Papers by Keyword: Joining

Abstract: The mechanical joining of continuous fiber-reinforced thermoplastics (cFRTP) and metal sheets represents a promising approach for manufacturing hybrid lightweight structures. To reduce the time and cost associated with extensive experimental investigations, numerical modeling strategies are increasingly applied. In this numerical study, a further step in the modelling strategy for the direct pin-pressing (DPP) process of cFRTP and metal sheets is presented. The study focuses on modeling and simulating the occurring deformation mechanisms of decomposition, compaction, and separation of individual rovings on the mesoscale to analyze the resulting material structure. For this purpose, two simplified models were derived. The textile architecture is represented based on micrographs of cross-sections and discretized using the finite element method. The deformation of individual rovings during joining leads to a deformation of their initial elliptical cross section. To capture this level of resolution, both a cohesive zone and a pure contact approach are applied within the rovings. The highly viscous thermoplastic melt is modeled as a fluid employing the Arbitrary Lagrange–Eulerian (ALE) method. Matrix and roving meshes are coupled to account for fluid–structure interaction (FSI) during process. The study shows that coupling of matrix and rovings is necessary to obtain more accurate predictions of the deformation behaviour. Furthermore, the cohesive zone approach is better suited to simulate the emerging deformation mechanisms.

Abstract: Clinched joints with non-rotationally symmetric geometries exhibit orientation-dependent mechanical behavior that is commonly neglected in structural-scale simulations. Reuleaux triangle shaped clinched joints, in particular, show pronounced in-plane anisotropy depending on their orientation. While such effects have been studied at joint and specimen scale, their relevance at the structural level remains largely unexplored. In this work, the influence of joint orientation on the bending response of a joined structure is investigated using numerical simulations. A simplified joint replacement model based on the *CONSTRAINED_SPR2 point-connector formulation in LS-DYNA is employed, with parameters calibrated from previously obtained experimental force displacement data. A hat shaped profile structure subjected to three-point bending is analyzed in a parametric study considering variations in joint orientation, joint spacing, and profile geometry. The results show that joint orientation has little influence during the initial deformation phase but becomes increasingly significant at larger displacements, where joint behavior governs load transfer. Orientation dependent effects are found to influence the global force displacement response and local load redistribution among joints, with magnitudes comparable to those induced by changes in joint spacing and structural geometry. The findings confirm that joint orientation effects remain relevant at the structural level and should be considered in the design of structures assembled using non-rotationally symmetric clinched joints.

Abstract: Hybrid joints made of steel and aluminium alloy produced by rotary friction welding enable load-adapted lightweight components. However, a major challenge is the inhomogeneous radial temperature distribution caused by different relative velocities between the specimen centre and edge during rotation. This effect leads to local insufficient bonding and reduces the overall joint strength, especially in the centre, where low relative rotation speeds occur. Previous studies mainly addressed preheating before the friction phase, whereas superimposed heating during the upsetting phase has not been investigated so far. To achieve temperature equalisation along the cross-section during rotary friction welding, a modified KUKA Genius plus machine equipped with joule heating was used to introduce an electric current during the upsetting phase. Experiments were conducted on EN AW-6082 (AA-6082) joined to 20MnCr5 (AISI 5120H). A three-step variation of current intensity (10, 24 and 36 A/mm²), alongside a reference without current, was investigated. Temperatures were monitored using type K thermocouples, confirming temperature equalisation. Mechanical performance was assessed by uniaxial tensile tests, while hardness measurements and metallographic analyses characterised the influence of superimposed heating on the interfacial microstructure. Joint strength improves up to 17% with increasing current, even under otherwise unsuitable welding parameters that would normally result in insufficient bond strength. This improvement is linked to a uniform temperature distribution and enhanced material flow, resulting in a defect-free specimen centre.

Abstract: The joining of metals and polymer-based materials has a very high interest for many industrial sectors, as it allows to achieve components combining the specific characteristics of each material class. Additive manufacturing technologies could boost the production of these joints, allowing the controlled deposition of a polymeric material over the metal substrate. The present research is aimed to study the feasibility of a joint concept that can be used to produce aluminium/polymer-based material joints through a 3D printing-supported technique. The innovative joint concept, which is based on an interlocking mechanism promoted by a deposited pin, was compared to two conventional concepts. The innovative joint concept allows the production of samples with good mechanical behaviour, in which the failure occurs outside the material overlapping zone. This design is very suitable to be tested for the production of dissimilar material joints.

Abstract: Riveting is the most important method for joining two sheets of different materials. In order to promote electromagnetic pulse riveting (EMR), the influence of the impact velocity will be studied in this paper in order to correctly model the electromagnetic field of the riveting process. There are many parameters associated to the riveting process, however, the interference fit is considered as the most important criterion to measure the riveting quality, which consequently will be associated to the impact velocity, being this the most important parameter. The use of the washer will be studied to guarantee the optimal flow of the material and to restrict the expansion of the rivet shaft, thus minimizing damage to the composite material. The interference generated between the rivet shaft and the hole of the sheets and the flow of the material will be developed by finite elements which will later be validated by means of experimental tests analyzing its final microstructure. Finally, the relationship between the impact velocity on the rivet head will be directly related to the distribution of the interference generated in the deformation, verifying that the impact velocity.

