Joining by sheet-bulk forming of tubes to sheets

Abstract This paper presents a new joining by forming process for connecting tubes to sheets that is carried out in two stages; (i) forming of an annular flange with rectangular cross section by partial sheet-bulk of the tube wall thickness and (ii) mechanical interlock by upsetting of the free tube end against a counterbored (flat-bottomed) sheet hole. The process allows connecting tubes to sheets made from dissimilar materials without protrusion of the tube end above the sheet surface, avoids the utilization of addition materials or adhesives, and produces joints that are easy to disassembly at the end of live, allowing recyclability of the tubes and sheets. The paper identifies the main variables and workability limits of the process and presents an analytical model to assist readers in the design of the new proposed type of joint. The analytical model is built upon volume incompressibility and fundamental concepts of plastic instability (buckling) and cracking. Experimentation and finite element modelling are utilized to validate the process and the corresponding analytical model.