Numerical Simulation-Based Overlay Welding Remanufacturing Analysis of Engine Casing Forging Dies

Literature Overview

Published in the journal of Hot Working Technology (Re Gongyiji) in 2017, Vol. 46, No. 9, pp. 157–159, 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 Forging Co., Ltd. presents a numerical simulation-based analysis of overlay welding remanufacturing for aero-engine casing forging dies. The research was supported by the National Natural Science Foundation of China and Chongqing Science and Technology Commission application development projects. The work employs Deform-3D finite element analysis software to simulate the forging process of engine casings, analyze die temperature and stress distributions, identify defects, and propose a dual-metal gradient overlay welding repair method.

Research Background and Motivation

Aero-engine casing forging dies are subjected to extreme thermal and mechanical loads during the forging process, leading to surface damage, cracking, and dimensional degradation over time. Traditional die repair methods often involve grinding away damaged material and re-hardening the entire die, which is time-consuming and may compromise the die's dimensional accuracy and structural integrity. Overlay welding offers a promising alternative for die remanufacturing, as it allows the addition of wear-resistant and thermally stable materials to the damaged surface without removing the entire die.

The challenge lies in the fact that engine casing dies experience complex temperature and stress fields during forging, with the maximum temperature and stress concentrated in specific regions. A uniform overlay welding repair may not adequately address the localized damage, and the thermal and mechanical compatibility between the overlay material and the die substrate must be carefully managed to prevent cracking and delamination during subsequent forging operations.

Finite Element Simulation of Forging Process

The authors employed the Deform-3D finite element analysis software to simulate the forging process of aero-engine casings. The simulation captured the temperature and stress distributions within the die during the forging operation, providing critical data for identifying damage-prone regions and designing an appropriate overlay repair strategy.

The simulation results reveal that both the maximum temperature and maximum equivalent stress occur in the middle transition fillet area of the upper die. This region is subjected to the most severe combined thermal and mechanical loading, making it the primary candidate for overlay welding repair. The surface and the region within 20 mm below the surface experience elevated stress and temperature, defining the critical zone that requires overlay protection.

Defect Analysis

The simulation identified two primary defect modes in the engine casing forging die: collapse and cracking. Collapse occurs when the die material undergoes excessive plastic deformation under combined thermal and mechanical loads, leading to loss of dimensional accuracy and surface quality. Cracking is caused by the high equivalent stress concentrations in the fillet regions, where the stress exceeds the material's yield strength and fracture toughness.

The collapse defect is particularly concerning because it directly affects the dimensional accuracy of the forged casing, which has stringent tolerance requirements in aero-engine applications. The cracking defect, while initially minor, can propagate during subsequent forging cycles, eventually leading to catastrophic die failure. Both defects are concentrated in the surface region and the 20 mm subsurface zone, confirming the simulation findings regarding the critical repair zone.

Dual-Metal Gradient Overlay Repair Strategy

Based on the simulation results, the authors proposed a dual-metal gradient overlay welding method for die repair. The concept involves depositing two different overlay materials in a gradient manner, with the first layer providing thermal and mechanical compatibility with the die substrate and the second layer providing enhanced wear resistance and thermal stability.

The dual-metal gradient approach addresses the fundamental challenge of overlay welding on dies: the need for both strong bonding to the substrate and excellent surface properties. The first layer acts as a metallurgical buffer, reducing the thermal and mechanical mismatch between the overlay and the die substrate. The second layer provides the enhanced surface properties required for die service. The gradient transition between the two layers reduces stress concentrations that could otherwise initiate cracking at the overlay-substrate interface.

Validation and Discussion

The finite element simulation results were compared with actual die behavior, demonstrating good agreement between the predicted and observed damage patterns. The simulation accurately identified the critical regions of high temperature and stress, validating the proposed overlay repair strategy. The maximum temperature of 678°C and maximum equivalent stress of 1830 MPa provide quantitative benchmarks for evaluating the effectiveness of the overlay repair.

The proposed dual-metal gradient overlay method represents a significant advancement in die remanufacturing technology. By targeting the repair to the specific regions identified through simulation, the method minimizes the amount of overlay material required while maximizing the repair effectiveness. The gradient approach reduces the risk of cracking and delamination, which are common failure modes in single-material overlay repairs.

Engineering Practice Implications

For engineers involved in aero-engine die maintenance and remanufacturing, this paper provides a systematic approach to die repair based on numerical simulation. The key steps include: (1) simulate the forging process to identify damage-prone regions, (2) analyze the temperature and stress distributions to define the critical repair zone, (3) select appropriate overlay materials based on the identified damage modes, and (4) implement a gradient overlay strategy to ensure metallurgical compatibility and surface performance.

The integration of finite element simulation with overlay welding technology represents a paradigm shift in die maintenance, moving from reactive repair to predictive and targeted remanufacturing. This approach can significantly extend die life, reduce maintenance costs, and improve the consistency of forged part quality.

Key Reflections

The use of finite element simulation to guide overlay welding repair decisions is a powerful example of how computational tools can enhance engineering practice. The ability to predict damage patterns and identify critical repair zones before they manifest as actual defects allows for proactive and targeted maintenance. For aero-engine manufacturing, where die quality directly impacts part quality and safety, this approach is particularly valuable.

Summary

This paper demonstrates the effectiveness of numerical simulation in guiding the overlay welding remanufacturing of aero-engine casing forging dies. The Deform-3D simulation identified the critical damage regions and provided quantitative data on temperature and stress distributions, enabling the design of a targeted dual-metal gradient overlay repair strategy. The proposed method addresses both thermal and mechanical damage modes while ensuring metallurgical compatibility between the overlay and the die substrate. For engineers in the aerospace manufacturing sector, this work highlights the value of integrating computational simulation with surface engineering techniques for advanced die remanufacturing.