Multiphase Flow Numerical Simulation and Experimental Optimization of Oxygen-Enriched Molten Pool Multi-Torch Weld Overlay Process
1. Definition and Technical Principles
The research titled "Numerical Simulation and Experimental Study on Multiphase Flow Coupling of Oxygen-Enriched Molten Pool Smelting with Top-Gun Swirl Vortex and Variable-Angle Side-Gun Configuration" represents an advanced computational and experimental investigation into the fluid dynamics of multi-torch weld overlay processes. This technology addresses the complex interactions between arc plasma, molten metal, shielding gas, and flux materials in a multi-gun welding system designed for high-performance cladding applications.
The fundamental principle involves coupling a top-mounted plasma or arc torch equipped with a swirl vortex generator (creating rotational flow in the shielding gas and molten pool) with variable-angle side guns that introduce additional heat input and filler material at optimized positions. The "oxygen-enriched molten pool" refers to controlled oxidation conditions within the weld pool, which influence microstructure formation, dilution control, and metallurgical bonding characteristics critical for clad product quality.
The multiphase flow framework accounts for:
- Gas phase: Shielding gas (Ar, CO₂, or mixtures) dynamics with rotational components induced by the top-gun vortex device
- Liquid phase: Molten metal pool behavior including convection patterns, buoyancy effects, and electromagnetic stirring
- Solid phase: Solidification front advancement, dendritic growth, and phase transformation zones
- Plasma phase: Arc plasma jet momentum transfer and thermal radiation coupling
2. Category and Business Positioning
This research falls squarely within the company's TIG/MIG Weld Overlay Technology Route, representing a frontier advancement in multi-torch cladding process optimization. In the broader capability matrix of Cladding Technology Shanxi Co., Ltd., this work bridges fundamental metallurgical research with production-grade process engineering, directly supporting:
- Development of proprietary WPS (Welding Procedure Specifications) for multi-torch overlay applications
- Process qualification for high-dilution-sensitive cladding systems (e.g., Ni-based alloys on carbon steel, stainless steel transition layers)
- Technical differentiation in competitive bidding for complex cladding projects requiring custom multi-pass overlay strategies
Compared to conventional single-torch TIG or MIG overlay, the multi-gun coupled configuration enables:
- Higher deposition rates through simultaneous multi-pass deposition
- Superior dilution control via geometric separation of heat sources
- Enhanced metallurgical bonding through controlled thermal cycling and pool geometry optimization
3. Technical Purpose and Value
The primary technical objectives of this research are threefold:
3.1 Molten Pool Geometry Optimization
Through multiphase flow numerical simulation (typically employing ANSYS Fluent, STAR-CCM+, or OpenFOAM with VOF/Level-Set methods), the research establishes predictive models for weld pool shape, penetration depth, and dilution ratio as functions of:
- Top-gun current and voltage parameters
- Swirl vortex intensity and frequency
- Side-gun angular positions (typically 30°–75° from vertical)
- Side-gun current and travel speed
- Oxygen partial pressure in the molten pool environment
3.2 Dilution Control and Metallurgical Integrity
For cladding applications governed by standards such as ASTM A240 (stainless steel clad plate), ASTM A516 (carbon steel base), ASME Section IX (welding qualifications), and GB/T 25724 (Chinese national standard for clad steel plates), dilution must be tightly controlled. The simulation provides quantitative prediction of base metal dilution into each clad pass, enabling:
- Optimization of layer-by-layer dilution reduction
- Minimization of the critical dilution threshold for alloy composition targets
- Prediction of crack susceptibility zones within the clad layer
3.3 Process Window Definition
The experimental validation component establishes robust process windows for production use, translating simulation predictions into actionable parameter ranges that ensure consistent product quality across different substrate geometries and thicknesses.
