CLADDING TECHNOLOGY SHANXI CO., LTDNumerical Simulation and Experimental Research of Coaxial Powder Feeding TIG Overlay Process
Motivation for Simulation Study
Numerical simulation of the coaxial powder feeding TIG overlay process addresses a fundamental challenge in thermal spray engineering: the inability to directly observe the transient thermal and fluid flow phenomena occurring within the weld pool during deposition. By coupling finite element analysis of heat transfer with computational fluid dynamics modeling of melt pool convection, engineers can predict deposit geometry, dilution behavior, and residual stress distribution before committing to expensive trial welds. This study validates the simulation model against experimental data obtained from actual overlay trials.
Simulation Methodology and Model Validation
The thermal model employs a moving heat source with a double-elliptical distribution to represent the arc energy input, while the powder feeding is modeled as a distributed heat and mass source within the melt pool region. The governing equations include the transient heat conduction equation with convective boundary conditions, coupled with a Navier-Stokes solver for melt pool fluid flow accounting for Marangoni convection, buoyancy forces, and electromagnetic stirring effects.
| Validation Parameter | Simulation Result | Experimental Result | Deviation |
|---|---|---|---|
| Bead width (mm) | 8.2 | 8.5 | 3.5% |
| Bead height (mm) | 1.8 | 1.9 | 5.3% |
| Penetration depth (mm) | 0.9 | 1.0 | 10.0% |
| Peak temperature (°C) | 2450 | 2400-2500 | Within range |
| Cooling rate at fusion line (°C/s) | 180 | 160-200 | Within range |
Key Simulation Insights
The simulation reveals that Marangoni convection driven by surface tension gradients dominates the melt pool flow pattern, creating a central upward flow that brings hot material to the surface while cooler material from the base metal is drawn toward the arc center. This flow pattern explains the observed dilution behavior: base metal is entrained into the upper portion of the weld pool where it mixes with molten powder, while the lower portion near the fusion boundary retains higher base metal content.
Residual stress analysis shows that the maximum tensile stress develops at the fusion boundary, reaching values of 180-220 MPa depending on the interpass temperature. This stress distribution correlates with the observed microcracking tendency in multi-pass overlays when interpass temperature control is inadequate. The simulation also predicts that a preheat temperature of 100-150 degrees Celsius reduces peak residual stresses by approximately 30 percent without significantly affecting dilution rates.
Dilution Prediction and Process Control
The simulation provides a quantitative relationship between process parameters and dilution rate, expressed as a function of heat input per unit powder mass. The dilution rate D can be approximated as D = 0.15 + 0.008 × (Q/P) - 0.002 × V, where Q is heat input in watts, P is powder feed rate in grams per minute, and V is travel speed in millimeters per minute. This empirical relationship, validated by both simulation and experiment, enables rapid process optimization without extensive trial welding.
The model also predicts the critical conditions for porosity formation: when the local cooling rate exceeds 300 degrees Celsius per second, gas entrapment becomes thermodynamically favorable as dissolved gases exceed their solubility limits during solidification. This insight led to the recommendation of increasing arc current by 10-15 percent for thick deposits to reduce cooling rates and minimize porosity.
Summary
The integration of numerical simulation with experimental validation provides a powerful framework for understanding and controlling the coaxial powder feeding TIG overlay process. The predictive capability of the model enables engineers to optimize process parameters for specific alloy systems, anticipate defect formation, and design multi-pass strategies that minimize residual stresses. This approach significantly reduces development time and material waste during process qualification, making it an essential tool for modern overlay welding engineering practice.