Hydro-Forming a Steel Tube Finite Element Model Design Greg Wilmes Finite Element Method MIE 605 – Spring 2003

Hydro-Forming of a Steel Tube • Background • Model Creation – Model Limitations – Contact elements – Load stepping • Findings • Future Work • Conclusion

Background

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

• Sheet Hydro-Forming – Hoods – Roofs • Tubular Hydro-Forming – Engine chassis – Frame Rails – Exhaust Systems

Primer: Tube Hydroforming a b c d e

F axial Massachusetts Institute of Technology Cambridge, Massachusetts P F axial

f

Derived from: Siempelkamp Pressen Systeme GmbH & Co.

Materials Systems Laboratory

Concerns During Hydroforming Process

Focus of this project • Create a Finite Element Model to simulate the hydro-forming process • Use the model to create a 3”x3” square tube from a 3” round tube.

Real World Example • • • • • 3-D parts Non-linear material properties Material variations Complicated geometry with bends and depressions Friction

Geometry Simplifications • 2-Dimensional • Symmetric • Deformation from Circle to Square • Rigid Target Surface • Constant Thickness 1.6mm

Pressu re

Governing Equation • Hoop Stress 

y



P



r t

P t r

Material Property Simplifications • Isotropic Expansion • Non-Linear – Experimental tensile test data – 20 points • Coloumb Friction Effects • No strain rate effects

Plastic Deformation of Low Carbon Steel

350 340 330 320 310 300 290 280 270 260 250 0 0.05

0.1

Strain

0.15

0.2

Model Creation • Element Type – Plane 42 • 4 noded • 2-Dimensional • • Non-Linear Options – Plane Stress Option – Local Coordinate System – Extra Shape Functions

Meshing • • Hydro-Form Die – Rigid Target • No mesh allowed Hydro-Form Blank – Mapped Mesh • Angled • Thickness split

Contact Elements • • Allows modeling of contact between two objects Used Contact Wizard – Rigid Target – Deformable Contact – No Separation (sliding) option – Coloumb Friction (0.27)

Solution Control Options • • • • Static – Quasi-Static Evaluation Non-Linear Solution Stepped Loading Auto Time Steps

Constraints • Target Die – Fully constrained – Cannot Move • Contact Blank – Symmetrically Constrained

Load Steps • Using a simple “do” loop – Slowly increase internal pressure – 380 MPa • Used second “do” loop – Maintain pressure for a period of time • Repeated for different meshing configurations

Findings Maximum Displacement 12.6

12.5

12.4

12.3

12.2

12.1

12 11.9

11.8

11.7

0 200 400 1200 1400 1600 600 800

Elements

1000 • • • Difference between 90 elements and 1400 elements was 0.032mm

0.3% difference Close to general manufacturing machining tolerances

Continued Work • • Refine Finite Element simulation to match real world parts – 3-Dimentions – Different materials – Different deformation shapes Stress State analysis

Conclusion and Thoughts • The Finite Element Method and Ansys seem to be appropriate for analyzing this problem • Model seemed as respond well with about 100 elements