Pulsed TIG Additive Manufacturing Research Progress - Literature Study Note

Literature Overview

This 2018 review article from Xi'an Shiyou University provides a comprehensive overview of pulsed TIG (PTIG) additive manufacturing (AM) technology. The study, supported by the university's young researcher startup fund (Grant No. 0104-134010025), examines the current state of pulsed TIG-based layer-by-layer metal deposition, including process principles, equipment configurations, material systems, and application potential. Additive manufacturing using TIG welding represents a promising approach for large-scale component fabrication where the speed and cost-effectiveness of arc processes are advantageous over powder-bed fusion or directed energy deposition with lasers.

Core Technical Principles

Pulsed TIG AM operates by depositing filler wire into a pulsed arc, building up material layer by layer in a controlled manner. The pulse modulation serves multiple critical functions:

Penetration control: The peak current determines the maximum penetration depth, while the background current maintains arc stability and promotes surface wetting.
Heat input management: The duty cycle (ratio of peak time to total pulse period) controls the average heat input, which is crucial for preventing thermal distortion and residual stress accumulation.
Droplet transfer regulation: Pulsed current enables short-circuit-free transfer of filler metal, producing a stable and repeatable deposition process.
Microstructure control: The periodic thermal cycling influences grain growth, precipitate formation, and phase transformation in deposited materials.

Process Parameters and Their Effects

Parameter	Typical Value	Primary Effect
Peak current	150-400 A	Penetration depth, dilution ratio
Background current	30-100 A	Arc stability, surface spreading
Pulse frequency	5-50 Hz	Heat input rate, solidification rate
Duty cycle	10-40%	Average thermal input
Wire feed speed	200-600 mm/min	Deposition rate
Travel speed	100-500 mm/min	Layer width, overlap
Shielding gas	Ar or Ar/CO2 mix	Arc stability, oxide formation
Layer thickness	1.0-3.0 mm	Build quality, dimensional accuracy

Material Systems and Applications

PTIG AM has been successfully demonstrated with the following material systems:

Carbon and low-alloy steels: Q235, Q345, 16Mn - suitable for structural components, molds, and tooling
Stainless steels: 304, 316L - for corrosion-resistant components and repair applications
Nickel-based alloys: Inconel 625, Incoloy 825 - for high-temperature and chemical processing equipment
Aluminum alloys: 6061, 7075 - for lightweight structural applications
Copper alloys: Cu-Ni 90/10, brass - for marine and electrical applications

The process is particularly attractive for bimetal component fabrication where a corrosion-resistant overlay layer needs to be deposited on a structural substrate. For example, Inconel 625 can be deposited as a wear and corrosion-resistant overlay on carbon steel substrates using PTIG AM, achieving bond strengths exceeding 200 MPa.

Quality Control and Defect Prevention

Common defects in PTIG AM include:

Porosity: Caused by inadequate shielding, high hydrogen absorption, or insufficient overlap. Countermeasures include increasing gas flow rate, preheating the substrate, and optimizing overlap ratio (>30%).
Cracking: Hot cracks in austenitic stainless steels and nickel alloys due to solidification cracking susceptibility. Using appropriate filler composition (e.g., adding Nb to Inconel 625) and controlling cooling rates are effective.
Delamination: Poor bond between layers due to insufficient heat input or contamination. Ensuring adequate overlap and surface cleanliness before each layer is critical.
Warping and distortion: Accumulated residual stress from repeated thermal cycling. Mitigation strategies include using lower heat input parameters, implementing intermediate stress relief treatments, and employing拘束 (constraint) fixtures.

Engineering Practice Considerations

For pressure vessel and piping applications, PTIG AM deposits must comply with applicable codes. ASME Section IX provides qualification procedures for additive manufacturing processes, and recent amendments have included specific requirements for arc-based AM. The key acceptance criteria include:

Minimum bond strength of 90% of base metal tensile strength
No porosity exceeding 10% area coverage (per ASTM E1012)
No cracks or lack of fusion (per visual and UT inspection)
Mechanical properties meeting base material specifications

The process offers significant advantages for repair and retrofit applications, where selective deposition of material on existing components can restore functionality without complete replacement. For hydrogenation reactor shells, PTIG AM can be used to build up nickel-based alloy cladding layers with controlled thickness and composition, providing an alternative to explosive cladding or roll-bonding for smaller components.

Study Insights and Future Directions

The PTIG AM technology represents a bridge between traditional welding and advanced manufacturing, offering the potential for on-demand, geometry-flexible metal deposition. The key challenges remain dimensional accuracy (currently ±0.5-1.0 mm), surface roughness (Ra 25-50 μm), and limited build speed compared to laser-based AM. Future development should focus on integrating real-time monitoring systems (optical pyrometry, acoustic emission) for process control, developing multi-wire configurations for increased deposition rates, and establishing comprehensive code qualification databases for structural applications. The technology holds particular promise for the energy sector, where large-scale repair and overlay applications can significantly reduce maintenance costs and extend equipment service life.