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The design of a sustainable manufacturing system: A case study of its
importance to product variety manufacturing
R.Jayachandran*, S.Singh, J.Goodyer, K.Popplewell
Department of Manufacturing and Management, Coventry University, Coventry, CV1 5FB, UK
Abstract
A key challenge for manufacturers is to not only design but manufacture products using a sustainable approach.
Manufacturing industries have started recognising that it is their responsibility to design a sustainable manufacturing
system which has less environmental impact and social disruptions and promotes wealth. This paper presents a case
for adapting current manufacturing system design methods to include environmental issues. A case study is presented
which uses an environmental process selection method to demonstrate how companies can transform into sustainable
practices in a large product variety environment. One of the key results is that the technology capability and
economic risk are the two main factors which prevent a company to adopt sustainable manufacturing.
Keywords: Manufacturing system, product variety, process selection.
Corresponding author: Tel: +44-2476-88-7088, Fax: +44-2476-88-8272
E-mail address: *[email protected], [email protected]
1. Introduction
In terms of sustainable development,
manufacturing industry is often cited as a source for
environmental degradation and social problems, but it
is the major source of wealth generation [1].
According to the Lowell Centre for Sustainable
Production, sustainable production is defined as the
creation of goods and services using processes andsystems that are non-polluting, conserving of energy
and natural resources, economically viable, safe and
healthful for employees, communities, consumers and
socially and creatively rewarding for all working
people [2]. Sustainable development consists of three
structural pillars namely society, environment and
economy, whilst at the same time it also involves
operational aspects such as consumption of resources,
natural environment, economic performance,
workers, products, social justice and community
development.
The concept of sustainable production
emerged at the United Nations conference on
environment and development in 1992; theconference concluded that the major source for
environmental degradation is unsustainable
production and consumption patterns [2]. Although
the concept of sustainable development was
developed in the last decade, most manufacturing
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companies are still looking for improving
environmental performance in their activities. The
last two decades of environmental consciousness
focused on end of pipe solutions i.e. reducing the
amount of hazardous emissions and substances after
manufacturing [3]. The focus has shifted from
controlling emissions to elimination or prevention at
source, which is a proactive approach. Firms adopting
a proactive approach consider the environmental
challenge as a competitive business opportunity
rather than as an obstacle. They integrateenvironmental aspects in all functions of the business
and the goal is zero waste.
This paper presents the importance of
concentrating on sustainable issues during the
Manufacturing System Design (MSD) phase. There
are many stages in the design of a manufacturing
system, typically covering process selection; capacity
planning, facility layout, etc. (see Fig. 1). It is the
intention of this paper to focus on one of the key
stages of MSD, which is process selection. A case
study is used to demonstrate how companies can
move to sustainable manufacturing practices in a
large product variety environment. The tools andmethodologies developed at each of the key areas of a
manufacturing system will transform the current
manufacturing system into a sustainable
manufacturing system.
2. Literature review
Product variety is defined as the number of
different versions of product offered by a firm at a
single point of time. Variety within the product arises
by varying the values of attributes from one product
to another such as material, dimensional, aesthetic
and performance attributes [4]. Increasing product
variety has implications over the operational
performance (production cost or outsourcing cost), sofrom a firms perspective a trade-off exists between
the product variety and operational performance. It is
also essential to design a manufacturing system that
can manufacture the new version of the product in a
sustainable way. Fig. 2 demonstrates how, by
focusing on sustainability not only in the product
design phase but also in the manufacturing system
design phase, environmental impact can be
minimised during manufacturing and at the end of a
products life. This is essential as the relationship
between manufacturing strategies and environmental
performance has come under close scrutiny. The
increase of environmental consciousness of thepublic, regulations due to environmental policies and
pressures from organised groups all sway companies
to adopt an Environmental Management System
(EMS). These systems are formulated to help an
organisation to evaluate the effectiveness of the
activities, operations and services [5]. However,
EMSs have been widely criticised by many authors
for being another standard and often yield only subtle
improvements.
The study of product variety has been looked
at from various perspectives such as economics,
marketing and manufacturing. Despite the
environmental drive from regulations or pressuresfrom stakeholders, none of the previous work
emphasises implications of product variety on the
environment [6]. As mentioned earlier, a trade-off
exists between the product variety and operational
performance. To overcome this trade-off, companies
migrate towards modular design where the final
product configuration is obtained by mixing and
matching of standard components. The modularity of
the product architecture has been accepted as a viable
solution to the product variety problem. At a
component or a part level, this is done by designing
products to an optimal near net shape, where variants
are generated from the optimal near net shape. Anincrease in variety of product would likely result in
an increase in a variety of raw material and resource
procurement. The product variety is often assumed to
yield high revenues and offer a competitive
advantage to the firm. However achieving
competitive advantage through increased product
variety is highly dependent on aligning marketing and
manufacturing strategies [7]. In the last few years,
there has been increased focus on consideration of
environmental issues during the product design and
Fig. 1. Manufacturing system design key stages.
