Research Progress of Pulsed TIG Additive Manufacturing Technology

Literature Overview

This paper, published in Materials Engineering in 2018 by Guo Longlong, He Yutian, Ju Luyan, Wu Zebing, Zhang Yong, Lv Lantao, and Wang Wenjuan from Xi'an Shiyou University, provides a comprehensive review of pulsed TIG additive manufacturing technology. The research was supported by the Xi'an Shiyou University Young Teacher Research Start-up Fund (Grant No. 0104-134010025). Additive manufacturing (AM) has emerged as a transformative technology for manufacturing complex geometries with material efficiency and design flexibility, and pulsed TIG AM represents a promising approach for depositing metals layer by layer using a pulsed tungsten inert gas arc as the heat source.

Core Technical Content

Pulsed TIG additive manufacturing involves the use of a pulsed TIG arc to melt and deposit wire or powder feedstock, building up a part layer by layer. The pulsed nature of the arc provides precise control over the heat input, which is critical for achieving good weld quality and dimensional accuracy. The key advantages of pulsed TIG AM include low equipment cost, high deposition rate, and the ability to use a wide range of metals and alloys.

Process Parameters and Their Influence

The pulse current amplitude determines the maximum heat input during each pulse, which directly affects the size of the melt pool and the penetration depth. Higher pulse currents produce larger melt pools and deeper penetration, but may also lead to excessive dilution and distortion. The background current maintains the arc stability between pulses, ensuring consistent arc attachment and preventing arc extinction. The pulse frequency affects the solidification rate and the resulting grain structure; higher frequencies produce finer grains due to the rapid solidification and remelting cycles.

Microstructural Characteristics

The microstructure of pulsed TIG AM deposits is characterized by a combination of columnar and equiaxed grains, with the relative proportion depending on the process parameters and the thermal history. The columnar grains grow preferentially along the heat flow direction, typically perpendicular to the deposition direction. The equiaxed grains form in regions where the temperature gradient is lower, such as at the boundaries between layers.

The microstructure of pulsed TIG AM deposits can be significantly improved by optimizing the process parameters. For example, increasing the pulse frequency can promote equiaxed grain formation, which improves the isotropy of the deposited material. Reducing the travel speed can increase the heat input and promote grain coarsening, which may be undesirable for some applications. The choice of filler metal also plays a critical role in determining the microstructure and mechanical properties of the deposited material.

Comparison of Pulsed TIG AM with Other AM Processes

Engineering Applications and Challenges

Pulsed TIG AM has several potential engineering applications, including the repair of worn or damaged components, the fabrication of large-scale structures, and the production of complex geometries that are difficult to manufacture using conventional methods. The low equipment cost and high deposition rate make pulsed TIG AM particularly attractive for industrial applications, where cost-effectiveness is a key consideration.

However, pulsed TIG AM also faces several challenges that need to be addressed for widespread adoption. First, the dimensional accuracy of pulsed TIG AM deposits is generally lower than that of laser or electron beam AM, which limits its application to high-tolerance components. Second, the surface quality of pulsed TIG AM deposits is often poor, requiring significant post-processing to achieve the desired surface finish. Third, the mechanical properties of pulsed TIG AM deposits can be anisotropic, with the properties varying significantly depending on the direction of measurement relative to the deposition direction.

Key Questions and Reflections

A significant question arising from this review is how the limitations of pulsed TIG AM can be overcome to expand its range of applications. The dimensional accuracy and surface quality issues can potentially be addressed through improved process control and the use of hybrid approaches, such as combining pulsed TIG AM with machining or other finishing processes. The anisotropy of the deposited material can be mitigated through optimized process parameters and the use of appropriate filler metals. Another important consideration is the development of simulation tools that can predict the microstructure and mechanical properties of pulsed TIG AM deposits, enabling more efficient process development and optimization.

Study Insights and Implications

This review provides a comprehensive overview of the current state of pulsed TIG additive manufacturing technology. The insights gained from this review have direct implications for the selection of AM processes for specific engineering applications. Engineers should consider the unique advantages and limitations of pulsed TIG AM when selecting a manufacturing process for a given application. The low equipment cost and high deposition rate make pulsed TIG AM an attractive option for many industrial applications, but the dimensional accuracy and surface quality limitations must be carefully evaluated. The work also highlights the need for continued research and development to improve the capabilities of pulsed TIG AM and expand its range of applications.