Numerical Simulation-Based Hardfacing Remanufacturing of Engine Casing Forging Dies

Literature Overview

This study by Xiong Yibo, Zhou Jie, He Xiong, Mao Tianhong, Li Pengchuan, and Wang Zhoutian from Chongqing University and China Second Heavy Industries Group Deyang Wanhang Forging Co., Ltd. (2017, Hot Working Technology, Vol. 46, No. 9) presents a comprehensive approach to the remanufacturing of aviation engine casing forging dies through numerical simulation and bimetallic gradient hardfacing. The research combines finite element analysis of the forging process with practical hardfacing solutions to address die failure modes such as collapse and cracking, providing a methodology that bridges computational analysis and manufacturing practice.

Engineering Context and Problem Statement

Aviation engine casing forging dies are subjected to extreme thermal and mechanical loading conditions during the forging process. The dies must withstand repeated cycles of high temperature and high pressure while maintaining dimensional accuracy and surface integrity. Over time, the die surfaces experience wear, thermal fatigue cracking, and plastic deformation, leading to reduced forging quality and shortened service life. Traditional die repair methods, such as grinding and machining, remove material and reduce the die's structural integrity, while complete die replacement is economically prohibitive due to the high cost of die materials and manufacturing.

The authors identify bimetallic gradient hardfacing as a promising remanufacturing approach that can restore and enhance the die surface properties while preserving the structural integrity of the base die material. The gradient hardfacing creates a transition zone between the hard, wear-resistant surface layer and the tough, ductile base material, which provides excellent resistance to both wear and thermal fatigue cracking.

Finite Element Analysis of Forging Process

The authors employed Deform-3D finite element analysis software to simulate the forging process of engine casings. The simulation provides detailed information on the temperature and stress distributions within the die during forging, which are critical for understanding the failure mechanisms and designing appropriate repair strategies.

The simulation results reveal that the maximum temperature and maximum stress in the upper die both occur in the intermediate transition fillet region. The highest temperature reaches 678°C, while the maximum equivalent stress is 1830 MPa. These values are significantly higher than in other regions of the die, indicating that this area is the most critical zone for die failure.

The authors emphasize that the region within 20 mm below the die surface experiences both high stress and high temperature, making it the critical zone for die repair. This finding directly informs the design of the hardfacing repair strategy, as the bimetallic gradient hardfacing should be applied to this specific region to effectively address the failure mechanisms.

Bimetallic Gradient Hardfacing Design

Based on the finite element analysis results, the authors propose a bimetallic gradient hardfacing approach for die repair. The gradient hardfacing consists of a transition layer that gradually changes from the base die material composition to the hardfacing alloy composition. This gradient structure eliminates the sharp interface between the hard, brittle hardfacing layer and the tough base material, which would otherwise be a crack initiation site under thermal and mechanical loading.

The hardfacing alloy selection is based on the requirement for high temperature strength, thermal fatigue resistance, and wear resistance. The authors recommend alloys with high chromium and molybdenum content to provide oxidation resistance and hot hardness, combined with appropriate carbon content to ensure adequate hardness and wear resistance. The transition layer composition is designed to minimize the coefficient of thermal expansion mismatch between the hardfacing layer and the base die material.

Process Implementation and Quality Control

The hardfacing repair process involves several critical steps that must be carefully controlled to ensure the quality and performance of the repaired die. Preheating is essential to reduce the thermal stress during hardfacing and to minimize the risk of cracking in the transition layer. The preheat temperature should be in the range of 300-400°C, depending on the die material and geometry.

The hardfacing process should be performed with controlled heat input to avoid excessive dilution of the hardfacing alloy and to prevent distortion of the die. Multi-pass welding with controlled interpass temperatures is recommended to achieve the desired gradient structure. Post-weld heat treatment, including stress relief annealing and possibly tempering, is necessary to relieve residual stresses and stabilize the microstructure.

Quality control measures include dimensional inspection to verify that the hardfacing does not interfere with the die cavity geometry, hardness profiling across the transition layer to confirm the gradient structure, and non-destructive testing such as magnetic particle inspection or ultrasonic testing to detect any internal defects.

Study Insights and Practical Value

This study exemplifies the powerful integration of numerical simulation and manufacturing practice in solving complex engineering problems. The finite element analysis provides quantitative data on the stress and temperature distributions that guide the design of the hardfacing repair strategy, while the practical implementation demonstrates the feasibility and effectiveness of the proposed approach. The bimetallic gradient hardfacing method offers a cost-effective alternative to complete die replacement, extending the service life of expensive forging dies and reducing manufacturing costs.

The methodology presented in this study can be adapted to other die repair applications in the aerospace and power generation industries, where forging dies are subjected to similar severe thermal and mechanical loading conditions. The key to successful application lies in the accurate characterization of the die loading conditions through numerical simulation and the careful design of the hardfacing strategy based on this characterization.