Draw Radius Research Articles

Application of multi draw radius deep draw die for increase in formability of redrawn cylindrical cups

Currently, deep drawing and redrawing are the primary methods used to create beverage cans. Research to increase the efficiency of this procedure is ongoing. This study aimed to improve the formability of redrawn cups by proposing a new technique, wherein a multi-die radius (MDR) die was used as a deep drawing die for producing deep-drawn cups and then redrawn once more to create the redrawn cup. It was found that a more uniformly deformed grain microstructure evolutions and cup wall thickness around the cup were achieved in the case of the MDR deep-drawing process compared with the conventional deep-drawing process. However, using the MDR deep-drawn cups to fabricate redrawn cup, the formability in terms of LDR could not be increased. However the formability in terms of cup wall thickness can be significantly increased by approximately 7% thicker.

An Adaptive Algorithm and Additively Manufactured Punch Used to Form Aluminum Sheet Metal Parts.

Self-adaptive mechanisms are gaining momentum in industrial processes. It is understandable that as the complexity increases, the human work must be augmented. Considering this, the authors have developed one such solution for the punch-forming process, using additive manufacturing, i.e., a 3D-printed punch, to draw into shape 6061-T6 aluminum sheets. This paper aims to highlight the topological study used to optimize the punch form shape, the methodology of the 3D printing process, and the material used. For the adaptive algorithm, a complex Python-to-C++ bridge was created. It was necessary as the script has computer vision (used for calculating stroke and speed), punch force, and hydraulic pressure measurement capabilities. The algorithm uses the input data to control its subsequent actions. Two approaches are used in this experimental paper, a pre-programmed direction and an adaptive one, for comparison purposes. The results, namely the drawing radius and flange angle, were statistically analyzed using the ANOVA methodology for significance. The results indicate significant improvements when using the adaptive algorithm.

Achievements of Nearly Zero Earing Defects on SPCC Cylindrical Drawn Cup Using Multi Draw Radius Die

In recent years, the old-fashioned cylindrical cup shapes are still widely used, and there are many defects which could not be solved yet. In the present research, the classical earing defects, which are mainly caused by the material mechanical property of the anisotropic property of the material (R-value), are focused on. The multi draw radius (MDR) deep drawing die is applied and investigated to achieve nearly zero earing defects by encountering the R-value during the deep drawing process. Based on the experiments, in different directions in the sheet plane, the somewhat concurrent plastic deformation could be controlled, and the uniform elongated grain microstructure and uniform strain distributions on the cup wall could be achieved. Therefore, on the basis of these characteristics, the earing defects could be prevented, and the nearly zero earing defects could be achieved. However, to achieve the nearly zero earing defects, the suitable MDR die design relating to the R-value should be strictly considered. In the present research, to apply the MDR die for the medium carbon steel sheet grade SPCC cylindrical drawn cup, the following was recommended: the large draw radius positioned at 45° to the rolling direction and the small draw radius positioned along the plane and at 90° to the rolling direction. Therefore, in the present research, it was originally revealed that the nearly zero earing defects could be successfully performed on the process by using the MDR die application.

Multi Draw Radius Die Design for Increases in Limiting Drawing Ratio

As a major sheet metal process for fabricating cup or box shapes, the deep drawing process is commonly applied in various industrial fields, such as those involving the manufacture of household utensils, medical equipment, electronics, and automobile parts. The limiting drawing ratio (LDR) is the main barrier to increasing the formability and production rate as well as to decrease production cost and time. In the present research, the multi draw radius (MDR) die was proposed to increase LDR. The finite element method (FEM) was used as a tool to illustrate the principle of MDR based on material flow. The results revealed that MDR die could reduce the non-axisymmetric material flow on flange and the asymmetry of the flange during the deep drawing process. Based on this material flow characteristic, the cup wall stretching and fracture could be delayed. Furthermore, the cup wall thicknesses of the deep drawn parts obtained by MDR die application were more uniform in each direction along the plane, at 45°, and at 90° to the rolling direction than those obtained by conventional die application. In the present research, a proper design for the MDR was suggested to achieve functionality of the MDR die as related to each direction along the plane, at 45°, and at 90° to the rolling direction. The larger draw radius positioned for at 45° to the rolling direction and the smaller draw radius positioned for along the plane and at 90° to the rolling direction were recommended. Therefore, by using proper MDR die application, the drawing ratio could be increased to be 2.75, an increase in LDR of approximately 22.22%.

