Robotic Welding of Metal Expansion Joints: Applications and Benefits

Abstract: Intelligent and digitalized manufacturing has become a mainstream approach for modern enterprises. The metal bellows expansion joint industry is also actively adopting these advanced manufacturing methods to improve production efficiency and product quality. However, the adoption of intelligent welding for circumferential seams in metal bellows has been relatively slow. This article uses the robotic welding of circumferential seams on metal expansion joints at a manufacturing enterprise as an example to briefly discuss the application of robotic welding in the industry.

As an elastic compensation element capable of accommodating axial, lateral, and angular movements, corrugated expansion joints offer reliable operation, excellent performance, and a compact structure. They are widely used in the chemical, metallurgical, power generation, and nuclear industries. With advances in science and technology, intelligent and information-driven manufacturing methods have been increasingly adopted in the corrugated expansion joint industry, improving production efficiency and enhancing product quality and reliability. However, the adoption of intelligent manufacturing technologies for circumferential seam welding of corrugated expansion joints has progressed relatively slowly. Currently, manual welding remains the primary method, although some enterprises have implemented mechanized welding using dedicated welding equipment. This article briefly discusses the application of robotic welding in the circumferential seam welding process through a case study of a manufacturing enterprise.

Common types of circumferential seam joints for corrugated pipes include:

a) Lap Joint b) Lock-Bottom Butt Joint

Figure 1. Types of Welded Joints

External welded joints are generally used in chemical, heating, and transportation applications, as well as in metal expansion joints with small pipe diameters where internal welding is not feasible. Due to its relatively low assembly precision, this type of joint is typically welded manually using conventional methods.

a) Lock-bottom Butt Joint b) Corner Joint-like Joint

Figure 2: Internal Welding Joint Types

Internal welded joints are generally used in the power industry. This type of joint requires a high-quality weld surface to prevent point discharge from high points on the inner surface of the pipe. Due to the stringent surface quality requirements, this type of joint requires high assembly precision and can be welded manually, mechanically, or robotically.

a) Internal End-Welded Joints b) External End-Welded Joints

Figure 3: Types of End-Welded Joints

End-welded joints are generally used for circumferential welding of precision metal bellows, primarily in aerospace, nuclear, and other high-end applications. Due to the specific application requirements and stringent requirements for weld quality and assembly precision, mechanized or robotic welding is generally employed. 

The bellows used in metal bellows expansion joints are generally thin-walled and multilayered, which limits the range of suitable welding methods. Manual welding is typically performed using tungsten inert gas (TIG) welding, while laser welding is used in a limited number of applications. Mechanized welding methods include TIG, microplasma, laser, and vacuum electron beam welding, while robotic welding generally employs TIG welding. These welding methods share a common characteristic: concentrated heat input, which enables better control of weld morphology and ultimately results in high-quality welds.

Robotic welding provides consistent and reliable weld quality and is widely used in industries such as automotive manufacturing, shipbuilding, and railway vehicle manufacturing. Gas metal arc welding (GMAW) is typically used for structural components. However, for metal bellows expansion joints, GMAW is generally unsuitable because the bellows are thin-walled and multilayered, making them prone to weld spatter. Therefore, tungsten inert gas (TIG) welding or microplasma arc welding, which produces virtually no weld spatter, is typically used.

The conventional approach to automated welding of bellows circumferential seams is to rotate the bellows while keeping the welding torch stationary. When the bellows specifications change, new rotating fixtures must be fabricated accordingly. If multiple bellows specifications are involved or the flange geometry varies, a considerable number of rotating fixtures may be required. Furthermore, a fixed welding torch cannot fully exploit the robot arm's flexibility and range of motion. Therefore, to facilitate robotic welding, the conventional welding positions for bellows circumferential seams must be optimized. This article focuses on internal welded joints. As shown in Figure 4, the horizontal rotation position of the lock-bottom butt joint is changed to a fixed horizontal position, while the corner joint is changed to a vertically fixed position with a horizontal weld seam.

a) Horizontal Position b) Vertical Fixed Horizontal Position

Figure 4. Types of End-Welded Joints

The arc force of argon arc welding is relatively weak. During horizontal-position welding, the molten pool is prone to sagging or collapsing, which adversely affects the surface quality of the weld. Therefore, the welding torch should be tilted upward at an appropriate angle, preferably approximately 15°. Since vertical fixed-position welding involves a fillet joint, the torch angle for robotic operations should be consistent with that of manual welding.

