CHAPTER 4 CFD AND FEA ANALYSIS OF DEEP DRAWING PROCESS

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Solomon Albert Sutton
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1 54 CHAPTER 4 CFD AND FEA ANALYSIS OF DEEP DRAWING PROCESS 4.1 INTRODUCTION In Fluid assisted deep drawing process the punch moves in the fluid chamber, the pressure is generated in the fluid. This fluid pressure depends on the process geometry and various process parameters. Estimation of fluid pressure by using flotran CFD analysis software. ANSYS - LS Dyna finite element simulation software is used to predict the radial, hoop and drawing stresses with varying fluid pressures. 4.2 DETERMINATION OF FLUID PRESSURE Ansys - Flotran CFD analysis is used to study the variation of pressure of fluid with different punch radius at constant speed of punch and also pressure variation with different punch speeds at constant punch radius using three fluids such as castor oil, olive oil and heavy machine oil. This pressure of fluid is to evaluate the blank holding pressure analization of stresses in this process. The element type is fluid 141 element from flotran CFD library is selected for meshing.the FLUID 141 element shown in fig.4.1 This figure shows FLUID 141 geometry, locations of node and coordinate system for this element. The element is defined by three nodes [triangle] or four nodes [quadrilateral] and by isotropic properties of material.

2 55 Fig.4.1 FLUID 141 Element geometry The fluid model is developed in Ansys preprocessing using geometric modeling approach. The resulted geometry with 2D geometric options are shown in fig.4.2 Fig.4.2 Geometric model ( axisymmetric) of the deep drawing process Using adaptive mesh, a converged mesh is shown in fig.4.3

56 Fig.4.3 Flotran CFD model of the process The total number of elements and nodes in the model are 7972 and 8364.

3 56 Fig.4.3 Flotran CFD model of the process The total number of elements and nodes in the model are 7972 and Boundary and loading conditions: Vx = Vy = 0 on the boundary and punch velocity, Vy = 10mm/sec. The fig.4.4 shows the boundary and loading conditions of process.

4 57 Fig.4.4 Boundary and loading conditions of the process Table 4.1 Variation of fluid pressure for different fluids by varying punch radius Punch radius Fluid Pressure P [ N/m 2 ] r p [mm] Heavy machine Olive oil oil Castor oil

5 58 Table 4.1 represents the variation of fluid pressure for three different fluids by increasing punch radius at constant punch speed u = 10mm/sec. From this methodology the fluid pressure is increases with increase in punch radius. The fluid pressure is also depends on the viscosity. When the viscosity of fluid is more, then the fluid pressure is high. The variation of fluid pressures is observed from the table at any punch radius is P olive oil < P Heavy machine oil < P castor oil The same procedure is used for study on variation of pressure of fluid with different punch speeds at constant punch radius using three fluids such as castor oil, olive oil and heavy machine oil with consideration of the process radius of punch 40mm and radius of die opening 45mm. Table 4.2 Variation of fluid pressure for different fluids by varying punch Speed. Punch speed Fluid Pressure P [ N/m 2 ] u [mm/sec] Heavy machine Olive oil oil Castor oil Table 4.2 represents the variation of fluid pressure for three different fluids by increasing punch speed. From this methodology the fluid pressure is increases with increase in punch speed. The fluid pressure is also depends on the viscosity. When the viscosity of fluid

6 59 is more, then the fluid pressure is high. The variation of fluid pressures is observed from the table at any punch speed is P olive oil < P Heavy machine oil < P castor oil. 4.3 FINITE ELEMENT ANALYSIS OF DEEP DRAWING PROCESS ANSYS - LS Dyna finite element simulation software is used to predict the radial, hoop and drawing stresses with varying blank radius, blank thickness, punch radius, fluid viscosities and fluid pressures. A 2d solid 162 ( Ansys-Ls dyna library) element is used to model the billet and punch and die is modeled with rigid elements. Coupled degrees of freedom is imposed between punch and billet and billet and die PLANE 162 Element Description PLANE162 is used for modeling 2-D solid structures in ANSYS LS- DYNA. The PLANE 162 element shown in fig.4.5.the element can be used either as a planer or as an axisymmetric element. The element is defined by four nodes having six degrees of freedom at each node: translations, velocities, and accelerations in the nodal x and y directions. A three-node triangle option is also available, but not recommended. Fig. 4.5 PLANE 162 Element geometry

7 60 The element is used in explicit dynamic analyses only. When using this element, the model must only contain PLANE162 elements - we cannot mix 2-D and 3-D explicit elements in the same model. Furthermore, all PLANE162 elements in the model must be the same type (plane stress, plane strain, or axisymmetric). The deep drawing process is simulated with condition axisymmetric. The Geometric model of deep drawing process along with the boundary conditions shown in fig.4.6 (a) Fig.4.6 (a) Geometric model of deep drawing process with boundary Conditions The boundary conditions with reasons are adopted for this process as follows. AB : Ux = 0 [ symmetric axis ]

8 61 BC, CD and DE : Ux = Uy = 0 [ fixed, i.e. Die is supported by ground ] EF : Uy = 0 [ blank holder support ] FG and EH : Ux = 0 [ normal to the blank surface ] The punch moves in y direction, hence punch velocity Vy=10mm/sec. Finite element model of the deep drawing process shown in fig.4.6 [b] Fig.4.6 [b] Finite element model of the deep drawing process The total number of elements and nodes in the model are 1160 and 1200 respectively. LS - Dyna explicit solver is used to predict the radial, hoop and drawing stresses by varying the radius and thickness of blank for different punch radius using three different fluids. The variation of these stresses are reported in chapters 5, 6 and 7.

Example 24 Spring-back

Example 24 Spring-back Summary The spring-back simulation of sheet metal bent into a hat-shape is studied. The problem is one of the famous tests from the Numisheet 93. As spring-back is generally a quasi-static