With the continuous improvement and improvement of living standards, people are increasingly using cars as vehicles. While the car brings convenience to people, it also brings many problems. Among them, the massive consumption of energy is one of the issues that need attention, and the energy crisis has always been a major global problem that plagues humanity. The heavier the car body, the more energy it consumes. Therefore, the automotive industry has been working to reduce the weight of the car without reducing the structural stability of the car. In order to meet this requirement, many new technologies are constantly appearing. In the process of using and developing many new technologies, tailor welding technology is one of them, which meets the specific requirements of reducing the weight of the vehicle while improving the safety of the structure of the automobile.
With the development of laser technology, laser processing has been widely used in the industry. Taking the steel and automobile industries as an example, laser processing technology has been vigorously promoted in various aspects such as continuous production and rolling of cold-rolled steel sheets and production of cars. In the supporting processing plants between steel mills and automobile factories, laser tailor welding technology has been used in recent years. Laser tailor welding technology can directly combine two or more steel plates with different surface treatments, different steel grades and different thicknesses into a blank by laser welding. The automobile factory directly uses this blank to punch into parts. . Because of their free combination, similar to the nature of tailoring, different steel plates can be spliced. Therefore, when this technology is introduced, such steel plates are called Tailor Welded Blanks. During the period from 1993 to 1997, the ULSAB (Ultra Light Auto Steel Body) project, jointly initiated by 35 steel mills and automobile manufacturers, promoted the use of laser tailor welding technology in body-in-white structural parts. Laser tailor welding technology has been widely used in structural members such as stringers, safety rafts, door panels, floors, and columns. At present, large auto companies such as General Motors, Volkswagen, Ford, Toyota, and Honda have already applied this new technology in their new model design.
The predecessor of laser tailor welding technology
Laser tailor welded blanks originated in the automotive industry in the 1980s. At that time, it was mainly to solve the problem that the width of the steel plate rolled out by the rolling mill of the steel mill was insufficient, and the tailoring welding technology was adopted to meet the demand of the wide-board in the automobile industry. Therefore, the steel plate of the same thickness was mainly welded. With the development of the automobile industry, the laser tailor-welded plate is developed in the direction of the poor thick plate, and the steel plates of different thicknesses can be tailor welded. At this time, the purpose of laser welding of the automobile steel plate is truly realized.
At present, laser tailor welding technology is a new technology widely used in the automotive industry to join two or more materials with different thicknesses before forming. The traditionally used process in the automobile factory is to press all the parts into parts and then connect them into a whole by spot welding. After adopting the new technology of laser tailor welding, it is changed to different strengths and thicknesses. The sheets are punched and joined by laser welding into a unitary blank, which is then integrally stamped.
Advantages of laser tailor welding technology
The tailor welded blanks produced by laser welding technology have great advantages. According to the research of foreign scholars, the advantages are as many as 37, which are mainly reflected in the following aspects:
(1) Reduction of the final body weight. In the application of automotive structural parts, the use of laser tailor welded blanks eliminates the need to use excess reinforcement, resulting in a reduction in overall body weight. By combining a different material and thickness in a steel plate, the overall body structure can be greatly simplified.
(2) Reduce the number of auto parts. The structural accuracy of the car body can be greatly improved, and many stamping equipment and processing operations can be reduced. Taking the application of the inner panel as an example, in the body design, the part has high requirements for the stamping forming performance. This means that a softer and thinner material is required. However, at the front of the same door inner panel, the joint between the hinge and the door requires sufficient strength to withstand the frequent use of the door. In the conventional process, it is necessary to use a reinforcing plate to enhance the strength of the door inner panel. This extra part requires a lot of work to complete the process in the workshop. Now, by using laser tailor welding technology, a large, softer, thinner material and a relatively small, harder, thicker material are joined by laser welding before joining into a door inner panel. Stamping into a single piece completely eliminates the need to use reinforcement.
(3) The utilization rate of raw materials is greatly improved, and waste is greatly reduced. The utilization of materials is greatly improved by the selective use of high-strength, thick materials in specific parts of the structural members. Through the use of the discharge technology in the blanking process, various steel plates are reasonably combined to greatly reduce the material engineering waste rate.
(4) The structural function has been greatly improved. By using laser tailor welding technology, the rigidity of the structure is greatly improved due to the reasonable combination of the strength and thickness of the material. The corrosion resistance of the structure is also improved. The more important role of using tailor-welding technology is to improve the anti-collision performance of the structural members through the combination of thickness and strength. At the same time, in the parts with collision requirements, the use of high-strength steel or thick plates, and in low-demand parts, the use of low-strength steel or thin plate, thereby greatly improving the anti-collision ability of automotive parts. Laser tailor welding is adapted to the need to strengthen the part to be strengthened. Through the connection of thick plate and thin plate or the connection of high-strength steel and low-strength steel, the effect of improving the safety of the car is much better than the thickness or strength of the steel plate. There is no change in the level. Compared with the conventional spot welding process, the size and shape accuracy of the stampings using the laser tailor welded blanks are greatly improved. Thereby the assembly accuracy of the vehicle body is improved. This will result in reduced vehicle noise and fewer overall assembly defects.
