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    The effects of proportional loading, plane stress, and constant thickness assumptions on hydro-mechanical deep drawing process

    , Article International Journal of Mechanical Sciences ; Volume 53, Issue 5 , 2011 , Pages 329-337 ; 00207403 (ISSN) Taghipour, E ; Assempour, A ; Sharif University of Technology
    Abstract
    The goal of this study is to evaluate the effects of proportional loading, plane stress, and constant thickness assumptions on hydro-mechanical deep drawing (HDD) by developing analytical models. The main model includes no simplifying assumption, and then each of the mentioned assumptions is considered in a specific model. The interrelationships between geometrical and mechanical variables are obtained in the finite difference form based on the incremental strain theory, thereby being solved by Broyden algorithm. Published experimental and FE results are used for evaluation of the results obtained in the present work. The results of models under proportional loading, plane stress, and... 

    , M.Sc. Thesis Sharif University of Technology Karimiyan, Hassan (Author) ; Asempour, Ahmad (Supervisor)
    Abstract
    In this research two stage deep drawing has been analyzed by the upper bound method. During this study, the deep drawings of cylindrical parts have been analyzed. In this method, for the first stage the whole deformation region is divided into five zones including punch bottom, punch radius, between punch and die, die radius and flange. Then, the geometric equations of each zones is generated by sweeping the section curves defined on the boundary of each zone. The velocity fields are expressed in a similar manner by sweeping the boundary velocity functions. At each stage, with the change of height between punch and die, the point location is changed and movement and tension in the sheet are... 

    A new mapping technique to consider intermediate stages in multistep deep drawing

    , Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 228, Issue 9 , June , 2014 , Pages 1557-1569 ; ISSN: 09544062 Shirin, M. B ; Assempour, A ; Sharif University of Technology
    Abstract
    The inverse solution is helpful to determine the drawability of a part and drawing parameters at the initial design stage. The usual inverse algorithms consider the drawing process that occurs in one step and therefore they are not able to analyze the processes which need more than one drawing step. Therefore, multistep inverse solution has been used for such problems. The multistep inverse solution deals with finding the initial guesses of nodal positions on intermediate stages and solving inverse equations between two consecutive steps. In this paper, a new mapping method has been developed to find the initial nodal positions on intermediate stages and the unfolding technique has been... 

    The effect of normal stress on hydro-mechanical deep drawing process

    , Article International Journal of Mechanical Sciences ; Volume 53, Issue 6 , 2011 , Pages 407-416 ; 00207403 (ISSN) Assempour, A ; Taghipour, E ; Sharif University of Technology
    2011
    Abstract
    Normal stress has some role in the deformation analysis of hydroforming processes. In this study, analytical modeling is pursued to evaluate the effect of normal stress on the hydro-mechanical deep drawing (HDD) process. Analyses are carried out for axisymmetric elements of the formed cup-shaped part for increments of the punch travel. The formulations are obtained using mechanical and geometrical relations and the finite difference method, thereby being solved by proper numerical algorithms. Furthermore, in the present work, part thickness is variable, the loading and straining are non-proportional, and bending/unbending effects over the part curvature are considered. The results show that... 

    , M.Sc. Thesis Sharif University of Technology Najimi Varzane, Masoud (Author) ; Asempour, Ahmad (Supervisor)

    Initial Blank Design of Deep Drawn Single Layer Composite parts Using Inverse Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Zamanian, Hashem (Author) ; Assempour, Ahmad (Supervisor)
    Abstract

    The inverse finite element method was derived from ideal forming to predict the development blank of sheet forming process and the strain distribution according to the geometry of final product. In this project we present an inverse finite element method to obtain strain and stress distribution in final shape and design initial blank of deep drawing process. The procedure is as follows: First, strain distribution in deep drawn part is estimated by kinematics. Then by using Hill’s anisotropic plasticity and according to the associated plastic flow rule, stress distribution is obtained in deep drawn orthotropic part.Finally, initial blank is designed by considering external forces between... 

    Estimation of Springback in Sheet Metal Stamping Using Inverse Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Marzban, Bahador (Author) ; Asempour, Ahmad (Supervisor)
    Abstract
    This work presents a quick method in estimation of spring back effect in sheet metal forming. In this method, the so called Inverse Finite Element Method (IFEM) has been adopted for compution of strains and also blank shape. Although the of element used is membrane, the effect of bending/ unbendiing is considered by addition of some extra forces as the bending forces to the nodal forces. The results of strain distribution obtained by IFEM are applied to another algorithm developed for computation of the spring back . this algorithm has been developed for the sections with plane starin assumption. Therefore, spring back of longitudinal parts, can be estimated by this method in a short time.... 

