Papers by Keyword: Joining by Forming

Abstract: The direct reuse of End-of-Life (EoL) automotive sheet metal offers significant environmental benefits, particularly when panels are flattened rather than remelted. However, the geometric irregularity and variable formability of reclaimed sheets require joining solutions that operate with minimal tooling and are compatible with flat-die pressing. This work introduces a novel rivet-based joining-by-forming process designed to create a mechanical interlock using only flat tools, enabling integration into the same hydraulic press used for EoL panel flattening.Finite element simulations were performed to optimize rivet geometry and study flange formation, stress distribution, and failure mechanisms. The optimized rivet design achieves stable outward flaring under axial compression, producing a functional joint without shaped dies. Experimental tests on reclaimed automotive sheets validated the joining concept and confirmed the deformation behaviour predicted numerically.The proposed method provides a low-cost, low-energy joining strategy suitable for reclaimed steels of uncertain formability and supports the development of circular manufacturing routes based on the direct reuse of automotive sheet metal.

Abstract: The reliable operation of an engineering structure is highly influenced by the joints of its structural elements. The selection of the applied joints is often determined by the function of the structure. In addition, the requirements for joints must be considered: strength, elongation, sealing, mobility, assembly, safety against loosening, feasibility, economy, design, etc. of the joint. The range of sheet materials used in the vehicle industry is very broad: manufacturers can choose the most suitable materials for a given purpose from a wide selection of materials, and it is also common to use sheets of several types of materials, with different thicknesses and physical and chemical properties, within a structural element. However, these sheets need to be combined in some way to produce a proper final product design. For combining thin sheet material, several different joining technologies are known. The aim of the study is the examination of clinched joints made of aluminium due to the highly increasing percentage of aluminium sheet usage in car bodies. The applied materials are EN AW 5754 and EN AW-1050 with different thicknesses. The joints were analysed by FEA and experimentally tested as well.

Abstract: Lightweight constructions become more and more important, especially in the mobility sector. In this industry, the increasingly strict regulations regarding the emissions of carbon dioxide can be achieved to a certain extent by reducing the vehicle weight. Thus, multi-material systems are used. Conventional joining techniques reach their limits when joining different materials due to different thermal expansion, unequal stiffness or chemical incompatibilities. This is why additional joining elements or adhesives are used. These must be viewed critically regarding a lightweight and resource-efficient production, since they add weight or complicate the recycling process of these components. Consequently, there is a great and growing need for new versatile joining technologies in order to overcome these challenges and to be able to react to changing process parameters and boundary conditions. Joining without an auxiliary element using pin structures formed directly from the sheet metal plane is one approach to meet these challenges. These pin structures are then joined by direct pressing into the joining partner. This is possible with a variety of material combinations, but is advantageous with regard to continuous fibre-reinforced thermoplastic composites (CFRTP), as the fibres do not have to be cut when joining CFRTP using pin structures. In this paper, the formability of pin structures made of a dual-phase steel DP600 (HCT590X + Z) is investigated. The extruded pin structures are joined by direct pin pressing with an EN AW-6014 to form tensile shear specimens. Different joining strategies are investigated to compare their influence on the joint strength. The results have shown that it is feasible to form suitable pins from a DP600 dual-phase steel to produce reliable connections with an aluminium sheet joined by direct pin pressing.

Abstract: The newly developed joining-by-forming technology “shear-clinching”, features a potentially single-stage process for joining UHSS without requiring any additional elements. Foundational studies have focused on the functionality of shear-clinching at a one-element sample. To ensure the safety of the industrial application of the shear-clinching technology, an investigation with component-like samples with several joints is required. This paper presents a detailed analysis of the material behaviour during the shear-clinching process with multi-element specimens to evaluate the influence of the neighbouring joints. In order to describe the influence of the neighbouring joints, the deformations resulting from the bending and material displacement are recorded without contact after the joining process: locally around the joining point and globally over the entire sample size. To minimize such bending effects, a tool-sided adaptation is provided. The results show the high potential of shear-clinching joining by UHSS and give further recommendations for future multi-material application.

