Papers by Keyword: Forming Limit

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Authors: K.H. Min, B.D. Ko, B.S. Ham, J.H. Ok, Beong Bok Hwang, H.S. Koo, Jung Min Seo
Abstract: In this paper, the forming limit of flange in radial extrusion process was analyzed by the rigid-plastic finite element method. The selected model material for simulation and experiments was AA 3105 aluminum alloy. The predictions from simulation were made in terms of axial and circumferential strains. Experiments also have been conducted to compare with the simulation results with regards to deformation pattern. Furthermore, the deformation pattern in forming of flange section was closely investigated and categorized in three cases such as sticking, separating and cracking. The analysis in this paper is focused on the transient extrusion process of material flow into the gap in radial direction for different gap heights and die corner radii. The results of present study were summarized in terms of evolution of surface strains in axial and circumferential directions measured from the finite element meshes located in the region where surface cracking occurred in experiments. The forming limit line was drawn in the relationship of circumferential and axial strain. It was concluded from this study that the forming limit line is influenced mainly by circumferential strain on free surface of flange. It was also predicted that ductile fracture on flange surface is likely to occur in the middle of flange gap under the condition of sticking deformation and near bottom of flange gap under the condition of separating deformation, respectively. The forming limit of flange in terms of flange diameter was expected about 2.5do, which is 2.5 times the diameter of original billet.
577
Authors: Marilena Butuc, Frédéric Barlat, José Grácio, Gabriela Vincze
Abstract: The present paper aims at a theoretical study of the forming limits of a sheet metal subjected to double strain path changes by using as reference material the AA6016-T4 aluminum alloy sheet. The simulation of plastic instability is carried out through the Marciniak-Kuczynski analysis. The initial shape of the yield locus is given by the Yld2000-2d plane stress yield function. The strain hardening of the material is described by the Voce type saturation law. Linear and several complex strain paths involving single and double strain path changes are taken into account. The validity of the model is assessed by comparing the predicted and experimental forming limits under linear and selected one strain path change. A good accuracy of the developed software on predicting the forming limits is found. A sensitive analysis of the influence of the type and value of the double prestain in the occurrence of the plastic flow localization is performed. A remarkable effect of the double strain path change on the sheet metal forming limits is observed.
127
Authors: Mariano Serenelli, María Bertinetti, Pablo Turner, Javier Signorelli
Abstract: The Forming Limit Diagrams (FLDs) of textured polycrystalline sheet metals were investigated using micro-macro averaging and two types of grain-interaction models: Full-Constraint (FC) and Self-consistent (SC) schemes, in conjunction with the Marciniak–Kuczynski (MK) approach. By referring to previous FLD studies based on the FC-Taylor model ─ Wu and coworkers [Effect of an initial cube texture on sheet metal formability, Materials Science and Engineering A, 364:182–7, 2004] and Inal and coworkers [Forming Limit comparison for FCC and BCC sheets, International Journal of Plasticity, 21:1255-1266, 2005] ─ we found that the MK-FC strategy leads to unrealistic results. In the former case, the researchers found that an increasing spread about the cube texture produces unexpectedly high limit strains. In the latter work, Inal et al. predicted a remarkably low forming-limit curve for a FCC material and an extremely high forming-limit curve for a BCC material, in the biaxial-stretching range. Our investigations show that simulations performed with the MK-VPSC approach successfully predict more reliable results. For the BCC structure, the MK-VPSC predictions do not give the extreme values predicted when calculations are carried out with the MK-FC approach. In the FCC case, with decreasing textural intensity ─ from the ideal cube texture, through dispersions around the cube texture with increasing cut-off angles, to a random texture ─ a smooth transition in increasing limit strains was obtained. Furthermore, these results suggest that the selected constitutive model is critical for predicting the behavior of materials that exhibit a qualitative change in crystallographic texture, and hence, evolve anisotropically during mechanical deformation.
327
Authors: Fung Huei Yeh, Ching Lun Li, Kun Nan Tsay
Abstract: This paper presents an explicit dynamic finite element method (FEM) in conjunction with the forming limit diagram (FLD) to analyze the forming limit for the various arc radii of punch in micro deep drawing of square cup. In the present study, the tensile test and friction test are performed to obtain the material parameters of the electro-deposited copper foil according to the ASTM standards. Importing these properties, the numerical analysis is conducted by the explicit dynamic FEM. The FLD in numerical simulation is used as the criterion of the forming limit in micro deep drawing of the square cup. The forming limit, deformed shape, punch load-stroke relationship, height of cup and thickness distribution of square cup, are discussed and compared with the experimental results. It shows that a good agreement is achieved from comparison between simulated and experimental results. When the arc radii of punch increase with Rp=0.2, 0.5 and 0.8mm, the limit drawing ratio increases from 1.90 to 2.03 and 2.10. The forming limit of square cup increases with an increase of the arc radii of punch. From this investigation, the results of this paper can be used as reference in the relative researches and applications of micro forming.
