Search

Transfer printing, a crucial technique for heterogeneous integration, has gained attention for enabling unconventional layouts and high-performance electronic systems. Elastomer stamps are typically used for transfer printing, where localized heating for elastomer stamp can effectively control the transfer process. A key challenge is the potential damage to ultrathin membranes from the contact force of elastic stamps, especially with fragile inorganic nanomembranes. Herein, we present a precision-induced localized molten technique that employs either laser-induced transient heating or hotplate-induced directional heating to precisely melt solid gallium (Ga). By leveraging the fluidity of localized molten Ga, which provides gentle contact force and exceptional conformal adaptability, this technique avoids damage to fragile thin films and improves operational reliability compared to fully liquefied Ga stamps. Furthermore, the phase transition of Ga provides a reversible adhesion with high adhesion switchability. Once solidified, the Ga stamp hardens and securely adheres to the micro/nano-membrane during the pick-up process. The solidified stamp also exhibits the capability to maneuver arbitrarily shaped objects by generating a substantial grip force through the interlocking effects. Such a robust, damage-free, simply operable protocol illustrates its promising capabilities in transfer printing diverse ultrathin membranes and objects on complex surfaces for developing high-performance unconventional electronics. A damage-free transfer printing method utilizing localized molten gallium enables the precise manipulation of fragile micro- and nano-films. The method offers adhesion regulation and reliability that cannot be easily achieved by fully liquefied stamps. [ABSTRACT FROM AUTHOR]

The theory and practice of stamping sheet parts for aircraft are reviewed and analysed. The problem of developing scientific grounds for constructing rational technological processes is noted to provide minimal work intensity and cost of manufacturing aircraft parts with the best quality. Forming operations of sheet stamping and its main advantages are considered. A classifier of research areas in the field of metal sheet stamping is developed. As an analysis of existing research shows, improving the sheetstamping process still remains relevant; much attention is paid to the influence of temperature, lubricants, and the configuration of stamping equipment on the sheetstamping process. The drawing quality of samples and the influence of deep drawing on the microstructure and texture of samples are considered. The morphologies of the protective coatings of steel sheets before and after deep drawing are studied. As known, the latent energy of deformation is an important integral characteristic of the substructural state of the metal after plastic deformation and accumulates all common hardening parameters. The influence of latent energy of deformation on the operational properties of parts, as well as on the dimensional stability of parts, is significant that is especially important for thin-walled and precision products. A model for controlling the quality of treatment based on the value of latent energy of deformation is proposed. [ABSTRACT FROM AUTHOR]

As a promising solution to the growing demand for lightweighting, hot stamping has gained considerable applications in the automotive industry. Over the past few decades, the market for hot stamping has experienced explosive growth, with ongoing advancements offering potential for further expansion of its applications. This paper provides a historical overview of hot stamping alongside an in-depth analysis of future trends. Scientific publications, patents and industrial applications of hot stamping are systematically reviewed, with major developments in materials, processes, tools, and other relevant aspects being highlighted. Through data analysis, the current state of hot stamping is comprehensively depicted, and the trends in the development of hot stamping are revealed. Additionally, the future of extending hot stamping technologies to a broader range of materials is discussed, with suggestions furnished from both academic and industrial perspectives. [ABSTRACT FROM AUTHOR]

