International Journal of Material Forming最新文献

The forming behaviour of a unidirectional non-crimp fabric (UD-NCF) consisting of polyamide stitches with a tricot-chain stitching pattern is explored. Notably, there are no stabilising tows orientated transverse to the main tow direction in this fabric, a common feature in many ‘quasi’ UD-NCFs, this allows extension of the stitch in the transverse direction under certain loading conditions. The lack of stabilising tows introduces a possible low-energy deformation mode to the UD-NCF, which is absent in biaxial fabrics and to a large extent in ‘quasi’ UD-NCFs. The in-plane shear behaviour is initially investigated using both standard ‘tightly-clamped’ picture frame tests and uniaxial bias extension tests. Preliminary results show a dramatic difference in results produced by the two test methods. During the picture frame test, fibres can be subjected to unintended tension due to sample misalignment in the picture frame rig. To mitigate error arising from this effect, the picture frame test procedure is modified in two different ways: by using an intentional pre-displacement of the picture frame rig, and by changing the clamping condition of test specimen. Results show that the modified picture frame test data contain less error than the standard ‘tightly-clamped’ test but also that the shear stiffness of the UD-NCF is notably lower when measured in the bias extension test compared to the picture frame test, mainly due to the difference in loading conditions imposed during the two tests.

The components’ lightweighting has been pursued, especially in the transport industry, for greenhouse gas reduction. Topology optimization, being able to allocate the material within a provided design space, is a mathematical method that can support the design of lightweight components, preserving, at the same time, their mechanical performances. In this paper, a standard shape of a component, specifically an automotive bracket, was topology optimized by estimating the impacts of the new designs from an eco-friendly point of view. A subtractive, an additive and a casting manufacturing process were considered as possible manufacturing routes achieving an optimized geometry of the component for each of them. The topology optimizations were performed considering each processes’ peculiarities, introduced as constraints. Same strength for a given set of loads and boundary conditions was the target of each analysis. The component’s lightening can be considered environmentally friendly just after assessing the impacts associated with all the stages of the product’ life cycle. Indeed, each phase of the product’ life cycle can be affected, differently, by the performed topology optimization taking into account the peculiarities of the employed manufacturing process. The overall considerations on the most environmentally safe strategies can, therefore, change according to the specificities of the optimized shapes. The topology optimization showed its utmost potentiality, from a sustainable point of view, if applied to additive manufacturing techniques for the advantages arisen by the capability to manufacture complex shapes benefiting also of reduction time process owing to less material to be deposited.

A large number of carbon emissions are generated in the life cycle of metal forming equipment. The movable components are the critical part of the mechanical system in the equipment, which accounts for the carbon emissions in both of manufacturing and use stages. Reducing carbon emissions of the components in the manufacturing stage by lightweight design may result in a significant increment of emissions in the use stage. To overcome the obstacle, a method of matching the mechanical system of metal forming equipment to reduce life cycle carbon emissions is proposed. The effect of the weight of the components that determine the manufacturing’s emission on the configuration of the drive units that determine the emission in the usage stage, was analyzed and quantified. Then, the drive units were reconfigured and optimized to meet the required output force and velocity with the different weights of the components to find the optimal scheme with the lowest emissions in the life cycle. The method was applied to a 2000-ton hydraulic forming equipment, and results indicate that 14.87% of the weight of the movable components can be reduced with a total carbon emissions reduction of 22.48%. The total carbon emissions were reduced by 35.94% compared to that of the movable components through the topology optimization method. The proposed matching method can assist in the low-carbon design of the mechanical system in metal forming equipment.

In this study, hydraulic pressure generation and small-scale cylindrical hydromechanical deep-drawing experiments were conducted using a novel die-integrated active high-pressure generation system. The most significant feature is the installation of a hydraulic pressure-generating piston structure inside the die, which enables a high-pressure generation process of 100 MPa or higher inside the die. In addition, by taking advantage of the size effect of a smaller die, a high hydraulic pressure is actively generated using the same equipment as in conventional drawing processes. It was discovered that a piston installed in the die can actively generate a hydraulic pressure of 100 MPa or higher based on the Pascal principle. By downsizing the die, a hydraulic pressure of 100 MPa or higher can be generated using only the power of a small press machine (50 kN). By actively applying high hydraulic pressure counter and radial pressures, small-scale drawability can be significantly improved. Furthermore, the application of the proposed system to single-action presses and progressive dies can enable hydromechanical deep drawing with optimized conditions for each process in a single motion.

The Collaborative Research Center 1153 is investigating an innovative process chain for the production of hybrid components. The hybrid workpieces are first joined and then formed by cross-wedge rolling. Pinion shafts were manufactured to investigate the behavior of the joining zone under increased complexity of the forming process. For this purpose, six types of workpieces produced by three types of joining processes were formed into pinion shafts. The reference process provides a shaft with a smooth bearing seat. It was found that the increased complexity did not present any challenges compared to the reference processes. A near-net shape geometry was achieved for the pinions made of steel.

The forming limit diagram (FLD), mechanical properties and fracture toughness of aluminum foil composites fabricated via accumulative roll bonding (ARB) process have been investigated as its novelty for the first time. To do this, AA1050/TiC composite foils with thickness of 0.2 mm have been fabricated from one up to twelve ARB passes at 320 °C. Also, optical microscopy (OM) was used to investigate the effect of cumulative forming process on the grain structure. The strength of samples improved to 168. 6 MPa after the 12th cumulative rolling pass, registering 248% improvement in comparison with initial AA1050 sample. Also, by cumulating the plastic strain at higher passes, the bonding quality among composite layers enhanced. SEM fracture surface morphology of samples showed the conversion of fracture mode to shear mode for composites fabricated at high number of passes. So, in comparison with the annealed sample, deep dimples are shrinking slowly and their number and depth were reduced. As the criterion of formability and at higher passes, the area under the FLDs, dropped sharply for one pass processed sample and then improved. Results of fracture test revealed that the value of fracture toughness enhanced continually and got to the 30 MPa.m^1/2 at the 12th pass. Grain refinement and ARB process nature are two main mechanisms which are responsible for all ductility changes and mechanical properties.

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.