(5) It is possible to produce wide-body cars. Due to the limitation of the mill mill width, the plate width provided by the steel mill has a certain limit. With the development of the automobile industry, the demand for wide plates is becoming more and more urgent. It is an effective and economical to use laser tailor welding. Process method.
The ULSAB project produced prototypes in 1998. The number of tailor welded blanks used in this ultralight vehicle reached 16 pieces, accounting for about 45% of the weight of the car. Thanks to the use of tailor welded blanks, the number of body parts was approximately Reduced by 25%, increased torsional stiffness by 65%, improved vibration characteristics by 35%, and enhanced bending stiffness.
Baosteel's research on laser tailor welding technology
Because laser tailoring technology has significant advantages compared with traditional methods, automotive manufacturers pay more attention to the performance of laser tailor welded blanks in the stamping process. Research on the performance of laser tailor welded blanks has become a hot topic. Compared with the base metal, the laser tailor welded blanks exhibit different performance characteristics. Studies have shown that laser butt welds have higher strength and hardness values ​​than the parent metal. This is due to the rapid cooling of the laser weld in a small weld pool. In most laser welded joints, the heat-affected zone structure consists of fine-grained, equiaxed crystals. A large number of experimental results show that the simulation technique can better predict the flow law of the weld seam of the laser tailor welded blank during the stamping process.
The research on the laser tailor welded blanks with different thicknesses and different materials shows that the forming properties of the laser tailor welded blanks have different degrees of decline compared with the parent metal, but a large number of experimental evidences indicate that the laser welds with good quality are in the form of stamping. No failure occurs. Figure 1 shows the relationship between the yield strength of the welded blank of the tailor welded blank and the base metal in different combinations.
Baosteel conducted a large number of experimental studies on the performance of forming limit diagrams of differential laser tailor welded blanks. Fig. 2 is the limit drawing experiment of the laser tailor welded blank. The results show that the maximum dangerous main strain at the weld of the laser tailor welded blank is 14%, and the minimum ultimate strain tailor welded blank under the strain path is 30%, so the minimum number of tailor welded blanks is The margin Δemin=16%. Therefore, the laser tailor welded blank in the weld area fully meets the forming requirements of automotive parts.
Figure 1 Comparison of performance of laser tailor welded blanks under different conditions
Figure 2 Laser tailor welded plate forming limit diagram performance
Production and application of Baosteel laser tailor welded blank
In automotive body-in-white structural components, more and more typical structural members such as stringers, door inner panels, safety rafts, and reinforcing panels use laser tailor welded blanks in the stamping process. According to statistics, in the current design of new body structural parts, there are 2 or 3 pieces of laser tailor welding technology per vehicle. Especially for those cars that are more expensive, more tailor welded blanks are used in their body design. By using a laser tailor welded blank, the crash resistance of the vehicle is greatly improved. As automotive designers and car manufacturers have realized that the use of laser tailor welded blanks in automotive structural parts can greatly simplify the production process, reduce production costs, improve the performance of the entire vehicle, and thus use lasers in more and more updated body structural parts. Tailor welded blanks.
China's research and application of laser tailor welded blank production is the most active in Baosteel. Since 1991, Baosteel has been tracking the laser tailor welding technology. In 1999, Baosteel Technology Center introduced the laser tailor welding test device to study the laser tailor welding technology. It has completed the process research of some parts of many automobile factories, and carried out the actual punch test to meet the requirements of the actual body parts for the laser tailor welded blanks. .
Since laser tailor welded blanks have many advantages for automobile manufacturers, laser tailor welded blanks are currently used on many new structural parts, and the demand for laser tailor welded blanks is rapidly increasing. On November 9, 2004, Baoshan Iron & Steel Co., Ltd. and Arcelor jointly invested and established a joint venture company (Shanghai Baosteel Arcelor Laser Tailored Blanks Co., Ltd.) to officially put into production, specializing in mass production of laser tailor welded blanks. . The joint venture company has introduced an advanced laser tailor welded plate production line, specializing in the production of laser tailor welded blanks to meet the needs of domestic automotive plants for laser tailor welded blanks. In the near future, the demand for laser tailor welded blanks in the Chinese automotive industry will gradually replace the import from foreign countries and the domestic production plants to meet the timely supply of laser tailor welded blanks.
Laser tailor welded blanks are a new technology that has emerged in the automotive industry in recent years. By using laser tailor welded blanks on automotive body-in-white structural parts, the weight of the vehicle body can be greatly reduced and the safety performance can be greatly improved. In the stamping process of the automobile factory, the materials are also used reasonably, and the material waste materials in the workshop can be greatly reduced.
The automobile industry's extensive use of laser tailor welded blanks is an inevitable trend in the development of the current era.
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