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Timothy W. SimpsonProfessor of Mechanical & IndustrialEngineering and Engineering DesignThe Pennsylvania State University

University Park, PA 16802 USA

phone: (814) 863-7136email: tws8@psu.edu

http://www.mne.psu.edu/simpson/courses/me546

ME 546 - Designing Product Families - IE 546

Commonality in Product Family Design

Commonality in Product Family Design

© T. W. SIMPSON

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Planning Product PlatformsPlanning Product Platforms

• Robertson and Ulrich (1998) advocate a three-step approach:1) Product plan – which products to offer when2) Differentiation plan – how products will be differentiated3) 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

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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CommonalityCommonality

• 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

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

• Result: not only a common hinge but also a common door mechanism

777 Passenger Door(Sabbagh, 1996)

98% of all door mechanisms are common

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Embraer Aircraft FamilyEmbraer Aircraft Family

EMBRAER 190

EMBRAER 195

EMBRAER 170

EMBRAER 175

95% Commonality

85% Commonality

95% Commonality

Common pilot type rating100% commonality in the cockpit

High level of commonality in system components100% flying commonality due to fly-by-wire system

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Airbus Aircraft FamilyAirbus 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 767-400ER, a more efficient “stretch” design of a smaller aircraft, in 1999 and 2000

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Boeing’s Blended-Wing-Body (BWB) Airframe CommonalityBoeing’s Blended-Wing-Body (BWB) Airframe Commonality

Scaling in size

200 250 300 350 400 450

BWB Family covering 200-450 passengers with:

• Identical Wings• Identical Cockpit• Identical & Similar Bays

Source: Boeing

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Growing a BWBGrowing a BWB

350

450

550

• Fuel volume available in wing• Adds passengers• Adds wing area • Adds span• ~Balanced• Aerodynamically Smooth

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Payload CommonalityPayload 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

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

BWB-450/-250Common

BWB-450/-250Common

BWB-450T-plug

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Tanker

Global Range Transport/Tanker

BomberC2ISR

Long-Range C

ommercial F

amily

180 Seats

270

360

475

570

7 Bay

3

6

5

4

Share Common Wing, Cockpit and Centerbody ElementsShare Common Wing, Cockpit and Centerbody Elements

C2ISRTanker Global Reach Freighter

Commercial Family

Bomber

RepresentativeCross Sections

BWB Common FleetBWB Common Fleet

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CommonalityCommonality

Discussion Activity: Count off 1, 2, 3, 4, 5, 6 and form groups (5-6 people/group):

1. Marketing2. Engineering3. Manufacturing4. Sales & Distribution5. Service6. 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.)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

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

Disadvantages of Commonality

• Lack of distinctiveness

• Hinder innovation and creativity

• Compromise product performance

Degree of Commonality

BestDesigns

PoorDesigns

IndividuallyOptimizedDesigns

Per

form

ance

DesignsBased on CommonPlatformOther disadvantages?

•

•

•

•

•

Despite disadvantages of commonality, it does provide a useful metric for assessing families of products.

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Common, Variant, & Unique PartsCommon, Variant, & Unique Parts

• Consider a set of three product variants

Variant 1

Variant 2

Variant 3

Common parts are shared by all of the

product variants and are identical the platform elements

Variant parts are shared by two or

more products that differ in one or more aspects (e.g., feature

size, color, etc.)

Unique parts are used to differentiate a variant from others

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

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Commonality IndicesCommonality 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 Component Part Commonality Index, CI(C)

Product Line Commonality Index, PCI Percent Commonality Index, %C Comprehensive Metric for Commonality, CMC

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Total Constant Commonality Index• Modified version of DCI• Relative index with absolute

boundaries between 0 and 1

Uses same symbol notation as DCI.

Commonality Index• Modified version of DCI• Fixed boundaries: 0 < CI < 1

where:u = number of unique partspj = number of parts in model j

vn = final number of varieties offered

Definitions of DCI, TCCI, & CIDefinitions 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

where:j = # of immediate parents component j has over a

set of end itemsd = 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 itemsEnd item = finished product or major subassembly

subject to a customer order or sales forecastParent item = any inventory item that has component

parts

dDCI

di

ijj

1

1

11

1

d

jj

dTCCI

nv

jjj

j

pp

puCI

1

max

max1

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Sample Calculations of DCI, TCCI, & CISample Calculations of DCI, TCCI, & CI

• Sample calculation of DCI and TCCI:

• CI sample calculation: Consider family of 6 computer mice, each having 20 parts:

Worst case:(no two parts alike)

Better case:(70 parts neededto make six mice)

5.020120

20701

CI020120

201201

CI

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.

