case study of 767 horizontal stabilizerdspace.mit.edu/.../0/class24767wingcasestudy.pdfcase study of...

© Daniel E Whitney

Case Study of 767 Horizontal Stabilizer

• Goals of this class– Carry through the topics of this course on one product

• Look in detail at a real aircraft structural assembly• Define and flow down KCs• Compare different assembly methods

– conventional one based on fixtures– proposed one based on part-to-part mating features

• Draw datum flow chains for them• Study the economics

767 Skin Subassembly

Photo courtesy ofVought Center Divof Northrop Grumman

© Daniel E Whitney

Focus of Study: 767 Horizontal Stabilizer

© Daniel E Whitney

Top Level Key Characteristics

AERODYNAMICS (gap betw skin and FTB & FTE)

STRENGTH(based on joining plus chordsand ends of spars)

PLUS CHORD

PLUS CHORD SPAREND

SPAREND

SKIN

GAPGAP

HORIZ ASSY 2

FTE

FTB

(gap between skins)

© Daniel E Whitney

Horizontal Stabilizer Subassemblies (current decomposition)

UPPER SKINASSEMBLY

LOWER SKINASSEMBLY

RIB

FORWARDTORQUEBOX

FORWARD SPAR

FIXEDTRAILINGEDGE

STRINGERS

PLUS CHORD

REAR SPAR

FWD SKIN

HORIZ ASSY 2

© Daniel E Whitney

PKCs for Horizontal AssemblyPKC #2 & #3: Aerodynamics affected

by these skin gaps

PLUSCHORD

PKC #1:Joint Strengthaffected byalignment betweenplus chord endsand spar end fittings.

FWD TORQUE BOX

FIXED TRAILING EDGE

FORWARD SKIN

AFT SKIN

SPAR END FITTINGS

SPAR END FITTINGS

SPLICE STRINGER

SPAR

PLUS CHORD

END FITTINGSPLICEPLATE

PLUS CHORD

(MISALIG

NED)

SPAREND FITTINGSPLICEPLATE

SHIM

JOINT STRENGTH PKC ACHIEVED SHIM NEEDED TO ACHIEVEJOINT STRENGTH PKC

© Daniel E Whitney

Current Total Process

SKIN GAP PKCDELIVERED BYDESIGN OFFIXTURE TOHOLD FTBAND FTESKIN SUBASSEMBLY

SKIN GAP PKCDELIVEREDBY SKINGAP AKC

PLUS CHORDALIGNMENT TOSPAR ENDS PKCDELIVERED BYP.C. ANGLETO SKINS AKC

FINAL ASSEMBLY

PLUS CHORDALIGNMENTTO SPARENDS PKC SKIN GAPS PKC

PLUS C

HO

RD AFT SKIN

FORWARD SKIN

SPLICE STRINGER

FIXED TRAILING EDGE

FORWARD TORQUE BOX

REAR SPAR

FORWARD SPAR

FTB-RIB-FTE SUBASSEMBLY

RIBS

PLUS CHORDALIGNMENTTO SPARENDS PKC

Figures for designing assemblies

© Daniel E Whitney

Top-Level KCs

RibsSS

FS

AS

FTB

FTE

PC

F Spar

A Spar

PKC #3

PKC #2

PKC #2

PKC #1

PKC #1

Skin Gap& rib align KCs

Skin Gap& rib align KCs

© Daniel E Whitney

Product Decomposition Based on Independent KCs

FTB

FTE

Ribs PCSS

FS

AS

F Spar

A Spar

© Daniel E Whitney

Decom

position/Subassemblies

Based on Independent K

Cs

RibsSS

FSAS

FTB

FTE

PC

F Spar

A Spar

SSFSAS

Ribs PC

F Spar

A Spar

FTB

FTE

PC

F Spar

A Spar

FTB

FTE

Ribs

© Daniel E Whitney

Sob

© Daniel E Whitney

Assembly Access Problem Eliminates an Attractive Assembly Sequence

If plus chords are assembledto spar ends before skinsare assembled to plus chords,then it will be almostimpossible to join skins andstringers to plus chords

