4th_week-1 - 성형 공정 Process Design in Metal Forming...

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Unformatted text preview: 성형 공정 Process Design in Metal Forming 2010 학년도 1학기 INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Contents Contents 1. Introduction 1) Process modeling 2) Finite element method Finite element method 2. Bulk Deformation Process Bulk Deformation Process 1) 2) 3) 4) Forging Rolling Extrusion Drawing 3. Sheet Metal Forming INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Introduction Introduction ▶ manufacturing • 주어진 재료를 이용하여 유용한 제품으로 만드는 과정 • 제작된 제품은 shape, size, accuracy and tolerance, appearance, properties 등 으로 정의되는 비교적 복잡한 형상을 지님 ■ classification of manufacturing process ▶ primary shaping process well geometry from the initially shape material • obtain s well- defined geometry from the initially n o shape material • casting , melt extrusion , die casting , pressing of powder metal ▶ • • • metal forming process forming process metal is formed by plastic deformation 기계적성질의 향상 및 scrap의 최소화 rolling , extrusion , cold/ hot forging , deep drawing 등 i INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Introduction Introduction ▶ metal cutting process • material removal process • sawing , turning , milling , broaching , grinding , etc. ▶ metal treatment processes • changes of properties or appearance while shape unchanged • heat treatment , anodizing , surface hardening ▶ joining • metallurgical joining : welding , diffusion bonding • mechanical joining : riveting , shrink fitting , mechanical assembly , etc. INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Introduction Introduction INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling • • lat e 70s & 80s , computer aided techniques in metal forming (desi n , 70 80 (d ig engineering, manufacturing ) increased considerably the trend is toward ever wider application of simulation and process design in the industr y th ▶ • • • ultimate goal in manufacturing research (development ) to determine the optimum means of producing sound products. optimization criteria may vary , depending on the product requirement . in met al forming , process design requires determination of deformation mechanics • for the proper process design , the influences of process parameters are investigated : friction condition , material properties , work-piece geometry , etc. • thus process modeling became a major concern in modern metal forming technology . INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling ▶ • • • • • approximate method of anal sis ly slip line field method : adequate for plane strain for perfect plastic material slab method Visio-plasticity method : combination of experiment and analysis upper (lower) bound method finite element method ▶ slab method • Work-piece is decomposed in several slab s is decomposed in several slab • approximate equilibrium equation s are solved with imposition of stress compatibility between slab s and boundary tractions • final result is a reason able load prediction with an approximate stress result is reason able load prediction with an approximate stress distribution INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling ▶ • • • slip line field method li fi used in plane strain for perfectly plastic materials (constant yield stress) uses the hyperbolic properties that the stress equations have in such cases construction of slip-line fields is still quite limited in predicting result s that give good correlations with experimental work , although producing an "exact " stress distribution INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling ▶ • • • visioplasticity method originated by Thomsen et al. combination of experiment and analysis after the velocity vectors have been determined from an actual test , strainrates are calculated and the stress distributions are obtained from plasticity equations • it helps to obtain reliable solutions in details for processes in which the experimental determination of the velocity vector s is possible INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling ▶ upper bound method • requires the guessing of admissible velocity fields (KAVF ), among which the best one is chosen by minimizing total potential energy. • information leading to a good selection of velocity fields comes from experimental evidence and experience. • this method can deliver a fast and relatively accurate prediction of loads and velocit distributions. ity di 1.2 Finite element method • Finite element technique, whose engineering birth and boom in the 1960s was due to the application of digital computers to structural analysis, has spread to a verity of engineering and physical science disciplines. • Lee and Kobayashi (1970s) developed the “matrix method”, the first application of FEM in the metal forming. INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling Basic concept of finite element method fi discretization a number of finite element is identified in the domain of function. the value of the function and its derivates, when appropriate, are specified at these points (called nodal point) • the domain of the function is represented by a finite collection of sub domains called finite elements and then assembled of the elements connected together on their boundaries • the function is approximated locally within each element by continuous functions determined by nodal point values. ▶ • • • INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling ▶5 1) 2) 3) 4) 5) general steps in FEM FEM Identification of the problem Definition of the element Establishment of the element equation The assemblage of element equations Numerical solution of the global equations ▶ Formulation of element equation 1) Direct approach Direct approach 2) Variational method 3) Method of weight residuals 4) Energy balance approach. INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling ► formulation of metal forming using the variational method a) formulate proper functional, depending on specific constitutive relations -> the solution of the original boundary value problem is obtained by the solution of the dual variational problem in which the first-order variation of the functional vanishes b) choose an approximate interpolation function (or shape function) c) express the functional locally within each element in terms of the nodal point values d) the local equations are then assembled into overall problem e) get stiffness equation by applying the stationar y condition f) the stiffness equation are solved under appropriate b.c. INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling ► main advantages of FEM FEM • capability of obtaining detailed solutions of the mechanics in a deforming body, namely velocities, shapes, strains, stresses, temperatures or contact pressure distributions etc. • the fact that a computer code, once written, can be used for a large variety of problems by simply changing the input data INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling 1.3 Solid formulation and flow formulation fl ► flow formulation • from the given (or assumed) current state (shape of body, temperature, inhomogeneity, material parameters, etc) find velocity. • rigid-plastic or rigid-viscoplastic assumption • neglect elastic strain terms : no need to check yield condition (always yield) • boundary conditions on Su , prescribed velocity on SF , prescribed traction SF prescribed traction • with the velocity, find strain rate : velocity-strain rate relationship stress : constitutive equation constitutive equation effective strain : path integral displacement : time integral INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling ► solid formulation • from the current state of the body and the internal distribution of stress, find velocity • elastic-plastic or elastic-viscoplastic assumption • phenomena associated with elasticity cannot be neglected : always check yield • boundar y conditions on Su , prescribed velocity on SF , prescribed traction rate • with the velocity, find strain rate : velocity-strain rate relationship stress rate : elastic constitutive equation rate elastic constitutive equation stress : path integral of stress displacement : time integral INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling • difficulties due to large deformation in metal finite deformation the rotational effect, etc stress integration : short time step ► another classification classification • static implicit formulation • dynamic explicit formulation INHA UNIVERSITY MetalForminGLab. 2010 1st Term Process Design in Metal Forming Process modeling Process modeling 1.4 Metal forming and the finite element method fi • simple extension of structural analysis technique to the plastic deformation regime -> hydrostatic extrusion, compression, indentation problem • due to the development of the numerical procedure based on the flow formulation, reliability and computational efficient is justified • inclusion of the effects of strain-rate and temperature in material properties and of thermal coupling -> hot and warm working range INHA UNIVERSITY MetalForminGLab. ...
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This note was uploaded on 03/24/2010 for the course ME 031 taught by Professor Kim during the Winter '10 term at Korea Advanced Institute of Science and Technology.

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