Views: 0 Author: Site Editor Publish Time: 2024-07-01 Origin: Site
Dual-beam laser welding is a modern laser welding technique that utilizes two laser beams simultaneously for welding applications. This technology combines the high energy density of laser beams with stable welding processes to enhance welding speed, control the heat-affected zone, and optimize weld quality.
Technology Principles and FeaturesConfiguration of Dual Beams:
Dual-beam laser welding typically employs two independent laser sources, each emitting a laser beam. These beams are precisely controlled through optical systems to overlap or focus in parallel within the welding zone.
Control of Welding Process:
Dual-beam welding allows adjustment of each laser beam's power, focusing depth, and position. This optimization facilitates precise control over energy distribution during welding, influencing melt pool formation and welding speed.
Advantages in Applications:
Increased Welding Speed: Dual-beam technology significantly enhances welding speed by reducing processing time through simultaneous action of two laser beams.
Precise Control of Heat-Affected Zone: By adjusting the power and position of both beams, it is possible to precisely control the heat input and melt zone, thereby reducing heat-affected zones and deformation.
Optimized Weld Quality: Dual-beam welding provides uniform and stable weld seam morphology, minimizing welding defects such as porosity and cracks.
Application Fields
Dual-beam laser welding technology demonstrates extensive potential across various industries:
Automotive Manufacturing: Used for high-speed welding of automotive components such as body frames and floor structures.
Aerospace: Applied in welding aerospace engine components and complex aircraft structures.
Electronics Industry: Utilized for high-precision welding of electronic devices and semiconductor components.
Metal Processing: Suitable for welding different types of metal materials, including aluminum alloys, titanium alloys, etc.
Technological Challenges and Future Trends
While dual-beam laser welding offers many advantages, it also faces challenges such as the complexity of optical systems, precise alignment of laser beams, and control of laser power. Future developments may focus on smarter welding systems, higher-power lasers, and more advanced process monitoring and control methods to further enhance welding quality and efficiency.
1. Principles of Dual-Beam Laser Welding
Dual-beam welding involves the simultaneous use of two laser beams during the welding process. Parameters such as beam arrangement, beam spacing, the angle between the two beams, focal position, and the energy ratio between the beams are all critical settings in dual-beam laser welding. Typically, there are two main beam arrangements used during the welding process, as illustrated in the diagram. One arrangement is a series alignment along the welding direction. This configuration reduces the cooling rate of the molten pool, thereby minimizing tendencies for quench hardening and the formation of pores in the weld. Another arrangement is parallel or cross-alignment on both sides of the weld seam in order to increase the flexibility.
Types of Welding Mechanisms in Serial Dual-Beam Laser Welding Systems
For a serial dual-beam laser welding system, there are three different welding mechanisms based on the spacing between the front and rear beams, as illustrated in the diagram:
First Type of Welding Mechanism:
In this type, the spacing between the two beams is large. One beam has a higher energy density and is focused on the surface of the workpiece to create a keyhole during welding. The other beam has a lower energy density and serves as a heat source for preheating or post-welding thermal treatment. This mechanism allows control over the cooling rate of the weld pool within a certain range, which is advantageous for welding materials sensitive to cracking, such as high-carbon steel and alloy steel. It also improves the toughness of the weld joint.
Second Type of Welding Mechanism:
Here, the focal point spacing between the two beams is relatively small. Each beam generates an independent keyhole in the same weld pool. This alters the flow pattern of the molten metal, helping to prevent defects such as undercut and weld bead protrusion, thereby enhancing weld seam formation.
Third Type of Welding Mechanism:
In this mechanism, the spacing between the two beams is very small, causing them to generate a single keyhole in the weld pool. Compared to single-beam laser welding, the larger size of this keyhole remains open, leading to a more stable welding process where gases are easily expelled. This reduces the occurrence of porosity and spatter, resulting in continuous, uniform, and aesthetically pleasing weld seams.
