Total life-cycle considerations in product design for sustainability: A framework for comprehensive evaluation

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10th International Research/Expert Conference
“Trends in the Development of Machinery and Associated Technology”
TMT 2006, Barcelona-Lloret de Mar, Spain, 11-15 September, 2006
TOTAL LIFE-CYCLE CONSIDERATIONS IN
PRODUCT DESIGN FOR SUSTAINABILITY:
A FRAMEWORK FOR COMPREHENSIVE EVALUATION
I.S. Jawahir
O.W. Dillon, Jr.
K.E. Rouch
Kunal J. Joshi
Anand Venkatachalam
Israd H. Jaafar
University of Kentucky
Lexington, KY 40506
USA
ABSTRACT
This paper presents a new framework for comprehensively evaluating the sustainability content of a
product through Product Sustainability Index (PSI) in terms of all three components of sustainability
(economy, environment and society) over its total life-cycle (pre-manufacturing, manufacturing, use,
post-use). This method is useful in comparing various competitive products of the same family. This
technique uses a visual representation of PSI to give an overview of the product’s inherent and built-
in sustainability levels in a simple and effective manner.
Keywords: Product Sustainability Index (PSI), total life-cycle, sustainability evaluation
1. INTRODUCTION
Traditional product design and manufacturing methods are based on a range of product characteristics such
as functionality, performance, cost, time-to-market, etc. Product design and manufacture in the 21st
century will require a greater integration of life-cycle data, sustainable product/process designs and their
implementation in the manufacture of innovative engineered products. This will apply to industrial and
consumer products, both in high volumes and small varieties, and in low volumes and large varieties. In
particular, the design and manufacturing practices for next-generation of manufactured products need to
undergo major changes from traditional approaches to include concerns that span the entirety of the
traditional life-cycle, and ultimately from the perspective of multiple life-cycles toward a (near) perpetual
product/material life. Novel design methodologies and innovative manufacturing techniques must be
developed to simultaneously address traditional characteristics and life-cycle issues including the
following major objectives:
• Reduction of manufacturing costs
• Reduction of product development
time
• Reduction of material use
• Reduction of energy consumption
• Increased operational safety
• Enhanced societal benefits
• Reduction of industrial waste
• Repair, reuse, recovery and recycling of
used products/materials
• Consideration of environmental
concerns
• Education and training of workforce
• Increased product and process
innovation
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This paradigm shift in product design and manufacture necessitates optimized methodologies
incorporating environmentally conscious, energy-efficient and lean product design and manufacturing
methods for sustainability with product maintenance, disassembly, material recovery, re-use, re-
manufacturing and recycling considerations. It promotes a systems thinking in the design of new
products and processes and calls for attention to the interests of all stakeholders in our living
environment. It requires devising new design methodologies, manufacturing processes, post-use
processes, and enterprise resource planning for simultaneously achieving the multiple objectives
including company’s profitability, bringing new products to market rapidly, conserving natural
resources with environmental concerns.
Sustainability studies in general have so far been focused on environmental, societal and economical
aspects including public health, welfare and environment over their full commercial cycle, defined as
the period from the extraction of raw materials to final disposition [1]. Sustainable products are
generally defined as those products providing environmental, societal and economical benefits while
protecting public health, welfare and environment over their full commercial cycle, from the
extraction of raw materials to final disposition, providing for the needs of future generations. It is also
generally known that sustainable products are fully compatible with nature throughout their entire
life-cycle [2]. Traditionally, the economic and environmental analyses performed for products
impacting the society are almost entirely developed for a single life-cycle of a product. Aspects such
as material recovery along with possible multiple reuse opportunities that are themselves associated
with economic gains, and societal and environmental benefits are hardly evaluated in current
manufacturing practice.
The idea of recycling, reuse and remanufacturing has in recent times emerged with sound, innovative
and viable engineered materials, manufacturing processes and systems to provide multiple life-cycle
products This is now becoming a reality in a range of application areas of product manufacture. The
old concept of “from cradle to grave” is now transforming into “from cradle to cradle” [3], and this is
a very powerful and growing concept in the manufacturing world which takes its natural course to
mature. Added to this is the awareness and the need for eco-efficiency and the environmental
concerns often associated with minimum toxic emissions into the air, soil and water; production of
minimum amounts of useless waste; and minimum energy consumption at all levels.
