Post on 11-Aug-2021
Extrusion Bending and ShapingS CWebinar Sponsored by AEC
Automotive Examples
Ferrari Modena
Audi A8 Audi A2
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Aluminum Space Frames
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Evolution of the Audi A8
Audi A8 (D2, 1994) Audi A8 (D3, 2002)
59
2375047
SheetExtrusionCasting
170
3859
SheetExtrusionCasting
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Parameters Affecting Extrusion Forming
Parameters Affecting Extrusion Forming
SECTIONSECTION• Cross Section Geometry• Wall Thickness• Circle Size• Tolerances
SHAPE• Spatial Configuration• Spatial Configuration• Length• Bend Radii• TwistMATERIAL
• Alloy • Bend Angle• Alloy• Temper• Time
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Single Hollow, Multiple Hollow, Open Sections
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R/d Ratio
Approximate maximum bending strainsApproximate maximum bending strainscan be calculated by - ε = d/2R (for pure bending)where,“R” is centerline bend radius
“d” is section depth
Note: For stretch bending, addthe amount of uniform axialstretch to the above for the total maximum strain
Rtotal maximum strain.
d
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Relationship Between R/d and Strain
R/d=2 ε = 1/(2*2) ε = 0.25 (25%)
R/d=10 ε = 1/(2*10) ε = 0.05 (5%)
R/d=100 ε = 1/(2*100) ε = 0.005 (0.5%)
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Material Property Comparison
45000
50000True Stress ‐ True Strain for Generic 6XXX Material
6XXX W + 26XXX W + 240
35000
40000
6XXX W + 2406XXX T46XXX T6
25000
30000
e Stress (P
SI)
10000
15000
20000True
0
5000
10000
0
0 0.05 0.1 0.15 0.2True Strain
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W to T4 - Time after Quench
Yield Strength is IncreasingUltimate Tensile Strength is IncreasingUltimate Tensile Strength is IncreasingFailure Strain is Decreasing
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Relating Failure Strain to R/d Ratio
Failure Strains
ε f = 18.5% (6XXX W + 2 hours)f ( )ε f = 17.5% (6XXX W + 240 hours)ε f = 16.0% (6XXX T4)ε f = 10.0% (6XXX T6)
For a Specific Part
R/d = 2 9 ε = 1/(2*2 9) ε = 0 17 (17%)R/d = 2.9 ε = 1/(2*2.9) ε = 0.17 (17%)
Then
Form the part 2 hours after quench, good, (17% < 18.5%)Form the part 240 hours after quench, maybe (17% ≈ 17.5%)Form the part in T4 temper, no good, (17% > 16%)Form the part in T4 temper, no good, (17% 16%)Form the part in T6 temper, no way, (17% » 10.0%)
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Material Property Comparison
70000
True Stress ‐ True Strain Mild Steel
50000
60000
6XXX W + 26XXX W + 2406XXX T4
40000
ress (P
SI)
6XXX T46XXX T6Mild Steel
20000
30000
True
Str
0
10000
0
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35True Strain
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Dimensional Variability – Spring back
Analysis Used to Predict R'Based on a Particular Set ofBased on a Particular Set of
Process Conditions
R
R'Die Design to Produce
Net Shape Part
R = Nominal Part RadiusR' = Radius to Compensate For Spring back
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Dimensional Variability – Spring back
NominalPart(Target)
Spring back CompensatedSpring back CompensatedProduction Die
V i P P tVarying Process Parameters& Material Properties
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Material Properties and Bending
Bending is primarily a strain driven process
Modulus of Elasticity primarily affects spring back behavior (elastic recovery) Spring back is an elastic process (no yielding during recovery)
Spring back occurs because the part is not in a state of static equilibrium under bending loads. When loads are released, the part
t t t t f t ti ilib ireturns to a state of static equilibrium.
Material Strength (yield strength) affects 2 areas: Size of machine required to bend Part dimensional tolerances (as the yield strength varies)
• Bending always introduces the same amount of strain in part• Stress levels will depend on the properties at the time of bending• Varying stress levels will change spring back behavior
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Stress Variation for Constant Bending Strain
45000
50000True Stress ‐ True Strain for Generic 6XXX Material
6XXX W + 26XXX W + 240
35000
40000
6XXX W + 2406XXX T46XXX T6
24,000 PSI Stress
46,500 PSI Stress
25000
30000
e Stress (P
SI)
20,500 PSI Stress
10000
15000
20000True
17,000 PSI Stress
0
5000
10000
7.5% Strain0
0 0.05 0.1 0.15 0.2True Strain
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Dimensional Variability Section Collapse
Bend Radius
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Section Collapse
B d R diBend Radius
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Effect of R/d on Section Collapse
ExtrudedCross Section
BendDeformation
Corrected BendDeformation
R/d>1000 No Problem
Air Pressure50<R/d<100
Air PressureDuring Bend
5<R/d<10Hard InternalM d l5<R/d<10 Mandrel
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Rotary Draw Bender
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Rotary Draw Bending
Bend: 2DCycle time: 30 to 50 sec per partInner support: Steel or plastic mandrelTolerance:
•Die Surface +/- 0.8 mm•Other Surfaces +/- 1 8 mm•Other Surfaces +/- 1.8 mm
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Rotary Draw Bend Typical Part
Plane 2
Plane 1
Constant R
St i ht L thStraight Length
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Rotary Draw Bend Typical Part
Plane 2
Constant R
Plane 1
Constant RStraight Lengthg g
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Stretch Bender
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Stretch Bending
Bend: 3DCycle time: 30 to 50 sec per partInner support: Air pressure (Alcoa patent)Tolerance:
•Die Surface +/- 0.7 mm•Other Surfaces +/- 1.5 mm
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Stretch Bend Typical Part
Plane 2
Plane 1Variable R
Variable R
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Section Collapse in Automotive Header Bow
4.9 mm
Center of part/die End of part/die4.0 mm
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Effect of Air Pressure on Section Collapse
Center of part/die End of part/die2.4 mm
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Special Tooling (“Snakes”)
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Special Tooling (“Snakes”)
Plastic Insert
Existing Top Plate
Bend Die
Snake
Plastic Insert
Bend Die
Automotive Stretch Bend Part
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Alternate Die Design
Flexible Snake
Part Section
Flexible Snake
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Alternate Die Design
Snake and Section
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Stretch Bender
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Gripper
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Process Design by Numerical Modeling
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Process Design by Numerical Modeling
8” Elevation Change
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Process Design by Numerical Modeling
12.0
14.0TC
Gripper Positions(i iti l d fi l)
4.0
6.0
8.0
10.0
on (r
elat
ive)
or
deg
rees
]
LiftTwistTilt
(initial and final)
-4.0
-2.0
0.0
2.0
0 10 20 30 40 50 60
Posi
tio[in
ches
-6.0Wrap Angle [degrees]
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Summary
The ability to bend a part is controlled by the amount of strain induced during forming.B di l i d th t f b di t iBending always induces the same amount of bending strain.Uniform axial strains induced by tension during forming can vary and must be added to bending strain to predict maximum tensile strain.Materials with higher modulus of elasticity (i.e., steel) will spring back less.Higher yield strength will result in more spring back (all other factors being equal).Natural aging in precipitation hardenable aluminum alloys results in increasing yield and ultimate tensile strength and decreasing ultimate tensile strain (elongation).Analysis can be used to design die contours and process parameters required to eliminate trial and error approaches to bent part production.
Questions?
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