During the welding process, the beams can also be angled relative to each other, similar to the parallel dual-beam welding mechanism. Experimental results indicate that using two beams angled at 30° with a spacing of 1-2 mm between them in high-power CO2 laser beams can achieve a funnel-shaped keyhole. This configuration provides a larger and more stable keyhole, effectively improving welding quality. In practical applications, adjusting the relative combination of the two beams according to different welding conditions can achieve different welding processes.
Methods for Implementing Dual-Beam Laser Welding
Dual-beam laser welding involves generating two separate laser beams, which can be achieved through different methods. Here are two common approaches:
Combination of Two Different Laser Beams:
Two distinct laser beams can be combined to form the dual-beam setup. These lasers may differ in their power levels, wavelengths, or other characteristics depending on the welding requirements. This method typically involves separate laser sources and combining optics to align and direct the beams towards the welding point.
Splitting a Single Laser Beam using Optical Systems:
Alternatively, a single laser beam can be split into two beams using optical splitting systems. This approach utilizes optical elements such as beam splitters or specialized optical systems to divide the single laser beam into two beams of different powers. The optical splitting can be achieved through techniques like using a beam splitter prism or other optical devices.
Diagrammatic Representation:
The diagram illustrates two principles of optical splitting using a focusing mirror as a beam splitter. This method showcases how a single laser beam can be split into two parallel beams with different power distributions. The optical configuration ensures that each split beam maintains its intended characteristics, allowing for precise control over the dual-beam welding process.
Using Reflective Mirrors for Optical Splitting in Dual-Beam Laser Welding
In dual-beam laser welding, reflective mirrors can also serve as beam splitters, positioned as the final mirror in the optical path. These mirrors, known as roof mirrors or ridge mirrors, consist of two intersecting reflective surfaces forming an angle. The intersection line of these surfaces runs through the middle of the mirror, resembling the ridge of a roof, as depicted in the diagram.
When a beam of parallel light strikes the roof mirror, it gets reflected by the two surfaces at different angles, thereby splitting into two beams. These beams are directed to different positions on the focusing lens and, after focusing, converge onto the surface of the workpiece at specific distances apart. By adjusting the angle between the two reflective surfaces and the position of the ridge, various configurations of split beams with different focal distances can be achieved.
Combinations of Different Laser Types in Dual-Beam Laser Welding
When combining two different types of laser beams for dual-beam welding, there are several configuration options:
High-Quality CO2 Laser with Semiconductor Laser:
One approach involves using a high-quality CO2 laser with a Gaussian energy distribution for the primary welding work, complemented by a semiconductor laser with a rectangular energy distribution for heat treatment tasks. This configuration is economical and allows independent adjustment of the power of each beam. By adjusting the overlap position of the CO2 and semiconductor lasers, a tunable temperature field can be created, ideal for precise control in welding processes.
YAG Laser with CO2 Laser:
Combining a YAG laser with a CO2 laser for dual-beam welding provides flexibility in adjusting welding parameters to suit different joint configurations.
Continuous Wave (CW) Laser with Pulsed Laser:
Integration of a continuous wave laser with a pulsed laser offers versatility in welding applications, balancing energy delivery between continuous and intermittent modes as needed.
Focusing Beam with Diverging Beam:
Another method involves combining a focused beam with a diverging beam for specific welding requirements, optimizing heat distribution and welding speed.
Dual-Beam Laser Welding Principle
3.1 Dual-Beam Laser Welding of Galvanized Steel Sheets
Galvanized steel sheets are commonly used in the automotive industry. Steel melts at around 1500°C, while zinc has a much lower boiling point of approximately 906°C. During fusion welding processes, significant zinc vaporization occurs, leading to instability in the welding process and the formation of porosity in the weld seam. The zinc vaporization not only affects the upper and lower surfaces but also impacts the joint interface, where zinc vapor release varies across different areas of the joint during welding. Some regions expel zinc vapor rapidly onto the molten pool surface, while others struggle to release zinc vapor efficiently, resulting in inconsistent welding quality.
