Joining Strategies for Double-Sided Self-Pierce Riveting

Abstract

Double-sided self-pierce riveting (DSSPR) has been presenting itself as a proper alternative to self-pierce riveting (SPR) with many advantages for joining geometries of different thicknesses and cross-sections. To ensure its successful future industrial application, this paper presents a detailed comparison between different strategies to produce mechanical joints by means of the DSSPR process and discusses its performance and feasibility. Results show that the use of flat-bottom holes in both sheets provide interesting results, since they allow for a precise positioning of the tubular rivet in specific pre-defined locations, thus avoiding an incorrect joining procedure. This strategy tightens the tolerances of the process, while keeping a suitable level of destructive performance as demonstrated by the lap shear tests. Pre-riveting of the sheet has also been shown to produce suitable results in combination with or without a flat-bottom hole in the opposite sheet. This strategy comes at a cost of a slightly lower performance than that obtained with flat-bottom holes in both sheets, although the requirements of force and energy to complete the joining process are smaller. The conclusions of this research work are essential for selecting the joining strategy with DSSPR according to the requirements of the intended application.

Double-Sided Self-Pierce Riveting: Electro-Mechanical Analysis of Dissimilar Al-Cu Half-Lap Butt Joints

“…The joining process was performed in a single or a double stroke at room temperature, either by placing the rivet directly between the sheets and compressing them into each other or by pre-riveting the harder copper sheet and then riveting the aluminium sheet in a secondary stage. This produced significant differences, as predicted by the work previously carried out by the authors in [6,7], and it will be further discussed in a following section. Some joints were cut lengthwise to measure the parameters of the deformed rivet that are presented in Figure 2, such as the final height h and diameter d and the resulting mechanical interlocking i.…”

“…Due to the larger resistance of the copper material, the amount of rivet penetration in that sheet was very reduced in comparison with the aluminium sheet (Figure 4a). In fact, during the joining process, the rivet is unable to penetrate the copper sheet at the same rate of the aluminium sheet, and, in turn, the amount of penetration at the aluminium side becomes higher until a point where the strain hardening levels produced in the aluminium sheet force the rivet to flare [6,7]. This resulted in a weaker joint, not only in terms of its mechanical resistance but also in terms of the electrical resistance, since under these conditions, proper contact between the sheets and rivet was not guaranteed.…”

“…The average results of these destructive tests are shown in the graph of Figure 6, where it can be observed that after a maximum force of approximately 5.2 kN, the separation of the joint started to occur. For reference purposes, an Al-Al riveted joint made from sheets with a thickness of 1.5 mm withstands a maximum force of around 2.2 kN [8], while for sheets with a thickness of 5 mm, the maximum force is around 10.2 kN [6]. Since a thickness of 2.5 mm is here subjected to tensile loads and the detachment occurs in the aluminium sheet, the maximum force value registered is in accordance with the expected performance of the DSSPR process.…”

“…This strategy allows us to combine the advantages of both lap and butt joints, since it extends the contact surface between the materials, which is limited to the side walls of the sheets for butt joints, while it allows the creation of a seamless upper and lower surface without protrusions, as is normally verified for lap joints, which, in turn, are able to offer a larger contact region and additional contact points between the sheets. Double-sided self-pierce riveting (DSSPR) has been investigated by the authors in recent years, and different joining strategies have been developed [6] to handle different combinations of materials [7] and thicknesses [8]. As the name implies, a double-sided tubular rivet is employed to produce a mechanical joint between sheets (Figure 1a).…”

Performance analysis of similar and dissimilar self-piercing riveted joints in aluminum alloys

“…21 The prediction of blocking value and bottom residual thickness of the molded joint through Back Propagation neural network are also known. 22 At present, the method of evaluating the quality of riveting is mainly used through the tolerance band method of the force-displacement curve. 23 However, the tolerance band formed by the upward and downward displacement of the qualified joint force-displacement reference curve is not only insensitive to lateral displacement, but also cannot monitor rivet offset, button cracking, and joint cracking.…”