assembly-oriented design
DESCRIPTION
Assembly-Oriented Design. Dan Whitney April 5, 2002. Poll. We design assemblies explicitly as part of our product development process Our suppliers design our assemblies We design things and our manufacturing engineers try to get us to change them - PowerPoint PPT PresentationTRANSCRIPT
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AOD for LGO 1© Daniel E Whitney04/21/23
Assembly-Oriented Design
Dan Whitney
April 5, 2002
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AOD for LGO 2© Daniel E Whitney04/21/23
Poll
1. We design assemblies explicitly as part of our product development process
2. Our suppliers design our assemblies3. We design things and our manufacturing
engineers try to get us to change them4. We design parts using the best CAD system in
the world and then we wonder why we have trouble assembling them
5. We don’t have any assembly problems
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AOD for LGO 3© Daniel E Whitney04/21/23
Scope of “Assembly”
• Assembly spans the entire range from point processes to business strategy
• Assemblies are things that do something– Attributes– Architecture– Families, platforms…
• Assembly is a process of putting things together– On the factory floor– Operations– Equipment– Ergonomics
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AOD for LGO 4© Daniel E Whitney04/21/23
Scope of Assembly - 2
• Design for assembly– Part handling and mating
– Part consolidation• Integral architecture favors performance
• Modular architecture favors business issues
• Design of assemblies - technical and business issues– Design intent
– CAD representation
– Key Characteristics
– Math models, constraint, tolerances
– Architectures, families, delayed commitment, flexibility
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AOD for LGO 6© Daniel E Whitney04/21/23
Sony Does DFA During Concept Design
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AOD for LGO 7© Daniel E Whitney04/21/23
Things an Assembly Theory Must Do
• Represent top-level goals for the assembly• Link these goals to requirements on the assembly
and the parts• Represent nominal and varied location of parts in
space• Provide for declaration of mutual constraint
between parts• Merge design of assembly and of assembly
processes, including adjustments and fixtures• Support a design process for assemblies that can
be added to CAD
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AOD for LGO 8© Daniel E Whitney04/21/23
This Theory of Assembly...
• Focuses on “Kinematic Assemblies”• Emphasizes Delivery of Key Characteristics (KCs)• Documents KC Delivery and Constraint with the
Datum Flow Chain (DFC)• Achieves Constraint with Assembly Features• Achieves DFC Robustness via Tolerance Analysis• Exploits Underconstrained Assemblies to Achieve
Adjustments
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AOD for LGO 9© Daniel E Whitney04/21/23
What Happens During Assembly
• People think assembly is fastening• Assembly is really the chaining together of
coordinate frames• These chains of frames “deliver” certain parts or
features on parts to desired places in space relative to other parts or features on them within tolerances
• Complete chains describe Key Characteristics of the assembly
• This theory of assembly generates a design process for assemblies based on creating these chains
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AOD for LGO 10© Daniel E Whitney04/21/23
“Chain of Delivery” of Quality
No single part “delivers” the KC.
Inner Fenders(Budd-Philadelphia) Body Frame
(Ford LAP)
Radiator Sup port(DECO)
C owl Top(Hawthorne)
Assembly Too ling (TESCO)
Fen der Skin(Bud d-Shelbyville)
Reinforcements(Wise, Metalform)
Fix ture Vendor C)
Parts Vendor BFixture Vendor F Part Vendor A
Part Vendor C
Structural Check Fixture:Fixture Vendor E
D-pillar Assembly Station:Fixture Vendor B
Fen der(Part:Bu dd -Shelbyville
C hecking fixture: M&M)Check Fixture Vendor D)
Hood(Ford-Chicago)
Assembly Fixture for Fender:Fixtu re Vendor A
CustomerFeature:Hood Fit toFender
Assembly Fixture for Hood: Fixture Vendor A
Closure Panel Check Fixture: Fixture Vendor G
OrganizationalBoundary
PART COUNT: 9PART SOURCES: 7TOOL COUNT: 5TOOL SOURCES: 4CHECK FIXTURE COUNT: 2CHECK FIXTURE SOURCES: 2DISPERSAL INDEX: 81%
LIF RIF
RS
LOF ROF
H
KC KC
BF
G
Liaison Diagram:
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AOD for LGO 11© Daniel E Whitney04/21/23
Maintaining Oversight on KCs
• To design the chains that deliver the KCs, we have developed the Datum Flow Chain (DFC)
• A DFC is an assembly-level statement of design intent that-– documents the chain that delivers the KC– identifies the parts that make up the chain– provides a skeleton for the strategy by which the parts will be
located in space as links in the chain
• Each step in the assembly process adds links to the chain and each subassembly is kinematically constrained
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AOD for LGO 12© Daniel E Whitney04/21/23
Office Stapler.
