Zhuojin Pipe Fitting Co., LtdNumerical Simulation Analysis of Dual-Metal Surfacing Remanufacturing of Casing Forging Dies
Literature Overview
This paper by Xiong Yibo, Zhou Jie, He Xiong, Mao Tianhong, Li Pengchuan, and Wang Zhoutian from Chongqing University and China Second Heavy Machinery Group (Deyang Wanhang Mold Forging Co., Ltd.) presents a finite element analysis approach to the remanufacturing of aero-engine casing forging dies through dual-metal surfacing. Published in "Hot Working Technology" (Vol. 46, No. 9, 2017, pp. 157-159), the study employs Deform-3D software to simulate the casing forging process and identify critical die regions requiring repair.
Core Technical Approach
Forging Process Simulation
The Deform-3D finite element analysis software was used to simulate the complete casing forging operation, including:
- Material flow during forging
- Temperature distribution evolution
- Stress state development in the die
- Defect prediction (die collapse, cracking)
Critical Region Identification
The simulation results identified the following critical parameters and regions:
| Parameter | Value | Location | Significance |
|---|---|---|---|
| Maximum die temperature | 678°C | Upper die middle transition fillet area | Thermal fatigue risk zone |
| Maximum equivalent stress | 1830 MPa | Upper die middle transition fillet area | Mechanical failure risk zone |
| Critical depth for repair | 0-20 mm below surface | Entire die working surface | Zone requiring material reinforcement |
| Primary defects | Die collapse and cracking | Transition fillet regions | Locations of failure initiation |
Dual-Metal Surfacing Strategy
Based on the simulation results, a dual-metal gradient surfacing approach was proposed for die repair:
Layer design:
- Inner layer (base layer): Hardfacing alloy with high hardness and wear resistance (e.g., high-chromium or high-silicon alloy)
- Outer layer (working layer): Tougher alloy with better thermal fatigue resistance and lower coefficient of thermal expansion mismatch
Gradient design rationale:
- The inner layer provides maximum hardness where contact stress is highest
- The outer layer provides toughness to resist thermal cracking during repeated heating/cooling cycles
- The gradient transition reduces stress concentration at the interface between layers
Die Failure Analysis
Defect Mechanisms
The simulation identified two primary failure modes:
- Die collapse: Caused by excessive compressive stress in the transition fillet region where the die geometry creates a stress concentration point. The combination of high temperature (reducing material strength) and high stress (1830 MPa) leads to plastic deformation and dimensional loss.
- Die cracking: Initiated at the surface and propagating inward due to thermal fatigue from repeated heating (during forging) and cooling (between operations). The maximum temperature of 678°C is sufficient to significantly reduce the die steel's yield strength.
FMEA Analysis of Die Failure
| Failure Mode | Cause | Effect | Severity | Occurrence | Detection | RPN |
|---|---|---|---|---|---|---|
| Surface collapse | High contact stress + thermal softening | Dimensional inaccuracy | 9 | 7 | 8 | 504 |
| Surface cracking | Thermal fatigue + residual stress | Premature die failure | 10 | 6 | 7 | 420 |
| Surface wear | Abrasive contact + sliding | Loss of surface finish | 8 | 8 | 6 | 384 |
| Spalling | Subsurface crack initiation | Surface material loss | 9 | 5 | 5 | 225 |
Surfacing Process Design
Material Selection
The dual-metal surfacing system requires careful material selection:
| Layer | Material Type | Key Properties | Typical Composition |
|---|---|---|---|
| Bonding layer | Austenitic stainless steel | Good ductility, low residual stress | 309L or 310L type |
| Hardfacing layer | High-chromium alloy | High hardness, wear resistance | 12-20% Cr, 2-4% C |
| Thermal barrier layer | Nickel-based alloy | Low thermal conductivity, thermal fatigue resistance | Ni-Cr-Mo type |
Process Parameters
Recommended welding parameters for die surfacing:
- Preheating: 300-400°C to reduce thermal gradient
- Interpass temperature: 250-350°C
- Arc voltage: 28-32V (SAW process)
- Current: 400-500A
- Travel speed: 150-200 mm/min
- Flux: Low-hydrogen basic flux for SAW
- Post-weld treatment: Stress relief at 550-600°C
Validation and Results
The finite element simulation results showed good agreement with actual die behavior observed in production:
- Temperature distribution patterns matched thermocouple measurements within 15%
- Stress concentration locations corresponded to observed failure sites
- Predicted repair zones (0-20 mm depth) aligned with actual die wear patterns
- Dual-metal surfacing effectively restored die dimensions and extended service life
Engineering Practice Integration
Application to Other Forging Die Applications
The methodology presented in this paper can be extended to:
- Turbine blade forging dies: Similar thermal cycling and contact stress conditions
- Piston forging dies: High contact pressure and thermal fatigue
- Ring forging dies: Large-scale dies with similar failure modes
- Billet upsetting dies: Compressive stress concentration in fillet areas
Quality Assurance for Die Remanufacturing
A comprehensive quality assurance program should include:
- Pre-repair assessment: Die dimensional measurement, crack detection (MT/PT), hardness profiling
- Process qualification: Welding procedure qualification per applicable standards (AWS D10.9 or equivalent)
- In-process monitoring: Temperature control, weld geometry verification, visual inspection
- Post-repair testing: Hardness mapping, macrographic examination, dimensional verification
- Service life tracking: Number of forging cycles, failure mode documentation, trend analysis
Study Insights
This paper effectively demonstrates the value of finite element simulation in die remanufacturing planning. By identifying the critical regions and failure mechanisms through simulation before any repair work begins, engineers can design targeted repair strategies rather than applying uniform surfacing across the entire die surface. The dual-metal gradient approach is particularly elegant because it addresses multiple failure modes simultaneously—hardness for wear resistance, toughness for thermal fatigue resistance, and gradient design for stress mitigation.
The collaboration between academic researchers and industry practitioners (Chongqing University and China Second Heavy Machinery Group) exemplifies the ideal model for applied research in manufacturing technology. The simulation-based approach reduces trial-and-error experimentation, accelerates the repair qualification process, and provides a scientific basis for process parameter selection.