International Journal of Material Forming最新文献

The isothermal high temperature pneumoforming process to form tubes at constant elevated temperatures by means of internal pressure is investigated. Two materials, a ferritic (X2CrTiNb18) and a martensitic stainless steel (X12Cr13) are used for the investigations. The required material characterization is performed at the temperature and strain rate of the actual process. A new method for quantifying thermal softening via the time-dependent decrease in static yield stress is presented. At a temperature of 1000 °C, the static yield stress decreases by 50% within 100 s for both materials. The numerical models are validated on the basis of the formed geometry and used to study the influence of maximum internal pressure, axial feed, holding time under load and die edge length on the final part geometry. It was observed, that with higher internal pressures and longer holding times smaller corner radii are formed for both materials. In contrast, a superimposed axial feed as well as the effective friction coefficient have a negligible influence on the formed geometry. With an increasing die edge length, smaller radii are formed with the ferritic stainless steel numerically and experimentally. By contrast, for the martensitic stainless steel, larger radii are observed numerically. Experimentally, the limited formability of these tubes weld seam becomes apparent. Based on the findings, process windows depending on the process parameters internal pressure and die edge length were derived. Numerically, forming limit curves of tubular semi-finished products under comparable conditions serve as a failure criterion. Good agreement with experiments was observed.

Various sandwich structures have been developed as lightweight structures. They have excellent specific stiffness owing to their low density. However, owing to the existence of various failure modes, which are classified into core shear failure, tensile fracture of the face sheet, buckling of the face sheet, and delamination, it is difficult to deform sandwich sheets without any failure. A new forming strategy was proposed in this study. Buckling of the face sheet during drawing was suppressed by filling the encapsulated media in a 3D core between the face sheets to exploit its hydrostatic effect. This process is similar to the freeze-bend method, in which the pipe is filled with ice during bending to suppress wrinkles and flattening. Ice, wax, and low-melting alloys were used as the encapsulated media, and their formability and ease of removal were investigated. Further, a shear strength test was performed on the specimens that were cut out from the drawn products to evaluate failure during forming. Based on these experimental results, the characteristics required for the encapsulated media were summarized.

Additive Manufacturing (AM) using Selective Laser Melting (SLM) has gained significant prominence across various industries involved in stainless steel part manufacturing. Selective Laser Melting makes it possible to manufacture parts with very complex geometry and with remarkable mechanical and physicochemical properties by controlling the microstructure via the appropriate choice of process parameters. This study presents a comprehensive literature review aiming to provide the scientific and technical communities with an overview of existing knowledge and experimental data regarding the effects of Selective Laser Melting parameters and conditions on the microstructure and mechanical properties of stainless-steel parts. The objective is to highlight the impact of various factors, such as process parameters, building atmosphere, post-heat treatments and initial powder characteristics on phase transformation, porosity and microcracks formation, microstructure evolution and mechanical properties of SLMed stainless steels. Additionally, the integration of emerging Smart Additive Manufacturing (SAM) requires experimental databases, properties prediction and processing parameters optimization to enhance the entire process spanning from design to final product.

To ensure correct filling in the resin transfer molding (RTM) process, adequate numerical models have to be developed in order to correctly capture its physics, so that this model can be considered for process optimization. However, the complexity of the phenomenon often makes it impossible for numerical models to accurately predict its behavior, limiting its usage. To overcome this limitation, numerical models are enriched with measured data to ensure their correct predictability. Nevertheless, the data used is often limited due to practical constraints, such as a limited number of sensors or the high costs of experimental campaigns. In this context, the present paper demonstrates the implementation of a numerical model enriched with data, called Hybrid Twin applied to the RTM process when few sensors are considered in the mold to be injected. The performances of the developed hybrid twin are tested in a virtual test for the injection of a 2D mold, where the hybrid twin constructed using a simplified numerical model allows to accurately predict a complex model’s resin flow-front over its entire time history.

The extrusion speed and deformation temperature are important factors affecting the microstructure development during the deformation. Microstructure development plays a crucial role in the performance of the mechanical properties of materials. In direct extrusion, the homogeneous evolution of the microstructure in the length of the extruded bar could be affected due to its non-isothermal exit temperature evolution. Thus, a new set-up is suggested with real-time controllable speed and temperature to characterize the influence of temperature on the microstructure and obtain its homogeneous development for the magnesium alloy. During the extrusion, the temperature of the extruded bar is evaluated by using the infra-red camera, and the extrusion speed is simultaneously controlled in real-time depending on the temperature difference between a set temperature reference and the one obtained from the infra-red camera. This suggested set-up of extrusion is evaluated in terms of the microstructure and temperature evolution of the extruded bar.