Perforated metals have many positive attributes, both aesthetic and practical, that make them a suitable material for many applications. Perforation of metals is the process of removal of materials from the sheet metal in different geometries, ornamental forms, or the punching/stamping of holes into metal sheets for practical or aesthetic reasons. This operation is based on different parameters such as the type of material, thickness of material, and open area, which can affect operations such as bending. This research paper focuses on the parametric multi-objective optimization of the press-brake bending process of perforated aluminum alloy, as well as the optimization of the impact of different parameters such as bend angle and blank variables (thickness and pitch perforation) on the springback of perforated aluminum alloys, and also investigates which variable can achieve the best product quality. Aluminum alloy (AA1300) thicknesses of 0.50, 1.00, and 1.50 mm were investigated in this study. The bend angles used are 60°, 90°, and 120°, whereas the blank parameters are plain, square perforated, circular, and staggered perforated. Bending was performed using the finite element method (FEM) tool Abaqus software. Afterward, the springback result of bending was optimized using the multi-objective optimization method. In the 60° bending angle, the perforation has a greater impact on the springback than in the 90° bending angle, and the 90° bending angle has a greater impact than the 120° bending angle. The springback of circular perforated sheet metal is roughly equal to that of the plain sheet metal. The springback of the square perforated sheet AA is nearly equal to that of the plain and other types of perforated aluminum alloys. [ABSTRACT FROM AUTHOR]

Background: The conventional isotropic elastic model neglects the anisotropy of sheet metals' elastic modulus, leading to inevitable errors in springback prediction. Objective: Aiming at the problem of anisotropic springback in the forming process of sheet metals, an orthotropic elastic model was established in this study, and the applicability of the model was analyzed. An accurate and convenient numerical solution method was proposed, considering the challenge of calibrating model parameters through experimental measurement. Methods: The reliability of the proposed parameter solution method is verified by uniaxial tensile and thin-walled tube torsion tests. To verify the anisotropic elastic model, both V-bending finite element simulation and experimental testing were conducted. Results: The proposed parameter solution method has good prediction accuracy, with an average relative error within 5%. The three-group sample solution method significantly reduces experimental and data processing workload, demonstrating the precision and user-friendliness of this method. The proposed model yields a significant enhancement in springback prediction accuracy when compared to the conventional isotropic elastic model. Conclusion: This study is basic research on the prediction of anisotropic springback, which can improve the simulation accuracy of the sheet metals forming process involving this problem, particularly in the anisotropic metal sheet stamping process. [ABSTRACT FROM AUTHOR]

Meso-and microforming is a technology to shape parts from extremely small metal billets. Parts with geometric dimensions are a few millimetres to a few micrometres. With the rapid development of the electrical-electronics industry and biomedical engineering, the technology of forming microscopic parts has been researched and applied because of its efficiency, accuracy, and high productivity. Deep drawing is an operation that turns flat sheet metal blanks into hollow, open-mouth parts. It is an essential process in sheet metal stamping. Micro deep drawing is one of the micro-shaping technologies that has been widely studied and applied in recent years. However, the bases for calculating technological and geometrical parameters in the micro-deep drawing have not yet been analyzed and evaluated in detail. Therefore, this paper has proposed a theoretical basis combined with simulation applied to the design of technology to manufacture a connector head part drawing die with a diameter of 300µm and height of 1500µm using materials SUS304 material. Numerical simulation also allows evaluation of the stamping part's internal stress state, the ability to pull the workpiece into the die, and the thickness distribution on the product wall. Experimental research has also verified that, with the determined parameters, the stamping parts meet the quality requirements. This indicates the proposed calculation methods for the tiny deep drawing operation are entirely suitable. The results of this research can be wholly applied to the production of micro-sized cylindrical cup parts using the deep drawing method. [ABSTRACT FROM AUTHOR]

Burn wounds are a common challenge for medical professionals. Current burn wound models hold several limitations, including a lack of comparability due to the heterogeneity of wounds and differences in individual wound healing. Hence, there is a need for reproducible in vivo models. In this study, we established a new burn wound model using the chorioallantoic membrane assay (CAM) as a surrogate model for animal experiments. The new experimental setup was tested by investigating the effects of the auspicious biophysical therapy, photobiomodulation (PBM), on the wound healing of an induced CAM burn wound with a metal stamp. PBM has been shown to positively influence wound healing through vascular proliferative effects and the increased secretion of chemotactic substances. The easily accessible burn wounds can be treated with various therapies. The model enables the analysis of ingrowing blood vessels (angiogenesis) and diameter and area of the wounds. The established model was used to test the effects of PBM on burn wound healing. PBM promoted angiogenesis in burn wounds on day 4 (p = 0.005). Furthermore, there was a not significant trend toward a higher number of vessels for day 6 (p = 0.065) in the irradiated group. Changes in diameter (p = 0.129) and the burn area (p = 0.131) were not significant. Our results suggest that CAM can be a suitable model for studying burn wounds. The novel experimental design enables reproducible and comparable studies on burn wound treatment. [ABSTRACT FROM AUTHOR]

