FENG Xianzhang, LI Kunpeng, CHEN Kai, ZHANG Qiming, YU Tian, FAN Bingpeng, ZHANG Keqiang, CHEN Jinping
The work aims to improve the forming quality of tubes by optimizing the process parameters of bending forming, to solve the problems of wall thickness thinning and cross-sectional distortion of IN625 nickel-based superalloy thin-walled tubes in the process of small bending radius bending forming. A thin-walled tube of IN625 nickel-based superalloy with outer diameter D=25.4 mm, wall thickness t=0.89 mm and relative bending radius R/D=2 (bending radius R) was taken as the object, and a finite element model was established to simulate the winding forming process of small bending radius. Taking the mandrel extension amount, mandrel clearance, briquetting clearance and bending die clearance as the optimization variables, the maximum wall thickness reduction rate and the maximum cross-sectional distortion rate as the evaluation indexes, the Box-Behnken response surface method was used to design the test scheme, and a quadratic regression model was established by Design-Expert software, so as to obtain the optimized process parameter combination. Finally, a DB2090 CNC pipe bender was used to carry out experiments to verify the effectiveness of the finite element simulation results and the optimization of process parameters. The optimized process parameters were determined as follows: mandrel protrusion of 4.2 mm, bending die clearance of 0.05 mm, mandrel clearance of 0.08 mm, and pressure block clearance of 0.12 mm. Based on these parameters, finite element simulations and rotary bending experiments were conducted at bending angles of 30°, 60°, and 90°. The simulated maximum wall thinning rates were 8.96%, 10.21%, and 10.85%, and the maximum cross-sectional distortion rates were 2.49%, 2.58%, and 2.68%, respectively. The corresponding experimental values were 9.77%, 10.53%, and 11.10% for wall thinning, and 2.68%, 2.72%, and 2.85% for cross-sectional distortion. The maximum relative errors between simulation and experiment results were 8.3% and 7.1%, respectively, both within the allowable range. No cracking or severe cross-sectional distortion occurred in the bent specimens, confirming the feasibility of the optimized parameter combination. In conclusion, the combination of finite element simulation, response surface optimization and experimental verification can effectively improve the forming quality of IN625 nickel-based superalloy thin-walled tubes with small bending radius. The optimized combination of process parameters not only makes the maximum wall thickness reduction rate meet the standard limit, but also effectively suppresses the cross-sectional distortion, which can provide a reference for the optimization of the bending forming process of similar thin-walled tubes.
