1.Introduction
Laser welding for heat exchanger plates combines advanced manufacturing techniques with innovative structural designs, widely used across industries such as light industry, chemical processing, and food production. Heat exchangers come in multiple configurations like shell-and-tube, honeycomb-jacketed, tube-sheet, capsule-type, channel, and prefabricated forms. Among these, honeycomb-jacketed plates are especially prized for their efficient heat transfer, making them ideal for industries such as petroleum, chemical processing, pharmaceuticals, and food processing, as shown in Figure 1.1. Featuring an upper and lower layered plate structure, these plates have a large surface area, densely packed seams, high seam counts, and stringent strength requirements. The welding process, due to the dense and numerous seams, is time-intensive and demands stability, as shown in the partial view in Figure 1.2; issues during welding may result in scrap. For optimal results, the welding must produce seams that are smooth, oxidation-free, and well-protected. This article examines methods to enhance welding quality and process stability for these large-scale heat exchanger plates.
Figure 1.1 Heat Exchanger Vessel
Figure 1.2 Weld Seam Trajectory (Partial View)
2.Laser Welding Equipmentfor Large-SizeHeat Exchanger Plates
Han’s Laser 6000W continuous fiber laser excels in high-efficiency processing across a range of applications, including cutting, pipe cutting, welding, surface treatment, 3D printing, and cleaning. Its high photoelectric conversion efficiency, broad modulation frequency range, strong anti-reflectivity, stability, and minimal maintenance make it an optimal choice for industrial manufacturing. In large-scale heat exchanger plate manufacturing, this fiber laser has been widely adopted for high-quality, high-efficiency processing, particularly when paired with automated machinery.
Figure 2.1 6000W Laser
3.Key Challenges in Large-Scale Heat Exchanger Plate Laser Welding
Laser welding offers high speed, deep penetration, and minimal distortion, but the high energy density of deep penetration welding often leads to issues. The intense laser beam melts and vaporizes the metal, creating metal vapor above the molten pool that can interfere with the laser beam (see Figure 3.1). If not controlled, this vapor may settle on the workpiece, causing visible contamination and welding defects such as spatter and undercutting (see Figure 3.2). Given the large dimensions (up to 10m in length and 2m in width) and extensive seam count (often exceeding 10,000 seams), it’s essential to achieve high-quality welds for each seam to maintain the overall weld integrity. Additionally, maintaining oxidation-free seams is crucial to high-quality welding, which requires protection at both the molten pool and cooling seam.
Figure 3.1 Fiber Laser Welding Metal Vapor
Figure 3.2 Welding Contamination, Spatter, and Oxidation
To achieve a high-quality weld, controlling both metal vapor diffusion and seam protection is paramount. This involves ensuring consistent coverage of shielding gas both during and after welding, often referred to as seam “delayed protection.”
4.Design of the Coaxial Airflow Device
Gas protection plays a crucial role in welding quality, as effective shielding can reduce defects and enhance stability. This article explores a dedicated airflow device designed specifically for heat exchanger welding, optimized through professional software for three key outcomes: improved vapor diffusion control to minimize surface contamination, comprehensive seam protection for high-quality welding, and durability.
A.Device Structure
The coaxial airflow device, as shown in Figure 4.1, consists of a gas chamber ring, jet plate, guide block, gas curtain cover, intake nozzle, and mounting bracket.
Figure 4.1 Structure of the Coaxial Airflow Device
B.Application Principle
The coaxial airflow device is mounted above the workpiece, aligned with the laser beam. For optimal results, a height of 4mm is recommended between the device and the workpiece surface. Greater height weakens protection, while lower height risks collision. Compressed air enters through the gas curtain nozzle, forming a transverse blowing airflow. Simultaneously, the protective gas nozzle dispenses welding shield gas through the jet plate to create multi-directional gas flows, including smoke-control flow, downward exhaust flow, inner exhaust flow, and expansion flow. Together, these flows control metal vapor diffusion and provide seam protection.
C.Airflow Analysis
To visualize the internal airflow within the coaxial device, a professional software simulation was conducted. The focus was on gas flow direction and shielding gas concentration, using nitrogen at 0.4 MPa, with a device-to-workpiece height of 4mm and a nozzle diameter of 2.5mm. The model is illustrated in Figure 4.2, with results shown in Figures 4.3 and 4.4.
Figure 4.2 Airflow Analysis Model of the Coaxial Airflow Device
In Figure 4.3, protective gas flow lines converge at the molten pool and diffuse upward through the laser channel, guiding metal vapor away from the workpiece surface to prevent contamination.
Figure 4.3 Flow Trajectory of Protective Gas Velocity
Figure 4.4 shows a concentration map, indicating an effective shielding gas zone without atmospheric intrusion, creating an expanded high-concentration protection area for optimal seam protection.
Figure 4.4 Component Distribution Diagram of Protective Gas Flow
5.Welding Application Test
The coaxial airflow device was installed on the laser welding equipment, with optimized parameters, to test welding on a large-format stainless steel heat exchanger plate (9m x 2m, with both upper and lower plates at 1.2mm thickness). The welding test (see Figure 5.1) demonstrated excellent results: no visible smoke stains, and clean, oxidation-free seams with bright surfaces (see Figure 5.2). The device’s nozzle was fabricated from durable copper, and, following a complete plate weld, showed no signs of wear or clogging.
Figure 5.1 Overall Welding Effect
Figure 5.2 Comparison of Weld Seams Before and After Process Optimization
After welding, the plate underwent a pressurized bulging test, achieving the required bulge height without seam separation, meeting all processing standards (see Figure 5.3).
Figure 5.3 Bulging Effect After Pressurization
6.Conclusion
By utilizing Han’s Laser 6000W continuous fiber laser in combination with the optimized coaxial airflow device, a high-quality, clean welding process was achieved for large-scale heat exchanger plates. The resulting welds were clean, oxidation-free, and high-strength, meeting client specifications for advanced manufacturing applications.