Study on the Forming Accuracy of TRIP Steel Products in ISF

Incremental Sheet Forming (ISF) is a flexible technology for forming customized productions in small batch, and has received wide attention, especially in the automobile manufacturing industry, where TRIP(Transformation Induced Plasticity) steel is widely used for its great ductility and high strength. But the springback of TRIP steel products is more serious than that of common steel ones, which induce the low dimensional accuracy and block the industrial application. This work would illustrate the experimental research on the dimensional accuracy of TRIP steel products in ISF. To make a reasonable accuracy evaluation, square cone-shaped samples of 1060Al and 08F steel were formed by ISF as the reference. By comparing the outline unconformity and the dimensional deviation, it comes to the conclusion that dimensional accuracy of TRIP steel sheet products is much lower than that of other materials.

Effect of Transformation on Springback for TRIP Steel Stamping

A relation between the Young’s modulus and the martensitic transformation during TRIP sheet steel stamping is investigated. A TRIP steel, TRIP600, is used to study the phenomenon. The transformation kinetics under different loading paths were gotten through simple-shear, uniaxial tension, plane strain and equibiaxial stretching tests. The Young’s modulus, which plays an important role in accurate springback prediction for TRIP steel sheet stamping, is changed with the martensitic transformation during TRIP steel deformation. To improve the accuracy of springback simulation, the constitutive model of the TRIP steel is developed considering the variation of the Young’s modulus with the martensitic transformation. The accuracy of the proposed method is verified by the experimental results.

Springback Prediction of the TRIP Sheet Steel Stamping

An enhanced elastic-plastic constitutive equation taking into account strain induced transformation is developed. The variation of the Young’s modulus with the martensitic transformation during stamping process is also introduced to improve the accuracy of springback simulation for TRIP steel. The accuracy of the proposed method is verified by comparing with the conventional FE model and experimental results. The enhanced material model is testified to be efficient in accurate prediction on springback for TRIP steels, which will put forward the application of TRIP steel sheet in auto body manufacturing.