Precision metal stamping is an industrial process that uses machines equipped with dies to transform flat sheet metal, either in blank or coil form, into various custom shapes. In addition to stamping, these metal presses can also perform a wide range of processes such as stamping, tooling, notching, bending, punching, flanging, coining and more. Precision metal stamping is widely used for the production of a wide range of products. It can be performed as a single-step operation where each stroke of the metal press produces the desired shape on the plate or in a series of steps. The increasing demand for precision metal parts in various industries from medical to automotive and aerospace has pushed precision metal stamping to the forefront of today's manufacturing. This is because it provides a high degree of design flexibility for defining and implementing tiny features with tight tolerances and unique configurations. [ABSTRACT FROM AUTHOR]

Copyright of Revista Iberoamericana de Ingeniería Mecánica is the property of Editorial UNED and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The sheet metal surface crack detection during manufacturing is an essential issue because of both the product quality and process productivity. Development of solutions to eliminate defective products during the metal forming process is crucial for the smooth production and for developing an appropriate tool geometry in the initial phase of the process. Currently, the methods of surface crack detection used in the industry are mostly related to visual inspection. These are methods that require operators of industrial facilities considerable attention and effort to capture emerging discontinuities on the sheet metal surface. Also, this situation results increase in the duration of the specific operations of stamping and significantly reduces productivity. Therefore, an industrial application of a non-contact laser technique that simultaneously provides the results of the speckle imaging is presented. The authors demonstrate a specially designed machine vision system along with experimental tools for the stamping operation. Proposed solution uses the phenomenon of speckle pattern that appears in the image of the investigated sheet surface produced by the laser beam emission. In this method, coherent laser light is emitted to the surface, where a speckle pattern is generated due to scatter reflection from the sheet metal surface and then, shift-and-add technique and image processing is applied. The proposed measurement technique consists, initially, of making a sequence of images of the tested object for the moving surface of the sheet. Secondly, the object's displacement quantity in each image is determined, and the position is corrected. The test object in each image is moved to the starting position, and all images are superimposed. It allows to obtain a high-quality image with visible surface defects. Finally, the dynamically changing speckle pattern intensity is evaluated using Gaussian-of-Laplacian edge detection to investigate a surface crack location due to the surface discontinues and light scattering. This process is recommended for machine vision imaging of distant objects, which works well in industrial conditions as well as online analysis. Also, from the speckle size measurement, an experimental procedure is employed to verify the best condition for vision system resolution. [ABSTRACT FROM AUTHOR]

Non-uniform plastic deformation can easily generate large residual stress in components, resulting in greater springback and warping. Electromagnetic forming (EMF) is a high-speed forming method that can reduce springback of parts. In this study, the warping deformation height after quasi-static sheet metal stamping was found to be 12.2 mm, due to large radial compressive and tensile stresses on both the inside and outside of the sheet fillet. When a radial magnetic force was applied at sheet edge, warping deformation was eliminated. The effects of blank holder gap and discharge voltage on sheet warpage were analyzed both experimentally and through numerical simulation. After coil discharging, radial stress on inner and outer surfaces of the sheet fillet significantly decreased. When the discharge voltage was 4.5 kV and the blank holder gap was 0.5 mm, the warping deformation height was reduced to 0.8 mm and the sheet surface was smooth. Therefore, electromagnetic forming is an efficient, high precision method that eliminates warping of parts. [ABSTRACT FROM AUTHOR]