Improvement of the drawing ratio of the anisotropic material behaviour under near plane strain conditions for DP600 characterized in elliptic hydraulic bulge test

The plane strain condition is one of the most frequent reasons for failure in a deep drawing process. State of the art material models do not consider this strain state in FE simulations. Since there is only the notched tensile test to determine the first principal stress, an improved testing setup is needed to characterize the first and second principal stresses up to high deformations to determine the material behaviour under plane strain conditions. Within this contribution, an innovative testing setup is used, which induces a near plane strain regime in the specimen with an elliptical hydraulic bulge test. Experiments are carried out in rolling and transversal direction for DP600. Based on the experiments, stress and stain based material characteristics are evaluated. For validation of the setup, square cups are deep drawn, which have a plane strain area at the drawing radius which causes cracking under this strain state. Due to the highly directional dependent material behaviour, the drawing ratio can be increased by considering the anisotropic material behaviour by cutting the blank in an optimized position according to the rolling direction.

Influence of asymmetrical drawing radius deviation in micro deep drawing

Nowadays, an increasing demand for small metal parts in electronic and automotive industries can be observed. Deep drawing is a well-suited technology for the production of such parts due to its excellent qualities for mass production. However, the downscaling of the forming process leads to new challenges in tooling and process design, such as high relative deviation of tool geometry or blank displacement compared to the macro scale. FEM simulation has been a widely-used tool to investigate the influence of symmetrical process deviations as for instance a global variance of the drawing radius. This study shows a different approach that allows to determine the impact of asymmetrical process deviations on micro deep drawing. In this particular case the impact of an asymmetrical drawing radius deviation and blank displacement on cup geometry deviation was investigated for different drawing ratios by experiments and FEM simulation. It was found that both variations result in an increasing cup height deviation. Nevertheless, with increasing drawing ratio a constant drawing radius deviation has an increasing impact, while blank displacement results in a decreasing offset of the cups geometry. This is explained by different mechanisms that result in an uneven cup geometry. While blank displacement leads to material surplus on one side of the cup, an unsymmetrical radius deviation on the other hand generates uneven stretching of the cups wall. This is intensified for higher drawing ratios. It can be concluded that the effect of uneven radius geometry proves to be of major importance for the production of accurately shaped micro cups and cannot be compensated by intentional blank displacement.

DESIGN AND FORMABILITY ANALYSIS OF FENDER COMPONENT

Fender is a front outerside member of a car, which covers the wheel side. It has so many small features with ups and downs. The binder surface is not a planer one in this case. This is because to reduce the draw depth and it has two rows of draw beads. It seems to be difficult to form due to their small radius fillets. In this analysis, there is a need to find out the forming feasibility of this component and if not possible in single stage then we need to modify the die design with least modification and need to optimize the draw bead profile and draw radius in such a way that we can get the good component in a single stage itself. For thin and very big forming dies, we need to do gravity analysis. If our die face is profiled one, then we may need to do binder wrap analysis. The binder wrap analysis results are taken to the forming analysis. After the forming analysis, if trimming is there means just before trimming analysis we have to do mesh coarsening. Then the coarsened mesh and its results are taken for trimming analysis. The results of the trimming analysis are taken to the spring back analysis. From the results of the spring back analysis, further we can cross check the spring back of the real component. The analysis results obtained is used in sheet metal industry for metal forming process.

