Transcript No Slide Title

Commonality in
Product Family Design
ME 546 - Designing Product Families - IE 546
Timothy W. Simpson
Professor of Mechanical & Industrial
Engineering and Engineering Design
The Pennsylvania State University
University Park, PA 16802 USA
phone: (814) 863-7136
email: [email protected]
http://www.mne.psu.edu/simpson/courses/me546
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Planning Product Platforms
• Robertson and Ulrich (1998) advocate a three-step approach:
1) Product plan – which products to offer when
2) Differentiation plan – how products will be differentiated
3) Commonality plan – which components/modules will be shared
Source: D. Robertson and K. Ulrich, 1998, "Planning Product Platforms," Sloan Management Review, 39(4), pp. 19-31.
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Overview of Today’s Lecture
• Examples of Commonality in the Aerospace Industry
• Discussion: Pros/Cons of Commonality
• Metrics for Commonality
• Comparison of Commonality Indices
• Using Commonality Indices for Redesign/Design
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Commonality
• Much of focus in product family design is to improve
commonality and standardization within the family
• What do we mean by commonality?

Possession of common features or attributes in either the
product or the manufacturing process for a set of products
• A product platform is defined “as the common elements,
especially the underlying core technology, implemented
across a range of products” (McGrath, 1995)
• Main advantage of commonality within a product family:

maintain economies of scale (and scope) in manufacturing and
production processes
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Boeing 777 Passenger Doors
• Each passenger door (8 total) has
different sets of parts with subtly
different shapes and sizes for its
position on the fuselage
• Challenge: make the hinge
common for all of the doors
777 Passenger Door
• Result: not only a common hinge
(Sabbagh, 1996)
but also a common door mechanism
98% of all door mechanisms are common
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Embraer Aircraft Family
EMBRAER 170
95% Commonality
EMBRAER 175
85% Commonality
EMBRAER 190
95% Commonality
EMBRAER 195
Common pilot type rating
100% commonality in the cockpit
High level of commonality in system components
100% flying commonality due to fly-by-wire system
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Airbus Aircraft Family
• Airbus A3XX Family: common height, width, cockpit
• The A330 cockpit is common to all other Airbus types
while Boeing’s 767-400 cockpit is common only with
the 757. This enabled the A330-200, a less efficient
“shrink” of a larger aircraft, to outsell Boeing’s 767400ER, a more efficient “stretch” design of a smaller
aircraft, in 1999 and 2000
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Boeing’s Blended-Wing-Body (BWB) Airframe Commonality
BWB Family covering 200-450
passengers with:
• Identical Wings
• Identical Cockpit
• Identical & Similar Bays
Scaling in size
200
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250
300
350
400
450
Source: Boeing
© T. W. SIMPSON
Growing a BWB
350
•
•
•
•
•
•
Fuel volume available in wing
Adds passengers
Adds wing area
Adds span
~Balanced
Aerodynamically Smooth
450
550
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Payload Commonality
• Each bay in the BWB is an identical “cross-section” and thus
lends itself to high part/weight commonality amongst the family
members
• The BWB-450 retains 97% of the BWB-250’s furnishings weight

Identical bagracks, seats, crew rest, lavs, galleys, sidewalls, ceilings, floors
BWB-450/-250
Common
BWB-450
T-plug
BWB-450/-250
Common
The BWB has significant benefits over families of tube and wing
transports with
its ability to cover the large airplane market with ONE cross section
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BWB Common Fleet
7 Bay
570
6
475
Global Range Transport/Tanker
5
360
4
C2ISR
270
3
Bomber
Tanker
180 Seats
Commercial Family
Representative
Cross Sections
Tanker
C2ISR
Bomber
Global Reach Freighter
Share Common Wing, Cockpit and Centerbody Elements
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Commonality
Discussion Activity:

Count off 1, 2, 3, 4, 5, 6 and form groups (5-6 people/group):
1. Marketing
2. Engineering
3. Manufacturing
4. Sales & Distribution
5. Service
6. Customers

In your group, take ~10 minutes to discuss (and take notes):
–
–
when and why is commonality good?
when and why is commonality bad?
based on your group’s role in product design and realization.
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Commonality (cont.)