In the past few years, researchers in the area of product and process sustainability have made attempts
to develop methodologies to assess/evaluate the level of sustainability in various stages during the life
of a product. This kind of assessment helps the manufacturer to identify non-sustainable elements
inherently present during any stage of the product life-cycle. Previous research has produced
qualitative results on product life-cycle which are mostly, with the exceptions of a few recent efforts
[4-5], difficult to measure and quantify. Hence, these analyses are largely non-analytical and less
scientific in terms of their perceived value of contributions. Moreover, product sustainability does not
just cover a simplistic assessment of the environment as a contributing measure; it involves a
comprehensive simultaneous assessment of the environmental, economic, and societal impact
categories, which are all interrelated. These three major components of sustainability are interlinked
and have some impact on every stage of the life-cycle of a product although the level of impact may
vary between different stages.
Legislation is one of the main motivational drivers for sustainable products. Examples of well known
legislative drivers include: (i) Waste Electrical and Electronic Equipment (WEEE) Directive [6], (ii)
Restriction of Hazardous Substances (RoHS) Directive [7], (iii) End-of-Life Vehicles (ELVs)
Directive [8], and (iv) Energy Using Product (EuP) Directive [9]. These legislative drivers place
responsibility of the product’s conformance to specified sustainability targets throughout its life-cycle
squarely on producers, manufacturers, and importers. The other major motivational drivers for
sustainable products are societal expectations and potential economic gains. In a recent work, two
specific scenarios, one involving the “economy” as the driver and the other showing the “society” as
the driver, both acting through “environment” are illustrated [10].
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This keynote paper highlights the significance of product design for sustainability by focusing on the need
for creating truly sustainable products to achieve societal, economic and environmental benefits. A new
framework for comprehensive evaluation of product sustainability is developed and presented in this paper.
This new methodology involves all four product life-cycle stages (pre-manufacturing, manufacturing, use
and post-use), and covers all three components of sustainability (economy, environment and society), all
integrated into a total ranking system to provide a composite sustainability score for a product.
2. TOTAL LIFE-CYCLE OF MANUFACTURED PRODUCTS – FOUR STAGES
Total life-cycle of a manufactured product consists of four key stages in a closed loop system: pre-
manufacturing, manufacturing, use and post-use. These four stages are shown in Figure 1.
Figure 1. Closed loop product life-cycle system showing the “6Rs” for perpetual material flow.
Pre-manufacturing: The foremost stage in the life-cycle of any product is the extraction of material from
their natural reserves. Raw material extraction is the process of excavating valuable virgin material from the
layers of the earth’s crust. These extracted virgin materials are then processed and consumed in the
manufacture of the final product. Pre-manufacturing includes mining metal ores and smelting them into metal
alloys, extraction of crude oil and processing it into hydrocarbons, cutting trees and transforming them into
usable wood or paper, etc. This stage also involves packaging, storage and transportation of the
processed/semi-processed products. Design for environment is also an integral part of this stage since it
involves conceptual design, in terms of environment, functionality, use, safety, and various other aspects of
the final product.
Manufacturing: Manufacturing is the phase where semi-processed materials are transformed into
finished goods for sale. The processing techniques (machining, forming, rapid prototyping, casting,
etc.) involved in this phase are quite diverse and are based on desirable performance characteristics
needed to be incorporated into the final product. Assembly is an integral part of the manufacturing
phase of a product life-cycle where manual or automated processing is used to join or integrate the
various parts. Depending on the complexity of product design this phase may vary from a couple to a
large number of steps. Product manufacture may involve – shaping metals into parts via molds or
cutting tools, assembling components into a product, storing and transportation of final parts, etc.
Product packaging and advertising are also generally considered to be a part of the manufacturing
phase.
Use: The use phase of the product life-cycle pertains primarily to the amount of time the consumer
owns and operates the product. During its use stage, the product needs to be energy-efficient, safe,
reliable, easy to operate, maintain, service/repair, etc. The product should be upgradeable to compete
with the newer models in order to last longer. The product becomes obsolete when one or several of
its desirable features cease to fulfill the consumer needs.
Post-use: After its use, the product reaches its end-of-life, where it can no longer satisfy the
consumer. Post-use also termed as end-of-life, is the final processing of a product for disposal,
incineration, recycling, remanufacturing, or other end-of-life processing. The concept of ‘6R’ can be
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effectively used in this stage to prolong the product life-cycle and also to ensure perpetual material
flow.
