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Hydro-Forming a Steel Hydro-Forming a Steel TubeTube

Finite Element Model DesignFinite Element Model Design

Greg WilmesGreg Wilmes

Finite Element MethodFinite Element MethodMIE 605 – Spring 2003MIE 605 – Spring 2003

Hydro-Forming of a Steel Hydro-Forming of a Steel TubeTube• BackgroundBackground

• Model CreationModel Creation– Model LimitationsModel Limitations– Contact elementsContact elements– Load steppingLoad stepping

• FindingsFindings

• Future WorkFuture Work

• ConclusionConclusion

BackgroundBackground

• Sheet Hydro-FormingSheet Hydro-Forming– HoodsHoods– RoofsRoofs

• Tubular Hydro-Tubular Hydro-FormingForming– Engine chassisEngine chassis– Frame RailsFrame Rails– Exhaust SystemsExhaust Systems

Hydro-Forming is a manufacturing process which forms complex shapes using uncompressible liquids.

Primer: Tube Primer: Tube HydroformingHydroforminga b

c d

FaxialFaxial

P

e

Derived from: Siempelkamp Pressen Systeme GmbH & Co.

f

Massachusetts Institute of TechnologyCambridge, Massachusetts Materials Systems Laboratory

Concerns During Concerns During Hydroforming ProcessHydroforming Process

Focus of this projectFocus of this project• Create a Finite Element Model to Create a Finite Element Model to

simulate the hydro-forming processsimulate the hydro-forming process

• Use the model to create a 3”x3” Use the model to create a 3”x3” square tube from a 3” round tube.square tube from a 3” round tube.

Real World Example Real World Example • 3-D parts3-D parts• Non-linear material Non-linear material

propertiesproperties• Material variationsMaterial variations• Complicated geometry Complicated geometry

with bends and with bends and depressionsdepressions

• FrictionFriction

Geometry SimplificationsGeometry Simplifications• 2-Dimensional2-Dimensional

• SymmetricSymmetric

• Deformation from Deformation from Circle to SquareCircle to Square

• Rigid Target SurfaceRigid Target Surface

• Constant Thickness Constant Thickness 1.6mm1.6mm

Pressu

re

Governing EquationGoverning Equation• Hoop StressHoop Stress

trP

y

t

rP

Material Property Material Property SimplificationsSimplifications

• Isotropic ExpansionIsotropic Expansion

• Non-LinearNon-Linear– Experimental tensile test Experimental tensile test

datadata– 20 points 20 points

• Coloumb Friction EffectsColoumb Friction Effects

• No strain rate effectsNo strain rate effects

Plastic Deformation of Low Carbon Steel

250

260

270

280

290

300

310

320

330

340

350

0 0.05 0.1 0.15 0.2

Strain

Stre

ss (M

Pa)

Model CreationModel Creation• Element TypeElement Type

– Plane 42Plane 42• 4 noded4 noded• 2-Dimensional2-Dimensional• Non-LinearNon-Linear• OptionsOptions

– Plane Stress OptionPlane Stress Option– Local Coordinate Local Coordinate

SystemSystem– Extra Shape Extra Shape

FunctionsFunctions

MeshingMeshing• Hydro-Form DieHydro-Form Die

– Rigid TargetRigid Target• No mesh allowedNo mesh allowed

• Hydro-Form BlankHydro-Form Blank– Mapped MeshMapped Mesh

• AngledAngled• Thickness splitThickness split

Contact ElementsContact Elements• Allows modeling of Allows modeling of

contact between contact between two objectstwo objects

• Used Contact WizardUsed Contact Wizard– Rigid TargetRigid Target– Deformable ContactDeformable Contact– No Separation No Separation

(sliding) option(sliding) option– Coloumb Friction Coloumb Friction

(0.27)(0.27)

Solution Control OptionsSolution Control Options• StaticStatic

– Quasi-Static EvaluationQuasi-Static Evaluation• Non-Linear SolutionNon-Linear Solution• Stepped LoadingStepped Loading• Auto Time StepsAuto Time Steps

ConstraintsConstraints• Target DieTarget Die

– Fully constrainedFully constrained– Cannot MoveCannot Move

• Contact BlankContact Blank– Symmetrically ConstrainedSymmetrically Constrained

Load StepsLoad Steps• Using a simple “do” loopUsing a simple “do” loop

– Slowly increase internal pressureSlowly increase internal pressure– 380 MPa380 MPa

• Used second “do” loop Used second “do” loop – Maintain pressure for a period of timeMaintain pressure for a period of time

• Repeated for different meshing Repeated for different meshing configurations configurations

FindingsFindings Maximum Displacement

11.7

11.8

11.9

12

12.1

12.2

12.3

12.4

12.5

12.6

0 200 400 600 800 1000 1200 1400 1600

Elements

Dis

plac

emen

t (m

m)

• Difference between 90 elements and 1400 elements Difference between 90 elements and 1400 elements was 0.032mmwas 0.032mm

• 0.3% difference0.3% difference• Close to general manufacturing machining tolerancesClose to general manufacturing machining tolerances

Continued WorkContinued Work• Refine Finite Element simulation to Refine Finite Element simulation to

match real world partsmatch real world parts– 3-Dimentions3-Dimentions– Different materialsDifferent materials– Different deformation shapesDifferent deformation shapes

• Stress State analysisStress State analysis

Conclusion and ThoughtsConclusion and Thoughts• The Finite Element Method and Ansys The Finite Element Method and Ansys

seem to be appropriate for analyzing seem to be appropriate for analyzing this problemthis problem

• Model seemed as respond well with Model seemed as respond well with about 100 elements about 100 elements