Cell spheroid culture can recapitulate the tissue microstructure and cellular responses in vivo. While there is a strong need to understand the modes of toxic action using the spheroid culture method, existing preparation techniques suffer from low efficiency and high cost. Herein, we developed a metal stamp containing hundreds of protrusions for batch bulk preparation of cell spheroids in each well of the culture plates. The agarose matrix imprinted by the stamp can form an array of hemispherical pits, which facilitated the fabrication of hundreds of uniformly sized rat hepatocyte spheroids in each well. Chlorpromazine (CPZ) was used as a model drug to investigate the mechanism for drug induced cholestasis (DIC) by agarose-stamping method. Hepatocyte spheroids showed a more sensitive detection of hepatotoxicity compared to 2D and Matrigel-based culture systems. Cell spheroids were also collected for staining of cholestatic protein and showed a CPZ-concentration-dependent decrease of bile acid efflux related proteins (BSEP and MRP2) and tight junction (ZO-1). In addition, the stamping system successfully delineated the DIC mechanism by CPZ that may be associated with the phosphorylation of MYPT1 and MLC2, two central proteins in the Rho-associated protein kinase pathway (ROCK), which were significantly attenuated by ROCK inhibitors. Our results demonstrated a large-scale fabrication of cell spheroids by the agarose-stamping method, with promising benefits for exploring the mechanisms for drug hepatotoxic responses. [Display omitted] [ABSTRACT FROM AUTHOR]

Purpose: This article seeks to establish a statistical analysis to estimate the time of stoppages in a stamping line, which have a high variability that generates an unreliable scenario for the production program. Likewise, this document shows the methodological sequence to carry out a statistical analysis in a case study at an industrial level, considering variables of a real scenario. Design/methodology/approach: The methodological sequence is divided into five stages. Initially, the information of the stamping process was collected, later the types of stoppage were categorized according to the characteristics of the process. A collection of historical data information on stoppage times was carried out. With the information collected, the percentage frequency of occurrence of stops due to tool changes and incidents in the process was determined, and they were characterized by a Weibull distribution. Finally, to verify the effectiveness of the downtime behavior, a model was developed to simulate the availability of the stamping line in the Vensim PLE® program. Findings: The model showed that the frequency analysis and the Weibull distribution obtained a similar behavior to reality. The study verified that it is necessary to establish a categorization of the characteristics of the downtimes, according to the characteristics of the pieces produced to evaluate the information, in this way, the times of change by tooling were established through a frequency of use and the stoppages by additional incidences to the process were better. Research limitations/implications: The basis for this study is the reliability of the information, especially in the data record. It has the disadvantage that the bias of the analyst is present when the information is recorded and analyzed. Practical implications: The methodology presented in this article is a reference for industrial applications in which it is required to establish improvement scenarios based on the reduction of stoppages present in the production lines. Originality/value: The importance of this study is that it was possible to establish a suitable workload allocation in the presses to optimize production. [ABSTRACT FROM AUTHOR]

The research on methods for monitoring sheet metal stamping is benefiting from the increased availability of enabling technologies such as sensors, data mining software, cloud computing, and artificial intelligence. The predictive maintenance policies of tools (punches and dies) can be targeted at monitoring progressive wear or at the detection of sudden failures or anomalies. Early detection of tool failure is the method preferred by the recent literature on data management in sheet metal stamping. However, the stamping of small parts poses challenges due to multiple tools and signals and limited visibility of die wear, requiring management of multiple sensors and data sources. This paper proposes a failure prevention approach for progressive die stamping using global and local force sensors with upper bounds for maximum values to indicate unhealthy conditions. The methodology was tested on millions of small washers made of carbon steel. The stamping process was implemented using a servo-press with a high rate. The press was equipped with eight in-process sensors, including strain gauges, thin foil force sensors, and acoustic sensors. The data of material properties, maintenance reports, statistical process control data, and in-process sensors were collected and stored in a data lake. By combining the in-process sensor acquisition with the corresponding log events and maintenance data in the same time span, it is possible to look for correlations among the variables and build an effective tool health prevention policy. [ABSTRACT FROM AUTHOR]