2.1 The “6R” Concept
In considering the material flow in a sustainable product life-cycle, the “3Rs” [11], i.e., Reduce, Reuse,
and Recycle have often been referred to as end-of-life processing strategies. However, a more
comprehensive and complete depiction would include three other “Rs”. These are Recover, Redesign,
and Remanufacture.
Reduce involves activities that seek to simplify the current design of a given product to facilitate
future post-use activities. Of all the end-of-life activities in the post-use stage, Reuse may potentially
be the stage incurring the lowest environmental impact mainly because it usually involves
comparatively fewer processes [12]. Recycle refers to activities that include shredding, smelting, and
separating. Recover represents the activity of collecting end-of-life products for subsequent post-use
activities. It also refers to the disassembly, and dismantling of specific components from a product at
the end of its useful life. Redesign works in close conjunction with Reduce in that it involves
redesigning the product in view of simplifying future post-use processes. Remanufacture is similar to
manufacturing. However, the difference is that it is not conducted on the virgin material but on an
already used product. The introduction of the “6R” concept into a product’s life-cycle is aimed at
reaching the condition of a perpetual material flow, resulting in a minimization of that product’s
ecological footprint [13, 14].
2.2 Closed Loop vs. Open Loop Life-cycle Systems
Figure 2 shows a closed loop, “cradle to cradle” product life-cycle system. Conversely, in an open
loop, “cradle to grave” life-cycle system, products are consumed and disposed of at the end of their
useful life. With this scenario, material resource, waste output, energy usage, and other system
emissions, etc., are all primarily a function of consumer demand.
Figure 2. Closed loop product life-cycle system.
To make a shift towards the closed loop system, at least three criteria of sustainable product
development must be met. These are: (a) minimization of material and energy resources needed to
satisfy the product function and the consumer demand, (b) maximization of expended resources usage,
and (c) minimization/elimination of adverse impacts of wastes and emissions. A closed loop product
system as typified in Figure 2 must fulfill at least the first two criteria ((a) and (b)) [15]. In this type of
product system, the activities of product reuse, remanufacture, and recycle circulates the material
within the product system. These activities reduce the requirement for new material extraction to feed
into the system, resulting in the reduction of the overall energy input requirement and emissions per
unit of the product consumption.
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It may be argued that such a closed loop system would not be beneficial, at least from the business
standpoint, to product manufacturers. This is especially for the market situation today where discrete
product sales is dominant and consumers continually demand new and varied products at the lowest
possible cost. With such an approach, the value associated with the reduced energy and raw materials
used are taken into account.
A paradigm shift towards “cradle to cradle” product development would persuade manufacturers to
invest more in ways to promote efficient material use and reuse. With such an approach, the values,
associated with the reduced energy and raw materials, used are taken into account. As a result, the
“cradle to cradle” paradigm shift that considers the life-cycle stages of reuse, remanufacture, and
recycle not only can work toward manufacturing a more sustainable product, but also would provide
realizable economic gains [15].
3. PRODUCT DESIGN FOR SUSTAINABILITY: THE PRODUCT SUSTAINABILITY
WHEEL
Six major product sustainability elements, each containing several sub-elements, have been identified.
Relative influence of each element on the product sustainability can be established if an appropriate
quantification method can be developed. Figure 3 shows the integral role of all six sustainability
elements and their sub-elements in generic form with equal weighting placed for each of the six major
elements. These interacting elements and sub-elements need to be fully studied for their effects on
product sustainability. Other relevant influencing elements and their relevant sub-elements can be
identified and added as needed. The educational challenges involved in developing a science-based
understanding of product sustainability through structured educational programs are described in a
recent paper [16].
Figure 3. Basic elements and sub-elements of product design for sustainability.
4. ANALYTICAL FOUNDATION OF PRODUCT DESIGN FOR SUSTAINABILITY
This section presents a recently developed new methodology for measuring the product sustainability.