BASE
HANDLE
CARRIER
ANVIL
ANVIL
CARRIER
PUSHER
STAPLES
RIVET
RIVET
PIN
AX
IS "A
"
AX
IS "B
"
"X" DIRECTION
"Y" D
IRE
CT
ION
SIDE VIEW
TOP VIEW
HAMMER
"Z" D
IRE
CT
ION
BASE
ANVILRIVET
CARRIER
HANDLE
PIN
STAPLES
PUSHER
Liaison Diagram
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AOD for LGO 13© Daniel E Whitney04/21/23
Datum Flow Chains in the Stapler
BASE
ANVILRIVET
CARRIER
HANDLE
PIN
STAPLES
PUSHER
BASE
ANVILRIVET
CARRIER
HANDLE
PIN
STAPLES
PUSHER
BASE
ANVILRIVET
CARRIER
HANDLE
PIN
STAPLES
PUSHER
BASE
ANVILRIVET
CARRIER
HANDLE
PIN
STAPLES
PUSHER
The datum flow chain is a chain of constraining mates from one end of the KC to the other.
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AOD for LGO 14© Daniel E Whitney04/21/23
Mates, Contacts, and KC Delivery
BASE
ANVILRIVET
CARRIER
HANDLE
PIN
STAPLES
PUSHER
MateContact
Mates give location.Contacts reinforce location.Variation travels from part to part along the chain of mates.
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AOD for LGO 15© Daniel E Whitney04/21/23
Coordinate Frames
.
BASE
HANDLEHAMMER
CARRIER
ANVIL
ANVIL
CARRIER
RIVET
RIVET
PIN
AX
IS "A
"AX
IS "B
"
"Y" D
IRE
CT
ION
SIDE VIEW
TOP VIEW
"Z" D
IRE
CT
ION
HANDLE
HAMMER
"X" DIRECTION
PIN
.
HANDLEHAMMER
BASE
CARRIER
ANVIL
ANVIL
CARRIER
STAPLES
RIVET
RIVET
AX
IS "A
"AX
IS "B
"
"X" DIRECTION
"Y" D
IRE
CT
ION
SIDE VIEW
TOP VIEW
"Z" D
IRE
CT
ION
HANDLE
HAMMER
PIN
CRIMPER
CRIMPER
STAPLE
PIN
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AOD for LGO 16© Daniel E Whitney04/21/23
Chains of F
rames =
A
ssembly
.
BASE
HANDLEHAMMER
CARRIER
ANVIL
ANVIL
CARRIER
RIVET
RIVET
PINA
XIS
"A"A
XIS
"B"
"Y" D
IRE
CT
ION
SIDE VIEW
TOP VIEW
"Z" D
IRE
CT
ION
HANDLE
HAMMER
"X" DIRECTION
STAPLES
KC
KC
PIN
STAPLESKC
KC
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AOD for LGO 17© Daniel E Whitney04/21/23
