International Journal of Material Forming最新文献

This study aims to provide precise predictions for the compression of reinforced polymers during the sheet Molding Compound (SMC) process, ensuring the attainment of a predefined structure while preventing material overflow during the process. The primary challenge revolves around identifying the optimal initial shape to prevent material rebound during the process. To confront this issue, a numerical model is utilized, faithfully simulating the SMC process and forming the foundation for our investigations. Furthermore, to optimize the pre-fill stage, a surrogate model is proposed to enhance modeling efficiency, and then an inverse analysis method is applied. This approach of minimizing material rebound during the SMC process results in a reliable metamodel to predict an initial mass shape accurately and at a low computational cost, thus ensuring the squeezed material fits the mold shape.

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.

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.