Papers by Keyword: Mechanical Joining

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Authors: Miriam Tofall, Marion Merklein, Raoul Plettke
Abstract: The increasing use of new materials with varying thicknesses within the automotive industry creates high demands on joining elements such as staking fasteners. Simultaneously statements about the feasibility of the design with joining elements already in the early stage of the development are necessary. The challenge is to define suitable element geometry, tool geometry and process parameters. To meet those requirements, a good understanding of the staking process is inevitable. According to the state of the art the examinations regarding the performance of staking fasteners under different conditions are totally conducted experimentally. This trial-and-error procedure leads to an extensive financial effort and to long development times for new elements. It is furthermore not possible to observe all influences of different process parameters. In the field of mechanical engineering the use of numerical simulation for complex constructions is a common technique. This paper deals with the applicability of the finite element method (FEM) on the joining of sheet metals with staking fasteners. In this matter the FEM is used to get scientific insights in the staking process and is also used to identify influencing variables and their interactions.
273
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.
693
Authors: Qing Yun Zhao, Hong Huang, Qing Dong Xiao, Feng Lei Liu
Abstract: For 7050-T7451 plate with the thickness of 16mm, ∅6 hi-bolts were installed with 0.11mm interference by electromagnetic riveting. Split-sleeve cold expansion was employed with 4% expansion. Combine joining of 4% expansion+0.11mm interference was carried out. The effect of strengthening was estimated from microstructure, stress and fatigue life. The results show that the microstructures are the same before and after strengthened. Along the installing direction, materials flow locate near the exit. Residual compressive stresses generate by strengthening process and gradually increase by the process of interference bolted joining, split-sleeve cold expansion and combine joining, within some diameter in the exit. The fatigue lives N50 also gradually increase by the process of interference bolted joining, split-sleeve cold expansion and combine joining.
365
Authors: M. Eshteyah, Meftah Hrairi, M.S. Dawood, A.K.M. Mohiuddin
Abstract: Clinching is one of the important new joining techniques, in which two plate metal parts are locally plastically deformed by mechanical interlock. Clinching is a mechanical joining method by using simple tools that consist of a punch, a die, and a blank-holder. The shapes of these tools are the most important parameters that control the final geometry of the clinch joints which in turn strongly affect the strength and quality of the final joint. In this study, finite element simulations are carried out to investigate some of the difficulties regarding the optimization of the process parameters, and major expected geometric parameters that will influence the strength, joinability, and the quality of the joint.
109
Authors: Stefan Veenaas, Frank Vollertsen
Abstract: The ongoing trend of miniaturization makes hybrid joint also for the micro range necessary. Existing solutions often have restrictions due to the principle of joining. Therefore a new joining technology, which is realized by a plastic forming process based on TEA-CO2-laser induced shock waves, is used at BIAS. This technology enables the joining of different sheet materials with thicknesses between 20 µm and 300 µm. The manufacturing of the joint is an incremental process where several laser induced shock waves are needed to form the undercut, which presents the joint itself. For the analysis of the incremental forming behavior of this process a 50 µm thick forming sheet of aluminum (Al99.5) is joined with a 100 µm thick stainless steel (1.4301) die sheet. The first ten laser pulses are leading to relative high induced strain while for forming of the undercut 200 laser pulses are needed. The incremental induced strain per laser pulse decreases exponentially with the amount of used laser pulses. This behavior is explained by the acting pressure distribution of the induced shock wave and the contact area.
1451
Authors: Dirk Landgrebe, Mathias Jäckel, Ronald Niegsch
Abstract: The importance of environment friendly mobility strengthens the need of lightweight design in the automotive industry. New electric car models, like the BMW i3, already have car body with a high amount of carbon fiber reinforced plastics (CFRP) to allow, as a result of the low vehicle weight, appropriate ranges without reloading the battery. Methods for joining materials like CFRP play a key role to implement lightweight designs into car body production. Conventional joining methods like spot welding cannot be used for such material combinations. Due to the good automation and possible combination with adhesive, mechanical joining techniques such as self-pierce riveting (SPR) are very relevant for joining these lightweight materials. While generally self-pierce riveting of CFRP with aluminium is possible, different damages e.g. delaminations, fiber or matrix fractures in the CFRP can occur during the joining process and have to be considered. This paper shows an analysis of these process induced damages when self-pierce riveting CFRP compound with aluminum sheet metal and investigates their influence on the joint strength. In our research the conventional SPR process of CFRP-aluminium joints is compared to the application of a new die concept for SPR in which a separated die is used to reduce the process induced delaminations in the CFRP. Additionally, these joining results are contrasted to SPR joints with pre-drilled CFRP components. Through the pre-drilling the damages in the CFRP can nearly be avoided completely and so these joints can be used as a reference. The results of the three processes to produce CFRP-aluminum joints are compared by micrographs, computed tomography and strength tests.
