First, what is a laser? The world's first laser beam was produced in 1960 by using a flash bulb to excite ruby crystal grains. Due to the limitation of the heat capacity of the crystal, it could only produce a very short pulse beam with a very low frequency. Although the instantaneous pulse peak energy can be as high as 106 watts, it is still a low energy output.
Laser technology uses a polarizer to reflect the beam generated by the laser so that it is concentrated in a focusing device to produce a beam of huge energy. If the focus is close to the workpiece, the workpiece will melt and evaporate within a few milliseconds. This effect can be used in the welding process. The emergence of high-power CO2 and high-power YAG lasers has opened up a new field of laser welding. The key to laser welding equipment is high-power lasers. There are two main categories. One is solid laser, also known as Nd:YAG laser. Nd (neodymium) is a rare aristocratic element, YAG stands for yttrium aluminum garnet, and its crystal structure is similar to ruby. The wavelength of the Nd:YAG laser is 1.06μm. The main advantage is that the generated beam can be transmitted through optical fiber, so a complex beam transmission system can be omitted. It is suitable for flexible manufacturing systems or remote processing, and is usually used for workpieces with high welding accuracy requirements. Nd:YAG lasers with output powers of 3-4 kilowatts are commonly used in the automotive industry. The other type is gas laser, also known as CO2 laser. Molecular gas is used as the working medium to produce an infrared laser with a uniform size of 10.6 μm. It can work continuously and output very high power. The standard laser power is between 2-5 kilowatts.
Compared with other traditional welding technologies, the main advantages of laser welding are:
1. Fast speed, large depth and small deformation.
2. Welding can be performed at room temperature or under special conditions, and the welding equipment is simple. For example, the laser beam will not deflect when passing through an electromagnetic field; lasers can perform welding in vacuum, air, and certain gas environments, and can weld through glass or materials transparent to the laser beam.
3. It can weld refractory materials such as titanium, quartz, etc., and can also weld heterogeneous materials with good results.
4. After the laser is focused, the power density is high. When welding high-power devices, the aspect ratio can reach 5:1 and up to 10:1.
5. Micro welding is possible. After the laser beam is focused, it can obtain a very small spot and can be accurately positioned, so it can be applied
It is used in the assembly and welding of micro and small workpieces in mass automated production.
6. It can weld inaccessible parts and implement non-contact remote welding, which has great flexibility. Especially in recent years, optical fiber transmission technology has been adopted in YAG laser processing technology, which has enabled laser welding technology to be more widely promoted and applied.
7. The laser beam can be easily split in time and space, enabling simultaneous multi-beam processing and multi-station processing, providing conditions for more precise welding.
However, laser welding also has certain limitations:
1. It requires high assembly precision of the workpieces and that the position of the laser beam on the workpiece cannot be significantly offset. This is because the laser spot size is small after focusing, the weld seam is narrow, and filler metal material is added. If the workpiece assembly precision or beam positioning precision does not meet the requirements, welding defects can easily occur.
2. The cost of lasers and related systems is relatively high, resulting in a large initial investment.