UPPERSKIN

SHIM

UPPER PLUSCHORD

STRINGER

PIVOT RIB ~SPAR~24"

LOWER PLUSCHORD

LOWERSKIN

SHIM

STRINGER

© Daniel E Whitney

Actual Subassemblies

RibsSS

FS

AS

FTB

FTE

PC

F Spar

A Spar

© Daniel E Whitney

Actual D

ecomposition

RibsSS

FSASPC

FTB

F Spar

FTE

A Spar

SSFSASPC

FTB

F Spar FTE

A Spar

Ribs

FTB

F Spar

FTE

A Spar

Ribs

© Daniel E Whitney

Type 1 and Type 2 Methods for One Subassembly - KC Flowdown Seems OK

Ribs

FTB

F Spar

FTE

A Spar

Ribs

FTB

F Spar

FTE

A Spar

F

© Daniel E Whitney

Second Subassembly Has Lost Its KC Links to Higher Level Assemblies

• Any assembly process for this subassembly must provide proxies for the missing KCs, regardless of whether the subassembly is made as a Type 1 or Type 2

• These KCs will be coupled• Note that no drawing of this

subassembly could be found

SS

FS

ASPC PKC #3

PKC #1

PKC #1PKC #2

PKC #2

© Daniel E Whitney

Possible Assembly Strategies

© Daniel E Whitney

Our Challenge

• Current assembly method relies on costly fixtures• Can a process be devised that does not rely on

fixtures other than for support against gravity?• Can such a process achieve the PKCs?• Would it be economical?• What new worker skills would be needed?• Can we figure out what the old process was doing

so we can reproduce it using new methods?

© Daniel E Whitney

Diagram of Assembly Analysis Process

Product Architecture

Assembly Sequence Generation

4

PKCs2

AKCs3

Prune into Families

5 Analyze Sequences

7

Assembly Decomposition

KC Flowdown1

Identify most promising family

6

Process Selection and Planning

10Equipment

Requirements

9

Propose Assembly Features

8

Skin Gaps

Joint Strength affected by this alignment.

FTB

FTE

Forward Skin

Aft Skin

PlusChord

ORIGINAL PKCs

ACHIEVE PKCsSEPARATELY(ASSEMBLY IMPOSSIBLE)

ASSEMBLY POSSIBLE-PKCs COUPLED

CURRENT METHODUSING FIXTURES

TWO ALTERNATE METHODSREQUIRING DIFFERENT AKCs

using hole and slot featuresusing edge features

12

12

ASSEMBLY LEVEL DATUMSPART LEVEL DATUMS

FORWARD SKIN

AFT SKIN

SPLICE STRINGER

MATING FEATURE (SLOT)MATING FEATURE (HOLE)

PKC #1 PKC #2 PKC #3

AKC #1

PKCs

AKCs

Assembly Feature AKCs Plus Chord

aft hole & forward slot

Aft Skin aft hole &

inboard slot

Fwd Skin inboard slot & fwd slot

Stringer #3 inboard

holes

Stringer #3 holes

AFT SKIN

PLUSCHORD

STRINGER #3

FORWARD SKIN

STRINGER

VSA RESULTS

© Daniel E Whitney

Wing Skin Subassembly

STRINGERS

PLUS CHORD

FWD SKIN

AFT SKIN

HORIZ ASSY 2

© Daniel E Whitney

Wing Skin Subassembly

upper splice plateupper plus chord

stringer #3(connects forward& aft skins)

