![September 1-5
Numisheet 2008
Interlaken - Switzerland
THE SPRINGBACK
Warm forming: diffused heating
Al 1050
Source: Keum Y.T., Han B.Y. [3]
5
Alessia Mentella](https://image.slidesharecdn.com/amentellanumisheet-120227034652-phpapp02/85/A-Mentella-numisheet-5-320.jpg)
![September 1-5
Numisheet 2008
Interlaken - Switzerland
SIMPLE BENDING TEST
Finite Element Model
Material data used for AZ31
m
e T − 18
A B C
170 412.16 0.0223
n
0.223
m Tmelting
0.06943 618 (
s = A + Ben ) &
1 + C ln 0.01 1 − T
− 18
melting
T [C°] E [MPa] poisson thermal exp [mm/mm*C°]
0 49500 0.30 0.00002400
20 49000 0.31 0.00002415 THERMAL BC:
100 46000 0.32 0.00002505 • NO HEAT SOURCE
200 43000 0.34 0.00002580 • NO HEAT EXCHANGE
300 40000 0.36 0.00002655 • CONDUCTION THROUGH
400 37000 0.38 0.00002715 THE WORKPIECE
500 34000 0.4 0.00002760
16
Alessia Mentella](https://image.slidesharecdn.com/amentellanumisheet-120227034652-phpapp02/85/A-Mentella-numisheet-16-320.jpg)
![September 1-5
Numisheet 2008
Interlaken - Switzerland
SIMPLE BENDING TEST
FEM Results
heating 120
100
Stress [Mpa]
80
Stress [Mpa]
60
40
20
20
0
0
0
0 0,02
0,02 0,04
0,04 0,06
0,06 0,08
0,08
Cold forming Heating
Cold forming
Cold forming Equivalent total strain
Cooling Springback total strain total strain
Equivalent Equivalent
Heating
18
Alessia Mentella](https://image.slidesharecdn.com/amentellanumisheet-120227034652-phpapp02/85/A-Mentella-numisheet-18-320.jpg)
![September 1-5
Numisheet 2008
Interlaken - Switzerland
STRETCH BENDING TEST
Some test results
AZ31 ~160 °C
23 °C
10%
( h1 − h2 ) − ( h1 − h2 )
cold warm
∆h % = 8%
( h1 − h2 )cold 6%
heating ∆h% 4%
s= 12 mm
2% s= 14 mm
s= 15 mm
0%
50 70 90 110 130 150
Tmax [°C]
21
Alessia Mentella](https://image.slidesharecdn.com/amentellanumisheet-120227034652-phpapp02/85/A-Mentella-numisheet-21-320.jpg)
![September 1-5
Numisheet 2008
Interlaken - Switzerland
STRETCH BENDING TEST
FEM Model
EXPLICIT APPROACH FORMING PHASE
• Quadrangular shell element (2mm side lenght) +
• 7 integration point through the thickness POST-DEFORMATION HEATING
IMPLICIT APPROACH
• Temperature assigned to the nodes SPRINGBACK SIMULATION
• No heat transfer with the environment
. T . T (°C) 20 500
ε ij = α T δ E [MPa]
ij Poisson
69000
0.33
60000
0.36
Thermal exp. [mm/mm*C°] 240x10-7 274x10-7
Yield Stress (MPa) 110 48
Plastic hardening moduli 0.20 0.20
22
Alessia Mentella](https://image.slidesharecdn.com/amentellanumisheet-120227034652-phpapp02/85/A-Mentella-numisheet-22-320.jpg)
A. Mentella numisheet
- 1. September 1-5 Numisheet 2008 Interlaken - Switzerland Localized warming of sheet metal parts for the reduction of springback Matteo Strano Antonio Del Prete [email protected] [email protected] Alessia Mentella Teresa Primo [email protected] [email protected] UNIVERSITY of CASSINO UNIVERSITY of SALENTO Department of Department of INDUSTRIAL ENGINEERING INNOVATION ENGINEERING Cassino (FR), ITALY Lecce (LE), ITALY
- 2. September 1-5 Numisheet 2008 Interlaken - Switzerland TABLE OF CONTENTS PURPOSE SIMPLE STRETCH THE BENDING CONCLUSIONS SPRINGBACK OF THE BENDING WORK TEST TEST What is the Presentation Experimental Experimental Further springback of the new equipment equipment developments method Springback compensation Experimental Experimental and reduction model model methods State of the art of some Some Test Some Test compensation methods Results Results for Al and Mg speciments FEM Model FEM Model and Results and Results 2 Alessia Mentella
- 3. September 1-5 Numisheet 2008 Interlaken - Switzerland THE SPRINGBACK 1. Flat sheet Empirical handbook rules Predictive Numerical simulation 2. Sheet bending with nominal techniques dimension punch Analytical algorithms Xitool Die 3. Elastic recovery of the sheet SPRINGBACK after the load release Target COMPENSATION Δyi Xi+1tool = Xitool + Δyi 4. Compensation of the springback with an Process adjustment method over-dimensioned punch Corrective methods Warm forming (tool heating) Die Δyi Warm forming (workpiece heating) Xi+1tool Xitool 3 Alessia Mentella