Within your group, count off A, B, C, D, E, F and re-group into:
A. An automobile company (e.g., Ford, Chrysler, Toyota)
B. A software company (e.g., Microsoft, Adobe, Corel)
C. A fast food chain (e.g., McDonalds, Burger King, Subway)
D. A computer manufacturer (e.g., Dell, Gateway, IBM, HP)
E. A furniture company (e.g., Herman Miller, Steelcase, IKEA)
F. A telecommunications company (e.g., Verizon, AT&T)

In your group, take ~10 minutes to discuss (and take notes):
–
what do you want to make common within your company
and the products that you offer?
–
what do you want to make distinct within your company
and the products that you offer?
in order to maintain your company’s competitive advantage.
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Advantages of Commonality
• Decrease lead times (and risk) in product development
• Reduce product line complexity
• Reduce set-up and retooling time
• Fewer components in inventory
• Fewer parts need to be tested and qualified
Other advantages?
•
•
•
•
•
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Disadvantages of Commonality
• Hinder innovation and
creativity
• Compromise product
performance
Other disadvantages?
•
•
•
•
•
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Performance
• Lack of distinctiveness
Individually
Optimized
Designs
Poor
Designs
Best
Designs
Designs
Based on
Common
Platform
Degree of Commonality
Despite disadvantages of
commonality, it does provide
a useful metric for assessing
families of products.
© T. W. SIMPSON
Common, Variant, & Unique Parts
• Consider a set of three product variants
Variant parts are
shared by two or
more products that
differ in one or more
aspects (e.g., feature
size, color, etc.)
Common parts are
shared by all of the
product variants and
are identical  the
platform elements
Variant 1
Variant 3
Variant 2
Unique parts are
used to differentiate
a variant from others
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When designing a product family, the goal is to:
• maximize the number of common parts,
• minimize the number of unique parts, and
• use the cheapest variant parts possible
© T. W. SIMPSON
Commonality Indices
• Commonality indices provide a surrogate measure for
estimating the benefits of a product family when
production cost information is not readily available
• There are a variety of metrics available in the literature
for measuring commonality of a set of products:
Degree of Commonality Index, DCI
 Total Constant Commonality Index, TCCI
 Commonality Index, CI
(C)
 Component Part Commonality Index, CI
 Product Line Commonality Index, PCI
 Percent Commonality Index, %C
 Comprehensive Metric for Commonality, CMC

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Definitions of DCI, TCCI, & CI
Degree of Commonality Index
• Most traditional measure of
component part standardization
• Reflects the average number of
common parent items per average
distinct component part
id
DCI 
where:
F
j i 1
j 1
j
d
Fj = # of immediate parents component j has over a
set of end items
d = total # of distinct components in the set of end
items
i = the total # of end items or the total # of highest level
parent items for the product structure level(s)
Component item = any inventory item other than an
end item that goes into higher level items
End item = finished product or major subassembly
subject to a customer order or sales forecast
Parent item = any inventory item that has component
parts
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Total Constant Commonality Index
• Modified version of DCI
• Relative index with absolute
boundaries between 0 and 1
d 1
TCCI  1  d
 F j 1
Uses same symbol notation as DCI.
Commonality Index
• Modified version of DCI
• Fixed boundaries: 0 < CI < 1
CI  1 
where:
u  max p j
vn
p
j 1
j
 max p j
u = number of unique parts
pj = number of parts in model j
vn = final number of varieties offered
© T. W. SIMPSON
Sample Calculations of DCI, TCCI, & CI
• Sample calculation of DCI and TCCI:
Source: Wacker, J. G. and Trelevan, M., 1986, “Component Part Standardization: An Analysis of Commonality
Sources and Indices,” Journal of Operations Management, 6(2), pp. 219-244.
• CI sample calculation:

Consider family of 6 computer mice, each having 20 parts:
120  20
Worst case: CI  1 
0
120  20
(no two parts alike)
70  20
Better case: CI  1 
 0.5
120  20
(70 parts needed
to make six mice)
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Definition of CI(C)
Component Part Commonality Index
• Extended version of the DCI
• Takes into account production
volume, quantity per operation,
and the cost of component part
• Does not have fixed boundaries:
1  CI
d
(C )
m
  F ij
d = total # distinct component parts used in all
the product structures of a product family
j = the index of each distinct component part
Pj = the price of each type of purchased parts
or the estimated cost of each internally made
component part
m = the total number of end products in a
product family
j 1 i 1
i = the index of each member product of a
product family
d
CI
(C )

