Papers by Keyword: Joining

Abstract: Global competition as well as social and scientific megatrends strongly influence the modern car manufacturing industry. One of the most important approaches is the implementation of lightweight constructions. Therefore, the usage of high performance materials with tailored properties gains importance. For safety-relevant components such as automotive passenger cells it is necessary to minimize deformation to reduce the risk of injury for the vehicle occupants during a car accident. Thus, hot stamped high-strength steels have been established. High-strength and low formability of this kind of materials represent new challenges for joining technologies. One possibility to join high-strength steels is the newly developed shear-clinching technology. Due to the use of a combined cutting and joining process, the connection of dissimilar materials with high difference in strength and formability can be achieved. Further research to ensure process reliability and to improve the strength of the joint is required. One possible approach for this is the numerical investigation of the material flow during the joining process. Therefore, the definition of process parameters for the finite element model is necessary. A big impact on the quality of the results has the accuracy of the used friction values. As established testing methods are not suitable for modeling the rather complex tribological system between the joining partners of the shear-clinching process, an innovative testing method is needed. Studies in the field of sheet-bulk metal forming already demonstrated the applicability of the ring compression test for sheet metals. This paper presents a concept for the adaption of the ring compression test to the specific needs of the investigated shear-clinching process. The numerical identification of the friction coefficients is validated by experimental data and first results are qualified by experimental and simulative shear-clinching joints.

Abstract: The paper is devoted to the permanent joining of powder parts by the pulsed electromagnetic field. The possibility of such joining was proved experimentally and testing the obtained samples. The method of permanent joining of powder parts employing technologies of the pulsed electromagnetic field is the most effective for joining powder parts with relatively high copper content (more than 10%) and when the thickness of powder parts is in the range from 2 to 10 mm. Using a concentrator of the electromagnetic field allows increasing pressure in a relatively small zone up to 2...3 times, which significantly increases the deformation of the material of joined parts and, consequently, the reliability of joints.

Abstract: Microwave has been applied to ignite the Self-propagating High-temperature Synthesis (SHS) of compacted Ni-Al mixtures, having 1:1 atomic ratio, in order to join Chemical Vapor Deposition (CVD) SiC ceramics and SiC/SiC composites. The average joint thickness of CVD SiC joint is about 200 μm and the Coefficient of Thermal Expansion (CTE) mismatch between CVD SiC and Ni-Al intermetallic compounds results in a interface bond strength inferior to that of the substrate and joining material; on the other hand, for the SiC/SiC composite joints, as a result of the porosity of SiC/SiC composites, the SHS products readily infiltrated into the pore spaces of the composite, leading to an increased porosity of the joint area and a better lower interface than the upper one. The mechanical strength of the joints has been evaluated by Single-Lap (SL) shear test at room temperature; neither of the ceramic joints nor the composites joint gave satisfactory results, but the ceramic joints reaching a maximum shear strength value of 56MPa exhibited a positive aspect for further experiments.

Abstract: Energy efficiency is becoming more and more important in high temperature processes or for high temperature applications. In order to achieve thermally efficient processes, heat accumulators and heat exchangers are increasingly being used to store or to recover the process heat [1]. Currently used commercial heat exchanger systems are based on stacked plates or tubes. Primarily they are produced from metals which have a high thermal conductivity and show gas-tightness. Ceramics or ceramic matrix composites (CMC) are novel material candidates due to their higher resistance in severe environments, their ability to withstand extremely high operating temperatures and especially, their high thermal shock resistance. In order to fabricate HX with ceramic designs, joining is the key technology to perform complex shaped components [2].

Abstract: Many energy conversion systems use thermal processes to convert chemical energy to mechanical or electrical energy. In these situations, microchannel components can be used to make heat exchangers and microreactors to make processes more energy efficient. Ceramic heat exchangers permit operation at higher temperatures than with other materials. Additionally, compact heat exchangers are highly efficient and cost-effective. This talk will describe principles of design, methods of fabrication, and joining methods for ceramic, compact heat exchangers for integration of such heat exchangers into practical applications. Particular emphasis will be placed on methods for joining silicon carbide to itself and the results of a novel bonding method that can be performed art relatively low temperatures in air. The mechanical behavior, at room temperature and elevated temperature, of this bonding method will be compared to that of diffusion bonded joints.

Abstract: A new type of laminar composite material has been developed by the bonding of ceramic and metal with a special agglutinate metal. A tube can be made of the laminar composite material and this tube can perform as an outer sheath of an immersion heater. Such heaters can be made to lager size and can be heated using a wide range of energy sources including electricity, gas and oil. Moreover this new heater tube is low cost and has a long working life, is convenient to use and requires little maintenance. This technology allows all kinds of zinc kettle to be heated by immersion heaters.

Abstract: Timber-concrete composite structures, which use advantages of both materials, are suitable for new works and reconstructions of civil and residential buildings. There are described many methods of joining between timber beam and concrete slab in technical literature. Joints are more and more sophisticated which brings higher demands on work control and technology. Main goal of the paper is in design technologically low demanding method of joining with steel plates and nails, to test its shear strength and to compare it with other similar joining .

Abstract: In the course of ongoing development of riveting technologies, various methods were developed in the last years. Riveting is one of the most important joining methods. Nowadays, pre-hole riveting methods have been widely used in aviation, automobile and other fields because of its advantages of simple joining process, low cost and light weight. This paper mainly presents several typical pre-hole riveting methods. Their technical characteristics, working principles and research status are introduced. Also, this paper proposes the limitations and future focuses of typical pre-hole riveting methods.

Abstract: High density graphite and silicon carbide powder (alpha phase) were used to obtain joints by Spark Plasma Sintering (SPS) technique. The joining of C/SiC was performed both by direct bonding (DB) and with the aid of a ceramic powder mixture (SiC+5%wt.B₄C) as intermediary joining material. The joints were performed in vacuum at 1900°C under 30 MPa with a dwell time of 3 minutes. The interface structures of the obtained joints were characterized from the structural and mechanical point of view. XRD analysis of both joints have shown only the presence of crystalline phases of SiC and C while the crystalline phase of B₄C was not detected due to its low content (5 wt.%) with a higher degree of amorphization of 9.1% for the junction with interlayer than that of the corresponding junction obtained by DB (5.5%). Interface compositional analyses and SEM images have shown that the process of diffusion bonding was the mechanism both for joining by DB and with a SiC+5wt%B₄C interlayer. The Vickers microhardness and Young Modulus values measured by nanoindentation evidenciated a strong increase of HV values (11 – 14 GPa) at interface for the junction with SiC+B₄C intermediate layer and, as expected, the highest stiffness (180-197 GPa).

Abstract: A mechanical clinching using counter pressure of a rubber disk was developed to join the ultra-high strength steel sheets having low ductility. In the proposed process, the interlock was increased by the increment of metal flow with the counter pressure of rubber disk in the die cavity. The two kind of ultra-high strength steel sheets having different ductility were used in the mechanical clinching. The effect of the shape of rubber disk on the deforming behaviour of the sheets was investigated. The joinability was improved under the appropriate shape of rubber disk for both sheets, and then the sheets having 56% of reduction area were successfully joined whereas the sheets were not joined without the counter pressure. Although the joinability of the sheets having 43% of reduction area was improved, the cracks occurred in the upper sheet around the punch sidewall. The maximum static load and the fatigue limit of the joined sheets were measured in the tension-shearing and cross-tension tests. It was effective for the improvement of joinability in the mechanical clinching of ultra-high strength steel sheets to use the counter pressure of the rubber disk.