Dual-beam laser welding offers solutions to the welding quality issues caused by zinc vaporization. One approach involves carefully matching the energy of the two laser beams to control the duration of molten pool existence and the cooling rate, thereby facilitating the escape of zinc vapor. Another method employs pre-drilling holes or grooves to release zinc vapor. As shown in Figure 6-31, this method utilizes a CO2 laser for welding, with a YAG laser positioned ahead of the CO2 laser. The YAG laser is used for pre-drilling holes or grooves. These pre-prepared holes or grooves provide pathways for the zinc vapor generated during subsequent welding, preventing it from being trapped in the molten pool and causing defects.
These techniques illustrate how dual-beam laser welding can effectively manage the challenges posed by zinc vaporization during the welding of galvanized steel sheets, ensuring improved welding stability and quality.
3.2 Dual-Beam Laser Welding of Aluminum Alloys
Due to the unique properties of aluminum alloys, laser welding encounters several challenges [39]: Aluminum alloys have a low absorption rate for laser energy, with initial reflectance exceeding 90% for CO2 laser beams. Welding aluminum alloys with lasers often results in the formation of pores, cracks, and alloy element burning. Establishing a stable keyhole during single-laser welding is difficult and maintaining its stability is also challenging.
Dual-beam laser welding addresses these challenges encountered in aluminum alloy welding. It facilitates the enlargement of keyhole size, preventing its closure and aiding in gas expulsion. Moreover, dual-beam welding reduces cooling rates, thereby minimizing the formation of pores and welding cracks. The welding process becomes more stable, leading to reduced spattering. Consequently, the surface finish of weld seams achieved through dual-beam welding is significantly superior to that achieved through single-beam welding.
As depicted in Figure 6-32, comparing CO2 single-beam and dual-beam laser welding of a 3mm thick aluminum alloy butt joint shows the distinct improvement in weld seam appearance achieved through dual-beam welding.
Research indicates that for welding 2mm thick aluminum alloys of the 5000 series, a dual-beam spacing of 0.6 to 1.0mm ensures a stable welding process. This spacing allows for the formation of larger keyhole openings, facilitating the evaporation and escape of magnesium elements during welding. When the spacing between the two beams is too small, stability similar to single-beam welding becomes challenging. Conversely, excessive spacing affects welding penetration, as illustrated in Figure 6-33.
Additionally, the energy ratio between the two beams significantly affects welding quality. For instance, in a serial arrangement with a spacing of 0.9mm between two beams, increasing the energy of the first beam appropriately—resulting in an energy ratio greater than 1:1 between the first and second beams—improves weld seam quality. This adjustment enhances the molten area and ensures a smooth and aesthetically pleasing weld seam even at higher welding speeds.
3.3 Dual-Beam Welding of Dissimilar Thickness Plates
In industrial production, it is common to weld together two or more metal plates of different thicknesses and shapes to create a jointed plate. This practice is increasingly prevalent in automotive manufacturing, where jointed panels find extensive application. Welding together plates of varying specifications, surface coatings, or material properties enhances strength, reduces material consumption, and lowers overall weight. A key challenge in panel welding is ensuring that the plates are prefabricated with high-precision edges and are assembled accurately.
Dual-beam welding of dissimilar thickness plates addresses these challenges effectively. It accommodates variations in gap between plates, alignment at the joint, relative thicknesses, and material types. This method allows welding of plates with larger tolerances for edges and gaps, thereby improving welding speed and weld seam quality.
The primary process parameters for dual-beam welding of dissimilar thickness plates can be categorized into welding parameters and plate parameters, as shown in the diagram. Welding parameters include the power of the two laser beams, welding speed, focal position, welding head angle, beam rotation angle relative to the joint, and welding offset amount. Plate parameters encompass material dimensions, properties, edge preparation, and gap between plates. Adjusting the power of the two laser beams according to specific welding goals is crucial. The focal position is typically set on the surface of the thinner plate to achieve stable and efficient welding.