4. Key Process and Implementation Points
4.1 Multi-Torch Configuration Parameters
| Parameter | Top Gun (Primary) | Side Gun (Secondary) | Optimization Target |
|---|---|---|---|
| Current (A) | 120–250 | 80–180 | Pool geometry stability |
| Travel Speed (mm/min) | 150–400 | 150–400 (synchronized) | Deposition rate / dilution balance |
| Side Gun Angle (°) | 0° (vertical) | 30°–75° (variable) | Heat input distribution |
| Swirl Frequency (Hz) | 0.5–5.0 | — | Pool stirring / gas coverage |
| Shielding Gas Flow (L/min) | 15–30 | 10–20 | Porosity prevention |
| Interpass Temperature (°C) | — | — | ≤150°C (typical) |
4.2 Simulation Methodology
The multiphase flow numerical simulation employs the following computational framework:
- Governing Equations: Navier-Stokes equations with Boussinesq approximation for natural convection, coupled with energy equation, species transport equation (for oxygen concentration tracking), and electromagnetic force source term (Lorentz force from arc current)
- Boundary Conditions: Arc heat flux modeled as Gaussian or double-Gaussian distribution; surface tension via Brinkman-type formulation; evaporation heat loss via Kelvin equation; oxygen diffusion from ambient
- Multiphase Model: Volume of Fluid (VOF) method for gas-liquid interface tracking, with dynamic surface tension correction for pool shape evolution
- Validation Metrics: Weld pool width/depth measurement (macrographic cross-section), dilution analysis (spectroscopy), porosity rate (ultrasonic testing per GB/T 11345 or ASTM E164)
4.3 Experimental Protocol
- Test Substrates: Q235B carbon steel, 0Cr18Ni9 (304L equivalent), 0Cr17Ni12Mo2 (316L equivalent), 15CrMo
- Filler Materials: ER309L, ER316L, ERNiCrMo-3 (625 equivalent), ERNi-27 (Stellite equivalent)
- Measurement Techniques: XRD phase analysis, SEM/EDS microstructure characterization, hardness profiling (Vickers HV0.2), dilution measurement via optical emission spectroscopy or ICP-OES
- NDT Verification: UT per GB/T 11345 / ASTM E164, PT per GB/T 18891 / ASTM E709, radiographic testing per GB/T 3323 / ASTM E94
5. Applicable Standards and Acceptance Criteria
The research outcomes feed directly into the following standards framework governing the company's cladding products:
| Standard | Scope | Relevance to Research |
|---|---|---|
| GB/T 25724-2010 | Clad steel plates — General technical conditions | Product specification compliance |
| GB/T 25725-2010 | Clad steel plates — Classification and marking | Nomenclature for multi-layer clad products |
| ASME Section IX | Welding, Brazing, and Fusing Qualifications | WPS/PQR qualification basis |
| ASTM A240/A240M | Stainless steel plate for pressure vessels | Clad layer material specification |
| NACE MR0175/ISO 15156 | Sour service materials | Clad composition requirements for H₂S environments |
| API 650/620 | Welded tanks for storage / pressure vessels | Application end-use qualification |
| NB/T 47015 | Pressure vessel welding procedure qualification | Chinese regulatory WPS qualification |
| GB/T 19542 | Submerged arc welding fluxes | Flux selection for oxygen-controlled processes |
Acceptance Criteria Specific to Multi-Torch Overlay:
- Dilution: ≤10% for single-pass Ni-based clad; ≤5% for multi-pass stabilized clad (per project specification)
- Metallurgical Bond: No lack of fusion detected by UT/PT; interfacial shear strength ≥50 MPa (per ASTM E2539 or equivalent)
- Microstructure: No untempered martensite in HAZ for low-alloy steel substrates; controlled grain size (≤0.1 mm in weld metal for Ni-based systems)
- Porosity: ≤Level 1 per GB/T 3323.1 or ASTM E94 classification
- Crack Resistance: No hot or cold cracks detected by PT/MT per GB/T 18891 / ASTM E709
6. Common Risks and Controls
| Risk Category | Description | Mitigation Strategy |
|---|---|---|
| Excessive Dilution | Base metal melting beyond target, compromising clad composition | Variable-angle side gun geometry optimization; reduced top-gun current; increased travel speed per simulation prediction |
| Porosity | Gas entrapment from inadequate shielding coverage in multi-gun configuration | Swirl vortex gas coverage enhancement; increased flow rates; nitrogen-free shielding verification |
| Hot Cracking | Solidification cracking in Ni-based or austenitic clad layers | Controlled oxygen level in pool; optimized solidification rate; pre-heat management; filler metal selection per ASME IX QW-462 |
| Interfacial Lack of Fusion | Inadequate wetting at clad-base metal interface | Top-gun vortex-induced pool stirring to enhance wetting; controlled interpass temperature; substrate surface preparation per GB/T 8898 |
| Process Instability | Arc oscillation or pool oscillation from coupled multi-gun interaction | Simulation-validated angle/current matching; synchronized torch motion control; real-time arc voltage monitoring |
| Simulation-Experiment Discrepancy | Numerical model predictions deviating from actual results | Iterative model calibration; sensitivity analysis; validated boundary condition refinement |
7. Application Across Company Technology Routes
7.1 TIG/MIG Weld Overlay (Primary Application)
This research directly advances the company's core TIG/MIG weld overlay capability. The multi-gun coupled process, validated through simulation and experimentation, enables:
- Automated multi-torch overlay systems: Integration of simulation-optimized parameters into robotic welding cells for large-area cladding (tubes, plates, pipes) with consistent quality
- Transition layer optimization: For dissimilar metal cladding (e.g., 309L transition between carbon steel and 316L clad), the variable-angle side gun approach allows precise control of the transition zone composition gradient
- High-dilution-sensitive systems: Ni-based overlays (Inconel 625, Stellite 6) on low-alloy steels where dilution must be minimized to preserve corrosion resistance and mechanical properties
- WPS qualification acceleration: Simulation provides pre-qualification parameter ranges, reducing the number of trial coupons required for ASME IX or NB/T 47015 PQR testing
7.2 Hydraulic Explosive Bonding (Complementary Application)
