Lightweight joining of polymer and polymer-metal sheets by sheet- bulk forming I.M.F. Bragança a , C.M.A. Silva b , L.M. Alves b , P.A.F. Martins b, * a ISEL, Instituto Superior de Engenharia de Lisboa, Instituto Polit ecnico de Lisboa, Rua Conselheiro Emídio Navarro, 1959-007 Lisboa, Portugal b IDMEC, Instituto Superior T ecnico, Universidade de Lisboa, Av. Rovisco Pais,1049-001 Lisboa, Portugal article info Article history: Received 11 November 2016 Received in revised form 3 January 2017 Accepted 9 January 2017 Available online 11 January 2017 Keywords: Joining by forming Joining of sheets Polymers Metals Experimentation Finite element analysis abstract This paper presents an environmentally friendly joining process based on sheet-bulk plastic deformation to connect two polymer (or a polymer and a metal) sheets perpendicular to one another. The method- ology draws from material characterization and finite element modelling, using an extension of the flow formulation to pressure-sensitive polymers, to experimentation in a laboratory tool setup and destruc- tive testing of the produced joints. The results allow characterization of the joinability window as a function of the major operating parameters and demonstrate the feasibility of the process to produce polymer and hybrid joints (poly- mer-metal) at room temperature. A variant to the proposed process is disclosed to handle situations where the elastic recovery of the polymer sheets needs to be better controlled. The overall content of the paper is an extension of a previous work of the authors for fixing longitudinally in position two metal sheets perpendicular to one another, and seems promising for the manufacture of lightweight joints made from polymers or polymers and metals. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction The automotive industry has been leading the way in light- weight and environmental friendly design in order to accommo- date the growing requirements of both legislation and consumers to improve fuel consumption and reduce gas emissions without compromising comfort and safety features. New applications exploiting the different properties of metals and polymers by means of composite laminate sheets are good examples of the ongoing efforts to reduce the weight of body structures, which account for 20%e30% of the total weight of standard passenger cars (Birch, 1994). In parallel to this, new joining processes based on adhesive bonding and mechanical fas- teners have also been developed to solve the technical problem of joining sheets (or assemble profiles) made from distinctly different materials (Barnes and Pashby, 2000a; Pickin et al., 2007). The development of new joining processes alternative to con- ventional and solid state welding (Barnes and Pashby, 2000b) is also related to the need of eliminating fumes and smoke in pro- duction facilities, avoiding distortions caused by the heating- cooling cycles, reducing costly and time-consuming quality in- spection procedures and assembling body structures and panels made from combination of high strength steels, aluminium alloys and composite laminates, among other materials. Despite the prominent role played by the automotive industry, the development of new processes to fabricate lightweight and recyclable products is a major trend across the entire manufacturing sector ranging from all types of vehicles to ma- chines, furniture and architectural applications, among other applications. This paper is built upon the above mentioned trends and chal- lenges and is aimed at investigating the utilization of a new me- chanical joining process to connect two polymer (or polymer and metal) sheets perpendicular to one another, at room temperature. The new process is based on joining by plastic deformation (Mori et al., 2013; Groche et al., 2014) and its environmental friendly characteristics are due to the avoidance of addition materials or adhesives and to the ease of disassemble at the end of life. In fact, the new proposed joint only involves two parts to take apart allowing recyclability of the polymer (or polymer and metal) sheets and enabling them to be reused. * Corresponding author. E-mail addresses: ibraganca@dem.isel.pt (I.M.F. Bragança), carlos.alves.silva@ tecnico.ulisboa.pt (C.M.A. Silva), luisalves@tecnico.ulisboa.pt (L.M. Alves), pmartins@tecnico.ulisboa.pt (P.A.F. Martins). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro http://dx.doi.org/10.1016/j.jclepro.2017.01.049 0959-6526/© 2017 Elsevier Ltd. All rights reserved. Journal of Cleaner Production 145 (2017) 98e104