The welding head angle is usually around 6 degrees; for thicker plates, a positive welding head angle can be used, where the laser tilts towards the thinner plate, as illustrated in the diagram. Conversely, for thinner plates, a negative welding head angle might be more suitable. The welding offset amount refers to the distance between the laser focus and the edge of the thicker plate. Adjusting this offset amount helps reduce weld seam depression and ensures a favorable cross-sectional weld seam.
Dual-beam welding of dissimilar thickness plates optimizes welding processes by adapting to the unique challenges posed by varying plate thicknesses and material properties, ultimately enhancing welding efficiency and seam quality.
3.3 Dual-Beam Welding of Dissimilar Thickness Plates
When welding plates with large gaps, one can effectively increase the diameter of the effective laser beam heating by rotating the angles of the dual beams to achieve superior gap filling capability. The width of the weld bead at the top is determined by the effective beam diameter of the two lasers, which is influenced by the beam rotation angle. A larger rotation angle results in a wider heating range of the dual beams, leading to a wider width of the weld bead at the top.
In the welding process, the two laser beams play distinct roles: one primarily penetrates the joint completely, while the other melts the thicker plate material to fill the gap. As shown in Figure 6-35, with a positive beam rotation angle (where the front beam acts on the thick plate and the rear beam acts on the weld seam), the first beam in front heats and melts the material on the thick plate, while the subsequent beam penetrates through. The first front beam partially melts the thick plate but contributes significantly to the welding process by melting the side of the thick plate for better gap filling and pre-melting the joint material, making it easier for the rear beam to completely penetrate the joint and thereby increasing the welding speed.
In contrast, in dual-beam welding with a negative rotation angle (where the front beam acts on the weld seam and the rear beam acts on the thick plate), the roles of the two beams are reversed. The front beam melts through the joint, while the rear beam melts the thick plate to fill the gap. In this scenario, the front beam must weld through the cold-state plate, resulting in a lower welding speed compared to using a positive beam rotation angle. Moreover, due to the pre-heating effect of the front beam, the rear beam will melt more of the thick plate material at the same power. Hence, it is advisable to reduce the power of the rear laser beam appropriately in such cases.
Generally, employing a positive beam rotation angle allows for a moderate increase in welding speed, while a negative beam rotation angle achieves better gap filling. Figure 6-36 illustrates the influence of different beam rotation angles on the cross-section of the weld bead.
3.4 Dual-Beam Laser Welding of Thick Plates
With the advancement in laser power levels and beam quality, laser welding of thick plates has become a practical reality. However, the high cost of high-power laser systems and the need for filler metal in welding thick plates pose significant challenges in practical production scenarios.
Dual-beam laser welding technology addresses these challenges effectively. It not only allows for increased laser power but also enhances the diameter of the effective beam heating area. This capability is crucial for improving the ability to melt and fill welding wire, stabilizing the laser keyhole, enhancing welding stability, and ultimately improving welding quality.
Dual-beam laser welding offers several advantages for welding thick plates:
Increased Laser Power: By combining two laser beams, the total available power for welding can be increased, which is particularly beneficial for thick plate welding that requires high energy input.
Enhanced Beam Heating Diameter: The dual-beam setup allows for a wider effective heating area, which is advantageous for melting and filling welding wire efficiently in thick plate welding applications.
Stabilized Laser Keyhole: The use of dual beams helps stabilize the laser keyhole during welding. This stability is crucial for maintaining consistent weld quality and preventing defects such as porosity.
Improved Welding Stability: Dual-beam welding contributes to overall welding stability by providing a more controlled heat input and better control over the welding process parameters.
Enhanced Welding Quality: Ultimately, the combination of increased power, enhanced beam heating diameter, stabilized keyhole, and improved stability results in higher welding quality, meeting the stringent requirements of welding thick plates.
In summary, dual-beam laser welding technology not only overcomes the limitations of single-beam welding in terms of power and heating capacity but also ensures better control and stability in welding thick plates. This makes it a valuable technique for various industrial applications where high-quality welds in thick materials are required.