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ME2110
Concurrent Design - DfX
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Design for X (DFX)
1. Design for Manufacture
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Design for X (DFX)
2. Design for Assembly
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Design for X (DFX)
• Design for Environment
• Design for Disassembly
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• Design for Maintenance
Design for X (DFX)
• Design for Safety
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Design for Assembly
• Methods consists of a design review by – Design and development personnel
– Production personnel
• The technique imposes – Discipline
– Objectiveness
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Aspects of Design for Assembly
• DFA is applicable to
– Products consisting of 20 -200 parts
– Mainly for mechanical parts (not electronic circuits)
– Dimensions lie between those of watches and cars
• No specialized knowledge of production means is
needed
• Requires 1-2 days to perform for a product
• Often 30% improvement in the assembly cost
• Can be performed in the various stages in the design
process and repeated
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Design for Assembly (Criteria)
• Execution of assembly operations
– Storing
– Handling
• Identifying, Picking-Up, Moving
– Positioning
• Orientating, Aligning
– Joining
– Adjusting
– Securing
– Inspecting
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Design for Assembly (Criteria)
• Standardization of assembly operations
• Use of existing assembly equipment and tools
• Use of standard assembly tools
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Design for Assembly (Criteria)
• Number of operations in overall assembly
• Favorable sequence (preassembly, parallel
assembly)
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Design for Assembly (Criteria)
• Possibility of automation
• Freedom from possible assembly errors
• Avoidance of damage to components
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Design for Assembly (Criteria)
• Avoidance of special
training of the assembly
staff
• Maintenance of safe
working conditions
• Observance of
ergonomic standards
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Questions for DFA Analysis
• Is it possible to eliminate part of the
process? – Can the product be assembled if the part is integrated
with another part?
• What is the cost to deliver a part to the
assembly with correct spatial orientation
and position?
• What does it cost to carry out the assembly
of the part?
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Questions for DFA Analysis
• During product operation, does the part move relative to other parts?
– Consider only gross motions
– Small motions can be accomplished by
deformation (such as elastic hinges)
• Must the part be of a different material than other parts?
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Pneumatic Piston Sub-Assembly
1 - Screw (2) (steel)
2 - Cover (steel)
3 - Spring (steel)
4 - Piston stop (nylon)
5 - Piston (aluminum)
6 - Main block (plastic)
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Design for Assembly Worksheet
1
Part
I.D
. N
um
ber
2 3 4 5 6 7 8 9 N
um
ber
of
tim
es t
he
op
era
tio
n is c
arr
ied
ou
t co
nsecu
tively
Tw
o-d
igit
man
ual
han
dli
ng
co
de
Man
ual
han
dli
ng
tim
e p
er
part
Tw
o-m
an
ual
insert
ion
co
de
Man
ual
insert
ion
tim
e p
er
part
Op
era
tio
n t
ime (
sec)
(2)*
[(4)
+ (
6)]
Op
era
tio
n c
ost
(¢)
0.4
* (
7)
Fig
ure
s f
or
theo
reti
cal
min
imu
m
part
s E
sti
mati
on
TM CM NM d e s i g n e f f i c i e n c y
N M
T M = = 3 *
Name of Assembly
TM = Total manual assembly time
CM = Total cost of manual assembly
NM = Theoretical minimum number of parts
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Pneumatic Piston Sub-Assembly
1 - Screw (2) (steel)
2 - Cover (steel)
3 - Spring (steel)
4 - Piston stop (nylon)
5 - Piston (aluminum)
6 - Main block (plastic)
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Worksheet for Pneumatic Piston
1
Part
I.D
. N
um
ber
2 3 4 5 6 7 8 9 N
um
ber
of
tim
es t
he
op
era
tio
n is c
arr
ied
ou
t co
nsecu
tively
Tw
o-d
igit
man
ual
han
dli
ng
co
de
Man
ual
han
dli
ng
tim
e p
er
part
Tw
o-d
igit
man
ual
insert
ion
co
de
Man
ual
insert
ion
tim
e p
er
part
Op
era
tio
n t
ime (
sec)
(2)*
[(4)
+ (
6)]
Op
era
tio
n c
ost
(¢)
0.4
* (
7)
Fig
ure
s f
or
theo
reti
cal
min
imu
m
part
s E
sti
mati
on
6
5
4
3
2
1
1
1
1
1
1
2
30
10
10
05
23
11
1.95
1.50
1.50
1.84
2.36
1.80
00
02
00
00
08
39
1.5
2.5
1.5
1.5
6.5
8.0
3.45
4.00
3.00
3.34
8.86
19.60
1.38
1.60
1.20
1.34
3.54
7.84
1
1
1
1
0
0
42.25 16.90 4
TM CM NM
Main Block
Piston
Piston Stop
Spring
Cover
Screw
0.29 d e s i g n e f f i c i e n c y N M
T M = = 3 *
Name of Assembly
Pneumatic Piston
