Evaluation of Friction Stir Weld Process and Properties for Aircraft
Transcript of Evaluation of Friction Stir Weld Process and Properties for Aircraft
The Joint Advanced Materials and Structures Center of Excellence
Evaluation of Friction Stir Weld Process and Properties Evaluation of Friction Stir Weld Process and Properties for Aircraft Applicationfor Aircraft Application
MMPDS InitiativesMMPDS Initiatives::Process Path Independence & Process Path Independence & InIn--Situ Fastener QualificationSitu Fastener Qualification
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Evaluation of Friction Stir Weld Process and Properties for Aircraft Application
• Motivation and Key Issues – FSW & FSSW are emergent joining technologies
• Aerospace applications are being developed to take advantage of cost benefits, part count reduction, lead-time flexibility, lowered environmental & ergonomic impacts, etc., of these joining processes
• However, each lacks sufficient supporting industry standards & design allowables data for safe, consistent industry-wide implementation
• Objective– Incorporate FSW & FSSW design allowables data into MMPDS
• Based on a performance and procedure specification methodology• Supported by developing industry standards (e.g. AWS, ISO, etc.)
• Approach– Develop & demonstrate protocols for incorporating FSW & FSSW
data into the MMPDS Handbook collaboratively• Demonstrate process path independence approach for butt & lap joints• Develop FSSW as “In Situ” fasteners & qualify as installed fasteners
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FAA Sponsored Project Information
• Principal Investigators & Researchers– Dwight Burford, PhD, PE– Christian Widener, PhD– Jeremy Brown, M.S.
• FAA Technical Monitor– Curt Davies
• Industry Participation– Boeing IDS: John Baumann, St. Louis; David Ogan, Wichita– Bombardier Aerospace: Ken Poston, Ireland; Bruce Thomas,
Montreal; Leo Kok, Toronto; Richard Meeske, Wichita– Cessna Aircraft: Ron Weddle & Ali Eftekhari, Wichita– Hawker Beechcraft: Byron Colcher & Phil Douglas, Wichita– Spirit AeroSystems: Casey Allen, Mike Cumming, Mark Ofsthun,
& Gil Sylva, Wichita
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Outline
• Qualification Initiatives– Performance Specifications– Butt & Lap Joint Initiatives
• Path Independent Study• In Situ Fasteners
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Process Performance Spec• Documentation• Objectives• Deliverables• etc.
CustomerRequirements
Process Procedure/Detail Spec• WPS (welding procedure
specifications)• PQR (procedure qualification
record)• etc.
SupplierControls
AcceptanceCriteria
Industry Specs (AWS, ISO, etc.)MMPDS* Data
*Metallic Materials Properties Development & Standardization (formerly MIL-HDBK-5)
Performance Spec ModelPerformance Spec Model
Qualification Initiatives
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Purpose
• The key to developing allowables for any material or process is that the expected variation must be understood and controllable within certain limits.
• Friction Stir Welding (FSW) is a relatively new thermo- mechanical processing and joining technique under investigation for its potential inclusion in the MMPDS or other similar standard properties data reference.
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Path Independence Tools
Classic TWI 5651 tool
WiperTM - large
Tri-fluteTM TrivexTM
Scroll WiperTM - small
Example drawingsExample drawings
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Path Independence Coupon & Fixture
• Material– 0.250 inch 2024-T351 bare– Provided by Cessna Aircraft– Three heat lots, randomized– Machined into 4” x 12” coupons
• Test Fixture– Side clamps– 4000 series anvil
10”
1.0”
0.75”typ.
1.50”
Mac
ro
X=kerfof blade ~0.12” typ.
12”
8”
Tens
ion
Tens
ion
Tens
ion
Mac
ro
Mac
ro Fatig
ue
• Test Coupons– (3) Tensile (ASTM E-8)– (3) Metallography– (1) Fatigue
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Design Allowables for FSW
• FSW Allowables– Statistically calculated minimum strength values that can be used for
design.• What is needed to calculate allowables?
– An understanding of the expected variation.• Random variation• Process controlled variation
– A statistical procedure for calculating allowables.– A sufficient number of representative samples to gain the necessary
confidence that the process is repeatable, reliable, and under control.
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Sources of Variation for FSW
• Welding Parameters– Strength varies from Low (<50% Joint Efficiency) up to the
theoretical maximum for a given tool.• Tool Design
– Affects the theoretical maximum for a given alloy/thickness combination.