The bellows is a flexible component with inherent axial length deviations arising from manufacturing. Once welded to the flanges, these deviations propagate to the overall length of the expansion joint. Although these deviations fall within acceptable manufacturing tolerances, they adversely affect robotic welding processes. Therefore, the fixed datum during welding should be established on a component whose weld deviation is relatively small. Consequently, the outer diameter of the flange to be welded is adopted as the positioning datum for both horizontal and vertical fixed-position welding. This requirement is readily met by the precision afforded by contemporary machining processes.

In order to improve both weld quality and productivity, the welding workstation can be supplemented with a laser-based positioning and seam tracking system, together with an arc voltage tracking system. The laser-based positioning and tracking system serves to rectify any misalignment between the welding torch and the weld seam centerline, whereas the arc voltage tracking system functions to maintain a stable arc length. Before welding, the entire welding process is programmed using the robot teach pendant, with laser positioning integrated into the program. During welding, the corresponding program can be called up as needed. It is important to note that both the arc stabilization period and the shielding gas post-flow time after arc extinction must be considered during program development.

Laser Positioning → Arc Initiation → Arc Voltage Tracking Activated → Welding → Arc Extinction → Arc Voltage Tracking Deactivated → Welding Torch Reset

Robotic welding improves the quality, consistency, and efficiency of metal expansion joint manufacturing. Its flexible motion capability reduces dependence on dedicated rotating fixtures, making production more adaptable to different bellows specifications and flange configurations. Programmable welding processes also support standardized production and facilitate the transition toward intelligent and digital manufacturing. In addition, the higher machining and assembly accuracy required for robotic welding can promote improvements in the overall quality and reliability of metal expansion joints, while enhancing manufacturers’ production efficiency and competitiveness.

In summary, the application of robotic welding to circumferential seams of metal expansion joints represents a significant step forward in the industry's transition toward intelligent and digitalized manufacturing.

Currently, the machining precision of metal expansion joint components is steadily improving, which provides a solid foundation for the adoption of robotic welding. However, to consistently meet the assembly quality requirements of robotic circumferential welding, tighter tolerances for component machining will be necessary. This increased precision not only ensures reliable joint fit-up and repeatable weld quality, but also serves as a catalyst for raising the overall product quality and reliability of metal expansion joints.

Furthermore, the flexibility of robotic systems — combined with auxiliary technologies such as laser positioning and seam tracking, as well as arc voltage tracking — enables stable, spatter-free welding of thin-walled, multilayer bellows with minimal manual intervention. The programmability of robotic workcells allows for rapid changeover between different product specifications, significantly reducing the reliance on dedicated tooling and enhancing production agility.

Beyond the immediate improvements in welding quality and productivity, the introduction of robotic welding technology opens the door to broader digital transformation within the corrugated pipe industry. By enabling data collection, process monitoring, and seamless integration with higher-level manufacturing execution systems, robotic welding lays the groundwork for smart factory operations. This technological shift will not only improve operational efficiency but also greatly strengthen the competitive position of forward-thinking enterprises in the industry.

In conclusion, while challenges remain — particularly in terms of component precision and initial capital investment — the long-term benefits of robotic welding in terms of quality, consistency, flexibility, and digital readiness far outweigh the costs. As manufacturing tolerances continue to tighten and automation technologies become more accessible, robotic welding is poised to become the standard rather than the exception in corrugated expansion joint production.