Experimental study on cross-section ovalization of thin-walled tube in NC bending process

Cross-section ovalization is one of the flaws in the thin-walled tube NC bending process. The effects of some parameters, such as mandrel ball numbers, mandrel extension length, bending angle, lubrication condition of pressure die, relative bending radius and material, on ovalization have been investigated by experimental method, and the effective methods to reduce the ovalization are proposed. The results show that increasing the ball numbers and mandrel extension length may reduce the ovalization, but leads to more remarkable wall thinning; the ovalization becomes more severe with the larger bending angle; the smaller the relative bending radius, the larger the ovalization is; the ovalization and wall thinning degrees are both smaller in the case of pressure die with dry lubricant; and under the same bending condition, the ovalization of LF2M tube is larger than the one of 1Cr18Ni9Ti tube.