Statistics on the production of a secondary tin show that its use in many countries reaches a significant amount. One of the most important sources of secondary tin is a scrap of white sheet metal formed by stamping various products, waste from used cans, and other obsolete tin products. In the present work, using chemical, electrochemical and physical methods, a technology for dissolving tin from used cans in alkaline solutions with the addition of p-nitroaniline and its electroextraction from solutions is proposed. The optimal conditions of dissolution and extraction (concentration and temperature of the medium, current density, current yield), as well as the chemical composition of the obtained metal tin, are determined. [ABSTRACT FROM AUTHOR]

The tailgate‐extension in a vehicle is a part that connects the upper and lower parts of the tailgate. Since this part does not require high strength, aluminum must be used in order to reduce the weight of the vehicle. However, when choosing aluminum, it is difficult to satisfy the shape quality with the existing manufacturing process. Therefore, this study was conducted for the purpose of optimizing the draw metal stamping process for the development of tailgate extensions for vehicles using aluminum. The response surface methodology was utilized to optimize the draw metal stamping process. The process design parameters were established as blank holding force, coefficient of friction and die speed. Finally, the reliability of the optimization process and finite element analysis was secured by conducting field experiments to review the derived optimal process conditions. [ABSTRACT FROM AUTHOR]

Sheet metal stamping is widely used for high-volume production. Despite the wide adoption, it can lead to defects in the manufactured components, making their quality unacceptable. Because of the variety of defects that can occur on the final product, human inspectors are frequently employed to detect them. However, they can be unreliable and costly, particularly at speeds that match the stamping rate. In this paper, we propose an automatic inspection framework for the stamping process that is based on computer vision and deep learning techniques. The low cost, remote sensing capability and simple implementation mean that it can be easily deployed in an industrial setting. A particular focus of this research is to account for the harsh lighting conditions and the highly reflective nature of products found in manufacturing environments that affect optical sensing techniques by making it difficult to capture the details of a scene. High dynamic range images can capture details of an environment in harsh lighting conditions, and in the context of this work, can capture highly reflective metals found in sheet metal stamping manufacturing. Building on this imaging technique, we propose a framework including a deep learning model to detect defects in sheet metal stamping parts. To test the framework, sheet metal 'Nakajima' samples were pressed with an industrial stamping press. Then optimally exposed, sequence of exposures, tone-mapped and high dynamic range images of the samples were used to train convolutional neural network-based detectors. Analysis of the resulting models showed that high dynamic range image-based models achieved substantially higher accuracy and minimal false-positive predictions. [ABSTRACT FROM AUTHOR]

A key lesson of the Wooster Group's production of Bertolt Brecht's learning play The Mother concerns the meaning of ownership in capitalism. Unlike other businesses that moved into SoHo during the wave of deindustrialization that began in the late 1960s, the group of actors that owns a former metal stamping factory at 33 Wooster Street shows that their relationship towards their means of production is not only economic, but also ethical. This is at the foundation of their distinct theatrical aesthetics. [ABSTRACT FROM AUTHOR]

Inhomogeneous metal flow in stamping non-axisymmetric parts makes material deformation in the flange critical, resulting in uneven sheet thickness distribution, high blank holder forces or even the need to use draw beads to compensate for large material draw-in. The paper presents an innovative mechatronic system for the adaptive control of the blank holder force, which integrates ferrofluidic actuators and non-contact sensors for the in-line material flow measurement, with the aim of exploring, through laboratory-scale experiments, the feasibility of its implementation in stamping processes and understanding the potential benefits to enable more reliable process design. [ABSTRACT FROM AUTHOR]

