Zhuojin Pipe Fitting Co., LtdNumerical Simulation of Overlay Welding Temperature Field for Hydraulic Support Cylinder Piston Rod
Literature Overview
This paper by Zhang Jin and colleagues from Anhui University of Science and Technology (2021, Hot Working Technology, Vol. 50, No. 9, pp. 122-124) presents a finite element analysis of the temperature field distribution during overlay welding of hydraulic support cylinder piston rods. The work was supported by the Anhui Provincial Department of Education Natural Science Foundation Key Project (KJ2019A0127). The research addresses a critical engineering problem in coal mining equipment maintenance, where hydraulic support piston rods undergo severe abrasive wear and require periodic overlay welding repair.
Numerical Methodology
The study used ANSYS software with APDL (ANSYS Parametric Design Language) programming and element birth-and-death technology to simulate the transient thermal analysis of the piston rod overlay welding process. Three preheat conditions were investigated: room temperature (20°C), 150°C, and 300°C.
| Parameter | Description |
|---|---|
| Simulation platform | ANSYS with APDL programming |
| Thermal analysis type | Transient thermal analysis |
| Preheat conditions | 20°C, 150°C, 300°C |
| Element technique | Element birth-and-death for layer-by-layer deposition |
| Output | Temperature field distribution patterns |
Key Results
The primary finding is that overlay welding at room temperature is prone to forming quenched hard microstructures in the weld, while preheating reduces the tendency for quench hardening. This result has direct implications for the mechanical properties and service life of the repaired piston rod.
Process Analysis and Engineering Considerations
Hydraulic support cylinder piston rods are typically manufactured from high-strength alloy steels (such as 40CrNiMo or similar grades) that have been through-hardened and tempered. The base material hardness is typically in the range of 28-32 HRC, and the overlay layer must match or exceed this hardness while maintaining adequate toughness to resist impact loading from coal and rock.
The temperature field distribution during overlay welding is governed by several factors:
- Heat input: Determined by welding current, voltage, and travel speed. Higher heat input leads to slower cooling rates and reduced quench hardening tendency.
- Preheat temperature: Directly affects the initial thermal gradient and the cooling rate at the weld zone.
- Base material thermal conductivity: Alloy steels have lower thermal conductivity than carbon steels, which concentrates heat in the weld zone and increases quench hardening tendency.
- Layer thickness and number of passes: Multi-pass overlay welding creates complex thermal histories that affect the final microstructure.
Preheat Strategy Comparison
| Preheat Condition | Cooling Rate | Quench Hardening Tendency | HAZ Hardness Risk | Recommended Application |
|---|---|---|---|---|
| 20°C (room temperature) | High | High | High risk of brittle martensite | Not recommended for high-strength steels |
| 150°C | Moderate | Moderate | Moderate risk | Suitable for low-carbon steels |
| 300°C | Low | Low | Low risk | Recommended for high-strength alloy steels |
Practical Implications for Piston Rod Repair
The numerical simulation results provide a quantitative basis for selecting preheat temperatures in piston rod overlay welding repair. In the coal mining industry, hydraulic support piston rods are critical safety components, and failure can lead to catastrophic roof falls. The following engineering recommendations can be derived:
- Preheat selection: For high-strength alloy steel piston rods (e.g., 40CrNiMo, 42CrMo), a preheat temperature of 250-300°C is recommended to reduce the risk of quench hardening and cold cracking in the heat-affected zone.
- Interpass temperature control: The interpass temperature should be maintained within the range of 200-300°C to prevent excessive cooling rates between passes.
- Post-weld heat treatment: Even with adequate preheat, post-weld tempering treatment at 550-650°C for 2-4 hours is recommended to relieve residual stresses and temper any hard martensite formed in the HAZ.
- Overlay material selection: The overlay material should be matched to the base material in terms of carbon equivalent and thermal expansion coefficient to minimize thermal stress.
Key Reflections
The use of element birth-and-death technology in the finite element model is a practical approach to simulating multi-layer overlay welding, as it allows the model to account for the sequential addition of material without requiring remeshing at each step. However, the accuracy of the temperature field prediction depends heavily on the heat source model used. The paper does not explicitly state which heat source model was employed, but a double-ellipsoidal (Goldak) heat source is typically used for arc welding simulations. The choice of heat source model significantly affects the predicted temperature field, particularly the peak temperature and the cooling rate at the weld centerline.
From a manufacturing perspective, the simulation results should be validated against thermocouple measurements on actual piston rods to ensure the model's predictive accuracy. Discrepancies between simulation and experiment can arise from simplifications in boundary conditions, material property assumptions, and heat source characterization. A sensitivity analysis varying the heat source parameters and boundary conditions would strengthen the predictive capability of the model.