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

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.

Wall thinning characteristics and prediction in numerical control bending of high strength Ti-3Al-2.5V tube

“…This is because that the hoop strain is considered for the theoretical models in this study, which is more in line with the tube practical bending process, while that is neglected in literature. 4 As observed in Figure 2(b), the theoretical results of wall thinning ratio both in this study and in literature 4 maintain a constant with increasing the bending angles in the whole bending process. The main reason is that the theoretical model of wall thinning ratio is independent of the bending angle.…”

“…In Table 6, the critical value F 1-α (f F , f E ) with significant level α of 0.1, 0.05, and 0.01 can be found out via the F distribution table, where f F is the degree of freedom for factor, f E is the degree of freedom for error. If F ≥ F 1-0.01 (2,4), it means that this factor is highly significant, and marks "**". If F 1-0.05 (2, 4)≤ F < F 1-0.01 (2,4), indicating that this factor is significant, and marks "*".…”

“…Until now, many studies about wall thinning characteristics of tube bending have been conducted by theoretical, experimental, and numerical method. Fang 4 deduced a theoretical model of wall thinning in tube bending based on plane stress and plane strain hypothesis. E and Li 5 derived a theoretical formula of wall thickness variation during tube bending according to plane strain hypothesis with considering the extra tensile force and the working way of the NC tube bender.…”

Numerical Study on Plastic Strain Distributions and Mechanical Behaviour of a Tube under Bending

“…In another investigation, Liu et al [47] conducted an experiment on the aluminium alloy 3A21 tubular pipe of a rectangular thin-walled cross-section and AM30 magnesium alloy tube to ascertain its cross-section distortion and the influence of production/bending die with vital factors affecting the distribution of wall thicknesses throughout the bending activity from numerical control bending. The bending of tubular sections to get an elbow can be described as a metal-plastic flow process which was carried out using similar process bending parameters [49][50][51][52][53][54]. Guo et al [55] conducted an investigation to examine the formability influence and increased axial tensions on equivalent curvature-diameter bending, excluding mandrels on 0Cr18Ni9 stainless steel tubes.…”

Mechanical Modeling of Tube Bending Considering Elastoplastic Evolution of Tube Cross-Section

“…Meanwhile, Li et al established a hybrid analytical–numerical model based on axial force balance to analyze the neutral layer shifting (NLS) phenomenon in the process of tube bending and thus proposed an innovative process to improve bend formability by analyzing the equilibrium conditions of bending moment and force in the process of tube bending [ 12 ]. They also constructed another method for calculating the radius of the neutral layer [ 13 ], and this method was used by Fang Jun et al [ 14 ] to analyze the thinning behavior of the 0Cr21Ni6Mn9N tube. Moreover, to improve the tube geometry, mechanical properties, and formability, an integrated machining strategy was proposed by Ma et al, which integrates cold bending operations and heat treatment, and the expected dimensional accuracy and mechanical properties were achieved [ 15 ].…”