m
m
 [ P  F  (V Q )]
j
j 1
ij
i 1
d
i
i 1
m
 [ P  (V Q )]
j 1
j
i 1
i
ij
ij
F ij
= the number of immediate parents for
each distinct component part dj over all the
products levels of product i of the family
m
F
= the total number of applications
(repetitions) of a distinct component part dj
across all the member products in the family
i 1
ij
Vi = the volume of end product i in the family
Qij = the quantity of distinct component part dj
required by the product i
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Sample Calculation of CI(C)
Example:
• 3 products
• 4 assembly levels
• 12 different parts
Computation of CI(C):
Source:
Jiao, J. and Tseng, M. M., 2000, “Understanding
Product Family for Mass Customization by
Developing Commonality Indices,” Journal of
Engineering Design, 11(3), pp. 225-243.
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Product Line Commonality Index (cont.)
P
S
PCI =
P
ni x f1i x f2i x f3i -
S
i=1
i=1
P
S
i=1
P
ni -
S
i=1
1
ni2
x 100
1
ni2
• f1i = part size and shape factor
• f2i = materials and manufacturing process factor
• f3i = parts assembly and fastening scheme factor
• fji = k/n where:

k is number of products which share component i

n is number of products that have component i
e.g., n = 3, k = {1, 2, or 3}

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Walkman Example
• PCI calculation for Sony products (Table 2 in [Kota00])
ni
4
4
4
4
…
(1/ni)2 f1i
0.625
1
0.625
1
0.625 0.75
0.625 0.5
…
…
• Sony PCI = 91%
• RCA PCI = 46.4%
• RadioShack PCI = 54.6%
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f2i
1
1
1
1
f3i
1
1
1
1
CCIi
4
4
3
2
…
…
…
Sum CCI =
Max CCI =
Min CCI =
PCI =
178.0
195.0
3.896
91.10
© T. W. SIMPSON
Drawback of PCI
• PCI provides a single number to characterize the
commonality within a product family

PCI measure by itself does not yield insight into ways to
improve commonality of individual products within family
• Siddique and Rosen (1998) developed percent
commonality indices which:
quantify commonality of components, connections, and/or
assembly stations
 are performed on a product by product basis, thereby providing
insight into ways to improve commonality of individual products
within the family

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Percent Commonality Index [SD98]
% Commonality = %Cx =
100 * common X
common X + unique X

where X can be components, connections, or assembly
workstations

% commonality can be calculated for each X, then combined to
form an overall commonality measure for the product family
Commonality = wcCc + wnCn + waCa
c = components
n = connections
a = assembly workstations
wj =weighting factor
[SD98] Siddique, Z. and Rosen, D. W., 1998, September 13-16, "On the Applicability of Product Variety Design
Concepts to Automotive Platform Commonality," Design Theory and Methodology - DTM'98, Atlanta, GA, ASME,
DETC98/DTM-5661.
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Assembly Graphs for Commonality Assessment
• Graph helps assess commonality of connections (and
assembly workstations) within a product family
• Typically drawn at the sub-assembly and (major)
component level
Volume Dial
Super Bass
Switch
FWD/REV
Switch
Face Panel
Gear
Housing
Rear
Housing
Belt Clip
= snaps
= wire
= c. strip
= solder
= prongs
= screws
= springs
= belt
= plastic
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Gear Train
Stop
Radio Ctrl
Switch
Play
Rev
Motor
FF
Mode Ctrl
Switch
Circuit
Board
Headphone
Connector
Radio
Solenoid
Tuning Gear
Housing
Battery
Coil
Tuning
Gear
© T. W. SIMPSON
Commonality Viewpoints
• Why assess commonality of:

components?

connections?

assembly workstations?
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Selecting a Commonality Index
• When selecting a commonality index, consider your company’s
perspective when evaluating the product family
Focus on the number of
common components
Focus on the nondifferentiating (nonunique) components
Focus on the number of
common connections,
and assembly
Focus on the cost
of the components
TCCI
CI
X
X
PCI
%C
CI(C)
X
X
X
• We do not recommend using DCI since it does not have fixed
boundaries, making comparisons difficult; same for CI(C), but no
other metrics include cost explicitly (we are working to fix that)
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• DCI, TCCI, CI are the easiest to
compute and most repeatable

need the same amount of information
(parts, number of parts in each
product, BOM)
• %C, PCI are less repeatable
(require human intervention)