- 4. September 1-5 Numisheet 2008 Interlaken - Switzerland THE SPRINGBACK Warm forming: diffused heating AZ31 AZ31 Source: F.K. Chen, T.B. Huang - Formability of stamping magnesium-alloy AZ31 sheets, Journal of Materials Processing Technology 142 (2003) 643–647 4 Alessia Mentella
- 5. September 1-5 Numisheet 2008 Interlaken - Switzerland THE SPRINGBACK Warm forming: diffused heating Al 1050 Source: Keum Y.T., Han B.Y. [3] 5 Alessia Mentella
- 6. September 1-5 Numisheet 2008 Interlaken - Switzerland THE SPRINGBACK Warm forming equipment 6 Alessia Mentella
- 7. September 1-5 Numisheet 2008 Interlaken - Switzerland PURPOSE OF THE WORK Springback reduction Locally increasing the temperature of the cold formed part, before removing the forming tools 7 Alessia Mentella
- 8. September 1-5 Numisheet 2008 Interlaken - Switzerland PURPOSE OF THE WORK • Cold forming a sheet metal part to a specified shape 1 • Locally heating the part up to a warm temperature 2 • Waiting until the part cools down 3 • Removing the loads and tools and let the part 4 springback 8 Alessia Mentella
- 9. September 1-5 Numisheet 2008 Interlaken - Switzerland THE BENDING TESTS SIMPLE BENDING TEST STRETCH BENDING TEST 9 Alessia Mentella
- 10. September 1-5 Numisheet 2008 Interlaken - Switzerland EXPERIMENTAL SETUP 10 Alessia Mentella
- 11. September 1-5 Numisheet 2008 Interlaken - Switzerland SIMPLE BENDING TEST Experimental model Size Material Initial Thickness 110×10 mm Aluminium alloy AA 1050-0 t0 = 0.6 mm; Thermocouple supports t0 = 1mm Magnesium alloy AZ31 t0 = 1.6 mm C W Low carbon steel (zinc coated) t0 = 1.5 mm Fictitious Active thermocouple thermocouple SANDWICH heating K-type thermocouple 11 Alessia Mentella
- 12. September 1-5 Numisheet 2008 Interlaken - Switzerland SIMPLE BENDING TEST Test procedure • Rectangular strips are cut and clamped on one short side with 1 maximum BHF. • Punch is moved up to 40-60 mm with nearly constant speed 2 (trapezoidal profile) and sheets are bent at room temperature. • Punch is stopped and samples are heated up to a known maximum 3 temperature Tmax, for a know heating time, with local heating. • Heater is removed and punch holds until the specimen is cooled to 4 about 30°C. • Punch moves down, the strip is unclamped and the final bending 5 angle aw is measured. 12 Alessia Mentella
- 13. September 1-5 Numisheet 2008 Interlaken - Switzerland SIMPLE BENDING TEST Some test results Al 1050-O W Al 1050-O W wall thickness 0.6mm Wall thickness 1mm W – 230°C W – 160°C 42°21’ 45°76’ C – 29°C C – 29°C 36°8’ 35°49’ C C 29° C 230° C 230° C 29° C 13 Alessia Mentella
- 14. September 1-5 Numisheet 2008 Interlaken - Switzerland SIMPLE BENDING TEST Some test results 30% 0.6 mm 25% α w − αc 1 mm 20% 15% ∆α % = ⋅100 αc ∆α% 10% 5% Al 1050-0 0% 25% 50 100 150 200 250 t0=1.55 mm 20% Temperature (°C) 15% ∆α% 10% AZ31 5% Carbon Steel 0% 100 150 200 250 300 350 Temperature (°C) 14 Alessia Mentella
- 15. PLAIN STRAIN 2D MODEL (4 NODE BRICK ELEMENTS) Alessia Mentella 2° PIOLA- KIRCHHOFF STRESS TENSOR September 1-5 THERMO- MECHANICAL ANALYSIS GREEN- LAGRANGE STRAIN TENSOR Finite Element Model Numisheet 2008 SIMPLE BENDING TEST Interlaken - Switzerland ELASTIC-PLASTIC MATERIAL (ISOTROPIC JOHNSON-COOK HARDENING) 15
- 16. September 1-5 Numisheet 2008 Interlaken - Switzerland SIMPLE BENDING TEST Finite Element Model Material data used for AZ31 m e T − 18 A B C 170 412.16 0.0223 n 0.223 m Tmelting 0.06943 618 ( s = A + Ben ) & 1 + C ln 0.01 1 − T − 18 melting T [C°] E [MPa] poisson thermal exp [mm/mm*C°] 0 49500 0.30 0.00002400 20 49000 0.31 0.00002415 THERMAL BC: 100 46000 0.32 0.00002505 • NO HEAT SOURCE 200 43000 0.34 0.00002580 • NO HEAT EXCHANGE 300 40000 0.36 0.00002655 • CONDUCTION THROUGH 400 37000 0.38 0.00002715 THE WORKPIECE 500 34000 0.4 0.00002760 16 Alessia Mentella
