece, and the input energy is large and the welding speed is fast. It is currently a widely used laser welding mode.
Main process parameters of laser welding
There are many process parameters that affect the quality of laser welding, such as power density, laser pulse waveform, defocus, welding speed and auxiliary blowing shielding gas.
1 laser power density
Power density is one of the most critical parameters in laser processing. With a higher power density, the surface layer can be heated to the boiling point within microseconds, resulting in a large amount of vaporization. Therefore, high power density is very beneficial for material removal processes such as drilling, cutting, and engraving. For a lower power density, it takes several milliseconds for the surface temperature to reach the boiling point. Before the surface layer vaporizes, the bottom layer reaches the melting point, which is easy to form a good fusion weld. Therefore, in heat conduction laser welding, the power density is in the range of 104-106W/cm2.
2 laser pulse waveform
The laser pulse waveform is not only an important parameter to distinguish material removal from material melting, but also a key parameter to determine the volume and cost of processing equipment. When the high-intensity laser beam hits the surface of the material, 60-90% of the laser energy will be reflected and lost on the surface of the material, especially gold, silver, copper, aluminum, titanium and other materials with strong reflection and fast heat transfer. During a laser pulse signal, the reflectivity of the metal changes with time. When the surface temperature of the material rises to the melting point, the reflectance will drop rapidly, and when the surface is in a molten state, the reflectance stabilizes at a certain value.
Main process parameters of laser welding
There are many process parameters that affect the quality of laser welding, such as power density, laser pulse waveform, defocus, welding speed and auxiliary blowing shielding gas.
1 laser power density
Power density is one of the most critical parameters in laser processing. With a higher power density, the surface layer can be heated to the boiling point within microseconds, resulting in a large amount of vaporization. Therefore, high power density is very beneficial for material removal processes such as drilling, cutting, and engraving. For a lower power density, it takes several milliseconds for the surface temperature to reach the boiling point. Before the surface layer vaporizes, the bottom layer reaches the melting point, which is easy to form a good fusion weld. Therefore, in heat conduction laser welding, the power density is in the range of 104-106W/cm2.
2 laser pulse waveform
The laser pulse waveform is not only an important parameter to distinguish material removal from material melting, but also a key parameter to determine the volume and cost of processing equipment. When the high-intensity laser beam hits the surface of the material, 60-90% of the laser energy will be reflected and lost on the surface of the material, especially gold, silver, copper, aluminum, titanium and other materials with strong reflection and fast heat transfer. During a laser pulse signal, the reflectivity of the metal changes with time. When the surface temperature of the material rises to the melting point, the reflectance will drop rapidly, and when the surface is in a molten state, the reflectance stabilizes at a certain value.
Laser welding pulse waveform of different materials
3 laser pulse width
Pulse width is an important parameter for pulsed laser welding. The pulse width is determined by the penetration depth and the heat-affected zone. The longer the pulse width, the larger the heat-affected zone, and the penetration depth increases with the 1/2 power of the pulse width. However, the increase in pulse width will reduce the peak power, so increasing the pulse width is generally used for heat conduction welding, and the weld size formed is wide and shallow, especially suitable for lap welding of thin and thick plates. However, lower peak power results in excess heat input, and each material has an optimal pulse width for upper penetration.
4 defocus amount
Laser welding usually requires a certain amount of defocus, because the power density in the center of the spot at the laser focus is too high, and it is easy to evaporate into holes. On each plane away from the laser focus, the power density distribution is relatively uniform.
There are two ways to defocus:
Positive and negative defocus. If the focal plane is above the workpiece, it is positive defocus, otherwise it is negative defocus. According to the theory of geometric optics, when the distance between the positive and negative defocus planes and the welding plane is equal, the power density on the corresponding planes is approximately the same, but in fact the obtained molten pool shape is somewhat different. When the defocus is negative, a greater penetration depth can be obtained, which is related to the formation process of the molten pool.
5 welding speed
The welding speed determines the welding surface quality, penetration depth, heat-affected zone, etc. The speed of welding will affect the heat input per unit time. If the welding speed is too slow, the heat input will be too large, which will cause the workpiece to burn through. If the welding speed is too fast, the heat input will be too small, resulting in impenetrable welding of the workpiece. The method of reducing the welding speed is usually used to improve the penetration depth.
6 Auxiliary blowing protective gas
Auxiliary blowing shielding gas is an essential process in high-power laser welding. On the one hand, it is to prevent the metal material from sputtering and contaminate the focusing mirror; on the other hand, it is to prevent the plasma generated during the welding process from focusing too much and prevent the laser from reaching the surface of the material. The laser welding process often uses gases such as helium, argon, and nitrogen to protect the molten pool to protect the workpiece from oxidation during the welding process. Factors such as the type of shielding gas, the size of the airflow, and the blowing angle have a greater impact on the welding result, and different blowing methods will also have a certain impact on the welding quality.
Helium is not easily ionized (higher ionization energy), which allows the laser to pass through smoothly, and the beam energy reaches the surface of the workpiece without hindrance. This is a very effective shielding gas for laser welding, but it is more expensive.
Argon gas is cheaper and denser, so the protection effect is better. However, it is susceptible to high-temperature metal plasma ionization, which shields part of the beam from hitting the workpiece, reduces the effective laser power for welding, and also damages the welding speed and penetration. The surface of the weldment protected by argon is smoother than that when protected by helium.
Nitrogen is less expensive as a shielding gas, but it is not suitable for welding some types of stainless steel, mainly due to metallurgical problems, such as absorption, which sometimes produces porosity in the overlapping area.
As a new type of welding technology, laser welding has the characteristics of high energy density, high speed, high precision, deep penetration, and strong adaptability. Its application range is becoming wider and wider. It can not only improve production efficiency, but also improve welding quality. Laser welding technology will play a more important role in the field of material processing.
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