4.1 A New Methodology for the Evaluation of Product Sustainability over the Total Life-cycle
A new comprehensive evaluation methodology to assess the sustainability content of any given
manufactured product, in terms of all three components of sustainability (economy, environment and
society), over its total life-cycle (pre-manufacturing, manufacturing, use and post-use), is presented in
this section. This rating system gives the ‘Product Sustainability Index (PSI)’ which is versatile
enough to be applied to a wide range of products. This system will assist product developers and
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manufacturers in achieving their sustainability targets. The new procedure for evaluating the PSI is
given below:
Step 1: The product developers need to identify potential influencing factors based on
national/international regulations, federal and state laws, and also based on what they consider to be
important from their own perspective. The product designers should not just focus on the economy
component of sustainability, but also look broadly at numerous environmental and societal aspects as
well. Similarly, to be effective, they should not just concentrate on the product pre-manufacturing and
manufacturing stages, but also consider the product’s use and post-use stages. After identifying the
potential influencing factors, product developers can form a [3×4] dimensional matrix, with the three
horizontal rows representing the components of sustainability – economy, environment and society,
and the four vertical columns representing the four product life-cycle stages – pre-manufacturing,
manufacturing, use and post-use.
Step 2: Product developers will have to conduct a detailed life-cycle assessment (LCA) of all
influencing factors that they have identified in the previous step to obtain the absolute values of these
factors to represent the anticipated sustainability levels. Once they have obtained these absolute
values for the influencing factors, they can then allocate a score/rating between 0-10 for each factor
(typically, with 0 being worst and 10 being best). Weighting can be applied to the influencing factors
based on their relative importance and company priorities. Some of these factors can be non-
quantifiable in which case the designer should assign a score based on his/her experience and
judgment.
Step 3: The template for the PSI matrix is shown in Table 1. The product designers need to record the
scores of the influencing factors in each box of the matrix. To evaluate the PSI, go across the matrix
and sum up the scores of each influencing factors in each matrix box and calculate the percentage
value using the equation (this equation represents the first box of the matrix) given below:
%100*)}10*/(]{[ 1)_()_( ∑
=
=
n
ii
pmenpmen nIFPSI …(1)
where,
PSI (en_pm) = Product Sustainability Index for Environment component of Pre-manufacturing
stage
IF (en_pm) = Influencing Factor rated on a scale of 0-10 for the Environment component
of Pre-manufacturing stage
n = Number of influencing factors considered
The PSI values for Society (PSI (so_pm)) and Economy (PSI (ec_pm)) can be calculated similarly. The
product sustainability index (PSI), for a single life-cycle stage, for instance pre-manufacturing, can be
evaluated by vertically adding the PSI of sustainability components over that particular life-cycle
stage, as shown in the equation below:
PSIpm = [PSI(en_pm) + PSI(so_pm) + PSI(ec_pm)]/3 …(2)
where,
PSI pm = Product Sustainability Index for Pre-manufacturing stage
PSI (en_pm) = Product Sustainability Index for Environment component of Pre-manufacturing
PSI (so_pm) = Product Sustainability Index for Society component of Pre-manufacturing stage
PSI (ec_pm) = Product Sustainability Index for Economy component of Pre-manufacturing stage
The PSI values for manufacturing (PSIm), use (PSIu) and post-use (PSIpu) stages can be obtained
similarly. The Product Sustainability Index (PSI) for the Environment component of Sustainability for
all four stages of product life-cycle can be calculated by horizontal summation of Product
Sustainability Indices of every stage of the product life-cycle as shown below:
PSIen = [PSI(en_pm) + PSI(en_m) + PSI(en_u) + PSI(en_pu)]/4 …(3)
where,
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PSI(en_pm) = Product Sustainability Index for Environment component of Pre-manufacturing
stage
PSI(en_m) = Product Sustainability Index for Environment component of Manufacturing stage
PSI(en_u) = Product Sustainability Index for Environment component of Use stage
PSI(en_pu) = Product Sustainability Index for Environment component of Post-use stage
Similarly, the PSI for Society (PSIso) and Economy (PSIec) components can be obtained. The overall
product sustainability index (PSITLC) for a product over its total life-cycle can be calculated as:
PSITLC = PSIso + PSIen + PSIec …(4)
The PSI scores can be interpreted as shown in Table 1.
