International Journal of Material Forming最新文献

This article deals with the thermoforming process, in which the plastic sheet is heated to a suitable temperature and stretched through a single-sided mould. This paper focuses on the study of thickness distribution along the final part through numerical simulation with T-SIM software and optical characterization of the practical process. PC LEXAN™ 8A13E films, with different initial thickness, were moulded by two types of moulding (positive and negative). It was intended to evaluate, characterize and correlate the effect of the process on the optical properties of the films. The findings of the study suggest that films formed with a negative mould exhibit more pronounced thickness variations compared to those formed with a positive mould, resulting in lower final thicknesses. Additionally, thicker films exhibit higher thickness variations after thermoforming, as supported by the experimental data. Regarding the optical characterization of the films, transmittance and reflectance tests were performed. In the case of transmittance, a significant increase in this property is observed after thermoforming, while a decrease in the reflectance values was observed. This paper is then focused on the study through numerical simulation and optical characterization of the thermoformed films, elucidating the dynamics inherent in the thermoforming process with transparent polycarbonate films, providing valuable insights for optimization and application across various industrial sectors.

Deep-drawing is a method in which flat sheets of metal are formed into complex 3-dimensional geometries. Three main types of challenges arise when transitioning from the macro-scale to micro-deep drawing. These can be summarised as: (1) tribological effects, which mainly stem from the relative difference in surface characteristics between the two size scales, (2) material behaviour effects which arise from the increasing heterogeneity of materials that have a decreasing number of grains that are deformed in forming, and (3) dimensional effects which relate to difficulties in handling and inspection of small components at high rates and challenges in manufacturing and monitoring of tool components for use in micro-deep drawing. Various methods or effects can be applied to micro-deep drawing processes to tackle these challenges. This paper reviews research on methods and effects that can be used to improve the robustness in micro-deep drawing processes. Small changes, such as the choice of lubricant and slight changes to the punch geometry are considered, but so are larger changes such as the use of ultrasonic vibration to improve formability and adjustable tooling. The influence of process monitoring and simulation on process robustness is also considered. A summary of methods and effects is drawn at the end to highlight potential space for innovation.

The subject of the research is the process of helical rolling of balls with a diameter of 15 to 125 mm for grinding mills. Analytical estimates of the equivalent strain and the rate of equivalent strain averaged within the volume of the metal were obtained. A simple formal model of equivalent strain distribution within the ball in the direction of the rolling axis is also proposed. The proposed solutions predict that in the working ranges of the rolling parameters the value of the volume-averaged strain can vary from about 0.6 to 5, meanwhile in the jumper area the equivalent strain is two orders of magnitude higher than in the axial zone. It is shown that the principal influence on the magnitude of strain is caused by ovalization of the workpiece during rolling, which leads to multiple repeated deformation of the same volumes of metal when the workpiece rotates. As an example, the use of obtained estimates to calculate the strain, strain rate, flow stress, force and rolling torque under the conditions of the real experiment performed by other authors is shown. The proposed models allow solving engineering problems of certain classes (for example, calculation of energy-force parameters) without using FEM software packages and are recommended for optimization and real-time control of the helical rolling of balls.

For isotropic materials, the von Mises yield criterion is generally used to interpret bulge test data and assess formability. In this paper, we investigate the role played by the ({J}_{3}) dependence of the plastic response on the behavior during stretch forming under pressure. To this end, we consider the isotropic yield criterion of Drucker, which involves a unique parameter c expressible solely in terms of the ratio between the yield stresses in shear and uniaxial tension, ({tau }_{Y}/{sigma }_{T}). In the case when ({tau }_{Y}/{sigma }_{T}=sqrt{3}), the parameter c = 0 and the von Mises yield criterion is recovered, otherwise Drucker’s criterion accounts for dependence on both ({J}_{2}) and ({J}_{3}). First, an analytical estimate of the ratio of the principal stresses at the apex of the dome is deduced. It is demonstrated that the stress ratio depends on the parameter c, the deviation from an equibiaxial stress state induced by changing the die aspect ratio is more pronounced for materials with higher ({tau }_{Y}/{sigma }_{Y}) ratio. Finite element predictions using the yield criterion and isotropic hardening confirm the trends put into evidence theoretically. Moreover, the F.E. simulations show that there is a correlation between the value of the parameter c that describes the dependence on ({J}_{3}) in the model and the strain paths that can be achieved in any given test, the level of plastic strains that develop in the dome, and the thickness reduction. Specifically, for a material characterized by c > 0 (({tau }_{Y}/{sigma }_{T}<1/sqrt{3})) under elliptical bulging, at the apex the plastic strain ratio is greater than in the case of a von Mises material, while the stress ratio is less. On the other hand, for a material characterized by c < 0 (({tau }_{Y}/{sigma }_{T}>1/sqrt{3})), the reverse holds true. The FE results also suggest that for certain isotropic materials neglecting the dependence of their plastic behavior on ({J}_{3}) would lead to an underestimation of the thickness reduction.

