CLADDING TECHNOLOGY SHANXI CO., LTDNumerical Simulation of Temperature Field During Piston Overlay Welding Using ANSYS
Literature Overview
This paper presents a finite element analysis (FEA) of the thermal field during overlay welding of piston components, utilizing ANSYS as the computational platform. Piston overlays are critical in internal combustion engines, hydraulic cylinders, and hydraulic pumps where the piston surface must withstand high-friction, high-temperature, and corrosive environments. The study models the transient heat transfer during multi-pass surfacing, examining how parameters such as welding current, travel speed, heat input, and pre-heat temperature influence peak temperatures, cooling rates, and thermal stress distributions in both the overlay and the base material.
Core Technical Points
Modeling Approach and Assumptions
The authors employed a 3D transient thermal model with the following key assumptions:
- Heat source modeled as a double-ellipsoidal Goldak distribution to represent the asymmetric penetration profile of GMAW or SAW processes.
- Material properties (thermal conductivity, specific heat, density) defined as temperature-dependent functions for both the overlay alloy (typically Stellite 6 or equivalent Co-Cr-W alloy) and the base material (cast iron or low-alloy steel).
- Convective and radiative heat losses from the surface modeled using Newton's law of cooling with a composite heat transfer coefficient of 15–25 W/(m²·K).
- Phase change effects (solidification and melting) incorporated via the enthalpy-temperature method.
| Parameter | Typical Value | Influence on Peak Temperature |
|---|---|---|
| Welding current (I) | 180–250 A | Higher I → higher peak T |
| Travel speed (v) | 0.2–0.4 m/min | Higher v → lower peak T |
| Arc voltage (U) | 22–28 V | Higher U → higher peak T |
| Pre-heat temperature | 100–300°C | Higher pre-heat → lower ΔT gradient |
| Heat input (q) | 8–14 kJ/mm | Primary driver of thermal profile |
Thermal Field Results and Validation
The simulation results show that the peak temperature in the weld zone reaches approximately 1600–1800°C for typical GMAW parameters, with the temperature gradient extending into the base material up to 15–25 mm from the weld centerline. The cooling rate at the fusion boundary was predicted to be in the range of 5–20°C/s depending on heat input and pre-heat conditions. These values were validated against thermocouple measurements embedded in physical trials, with deviations generally within 5–10%, confirming the model's reliability for engineering prediction.
Thermal Stress and Distortion Implications
A secondary analysis incorporated elastic-plastic thermal stress calculations. The results revealed that the maximum thermal stress in the overlay layer reaches 350–500 MPa under constrained conditions (e.g., thick piston walls or multi-pass builds). This is particularly significant for piston applications where dimensional accuracy is critical—thermal distortion exceeding 0.1 mm can affect seal integrity and clearance fit. The study recommends a post-weld stress relief treatment at 550–650°C for 2–4 hours, which the simulation predicts reduces residual stresses by approximately 60–75%.
Process Optimization Insights
The numerical approach enables systematic parametric studies that would be prohibitively expensive through physical trials alone. Key optimization findings include:
- A heat input of 10–12 kJ/mm provides the best compromise between adequate fusion and manageable thermal distortion for GMAW overlay of piston surfaces.
- Pre-heating to 200°C reduces the maximum thermal gradient by approximately 20%, significantly lowering cracking risk in high-carbon base materials.
- Multi-pass strategies with interpass temperature control between 150–250°C effectively limit the thermal cycling damage to the base material.
Key Questions and Reflections
While the thermal model is robust, it does not fully capture metallurgical transformations such as martensite formation in the heat-affected zone (HAZ) or carbide precipitation in the overlay. A coupled thermo-metallurgical model would provide more complete predictions of final mechanical properties. Furthermore, the study assumes a flat or simple cylindrical geometry; real pistons with complex profiles (grooves, chamfers, cross-hatching for oil retention) introduce geometric effects that may alter local heat flow patterns. Engineers should treat the simulation results as guidance rather than definitive predictions for complex geometries.
Study Insights and Implications
This work demonstrates the substantial value of FEA in overlay welding process development, particularly for reducing trial-and-error costs and accelerating qualification cycles. For engineers involved in piston overlay specification, the thermal simulation provides a quantitative basis for setting process parameters and pre-heat requirements, complementing rather than replacing the practical experience and standard-based qualification (NB/T 47014, ASME IX) that remain essential for production certification.