Papers by Keyword: Earing

Abstract: Pure Niobium is a material of interest for high-energy-physics applications including superconducting accelerators. Cold-rolled sheets of Nb exhibit significant plastic anisotropy. Here we report on the mechanical and forming properties of 99.95% pure, 1.02 mm thin, cold-rolled sheet. Uniaxial tension, biaxial tension and disc compression experiments are performed, the first two at multiple angles to the rolling direction of the sheet. The material is very ductile (uniform elongation ~30%), and exhibits significant plastic anisotropy (e.g., the R-values range from 1.2 in 45^o to 2.5 in 90^o). The results are used to calibrate the Yld2000-2D anisotropic yield function, with an exponent of 6 as Nb is BCC. They are also used to extract the hardening curve beyond the limit load in uniaxial tension. Deep-drawing experiments are performed using a die of 27.6 mm dia. and a punch of 25.4 mm dia. Blanks of various diameters are used. The successfully drawn cups exhibit significant earing. The experiments are simulated using Abaqus/Standard and shell elements. It is shown that a properly calibrated material model enables the numerical simulations to match the experiments.

Abstract: The paper describes an experimental verification of a previously proposed formula establishing the relationship between the crystallographic parameters of a rolled sheet and the anisotropy index in a hot-rolled aluminum alloy. The main texture components were identified in the hot-rolled 3104 alloy using the X-ray structure analysis. The crystallographic parameters and anisotropy indices were then calculated both for the entire workpiece and for each individual texture component. The earing level of the hot-rolled workpiece was determined using the process of cylindrical cup drawing. Cup formation was also simulated using the finite element software package PAM STAMP. The earing data obtained through t simulation were compared with experimental results. For the validation of the calculations the hot-rolled workpiece anisotropy indices were also experimentally determined.

Abstract: Refinement of the grain diameter of the micro structure of Aluminium foil with a thickness of 300μm has been done through the ARB process up to fourth cycles with 72 layers that are proven to increase formability in micro forming a cup. Grain size was measured from the full annealed condition, of the ARB process, and the results of ARB process followed by stress relieved. Formability of the formation of a cup which is expressed as the LDR has increased from 1.87 for the material conditions of full annealed to 2.00 for the ARB process followed by stress relieved in a single step process. In addition to improved formability obtained in a cup formation, grain refinement in the microstructure can also reduce cup earing and wrinkle on the cup wall.

Abstract: One of the methods for increasing the degree of deformation in the deep drawing of the cylindrical parts is the method with the combined restraint. In this process, due to the high degree of deformation, the earing is pronounced and affects the quality of the final part. The paper focuses in optimization the blank shape in this process applying a method which combines a mathematical relation with the results of the numerical simulation. The mathematical relation connects the radii of the initial blank at the different angles with the sizes of the part heights at different angles. The numerical simulation using FEM was used for the heights determination at the main anisotropy directions considering different initial blank dimensions. An experimental work was done for certify the numerical results. The results confirmed that the optimization of the blank shape in deep drawing with the combined restraint is a key for improving the deformation process, for reduction the earing and for minimizing the material consumption.

Abstract: This study developed a new polycrystal plasticity model by deducing a set of linear controlling equations with respect to the controlling equation of rate dependent crystal plasticity (RDCP). It was proved numerically efficient and stable by means of the comparison with experiment and an implicit model. The model was then applied to describe earing in deep drawing process. Remarkable effects of rate sensitivity coefficient of the material, drawing speed and dies clearance on earing were found.

Abstract: In this work, we discuss a finite strain material model for evolving elastic and plastic anisotropy combining nonlinear isotropic and kinematic hardening. The evolution of elastic anisotropy is described by representing the Helmholtz free energy as a function of a family of evolving structure tensors. In addition, plastic anisotropy is modelled via the dependence of the yield surface on the same family of structure tensors. Exploiting the dissipation inequality leads to the interesting result that all tensor-valued internal variables are symmetric. Thus, the integration of the evolution equations can be efficiently performed by means of an algorithm that automatically retains the symmetry of the internal variables in every time step. The material model has been implemented as a user material subroutine UMAT into the commercial finite element software ABAQUS/Standard and has been used for the simulation of the phenomenon of earing during cylindrical deep drawing.

Abstract: During the thermo-mechanical processing of aluminium sheet products in commercial production lines the material experiences a complex history of temperature, time and strain paths, which result in alternating cycles of deformation and recrystallization with the associated changes in microstructure and, especially, crystallographic texture. Thus, computer-based alloy and process development requires integration of models for simulat¬ing the evolution of microstructure, microchemistry and crystallographic texture into process models of the thermo-mechanical production of Al sheet. In the present paper the influence of texture on the anisotropic properties is explored for various industrially processed aluminium alloy sheets for packaging applications. Besides the use of experimentally measured sheet textures as an input for the anisotropy calculations, particular attention is given to the use of modelled textures. Here, results from a comprehensive through-process modelling of the texture evolution during the thermo-mechanical production of aluminium sheet are utilized. Eventually, this will enable us to predict the evolution of texture and the resulting properties along the entire process chain and hence to improve product quality of aluminium sheet products avoiding laborious and expensive plant trials.

Abstract: Earing is often undesirable in the production of deep drawn containers because it results in a nonuniform cup height. A finite element model for earring analysis is developed considering only the flange area of the sheet. It was found that the draw-in depth of the flange increases with the increase of the r value, and it remains invariable when r value is larger than 2. With the increase of the r value, the max thickness decreases and the min thickness increases. If △r>0, four earings are formed. If △r =0, the material characteristics in all the planar directions are same. The flange uniformly flows into the die cavity, no earing is formed. If △r<0, four earings are formed. The earing distribution is dominated by r₀, r₄₅ and r₉₀. Both r and △r have much effect on the earing distribution.

Abstract: Computer-based alloy and process development requires integration of models for simulating the evolution of microstructure, microchemistry and crystallographic texture into process models of the thermo-mechanical production of Al sheet. The present paper focuses on recent developments in linking softening modules that simulate the progress of recovery and recrystallization with the following texture changes to deformation and microchemistry models. The potential of such coupled simulations is illustrated by way of the thermo-mechanical processing of Al-Mn-Mg AA 3104 can stock. In particular, the impact of inter-stand recrystallization between the tandem hot rolling passes as well as recrystallization during coil cooling (“self-annealing”) on the resulting hot strip and final gauge textures are explored. Finally, the predicted textures are input into a polycrystal-plasticity approach to simulate anisotropic properties (earing behaviour) of the sheets. Thus, it is possible to link the materials properties at final gauge to the decisive steps of deformation and recrystallization along the thermo-mechanical process chain.

Abstract: The parameters such as aniotropic property, blank holder force and friction coefficient between tool and blank are not only effect on the forming force, stress and strain distribution of the worpiece, but also on the earing in products. In this paper, the finite element method is used to investigate the earing of the deep drawing process. In order to verify the prediction of FEM simulation of the earing in the cylindrical cup drawing process, the experimental data are compared with the results of the current simulation. A finite element analysis is also utilized to reduce the earing profile of the drawn products, a reverse forming method for obtaining the initial blank’s shape according to the forward cup deep drawing simulation is proposed.