During the high-speed forming processes, the metallic sheets are usually deformed under the biaxial tensile condition. The strain rate of metallic sheets often exceeds 10² s^− 1. It is essential to determine the strain-rate-sensitive hardening model of metallic sheets for accurate numerical simulation of the high-speed forming processes. Thus, an electromagnetic hydraulic bulge experiment is proposed to determine the strain-rate-dependent hardening model of metallic sheets under the biaxial tensile condition with the strain rate of 10² s^− 1. It is convenient to numerically simulate the electromagnetic hydraulic bulge processes. Hence, the strain-rate-dependent hardening models of metallic sheets can be determined by the inverse identification procedure of updating the numerical simulation. The electromagnetic hydraulic bulge experiments of SUS304 stainless steel sheet and AA5052-O aluminum alloy sheet were performed for the inverse identification of Johnson-Cook hardening model. The discrepancy between the experimental results and numerical simulation was minimized by optimizing the parameters of strain-rate-dependent hardening models. The dynamic flow stress curves of SUS304 stainless steel sheet and AA5052-O aluminum alloy sheet were higher than the static ones. However, the AA5052-O aluminum alloy sheet exhibits more significant strain-rate hardening effect than the SUS304 stainless steel sheet. The inverse identification of strain-rate-dependent hardening model of metallic sheet was validated by comparing the simulated and experimental results of electromagnetic micro-hydroforming of micro-channel.

The initial temperature of the preform has an important influence on the stretch and blowing step of the process to produce PET bottles. A complete 3D modelling of the heat part of the stretch blow molding machine including meshing is a long and complex task. Solving Navier Stokes equation coupled with the thermal problem takes more than one week using ANSYS/Fluent software. The numerical simulation of infrared (IR) heating taking into account the ventilation effect is very time-consuming. This work proposes a simplified approach to achieve quickly the numerical simulation in order to have an estimation of the temperature distribution in the preform. In this approach, the IR heating flux coming from IR lamps and the ventilation model are calculated in a semi analytical way and are applied as the boundary conditions of the simulation in COMSOL where only the preform is meshed. This approach is validated by comparing our numerical results with the experimental temperature distribution of PET preform.

Roll forming is a sheet metal forming operation that incrementally forms flat sheets into a desired profile geometry. The process is characterized by a high material utilization and a high output quantity. Concomitant with these advantages, profile defects such as bow and twist of the profile can occur. In the literature, an inhomogeneous longitudinal strain distribution across the profile cross-section is considered to be the cause of these defects. However, a quantitative cause and effect analysis is missing up to now. This paper presents an analytical model that shows a quantitative relationship between profile defects and the underlying longitudinal strain distributions. The model can be used to calculate the longitudinal strain distribution of a roll-formed profile across its cross-section based on given values for bow and twist or vice versa. It is compared with results from simulations and experiments and clearly reveals the cause for twist and bow in roll forming.

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Approximately half of global steel production is dedicated for manufacturing sheets. Due to global warming, geopolitical instabilities and rising raw material costs, recycling sheet metal is increasingly important. Conventional recycling has inefficiencies, therefore improving material efficiency and adopting circular economy strategies is necessary to halve CO₂ emissions by 2050. This paper presents a review of sheet metal reuse techniques and introduces an innovative remanufacturing framework of curved steel sheet, with a special focus on the automotive sector and car-body panels. To support the framework presented, an experimental procedure on small-scale samples was carried out. The material tested was DC 0.4 steel parts (0.8 mm thick) characterized by different curvature radii. The material was reshaped and flattened under different conditions to understand the effect of the process variables onto the final quality of the remanufactured parts. The experiments showed that even parts with small curvatures can be flattened and reshaped with success. Lastly, to support the general remanufacturing framework presented, some flattening simulations of a large car-body are presented, revealing the importance of implementing a dwelling stage in the process and the advantage of performing such process with heated tools.

Important developments have been achieved for self-pierce riveting with the utilization of a double-sided tubular rivet that is able to join sheets of similar and dissimilar materials with different and larger thicknesses, while remaining hidden in-between the sheets after the joining process is completed. Nevertheless, the performance of those joints can still be improved by an optimization of the rivet parameters, mainly the chamfered angle of the rivet ends and the ratio between the initial height and thickness of the rivet. In this paper, the correct parameter combination is established by the performance of the obtained joint to shear destructive tests, the requirements of force and energy, as well as the dimension of the protuberance produced above the sheets surface. The influence of the introduction of an additional rivet in the overall performance of the mechanical joint is also discussed. Joints of different thinner and thicker sheets are analysed, as well as the combination between those thicknesses, to extend the range of applications of the new joining by forming process.