Influence of tribology size effect on Stribeck curve in micro deep drawing

The lubricant viscosity is one parameter for optimizing drawing processes. The influence is due to the velocity depending friction behaviour between work piece and tool, as well as the effective process forces and resulting pressures in the lubricant. Because of the tribological size effect, the knowledge gained in macro processes cannot be transferred directly to micro forming processes. To understand the influence of the drawing speed, several parameters as the drawing radius and viscosity of lubricants are varied in this work. The resulting Stribeck curves show a varying effect of the different kinematic viscosities. High viscosity lubricant reduces the occurring friction significantly at low Stribeck numbers, but increases friction with rising Stribeck number extremely. Concluding the results, it can be stated that the hydrodynamic friction demands a relevant portion of the overall friction in micro forming process especially at high drawing velocities, which cannot be explained by the lubricant pocket model.

Sheet Metals Forming Die Design Using Finite Element Analysis and the Taguchi Method

Sheet metal deep-draw die is primarily constructed with draw bead, which is then modified based on trial and error to obtain a successful forming without splitting. This work aims at a robust design of forming die using numerical analysis and the Taguchi method. A three dimensional elastoplastic finite element model of a sheet metal forming process of SPCEN steel has been successfully developed using the material flow stress obtained from the modified Erichsen cup test. The model was validated with the actual forming experiment and the results agreed well. The influence of draw bead parameters on splitting and thinning distributions were examined using the Taguchi method. Four parameters, namely the friction coefficient, draw bead height, radius and shoulder radius were investigated. The Taguchi main effect analysis and ANOVA results show that the height and shoulder radius of the draw bead are the most important factor influencing the thinning distribution. Applying the Taguchi method and using the minimum thinning percentage as the design criteria, the optimum die design was identified as height, radius, shoulder radius and the friction coefficient of 4, 8, 8 mm and 0.125 respectively. The verified finite element model using the optimum die design was conducted. The predicted Taguchi response was within 5.9% from finite element analysis prediction. The improvement in the reduction of thinning percentage was 22.35%.

Experiences from experimental and numerical springback studies of a semi-industrial forming tool

The work reported in the present paper constitutes a part of a project on simulation of springback in sheet metal forming. Previous work in this project has been concentrated on material modeling and characterization with focus on springback applications. It has been demonstrated that, with proper considerations of all aspects of the material model and the material properties, excellent springback results can be obtained for simple problems. At the simulation of real, industrial parts, a number of additional problems are encountered. Many of these problems are associated with deviations from nominal geometries and other properties. These are examples of factors that influence the outcome of the forming process, but are unknown to the analyst, and can therefore not be considered in the simulation of the forming process. Other phenomena are known to exist, but due to their complexity, they are practically impossible to consider in industrial simulations. Examples of such phenomena are the true frictional behavior in contacts between the blank and the tools, and the flexibility of the press and the forming tool. The influence of these kinds of effects is discussed in the present paper. In the current study, a semi-industrial tool, specially designed to catch those springback problems that are encountered in the forming of real industrial, parts, is used. The tool includes several characteristics that can be found in typical forming tools, such as several draw radius steps and change-over in section geometries. Effects like flange/wall angle changes, sidewall curl and twist are obtained at springback. The sensitivity of the predicted springback is evaluated with respect to various numerical factors, such as the friction coefficient, the material model, and the mesh density. Finally, the quality of the predicted springback behavior for four different materials, commonly used in the automotive industry, is evaluated.

Determination of size-dependent friction functions in sheet metal forming with respect to the distribution of the contact pressure

The aim of this paper is to optimize the analytical model developed in previous work (Hu et al. in Determination of the friction coefficient in deep drawing, process scaling. In: Vollertsen F, Hollmann F (eds) Proceeding of the 1st colloquium of DFG priority program process scaling. BIAS-Verlag, ISBN 3-933762-14-6, Bremen, pp 27–34, 2003; Hu and Vollertsen in J Technol Plast 29:1–9, 2004; Vollertsen and Hu in Annu CIRP 55(1):291–294, 2006) with respect to the distribution of the contact pressure at the drawing radius. A size-dependent friction function was acquired based on the experimentally measured punch force from strip drawing with deflection, which can identify the tribological size effects in sheet metal forming. This function was implemented in the FEM-simulation. The distribution of the contact pressure at the drawing radius was assumed to be uniform in the previous analytical model, which is not right, since the simulated punch force versus punch travel curve showed a difference of about 11% from the experimental curve (Vollertsen and Hu in Annu CIRP 55(1):291–294, 2006). In the new analytical model the non-uniform distribution of contact pressure between the work piece and the tools was taken into account. The simulated curve using the friction function from the new model shows a better agreement with the experimental curve.

