Development of Experimental Method to Improve Sheet Metal Formability by Transverse Normal Stress

2011 ◽  
Vol 189-193 ◽  
pp. 2949-2956 ◽  
Author(s):  
Zhe Wang ◽  
Xiao Ming Lai ◽  
Zhong Jin Wang ◽  
Qing Xin Cui ◽  
Wen Tao Li
Keyword(s):  
Sheet Metal ◽  
Hydrostatic Stress ◽  
Experimental Tests ◽  
Normal Pressure ◽  
Viscous Medium ◽  
Analytical Approximation ◽  
Loading Path ◽  
Dome Height ◽  
Sheet Metals ◽  
Softening Effect

To make full use of the promotion potential of hydrostatic stress on the formability of sheet metal, several foundational questions met in practical application of double-sided pressure forming technique are studied in this paper. The theoretical analysis of sheet metal deformation during the double-sided pressure bulging process is carried out, and an analytical approximation for normal pressure loading path that secures out-of-plane stress ratio, γ, continuously increasing (dγ ≥ 0 holds) is presented. Utilization of the relationship between the theoretical approximation for normal pressure load and material hardening properties, a novel double-sided pressure forming method is proposed—the viscous pressure bulging (VPB) of the overlapping sheet metals, in which a highly viscous but flowable semi-solid medium is used as the soft die and the target sheet metal is deformed under the constraints from viscous medium on one side and overlapping sheet on another side. To confirm the efficiency of the proposed method, the VPB test of overlapping sheet metals is simulated by DEFORM-2D, and the experimental tests are also carried out. The results show that σ3 provided by overlapping sheet can overcome the diminishing of γ value caused by evolving strain-hardening and geometric softening effect in the post-diffuse necking stage. The experimental obtained increase of the limit dome height (LDH) of double-sided pressure bulging specimen is 12.6% compared with that of single-sided pressure bulging specimens.

Effect of Loading Location of Viscous Medium on Sheet Deformation in Viscous Pressure Bulge (VPB) Test

2010 ◽  
Vol 154-155 ◽  
pp. 775-780
Author(s):  
Jian Guang Liu ◽  
Zhong Jin Wang ◽  
Qing Yuan Meng ◽  
Yu Long Zheng
Keyword(s):  
High Pressure ◽  
Sheet Metal ◽  
Deformation Behavior ◽  
Central Zone ◽  
Viscous Medium ◽  
Dome Height ◽  
Loading Mode ◽  
Viscous Pressure ◽  
Viscous Pressure Forming ◽  
Sheet Deformation

Viscous pressure forming (VPF) uses a highly viscous but flowable material as pressure-carrying medium (PCM). Due to the relative low flowability of viscous medium compared with fluid, nonuniform pressure distribution in viscous medium can be used to control and regulate the deformation sequence of the workpiece through controlling the loading mode of viscous medium. In the present study, viscous pressure bulge (VPB) tests with three kinds of loading location of viscous medium (central zone, corner zone and the whole deformation zone) are conducted and the influences of loading location of viscous medium on sheet deformation behavior are investigated via numerical simulations and experiments. It is found that changing the loading location of viscous medium can greatly affect the deformation behavior of sheet metal. When the viscous medium is injected from the die corner zone, a local high pressure formed at the corner zone of sheet metal and a higher limiting dome height and strains are obtained.

The Biaxial Stress-Strain Curves of Sheet Metals

2010 ◽  
Vol 44-47 ◽  
pp. 2519-2523
Author(s):  
Hai Bo Wang ◽  
Min Wan ◽  
Yu Yan ◽  
Xiang Dong Wu
Keyword(s):  
Transverse Direction ◽  
Biaxial Loading ◽  
Testing Machine ◽  
Rolling Direction ◽  
Biaxial Stress ◽  
Loading Path ◽  
Sheet Metals ◽  
Stress Strain ◽  
Loading Paths ◽  
Loading Ratio

Biaxial tensile tests of 5754O aluminum alloy sheet and B170P1 steel sheet were performed under linear loading paths with cruciform specimens and a biaxial loading testing machine. The stress-strain curves under different loading paths were obtained. It is found that the loading path has a significant influence on the stress-strain curves, i.e., the stress-strain curves vary with the loading path. The stress-strain curves in the rolling direction become higher with the decrease of the loading ratio (the ratio of the load along the rolling direction to that along the transverse direction) from 4:0 to 4:4. Meanwhile the stress-strain curves in the transverse direction become lower with the decrease of the loading ratio from 4:4 to 0:4. Based on Yld2000-2d yield criterion, the experimental phenomena of the two kinds of sheet metals under biaxial tension were explained theoretically.