Background: The anisotropic behavior of sheet metal has a significant influence on the plastic forming process, especially the accurate description of the plastic flow (r-value).The purpose of this paper is to reveal the influence of different evolutionary r-value solution methods on yield model prediction.Uniaxial and biaxial tensile experiments were carried out for DP590. The principles and results of r-value calculation based on slope method and polynomial fitting method are compared and analyzed. On this basis, the inverse solution method based on exponential function is established. The prediction results of Hill48, Hill48-non and Yld2000-2D yield models based on different r-value solution methods were compared. Furthermore, anisotropic yield models calibrated by different r-value solution methods are used as user material subroutine (VUMAT) to achieve cup-drawing simulation in ABAQUS.In the theoretical prediction of anisotropic yield model, the prediction accuracy of the three yield models is the best when the new inverse exponential function method is used. The earing height obtained by the three yield models based on inverse exponential function method calibration is more consistent with the physical experiment, while the prediction accuracy of the traditional slope method is the worst.The appropriate r-value solution method can improve the predictive accuracy of anisotropic yield model. The research results provide a method for the anisotropic parameter calibration strategy of yield model considering anisotropic evolution, and provide an effective reference scheme for improving the prediction accuracy of deformation behavior in sheet metal stamping.Objective: The anisotropic behavior of sheet metal has a significant influence on the plastic forming process, especially the accurate description of the plastic flow (r-value).The purpose of this paper is to reveal the influence of different evolutionary r-value solution methods on yield model prediction.Uniaxial and biaxial tensile experiments were carried out for DP590. The principles and results of r-value calculation based on slope method and polynomial fitting method are compared and analyzed. On this basis, the inverse solution method based on exponential function is established. The prediction results of Hill48, Hill48-non and Yld2000-2D yield models based on different r-value solution methods were compared. Furthermore, anisotropic yield models calibrated by different r-value solution methods are used as user material subroutine (VUMAT) to achieve cup-drawing simulation in ABAQUS.In the theoretical prediction of anisotropic yield model, the prediction accuracy of the three yield models is the best when the new inverse exponential function method is used. The earing height obtained by the three yield models based on inverse exponential function method calibration is more consistent with the physical experiment, while the prediction accuracy of the traditional slope method is the worst.The appropriate r-value solution method can improve the predictive accuracy of anisotropic yield model. The research results provide a method for the anisotropic parameter calibration strategy of yield model considering anisotropic evolution, and provide an effective reference scheme for improving the prediction accuracy of deformation behavior in sheet metal stamping.Methods: The anisotropic behavior of sheet metal has a significant influence on the plastic forming process, especially the accurate description of the plastic flow (r-value).The purpose of this paper is to reveal the influence of different evolutionary r-value solution methods on yield model prediction.Uniaxial and biaxial tensile experiments were carried out for DP590. The principles and results of r-value calculation based on slope method and polynomial fitting method are compared and analyzed. On this basis, the inverse solution method based on exponential function is established. The prediction results of Hill48, Hill48-non and Yld2000-2D yield models based on different r-value solution methods were compared. Furthermore, anisotropic yield models calibrated by different r-value solution methods are used as user material subroutine (VUMAT) to achieve cup-drawing simulation in ABAQUS.In the theoretical prediction of anisotropic yield model, the prediction accuracy of the three yield models is the best when the new inverse exponential function method is used. The earing height obtained by the three yield models based on inverse exponential function method calibration is more consistent with the physical experiment, while the prediction accuracy of the traditional slope method is the worst.The appropriate r-value solution method can improve the predictive accuracy of anisotropic yield model. The research results provide a method for the anisotropic parameter calibration strategy of yield model considering anisotropic evolution, and provide an effective reference scheme for improving the prediction accuracy of deformation behavior in sheet metal stamping.Results: The anisotropic behavior of sheet metal has a significant influence on the plastic forming process, especially the accurate description of the plastic flow (r-value).The purpose of this paper is to reveal the influence of different evolutionary r-value solution methods on yield model prediction.Uniaxial and biaxial tensile experiments were carried out for DP590. The principles and results of r-value calculation based on slope method and polynomial fitting method are compared and analyzed. On this basis, the inverse solution method based on exponential function is established. The prediction results of Hill48, Hill48-non and Yld2000-2D yield models based on different r-value solution methods were compared. Furthermore, anisotropic yield models calibrated by different r-value solution methods are used as user material subroutine (VUMAT) to achieve cup-drawing simulation in ABAQUS.In the theoretical prediction of anisotropic yield model, the prediction accuracy of the three yield models is the best when the new inverse exponential function method is used. The earing height obtained by the three yield models based on inverse exponential function method calibration is more consistent with the physical experiment, while the prediction accuracy of the traditional slope method is the worst.The appropriate r-value solution method can improve the predictive accuracy of anisotropic yield model. The research results provide a method for the anisotropic parameter calibration strategy of yield model considering anisotropic evolution, and provide an effective reference scheme for improving the prediction accuracy of deformation behavior in sheet metal stamping.Conclusions: The anisotropic behavior of sheet metal has a significant influence on the plastic forming process, especially the accurate description of the plastic flow (r-value).The purpose of this paper is to reveal the influence of different evolutionary r-value solution methods on yield model prediction.Uniaxial and biaxial tensile experiments were carried out for DP590. The principles and results of r-value calculation based on slope method and polynomial fitting method are compared and analyzed. On this basis, the inverse solution method based on exponential function is established. The prediction results of Hill48, Hill48-non and Yld2000-2D yield models based on different r-value solution methods were compared. Furthermore, anisotropic yield models calibrated by different r-value solution methods are used as user material subroutine (VUMAT) to achieve cup-drawing simulation in ABAQUS.In the theoretical prediction of anisotropic yield model, the prediction accuracy of the three yield models is the best when the new inverse exponential function method is used. The earing height obtained by the three yield models based on inverse exponential function method calibration is more consistent with the physical experiment, while the prediction accuracy of the traditional slope method is the worst.The appropriate r-value solution method can improve the predictive accuracy of anisotropic yield model. The research results provide a method for the anisotropic parameter calibration strategy of yield model considering anisotropic evolution, and provide an effective reference scheme for improving the prediction accuracy of deformation behavior in sheet metal stamping.Graphical Abstract: The anisotropic behavior of sheet metal has a significant influence on the plastic forming process, especially the accurate description of the plastic flow (r-value).The purpose of this paper is to reveal the influence of different evolutionary r-value solution methods on yield model prediction.Uniaxial and biaxial tensile experiments were carried out for DP590. The principles and results of r-value calculation based on slope method and polynomial fitting method are compared and analyzed. On this basis, the inverse solution method based on exponential function is established. The prediction results of Hill48, Hill48-non and Yld2000-2D yield models based on different r-value solution methods were compared. Furthermore, anisotropic yield models calibrated by different r-value solution methods are used as user material subroutine (VUMAT) to achieve cup-drawing simulation in ABAQUS.In the theoretical prediction of anisotropic yield model, the prediction accuracy of the three yield models is the best when the new inverse exponential function method is used. The earing height obtained by the three yield models based on inverse exponential function method calibration is more consistent with the physical experiment, while the prediction accuracy of the traditional slope method is the worst.The appropriate r-value solution method can improve the predictive accuracy of anisotropic yield model. The research results provide a method for the anisotropic parameter calibration strategy of yield model considering anisotropic evolution, and provide an effective reference scheme for improving the prediction accuracy of deformation behavior in sheet metal stamping. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental studies aimed at determining constitutive parameters for selected constitutive equations of flow stress as a function of the natural aging time of 2 mm thick AlCu4Mg1 (AW-2024) sheet. The knowledge of these constitutive parameters as a function of aging time is necessary to analyze and model the processes of forming sheet metal stampings after heat treatment during natural aging. The constitutive parameters in individual constitutive equations were determined on the basis of the approximation of the course of strain hardening curves. The courses of these curves for the tested natural aging times in the range of 0–120 minutes after heat treatment were made on the basis of uniaxial stretching tests of samples taken in the directions of 0o, 45o and 90o to the direction of sheet rolling. The values of constitutive parameters as a function of natural aging time were determined for four popular models of flow stress: Hollomon, Swift, Voce and El-Magd. Moreover, the relationship between the natural aging time and the value of the yield strength in the tested aging time range was determined, and the accuracy of the investigated constitutive equations for describing the course of the flow stress of the tested sheet material was assessed on the basis of the analysis of approximation errors. [ABSTRACT FROM AUTHOR]