TM = Total manual assembly time
CM = Total cost of manual assembly
NM = Theoretical minimum number of parts
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Redesigned Pneumatic Piston
1 - Snap on cover
and stop (plastic)
2 - Spring (steel)
3 - Piston (aluminum)
4 - Main block (plastic)
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Worksheet for Redesigned Piston
1
Pa
rt I.D
. N
um
be
r
2 3 4 5 6 7 8 9 N
um
ber
of
tim
es t
he
op
era
tio
n is c
arr
ied
ou
t co
nsecu
tively
Tw
o-d
igit
ma
nu
al
han
dli
ng
co
de
Ma
nu
al
ha
nd
lin
g
tim
e p
er
pa
rt
Tw
o-d
igit
ma
nu
al
ins
ert
ion
co
de
Ma
nu
al
inse
rtio
n
tim
e p
er
pa
rt
Op
era
tio
n t
ime
(se
c)
(2)*
[(4)
+ (
6)]
Op
era
tio
n c
ost
(¢)
0.4
* (
7)
Fig
ure
s f
or
theo
reti
cal
min
imu
m
part
s E
sti
mati
on
4
3
2
1
1
1
1
1
30
10
05
10
1.95
1.50
1.84
1.50
00
00
00
30
1.5
1.5
1.5
2.0
3.45
3.00
3.30
3.50
1.38
1.20
1.34
1.40
1
1
1
1
13.29 5.32 4
TM CM NM
Main Block
Piston
Spring
Cover & Snap
0.90 d e s i g n e f f i c i e n c y N M
T M = = 3 *
Name of Assembly
Pneumatic Piston
(re-design)
TM = Total manual assembly time
CM = Total cost of manual assembly
NM = Theoretical minimum number of parts
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Design for Automated Assembly (Concepts)
• Layered design
– Clamshell base
– Sequential assembly
– Uni-directional
• Self-alignment
– Chamfer/countersink
– Posts/locating stops
• Combine detail parts
– Screws & washers
– Plastic moldings
– Castings
• Symmetry
• Direct drive systems
– Helical or gear vs.
Belt/pulley
• Common fasteners
– Minimize screws
– Snap fasteners
• Minimize springs
– Molded
– Compression coil
– Extensive coil
• Minimize cables
– Integrated packaging
– Solid connectors
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Example of Layered Assembly
Snaps
Snaps
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Compliance and Assembly
Avoid Better Best
No Chamfers Bottom Part
Chamfered
Top Part
Chamfered
Both Parts
Chamfered
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Self Alignment of Parts
This part could be oriented in any direction
These parts can be oriented only one way
Hole to accept
swaged part
Hole to accept
notched part
“D” shaped hole
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Nesting of Parts
This part could be
placed in any
orientation and not be
secured
This part has a “nest”
to orient and help it
secure
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Nonfunctional External Feature for Orientation
This slot would be
hard to detect
Pin to help orient slot
Chamfer to help orient slot
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Symmetry
Orientation Required
Preferred
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Tangling
These parts can tangle easily
The same parts redesigned, will not tangle
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Tangling (continued)
Parts that
interconnect will not
feed
Springs with open
loops will tangle
Springs with closed
loops will not tangle
A fillet will keep the
parts from
interconnecting
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Methods to Avoid Jams (1 of 2)
This results in
shingling
Base causes leading
edge to be lower
than trailing edge
Direction of
Flow
A nonfunctional corner
can eliminate this
problem
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Methods to Avoid Jams (2 of 2)
Rounded corners
can prevent jams
Mating surfaces with
sharp edges can cause
jams
A groove can prevent
jams by centering the
part
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Substitutes for Fasteners
Avoid designs that require fasteners
Design parts that snap together
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Joining Moving Parts without Fasteners
C-Clip
Chamfere
d Surface Snaps
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Fasteners
Preferred: Have flat vertical sides for vacuum pickup
Avoid
Socket Head Fillister Head Hex Head
Round Head Flat Head
Round Side Slant Side
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Cables and Connectors
Avoid:
Components that are
connected with cables to
circuit board
Preferred:
Components that are
plugged on a slave circuit
board
Example of a slave circuit board
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Cables and Connectors
Example of a secured cable
If the use of a cable cannot be
avoided. Have the cable plugged into
a dummy connector to locate the
cable end.
Then a robot can locate
the connector and plug it
in.
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Motion and Design
Avoid: Three motions required for insertion
Slot
Snaps
Preferred: Only one motion required
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DfA - Construction
Photographs courtesy of Dr. Singhose
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Photographs courtesy of Dr. Singhose