On the Formability/Instability of Stretch-Forming Sheet Metals

1992 ◽  
Vol 45 (3S) ◽  
pp. S154-S164 ◽  
Author(s):  
A. E. Bayoumi ◽  
R. Joshi
Keyword(s):  
Deformation Behavior ◽  
Shear Banding ◽  
Theoretical Models ◽  
Plastic Instability ◽  
Experimental Methodology ◽  
Manufacturing Processes ◽  
Sheet Metals ◽  
Stretch Forming ◽  
Electronic Components ◽  
Uniform Deformation

Manufacturing processes of aircraft, automobile and electronic components involve a lot of stretch-forming of sheet metals. The processes contain a large amount of straining which, in turn, may lead to plastic instabilities such as necking, slip formation or shear banding. Understanding the instability phenomenon requires the development of constitutive description of material characterizing the plastic instability and post uniform deformation behavior. The previous work on plastic instability usually lacks the experimental verification of the theoretical models. This may be owing to the complexity involved in designing a suitable experimental methodology for accurate measurements of strain in the locally deforming zone as the deformation progresses rather rapidly once the local neck sets in. A review of the important methodologies and analyses that were and are used in investigating instability of sheet metal in uniaxial tension is presented in this paper. Some supporting results are also presented.

Evaluation of Non-Uniform Deformation of Multi-Layered Ceramic Sheets with Printed Electrodes during Compression

2011 ◽  
Vol 418-420 ◽  
pp. 1647-1653
Author(s):  
Fumio Naruse ◽  
Naoya Tada
Keyword(s):  
Deformation Behavior ◽  
Recent Trend ◽  
Video Camera ◽  
Transverse Displacement ◽  
Compression Tests ◽  
Electronic Components ◽  
Uniform Deformation ◽  
Digital Video Camera ◽  
Layered Ceramic

With the recent trend of down-sizing and more efficient use of electric power in electric appliances, there is a growing need of smaller electronic components, such as multi-layered ceramic capacitors (MLCCs). However, it was found that the non-uniform deformation occurred in MLCC block during the pressing process and it hinders the miniaturization of MLCCs. In this study, compression tests of multi-layered ceramic sheets with printed electrodes were carried out and the deformation behavior was observed in situ and recorded by digital video camera. The change in area fraction and transverse displacement were evaluated and the deformation mechanism was inferred from the results.

Numerical Analysis for Process Parameter Effect in Electromagnetic Impact Welding of Aluminum Alloy Sheet

2014 ◽  
Vol 548-549 ◽  
pp. 297-300
Author(s):  
Dae Yong Kim ◽  
Hyeon Il Park ◽  
Ji Hoon Kim ◽  
Sang Woo Kim ◽  
Young Seon Lee
Keyword(s):  
Aluminum Alloy ◽  
Numerical Analysis ◽  
Deformation Behavior ◽  
Three Dimensional ◽  
Alloy Sheet ◽  
Aluminum Alloy Sheet ◽  
Sheet Metals ◽  
Charge Voltage ◽  
Flat Sheet ◽  
Impact Welding

Studies on electromagnetic impact welding between similar or dissimilar flat sheet metals using the flat one turn coil have been recently achieved. In this study, three dimensional electromagnetic-mechanical coupled numerical simulations are performed for the electromagnetic impact welding of aluminum alloy sheets with flat rectangular one turn coil. The deformation behavior during impact welding was examined. The effect of process parameters such as charge voltage, standoff distance and gap distance were investigated.

An Investigation of Wall Curl Reduction Through Post-Stretch Forming

2004 ◽  
Author(s):  
Z. C. Xia ◽  
F. Ren
Keyword(s):  
Automotive Industry ◽  
Sheet Metals ◽  
Stretch Forming ◽  
Deformation History ◽  
Forming Process ◽  
Industrial Environment ◽  
Metal Thickness ◽  
Implementation Techniques ◽  
Benefits And Costs ◽  
Channel Type

When sheet metals go through drawbeads or die corners, stress differentials are generated across metal thickness. The draw wall will curl up upon release of stamping tools, resulting in so-called wall curl. It is a serious problem in the deep drawings of U-channel type of structures such as rails. Numerical modeling is conducted to investigate a post-stretch forming process for wall curl reduction. In this process a set of lockbeads in the binder activates just before the end of punch stroke, locking the remaining blank in the binder. The continuation of the punch stroke then creates a final increment of pure stretch. It is most effective for deep drawings of U-channel type of structures such as rails. This technique is also known as “post-stretch” or “shape set” in the automotive industry and in the literature. Finite element simulations for a straight channel are conducted in order to understand the wall curl reduction mechanism of the process and to determine its effectiveness. After an examination of deformation profile after drawing and wall curl as a result of springback, various magnitude of post-stretch amount is modeled and their deformation history is analyzed. It is found that a post-stretch strain around 2% almost completely eliminates wall curl. CAE investigations demonstrate that the technique is equally applicable to more complex 3D channel, where a step channel is examined. The effectiveness of this concept is demonstrated by laboratory experiment on the forming of a U-channel. Various implementation techniques for the process in an industrial environment are also suggested, together with a discussion on the associated benefits and costs for production use.

