Journal of Manufacturing Processes 31 (2018) 812–822 Contents lists available at ScienceDirect Journal of Manufacturing Processes j ourna l ho me pa g e: www.elsevier.com/locate/manpro Friction-assisted clinching of Aluminum and CFRP sheets Francesco Lambiase a,b,∗ , Alfonso Paoletti a,b a Dept. of Industrial and Information Engineering and Economics, University of L’Aquila, via G. Gronchi 18, Zona Industriale di Pile, 67100 (AQ), Italy b University of Naples Federico II, CIRTIBS Research Centre, P.le Tecchio 80, 80125 Naples, Italy a r t i c l e i n f o Article history: Received 16 July 2017 Received in revised form 13 January 2018 Accepted 13 January 2018 Keywords: Mechanical fastening Joining Aluminum alloy Composite materials Clinching CFRP Formability Forces a b s t r a c t The employment of a rotating tool when joining thin aluminum sheets with Carbon Fiber Reinforced Polymer (CFRP) laminates by means of clinching is investigated. This new process, named friction-assisted clinching, was aimed at increasing the aluminum formability and at the same time reducing the joining forces. An instrumented servo-drilled machine was employed to measure the plunging force and torque during the joining process. The influence of the main process parameters (hole diameter in the CFRP sheet, die anvil depth, tool fillet radius and residual sheet thickness) on quality of the joints and strength was determined. Morphological analysis and mechanical characterization based on single lap shear tests were performed to evaluate the difference among the joints. According to the achieved results, the employment of friction clinching allowed increasing dramatically the material formability and enabled the production of joints without fractures even with sharp pin tools. The advantages of this advanced joining process can be potentially applied to conventional clinching of materials with poor ductility either friction clinching allows increasing the undercut dimension by using sharper tools, which produces higher material flow and leads to an increase in the joint strength. © 2018 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved. 1. Introduction Multi-material assemblies and joining processes of such hybrid structures are gaining increasing interest due to the growing employment in different fields including automotive and aircraft industries, civil structures, medical devices, etc. In these assem- blies, the characteristics of the materials, differing by physical, mechanical, and technological behavior are exploited to improve the overall performance. These structure often involve metals, polymers and composite materials (with both thermosetting either thermoplastic materials). Because of the great difference among these materials, welding processes, which require that the materi- als show similar chemical structure and thermal properties (such as the melting points), are not generally suitable for theis purpose. Adhesive bonding and mechanical joining processes are often involved for this scope. Mechanical joints are characterized by high static and dynamic load capacity and do not require extensive sur- face preparation with exception of preliminary drilling of both the sheets. The drilling process and the adoption of external fasten- ing element (such as screws or rivets) involve time-consuming and costly preliminary work, require additional material (the ∗ Corresponding author at: Monteluco di Roio, 67040 (AQ), Italy. E-mail address: francesco.lambiase@univaq.it (F. Lambiase). connecting element), and increase the structure weight. In addition, hole-drilling may come with damage of the composite material, fiber interruption, and stress concentration. Despite of mechan- ical joining processes, in adhesive bonds the load is distributed over the entire overlapping area [1–3]; in addition, the absence of holes lead to lower stress concentration. Nevertheless, adhe- sive bonds are often characterized by a reduced elongation at break, usually smaller than 10% [4–6] and catastrophic failure. In addition, the long curing time and surface preparation (includ- ing etching, grinding, and degreasing), result in long processing time, high environmental impact and low standardization of the mechanical behavior. To overcome the above-mentioned limita- tions, the industrial research is focusing on the development of new joining processes to ensure high repeatability, automatization and productivity. This represents the key step to allow the wider diffusion of such high-performing hybrid structures. To this end, three categories of new joining methods were developed namely, heat-assisted joining, thermoforming and fast mechanical join- ing processes. In heat-assisted joining processes, such as friction spot joining [7–9], friction lap welding [7,10], ultrasonic welding [11], and laser-assisted joining [12,13], the adhesion between the components is produced by melting the thermoplastic matrix of the composite on the metal substrate. On the other hand, ther- moforming joining processes e.g. friction-based stacking [14,15], infrared stacking [16,17], friction riveting [18,19], injection joining https://doi.org/10.1016/j.jmapro.2018.01.014 1526-6125/© 2018 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.