| BR1500HS is a special kind material of high-strength steel for thermoforming, and the seamless welded tubes made by BR1500 HS are widely used in auotmotive bumper frame structure to achieve the purpose of energy conservation and emisssion reduction under the condition of lightweight and safety. The traditional forming and induction hardening process of BR1500 HS high-strength steel tube is separated into formative stage and induction hardening stage, with the flexibility is poor and the forming is easy to be restricted by the mold in the cold bending forming stage. Therefore, it has a great significance for guiding the design and manufacture of high-strength steel tube to master the technology of hot bending without mould and obtain the influence of geometry and process parameters to formability.Based on the isothermal tensile tests of BR1500 HS, the relationship equation of flow stress, strain rate and strain for rectangular tube bending is established, whice provides a theoretical basis for the setting of numerical parameters. The distribution of magnetic intensity of high-strength steel tube in the process of induction heating is obtained by calculating, besides, induction coil and the non-mould hot bending device has been designed.Based on the plane assumption and plastic deformation theory, the condition of stress-strain has been analyzed in the deformed region during bending, and threedimensional stress-stain state of tube under the combined action of bending moment and friction force is computed. The relationgship between the plastic deformation energy and wrinkling energy is established on the minimizing energy principle, and the prediction formula of wrinkling limit for tube is proposed, besides, the influence factors of tube forming performance are analyzed according to the formula of stress-strain and the prediction formula of wrinkling limit.Through the sequential coupling simulation of ANSYS and ABAQUS for the hot bending forming of high-strength steel, with the node information of electromagnetic and temperature in ANSYS combined with calculation of temperature field and structuire field in ABAQUS, the influences of different geometric parameters and process parameters on the cross section ovality, springback angle and wrinkling limit are ana lyzed.The experiments of hot bending forming without mould of BR1500 HS highstrength steel tube are carried out, and the influences of different geometric parameters and process parameters on the cross section ovality and springback angle are analyzed. Through the comparsion with experimental data and numerical simulation, both are in good consistency. The average error of cross section ovality is less than 15.18% and the average error of bending angle is less than 0.95%, which verifies the correctness of simulation model. |