upper skin

shimUp

Outboard

attached tocenterbox

part of rib

PLUSCHORD

FORWARD SKIN

AFT SKIN

STRINGER

STRINGER #3

Plus Chord Joint

© Daniel E Whitney

Liaison Diagram

SpliceStr3

AftSkin

Str1-2

PlusChord

Str4-11

FwdSkin

© Daniel E Whitney

Current Skin Assembly Process

PLUSCHORD FWD SKIN

AFT SKIN

FIXTUREEVERYTHING INDEXES OFF THE FIXTURE

SPLICE STRINGER

© Daniel E Whitney

Current Skin Assembly Process - 2

Forward Skin

Aft Skin

PlusChord

Splice stringer

Fixture

Track for Rout er t o Trim Forward Skin Edge

© Daniel E Whitney

Assembly KC #1 & #2

#1 #2

© Daniel E Whitney

Datum Flow Chain for Current Skin Process

Fixture

SpliceStr3

AftSkin

Str1-2

PlusChord

Str4-11 FwdSkin

Plus ChordAngle KC

Skin GapKC EXPLICIT DATUM TRANSFER

CONTACT WITHOUTDATUM TRANSFER

KC

© Daniel E Whitney

New Process #1: Fixtureless (Type 1)

HOLES CHOSEN FOR LOCATIONSLOTS CHOSEN FOR LOCATION, THERMAL & SHOT PEEN GROWTH ACCOMMODATIONALL SLOTS DRILLED OUT TO FULL SIZE HOLES AT FINAL ASSEMBLY

BIGGEST THERMALDIFFERENCE

SMALLESTFULL SIZE

HOLE

ASSEMBLY LEVEL DATUMSPART LEVEL DATUMS

FORWARD SKIN

AFT SKIN

SPLICE STRINGER

PLUS CHORD

MATING FEATURE (SLOT)MATING FEATURE (HOLE)

© Daniel E Whitney

PKC Delivery Map for New Process #1

PKC #1 PKC #2 PKC #3

AKC #1

Str 3 inbdholes

PC aft hole& fwd hole

AKC #2 AKC #2

Aft skinaft hole &inbd hole

Fwd skininbd hole

& fwd slot

Skins & str 3holes & slots

Size/shapeof skins

Hole/slotlocations onskins & str 3

PKCs

AKCs

Assy features

Mfr features Size/shapeof PC and

hole locations

Coord. ofslot lengt hand hole size

© Daniel E Whitney

Datum Flow Chain for New Process #1

EXPLICIT DATUM TRANSFER

CONTACT WITHOUTDATUM TRANSFER

KC

Note: in existing process,skin-plus chord is a contact.In new process it is a mate.Skin G

ap AKC

Plus Chord

Angle AKC

Plus ChordAngle AKC

SpliceStr3

AftSkin

Str1-2

PlusChord

Str4-11

FwdSkin(6)

(6)

(6)

(6)(1)

(5)

© Daniel E Whitney

New Process #2

FORWARD SKIN

AFT SKINSPLICE STRINGER

PLUS CHORD

PLUSCHORD

STRINGER

SKIN

SHIM

SPACER TOOLS

LAYUP TABLE FEATURES

© Daniel E Whitney

Assembly Features for Process #2

P L U SC H O R D

AFT SKIN

ASSEMBLY LEVEL DATUMSPART LEVEL DATUMSMATING FEATURE (HOLE OR SLOT)MATING FEATURE (EDGE)

FORWARD SKIN

SPLICE STRINGER

© Daniel E Whitney

Datum Flow Chain for New Process #2

Plus Chord

Angle AKC

Plus ChordAngle AKC

SpliceStr3

AftSkin

Str1-2

PlusChord

Str4-11

FwdSkin(6)

(6)

(6)

(6)(1)

(5)

T

TSkin G

ap AKCF

(5)

(6)

(1)

© Daniel E Whitney

KC Deliverability Map - Process #2PKC #1 PKC #2 PKC #3

AKC #1

Fwd skininboard surf

PC aft holehole

AKC #2 AKC #2

Tool locationat fwd end of

plus chord

Atf skin aft Hole & inboard

surface Skin gaptool size

CNC worktable

Part sizes &hole

locations

PKCs

AKCs

Assy features

Mfr features

© Daniel E Whitney

Tolerance Analysis of KC Delivery

• VSA was used to on each candidate new process

• Results show that process 1 is unable to deliver AKC & PKC 1 all the time because the holes in the splice stringer can’t be placed accurately enough

