Webinar SCSponsored by AEC€¦ · Audi A8 (D2, 1994) Audi A8 (D3, 2002) 59 237 47 50 Sheet...

Extrusion Bending and ShapingS CWebinar Sponsored by AEC

Automotive Examples

Ferrari Modena

Audi A8 Audi A2

Alcoa Proprietary Information

Aluminum Space Frames


Evolution of the Audi A8

Audi A8 (D2, 1994) Audi A8 (D3, 2002)

59

2375047

SheetExtrusionCasting

170

3859

SheetExtrusionCasting


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


Single Hollow, Multiple Hollow, Open Sections


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


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%)


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


W to T4 - Time after Quench

Yield Strength is IncreasingUltimate Tensile Strength is IncreasingUltimate Tensile Strength is IncreasingFailure Strain is Decreasing


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%)


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


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


Dimensional Variability – Spring back

NominalPart(Target)

Spring back CompensatedSpring back CompensatedProduction Die

V i P P tVarying Process Parameters& Material Properties


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


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


Dimensional Variability Section Collapse

Bend Radius


Section Collapse

B d R diBend Radius


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


Rotary Draw Bender


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


Rotary Draw Bend Typical Part

Plane 2

Plane 1

Constant R

St i ht L thStraight Length


Rotary Draw Bend Typical Part

Plane 2

Constant R

Plane 1

Constant RStraight Lengthg g


Stretch Bender


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


Stretch Bend Typical Part

Plane 2

Plane 1Variable R

Variable R


Section Collapse in Automotive Header Bow

4.9 mm

Center of part/die End of part/die4.0 mm


Effect of Air Pressure on Section Collapse

Center of part/die End of part/die2.4 mm


Special Tooling (“Snakes”)


Special Tooling (“Snakes”)

Plastic Insert

Existing Top Plate

Bend Die

Snake

Plastic Insert

Bend Die

Automotive Stretch Bend Part


Alternate Die Design

Flexible Snake

Part Section

Flexible Snake


Alternate Die Design

Snake and Section


Stretch Bender


Gripper


Process Design by Numerical Modeling



8” Elevation Change



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]


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?


Webinar SCSponsored by AEC€¦ · Audi A8 (D2, 1994) Audi A8 (D3, 2002) 59 237 47 50 Sheet...

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