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CLOSED LOOP CONTROL OF THE CLOSED LOOP CONTROL OF THE 3D BENDING PROCESS3D BENDING PROCESS

K. Kuzman (3)

Faculty of Mechanical Engineering, University of Lju bljanaTECOS – Slovenian Tool and Die Development Centre, C elje, Slovenia

Submitted by M.Geiger (1), Germany

TECOS TECOS –– Slovenian Tool andSlovenian Tool andDie Development CentreDie Development Centre

1. 1. INTRODUCTIONINTRODUCTION

2. 2. PRELIMINARY INVESTIGATIONSPRELIMINARY INVESTIGATIONS

3.3. MATHEMATICAL MODEL OF THEMATHEMATICAL MODEL OF THE

STABILIZATION ALGORITHMSTABILIZATION ALGORITHM

4. 4. MODEL EVALUATIONMODEL EVALUATION

5. 5. FEED BACK SYSTEMFEED BACK SYSTEM

6. 6. CONCLUSIONSCONCLUSIONS

1. 1. INTRODUCTIONINTRODUCTION

Modern metalModern metal --forming processes have twoforming processes have twovery demanding goals: very demanding goals:

•• to produce net shape components to produce net shape components

•• to assure stable zeroto assure stable zero --defect productiondefect production

1. INTRODUCTION1. INTRODUCTION

The metalThe metal --forming system consists of severalforming system consists of severalinfluential parameters, the most important are:influential parameters, the most important are:

•• incoming material incoming material •• toolstools•• the forming machine the forming machine •• tribology tribology •• the forming process itself. the forming process itself.

These parameters are in close correlation, resultin g in aThese parameters are in close correlation, resultin g in ahighly nonhighly non --linear thermolinear thermo --elastoplastic problem.elastoplastic problem.

1. INTRODUCTION1. INTRODUCTION

1. INTRODUCTION1. INTRODUCTION

Correlation between the part width and the flow str ess of wire.Correlation between the part width and the flow str ess of wire.

0

0.2

0.40.6

0.8

1

0 100 200 300 400 500l [m]

bre

l , Y

rel

Kuzman, K., 1999, Some Research and Development Efforts in Cold Forging,in Geiger. M. (ed.): Umformtechnik Plus, Meisenbach Verlag, Bamberg, 199-206

how to assure zero defect production ?how to assure zero defect production ?

•• to narrow tolerances of the process parameters to narrow tolerances of the process parameters

•• to redesign the process by repositioning it intoto redesign the process by repositioning it into

stable technological windows stable technological windows

•• to implement closed loop controlto implement closed loop control

but: but: prior taking decissions to make cost evaluationprior taking decissions to make cost evaluation

1. INTRODUCTION1. INTRODUCTION

The paper presents the possibility to control the The paper presents the possibility to control the mechanical properties of the wire material, since I t mechanical properties of the wire material, since I t was experimentally verified that they are the most was experimentally verified that they are the most important for a stable shape of 3D bent products.important for a stable shape of 3D bent products.

1. INTRODUCTION1. INTRODUCTION

b(l) [mm]

3D bent product

2. 2. PRELIMINARY INVESTIGATIONSPRELIMINARY INVESTIGATIONS

2. 2. PRELIMINARY INVESTIGATIONSPRELIMINARY INVESTIGATIONS

0

0.2

0.40.6

0.8

1

0 100 200 300 400 500l [m]

bre

l , Y

rel

Correlation between the part width and the flow str ess of wire.Correlation between the part width and the flow str ess of wire.

( )minmax

minrel bb

b)l(bb

−−=

( )minmax

minrel YY

Y)l(YY

−−=

3D bent product and its width fluctuation.

3. 3. MATHEMATICAL MODEL OF THEMATHEMATICAL MODEL OF THESTABILIZATION ALGORITHMSTABILIZATION ALGORITHM

3. 3. MATHEMATICAL MODEL OF THEMATHEMATICAL MODEL OF THE STABILIZATION ALGORITHMSTABILIZATION ALGORITHM

Schematical representation of the wire straightener in one planeSchematical representation of the wire straightener in one plane ..

i

i

i r

dzdx

dz

xd

k1

1

32

2

2

=

+

=∑

−

=

=1

2

n

ii

TOT kk

ki - wire curvature at roller I kTOT - total wire curvature

3. 3. MATHEMATICAL MODEL OF THEMATHEMATICAL MODEL OF THE STABILIZATION ALGORITHMSTABILIZATION ALGORITHM

Flow stresses Flow stresses ( obtained by tensile tests on wires straitened( obtained by tensile tests on wires straitenedbbyy different roller presettings) different roller presettings) for two different wire qualities infor two different wire qualities in

ddependenceependence to different total cyclic deformations. to different total cyclic deformations.