• This also hurts PKC 2 and 3

• Process 2 is able to deliver all 3 PKCs 100% of the time

© Daniel E Whitney

Matlab(TM) Analysis

• Assumed assemblers could maneuver the wing skin laterally and angularly

• Assumed smaller variation in hole and slot placement

• Determined that only a few assemblies would fail

© Daniel E Whitney

Parts and Their Frames

AFT SKIN

H1S2

2

3

12"

3"

3"12"

SPLICE STRINGER3

4

6"

FORWARD SKIN

G3S1

4

42"

3"

12" 336"G1

P2

P4

5

P3

1

63"

PLUSCHORD

3"

© Daniel E Whitney

Parts Assem

bled and Frames

Aligned

FTE

RIBS

FTB

PLUSCHORD

FORWARD SKIN

SPLICE STRINGER

AFT SKIN

G1G2

G3

G4

S1P2

H1S2

P41

2

3

4

5

a

b

STRENGTH KC

P3

63"

0.045"

0.045"AERODYNAMIC KC

351"

ENDFITTING

FOR

WA

RD

AFT

INBOARD OUTBOARD

© Daniel E Whitney

Sample Space for Tolerance Analysis

Y1

X2

0.010"

-0.010"

63.03"63.00"62.97"

0.0127"

-0.0127"

NO ADJUSTMENTNEEDED

ADJUSTMENT POSSIBLEBY TRANSLATION

AND CW ROTATION


AND CCW ROTATION

.005"

-.005"

0.015*5.25/29.25=.0027

23

4

5



© Daniel E Whitney

Matlab(TM) Results

-0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

f ixt ure and FTB-ribs-FTE modeled as ±0.008 and plus chordmodeled as ±0.01

© Daniel E Whitney

Pros & Cons of Proposed Processes

Current Process Proposed Process #1 Proposed Process #2Pros • Delivers all AKCs

and PKCsrepeatably

• Delivers AKC #2and PKC #3repeatably

• Completely flexiblemethod

• No dedicatedfixtures

• Uses existing fabequipment

• Least costly• Controls critical

interfaces

• Delivers all AKCsand PKCsrepeatably

• Completely flexiblemethod

• Uses existing fabequipment

• Controls criticalinterfaces

Cons • Inflexible fixtures• Variation absorbed

at stringer-pluschord interface

• Fails to deliverAKC #1 on a fewassemblies

• PKC #1 & #2 notdelivered

on those sameassembies

• Requires higher-functionality tackfixture (highercost)

• Requires a limitednumber of smallfixtures

© Daniel E WhitneyAssembly Holding FixtureAssembly Holding Fixture

767 Raked Wing Tip Determinant Assembly767 Raked Wing Tip Determinant Assembly(inner mold line view)(inner mold line view)