While the multi-torch process is primarily a thermal technique, the research contributes to hydraulic explosive bonding qualification in the following ways:
- Post-bonding repair and overlay: Areas of explosive bonding with surface defects or insufficient bonding ratio can be locally repaired using the optimized multi-torch overlay process
- Hybrid bonding technology: Combining explosive bonding for initial metallurgical bond formation with subsequent multi-torch overlay for thickness build-up — the simulation data informs thermal input limits to preserve the explosive bond interface
- Interface characterization: The multiphase flow simulation methodology can be adapted to model the fluid dynamics during hydraulic explosive bonding, particularly the pressure wave propagation and collision interface behavior
7.3 Explosion Welding (Process Design Support)
For the explosion welding route, the research provides indirect but valuable contributions:
- Thermal simulation methodology transfer: The multiphase flow modeling framework (VOF, energy coupling, species transport) can be extended to simulate post-explosion thermal events including residual stress relief welding
- Clad thickness augmentation: Where explosion welding achieves only thin clad layers (typically 3–15 mm), subsequent multi-torch overlay adds thickness — the process parameters must be calibrated to avoid disrupting the explosion bond interface
- Material qualification data: Experimental results on dilution, microstructure, and mechanical properties provide reference data for comparing welded overlay with explosion-welded interfaces in customer qualification packages
8. Contribution to Qualification Building, Product Delivery, and Customer Value
8.1 Qualification Building
- WPS/PQR Development: The research generates a comprehensive parameter database that directly supports the development and qualification of proprietary welding procedure specifications. Each simulated and experimentally validated parameter set becomes a candidate WPS requiring only formal PQR testing per ASME IX Part Q or NB/T 47015 to achieve qualified status.
- Welder/Equipment Qualification: The multi-torch system qualification requires demonstration of parameter control capability. The research establishes the acceptable parameter ranges, tolerance bands, and monitoring requirements needed for equipment and operator qualification records.
- Third-Party Certification Readiness: With simulation-backed parameter optimization and experimental validation, the company is positioned to achieve certifications from organizations such as TÜV, DNV, LR, and CNAS-accredited bodies for specific cladding applications.
8.2 Product Delivery Enhancement
- Reduced Rework Rates: Simulation-predicted optimal parameters minimize the probability of porosity, cracking, and excessive dilution, directly reducing NDT failure rates and rework costs. Industry benchmarks suggest 40–60% reduction in rework for simulation-optimized processes versus empirical parameter selection.
- Increased Deposition Efficiency: Multi-gun simultaneous operation achieves deposition rates of 2.5–4.0 kg/h compared to 1.0–1.5 kg/h for single-torch TIG overlay, reducing production time by 50–70% for large-area cladding jobs.
- Consistent Quality Across Batches: Simulation-validated process windows provide robust parameter ranges that maintain quality despite minor variations in base material, ambient conditions, or consumable lot-to-lot differences.
8.3 Customer Value Proposition
- Technical Credibility: Demonstrating simulation-backed process development distinguishes the company from competitors relying solely on empirical trial-and-error methods. This is particularly valued by end-users in nuclear, petrochemical, and power generation sectors requiring rigorous qualification documentation.
- Custom Solution Capability: The multiphase flow simulation framework can be adapted to customer-specific requirements — unusual substrate geometries, exotic clad materials, or extreme service conditions — providing rapid process development without extensive physical trial runs.
- Lifecycle Cost Reduction: By optimizing dilution control and microstructure through simulation, the company delivers clad products with superior corrosion resistance and fatigue performance, extending asset service life and reducing customer lifetime maintenance costs.
- Standards Compliance Documentation: The research generates comprehensive technical documentation supporting compliance with NACE MR0175/ISO 15156 (sour service), ASME BPV Section VIII (pressure vessels), and GB/T 150 (Chinese pressure vessel code), facilitating customer project approval and regulatory inspection.
9. Summary and Strategic Significance
The "Oxygen-Enriched Molten Pool Multi-Torch Multiphase Flow Simulation and Experimental Study" represents a significant intellectual property asset for Cladding Technology Shanxi Co., Ltd. It transforms empirical cladding practice into a predictive, science-based engineering discipline. The integration of computational fluid dynamics with multi-torch experimental validation establishes a process development paradigm that accelerates qualification timelines, reduces production risk, and enhances the company's technical positioning in the competitive clad materials market.
From a strategic perspective, this research:
- Creates a proprietary process knowledge base that is difficult for competitors to replicate without equivalent R&D investment 2. Supports patent filing for the multi-torch configuration, swirl vortex device, and variable-angle geometry optimization methodology
- Enables scalable process transfer from laboratory validation to production automation with high confidence in quality outcomes
- Provides technical authority in customer technical discussions, particularly for complex projects requiring custom multi-layer clad designs
As the company continues to expand its capability portfolio across TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding routes, this simulation-driven approach establishes a common technical foundation that unifies process development methodology across all three routes, creating synergistic value for multi-route hybrid cladding solutions.