Some of the influencing factors can be subjective and company-specific, in which case, the company
can still use the PSI technique for self-assessment of its products to meet its internal sustainability
goals. This technique will help the product designers and manufacturers to identify opportunities to
improve the performance of their product over its total life-cycle. The visual representation of the
influencing factors in terms of economy, environment and society components of sustainability for a
generic product is shown in Figure 4. The three concentric circles represent the three components of
sustainability (Economy, Environment, and Society). The influencing factors are listed on the
periphery of the outer circle. A rating scale for each influencing factor that cuts through all three
sustainability component circles with markings of 0-10 indicates the impact of that particular
influencing factor for the three sustainability components. It is interesting to note that in this figure,
each influencing factor is represented to have possible direct or indirect impact on all three
sustainability components. For example, the hazardous substance content in an automobile can have a
direct influence on the environment, whereas it can have an indirect impact on the society and the
economy. Disposal of hazardous substances causes unwanted additional economic burdens on the
manufacturer. Seepage of these substances that leads to environmental pollution and contamination
also causes unwanted environmental and societal burdens. Decontamination procedures also place
unwanted economic burdens on the manufacturer. This example shows an interrelationship between
all three components of sustainability caused by a single influencing factor - hazardous substance in a
product.
5. CONCLUSIONS
The new methodology presented in this paper provides a comprehensive evaluation of
product sustainability covering all four stages of product life-cycle and it represents all three
components of sustainability. This new technique will significantly assist product developers
and manufacturers in evaluating the existing product in its entirety and will help to improve
the future upgrades for existing product families in terms of economic, environment and
society components of sustainability. This methodology needs a joint effort and commitment
from legislators, product developers, manufacturers, researchers, etc. to standardize the
scoring system and to subgroup the influencing factors that affect the product sustainability.

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Table 1. A framework for a comprehensive total life-cycle evaluation matrix for product sustainability (using fictitious numbers).
Pre-manufacturing Manufacturing Use Post-use
Score
out of 10 Score
out of 10 Score
out of 10 Score
out of 10
Material Extraction 7 Production Energy Used 7 Emissions 9 Recyclability 7
Design for Environment 8 Hazardous Waste Produced 9 Functionality 8 Remanufacturability 8
Material Processing 6 Renewable Energy Used 8 Hazardous Waste Generated 9 Redesign 7
Landfill Contribution 7
(%) PSI(en_pm) = 70 (%) PSI (en_m) = 80 (%) PSI(en_u) = 86.67 (%) PSI (en_pu) = 72.5
Worker Health 8 Work Ethics 7 Product Pricing 7 Take-back Options 7
Work Safety 8Ergonomics 7Human Safety 9Re-use 6
Ergonomics 7 Work Safety 8 Upgradeablility 7 Recovery 7
Complaints 8
(%) PSI(so_pm) = 76.67 (%) PSI(so_m) = 73.33 (%) PSI(so_u) = 77.5 (%) PSI(so_pu) = 66.67
Raw Material Cost 6 Production Cost 6 Maintenance Cost 7 Recycling Cost 7
Labor Cost 3 Packaging Cost 7 Repair Cost 6 Disassembly Cost 8
Energy Cost 8 Consumer Injury Cost 8 Disposal Cost 4
Transportation Cost 5 Consumer Warranty Cost 7 Remanufacturing Cost 7
(%) PSI(ec_pm) = 45 (%) PSI (ec_m) = 65 (%) PSI (ec_p u) = 70 (%) PSI(ec_pu) = 65
(%) PSIpm = 63.89 (%) PSI m = 72.78 (%) PSIu = 78.06 (%) PSI pu = 68.06
(%) PSI
TLC
=
70.69
(%) PSIec =
Influencing Factors in the Product Life-cycle Stages
(%) PSIen = 77.29
(%) PSIso = 73.54
61.25
Sustainability Components
Society
Environment
Economy
Note: The integrated PSI in the last column and row (denoted by PSITLC ) shows the
computed total sustainability index with equal weighing for all elements and sub-elements.
Symbol
Score Excellent
85-90% Good
70-84% Average
50-69% Poor
< 50%
Visual representation of the PSI

10
0
10
0
10
0
Reliability
Recyclability
Air Pollution
Material
Consumption
Price of Product
Fuel Economy
Hazardous
Substance
Worker
Safety
Society Environment Economy
10
0
10
0
10
0
Reliability
Recyclability
Air Pollution
Material
Consumption
Price of Product
Fuel Economy
Hazardous
Substance
Worker
Safety
Society Environment Economy
Figure 4. An example of a generic product sustainability score showing the influence of various
factors on society, environment and economy and their sustainability ratings.
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