In sheet-forming operations, it has been sought to always obtain the maximum elongation of the material without the occurrence of defects, a condition that is of fundamental importance to know the ...performance of the sheet metal in industrial processes. In view of this need, the FLCs (forming limit curves) of the used metal sheets are determined, which provide an excellent condition for the evaluation of the material stamping limit. Deformation levels lower than FLC, considering a safety margin, are considered satisfactory in industrial operations. Based on this, the objective of this work was the adequacy of a test machine and the development of a method to obtain the FLC of sheet metal at the beginning of the material’s bonding, thus seeking a more precise result of the formability of the main steels used in the industry, advanced high strength steels. For this, an initial analysis of the hydraulic press was carried out where, taking advantage of the displacement and oil pressure sensors present, a new control program was determined in the PLC (programmable logic controller), to parameterize the points that precede the rupture of the sheet during the stamping test. Under these conditions, the FLC of the dual-phase steel DP600 was determined until its rupture and, later, until the point of its beginning, which allowed the definition of the real limit of formability of this material. In addition to the conclusion regarding the behavior of the material, considering the industrial processes, the results obtained also allow the determination of set points of machines more adequate to the limits of deformation of the sheet metal used. The FLC presented a variation, characterized by a small increase in the formability limit for the tests with hydraulic press temperature control conditions. The results highlighted higher temperatures on the pump, followed by the distributing block and the pressure sensor, concluding that the major influence critical point on the FLC result was the hydraulic pump.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The advanced high-strength steels (AHSS) have become an interesting alternative to the automotive industry to reduce vehicle weight and therefore reduce fuel consumption. However, the wide variety of ...applications in the automotive industry is still limited due to challenges in its formability and unloaded behavior of these steels popularly called as springback. Computational tools for numerical simulation have been employed in the industrial environment to help predict the occurrence of springback and defining the appropriate parameters to eliminate or reduce their magnitude. However, the accuracy of the numerical results for AHSS still failed to reach a satisfactory level. The limitation in predicting the springback of AHSS by means of finite element method (FEM) is assigned to computationally difficult to characterize the mechanical behavior of these steels during the plastic strain. The variation of elastic modulus during plastic strain is considered as a major cause of non-linearity of the behavior of these steels. This work aims to study the declining behavior of the modulus of elasticity with an increasing plastic strain objecting to an improvement in the computational prediction of the springback phenomenon of AHSS. Specimens of various AHSS steels were loaded and unloaded in uniaxial tension in 0°, 45°, and 90° to the rolling direction. For all AHSS, it was found that the elastic modulus decreases during loading and unloading after each acquired plastic strain approximately up to 10% of plastic strain and then saturates at higher strain values. Further, the L-bending test was simulated where the change of elastic modulus with respect to plastic strain as observed in the uniaxial tension test is informed through the user subroutine VUSDFLD material model. The springback results were then compared with the experiments. It was found that predictions are in close agreement with experiments after informing the model with the decline of elastic modulus with respect to plastic strain through user subroutine material model as compared to the baseline model.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
During the development of an automobile part obtained by stamping process, time and money are required aiming process planning and setup of a new tooling. One of the difficulties in stamping is to ...know if the chosen material will have sufficient formability to reach the final form required by the project. Because of this difficulty, it is very interesting to propose a method that can accurately simulate the forming process. The failure criteria can be mathematical or empirical models capable of determining the onset of necking for each stress/strain states. It is interesting to find a failure criterion that can be easily determined and provides a good ability to detect the failure accurately. In this study, six different failure criteria were studied. Five of them are classified as ductile damage models and they depend on the stress triaxiality and plastic strain. The last criterion depends only on the deformations in the main directions and it is called the forming limit curve (FLC). Computational models through finite element analysis (FEA) were used. The formability was evaluated by monitoring the displacement of the punch until the failure of the material. Lou and Huh criterion and Johson-Cook criterion have been able to provide approximation errors in the range of 0.7–5% which makes them interesting for practical implementation in the industry.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Mostly, stamping industries, especially the automobile, uses a single machine to manufacture several parts. As a result, a time to try out stamping tools to start a new production cycle is often ...necessary. To reach the expected degree of satisfaction for the product, the tryout involves: choosing a material with better formability, adjustments in the design of punches, dies, and components that assemble the tooling. For this, the development of laboratory tests, which allows a better understanding of material stamp-ability and the influence of tooling parameters, become essential for smooth preparation for production and the development of more accurate computational models. Given these challenges, the present work studies the influence of the drawbead geometry and the blank holder force (BHF) on the stampability of DP780 steel. For this, an interchangeable drawbead system was developed for a Nakazima test tool. The four drawbead geometries were used: flat (without salience projection), circular, triangular, and square. In addition, three-level of BHF were used. For each set of drawbead geometry and BHF, the forming limit curve (FLC) of DP780 steel was obtained and analyzed. From the results, it was possible to observe the best configuration of drawbead and BHF. Furthermore, the results showed clear gains in formability and the influence of drawbead geometry and BHF on the DP780 stamping.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