The 6xxx Al–Mg-Si heat-treatable alloy is lightweight, has good formability before baking-hardening, and enhanced strength after baking. The aluminum alloy is to replace steel in many automotive stamping sheet metal parts. However, under the normal hot rolling process, 6xxx aluminum alloy is prone to surface roping defects, owing to the uneven texture in the thickness direction. Aluminum with severe roping can also produce curling of the specimen in a uniaxial tensile test. The literature and related phenomena infer that the material thickness direction does not have a uniform r value. The r value measured by the test machine does not represent the actual whole r value of the material. Therefore, in this paper, the actual r values of the top and bottom surfaces of the material are derived from the geometry of the curl of the specimen. An alkali etching method is developed to layer the aluminum sheet's thickness. The layer is used for tensile testing to verify the aluminum sheet's actual r value and derive the difference in r value. Then, experiments and numerical simulations are used to show that the variation of thickness direction r is the leading cause of curl in the tensile specimen. Furthermore, the numerical simulation was used to evaluate the difference in r value of an aluminum sheet in each thickness layer and the effect of thickness layer on curl and then make a reasonable explanation and correction of the difference between the tensile test and simulation. Using this method can obtain a more accurate r value as the material parameter for each thickness direction of an aluminum sheet, which certainly improves the accuracy of numerical simulation and analysis for other forming processes. [ABSTRACT FROM AUTHOR]