• Site / Facility– Varies up to theoretical maximum, and is affected by fixturing,
machine type, control system tuning, operator, lab conditions, etc.
• Base Material– Joint strengths can be affected by large variations in parent
material strength and material thickness.
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Path Independence Study – Tool Variability
WSUWSU
Parameter Parameter HHHH
66
Parameter Parameter LLLL
Parameter Parameter LHLH
Parameter Parameter HLHL
Heat/Lot Heat/Lot 11
Heat/Lot Heat/Lot 22
Heat/Lot Heat/Lot 33
3 tensile specimens per panel3 tensile specimens per panel
Tool 1Tool 1 Tool 2Tool 2 Tool 3Tool 3 Tool 4Tool 4 Tool 5Tool 5 Tool 6Tool 6
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Results
• Stable process zones were identified for three of the tools during the second round DOE– S-basis values were calculated for each tool– T99 and T90 values were calculated for pooled data
from the three tools.• Acceptable parameters were found for the
remaining tools, but were not fully optimized.
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Process Windows
RPM
5.00
10.00
15.00
20.00
100 200 300 400 500 600 700 800 900
25.00
Phase One Tested Phase One Tested WindowsWindows
Phase Two Tested Phase Two Tested WindowsWindows
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Tensile Test Results
D E S I G N -E XP E R T P lo t
U TSX = A : R P MY = B : I P M
A c t u a l F a c t o rC : F o rg e = 1 0 5 0 0 . 0 0
50. 9281
52 . 5447
54. 1612
55 . 7778
57. 3944
UTS
250 . 00
287. 50
325. 00
362 . 50
400. 00
7 . 00
9 . 25
11 . 50
13 . 75
16. 00 A : R P M
B : I P M
IPMIPM
RPRP MM
RR22 = 0.9051= 0.9051
DESIGN-EXPERT Plot
UTSX = A: RPMY = B: IPM
Actual FactorC: Forge = 10500.00
58.0881
59.5256
60.9631
62.4006
63.8381
UTS
300.00
375.00
450.00
525.00
600.00
10.00
12.00
14.00
16.00
18.00
A: RPM
B: IPM
++ RRPPMM++ IIPPMM
RR22 = = 0.87140.8714
DESIGN-EXPERT Plot
UTSX = A: RPMY = B: IPM
Actual FactorC: Forge = 9000.00
48.64
52.0305
55.421
58.8115
62.2019
UTS
250.00
287.50
325.00
362.50
400.00
7.00
8.50
10.00
11.50
13.00
A: RPM
B: IPM
-- RRPPMM
++ IIPPMM
RR22 = 0.6104= 0.6104
D ESIGN -EXPER T Plot
U TSX = A: R PMY = B: IPM
Ac tual F ac torC : F orge = 8000.00
57.8542
59.9353
62.0164
64.0976
66.1787
UTS
300.00
350.00
400.00
450.00
500.00
10.00
11.50
13.00
14.50
16.00
A: RPM
B: IPM
RR22 = 0.7306= 0.7306
DESIGN-EXPERT Plot
UTSX = A: RPMY = B: IPM
Actual FactorC: Forge = 7500.00
59.5907
61.249
62.9073
64.5657
66.224
UTS
300.00
350.00
400.00
450.00
500.00
10.00
11.50
13.00
14.50
16.00
A: RPM
B: IPM
RR22 = = 0.85500.8550
D E S I G N -E XP E R T P lo t
U TSX = A : R P MY = B : I P M
A c t u a l F a c t o rC : F o rg e = 4 8 7 5 . 0 0
55. 9929
58 . 3923
60. 7917
63. 1912
65. 5906
UTS
400. 00
500 . 00
600. 00
700 . 00
800. 00
10. 00
12. 50
15 . 00
17. 50
20. 00 A : R P M
B : I P M
RR22 = 0.7596= 0.7596
• 11 welds, 5 parameter sets• 30 tensile coupons• S-basis = 59.5 ksi
• 13 welds, 11 parameter sets• 39 tensile coupons• S-basis = 60.9 ksi
• 10 welds, 10 parameter sets• 32 tensile coupons• S-basis = 59.7 ksi
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Tensile Results: 0.6” Small Wiper
• Optimized zone– RPM: 300 – 800– IPM: 6.6 – 15– Forge load: 4500 – 5500– 1 tool, 11 welds,
5 parameter sets, 30 tensile coupons
– Max. 67.9 ksi– Min. 61.1 ksi– Avg. 65.1ksi– Stdev 1.833 ksi– K99 = 3.064– Sbasis = 59.5 ksi
D E S IG N -E XP E R T P lo t
