Development and Application of Copper Strip Butt TIG Welding Special Machine

Literature Overview

The paper by Luo Ping, Jiang Sichuan, Tao Wen, Jin Kaiping, and Liu Shaolin, published in "Electric Welder" (Vol. 44, No. 9, 2014, pp. 49-52), documents the development and industrial application of a specialized TIG welding machine for butt welding of copper strips. Developed by Chengdu Welding Research Weida Technology Co., Ltd., this equipment incorporates PLC-based control, automatic head/tail trimming, and automatic centering functions to achieve high-quality longitudinal seam welding of copper strip materials. The successful application to iron bronze strip welding demonstrates the versatility of the approach and its potential for other non-ferrous metal strip welding applications.

Technical Background and Application Context

Copper strip welding is a critical process in the production of copper tubes, electrical busbars, and various copper-based structural components. The traditional approach to joining copper strips involves overlapping and brazing, which results in material waste and reduced cross-sectional integrity. Butt welding, by contrast, produces a full-penetration joint with no material loss, but requires precise alignment, consistent heat input, and effective shielding to achieve acceptable weld quality.

The specific challenge addressed by this development is the welding of copper strips produced by rolling mills, where the strip is fed continuously and must be joined at the transition between rolls. The lead-in and lead-out sections (head and tail) of each roll are typically of inferior quality and must be trimmed before welding. Additionally, small coil materials need to be adapted to high-throughput precision rolling equipment, necessitating reliable and repeatable butt welding between coil segments.

Equipment Architecture and Control System

The specialized welding machine integrates several subsystems into a unified platform. The PLC (Programmable Logic Controller) serves as the central control unit, orchestrating the sequence of operations from material loading through welding to post-weld inspection. The automatic centering mechanism ensures that the two strip ends are aligned with minimal offset, which is critical for achieving uniform weld geometry and avoiding misalignment defects.

The arc voltage control function is a key feature that distinguishes this equipment from generic TIG welding machines. By monitoring the arc voltage in real time and adjusting the welding parameters accordingly, the system compensates for variations in strip thickness, alignment, and gas flow that would otherwise cause weld quality fluctuations. This closed-loop control approach is analogous to the adaptive control strategies used in modern robotic welding systems.

Welding Process Optimization for Iron Bronze

Iron bronze, a copper-tin alloy containing iron, presents unique welding challenges due to its physical properties. The thermal conductivity of iron bronze is lower than pure copper but higher than many other copper alloys, requiring careful heat input management to achieve full penetration without excessive dilution or distortion. The melting range of iron bronze is relatively narrow, which promotes hot cracking if the solidification rate is too fast or if the weld metal composition is not properly controlled.

The authors achieved single-sided welding with double-sided formation, a desirable outcome that indicates symmetric heat distribution and adequate shielding on both sides of the joint. This result is particularly significant for production welding, where access to both sides of the joint may be limited. The small welding deformation achieved suggests that the heat input was well-controlled, likely through a combination of moderate welding current, appropriate travel speed, and possibly preheating to reduce thermal gradients.

The welding process parameters for iron bronze strip typically involve currents in the range of 150-300 A depending on strip thickness, travel speeds of 200-600 mm/min, and argon shielding gas flows of 10-15 L/min. The tungsten electrode is typically a 2% thorium-oxide or 2% lanthanum-oxide alloy for its excellent electron emission characteristics and resistance to erosion at high currents.

Engineering Design Considerations

The development of this specialized equipment reflects several important engineering principles. The use of PLC control provides flexibility for adapting the welding sequence to different material specifications and production requirements. The automatic centering function addresses the practical challenge of manual alignment variability, which is a common source of weld defects in manual or semi-automatic welding operations.

The head and tail trimming function is a practical solution to the quality variability inherent in rolled strip products. By removing the sections most likely to contain surface defects, inclusions, or dimensional inconsistencies, the system ensures that only material of acceptable quality enters the welding process. This is a form of source-based quality control, consistent with the FMEA (Failure Mode and Effects Analysis) philosophy of preventing defects rather than detecting them after they occur.

The adaptability of the welding control program to other non-ferrous metal strips is a significant advantage. By modifying the parameter set, the same equipment can potentially be used for aluminum strip, brass strip, or other copper alloy strips, provided that the thermal properties and metallurgical behavior are characterized and the appropriate filler metal and shielding gas are selected.

Practical Application and Quality Assessment

The successful application to iron bronze strip welding demonstrates the equipment's capability in a real production environment. The quality assessment criteria for this application would include weld penetration (verified by cross-sectional examination), absence of hot cracks (verified by visual inspection and possibly dye penetrant testing), weld geometry (verified by dimensional measurement), and mechanical properties (verified by tensile testing).

For production environments, the key performance indicators would include welding cycle time, weld pass rate, and equipment availability. The PLC-controlled sequence should minimize non-welding time, and the automatic functions should reduce operator intervention and variability. The arc voltage monitoring provides a real-time quality indicator; deviations from the expected voltage profile can signal misalignment, gas contamination, or electrode wear, prompting corrective action before a defective weld is produced.

Key Reflections and Engineering Implications

This paper represents a successful example of specialized equipment development for a specific industrial application. The approach of integrating multiple functions into a single platform, controlled by a programmable logic controller, is a practical and cost-effective solution for production environments where welding quality consistency is paramount.

The principle of single-sided welding with double-sided formation is particularly noteworthy from a metallurgical perspective. Achieving this result requires careful control of the heat input distribution and the shielding gas flow to prevent oxidation on the back side of the weld. For copper alloys, which are highly susceptible to oxidation at elevated temperatures, the back-side shielding is critical to preventing copper oxide inclusion formation that would compromise mechanical properties and corrosion resistance.

For engineers considering similar applications, the key design considerations include the selection of appropriate tungsten electrode composition for the specific alloy being welded, the optimization of gas flow rates to provide adequate shielding without causing turbulence, and the implementation of real-time monitoring parameters that can serve as process capability indicators. The PLC programming should incorporate interlocks and safety features that prevent operation when critical parameters are outside acceptable limits, in line with the principles of functional safety.