Research On The Formability Of Tailor Welded Blanks And Its Application In The Deep Drawing For A Square Box

Tailor-welded blanks(TWBs) are constituted of two or more materials with different strengths or thicknesses or surface coatings joined together to form a single part before the forming process. With increasingly society demand of environmental protection and energy conservation, TWBs are more and more widely used in automotive industry and play a great important role in reducing the weight and enhancing the safety of automotive body structures. However, due to the different thicknesses or strengths of TWBs base materials and the presence of weld and heat affected zone, TWBs forming technology is very different from the conventional single sheet. There are many new technical issues of TWBs forming which have not been well solved, such as the TWBs laser welding, the welded zone impact on the TWBs forming result, forming limit and other problems. Therefore, it is very significant to research on the laser welding processing, the elastoplastic mechanical properties of the weld and heat affected zone metals determining, the forming limit of TWBs obtainning and the deep drawing controlling.Firstly, the influence of different welding power and welding speed on the macro quality of laser welded joint of TWBs were studied, the reasonable welding parameters were given, and then the quality inspection of laser welded joint of TWBs were carried out based on the microstructure analysis and micro Vickers hardness test. The average and non average elastoplastic mechanical properties measurement model of TWBs weld and heat affected zone metals were built using “small size” TWBs specimen uniaxial tensile test, rule of mixture and nanoindentation technology. The Erichsen cupping tests were conducted by combining numerical simulation with physical experiment, which compared the effect on the forming results of TWBs when the elastoplastic mechanical properties of the weld and heat affected zone metals neglected or considered.Based on the elastoplastic mechanical properties of the weld and heat affected zone metals obtained by a nanoindentation test, a theoretical calculation model was established for the forming limit of TWBs of the same materials with same thicknesses on the basis of plastic constitutive relations and Hosford yield criteria. The GTN(Gurson-Tvergaard- Needleman) damage model was established to predict the forming limit of TWBs of different thicknessed by the finite element software ABAQUS and coupled the Mises yield criterion with GTN damage model. Experiment of hemispherical punch bulging test was designed, which changed specimen width to obtain the complete forming limit diagram of TWBs in different strain condition. Meanwhile, the prediction and experimental results were compared to validate the accuracy of forming limit prediction model.The finite element numerical simulation model of TWBs square box deep drawing forming was established, which considered the elastoplastic mechanical properties of the weld and heat affected zone metals and set the TWBs forming limt diagram as the cracked criterion of TWBs square box deep drawing forming. The blank holder force influenced on the deep drawing limit, weld line movement and side wall wrinkling(for the class of square shaped cone wall components) was analyzed during the TWBs square box deep drawing forming, and then the better blank holder force loading curve was given.Artificial neural network was introduced, the main influence factors in the process of TWBs square box deep drawing forming were analyzed, and the better blank holder force artificial neural network prediction model was established for the TWBs square box deep drawing forming. The training samples of neural network prediction model were constructed based on the orthogonal experimental design and finite element numerical simulation. Thus, the accurate blank holder force control law was realized.Finally, the experimental system of TWBs square box deep drawing forming was developed. In the deep drawing variables of P(drawing pressure), Q(blank holder force) and h(drawing stroke) acquisition experiments, LabVIEW virtual instrument and technology were used for the data acquisition system of TWBs square box deep drawing forming experiment. The mould of TWBs square box deep drawing forming was designed, the thickness ratio, blank holder force and mould parameters impacted on the forming results of TWBs square box deep drawing forming were also discussed.