Asymmetric-Shaped Bending of Adhesively Bonded Sheet Metals

2016 ◽  
Vol 725 ◽  
pp. 630-635 ◽  
Author(s):  
Taro Tokuda ◽  
Takeshi Uemori ◽  
Tetsuya Yoshida ◽  
Michihiro Takiguchi ◽  
Fusahito Yoshida
Keyword(s):  
Sheet Metal ◽  
Final Stage ◽  
Fem Analysis ◽  
Sheet Metals ◽  
Analysis Method ◽  
Adhesively Bonded ◽  
Forming Process ◽  
Maximum Shear Strain ◽  
The Press ◽  
A New Technique

In sheet metal industries, press-formed sheet elements are usually adhesively bonded together at the final stage of assembly. Instead of such a conventional process, the present authors proposed a new technique that first flat sheets are adhesively bonded together and then press-formed into the final products. In previous study, the problem of the die-bending (V-bending and hat-shaped bending) with symmetrical shape has studied. In this study, asymmetric-shaped bending of adhesively bonded sheet metals was investigated by experiments and FEM analysis method. In the case of asymmetric-shaped bending, it was found that the timing of contact from the die corner to the die hypotenuse is early in the press-forming process compared with symmetrical bending (V-bending and hat-shaped bending). For the FEM analysis results, the maximum shear strain in asymmetric-shaped bending was smaller than that in symmetric-shaped bending at the hat-shaped side. Thus, the shape of the die has a large influence on the die-bending of adhesively bonded sheet metals.

State of the Art of Constitutive Model of Concrete Materials Based on Damage Mechanics

2011 ◽  
Vol 194-196 ◽  
pp. 848-852
Author(s):  
Duo Xin Zhang ◽  
Qing Yun Wang
Keyword(s):  
Constitutive Model ◽  
Damage Mechanics ◽  
State Of The Art ◽  
Constitutive Models ◽  
Experimental Tests ◽  
Constitutive Relationship ◽  
Model Parameters ◽  
Softening Effect ◽  
Volumetric Expansion ◽  
Concrete Materials

This study centered on the development of constitutive model of the material based on damage mechanics. Volumetric expansion, unilateral behavior and softening effect have been pointed out as three difficulties during setting constitutive model of concrete, the applicable and deficiency of the existed constitutive relationship been reviewed, and the methods used to deal above difficulties were overviewed, Meanwhile, the background of existed model has been summarized and listed systematically. The development of a thermodynamic approach to constitutive model of concrete, with emphasis on the rigorous and consistency both in the formulation of constitutive models and in the identification of model parameters based on experimental tests has been potential direction of the future study, and hoped furnished basement for the elastic to plastic coupled damage mechanics constitutive model of concrete.

Forming 3D Sheet Metals by Means of Continuous Rolling Method

2009 ◽  
Vol 16-19 ◽  
pp. 570-574 ◽  
Author(s):  
Zhi Qing Hu ◽  
Ming Zhe Li ◽  
Xue Peng Gong ◽  
Zeng Ming Feng
Keyword(s):  
Sheet Metal ◽  
Three Dimensional ◽  
Sheet Metals ◽  
Continuous Rolling ◽  
The Core ◽  
3D Surface ◽  
Multipoint Forming ◽  
Rolling Method ◽  
Novel Method

In this paper, we present a novel method of using the continuous rolling to fabricate three-dimensional sheet metal. The core bendable roller is composed of the flexible axis and the controllable equipment. The transversal shape of the sheet metal can be realized by regulating the controllable equipment to make the axis of bendable roller bent; the longitudinal shape is formed by driving the three bendable rollers rotated and the top roller making a displacement synchronously. Some experiments were performed and typical 3D surface parts were formed. Based on the results of the experiments, the effects of the thickness and the rolling times are discussed. The results of the research will be beneficial to define the parameters and perfect the theory of continuous multipoint forming of multiform 3D parts.

scholarly journals Experimental and FEM Analysis of Void Closure in the Hot Cogging Process of Tool Steel

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 538 ◽  
Author(s):  
Marcin Kukuryk
Keyword(s):  
Hydrostatic Stress ◽  
Effective Strain ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Fem Analysis ◽  
Experimental Tests ◽  
Reduction Ratio ◽  
Compression Process ◽  
Void Closure ◽  
Axial Defects