Copper alloys are extensively used in the manufacture of electrical and electronic components, which strength depends on the material mechanical properties, which in turn depend on the metallurgical state. Even though the mechanical properties remain within the specifications, the subsequent formability limits may depend strongly on the material batch. Considering the forming stage to manufacture plug-in type connectors made of CuSn6P thin sheets, a crack may appear in the components, in the bent area subject to high strains, when changing the material batch. The aim of this study is to take account of these variations of the mechanical behavior through a probabilistic approach, to predict the formability limit. The mechanical properties of the materials from the two batches were characterized in tension, to highlight the differences. The initial yield stress and the tensile strength are higher for one material, while the maximum equivalent plastic strain at rupture, determined through a hybrid experimental-numerical approach, is lower. And a significant difference in the transverse anisotropy coefficient is evidenced. A 3D parametric finite element model of the forming stage is developed to investigate the role of some mechanical properties and process parameters on the formability limit in bending. The range of the parameter values comes from the experimental data. Their influence is evaluated through a design of experiments, with the aim of highlighting the influence of the variations of the mechanical properties and process parameters on the fracture criterion, using a probabilistic approach with Gauss’s law.

The article presents and discusses the problem of determining and characterizing the cracking limits of cross-rolled specimens. The limit values were determined in accordance with the hybrid Pater criterion. For the study, the author’s test method was used, which allows the determination of the cracking moment, formed as a result of the Mannesmann effect during the compression of specimens in the channel. In order to determine the values needed to describe the cracking criterion, it was necessary to perform laboratory tests and numerical simulations of the process of compression in the channel of discs made of EA1T steel under hot forming conditions. Experimental tests were carried out for forming processes at 950 °C, 1050 °C and 1150 °C. The tested material had a disc shape with a diameter of 40 mm and a length of 20 mm, during the pressing process the diameter of the disc was reduced to a diameter of 38 mm. The increase in forming temperature caused a significant increase in the forming path until cracking occurred. Numerical tests were carried out in the finite element calculation environment Simufact.Forming 2021. The stress and strain distributions in the specimen axis were analysed during the tests, which were then used to calculate the hybrid cracking criterion limit according to Pater. After calculations according to the Pater criterion and after statistical analysis, the cracking criterion limits were obtained.

The internal hydrodynamic parameters of extrusion liquefier and bonding neck have an important influence on the forming quality of material extrusion additive manufacturing (MEAM) products. To investigate the relationship, theoretical research and experimental analysis are carried out on both the melt flow behavior (MFB) of the molten polylactic acid (PLA) inside the extrusion liquefier and the bonding neck. They are theoretically modelled based on Newton's power law equation and the viscous sintering phenomenon of the extrudate, respectively. The measurement on the melt pressure drop is then performed with a self-made equipment, and the bonding neck of the sample is observed and measured by scanning electron microscope (SEM). Through the comparison between the predicted and measured results, the proposed theoretical models are validated, and they can give reliable predictions in terms of MFB and bonding neck. The results also show that increasing the extrusion temperature and width will reduce the hydrodynamic parameters (pressure drop, shear stress and apparent viscosity), and increase the bonding neck size of the sample, and thereby improve the forming quality of MEAM products. While for the printing speed, the situation is to the contrary.

This study employs a finite element thermo-mechanical model, using a Lagrangian incremental setting to investigate friction extrusion (FE) under varying process conditions. The incorporation of rotation in FE generates substantial frictional heat, leading to significantly reduced process forces in comparison to conventional extrusion (CE). The model reveals the interplay between temperature, strain, and strain rate across different microstructural zones of the resulting wire. Specifically, the sticking friction condition in FE enhances initial shear deformation, aligning with a homogeneous spatial strain distribution and predicting complete grain refinement in the extruded wire, as per Zener-Hollomon calculations. On the other hand, under the sliding friction condition in FE, the shear deformation is reduced which results in an inhomogeneous microstructure in the extruded wire. The analysis of material flow in the workpiece reveals distinct transitions from the base material to the thermo-mechanically affected zones. The simulated process force, thermal history, and microstructure during sliding friction conditions align well with the findings from performed friction extrusion experiments.

We present a methodology for automated forming of metal plates into freeform shapes using shot peening. The methodology is based on a simulation software that computes the peening pattern and simulates the effect of its application. The pattern generation requires preliminary experimental characterization of the treatment. The treatment is applied by a shot peening robot. The program for the robot is generated automatically according to the peening pattern. We validate the methodology with a series of tests. Namely, we form nine aluminum plates into doubly curved shapes and we also shape model airplane wing skins. The article describes the complete workflow and the experimental results.

This paper provides a modeling method for predicting the internal structure of three-dimensional (3D) angle-interlock woven fabric. Inspired by the digital element method, the numerical model of micro-scale was established by using truss element. The numerical model was compared with the Computed Tomography (CT) cross-sectional scan of the actual fabric sample, and the results were consistent. The mechanical properties of the 3D angle-interlock woven fabric is closely related to the fabric’s structure. Therefore, by changing the tension at both ends of the yarn tows to explore the influence on the yarn tows’ geometry, it was found that different tensions affects the cross-sectional areas and crimp angles of the yarn tows. On the basis of fabric forming, multi-shape molds were designed to press the fabric into different shapes, which were semi-hexagonal, arc-shaped and L-shaped. The results of numerical simulation showed that the fabric will undergo inter-layer slip when compressed, especially in the region where the mold deformation is large.