U TSX = A : R P MY = B : IP M
A c t ua l F ac t o rC : F o rge = 4875 .00
55. 9929
58. 3923
60.7917
63.1912
65.5906
UTS
400.00
500. 00
600.00
700.00
800.00
10.00 12.50
15. 00
17.50
20.00 A : RP M
B : IP M
RR22 = 0.7596= 0.7596
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DATA SET RANGE PLOT
0123456789
1011121314151617181920
55 57 59 61 63 65 67 69DATA VALUE
DA
TA S
ET N
UM
BER
2024-T3, UTS, LAB
= Set Averages= Recommended B-basis =Mean
ANOVA Analysis using 4 – FSW Tools
Sm. WiperSm. Wiper™™
TrivexTrivex™™
((unoptimizedunoptimized))
TriTri--fluteflute™™
Lg. WiperLg. Wiper™™
= Recommended A-basis
QUANTILE BOX PLOT
61.536
62.536
63.536
64.536
65.536
66.536
67.536
0 10 20 30 40 50 60 70 80 90 100
PERCENT RANKED DATA
PRO
PER
TY V
ALU
E
2024-T3, UTS, LAB
N = 55 couponsN = 55 coupons
BB--basis = basis = 62.5 ksi62.5 ksi
AA--basis = basis = 60.7 ksi60.7 ksi
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Reported Data on 2024-T3Table 1: Reported Tensile Results for As-Welded 2024-T3*
Material Thickness Ultimate Tensile Strength Weld Elongation (%) Ref.0.040-in. (1 mm) 58.9 ksi (406 MPa) 6.0 5
0.064-in. (1.6 mm) 66.9 ksi (461 MPa) 11 6
0.080-in. (2 mm) 64.7 ksi (446 MPa) 13.0 7
0.080-in. (2 mm) 64 ksi (441 MPa) 16.3 8
0.090-in. (2.25 mm) 53 ksi (366 MPa) - - 9
0.100-in. (2.5 mm) 71.1 ksi (490 MPa) 17 10
0.125-in. (3.2 mm) 63.5 ksi (438 MPa) 12.2 5
0.l60-in. (4 mm) 62.7 ksi (432 MPa) 7.6 11
0.200-in. (5 mm) 59.5 ksi (410 MPa) 5.1 12
0.250-in. (6.35 mm) 60.9 ksi (420 MPa) -- 13
Average 62.5 ksi (431 MPa) 11Std. Dev. 4.90 ksi (33.8 MPa) 4.5
*2024 is a precipitation strengthened Al alloy that naturally ages to a stable temper within 96 hrs Calculated Path Independence Calculated Path Independence
TT9090 value was also 62.5 ksivalue was also 62.5 ksi
• 70% of the averages reported in literature would meet these calculated T99 values.
• 60% of the averages reported in literature would meet these calculated T90 values.
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Yield Strength
• Yield strength appears to be much less sensitive to welding parameters.
• For the large Wiper™ tool (FSW07026) over the entire DOE (17 welds):– UTS = 62.9 ± 3.46 ksi– YS = 45.1 ± 0.84 ksi
• For the Triflute™ tool (FSW07027) over the entire DOE (17 welds):– UTS = 62.2 ± 5.21 ksi– YS = 45.5 ± 0.90 ksi
Stress vs. Strain
0
10
20
30
40
50
60
0 0.005 0.01 0.015 0.02 0.025 0.03
FSW07026_2_T4 Yield
1st Modulus: 10.712 MpsiYield Point: 45.61 ksi
Secondary Modulus: 10.057 MpsiYield Point: 46.02 ksi
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Yield Data – Four Best Tools – Over the Entire Parameter Range
DATA SET RANGE PLOT
0123456789
101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657
39 41 43 45 47 49 51DATA VALUE
DA
TA S
ET N
UM
BER
2024-T3, UTS, LAB
= Set Averages= Recommended B-basis =Mean
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Fatigue Testing
• Screening Tests– Stress level targeted for
104 – 105 cycles.– Load 5000 lbs, R = 0.1, 20 Hz– Purpose to evaluate if optimum parameters based on strength and
failure mode are also optimum for fatigue.
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Typical Fatigue Failures from Screening Test
• Welding defects can be readily identified in the fracture surface of welded coupons
• When defects were not present, the fatigue performance was observed to be close to parent material.