One of the major manufacturing processes to produce components from flat sheets is forming. The automotive industry is one of the highest markets for stamped parts and is, thus, a major driving force ...for the development of new materials and technologies. In recent decades, there is increasing competition and growing demand for light weight, high-performance, and crashworthiness structures in the automotive vehicle forced steel industry, automakers, and the scientific community to focus more on efficient manufacturing. In recent decades, the increasing competition and growing demand for steel structures in automobiles was observed, especially for advanced high-strength steel (AHSS) parts. Thus, a better understanding of the formability of these materials is necessary to reduce costs and optimize the process. In order to better understand the mechanical behavior of AHSS, many authors have been researching the fracture aspects related to the stamping conditions. The main aim of this study was to analyze the type of fracture in DP600 steel when subjected to different stress/strain states (uniaxial and biaxial stress and plane strain) imposed by deep drawing and stretching. The experimentations led to a detailed understanding of the influence of stress/strain state in the mechanism of fracture, particularly, under plane strain—which showed quasi-cleavage regions surrounded by dimples. In addition, the microstructural analysis confirmed that the DP600 steel can show ductile fractures with some aspects of brittle behavior, depending of which stress/strain state was used for deformation. As a result, the DP600 forming limit curve related to micromechanisms of fracture generated by uniaxial and biaxial tensile stress and plane strain was presented.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In sheet forming operations, the conventional way to provide the limit condition for material stamping is through Forming Limit Curves (FLC). Iso 12004-2 1 point out Nakazima test as a precursor of ...FLC data. However, the Nakazima test is carry out until rupture limit, which overcome the frontier of real thinning of the sheet, considered to be at the onset of necking. In this work we propose a modified Nakazima test to reach the onset of necking and present the potential use of FLC at necking as a natural security factor for DP600 steel. The correlation between DP600 rupture and necking are presented for different sheet dimensions. As main result, 95% of rupture pressure and 95% of rupture punch displacement are in accordance with the pressure and displacement of the onset of necking. This proportion minimizes the error function and can be applied for all the sheet lateral dimensions.
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CEKLJ, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Changes are often necessary during the tryout of stamping tools. These changes may range from adjustments on die and punch designs to the selection of a new material with better formability ...characteristics. All these actions, however, require time and money creating the need for better initial sheet metal evaluation. Hence, increasing attention has focused on the development of laboratory tests that enable stamping companies to know more about the sheet metal stampability or that can, at least in part, ensure that their stamped products are produced without major problems. Identification of high stress region on stamping may allow for better tool stamping adjustment during tests, rendering a more uniform material's deformation and leading to the production of higher quality parts. Increasing attention has focused on the material evaluation based on the tool geometries in order to calculate the strain distribution. This study deals with an evaluation of four punch models with varied geometries in addition to the traditional Nakazima test tool. An evaluation was also made of the major true strain distribution profile at points distributed linearly from the region close to the die shoulder to the punch center.
The forming tests are being developed with the purpose of enabling forming companies to better understand the sheets formability. The identification of the regions where tension-tension, ...tension-compression, and/or plane strain occurred during the forming process can aid the process planning through the tools geometry optimization. This work consisted of evaluating, experimental and numerically, the major true strain obtained with different punch designs, which were used in addition to the traditional Nakazima test tool. The main objective was to study the true strain profile as an alternative method to analyze the tool design influence on stretching forming of high stampability steels (DC 06). The friction coefficient was investigated, and an evaluation was also made of the chosen program's response quality (validation). The results are given as a major true strain distribution profile at points distributed linearly from the region close to the die radius to the punch pole. The result expectation is to help the process planning and the material evaluation based on the correct tool design specification in order to obtain the desired true strain distribution in the formed part.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In sheet metal stamping, several variables must be taken into account such as the material's mechanical properties, the tool's geometry, interface lubrication between punch and sheet metal and ...deformation rate, among others. This paper reports on a study of the lubricant's influence on the stretching forming process. The lubricants used ranged from liquid, such as mineral and vegetable oils with extreme pressure additives and synthetic fluids to solid PVC (polyvinyl chloride) and polyurethane films. In this work, the main objective was to study a minor strain profile as an alternative method to analyze the influence of solid and liquid lubricants on stretching forming of high stampability steels (DC 06). The minor true strain distribution profile was obtained, from the die radius to the punch pole, from stamping tests with stretching characteristics. Analyses of the strain distribution profile and of the fracture position allow an evaluation of the lubrication efficiency. Of the five lubricants studied, the results indicated that the solid polyurethane film yielded the best performance, promoting a more homogeneous distribution profile of the minor true strain (ε2), increasing from the die radius to the punch pole, where tearing of the metal sheet occurred.
Promjene su često potrebne prilikom testiranja alata za štancanje. Te promjene mogu varirati od promjena na matrici i dizajnu žiga do odabira novih materijala sa boljim karakteristikama oblikovanja. ...Identifikacija područja na izratku gdje istezanje, duboko vučenje i/ili ravninsko deformiranje nastaje tijekom procesa oblikovanja može dozvoliti da proces teče glatko preko optimizaciju alatne geometrije. Danas se pažnja posvećuje na ispitivanje materijala baziranog na alatnoj geometriji. U ovome radu, efekt krivulje očvršćivanja za modele žigova sa promjenjivim geometrijama su analizirane u dodatku sa tradicionalnom metodom Nakazima za ispitivanjem alata. Otkrilo se je da markirano smanjenje radijusa alata (R1 i R2 radijus) smanjuje potencijal na način da se smanjuje glavno naprezanje.
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