Evaluation of plastic formability of layered metal sheets bonded by adhesives using conical cup testing

Abstract

Adhesive bonding is the preferred method for joining dissimilar materials owing to the low weight of adhesives. To evaluate the application of adhesive bonding to multi-materialization, in this study, we used conical cup testing as an integrated formability test method to assess the forming limit of bonded multi-layered metal sheets, comparing them with the equivalent unitary sheets. The conical cup testing equipment used in this study was designed and produced based on JIS Z 2249, with a viewing port that can be used to observe the deformed bottom of the specimens during the conical cup test. Multi-layered specimens composed of aluminum (Al) and steel (steel plate cold-rolled commercial (SPCC) steel) layers were produced using acrylic and epoxy adhesives, and single-(material)-layered specimens composed of layers of the same material were also produced. In addition, the unitary specimens of the materials without any bonding were examined as reference materials. The experimental results showed that the forming limits of the single-(material)-layered Al specimens (pure aluminum A1050 and aluminum alloy A5052) were nearly identical to those of the unitary specimens. Therefore, the use of the adhesive improved the formability of the Al sheet to that of the corresponding unitary specimen with twice the thickness. The results of the A5052-SPCC multi-layered specimen bonded by acrylic adhesive were compared with those of the SPCC unitary specimen, and its forming limit increased by 35% with a notable 33% reduction in weight, demonstrating the enhanced performance of the multi-layer structure. The reason for the improvement in formability may be the suppression of the abrupt increase in surface roughness, which otherwise leads to plastic instability.

Keywords

• multi-layered metal sheet
• adhesive
• conical cup test
• plastic formability
• aluminum
• steel