    Development of a model for Hydro-Mechanical Deep Drawing Process to Analyze the Effects of Assumptions and Parameters

    , M.Sc. Thesis Sharif University of Technology Taghipour, Ehsan (Author) ; Assempour, Ahmad (Supervisor)
    Abstract
    It is the goal of this thesis to develop an analytical model for the hydro-mechanical deep drawing (HDD) process of an axisymmetric sheet metal with the fixed gap method to evaluate the effects of some assumptions such as: proportional loading, plane stress, and constant thickness conditions. The effect of parameters on the HDD process is also studied. The main model is developed with considering the normal stress and part thickness change, non-proportional loading, bending and unbending effects at the top of the cup wall. The interrelationships between geometrical and mechanical variables are obtained in the finite difference form based on the incremental strain theory, thereby being solved... 

    Application of Inverse Isogeometric Methodology in Analysis of Multi-Step Sheet Metal Stamping Processes

    , M.Sc. Thesis Sharif University of Technology Isazadeh, Amir Reza (Author) ; Assempour, Ahmad (Supervisor)
    Abstract
    Recently, isogeometric methodology has been successfully implemented in one-step inverse analysis of sheet metal stamping processes. However, these models are not capable of analyzing forming processes which require severe deformation and/or several forming stages. This paper presents a multi-step inverse isogeometric methodology to enhance the precision of one-step models in predictions of the initial blank, strain distributions, and drawability of the formed parts. This methodology deals with the minimization of potential energy, deformation theory of plasticity, and considering membrane elements. The presented methodology utilizes the NURBS basis functions to create the final, middle, and... 

    Some improvements on the unfolding inverse finite element method for simulation of deep drawing process

    , Article International Journal of Advanced Manufacturing Technology ; Vol. 72, issue. 1-4 , 2014 , pp. 447-456 ; ISSN: 02683768 Bostan Shirin, M ; Assempour, A ; Sharif University of Technology
    Abstract
    The linear unfolding inverse finite element method (IFEM) has been modified and enhanced by implementing large deformation relations. The method is helpful to predict forming severity of the part that should be deep drawn as well as its blank shape and strain distribution in preliminary design stage. The approach deals with minimization of potential energy and large deformation relations with membrane elements. To reduce the computation time, the part is unfolded properly on the flat sheet and treated as 2D problem. Moreover, the nonlinear stress-strain relationship of plastic material properties has been considered to increase the accuracy of the results. An experiment set up has been... 

    Development of Inverse Isogeometric Formulations in Simulation of Sheet Metal Forming Processes

    , Ph.D. Dissertation Sharif University of Technology Shamloofard, Mansoor (Author) ; Assempour, Ahmad (Supervisor)
    Abstract
    This research presents inverse isogeometric models based on the deformation theory of plasticity to predict the blank and strain distribution in sheet metal forming processes. In this study, the NURBS functions are utilized for both modeling of a final part and analysis of the forming process. Therefore, the developed models require only one modeling and analysis representation, in contrast to finite element models which deal with two separate modeling and analysis representations. In this research, a membrane one-step inverse isogeometric model is initially presented to analyze sheet metal forming processes. This method has various advantages such as solving the governing equations in... 

    Identification of optimum parameters of deep drawing of a cylindrical workpiece using neural network and genetic algorithm

    , Article World Academy of Science, Engineering and Technology ; Volume 78 , 2011 , Pages 211-217 ; 2010376X (ISSN) Singh, D ; Yousefi, R ; Boroushaki, M ; Sharif University of Technology
    2011
    Abstract
    Intelligent deep-drawing is an instrumental research field in sheet metal forming. A set of 28 different experimental data have been employed in this paper, investigating the roles of die radius, punch radius, friction coefficients and drawing ratios for axisymmetric workpieces deep drawing. This paper focuses an evolutionary neural network, specifically, error back propagation in collaboration with genetic algorithm. The neural network encompasses a number of different functional nodes defined through the established principles. The input parameters, i.e., punch radii, die radii, friction coefficients and drawing ratios are set to the network; thereafter, the material outputs at two...