Pulse TIG Welding Arc Temperature Field Calculation Based on Standard Temperature Method

Literature Overview

This paper by Xiao Xiao, Hua Xueming, Wu Yixiong, and Li Fang from the Welding Engineering Research Institute of Shanghai Jiao Tong University and the Shanghai Key Laboratory of Laser Manufacturing and Material Modification, published in Spectroscopy and Spectral Analysis (2012, Vol. 32, No. 9, pp. 2327-2330), presents a spectroscopic approach to measuring the arc temperature field in pulse TIG welding. The study combines high-speed photography, spectral analysis, Abel transformation, and the standard temperature method to determine the spatial distribution of arc temperature at peak and base current moments of the pulse waveform.

Pulse TIG Welding Background

Pulse TIG welding modulates the welding current between a peak value and a base value at a defined frequency, offering several advantages over continuous TIG welding. The peak current provides sufficient energy for deep penetration, while the base current allows the weld pool to partially solidify between pulses, reducing overall heat input and minimizing distortion. This technique is widely used for thin-section welding, dissimilar metal joining, and applications where precise control of the weld pool is required.

Pulse TIG Welding Parameters

Standard Temperature Method

The standard temperature method is a spectroscopic technique for determining the temperature of a plasma by comparing the measured spectral line intensities of a species with known temperature-dependent emission characteristics. The method requires knowledge of the emission coefficient as a function of temperature for a selected spectral line, along with the measured intensity of that line from the plasma.

The study focuses on the argon atomic spectral line at 794.8 nm, which is a strong emission line in argon plasma and is well-suited for temperature measurement. The authors calculated the relationship between argon particle number density and temperature, as well as the relationship between the emission coefficient of the 794.8 nm line and temperature. These theoretical relationships provide the basis for converting measured spectral intensities into temperature values.

Spectroscopic Parameters

Measurement Methodology

The measurement approach involves several key steps. First, high-speed photography captures the arc image at the 794.8 nm wavelength, synchronized with the pulse waveform to record images at specific moments in the pulse cycle. The arc image provides the spatial distribution of spectral line intensity. Second, the Abel transformation is applied to convert the two-dimensional projected intensity distribution into the three-dimensional radial intensity distribution, assuming cylindrical symmetry of the arc. Third, the standard temperature method is applied to convert the radial intensity distribution into a radial temperature distribution.

The use of high-speed photography is essential because the pulse TIG arc changes rapidly during the pulse cycle. Capturing images at peak and base current moments provides insight into how the arc temperature distribution evolves with the pulse waveform, which is critical for understanding the weld pool dynamics and heat input characteristics of pulse TIG welding.

Results and Analysis

The study reports the arc temperature field distributions at peak and base current moments. At peak current, the arc exhibits higher temperatures and a more concentrated temperature profile, consistent with the increased current density and energy input. At base current, the arc temperature is lower and the temperature profile is more diffuse, reflecting the reduced energy input and expanded arc column.

The temperature field data obtained through this method provides quantitative information about the arc heat source that can be used to improve welding simulation models. The spatial and temporal resolution of the temperature measurements allows for the development of more accurate heat source models that capture the dynamic behavior of the pulse TIG arc.

Arc Temperature Field Characteristics

Engineering Practice Implications

For engineers working with pulse TIG welding, the arc temperature field data presented in this study has several practical applications. First, it provides a basis for understanding how the pulse waveform affects the arc heat source, which is directly related to weld pool dynamics, penetration depth, and weld geometry. Second, the temperature field data can be used to validate and improve computational welding models, which are increasingly important for process optimization and quality prediction.

The spectroscopic measurement approach demonstrated in this study is non-intrusive and does not disturb the welding process, making it suitable for measuring arc characteristics in production environments. The technique can be adapted to measure other spectral lines and to characterize different welding processes, providing a versatile tool for welding diagnostics.

Key Reflections

This study demonstrates the power of spectroscopic methods for characterizing welding arcs with high spatial and temporal resolution. The combination of high-speed imaging, Abel transformation, and the standard temperature method provides a comprehensive approach to arc temperature measurement that captures the dynamic behavior of the pulse TIG arc.

The choice of the 794.8 nm argon line is practical, as argon is the most commonly used shielding gas in TIG welding and this spectral line is strong and well-characterized. The standard temperature method, while requiring careful calibration and knowledge of plasma physics, provides a direct measurement of arc temperature that is independent of the assumptions inherent in computational models.

For process development and quality assurance, the ability to measure arc temperature fields in real time or near-real time opens possibilities for adaptive welding control systems that adjust process parameters based on measured arc characteristics. This represents a shift from open-loop to closed-loop welding control, which could significantly improve weld quality consistency and reduce scrap rates.

In conclusion, this research contributes a valuable measurement methodology for pulse TIG welding arc characterization, providing the quantitative data needed to improve process understanding, simulation accuracy, and ultimately weld quality. The spectroscopic approach is non-intrusive, versatile, and capable of capturing the dynamic nature of pulsed welding arcs, making it a powerful tool for welding research and development.