Plastic bending of adhesive-bonded sheet metals

doi:10.1016/S0924-0136(01)00637-9

Journal of Materials Processing Technology

Volume 113, Issues 1–3, 15 June 2001, Pages 743-748

https://doi.org/10.1016/S0924-0136(01)00637-9 Get rights and content

Abstract

Adhesive bonding is becoming one of the popular joining techniques in sheet metal industries, since it has some advantages over other techniques such as welding and diffusion bonding, e.g., any dissimilar metals are easily adhesive-bonded together, and the adhesive layer existing between the two sheet metals can play the role of vibration damping. Usually, press-formed sheet metal elements are jointed together at the final stage of assembly. However, if it could be possible to press-form adhesive-bonded flat sheet metals into the final products, this would be an excellent technique from the viewpoint of high productivity.

In the present work, the plastic bending of adhesive-bonded sheet metals was investigated by performing V-bending experiments. A serious problem encountered in the V-bending was bending-induced large transverse shear deformation of the adhesive layer, which leads to geometrical imperfection of the bent sheets (so-called ‘gull-wing’ bend), and in some extreme cases, it causes the delamination of the sheet. It was found both from experimental observations and from elasto-plastic stress analysis that the large shear deformation progresses rapidly only at the final stage of V-bending. Consequently, the air-bending operation for adhesive-bonded sheet metals is recommended for suppressing the shear deformation of the adhesive layer to within an acceptable limit.

Introduction

Recently, several types of high strength adhesives have become available for assembling structural elements, consequently, adhesive bonding is being used increasingly in many fields of industry. Adhesive bonding has several advantages over other joining techniques such as welding and diffusion bonding, e.g., any dissimilar metals are easily bonded together, and there is no need to care about the thermal strain which is often induced by welding, and moreover, the adhesive layer can play the role of vibration damping.

In the sheet metal industries, press-formed sheet elements are usually adhesive-bonded together at the final stage of assembly. Instead of such a conventional process, if it could be possible to make the process sequence inverse in such a way that first flat sheets are adhesive-bonded together and then press-formed into the final products, it would be an excellent technique from the viewpoint of high productivity.

However, in this new process, some difficulties may be encountered, i.e., delamination and geometrical imperfection of the sheets, caused by large shear deformation of the adhesive layer. Concerning a similar problem, some original papers [1], [2], [3], [4], [5] and also review papers [6], [7] on the plastic forming of metal–resin composite sheets have been published, however, to the authors’ knowledge, they dealt with overall-laminate sheets, and not with partially lapped (adhesive-bonded) sheets.

In the present work, it was investigated whether it would be possible to use this new technique of the press-forming of adhesive-bonded sheet metals in real operations, by performing V-bending experiments, as well as by numerical simulation. The mechanism of shear deformation of the adhesive layer in the course of bending, and also the bending conditions for suppressing the large shear, will be discussed.

Section snippets

Mechanical properties of the adhesive and the sheet metals

The adhesive employed in the present work was an acrylic adhesive M-372-20 Hardrock (Denki Kagaku Kogyo). This adhesive has high ductility as well as high strength of the same level as conventional epoxy adhesives. An aluminium alloy sheet (A5083P-0) of 1.0 mm thickness and mild steel sheet (SPCC) of 0.8 mm thickness were used.

The stress–strain curves obtained from uniaxial tension tests for the aluminium alloy and the mild steel are shown in Fig. 1. The stress–strain relationship for both of the

Numerical analysis

In order to determine an appropriate bending condition for a given specimen, it is of vital importance to predict quantitatively the stress and strain induced by bending. The experimental results shown in Section 2 indicate that air-bending is more suitable than die-bending for adhesive-bonded sheets, therefore, the present analysis was restricted to air-bending.

The idealized model of deformation of each layer of a bonded sheet is illustrated in Fig. 9(a) and (b). For the deformation of face

Results and discussions

From the numerical simulation, much important information will be provided for determining appropriate bending conditions, such as the lap length and die-span, for a given adhesive and sheet metals.

Fig. 12(a) and (b) shows the numerical results for the distribution of shear strain in the adhesive layers, together with the corresponding experimental results on the adhesive-bonded aluminium alloy sheet (A5083 in Fig. 12(a)) and the mild steel sheet (SPCC in Fig. 12(b)). The numerical results are

Concluding remarks

In the present paper, whether it is possible to perform the V-bending of adhesive-bonded sheet metals was investigated. In some cases, large shear deformation occurred in the adhesive layer, which sometimes lead to delamination and geometrical imperfection of the sheets. However, if an appropriate choice of the bending conditions is made, the large shear deformation can be suppressed.

The deformation characteristics found in V-bending experiments, as well as from the numerical simulation, for

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