Initiation
Micro VoidsLOP
Surface galling
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Fatigue Results
Fatigue of 2024-T351 6.3 mm (0.250-in.)Friction Stir Welded vs. Parent (LT)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
1.E+03 1.E+04 1.E+05 1.E+06 1.E+07
Cycles to Failure
Load
(ksi
)
Parent LTLg. Wiper(TM)
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Survey of Other Reported Fatigue Results
Comparison to Fatigue Data in the Literature for FSW Butt-welds in 2024-T3
050
100150200250300350400450500
1.E+04 1.E+05 1.E+06 1.E+07
Cycles to Failure
Max
. Stre
ss (M
Pa)
Magnusson and Kallman (milled) - 2 mmMagnusson and Kallman (as-welded) - 2 mmBussu and Irving (skimmed) - 6.3 mmKlaestrup Kristensen et al. (as-welded) - 6 mmBiallas et al. (as-welded) - 1.6 mmWSU Wiper (as-welded) - 6.3 mmKumar et al. (sanded) - 3.2 mmParent L-T
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Path Independence – SCC Testing
• SCC Testing – 32 samples – PER ASTM G64, G47, and G58– 4 point bend – 2-in. apart - 23 ksi – verified by strain gauge– Alternate Immersion – 3.5% NaCl– As-welded – tested to parent material rating 50% of Y.S. for LT – TEST COMPLETE - After 40 days – No Failures – Meets Parent Specification
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Summary & Conclusions
• It has been demonstrated that a number of different tool designs can be used to produce a sound friction stir welded joint in 0.250-in. 2024-T351.
• These results are in reasonable agreement with reported results for 2024-T3 in a range of thicknesses.
• This is not to suggest that one tool may not provide any particular advantage over another in terms of productivity, fatigue, etc.
• For allowables or a performance specification, it is unnecessary to define exact tool geometries. – Tool geometries would be found in the weld process
specifications of individual suppliers or producers, but should not be a requirement to meet performance goals
• The next phase is round robin testing…
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Road Map for FSW Allowables Development…
FAA/NIS FAA/NIS ““Evaluation of Friction Stir Evaluation of Friction Stir Weld Process and Properties for Weld Process and Properties for
Aircraft ApplicationAircraft Application””
Path IndependencePath Independence––tool and process variationtool and process variation
Round Robin Testing Round Robin Testing ––site to site variationsite to site variation
Report the Path Independence final Report the Path Independence final results to the FAA via a DOT/FAA/AR results to the FAA via a DOT/FAA/AR
Draft new sections for inclusion Draft new sections for inclusion in the MMPDS for FSWin the MMPDS for FSW
Begin testing for allowablesBegin testing for allowables
A performanceA performance--based based specification approachspecification approach
Conducted atConducted at
Wichita State UniversityWichita State University
Underway Underway –– Expected completion Expected completion April 2009April 2009
Does FSW Does FSW belong in belong in
the the MMPDS?MMPDS?
STOP
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Outline
• Qualification Initiatives– Performance Specifications– Butt & Lap Joint Initiatives
• Path Independent Study• In Situ Fasteners
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Qualification of “friction stir spot welds” as In SituFasteners tested & analyzed similar to Installed Fasteners
FSSW: unique fine-grained metallurgical structure extending into components
Resistance Spot Weld: joining surfaces across interface
Lap Joint Initiative
Rivet: installed in hole and compressed to form tight joint
(Compatible with faying surface sealants)
(Compatible with faying surface sealants)
(Not compatible with faying surface sealants)
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• Benefits of Friction Stir Swept Spot Joints– Discrete fastener locations
• Separated by parent material (similar to rivets)• Discontinuous HAZ along joint line
– Dual-thickness joint vs. hole with filler (e.g. rivet) • “Pad up” effect vs. stress concentration (rivet hole)• Long-term stiffness & stress concentration considerations,
e.g. in aging aircraft– Elimination of filler material, i.e. fastener
• Fabricate fastener in place by mechanically working parent material (finer grain)
• Produces integral fastener • Supports part count reduction
Lap Joint Initiative: In Situ Fasteners
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• Benefits of friction stir swept spot joints (cont’d)– Tailorable spot size and shape
• More latitude than with rivets (diameter constraints, etc.)• Orient shape to control stress, crack growth, etc.• Placement of advancing vs. retreating side on periphery of
spot (i.e. in situ fastener)– Rapid installation (minimal HAZ)– Randomize sequence of installation (to lower
distortion)– Potentially installed via robot vs. gantry
• Lower cost solution• Field installation & repairs
– Simplified tooling (lower normal and lateral forces)– Compatible with faying surface sealants
Lap Joint Initiative: In Situ Fasteners
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In Situ Fasteners Qualified as Installed Fasteners
• Approach– Develop & test a methodology for qualifying different types of
friction stir spot welding (FSSW) joints as in situ fastener systems
– Treat individual “spots” as installed fasteners• Parent material is used to form an integral mechanical fastener in
place between two or more materials joined by a lap joint• Background
– In both static & dynamic tests, appropriately designed FSSW (e.g. swept spots) joints are proving stronger than rivets
• Spots are integral with the parent material• Their size and shape can be tailored to support design• They appear to provide favorable residual stresses & a pad up
effect– FSSW joints are expected to be the most straightforward friction
stir-related technology to qualify for inclusion in the MMPDS because they are the most like mechanical fasteners, e.g. discrete.