Abstract: A combination of several manufacturing process steps in a simultaneous manner allows to save energy costs, reduce investment and economic logistical efforts. This paper provides the contribution reports on particular research work performed by the Institute for Metal Forming Technology, which deals with gearwheel bodies manufactured by lateral extrusion (forging). The scope of this paper focuses on the joining process and achievement of desired properties for forged wheel bodies. At the beginning of the forming process, a blank is placed in a ring having an axial and tangential profile. Due to a force application on the face surface, the material flows into the ring radially and in the following, the joint provides both a form and press fit. Since the forming and joining process is conducted in one step, the lubricant for the forming process must fulfil two requirements. First, low friction for the manufacturing process is advised. On the contrary, the joint gearwheel needs to transmit the applied load during use. In order to determine the influences of two different lubricants onto both the manufacturing processes and static torque application, experimental investigations were performed

Abstract: This paper presents a new joining by forming process for connecting tubes to sheets. The process consists of forming an annular flange with rectangular cross section by partial sheet-bulk of the tube wall thickness and performing the mechanical interlock by upsetting the free tube end against a flat-bottomed (counterbored) sheet hole. The presentation identifies the variables and the workability limits of the process and includes an analytical model to assist readers in the design of the new joints. The new proposed joining by forming process and the corresponding analytical model are validated by experimentation and numerical simulation using finite element analysis. The process allows connecting tubes to sheets made from dissimilar materials at room temperature, avoids the utilization of addition materials or adhesives and produces joints that are easy to disassembly at the end of live, allowing recyclability of the tubes and sheets.

Abstract: The direct integration of piezo elements into micro-structured aluminum sheets is a new approach for adaptronics and lightweight constructions. With the integration of the active piezoceramic elements the aluminum sheets gain sensor and actuator functionalities. The mechanical interconnections and the preload of the piezoceramic elements are an important issue for the sensor and actuator capability of the later smart material. Post-process inspection methods to characterize the mechanical interconnection of the joining partners and the performance of the transducer after the joining operation are state of the art. Scope of the paper is the development of a novel in-process monitoring method that utilizes the piezoceramic transducer as inherent sensor for failure mode detection and preload evaluation during the joining by forming operation. Within this study, results of forming experiments with array batches of interconnected piezoceramic elements are presented. The piezoceramic batches are electrically contacted inside the joining tool and utilized as material inherent sensor during joining by forming experiments. Test samples are characterized by impedance spectroscopy during the joining operation. Based on the experimental results, a novel in-process-monitoring method utilizing the piezoceramic joining partners as inherent sensor is outlined. It is shown, that with this method a sufficient preload can be adjust on the basis of the intensity of the resonance peak without an overload. Furthermore, error effects to the transducer can be detected at an early stage.

Abstract: To comply with increasing product requirements, the use of function-optimized materialsis claimed. Joining technology thereby becomes increasingly important to use high strength materialonly in postulated sections. Staking is a joining by forming technology that is highly reliable andcost efficient. High process forces and sufficient formability of the material limit the suitability inclaimed miniaturization for use in industrial applications. A promising approach to break these processlimitations is the use of superposed high frequency oscillation, whereby joining forces could bedecreased. The present study indicates first trials of an ultrasonic (US) assisted staking process of highstrength martensitic steel. Based on high temporal instrumentation, such as laser vibrometer, contactdetection and high-resolution force measurement, the process sequence is characterized and studiedin detail. The researches confirm high potential in force reduction of mean values due to superimposedhigh frequency oscillation with a high dependency on amplitudes. In process, two differentforce-characteristics within three regimes can be identified. Since US assisted forming processes arewell known in literature with harmonic oscillating force signals during process, hammering and soirregular force peaks with changes in contact signal within process, are identified for first time anddemonstrate a highly promising field of application.

Abstract: Smart structures consisting of a load carrying structure and smart materials with actuatory and sensory capabilities feature high potential in numerous applications. However, to master the assembly conditions of smart structures, there is a need to integrate additional design parameters such as prestress of the smart material, critical loads and electric contacting as well as insulation into the process development. This paper focusses on the design of an incremental bulk forming process to integrate piezoceramic components into an aluminum tube simultaneously to the manufacturing process. Axial forces imposed on the piezoceramic are investigated numerically and experimentally to verify the design of critical components and the process control. Within this investigation, in situ measurement of the direct piezoelectric effect provides a method to validate the numerical design with regard to failure of the piezo tube and the functional properties of the overall structure.

Abstract: Joining using forming processes in the field of bulk metal forming is currently experiencing a renaissance both within research projects in academia and industrial manufacturing processes. One main challenge of such research activities is any improvement of joint strength. In contrast to conventionally joined interference fits, such components can be manufactured without heating or thermal loads. Within framework of the priority program SPP 1640 of the German Research Foundation, a common lateral extrusion process for a solid internal part and an external tube actually is being developed at the Institute for Metal Forming Technology, Stuttgart. Aim of this project is to manufacture a form-closed as well as force-closed joint composed by a high strength external material and a light weight internal material for light-weight components. The present work describes numerical investigations of this process and shows aspects of process development. This includes, among other things, development of a new tool concept, which provides divided punches to determine the influence of different punch motion on the forming and joining process. Spring back behavior, induced residual stress distribution and occurring contact area depending on different material combinations are also investigated. Moreover, the process limits regarding component geometry and force requirement are shown.