Research on strain distribution of thin-walled tube in NC bending process using grid method

Applying the grid method, the distribution laws of the tangential, hoop and normal strains of LF2M and lCrl8Ni9Ti tube with φ50 mm × l mm × R100 mm (out diameter × wall thickness × bending radius) have been investigated in the NC bending process. The results show the following: The tangential strain at the extrados of LF2M tube is larger than that of lCr18Ni9Ti tube, but the tangential strain at the intrados of LF2M tube is smaller than that of lCrl8Ni9Ti tube, which leads to that the thinning ratio at the extrados of LF2M tube is larger than that of lCrl8Ni9Ti tube and the thickening ratio at the intrados of LF2M tube is smaller than that of lCrl8Ni9Ti tube. In the NC bending process of thin-walled tube with small bending radius, the maximal hoop strain can reach 1/3 of the tangential strain and can not be neglected. With the bending angle increasing, the tangential, normal and hoop strain increase, but the increasing amplitude of hoop strain is smaller than the others. The thickness change at the extrados of LF2M tube is larger than that at the intrados and as to lCrl8Ni9Ti tube the thickness change at the two position is almost equal, because the tangential strain at the extrados of LF2M tube is larger than that at the intrados and the tangential strain in the two position of lCrl8Ni9Ti tube is almost equal.