Wall thinning behaviors of high strength 0Cr21Ni6Mn9N tube in numerical control bending considering variation of elastic modulus

Jun Fang,Shiqiang Lu,Kelu Wang,Xuguang Min,Fang Ouyang,Botao Xiao

doi:10.1177/16878140211021241

Abstract

Wall thinning, as one of the key defects in tube bending determined the forming quality and limit, is more easily to occur due to the specific properties of high strength 0Cr21Ni6Mn9N stainless steel tube (0Cr21Ni6Mn9N-HS tube). To achieve tube accuracy numerical control (NC) bending forming, the wall thinning characteristics of the 0Cr21Ni6Mn9N-HS tube should be clarified. An analytical model was proposed to reveal the essential relation between tube parameters and wall thickness distribution. Considering the varied elastic modulus, a finite element (FE) model was applied to explore the wall thinning under different geometrical and process parameters. Using the modified multi-parameter sensitivity analysis method combined with FE simulation, the sensitivity of the wall thinning to geometrical and process parameters was carried out. The experiments of NC tube bending were conducted to validate the analytical and simulate results. The results show that the varied elastic modulus can enhance the wall thinning degree, but has no obvious effect on wall thinning characteristics. The wall thinning characteristics under different geometrical and process parameters are revealed and the reasonable parameters ranges for the 0Cr21Ni6Mn9N-HS tube in NC bending are obtained. The most sensitive parameter on wall thinning is the relative bending radius, while the bending angle is the least one.

Highlights

Metallic tube and tubular parts play a crucial part in many key industrial fields as ‘‘bleeding’’ transforming because of their special characteristic of hollow structure and excellent whole performance.[1]
To obtain reasonable bending forming parameters, the wall thinning behaviors of the 0Cr21Ni6Mn9N-HS tube in numerical control (NC) bending considering the variation of elastic modulus under different forming conditions should be clarified
The results are of great theoretical significance and practical application value to achieve the tube precision NC bending forming

Summary

Introduction

Metallic tube and tubular parts play a crucial part in many key industrial fields as ‘‘bleeding’’ transforming because of their special characteristic of hollow structure and excellent whole performance.[1]. On the basis of the geometrical characteristics of tube bending and plastic deformation theory, the theoretical model of wall thinning for thin-walled tube bending was established by Li et al.[6] Using the plastic deformation theory, Lu et al.[7] presented several analytical formulae with respect to stress, neutral layer deviation, wall thickness variation and cross section distortion to explore the phenomena of tube bending. By finite element (FE) numerical simulation method, Fang et al.[13] addressed the effects of geometrical parameters on wall thickness variation and cross section distortion of high strength TA18 tube during NC bending. For the 0Cr21Ni6Mn9N-HS tube bending, Fang et al.[18] established a three dimensional (3D) elastic plastic FE model of the 0Cr21Ni6Mn9N-HS tube in NC bending and explored the influences of friction conditions[19] and mandrel parameters[20] on wall thinning and cross section distortion. According to the Hencky total strain theory including elastic strain and assumption (2), the stress-strain relationship in the plastic deformation region can be written as:

À 2 sc

Evaluation of theoretical and FE models

Conclusions