need information subject to variation
• Ease of computation and
repeatability of the CI(C) depends
on the data available (simple
BOM, component costs, etc.)
Ease of data collection
Comparison of Commonality Indices
DCI
TCCI
CI
CI(C)
%C
PCI
Repeatability
• For a detailed comparison and pros/cons of each, see:
Thevenot, H. J. and Simpson, T. W. (2005) “Commonality Indices for Assessing Product
Families,” Product Platform and Product Family Design: Methods and Applications
(Simpson, T. W., Siddique, Z, and Jiao, J., eds.), Springer, New York, pp.107-129.
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Using Commonality Indices for Redesign
• Consider the following six computer mice
Phase 1: Data Gathering – we used dissection
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Phases 2 & 3: Commonality and Optimization
• Phase 2: Commonality Assessment – PCI chosen to
P
P
1
consider changes in
ni * f1i * f 2i * f 3i   2

size/shape, material, PCI  i 1
i 1 ni
*100
P
1
manf, and assembly
P*N 
n
i 1
2
i
• Phase 3:
Optimize
Family –
GA runs to
determine
parameter
settings for
problem
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Phases 3: Optimization Results
Results from
optimization
(graphical)
Δ
Accompanying list of
component redesign
recommendations
and corresponding
change in PCI value
•
•
•
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•
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Phase 4: Recommendations for Redesign
• Largest DPCI by first redesigning receptor in Products 3, 5, 6…
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Using Commonality Indices for Design
• Military had a goal to create three variants – the CTOL, CV and
STOVL aircraft – of the F-35 Joint Strike Fighter (JSF), the 5th
generation, single-engine, single-seat aircraft with supersonic
dash capability and some degree of stealth (http://www.jsf.mil/)
• To reduce development, production, and operation and support
costs, component commonality targets of 70-90% were set to
maximize commonality in the airframe, engine, and avionics
components and save an estimated $15 billion

“[The JSF’s unique development approach] avoids the three parallel
development programs for service-unique aircraft that would have
otherwise been necessary” (Letter from Secretary of Defense William S.
Cohen to Rep. Jerry Lewis, June 22, 2000)
• Unfortunately, as the project progressed, the actual commonality
within the family of three aircraft fell far short of these targets,
with final values in the 30-40% range
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Commonality within JSF
Source: http://www.jsf.mil/
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Cousin Parts?
• Commonality indices such as PCI (Product Line
Commonality Index) differentiate parts based on:

Size & Shape

Materials & Manufacturing

Assembly & Fastening
Type of Part
Common
Size &
Shape
Same
These can be used to define
part commonality as follows:
Part Features
Materials &
Manufacturing
Same
Assembly &
Fastening
Same
Variant (Sibling parts)
Differ in only one area; same in other two
Variant (Cousin parts)
Same in only one area; different in other two
Unique
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Different
Different
Different
© T. W. SIMPSON
2008 Saturn Vue
• The 2008 Saturn Vue SUV, a full redesign, is nearly identical to
the German Opel Antara model that General Motors, parent to
both brands, sells in Europe. Saturn is trying to morph from
GM's touchy-feely brand to its Euro marque, so it kept as much
German feel as possible. GM is trying to cut costs by sharing
development and components rather than starting from scratch
on each new vehicle. Besides being a near-twin of Antara,
including visually, Vue shares some underpinnings with GM's
Chevrolet Equinox and Pontiac Torrent, and with GM affiliate
Suzuki's XL-7, but shares no body parts. "Call them 'cousins,'
not 'siblings,'" says Saturn's Mike Morrissey. There's an art to
this commonality. How much do you keep for the sake of low
cost? How much do you change to appeal to buyers in a specific
market -- America, for example? GM's last try to hew so tightly to
an Opel design resulted in a U.S. minivan line so bad it drove
GM from the minivan market.
- J. R. Healey, USA Today, 2B, Feb. 22, 2008
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Closing Remarks
• Commonality indices are to product family redesign
what DFMA is to product redesign
• Commonality indices can provide useful information
regarding the extent of similar and unique components
within a family
• The computation of many of these metrics can be
automated if necessary information (e.g., BOM) is
readily available
• Methods to support product family redesign based on
improving commonality have great potential
• More comprehensive metrics for commonality and
commonality/diversity are being developed
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