CLADDING TECHNOLOGY SHANXI CO., LTDExperimental and Numerical Analysis of Angular Distortion in Weld Overlay Cladding
Literature Overview
This study investigated the dynamic process of angular distortion during weld overlay cladding operations through a combination of experimental measurements and finite element method (FEM) numerical simulations. Angular distortion is one of the most challenging manufacturing defects in cladding operations, particularly for thin-walled components such as heat exchanger tubes, thin-walled pressure vessels, and cladding plates with thickness ratios below 3:1. The research employed thermocouple arrays, digital image correlation (DIC), and strain gauges to capture the real-time deformation behavior during multi-pass overlay welding.
Experimental Methodology and Key Observations
The experimental setup involved depositing multiple weld passes on the surface of carbon steel plates (Q345R, 16Mn) and stainless steel plates (304, 316L) using submerged arc welding (SAW) and gas metal arc welding (GMAW) processes. The angular distortion was measured at multiple locations along the weld length and at various distances from the weld centerline. The following experimental conditions were tested:
| Test Condition | Base Metal | Overlay Material | Weld Process | Passes | Max Angular Distortion (mm) |
|---|---|---|---|---|---|
| A | Q345R, 6mm | 304 SS | SAW | 3 | 2.8 |
| B | Q345R, 10mm | 304 SS | SAW | 3 | 1.6 |
| C | 16Mn, 8mm | 316L SS | GMAW | 4 | 2.2 |
| D | 16Mn, 12mm | 316L SS | GMAW | 4 | 1.1 |
| E | Q345R, 6mm | 304 SS | SAW (reverse sequence) | 3 | 0.9 |
The experimental results clearly demonstrated that angular distortion is inversely proportional to base metal thickness and is significantly affected by the welding sequence. The reverse welding sequence (welding from the back side in alternating directions) reduced angular distortion by approximately 65% compared to the conventional single-direction sequence.
Numerical Simulation Results
The FEM analysis employed a coupled thermo-mechanical approach, where the thermal analysis was conducted first to determine the temperature field distribution, and the mechanical analysis was then performed using the temperature field as a thermal load. The simulation incorporated a plastic-elastic constitutive model with temperature-dependent material properties. The following key parameters were used in the simulation:
| Simulation Parameter | Value | Description |
|---|---|---|
| Mesh Element Size | 1.0–2.0 mm | Near the weld zone; 5.0 mm in remote areas |
| Heat Input Model | Double-ellipsoidal | Based on Rosenthal's solution |
| Heat Input Rate | 1.2–1.8 kJ/mm | Varied by welding parameters |
| Thermal Conductivity | 45–60 W/(m·K) | Temperature-dependent |
| Young's Modulus | 200–210 GPa | Room temperature value |
| Yield Strength | 345 MPa (Q345R) | At room temperature |
The numerical results showed good agreement with experimental measurements, with prediction errors within ±15% for most test conditions. The simulation revealed that the primary mechanism driving angular distortion is the asymmetric plastic deformation of the base metal beneath the overlay weld, caused by the non-uniform temperature distribution during welding.
Distortion Control Strategies
Based on both experimental and numerical findings, the following distortion control strategies were identified:
- Reverse welding sequence: Welding in alternating directions to create opposing distortion forces that partially cancel each other out.
- Back-plate clamping: Using rigid backing plates to constrain the base metal during welding, with the plates removed after PWHT.
- Intermittent welding: Welding in short segments with controlled spacing to reduce the cumulative thermal load on the base metal.
- Pre-heating: Applying uniform pre-heat to reduce the thermal gradient between the weld zone and the surrounding base metal.
- Symmetric welding: For double-sided cladding, welding both sides simultaneously to achieve thermal symmetry.
Engineering Practice and Quality Control
The study provides practical guidance for engineers fabricating clad plates and cladded pressure vessel components. The following quality control measures are recommended based on the findings:
- For cladding plates with thickness ratios below 3:1, angular distortion should be monitored at every 500 mm interval along the weld length using a straight edge and feeler gauge.
- The maximum allowable angular distortion per ASME Section VIII Division 1 is typically 0.5% of the plate width, but for critical applications such as heat exchanger tubesheets, tighter tolerances of 0.25% should be specified.
- Post-weld straightening should be performed using mechanical methods (pressing) rather than thermal methods to avoid introducing residual stresses that could compromise the overlay layer bond strength.
- Finite element simulation should be conducted as part of the process qualification for new cladding configurations to predict and minimize distortion before production welding begins.
Study Insights and Reflections
This study exemplifies the powerful synergy between experimental measurement and numerical simulation in solving practical manufacturing challenges. The dynamic measurement of angular distortion during welding, combined with the predictive capability of FEM analysis, provides a comprehensive understanding of the deformation mechanisms and enables proactive control strategies. The finding that reverse welding sequences can reduce distortion by more than 60% is particularly actionable for production engineers seeking to improve fabrication efficiency without compromising quality. The study also highlights the importance of considering the entire welding sequence, not just individual pass parameters, when designing cladding processes for distortion-sensitive applications. This holistic approach to process optimization is essential for achieving both dimensional accuracy and metallurgical quality in clad component fabrication.