Strain distribution characteristics of welded tube in NC bending process using experimental grid method

To understand the reason of defects and the basic mechanics involved in the welded tube numerical control bending process, it is important to study the effects of the weld and processing parameters on the strain distributions of the tube. The grid method that combines with vision-based surface strain measurement system GMASystem is used to research the strain distributions of the bent tube experimentally. The results show that the weld has a limited effect on the strain evolution as the weld is not located in the region of locally highest strains. As the weld line locates on the outside, the maximum tangent and thickness strain decrease by 0.94 and 8.78 %, while the maximum hoop strain increases by 22.15 % as compared with that the weld line locates on the middle. As the weld line locates on the outside and inside, the thickness strain decreases obviously in the weld region. The variation of thickness strain is little with smaller mandrel extension length, and the maximum thickness strain increases by 21.38 % as the extension length changes from 6 to 10 mm. The thickness strain decreases with larger push assistant level. The maximum thickness strain increases with larger bending angle.