Sheet Metal 2007

Paper Title Page

Authors: Xiao Cong He, Ian Pearson, Ken W. Young
Abstract: Self-pierce riveting (SPR) is nowadays widely used in the car manufacturing industry where aluminium alloys are used for body construction. For the design of mechanical structures, formed by the joining of component parts, a knowledge of the vibration characteristics of different joint types (adhesive bonding, spot welding, SPR etc) is essential. The free transverse vibration characteristics of single lap-jointed encastre SPR beams are investigated theoretically in this paper using the three dimensional finite element method (FEM). Numerical examples are provided to show the influence on the natural frequencies, natural frequency ratios and mode shapes of these beams caused by variations in the material properties (E and υ) of the sheet material. It is shown that the transverse natural frequencies of single lap jointed encastre SPR beams increases significantly as the Young’s Modulus of the sheets increases, but only slight changes are encountered for variations of Poisson’s Ratio. It is found that an exponential curve gives an acceptable fit to the relationship between natural frequency and Young’s Modulus. As expected, odd modes shapes were found to be symmetrical about the mid-length position and even modes were anti-symmetrical.
Authors: Eleonora Atzeni, Rosolino Ippolito, Luca Settineri
Abstract: The present paper aims at defining a numerical tool for the efficient design of the selfpiercing riveting process by means of FE simulations. Abaqus Explicit v.6.4 software has been used to establish a model for 3D simulation of the joining process and of the shearing test on the riveted joint, in order to understand the joint formation and failure mechanisms. The obtained indications have been validated experimentally through joint sectioning and comparison between real geometry and numerical results. Furthermore, shear tests have been performed to compare the experimental and numerical results in terms of joint resistance.
Authors: Xiao Cong He, Ian Pearson, Ken W. Young
Abstract: Self-pierce riveting (SPR) is a sheet material joining technique which is suitable for joining dissimilar materials, as well as coated and pre-painted materials. Published work relating to finite element analysis of SPR joints is reviewed in this paper, in terms of process, static strength, fatigue strength, vibration characteristics and assembly dimensional prediction of the SPR joints. A few important numerical issues are discussed, including material modelling, meshing procedure, failure criteria and friction between substrates and between rivet and substrate. It is concluded that the finite element analysis of SPR joints will help future applications of SPR by allowing system parameters to be selected to give as large a process window as possible for successful joint manufacture. This will allow many tests to be simulated that would currently take too long to perform or be prohibitively expensive in practice, such as modifications to rivet geometry, die geometry or material properties. The main goal of the paper is to review recent progress in finite element analysis of SPR joints and to provide a basis for further research.
Authors: C. Borsellino, G. Di Bella, V.F. Ruisi
Abstract: The efforts of new automotive industry are mainly directed towards the substitution of aluminum for steel in the body structure because the aluminum structures are lighter than traditional steel ones and meet the requirements, in terms of both vehicle design and manufacture. However, this substitution is not so automatic, but it is important to study the material properties and the structure design, focusing the attention on the methods of joining. Welding, typical technique to joint steel parts, is particularly difficult when applied on aluminum ones and then, in many cases, the adhesive bonding is preferred. To optimise the joint performances it is necessary to pre-treat the metal surface, not only to remove contaminants, but also to provide the intimate contact needed for the adhesive to successfully bond with the adherent surface. The mere cleaning of aluminum surfaces is not suitable for their bonding due to the oxide layer that naturally occurs on exposure to air so we need to apply a more effective treatment (mechanical or chemical etching) to increase the adhesion capability of the substrates. In this work different adhesive joint configurations (single lap) between aluminum substrates are studied. Two different resins are employed to evaluate the influence of the adhesive on the joint performances. Moreover the aluminum sheets are treated with a chemical etching with two different procedures.
Authors: Hartmut Hoffmann, Christoph Hein, Seok Moo Hong, Hyun Woo So
Abstract: The increasing individualization of products assigns manufacturing companies to new tasks like manufacturing various products in a more efficient way. This progression in the market leads on the one hand to a new product design and on the other hand to an improved production process. Both are necessary to reduce assembly, service and recycling costs. Hence the joining technology is and will become more and more important. The conventional joining technologies like welding, bonding, bolting or clamping have their own disadvantages especially in the field of flexibility. In order to reduce the effort for assembling and disassembling by retaining the requirements of the connection a new innovative joining technology is needed. In this study a new joining technology is introduced to become faster and more flexible in assembling and disassembling. The basic idea of this manufacturing technology comes from a “metal hook and loop fastener”. A hook and loop fastener consisting of metal has a lot of advantages for the fields of industrial assembly, service and recycling. Similar to the synthetic hook and loop fastener a metal one is characterized by easy closing and opening without special tools. And in comparison to the synthetic hook and loop fastener the transmissible forces are very high. An additional benefit can be gained for instance in shock absorbing or resistance against chemical and thermal influence. Two solutions are followed up to invent the “metal hook and loop fastener”. A one-to-one copy of the conventional hook and loop fastener is constructed in metal and specific solutions for the use of metal are tested. A conventional finite element program was used in order to optimize the construction of a metal cocklebur and the results show a good agreement with the experiment.
