Development trend of laser welding and problems to be further explored

1. Composite welding (YAG laser and pulsed MIG composite welding, Nd:YAG and excimer laser superposition)

While extensively applying laser welding technology, people continue to conduct in-depth research and find that it has certain disadvantages: in the laser welding process, the base metal is melted and vaporized by heat to form deep-melting pores filled with metal vapor. Metal gas and laser action form a plasma cloud. The plasma cloud absorbs and reflects the laser, reduces the absorption rate of the laser by the metal material, and reduces the energy utilization rate of the laser. The interface of the welding base material is required to be high and easy to produce misalignment; it is easy to generate pores and cracks; There are recesses in the interface between the parts, the welding process is unstable, etc. In order to eliminate or reduce the defects of single heat source laser welding, people use the heating characteristics of other heat sources to improve the heating of the workpiece by laser based on the advantages of laser heating. Therefore, the laser is combined with other heat sources for composite heat source welding. There are mainly laser and arc, laser and plasma arc, laser and induction heat source composite welding and double laser beam welding. The combination of laser and arc welding combines the advantages of laser and arc, combining the high energy density of the laser with the large heating zone of the arc.

1) can increase the weld penetration

2) Improve welding speed and productivity

3) Improve joint performance

4) Reduce equipment cost At the same time, through the interaction of laser and arc, improve the coupling characteristics of laser energy and the stability of arc to obtain a comprehensive effect. However, the introduction of the arc increases the heat input of the weld, which inevitably increases the weld heat affected zone and thermal deformation.

2, laser welding control (melting pool size, plasma effect, etc.), laser welding model

In the research of penetration control of laser welding process, it is a key problem to establish the relationship between the shape parameters of the molten pool and the welding process. In the experimental process, the richer the shape information of the molten pool is obtained, the more the effect of the penetration control of the welding process is. ideal. Many scholars have calculated the temperature field, liquid flow and pore size of laser welding according to the small hole mechanism in laser deep-fusion welding, and achieved certain effects. For example, Dowden et al. proposed an inverse tough absorption model of incident laser. It is assumed that the energy is transmitted to the small hole wall through the conduction mechanism, and a maximum theoretical penetration is obtained by the heat conduction equation. Sonti et al. used a two-dimensional finite element nonlinear model to carry out the three-dimensional calculation of the aluminum alloy laser deep-melting welding process. The three-dimensional temperature field of laser welding is obtained. Downden analyzes the energy and pressure balance in the small hole, and establishes a general mold for liquid and vapor flow in a small hole. Wang Haixing et al. The method of pool size was tested, improved and popularized. From the energy balance in the laser welding process, the size of the molten pool under different welding conditions was predicted. Liu Shunhong carried out the analysis and numerical simulation of the temperature field of thin-plate laser welding in space. The weighted residual method is used in the domain, and the finite difference method is used in the time domain to discretize the thermal and thermal properties of the material. Correlation of melting latent heat influence of radiation and a convection temperature field, finite element equation, and the preparation of the corresponding program. With the improvement of the image sensing method, one can obtain more characteristic information of the shape of the molten pool from the molten pool image, such as the width, length and area of ​​the molten pool, and use this information to establish a relationship with the laser welding process parameters. The relationship will play an important role in the quality control of laser welded welds, which will be an important direction of laser welding research.

3. Laser welding laser generator and its process development trend

The lasers used in current laser welding are mainly high-power CO2 lasers and pulsed Nd:YAG lasers. The development of lasers is still focused on the development of laser equipment, such as improving the stability and life of power supplies, and solving high power for CO2 gas lasers. The discharge stability of the laser is to develop a large-capacity, long-life optical pump excitation source for YAG solid-state lasers. The direct diode array laser output wavelength in the near-infrared region has an average laser power of lkW, and the photoelectric conversion efficiency is close to 50%. These laser devices and technologies will play a greater role in soldering applications. In laser processing plus beam quality and processing peripheral devices, we should study the laser beam quality requirements, laser beam and processing quality monitoring technology, optical system and processing head design and development, and carry out welding process and materials, welding Process-to-equipment requirements and welding process parameter monitoring and control technology research to master the welding process of ordinary steel, non-ferrous metals and special steel.

The flame will be extinguished because of the loss of heat after going through the narrow pores of the heat conductor. The Flashback Arrestor is designed and manufactured using this principle.