767 Raked Wing Tip Determinant Assemblyby Boeing

Source: Fred Swanstrom, Boeing

© Daniel E Whitney

DFC for Wing Assembly as a Type 2Two KCs inconflict

SpliceStr3

AftSkin

Str1-2

PlusChord

Str4-11

FwdSkin

Plus ChordAngle AKC

Skin Gap AKC

SKIN G

AP PKC

FTE

FTB

FIXTURE RIBS

Skin Gap PKC

Skin Gap PKC

Plus ChordAlignment PKC


© Daniel E Whitney

DFC for Wing Assembly as a Type 1Two KCs stillin conflict

SpliceStr3

AftSkin

Str1-2

PlusChord

Str4-11

FwdSkin

Plus Chord

Angle AKC

Plus ChordAngle AKC

Skin Gap AKC

Skin Gap PKC

Skin Gap PKC



SKIN G

AP PKC

FTE

FTB

RIBS

figs for designing assemblies

© Daniel E Whitney

“Impossible” as a Type 2KCs do not conflict

Skin Subassembly

SpliceStr3

AftSkin

Str1-2

Str4-11

FwdSkin

Skin Gap AKC

Skin Gap PKC

Skin Gap PKC

SKIN G

AP PKC

FTE

FTB

FIXTURE RIBS

Plus

Cho

rdAl

ignm

ent P

KC

Plus Chord

Alignment PKC

PlusChord

© Daniel E Whitney

“Impossible” as a Type 1KCs do not conflict

Skin Subassembly

SpliceStr3

AftSkin

Str1-2

Str4-11

FwdSkin

Skin Gap AKC

Skin Gap PKC

Skin Gap PKC

Plus

Cho

rdAl

ignm

ent P

KC

Plus Chord

Alignment PKCSKIN

GAP PKC

FTE

FTB

RIBS PlusChord

© Daniel E Whitney

Rib-Spar as a Type 2 Assembly

Fairness PKCStrength PKCFwd Torque

Box

Fixed TrailingEdge

Rib

Step 1: Put FTB andFTE in Fixture

Step 2: Put in ribs

FTB-Rib-FTE assy

© Daniel E Whitney

DFC for Rib-Spar as a Type-2

FTE

FTB

FIXTURE RIBS

(1)

(5)

SKIN G

AP& R

IB ALIGN

PKC

(6)

(6)

© Daniel E Whitney

Rib-Spar as a Type 1 Assembly

Step 1: Put FTE onSupport

Step 2: Add ribs Step 3: Add FTE

FTB-Rib-FTE assy

© Daniel E Whitney

Cost Analysis -1• The basis for analysis was the KC-driven

Precision Assembly (PA) process for the 767 horizontal upper skin assy.

• PA time and cost were estimated for the 767 skin• The 767 cost/time analysis was scaled for the

remaining 747 & 767 assemblies Vought makes for Boeing.

• PA assumed to be accomplished in three distinct cells: Tack, CNC Auto-Rivet, Final Assembly

• These cells all require new investment

© Daniel E Whitney

Cost Analysis - 2

• Baseline times for each step were taken from Vought’s estimates for its process.

• Required cell time for MIT’s processes was estimated based on Vought’s times and a distribution of realization factors applied to obtain an assembly time for each cell.

• A computer simulation was conducted to determine the necessary capital equipment.

© Daniel E Whitney

Simulation Scenarios

• Three PA processes were developed and analyzed.

• The 3 processes are “Vought,” “MIT 1,” and “MIT 2”• “Vought” is Vought’s proposed PA process• “MIT 1” uses holes and slots. It was derived from “Vought” by applying the KC flowdown

method. “MIT 2” uses NC tack cell

• Three scenarios were studied:- All Boeing assemblies, all programs- Four representative assemblies- Introduction of a new assembly- New assembly would require new fixed tool but not new PA equipment

• One and Two shift operations

© Daniel E Whitney

Results - 1

• PA estimated to reduce process time by approximately 50%. At current demand this results in approximately XX hours saved annually.* Value of flexibility, “image,” and freed-up floor space not included.

• Annual savings = $X Million (assumes all assemblies converted to PA at a rate of $XX/hour.)– VOUGHT TO BE = 54% OF AS IS TIME– MIT 1 = 43% OF AS IS– MIT 2 = 42% OF AS IS– *ACTUAL NUMBERS ARE PROPRIETARY

© Daniel E Whitney

Results - 3

• Estimated equipment investment to implement PA (example for MIT 1)

All Parts 4 PartsOne Shift $21.4M $14.1Two Shifts $14.1M $7.3

(assumes cost per cell is Tack $2M, A-R $4.8M, Final Assembly $0.5M)

© Daniel E Whitney

Results - 4

• Current economics did not justify the new process• The new process becomes economical if Vought

gains new business for which it can use the new cells, thus saving the cost of new hard fixtures

• Training and cultural issues remain to be evaluated– Adjusting by hand becomes adjusting via computer– Ad hoc process becomes a preplanned and designed

one requiring more manufacturing knowledge during design

– More communication between fab and assembly shops needed

case study of 767 horizontal stabilizerdspace.mit.edu/.../0/class24767wingcasestudy.pdfcase study of...

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