1493
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 joints 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 joints of acceptable quality. In this paper two new clinching methods “dieless clinching” and “dieless rivet-clinching” shall be introduced. Both methods work with a flat anvil as a counter tool, thus offering important advantages for the application in joining of Mg/Mg, Al/Mg or Fe/Mg joints. In joining by forming with a flat counter tool the proportion of crack inducing tensile stresses in the bottom part during the joining process is very low. Moreover the heat transfer between the heated anvil and the parts is comparatively fast. That makes it possible to decrease the heating time in joining by forming with a flat counter tool to only one second or less. The dieless clinching process was simulated using the Finite Elements Method (FEM) to analyze the influence of geometrical parameters of the punch and the process parameter clamping force. Furthermore the limitations of the new dieless joining method were investigated.
3949
Authors: Kenichiro Mori
Abstract: As the scale and complexity of products such as aircraft and cars increase, demand for new functional processes to join mechanical parts grows. The use of plastic deformation for joining parts potentially offers improved accuracy, reliability and environmental safety as well as creating opportunities to design new products through joining dissimilar materials. This paper aims to provide an overview of the state of the art in such joining processes, including cold welding, friction stir welding, joining by forming, self-pierce riveting and mechanical clinching. The paper includes description of the mechanism of joint formation, joint strength and applicability.
29
Authors: Stefan Veenaas, Frank Vollertsen
Abstract: The ongoing trend of miniaturization and increasing function integration makes it necessary to join different sheet materials in the micro range. Conventional joining processes cannot be scaled down to smaller dimension due to so called size effects. Thermal based joining processes, like welding or brazing can lead to distortion, which are more critical in the micro range. Normally ceramic materials can only be joined using extra joining elements like glue or bolts. Laser shock joining is a promising mechanical joining process for delicate material combinations. This process usesTEA-CO2-laser induced shockwaves. Several pulses are applied at one point to achieve high forming degrees without increasing the energy density beyond the ablation limit. The laser irradiates on the forming sheet and creates a plasma plume above the surface, which leads to a shockwave. This shockwave pushes the material in the joining area and creates an undercut which presents the joint itself. The laser induced shockwave is used to create an undercut underneath the other material. The form closure between the two materials enables a joint. So far, investigations were performed to identify the process window and the joining strength for aluminum and steel joints. The influence of die sheet materials is negligible, so that this process can be used for joining of dissimilar materials like aluminum and glass. Therefore, in this paper the suitability of this process for the mechanical joining of aluminum and glass is investigated. It is found that the tools need to be adjusted for the joining process. It is shown that a mechanical joining of aluminum and glass is possible. The joining strength is 53% of the theoretical maximum of the material strength of the aluminum. The limiting factor is the strength of the glass, which is breaking during the tensile tests.
369
Authors: Welf Guntram Drossel, Mathias Jäckel
Abstract: Lightweight materials, such as aluminum die castings, are used more and more for automotive applications. Due to the limited weldability, joining these materials by self-pierce riveting has been established. The challenge in this regard is that these materials, especially new high strength aluminum die castings, have a limited ductility, while the joining processes locally induce large plastic deformations. Consequently, joining by forming of these materials can be accompanied by cracks, which develop during the forming operation. This paper shows the experimental and numerical investigation of a new die concept for self-pierce riveting materials with limited ductility. At the new tool concept the riveting die is separated and a movable die element is used. This element allows that the parts are superimposed with compressive stresses during the self-pierce riveting process. In the paper it can be shown, that in contrast to the conventional process crack-free joints can be generated by using the new tool concept. Determination of the joining parameters and the die design was supported by simulative investigations. Additionally, the new and the conventional self-pierce riveting process are compared on the basis of results from the experimental investigations.
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