Abstract: Currently, welding is the most efficient way for joining of plastic. Due to its rapid heating, efficiency in term of time and energy, and ability to be applied on components of any shape, microwave welding stands out from other welding methods. Additionally, SiCNWs was proposed as the microwave susceptor for the microwave welding of thermoplastic in this work due to its high dielectric loss and biocompatibility. To produce microwave welded joint, SiCNWs was first mixed with acetone to obtain a SiCNWs suspension. After that, SiCNWs was drop casted onto the targeted area of PP, allowed to dry and then microwave irradiated. In this work, the microwave heating time studied ranged from 15 s to 20 s. SEM and single lap shear test were used to characterise the microwave welded joint. From the findings, the tensile strength increased as the microwave heating duration increased from 15 s to 18 s, due to formation of SiCNWs/PP nanocomposite welded joint layer with increasing thickness. Yet, when the microwave heating time was prolonged to 20 s, the tensile strength decreased to 0.85 MPa. Besides, a void was observed at the welded joint and it is believed that the presence of void causes the welded joint to weaken when force is applied. Under properly regulated of microwave heating time, a strengthened nanocomposite welded joint can be produced which demonstrate great promise in plastic welding.

Abstract: The article’s primary purpose is to give a technological assessment of manufacturing complex-shaped parts using powder metallurgy. The process is considered in the example of a complex-shaped product consisting of several elements manufactured separately from the Fe-C-Cu powder mixture and then combined into a single structure. The joining was carried out by impregnation of porous structural elements with the fusion of copper-containing material. It has been demonstrated that the infiltration process is affected by many factors: porosity of structural elements, wettability of their pore channels, fluid flowability of the infiltrating material, and other factors. The research was carried out on the mass products - centrifugal pump stages for oil production. The elements compaction was carried out on hydraulic press at a pressure of 500 MPa, which ensured the average density of the parts after sintering up to 7.8-8.4 g/cm³. During sintering and impregnation, various types of defects of the pieces were detected, which were caused by the excessive thickness of the infiltrating material, different densities of the walls, and insufficient wettability in the connection zones of the elements.The investigations have shown that manufacturing complex components by prefabricating single elements and their subsequent sintering combined with infiltration is feasible. It can be done in a chamber furnace as well as with belt sintering. However, it is necessary to carefully prepare the mold before sintering, choose the infiltrating agent, and analyse possible disadvantages.

Abstract: Friction stir welding (FSW) is an advanced solid-state metal joining technique. This operation fuses adjacent materials through the use of a non-consumable, rotating tool, which is plunged into and travels along the seam of the materials. Since this joining method avoids the bulk melting of the base materials, it is considered a relatively energy efficient process. Additionally, the strength of the base material is often improved due to significant grain refinement resulting from the stirring action of the tool at relatively low temperatures. Another inherent benefit is that the joint thickness, which is dependent on the length of the pin, can be much greater than most other joining processes and can also be well controlled. This joining method conventionally relies on the friction at the tool-base material interface to stir materials. Other research has implemented complex tooling to mechanically enhance this stirring action. However, these tools are often expensive, requiring a high level of capability within industry. In order to improve the weld strength of FSW, a novel toolpath is utilized which significantly improves the mechanical mixing of the constituent materials without the need for complex tooling, such as tools with threaded pins. The path currently investigated forms a curl as it travels both perpendicular and parallel to the joint. This motion is used to extend the stirring action of the tool to regions outside the immediate joint area. It was found that this tool path is effective in improving weld strength under specific process parameters. Constraining the tool's axis normal to the workpiece surface resulted in a void that was formed in the majority of tests; however, this void was eliminated with modification of the process parameters. An uneven distribution of heat was recognized within this testing in which one side of the joint was hotter than the other. This observation may be used in future studies to perform multi-material joining where it is often necessary to increase the temperature of one material more than the other.

Abstract: Joining and local forming processes for fibre-reinforced thermoplastics (FRTP) like hole-forming or variations of the clinching process require an in-depth understanding of the process induced effects on meso-scale. For numerical modelling with a geometrical description of a woven fabric, adequate material models for a representative unit cell are identified. Model calibration is achieved employing a mesoscopic finite-element-approach using the embedded element method based on tensile tests of the consolidated organo-sheets and a phenomenological evaluation of photomicrographs. The model takes temperature dependent stiffness and fibre tension failure into account.

Abstract: The increasing use of multi-material constructions lead to a continuous increase in the use of mechanical joining techniques due to the wide range of joining possibilities as well as the high load-bearing capacities of the joints. Nevertheless, the currently rigid tool systems are not able to react to changing boundary conditions, like changing the material-geometry-combination. Therefore research work is crucial with regard to versatile joining systems. In this paper, a new approach for a versatile self-piercing riveting process considering the joining system as well as the auxiliary joining part is presented.