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Definition of CI(C)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:

)]([

)]([

11

1 11)(

ij

m

ii

d

jj

d

jij

m

ii

m

iijj

C

QVP

QVP

CI

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

i = the index of each member product of a product family

= the number of immediate parents for each distinct component part dj over all the products levels of product i of the family

= the total number of applications (repetitions) of a distinct component part dj across all the member products in the family

Vi = the volume of end product i in the family

Qij = the quantity of distinct component part dj required by the product i

ij

m

iij

1

d

j

m

iij

CCI1 1

)(1

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Sample Calculation of CI(C)Sample Calculation of CI(C)

Computation of CI(C):

Example: • 3 products• 4 assembly levels• 12 different parts

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.)

Product Line Commonality Index (cont.)

• 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}

PCI =

ni x f1i x f2i x f3i - i = 1

P

i = 1

P

i = 1

Pni -

i = 1

P 1ni

2

1

ni2

x 100

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Walkman ExampleWalkman Example

• PCI calculation for Sony products (Table 2 in [Kota00])

• Sony PCI = 91%• RCA PCI = 46.4%• RadioShack PCI = 54.6%

ni (1/ni)2 f1i f2i f3i CCIi

4 0.625 1 1 1 4 4 0.625 1 1 1 4 4 0.625 0.75 1 1 3 4 0.625 0.5 1 1 2 … … … … … …

Sum CCI = 178.0 Max CCI = 195.0 Min CCI = 3.896 PCI = 91.10

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Drawback of PCIDrawback 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]

Percent Commonality Index [SD98]

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 = %Cx = 100 * common X

common X + unique X

wcCc + wnCn + waCa Commonality =c = componentsn = connectionsa = assembly workstationswj =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

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

= snaps

= solder

= wire

= prongs

= springs = belt

= screws

= c. strip

= plastic

Volume Dial

Face Panel Gear Housing

Rear Housing

Belt Clip

Motor Circuit Board

Stop Rev FFHeadphone Connector

Radio

Tuning Gear

Tuning Gear Housing

Mode Ctrl Switch

Solenoid

Super Bass Switch

Gear Train

Play

Battery Coil

FWD/REV Switch

Radio Ctrl Switch

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Commonality ViewpointsCommonality Viewpoints

• Why assess commonality of: components?

connections?

assembly workstations?

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Selecting a Commonality Index Selecting a Commonality Index

TCCI CI PCI %C CI(C)

Focus on the number of common components

X X      

Focus on the non-differentiating (non-unique) components

    X    

Focus on the number of common connections,

and assembly      X  

Focus on the cost of the components

        X

• When selecting a commonality index, consider your company’s perspective when evaluating the product family

• 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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Comparison of Commonality IndicesComparison of Commonality Indices

• 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.)

CI(C)

RepeatabilityE

ase

of

dat

a co

llec

tio

n

%CPCI

DCITCCI

CI

• 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

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

Phases 2 & 3: Commonality and Optimization

• Phase 2: Commonality Assessment – PCI chosen to consider changes insize/shape, material, manf, and assembly

• Phase 3:Optimize Family –GA runs todetermineparametersettings forproblem

100*1

*

1***

12

1 12321

P

i i

P

i

P

i iiiii

nNP

nfffn

PCI

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Phases 3: Optimization ResultsPhases 3: Optimization Results

Δ

• • • • • •

• • • • • •

• • • • • •

Results fromoptimization(graphical)

Accompanying list of component redesign

recommendations and corresponding

change in PCI value

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Phase 4: Recommendations for RedesignPhase 4: Recommendations for Redesign

• Largest PCI by first redesigning receptor in Products 3, 5, 6…

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Using Commonality Indices for Design

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 JSFCommonality within JSF

Source: http://www.jsf.mil/

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Cousin Parts?Cousin Parts?

• Commonality indices such as PCI (Product Line Commonality Index) differentiate parts based on:

Size & Shape

Materials & Manufacturing

Assembly & Fastening

Size & Shape

Materials & Manufacturing

Assembly & Fastening

Same Same Same

Different Different Different

Part Features

Unique

Differ in only one area; same in other two

Same in only one area; different in other two

Type of Part

Common

Variant (Sibling parts)

Variant (Cousin parts)

These can be used to definepart commonality as follows:

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2008 Saturn Vue2008 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 RemarksClosing 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