Research Progress of Pulsed TIG Additive Manufacturing Technology

Literature Overview

This review paper by Guo Longlong and colleagues from Xi'an Shiyou University, published in Journal of Materials Engineering (Vol. 46, No. 12, pp. 10–17, 2018), provides a comprehensive overview of pulsed TIG (PTIG) additive manufacturing technology. Funded by Xi'an Shiyou University's Young Teacher Research Startup Fund (0104-134010025), the paper synthesizes experimental and numerical simulation research on form quality control, microstructure evolution, and mechanical property management in PTIG AM.

Technology Fundamentals and Advantages

PTIG additive manufacturing belongs to the broader category of arc additive manufacturing (ArcAM) technologies. Its distinguishing advantages include:

Low equipment cost compared to laser or electron beam AM systems
High deposition rates suitable for large structural components
High material utilization with minimal powder or wire waste
Compatibility with a wide range of metallic materials

The pulsed nature of the TIG arc provides unique advantages for additive manufacturing:

Parameter	Effect	Benefit
Pulse frequency	Controls heat input per layer	Reduces interlayer cooling time
Peak current	Determines maximum penetration	Controls layer bonding
Background current	Maintains arc stability	Prevents arc extinction
Pulse duration	Controls energy distribution	Manages thermal gradient

Form Quality Control

The review identifies several critical quality factors in PTIG AM builds:

Layer-to-layer bonding quality: Insufficient overlap or excessive overlap leads to lack of fusion or dilution defects. The pulsed waveform must be optimized to ensure adequate melting of the previous layer while avoiding excessive remelting.
Dimensional accuracy: Thermal distortion accumulates over multiple layers, requiring compensation strategies. The lower heat input of pulsed operation compared to continuous TIG helps mitigate distortion.
Surface roughness: Wire feed consistency, torch positioning accuracy, and arc stability all contribute to surface quality. Typical surface roughness values range from Ra 5–20 μm depending on process parameters.
Porosity formation: Gas entrapment during rapid solidification is a persistent challenge. The pulsed waveform can be optimized to allow gas escape during low-current phases.

Microstructure and Property Control

The review highlights that PTIG AM microstructures are characterized by:

Columnar grains growing preferentially in the build direction due to directional heat extraction
Fine grain refinement at interlayer boundaries due to repeated thermal cycling
Potential for texture development depending on base material and process parameters
Heterogeneous microstructure between weld center and interlayer regions

For steel components, the microstructure typically consists of martensite or bainite in the weld region with varying grain sizes depending on cooling rates. The mechanical properties are generally isotropic in the transverse direction but may show anisotropy in the build direction.

Identified Research Gaps and Future Directions

The authors identify five key research directions that remain to be addressed:

Mechanism study of process factors on form quality—understanding the fundamental physics of how pulse parameters affect deposition geometry
Defect formation mechanisms and suppression measures—particularly for porosity and lack of fusion
Numerical simulation of melt pool microstructure evolution—coupling thermal-microstructure models for predictive capability
Residual stress and distortion control mechanisms—developing strategies for in-situ stress management
Microstructure-mechanical property relationship models—enabling property prediction from process parameters

Engineering Relevance to Pipe and Fitting Fabrication

For the pipe and fitting industry, PTIG AM technology holds significant potential for:

Manufacturing complex pipe fittings (multi-bend elbows, complex tees) without forming or machining
Producing repair welds and overlay cladding for corrosion-resistant applications
Fabricating custom transition pieces and reducers with variable wall thickness
Creating prototype pipe components for rapid product development

The relatively low equipment cost of PTIG AM compared to other arc AM technologies makes it particularly attractive for mid-volume production of specialized fittings where traditional manufacturing methods are economically impractical.