- 17. September 1-5 Numisheet 2008 Interlaken - Switzerland SIMPLE BENDING TEST FEM Results 20% AZ31 – wall thickness 1.6mm 53.55° 19% Tmax=320°C 46.45° αW αC % Δα% 18% 17% ∆α%= 15% AZ31 16% 100 200 300 400 Temperature (°C) 17 Alessia Mentella
- 18. September 1-5 Numisheet 2008 Interlaken - Switzerland SIMPLE BENDING TEST FEM Results heating 120 100 Stress [Mpa] 80 Stress [Mpa] 60 40 20 20 0 0 0 0 0,02 0,02 0,04 0,04 0,06 0,06 0,08 0,08 Cold forming Heating Cold forming Cold forming Equivalent total strain Cooling Springback total strain total strain Equivalent Equivalent Heating 18 Alessia Mentella
- 19. September 1-5 Numisheet 2008 Interlaken - Switzerland STRETCH BENDING TEST Experimental model Size Material Initial Thickness 220×10 mm Aluminium alloy AA 1050-0 t0 = 1mm Magnesium alloy AZ31 t0 = 1.6 mm Aluminium alloy AA 2024-T3 t0 = 0.3 mm 19 Alessia Mentella
- 20. September 1-5 Numisheet 2008 Interlaken - Switzerland STRETCH BENDING TEST Test procedure • Rectangular strips are cut, painted and clamped on both sides with 1 maximum BHF. • Punch is moved up to a maximum dome height h1 (10-30 mm) with 2 nearly constant speed and sheets are bent at room temperature. • Punch is stopped and samples are heated up to a known maximum 3 temperature Tmax, for a know heating time, with local heating. • IR heater is switched off and punch holds until the specimen is 4 cooled to about 30°C. • Punch moves down, and the residual dome height h2 is measured; 5 strips are unclamped. 20 Alessia Mentella
- 21. September 1-5 Numisheet 2008 Interlaken - Switzerland STRETCH BENDING TEST Some test results AZ31 ~160 °C 23 °C 10% ( h1 − h2 ) − ( h1 − h2 ) cold warm ∆h % = 8% ( h1 − h2 )cold 6% heating ∆h% 4% s= 12 mm 2% s= 14 mm s= 15 mm 0% 50 70 90 110 130 150 Tmax [°C] 21 Alessia Mentella
- 22. September 1-5 Numisheet 2008 Interlaken - Switzerland STRETCH BENDING TEST FEM Model EXPLICIT APPROACH FORMING PHASE • Quadrangular shell element (2mm side lenght) + • 7 integration point through the thickness POST-DEFORMATION HEATING IMPLICIT APPROACH • Temperature assigned to the nodes SPRINGBACK SIMULATION • No heat transfer with the environment . T . T (°C) 20 500 ε ij = α T δ E [MPa] ij Poisson 69000 0.33 60000 0.36 Thermal exp. [mm/mm*C°] 240x10-7 274x10-7 Yield Stress (MPa) 110 48 Plastic hardening moduli 0.20 0.20 22 Alessia Mentella
- 23. September 1-5 Numisheet 2008 Interlaken - Switzerland STRETCH BENDING TEST FEM Results IR heater Without post-deformation heating With post-deformation heating 23 Alessia Mentella
- 24. September 1-5 Numisheet 2008 Interlaken - Switzerland CONCLUSIONS A new method for the reduction of springback has been presented, based on warm heating of the sheet metal blanks after forming and before springback. 1. The experimental evidence has shown the method is effective for simple bending, stretch bending and draw bending; 2. Numerical simulation run with a fully implicit integration; a small strain formulation and solid (brick) elements is able to provide a thermo mechanical description of the phenomena involved in the process; 3. Mixed explicit/implicit simulation with shell elements did not provide satisfactory results. 24 Alessia Mentella
- 25. September 1-5 Numisheet 2008 Interlaken - Switzerland FURTHER DEVELOPMENTS 1. Deeper investigate the reasons and the main mechanisms of the phenomenon; 2. Test the procedure on a more complex geometry workpiece; 3. Deeper understand the location of the heating points. Acnowledgement The Italian Ministry of research (MUR) founded the present research under the “PRIN ‘05” program titled SMART. 25 Alessia Mentella
- 26. September 1-5 Numisheet 2008 Interlaken - Switzerland Localized warming of sheet metal parts for the reduction of springback Matteo Strano Antonio Del Prete [email protected] [email protected] Alessia Mentella Teresa Primo [email protected] [email protected] THANK YOU FOR YOUR ATTENTION! UNIVERSITY of CASSINO UNIVERSITY of SALENTO Department of Department of INDUSTRIAL ENGINEERING INNOVATION ENGINEERING Cassino (FR), ITALY Lecce (LE), ITALY