Zhuojin Pipe Fitting Co., LtdNumerical Simulation of Temperature Field During Plunger Overlay Welding Process Using ANSYS
Literature Overview
The paper by Zhang Guozheng (2017), published in "Foundry Technology" (Vol. 38, No. 9, pp. 2265-2267), presents a three-dimensional finite element numerical simulation of the welding temperature field during surface overlay welding of a composite metal layer onto 45 steel plunger components using ANSYS software. The study investigates the temperature field evolution at different welding speeds and at arbitrary time points during the welding process, providing quantitative data for welding process optimization and subsequent structural fatigue analysis. The classification code TG455 confirms the welding process focus, and the application to plunger components indicates relevance to hydraulic and automotive engineering applications where plungers are subjected to severe wear and impact loading.
Numerical Simulation Methodology
The finite element model was developed using ANSYS software with a three-dimensional geometry representing the plunger component and the overlay weld deposit. The welding heat source was modeled as a moving heat flux boundary condition, with the heat input rate and distribution characterized based on experimental welding parameters. The temperature-dependent material properties of both the base metal (45 steel) and the overlay alloy were incorporated into the simulation to capture the nonlinear thermal behavior during heating and cooling.
Simulation Parameters and Assumptions
| Parameter | Value or Specification | Notes |
|---|---|---|
| Base metal | 45 steel | Medium-carbon structural steel |
| Overlay material | Composite metal alloy | High-hardness wear-resistant alloy |
| Welding process | Arc overlay welding | Heat source modeled as Gaussian or double-elliptical |
| Heat input | Variable with welding speed | Higher speed reduces heat input per unit length |
| Thermal conductivity | Temperature-dependent | Linear and phase-change regions accounted for |
| Specific heat | Temperature-dependent | Includes latent heat of fusion |
| Density | Temperature-dependent | Thermal expansion considered |
| Mesh type | Three-dimensional solid elements | Refined near weld zone |
| Time step | Adaptive | Smaller steps during rapid temperature changes |
The moving heat source model captures the transient nature of the welding process, where the temperature field evolves continuously as the arc travels along the weld path. The Gaussian or double-elliptical heat source distribution accounts for the asymmetric heat input between the leading and trailing edges of the weld pool, which is critical for predicting the temperature gradient and solidification direction in the weld metal.
Temperature Field Analysis Results
The simulation results reveal the spatial and temporal evolution of the temperature field during overlay welding at different welding speeds. Key observations include:
Effect of Welding Speed on Temperature Field
| Welding Speed | Peak Temperature | HAZ Width | Cooling Rate | Solidification Characteristics |
|---|---|---|---|---|
| Low speed | Higher | Wider | Slower | Coarser grain structure expected |
| Medium speed | Moderate | Moderate | Moderate | Balanced grain structure expected |
| High speed | Lower | Narrower | Faster | Finer grain structure, higher residual stress |
At lower welding speeds, the heat input per unit length is higher, resulting in elevated peak temperatures and a wider heat-affected zone. The slower cooling rate allows more time for grain growth and phase transformation, potentially leading to coarser microstructures in both the weld metal and HAZ. At higher welding speeds, the reduced heat input produces lower peak temperatures and a narrower HAZ, with faster cooling rates that promote finer grain structures but may increase the risk of cracking due to higher thermal gradients and residual stresses.
Temperature Distribution and Cooling Patterns
The temperature field during welding exhibits a characteristic pattern of rapid heating followed by gradual cooling. The peak temperature at the arc position reaches the melting point of the overlay alloy, while the temperature decreases rapidly with distance from the weld centerline. The cooling rate is highest immediately after the arc passes and decreases exponentially with time, with the final cooling rate determining the as-welded microstructure of the overlay layer and HAZ.
The simulation provides quantitative temperature-time curves at specific locations within the weld zone, which can be correlated with microstructural predictions using transformation kinetics models. For example, the cooling rate from 800 °C to 500 °C (C800-500) is a critical parameter for predicting the formation of martensite, bainite, or pearlite in the weld metal and HAZ.
Implications for Process Optimization
The numerical simulation results provide valuable guidance for optimizing the overlay welding process parameters to achieve desired microstructural and mechanical properties in the repaired plunger component:
- Welding speed selection: The optimal welding speed balances deposition rate, heat input, and cooling rate to achieve the target microstructure. Too low a speed produces excessive heat input and coarse grains; too high a speed produces excessive residual stress and potential cracking.
- Heat input management: The total heat input per unit length (Q = VI/u, where V is voltage, I is current, and u is welding speed) must be controlled to prevent excessive HAZ growth while ensuring adequate fusion and wetting.
- Preheat and interpass temperature: The simulation can predict the effect of preheat and interpass temperature on the cooling rate and HAZ microstructure, enabling optimization of these parameters to minimize cracking risk.
- Residual stress prediction: The temperature field data can be used as input for subsequent thermomechanical simulations to predict residual stress distribution, which is critical for fatigue life assessment of the repaired component.
Connection to Structural Fatigue Analysis
The paper notes that the temperature field simulation provides an important basis for subsequent structural fatigue analysis of the weld joint. The residual stress distribution, microstructural characteristics, and hardness profile of the overlay weld are all influenced by the welding temperature field, and these factors collectively determine the fatigue performance of the repaired component. In plunger applications, where cyclic loading and impact are common, the fatigue resistance of the overlay weld is as important as its wear resistance.
The integration of thermal simulation with structural analysis represents a comprehensive approach to weld repair evaluation, where the welding process is optimized not only for microstructural quality but also for long-term structural integrity under service loading conditions. This multi-scale approach—from thermal simulation to microstructural prediction to fatigue life estimation—provides a rigorous engineering methodology for overlay weld repair design.
Study Insights and Conclusions
This study demonstrates the value of finite element numerical simulation as a tool for understanding and optimizing the overlay welding process for plunger repair applications. The three-dimensional temperature field analysis provides quantitative data that would be difficult or impossible to obtain through experimental measurement alone, enabling detailed investigation of the effects of welding speed, heat input, and other process parameters on the thermal history of the weld zone. The results support the development of optimized welding procedures that balance wear resistance, toughness, and fatigue performance in the repaired component. For engineering practice, the numerical simulation approach offers a cost-effective and systematic method for process development, reducing the need for extensive trial-and-error experimentation while providing deeper insight into the underlying metallurgical mechanisms that govern overlay weld quality.