Toward Understanding Size-Dependent Plasticity of Nanolayered Metallic Composites

2009 ◽  
Vol 633-634 ◽  
pp. 637-646
Author(s):  
G.P. Zhang ◽  
Y.P. Li ◽  
X.F. Zhu
Keyword(s):  
Fracture Stress ◽  
Shear Banding ◽  
High Hardness ◽  
Plastic Instability ◽  
Indentation Load ◽  
Bending Test ◽  
Tensile Fracture ◽  
Length Scale ◽  
Length Scales ◽  
Three Point Bending

Deformation and fracture behaviors of Cu/Au and Cu/Cr multilayered composites with different length scales were investigated by using instrumented-indentation and three-point-bending methods. It is found that with decreasing the length scale (layer thickness and grain size), both multilayers tend to produce plastic instability via localized shear banding under indentation load in spite of high hardness they have, while quasi-brittle fracture under relatively low fracture stress prevails at three-point-bending test. Especially, the compressive flow stress and the tensile fracture stress exhibit inverse trend of variation with the length scales, which implies different mechanisms. Such length scale dependent deformation and plasticity were analyzed concerning size and interface effects under different stress state.

Non-Thermal Laser Stretch-Forming

2005 ◽  
Vol 6-8 ◽  
pp. 433-440 ◽  
Author(s):  
H. Schulze Niehoff ◽  
Frank Vollertsen
Keyword(s):  
Power Density ◽  
New Technology ◽  
Thin Sheet ◽  
Laser Pulses ◽  
Dome Height ◽  
Co2 Lasers ◽  
Sheet Metals ◽  
Stretch Forming ◽  
Process Technology ◽  
New Process

A new process technology for stretch-forming of thin sheet metals is presented within this paper. This new technology is based on shock waves as a source for the forming energy, which are created through laser pulses. The results of some preliminary experiments show, that stretchforming with laser pulses is possible. The influence of parameters like defocussing, power density, pulse energy, number of pulses and material are worked out with excimer-laser pulses. The results show, that uniform shaped domes with a dome height over 250 µm with diameters of 1.4 mm could be produced. More recent studies show that even better results can be reached through the use of TEA-CO2-Lasers, since no confinement is needed and ablation at the surface is avoided. The absence of ablation at the surface makes this new technology even more interesting, since not only the surface remains accurate, but also since several pulses can be applied at one point and thus higher forming degrees can be reached without increasing the power density.

Influence of the Contact Pressure on the Rolling Resistance Moments in Dry Ball-Race Contacts

2014 ◽  
Vol 658 ◽  
pp. 305-310
Author(s):  
Alina Corina Dumitrascu ◽  
Gelu Ianus ◽  
Dumitru Olaru
Keyword(s):  
Theoretical Model ◽  
Contact Pressure ◽  
Rotational Speed ◽  
Ball Bearing ◽  
Rolling Resistance ◽  
Theoretical Models ◽  
Hertzian Contact ◽  
Experimental Methodology ◽  
Experimental Values ◽  
Good Agreement

Based on a theoretical model and an experimental methodology for defining the rolling resistance moments in a modified thrust ball bearing having only 3 balls, the authors experimentally investigated the influence of the Hertzian contact pressure on rolling resistance moments between a ball and a race. The experiments were realized with balls having diameters between 1.588 mm and 4.762 mm with maximum Hertzian pressure between 0.2GPa and 1GPa, operating for rotational speed between 60rpm to 210 rpm. The experiments evidenced that the measured values of the rolling resistance moments have higher values that the theoretical hysteresis and curvature rolling resistance moments for low contact pressure. By increasing of the contact pressure to 1GPa the experimental values for rolling resistance moments are in good agreement with the theoretical models.

Hydrodynamic Lubrication in Simple Stretch Forming Processes

1984 ◽  
Vol 106 (1) ◽  
pp. 70-77 ◽  
Author(s):  
W. R. D. Wilson ◽  
J. J. Wang
Keyword(s):  
Plastic Deformation ◽  
Plane Strain ◽  
Sheet Metal ◽  
Hydrodynamic Lubrication ◽  
Theoretical Models ◽  
Newtonian Liquid ◽  
Stretch Forming ◽  
Exponential Variation ◽  
Plane Strain Case

Theoretical models for the hydrodynamic lubrication of plane strain and axisymmetric sheet metal stretch forming processes with cylindrical and spherical headed punches, respectively, are developed. The lubricant is treated as an isoviscous Newtonian liquid for both geometries. In addition, the influence of sheet heating due to plastic deformation with an exponential variation of viscosity with temperature is analyzed for the plane strain case.

scholarly journals Finite Element Analysis of Stretch Forming of an Open Profile Made of Ultra-High Strength Martensitic MS1500 Steel

2021 ◽  
Author(s):  
Mehmet Okan Görtan ◽  
Ümit Türkmen
Keyword(s):  
Finite Element ◽  
High Strength ◽  
Roll Forming ◽  
Sheet Metals ◽  
Stretch Forming ◽  
Forming Process ◽  
Element Analysis ◽  
Open Profile ◽  
Fe Simulations ◽  
Forming Characteristics

Stretch forming process is primarily used for generating curved structures from sheet metals such as car body panels or aircraft fuselage panels. Although there are large number of studies about stretch forming, these investigations focus mainly on flat sheet metals. However, various parts especially in the automotive industry, such as passenger car fenders are first preformed to a profile and afterwards stretch formed to generate desired final geometry. Moreover, as a consequence of weight reduction activities, these fender parts are usually made of ultra-high strength steels (UHSS) in the last two years. In the current study, stretch forming characteristics of an open profile made of martensitic UHSS (MS1500) are investigated using finite elements method (FEM). Used geometry was an asymmetrical hat profile which was preformed using roll forming prior to stretch forming. Mechanical properties of the material used is characterized using tensile test and modeled using Swift isotropic strain hardening rule. Strain and stress distribution along the bend section, geometry and springback in the final part as well as forming force have been investigated using finite element (FE) simulations. A twist has been observed in the final product along its longitudinal axis. To validate the FE results, experiments have been conducted. Twist problem is also detected in the manufactured samples. The amount of springback in produced part was similar to the experiments. It is found that FE simulations can model stretch forming process of open profiles accurately.

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