Journal of Materials Processing Technology 182 (2007) 352–357 Finite element simulations of the clinch joining of metallic sheets A.A. de Paula a , M.T.P. Aguilar b , A.E.M. Pertence c , P.R. Cetlin a,∗ a Department of Metallurgical and Materials Engineering, UFMG, Rua Espirito Santo 35, 2 o Andar, 30160-030 Belo Horizonte, MG, Brazil b Department of Materials and Construction Engineering, UFMG, Rua Espirito Santo 35, 2 o Andar, 30160-030 Belo Horizonte, MG, Brazil c Department of Mechanical Engineering, UFMG, Cidade Universit´ aria, Pampulha, Belo Horizonte, MG, Brazil Received 5 June 2006; received in revised form 19 July 2006; accepted 21 August 2006 Abstract The joining method by clinching was simulated utilizing a finite element analysis (FEA) for various punch and die geometries. The simulations covered the effect of these changes on the joint undercut and neck thickness. The relevant geometrical aspects of the punch/die set were determined. The joint separation by applying normal forces to the sheets was also simulated; since this simulation involves some sheet bending, a new method for the evaluation of the separation force was simulated, eliminating the sheet bending during detaching. The importance of an adequate undercut on the joint strength was confirmed. © 2006 Elsevier B.V. All rights reserved. Keywords: Clinching; Sheets; Finite element analysis 1. Introduction Joining of metallic sheets is fundamental in the manufac- turing of thin walled structures. Traditional joining methods involve screws, rivets or welding. Rivets and screws need a pre- vious punching or drilling of the sheets and present difficulties regarding the control of the joining pressure. Welding demands localized heating of the material, which may lead to changes in the mechanical properties of the materials. An alternate method for the joining of sheets is known as clinching [1–6], and involves a localized cold, mechanical deformation of the sheets, as illus- trated in Fig. 1 for a circular joining region. Clinching resembles a sheet forming operation; there is, however, almost no flow of the material outside the clinched region towards the joint. The initial steps of the operation thus correspond basically to the pure stretching of the material. A fundamental difference of clinching, in relation to traditional sheet metal forming, is that there is a deliberate forging of the adjacent sheets between the die and the punch at the bottom of the joint. The total thickness of the two sheets to be joined is reduced to a fraction of their initial thickness in the bottom of the joint, with typical thickness reductions of the order of 60%. The compression of the two sheets leads to a radial movement ∗ Corresponding author. Tel.: +55 31 3238 1849; fax: +55 31 3238 1815. E-mail address: pcetlin@demet.ufmg.br (P.R. Cetlin). of the material and to the filling of grooves placed in the die, as shown in Fig. 1. The final general geometry of the clinched joint is illustrated in Fig. 2, where the important features of the joint are also displayed [6]. An important characteristic of a joint is the force necessary to separate the sheets. This force depends on the neck thickness and on the undercut, displayed in Fig. 2. Thin necks will lead to sheet separations involving the fracture of the upper sheet in the neck. Small undercuts lead to low separating forces, associated with the vertical sliding apart of the two sheets. Clinched joints have been tested in two ways, as shown in Fig. 3 [4]. The detaching of the sheets (Fig. 3(a)) involves sheet bending, that facilitates the opening of the joint and the separation of the sheets. On the other hand the loading under shearing (Fig. 3(b)) is completely different from that in Fig. 3(a), and the comparison of the results of both tests can be difficult. Mota and Costa [4] have compared the performance of clinched (using TOX ® dies) and spot welded joints in low car- bon steel sheets for automobiles. The clinched joint diameter was 8 mm and the bottom of the clinched joint corresponded to a thickness reduction of 84%, with a final value of 0.2 mm. The authors employed both testing methods displayed in Fig. 3. Under shearing (Fig. 3(b)), the clinched joints were 50% weaker than the spot-welded ones. Clinched joints were 70% weaker than the spot welded ones, under detaching loads (Fig. 3(a)). Varis [1,2] tested clinched joints under shear (Fig. 3(b)) in high strength structural steel sheets of various thicknesses and 0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.08.014