Numerical and experimental study on the layer arrangement in the incremental forming process of explosive-welded low-carbon steel/CP-titanium bimetal sheet

In this paper, the effect of layers' arrangement of explosively welded low-carbon steel/commercially pure titanium (St/CP-Ti) bimetal sheet has been investigated in the single point incremental forming process (SPIF) experimentally and numerically. The main reason to carry out such a process is taking the advantages of materials with different properties, such as high strength, low density, low price, and corrosion resistibility, at the same time and in a single component. The composite sheet behavior in a forming process differs from single-layer sheets and depends on the layers' arrangement and thicknesses. In this regard, the effect of layers' arrangement on the forming behavior of (St/CP-Ti) bimetal sheet is of particular interest in the present study. Therefore, several tests were conducted to investigate the influences of some variables, such as layers' arrangement and different vertical steps down on the variations of force versus time diagram. Based on the obtained results, the arrangement of Ti-St showed a higher forming force than St-Ti, and the force difference between two arrangements increased with an increase in vertical steps down; as for vertical steps down of 0.1, 0.2, and 0.3, the force difference for the two arrangements was about 8, 15, and 25%, respectively, which showed good agreement with the FEM results. Also, microstructural studies showed that the twin density in the structure would differ, such that the twinning density of titanium layer in Ti-St mode was increased more than twice as much as the St-Ti mode and therefore would show more work hardening during the deformation, which was considered as a factor for the force difference in both types of arrangements. Also, the scanning electron microscope studies of the formed specimen's surfaces showed a better surface quality in the samples with the St-Ti arrangement, which is due to the titanium sticking friction with the forming tool that causes in the samples with the Ti-St arrangement.