In this paper, a compact 3 kW air-cooled fuel cell stack consists of 95 single cells with metallic bipolar plate is designed. Compared with graphite bipolar plates, metal stamping bipolar plates are lighter in weight, smaller in size and faster in heat conduction, therefore the transient behaviors of the voltage and temperature of each cell are analyzed. The results show that the heat distribution of the air-cooled fuel cell is very uniform, and the temperature difference between the inlet and outlet of cathode air of the fuel cell is lower than 15 °C. The individual cell voltage uniformity percentage variation value reaches 7% when the drop in the loading current is over 25 A. Moreover, the voltage uniformity variation value is higher than 4% when the loading current output exceeds 35A. Thus, a large drop in loading and a high loading current easily increase the voltage uniformity variation value. Long-term continuous operation has a negative influence on the performance of the stack, especially the last fuel cell near the anode outlet. Anode purging can effectively alleviate the uniformity percentage variation in the voltages. The designed air-cooled fuel cell exhibits good performance and strong environmental adaptability. • Ultra-thin gold-plated metal bipolar plates. • The temperature difference in a single fuel cell is lower than 15 °C. • Continuous operation has negative influence on the fuel cell near the anode outlet. • The designed air-cooled stack exhibits strong environmental adaptability. [ABSTRACT FROM AUTHOR]

3D printed polymer composite materials offer a cost-effective and rapid tooling option for prototyping, and low-cost, low-volume sheet metal forming applications. Due to the high anisotropy in mechanical properties of 3D printed composites, accurate characterization and finite element modeling of the material become paramount for successful design and application of these forming tools. This paper presents experimental characterization of 3D printed fiber–reinforced polymer composite material at various strain rates. A homogenized material model with orthotropic elasticity and the Hill 1948 anisotropic yield criterion were then calibrated based on these experimental data. Finite element simulations of the stamping of high-strength steel sheets using composite tooling were performed, and tool deformation was predicted and compared with experimental measurements. FE simulation results were in good agreement with stamping experiments performed with polymer tooling. It was found that the anisotropy and strain rate sensitivity of 3D printed polymer composites play a significant role in their performance as tooling materials. [ABSTRACT FROM AUTHOR]