Basic ideaBasic idea

Low carbon cold drawn wire material normally Low carbon cold drawn wire material normally exhibits cyclic softening when being exposed to exhibits cyclic softening when being exposed to alternating plastic deformation [Huml], if the tota l alternating plastic deformation [Huml], if the tota l amount of cyclic deformation amount of cyclic deformation kTOTkTOT is high, the is high, the material can harden again. material can harden again.

It can be concluded that the softening or hardening It can be concluded that the softening or hardening depends on the material and the amount of reversed depends on the material and the amount of reversed plastic deformation (plastic deformation ( kTOTkTOT). By controlling it, it ). By controlling it, it would be possible to control the flow stress of wir e would be possible to control the flow stress of wir e coming out of the straightener.coming out of the straightener.

3. 3. MATHEMATICAL MODEL OF THEMATHEMATICAL MODEL OF THE STABILIZATION ALGORITHMSTABILIZATION ALGORITHM

Numerical model of the wire straightener can beNumerical model of the wire straightener can beexpressed by the functions expressed by the functions ff and and vv, which are the core, which are the coreof the stabilization algorithm:of the stabilization algorithm:

3. 3. MATHEMATICAL MODEL OF THEMATHEMATICAL MODEL OF THE STABILIZATION ALGORITHMSTABILIZATION ALGORITHM

)k,k,D,K,'n,Y,E,d,d(f)k,F( iinicycyxfini =

)k(vx ii =

3. 3. MATHEMATICAL MODEL OF THEMATHEMATICAL MODEL OF THE STABILIZATION ALGORITHMSTABILIZATION ALGORITHM

Measured values and explanation of the stabilizatio n procedure.Measured values and explanation of the stabilizatio n procedure.

3. 3. MATHEMATICAL MODEL OF THEMATHEMATICAL MODEL OF THE STABILIZATION ALGORITHMSTABILIZATION ALGORITHM

Schematic representationSchematic representation

of the stabilization algorithm.of the stabilization algorithm.

4. MODEL EVALUATION4. MODEL EVALUATION

4. 4. MMODEL EVALUATIONODEL EVALUATION

Courtesy of NIKO, 2000

Experimental equipement in the productionExperimental equipement in the production

Wire bending machine equiped with the experimental wire straightener

4. 4. MMODEL EVALUATIONODEL EVALUATION

Laser measuring head for onLaser measuring head for on --line control of wire diameterline control of wire diameter

Basic characteristics:

• Range 0.1 – 10 mm• Resolution: 0.1µm• Repeatability: 0.3 µm• Measuring field: 13X13

4. 4. MMODEL EVALUATIONODEL EVALUATION

New and old roller positionsNew and old roller positions

1 3 5 7

2 4 6

4. 4. MMODEL EVALUATIONODEL EVALUATION Experimental evaluation of the proposed model: Experimental evaluation of the proposed model: A A -- wire path, B wire path, B -- product geometry (width b product geometry (width b -- Figure 1), before (jFigure 1), before (j thth interval) interval)

and after presetting (j+1and after presetting (j+1 stst interval) of the rollers.interval) of the rollers.

AA

BB

5. FEED BACK SYSTEM5. FEED BACK SYSTEM

5. FEED BACK SYSTEM5. FEED BACK SYSTEM

Schematic representation of the

close loop control system for

a two plane roller straightener.

6. CONCLUSIONS6. CONCLUSIONS

6. CONCLUSIONS6. CONCLUSIONS

Closed loop contol of the 3D bending process ispossible when

• affecting the mechanical properties of the incomingmaterial by roller straighteners

• using process stabilisation algorithm

• from force measurements to flow stressesdetermination and then to reposition of rollers

6. CONCLUSIONS6. CONCLUSIONS

Benefits

• it is not necessary to narrow the mechanical proper tiesof the incoming material (which is expensive)

• the method can be used not only for wire but also f orsheet metal

APPENDIXAPPENDIX Elements of wire bending force calculation for cycl ic loading

1icyc.0i DYY −⋅=

.constY ≠

(l))(FflY ii1)( −==

Ref.: Nastran, M., 2002, A contribution to the stability of the coldforming process of wire, PhD Thesis, University of Ljubljana.

i–th roller

(Yanagi, Maeda, Hattori)