In the present study, a new complex methodology for the analysis the closure of voids and a new forging system were developed and tested. The efficiency of the forging parameters and the effective geometric shapes of anvils to improve void closure were determined. A new cogging process provided a complete closure of an ingot’s axial defects, as confirmed by experimental tests. The evolution behavior of these defects with different sizes was investigated during the hot cogging process by means of the professional plastic forming software Deform-3D. A comprehensive procedure was developed using the finite-element method (FEM) for the three-dimensional cogging process and laboratory experimentation to predict the degree of void closure. The hot multi-pass cogging process was used to eliminate void defects in the forgings so as to obtain sound products. In the compression process, the effects of the reduction ratio and forging ratio, the void size, and the types of anvil were discussed to obtain the effective elimination of a void. For the purpose of the assessment of the effectiveness of the void closure process, the following indices were introduced: the relative void volume evolution ratio, the relative void diameter ratio, and the internal void closure evaluation index. Moreover, the void closure process was assessed on the basis of stress triaxiality, hydrostatic stress, forging ratio, value of local effective strain around the void, and critical reduction ratio. The results of this research were complemented by experiments predicting the formation of fractures in the regions near the void and in the volume of the forging in the course of the cogging process. The comparison between the predicted and the experimental results showed a good agreement.

The Effect of the Initial Stress and Strain State in Sheet Metals on the Roller Levelling Process

2015 ◽  
Vol 651-653 ◽  
pp. 1023-1028 ◽  
Author(s):  
Markus Grüber ◽  
Marius Oligschläger ◽  
Gerhard Hirt
Keyword(s):  
Process Control ◽  
Initial Stress ◽  
Sheet Metal ◽  
Process Parameters ◽  
Kinematic Hardening ◽  
Sheet Material ◽  
Stress And Strain ◽  
Fe Model ◽  
Sheet Metals ◽  
Initial State

Due to increasing requirements regarding the flatness of sheet metals, the process of roller levelling is of particular importance. The process itself is influenced by a high number of parameters such as machine design, sheet dimension, and material properties. Therefore, it is desirable to provide an online process control to react on changes of those process parameters. One possible approach for the layout of a process control and the identification of reference values is the use of the Finite Element Method (FEM). Considering the alternate bending a sheet metal undergoes when passing through a roller leveller, kinematic hardening of the sheet material must be taken into account. Additionally, the initial stress and strain distribution of the sheet metal – e.g. induced by coiling – has an influence on the material behaviour and consequently on the process parameters. With respect to these effects, a coupled FE model, which accounts for the initial state of the sheet metal, is introduced. An inverse calculation of material parameters describing the behaviour under cyclic load conditions has been done for an aluminium alloy AA5005 and a mild steel DC01. Based on this numerical setup, the influence of the initial stress state in the pre-levelled sheet metal on the roller levelling process has been deduced. Accompanying experiments on a down-sized roller leveller were carried out for a validation of the numerical setup.

Off-Line Testing of Tribo-Systems for Sheet Metal Forming Production

2014 ◽  
Vol 966-967 ◽  
pp. 3-20 ◽  
Author(s):  
Niels Bay ◽  
Ermanno Ceron
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Deep Drawing ◽  
Metal Forming ◽  
Normal Pressure ◽  
Environmentally Benign ◽  
Interface Pressure ◽  
Test Conditions ◽  
Interface Contact ◽  
Very High

Off-line testing of new tribo-systems for sheet metal forming production is an important issue, when new, environmentally benign lubricants are to be introduced. To obtain useful results it is, however, vital to ensure similar conditions as in the production process regarding the main tribo-parameters, which are tool/workpiece normal pressure, sliding length, sliding speed and interface contact temperature. The paper describes a generic methodology for such tests exemplified on an industrial, multistage deep drawing example, where deep drawing is followed by two successive re-drawing operations leading to very high tool/workpiece interface pressure and temperature in the second re-draw. Under such conditions only the best lubricant systems work satisfactory, and the paper shows how the performance of different tribo-systems in production may be predicted by off-line testing combined with numerical modelling in order to ensure proper test conditions.

3D Loading Path-Generating Method for FEM Simulation of Incremental Sheet Metal Forming Process

2010 ◽  
Vol 97-101 ◽  
pp. 2810-2815 ◽  
Author(s):  
Yan Xu ◽  
Shuang Gao Li ◽  
Lin Gao
Keyword(s):  
Sheet Metal ◽  
Incremental Forming ◽  
Thickness Distribution ◽  
Fem Simulation ◽  
Loading Path ◽  
Forming Process ◽  
Forming Simulation ◽  
Generating Method ◽  
Incremental Sheet Metal Forming ◽  
3D Loading

Incremental forming of sheet metal is difficult to be simulated for its complicated 3D loading path. In this work, an acceptable approach to generate 3D loading path, called “virtual guiding model method” is accomplished. The method, which has the similar idea with the conventional copy mill, is based on FEM and the basic principle of kinematics. With the help of the method, multi-stage incremental forming of a drawing typed square cup was simulated in the FEM software-PAMSTAMP and experimented. Through measuring the thickness distribution the vertical edge of the cup, the most difference between them is less than 0.05mm, which is satisfied with engineering request, and the results shows that the 3D loading path generating method is one of the most effective way to realize the incremental forming simulation.

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