On the role of shear strength in sandwich sheet forming

This paper deals with the design of thin, all-metal sandwich sheets for forming applications. Draw bending experiments have been performed on thin prototype sandwich materials with metallic cores of 10% relative density. The experimental results reveal core shear failure as the dominant failure mechanism. Detailed finite element analysis has been carried out to gain further insight in the mechanics of bending and unbending of sandwich sheets. Based on theoretical analysis, design maps have been constructed describing the required core shear strength as a function of the face sheet properties as well as the sandwich core thickness and the draw radius. Furthermore, the relationship between shear strength and relative density has been determined for perforated sandwich core materials. The main result of this study is that the shear strength of formable sandwich sheets should be at least one order of magnitude higher than that of most commercial cellular solids. Here, perforated sandwich cores of relative densities above 25% are suggested to prevent sandwich sheets from core shear failure in forming operations.

Analysis of surface topography changes in steel sheet strips during bending under tension friction test

In order to investigate the frictional behaviour and the change in surface roughness of different sheet topographies, a bending under tension friction test, BUT, was used. This test exposes the material to bulk-plastic deformation under conditions similar to those present in the drawing radius of a real tool. Each steel sheet material has been tested under different lubrication conditions. To measure the sheet surface topography a 3D stylus technique was used. For each steel strip the original surface, the area in contact with the tool and the resulting surface topography were measured. When comparing “standard” 3D surface roughness data for original and final surfaces, no correlation with friction data was obtained. However, with a special evaluation technique good correlation with oil retention volume and frictional behaviour was found for the surface in contact with the tool. By using measurements from the contact area, filtering the measured surface in two steps, firstly with a 5th degree polynom to get rid of the circular form and secondly with a ball filter to get rid of the waviness located in the topmost layer in the surface and then plotting the bearing area curve for the filtered surface on a probability paper, the real area of contact for each steel sheet surface can be determined, as well as the number of oil pockets and their mean area. The oil pockets were estimated by using a software in which areas of peaks were estimated, on a surface inverted at the level of the real area of contact. By plotting the mean area of the oil pockets versus the coefficient of friction for a sheet material with an excess amount of lubricant, a relationship is determined.

Biological movements look uniform: evidence of motor-perceptual interactions.

Six experiments demonstrate a visual dynamic illusion. Previous work has shown that in 2-dimensional (2D) drawing movements, tangential velocity and radius of curvature covary in a constrained manner. The velocity of point stimuli is perceived as uniform if and only if this biological constraint is satisfied. The illusion is conspicuous: The variations of velocity in the stimuli exceed 200%. Yet movements are perceived as uniform. Conversely, 2D stimuli moving at constant velocity are perceived as strongly nonuniform. The illusion is robust: Exposure to true constant velocity fails to suppress it. Results cannot be explained entirely by the kinetic depth effect. The illusion is evidence of a coupling between motor and perceptual processes: Even in the absence of any intention to perform a movement, certain properties of the motor system implicitly influence perceptual interpretation of the visual stimulus.

Research on Deep Drawing : 2nd Report, Friction of the Holder and the Die Surfaces

Continued from last report, the character of friction of the holding surface is more fully examined, also the character of friction resistance of the die surface as well as that of bending resistance of material over the drawing radius is discussed indirectly, and these are reported in this paper. The experimental works are carried out with tin plate blanks and steel die in conditions almost the same as in the preceding report.