Authors: C. Borsellino, G. Di Bella, V.F. Ruisi
Abstract: In this paper a development of clinching, called flat clinching, is presented. After a press clinching process, the joined sheets have been deformed by a punch with a lower diameter against a flat die. In this way a new configuration is created with a geometry that has no discontinuity on the external surface (bottom). A new procedure has also been tested: the second step is perfomed by pressing the joint between two flat dies. This second case has revealed itself to be very effective.Tensile tests have been done to compare the joints strength among the various joining techniques. Moreover some joints have been cut to analyse the changing of the contact line shape and how its characteristics parameters can influence the bonding performances. To optimise the process a finite element analysis has been performed.
Authors: Reimund Neugebauer, Stephan Dietrich, Christian Kraus
Abstract: Joining by forming of magnesium alloys is restricted by the limited forming capability of magnesium at room temperature. For this reason heating of the parts to temperatures of 220 °C or more is required to form connections without cracks. State-of-the-art joining by forming methods (such as clinching or self-pierce riveting) are usually working with a contoured die as a counter tool. Researches on these joining methods have shown that a minimum heating time of 3 to 6 seconds is needed to achieve connections of acceptable quality. New joining by forming methods working with a flat anvil as counter tool make it possible to decrease the heating time considerably. In this paper two methods – the dieless clinching and the dieless rivet-clinching – and their potential for the joining of magnesium parts shall be introduced in detail. The results of extensive research on the influence between heating parameters and the formation of the connections as well as the results of tensile test done to characterize the strength of dieless joined connections are discussed.
Authors: Riccardo Bini, Michele Monno
Abstract: A numerical model of the electric arc is coupled to a model for the convective flow in the molten pool of a stainless steel sheet during a stationary TIG welding process. This approach allows us to predict the shape of the bead, which is determined by the balance between the Marangoni forces on the free surface and the radial drag from the arc jet impingement. The surface tension of the molten steel is greatly influenced by its temperature and sulphur content, as experiments showed very different bead shapes associated to the same welding parameters. We simulate three sulphur contents, namely 10 ppm, 40 ppm and 100 ppm, showing their effects on the velocity and temperature distributions in the molten pool. A transition between drag-dominated and surface tension-dominated pools is found at a sulphur content of few dozens, in agreement with previous experimental observations.
Authors: Fabrizio Quadrini, Loredana Santo, Federica Trovalusci
Abstract: In the present study the use of diode laser for stainless steel aesthetic welding is considered. In fact the surface smoothness of the weld bead, attributed to the mode stability of the laser system, suggests its application for aesthetic weld joint. The aims of this work were to: define a process map, based on an aesthetic criterion; mechanically characterize the weld joints (by Vickers micro-hardness and tensile test); analyse the surface of the specimens in terms of roughness. Moreover, gas tungsten-arc (TIG) weld joints were carried out and analogously tested to make a comparison with the diode laser results. Good aesthetic butt joints were obtained with diode laser welding. The same results were found working with constant power speed ratio (i.e. constant fluence). Comparison between TIG and Laser Beam Welding (LBW), showed no significant difference in roughness, while ultimate tensile load was higher for TIG welding. The differences in joint strength depend on the different cross-sectional area and on the extension and microstructure of the base metal, heat-affected zone and melted zone. However, diode laser technology allows to obtain smaller bead size.
Authors: Giuseppe Casalino, Abdul Ghani Olabi, N. Cipriani, A. Rotondo
Abstract: The residual stress in steel welding can highly influences the performance of the joint during its working life. Both boundary conditions and metal phase transformations have influence on the levels of the residual stress in the weld. In this paper the residual stress for AISI 4047 bead-on-plate samples were measured by strain gage method after laser welding with different values for the laser speed and power, and focus height. The laser used for this project was the ROFIN DC 015 Industrial CO2 Slab Laser. This laser, registered as class 4 laser product in accordance with the European Norm EN 60825 is an high frequency excited, diffusion cooled C02 gas laser, designed to be used for processing materials in a industrial environment. The measurement procedure was performed on all the welded specimens taking notes of 3 strains (ε1 ε2 ε3) relative to as many gages at different depths, following the American Society for Testing Materials (ASTM) standard. Thereafter the residual stresses were calculated by means of a non-linear finite element analysis. The analysis took in account the thermo-mechanical phenomena with temperature dependent steel properties. The other considered also the phase transformation and phase-dependent thermal and mechanical properties.

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