Dash
L. Fender
R. Fender
L. Body Side R. Body side
L. DoorR. DoorUnderbody
R. ApronL. Apron
L. I. Shot.R. I. Shot.L. O. Shot.
R. O. Shot.
L. O. RailR. O. Rail
Hood
L. Hinge R. Hinge
Bolster
Hood Latch
L. Lamp R. Lamp
Fascia
L. I. Rail R.I. Rail
y, z
F1
L. BracketL. Bracket
x, x,y, z
y,z
x, z, x,
y, z
y
x
yy
z, y
x, x
66
x, z, x, y, z
x, x,y, z
66
Hood fixture
F F
F F6
6
66
FF Fx, z, x, y x, z x, y
6
F
F
F
F
6
z, x y
z, x y
Fx, x
y, z, y, z y, z, y, z
z, y
y
x, y, z
x, y, z
xy, z
x, y, z x, y, z
F
F
Datum Flow Chain for Car Front End
Drawn by Gennadiy Goldenshteyn, MIT Student
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AOD for LGO 18© Daniel E Whitney04/21/23
DFC for Aircraft Circumference
KEEL ANDLOWER LOBESUPPLIER'S
FIXTURE
FRAMESUPPLIER'S
FIXTURE
SIDE PANELSUPPLIER'S
FIXTURE
CROWN PANELSUPPLIER'S
FIXTUREFRAMESUPPLIER'S
FIXTURE
FINAL ASSEMBLER'STHIRD FIXTURE
FINAL ASSEMBLER'S FEATURE
SUPPLIER'S FEATURE
SAME FEATURE USED BYSUPPLIER AND FINAL ASSEMBLER
DATUMSHIFT
FINAL ASSEMBLER'SSECOND FIXTURE
FINAL ASSEMBLER'SFIRST FIXTURE
HANDTOOL
OVER-CONSTRAINT
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AOD for LGO 19© Daniel E Whitney04/21/23
DFC Carries Design Intent
• Designer declares how KCs will be delivered• Intent is expressible in CAD terms• Intent expressed this way is independent of CAD
vendor• DFCs can be bookshelved for future use
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AOD for LGO 20© Daniel E Whitney04/21/23
Connective Assembly Model
Parts A and B are joined by two features
The nominal location of part B can be calculated from the nominal location of part A using 4x4 transform math
TT
T
AF
FB
AB
A
B
TAF
AT
FB
B
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AOD for LGO 21© Daniel E Whitney04/21/23
Varied Part Location Due to Variation
TT
T
AFFB'
AB'
AB'
TBB'
The varied location of Part B can be calculated from the nominal location of Part A. This processcan be chained to Part C, etc., including errors onPart B. It uses the same math as the nominal model.
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AOD for LGO 22© Daniel E Whitney04/21/23
Stapler Variations.
CARRIER
STAPLE
ANVILRIVETCRIMPER
X ERROR
ANVIL
RIVETCRIMPER
CARRIER
STAPLES
Y ERROR
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AOD for LGO 23© Daniel E Whitney04/21/23
When Parts are Joined, Degrees of Freedom are Fixed
• Parts join at places called assembly features• Different features constrain different numbers and
kinds of degrees of freedom of the respective parts (symmetrically)
• Parts may join by– one pair of features
– multiple features
– several parts working together, each with its own features
• When parts mate to fixtures, dofs are constrained
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AOD for LGO 24© Daniel E Whitney04/21/23
Overconstrained and “Properly” Constrained Assemblies
• Assemblies that function by geometric compatibility and force/moment equilibrium are called– statically determinate– “properly” constrained– “kinematic” or “semi-kinematic”
• Assemblies that require the other principle of statics (stress-strain relations) are called– statically indeterminate– “over-constrained”
• Constraint is a property of the nominal design
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AOD for LGO 32© Daniel E Whitney04/21/23
Summary of Assembly Theory - Nominal Design
• An assembly is a set of parts that deliver their quality, defined by the KCs, as a result of the geometric relationships between the parts (and fixtures)
• Designing an assembly means designing these relationships in terms of one DFC per KC– The DFC documents the nominal relationships in terms of
constraint– The DFC passes from part to part via mates
• The nominal design is a constraint structure• Assembly features create the constraint relationships
at each mate
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AOD for LGO 33© Daniel E Whitney04/21/23
Summary of Assembly Theory - Variation Design
• Tolerances should assure the robustness of the DFC• KC delivery is verified by a tolerance analysis of
each DFC• Tolerances on parts derive from tolerances on the
KCs• Part tolerances are sublinks of the DFC• Type-1 assembly-level tolerances come from part
tolerances• Type-2 assembly-level tolerances can be altered by
adjustments to the assembly process
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AOD for LGO 35© Daniel E Whitney04/21/23
Assembly Design Process
Nominal Design:
Identify each KCDesign a DFC for it
Choose features to build constrained DFCCheck for proper constraint
Check for KC conflictFind a suitable assembly sequence
Variational Design:
Check for robustness of DFC against variationsCheck achievement of each KC using tolerance analysis
See if a different assembly sequence gives better variation
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AOD for LGO 36© Daniel E Whitney04/21/23
Assembly Course Topics
• Assembly in the small:– Physics of part mating
• Assembly in the large:– Key characteristics
– Constraint
– Tolerances
– DFA
– Product architecture, customization
• A class project on these topics lasts all term