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Background
• Types of Friction Stir Spot Welding (FSSW)– Plunge (Poke) Spot (Mazda)– Swept Spots
• Squircle™ (TWI)• OctaSpot™ (WSU)
– Friction (refill) Spot Welding (GKSS)
– Swing Spot (Hitachi) – High Rotational Speed
(HRS) FSSW (WSU)– etc.
Plunge (Poke) Spot
Swept Spot
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Background – Octaspot™ Tool Path
1) Plunge 2) Move Out 3) Begin Sweep
4) Perimeter Undulation5) Complete Sweep
6) Move In & Retract
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Procedure
• Materials– Alloys
• 2024-T3 - 1.0 mm thick (0.040 inches)– Surface Treatments
• Bare (untreated)• Clad• Chromic Acid Anodized (CAA)• AlodineMaterials (cont.)
– Sealants• PRC-DeSoto PR-1432 GP• Pelseal PLV 6032
– Tool Options• Psi• Counterflow• Modified Trivex
Base Metal
Sealant
Surface Treatment
1
2
3
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Procedure
• Tool and Parameter Selection– 3rd DOE – NASM 1312-4 Dual
Opposing Spot Configuration• CAA Material• PR-1432 GP Sealant• Refined from 2nd DOE• Variables
– Rotation Speed– Travel Speed– Lead Angle– Forge Load (Load Control)
• Response– Ultimate Tensile Load– Failure Mode
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FSSW Through Surface Sealant Results
• Surface treated material with the PR-1432 GP sealant have strength equivalent to that of Bare with no sealant.– Sealants can increase the strength of the coupon– Surface treatments and sealants appear to increase scatter
• Calculated S-basis strengths– S-basis ultimate load per spot = 1113 lbs– 30 coupons, 3 parameter sets, 6 batches
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Handbook Data / Tables
Pin tool (part # and description)Sheet materialFSSW Diameter, in.(nominal swept diameter of pin tool)
Sheet thickness, in.0.0250.0320.040 1003 1164 13150.0500.0630.0710.0800.0900.1000.125
Ultimate Strength, lbs
3/16 (0.1875)
7/32 (0.21875)
5/16 (0.3125)
2/7 (0.295)
1/3 (0.333)
1/4 (0.250)
9/32 (0.28125)
2024-T3WSU-07-0055-0400-06 - Counterflow Pin Tool
1/8 (0.125)
5/32 (0.15625)
Pin tool (part # and description)Sheet materialFSSW Diameter, in.(nominal swept diameter of pin tool)
Sheet thickness, in.0.0250.0320.040 801 827 9500.0500.0630.0710.0800.0900.1000.125
Ultimate Strength, lbs
WSU-07-0055-0400-01 - Concave Trivex Pin Tool2024-T3
1/8 (0.125)
5/32 (0.15625)
3/16 (0.1875)
7/32 (0.21875)
2/7 (0.295)
5/16 (0.3125)
1/3 (0.333)
1/4 (0.250)
9/32 (0.28125)
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A Look Forward
• Expected Outcomes & Benefit to Aviation– Verified qualification
methodology & procedure• Testing & certification• Controls & acceptance
criteria• Consistent & safe designs
– Organized & certified design data
• MMPDS (Mil HDBK 5) type data
• S, A, & B basis – Design Parameters and
Process Guides• Process & performance
Specifications• Comparative data
– Cost effective lean/green aerospace technology
• Low energy use• Reduced cycle/manufacturing
time• Part count reduction• Reduced weight• Low emissions,
environmentally friendly (no sparks, fumes, noise, or harmful rays)
• Low Ergonomic Impact• Future needs
– Continued program support towards implementation