Simulation Techniques in Manufacturing Technology Lecture 4 · Simulation Techniques in...

© WZL/Fraunhofer IPT

Sheet Metal Forming II

Simulation Techniques in Manufacturing Technology

Lecture 4

Laboratory for Machine Tools and Production Enginee ring

Chair of Manufacturing Technology

Prof. Dr.-Ing. Dr.-Ing. E.h. Dr. h.c. Dr. h.c. F. Klocke

Seite 2© WZL/Fraunhofer IPT

Economical aspects of process modelling4

Case Study3

Simulation of Sheet Metal forming2

Introduction1

Outline


Historical development of the FEM

� 230 v.Chr.: Calculation of the Pi-number and the circumference by adding of finite number of filaments (Archimedes of Syrakus)

� 1851: Solution of the minimal area problem by Schellbach

� 1909: Introduction of the Ritz solution method

� 1915: Introduction of the weighted residual solution method by Galerkin

� 1943: Introduction of the variation solution method by Courant

� 1960: The terminology Finite Element Method first used by Clough

� ab 1970: Development of the first commercial FE-software

Source: Domenico Fetti, Columbia Encyclopedia

time

Archimedes

Ritz

Galerkin

Courant


Why process modelling?

Car BodyTime Cost

Quality

Increase quality

Apply new materials(Al, Mg, …)

Use material moreefficiently

Reduction of toolcost

Reduction of leadtime

Reduction of timerequired for training

Increase reliabilityof production

Manufacture complex parts

Reduction of pre production trials

Source: BMW


Integration of process modelling into the process c hain

Source: BMW

Designof car

exterior

Part design

Partproduction

Means of production Tool manu-facturing and testingTool designPlanning

Sheet metal forming simulationPart evaluation Process optimisation

Sof

twar

e so

lutio

nA

pplic

atio

nP

roce

ss c

hain

Methods applied:- 2D modelling- one-step modelling- modelling with membrane elementsShort computation time with sufficient precision

Methods applied:- Simulation with membrane elements- Simulation with shell elements

High Precision within acceptable computation times



Case Study3


Introduction1

Outline


Disadvantages:

� difficult selection of cross sectionsto be modelled

� less accurate results

Commercial FE codes for sheet metal forming

2D Modelling of selected cross sections:

� Abaqus www.abaqus.com

� Ansys www.ansys.com

� Autoform 2D www.autoform.ch

� Deform 2D www.deform.com

� Marc www.marc.com

Advantages:

� reduced computation time

� less sensitive to quality of inputdata

� usually less input data required

Source: BMW / Fontana Pietro SPA


One-step simulation:

� Isopunch

� SIMEX

� Corps

� AutoForm Onestep

� ...

Advantages:

� reduced computation time

� usually less input data required

� suitable tool for part evaluation

Disadvantages:

� decreasing significance due to increasing computing power

� still not very accurate

Source: BMW



Model with membrane elements:

� AutoForm Incremental

� Abaqus

� ...

Advantages:

� acceptable computation time

� suitable tool for part evaluation

� suitable for process optimisation

� basically accurate results

Disadvantages:

� long computation time

� problems when severe bending occurs

� not accurate enough in predicting wrinkles

� requires high quality input dataSource: BMW



Model with shell elements:

� PAM-STAMP

� Optris

� DYNA-Form

� Indeed

� ...

Advantages:

� state of the art tools for processoptimisation

� very accurate results

Disadvantages:

� long computation time leads to long response time

� requires high quality input data

Source: BMW




Case Study3


Introduction1

Outline


Procedure of FE-Analysis

CAD-model

Idealization

Diskretization

Boundary conditions

FE-Analysis

Interpretation of the results

Pre-processor

Solver

Post-processor

====

23

13

12

22

11

13

23

33

2212

1211

13

23

12

22

11

0000

0000

0000

000

000

γγγεε

τττσσ

G

G

G

GG

GG


Material Laws

� Modelling of the material behavior based on mathematical material laws

� Deduction of the modelling parameters from experimental data:

– Elastic material behavior: Young’s Modulus, Poisson’s ratio, elastic anisotropy

– Plastic material behavior: flow curve, strain hardening parameter, plastic anisotropy

� Usage of ideal-plastic material models are mostly sufficient for bulk forming

� Usage of elastoplastic material models in sheet metal forming simulations

� Consideration of plane anisotropy for sheet metal forming simulations

Elastic

σ

ϕIdeal-plastic

σ

ϕ

Plastic withstrain hardening

σ

ϕElastoplastic withstrain hardening

σ

ϕ

Low accuracy / low calculation time

High accuracy / high calculation time


Friction laws in metal forming� Coulomb friction:

� Shear friction:

with

� Wanheim and Bay developed a more general friction law with a continuous transition of the two friction laws mentioned above:

σN – Normal stress

τR – Shear stress

µ,m – Friction coefficients

f – Friction factor

α – Ratio of the contact areas

Coulomb friction

Shear friction

Reality

Orowan

Shaw / Wanheim und Bay

Reality

Nσ

Nσ

Rτ

Rτ

NR σµτ ⋅⋅⋅⋅====

kmR ⋅⋅⋅⋅====τ3fk

k ====

kfR ⋅⋅⋅⋅⋅⋅⋅⋅==== ατ


Part Evaluation: One step method

Steps:

1) Create mesh from 3DCAD model

2) create blank holder

3) simplified add-on

4) computation

5) interpretation of results

Source: BMW



Source: BMW

Steps:




4) computation



Contact stress distribution for circular tool geome try

drawing direction

Contact concentration

FSt,max = 64,5 kN

0

400

100

200

300

0

400

100

200

300

Contact-stressesσ

N / MPa

0

70

0 35Stroke s / mm

Pun

ch fo

rce

FS

t/ k

N

A-A

A-A

Anisotropy effect


Alternative tool geometries

Lamé (a = 10 mm; b = 8 mm; n = 3)

Lamé (a = 10 mm; b = 8 mm; n = 4)

0

400

100

200

300

ContacktstressesσN / MPa

Lamé (a = 10 mm; b = 7 mm; n = 3)

Lamé (a = 12 mm; b = 7 mm; n = 3)

0

70

0 35Stroke s / mm

Pun

ch fo

rce

FS

t/ k

N

FSt,max = 64,5 kNFSt,max = 61,8 kNFSt,max = 61,8 kNFSt,max = 60,1 kNFSt,max = 63,1 kN


Reduction of stress concentration and wear using th e Lamé-curve

Contact stressσN / MPa

Areas with increased

contact stress

Circle-curve Lamé-curve

gradually increasing

contact stress

direction of pull direction of pull


Process optimisation: Forming process

CAD-datatool & blank

Meshing

Process boundary conditions

Contact formulation

GENERIS

Material-data

PAM-STAMP Input file


Process optimisation: Forming sequence

Source: BMW


Case study: Process optimisation by improved tool d esign

Source: BMW

Part geometry Workpiece end geometry Initial workpiec e geometry

Tool geometryTool geometry (cut view)



Source: BMW


Case study: Evaluation of wrinkling

distribution of effective strain during and after the drawing process

Source: BMW


Process optimisation: Evaluation of wrinkling

Source: BMW

distribution of effective stress during and after the drawing process


Process optimisation: Comparision between simulatio n and real part

Source: BMW

wrinkling


Process optimisation: Comparision between simulatio n and real part

Source: BMW

rupturing



Case Study3


Introduction1

Outline


Modelling sheet metal forming: Quality of the compu ted results

0+springback

++++wrinkles

+++rupture

Quality

qualitatively quantitatively

Result


Flow chart of a modelling project

Partgeometry

Materialselection

Tools(CAD)

Processparameters

SimulationStart tool

design

no

yes

Part design Boundary Conditions Simulation


Effort for a sheet metal modelling project

Change of responsible effort CAD effort Simulation

Process parameters (friction, beads, ...)

Process design ---- 1h --3h

die setup (blank holder, etc. ...)

Process design 1d -- 1w 3h -- 1d

Material quality and thickness

Body design ---- 1h -- 3h

Part geometry Body design 1d --1w 3h -- 1d

Total effort for a medium sized part: Usually 2 wee ks


Preprocessing effort for a modelling project in she et metal forming

1993 2009

1W

2 W

3 W

Effort for preprocessing


Development of computing power and computation time

100%

1993 2009

20%

Increase of computing power

1993 2009

50h

15h

Reduction of computation time for a large car body

part


Development of hardware cost

1993

Hardware cost

2009

100 %

< 1 %


Prerequisites for the industrial application of pro cess modelling

Time: Cost: Quality:

Short responsetimes

Low projectcost

Reliable results

Integration into the process chain of a car body


Simulation of crashworthiness for the Ford Explorer (LS-Dyna)

Source: Livermore Software Technology

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