660
Authors: Fung Huei Yeh, Ching Lun Li, Kun Nan Tsay
Abstract: This paper presents an explicit dynamic finite element method (FEM) in conjunction with the forming limit diagram (FLD) to analyze the forming limit for the SPCC foil in micro deep drawing of square cup. In the present study, the tensile, anisotropic and friction test are performed to obtain the material parameters of the alloy foil according to the ASTM standards. Importing these properties, the numerical analysis is conducted by the explicit dynamic FEM. The FLD in numerical simulation is used as the criterion of the forming limit in micro deep drawing of the square cup. The forming limit, punch load-stroke relationship, deformed shape and thickness distribution of square cup, are discussed and compared with the experimental results. It shows that a good agreement is achieved from comparison between simulated and experimental results. The limit drawing ratio in micro deep drawing of square cup is 2.08 in this paper. From this investigation, the results of this paper can be used as reference in the relative researches and applications of micro forming.
344
Authors: Kang Chen, Cheng Yun Peng, Tao Zhou, Bao Bao Li
Abstract: Blank holder force of box deep drawing is studied changes with time and displacement by DYNAFORM numerical simulation software. The results shows that, when the straight edge part of the blank holder force is constant, rounded part adopts small blank holder force can significantly improve the forming limit of box deep drawing, but the wrinkle is still evident. If the straight edge and rounded part of the blank holder force changes with time, not only deep drawing limit increase, wrinkles are also significantly reduced, indicating that the forming limit of the box shaped part is more effective on the blank holder force changes over time than with the position variation.
2694
Authors: Yu Qin Guo, Xin Yang, Juan Juan Han, Wei Chen
Abstract: Aimed at Zr44Ti11Cu10Ni10Be25 amorphous alloy and based on POLYFLOW software, studies the influence of die inlet diameter, blowing pressure and die transition fillet on the blow molding performance of tube blank systemly, and raises a new evaluation index to evaluate the formability of amorphous tube blank, limit height to diameter ratio (LHTDR) . The simulation results indicate that the forming limit of tube blank can be multiple improved with the decrease of die inlet diameter, blowing pressure has a significant effect on the forming limit which can be improved by decreasing the pressure, and the larger of the die transition fillet the higher of the forming limit in certain range. Finally, a set of reasonable process parameters is given which has great significance for guiding the formulation of blow molding process scheme.
3827
Authors: Ryutaro Hino, Masato Nakamura, Yo Ishida, Fusahito Yoshida
Abstract: This study presents a new type of sheet metal laminate for lightweight products, and investigates its plastic behavior and formability. The sheet metal laminate consists of three layers, i.e. two thin skin sheets and a perforated core sheet with round holes, which are bonded together by diffusion bonding. Pure copper sheets are used for both of the core and the skins. Plastic deformations of the laminate and its component layers under uniaxial and biaxial tension are examined experimentally and analytically. Results of uniaxial stress-strain responses and yield loci (contours of plastic work) show that the perforated core sheet exhibits anisotropic behavior induced by the hole array but the laminated sheet becomes rather isotropic. Forming limit diagrams of the laminate and its component layers are also obtained by performing stretch forming test. Forming limit of the perforated core sheet is markedly lower than that of the monolithic sheet, and that of the thin skin is in between. It is found that forming limit of the laminate is comparable to that of the thin skin.
254
Authors: Masaaki Otsu, Yosuke Katayama, Takayuki Muranaka
Abstract: An effect of tool rotation direction on forming limit in friction stir incremental forming was studied. A 3-axes NC milling machine and a hemispherical tool which with a diameter of 6 mm made of high speed steel was used for forming. The thickness of commercial A5052-H34 aluminum sheet was 0.5 mm. The forming tool was moved from the outside to inside in a pitch of 0.5 mm spirally, and the sheets were formed into frustum of pyramid shape. Formability evaluated by minimum wall angle of the pyramid was investigated by changing a tool rotation rate, tool feed rate and tool path direction. When the tool paths were clockwise and counter clockwise, they were defined to “advancing direction” and “retreating direction” as well as in friction stir welding, respectively. From the experimental results, forming limits by both rotation directions of advancing and retreating were almost the same, however, the range of formable working conditions in advancing direction was slightly wider than that in retreating direction. Evaluating the forming limits in relative velocity between the tool surface and the sheet, no difference of forming limit was obtained between forming in advancing direction and retreating directions.
390
Authors: Tomoyuki Hakoyama, Toshihiko Kuwabara
Abstract: Multiaxial tube expansion tests (MTETs) were performed to measure the multiaxial plastic deformation behavior of a cold rolled interstitial-free (IF) steel sheet for a range of strain from initial yield to fracture. The testing machine is capable of applying arbitrary principal stress or strain paths to tubular specimens using an electrical, closed-loop servo-control system for an axial force and an internal pressure. Tubular specimens with an inner diameter of 44.6 mm were fabricated from a cold rolled IF steel sheet with a thickness of 0.7 mm by roller bending and laser welding. Many linear stress paths in the first quadrant of stress space were applied to the tubular specimens to measure the forming limit strains and forming limit stresses of the as-received sheet sample, in addition to the contours of plastic work and the directions of the plastic strain rates. It was found that the shapes of the measured work contours changed with increasing plastic work. The observed differential hardening behavior was approximated by changing the material parameters and the exponent of the Yld2000-2d yield function (Barlat et al, 2003) as functions of the reference plastic strain. The hydraulic bulge tests were also conducted to measure the forming limit strain and forming limit stress for equibiaxial tension and to determine the equivalent stress-equivalent plastic strain relation for a larger strain range. The forming limit curve and forming limit stress curve were calculated using the Marciniak-Kuczyński-type approach. The calculated results were in fair agreement with the measurement.
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