Process selection
Capacity planning
Equipment selection and design
Facility design
Material handling systems
Integrated supply chain
People
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development leading to the development of new
paradigms such as Design for X (Environment,
Recycle, and Reuse etc), Life Cycle Assessment
(LCA), EMS, Cleaner Production tools etc. However
EMS and Cleaner Production tools play a crucial role
once the product, manufacturing processes and
manufacturing system have been designed. In the few
exceptional cases where companies adopt concurrent
engineering, the time of identification of
environmental aspects vary depending upon the
concurrency of the product development process. As
most manufacturers are moving towards offering high
product variety to their customers, developing
manufacturing systems to meet the objectives such as
economy, flexibility, lead time, delivery, etc. is a
challenging task. The decisions during the design of
manufacturing systems for high product variety
should consider not only the operational and
economic issues but the environmental performance
as well.
As been outlined previously in Fig.1, a
typical approach to MSD does not include anyenvironmental issues. This paper proposes that
typical MSD methods can be adapted to include
environmental issues at each of the key stages of
MSD so that sustainable manufacturing systems can
be achieved. In the interest of brevity, all key stages
are not discussed in this paper. However, this paper
focuses on just one of the key MSD stages, i.e.
process selection, which is outlined in Fig. 3. Here
environmental issues such as consumption of
material, energy, water, use of toxic materials in the
process and emissions from the process are
considered along side traditional issues such as
product characteristics, production environment
capabilities, etc.
3. Case Study
Company A is the collaborating organisation
for this research project and is a large multinational
automotive component manufacturing company.
Company A utilises powder metallurgy and sintering
technology to produce a variety of automotive
components. The case study with Company A
analysed the introduction of a new product variety
(Product X, see Fig. 4). The new product is a
circular plate with a specified thickness and a specific
bore diameter. This component would be part of an
assembly for the powertrain system. However, it was
noted that within this range, many product variants
will be developed over the next few years to penetrate
different markets whereby, the range will expand by
varying the stepped bore coupled with varying inner,
outer diameters and thicknesses as shown in Fig. 4.
The traditional process (selected without theconsideration of environmental issues) of producing a
variety of these products is by centrifugal casting. A
long bar is produced by centrifugal casting followed
by machining to achieve the final dimensions. These
two processes produce high levels of metal waste
such as casting defects resulting in scrapping the
entire length of the bar which is up to one metre and
machining wastes such as swarf, and defects. The
machining processes involved are parting, two
turning and one boring operation and the respective
waste for each operation is shown in Table 1. The
Fig. 2. The importance of designing products and manufacturing systems for sustainability.
Minimises environmental
impact
Product use
Product end of life
Maximises recovery, reuse, and substitute for rawmaterials through sustainable practices
Sustainable product development
Sustainable product design and
development
Sustainable manufacturing systemdesign
Sustainable manufacturing
Sustainable Manufacturing System Design
Manufacturing system requirementsManufacturing process selectionSelection and design of equipmentManufacturing system configurationManufacturing system implementationManufacturing system reconfigurationRecoverable /Reverse manufacturing
Product stewardship, Sustainable consumption,
Environmental practices Regulations, Corporatestrategies, Green supply chain, Design for X,
LCA.
Traditional product development
Product design
Manufacturing system design
Manufacture
Manufacturing
aste
Product use
Product disposal
Market requirements
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BoreVariable
Circular PlateVariable
Thickness Variable
Stepped Height/Angle
Variable
environmental impacts of manufacturing the productare high energy used in the casting process, defect
rates in the casting process, machining wastes and
swarf produced for every product. Among all the
metal swarf from the machining processes, the
volume of steel and cast iron swarf produced has a
significant impact over the environment and cost. The
metal swarf requires appropriate storage space,
involves transportation cost and the volume of swarf
generated in company A is tremendous. As the swarf
is coated with a thin layer of oil particles, re-melting
of swarf without processing provides low efficiency
and also generates pollution due to burning of oil in
the swarf. Finally the low value of steel does notenable metal manufacturers to recycle steel swarf
economically. These factors forced manufacturers to
dispose the swarf as a solid or hazardous waste
depending upon the legislative requirements.
Furthermore, the rising cost to landfill affects the
disposal of wastes, such as swarf. Apart from these
wastes, the company is uncertain about the
production volume of each of the product which
forces it to stock a wide range of raw materials
utilising a large amount of space and energy.
In an attempt to reduce the environmental
impact and to transit towards sustainable
manufacturing, the same product variety is analysedusing the process selection stage of the
Manufacturing System Design (MSD) shown in Fig.
3.Though it can be inferred that much of the
environmental impact occurs actually in the
manufacturing phase, the decisions on various
manufacturing activities of a product is made at
various levels of the MSD process such as process
planning, capacity planning, etc.
By applying the process selection
methodology, capable, potential and preferred
processes are determined. Capable processes are
defined as the processes suitable for manufacturing
with product material and volume as the inputs, and
may be identified by the PRIMA matrix developed by
Swift and Booker [8]. The capable processes are shell
moulding, ceramic moulding, centrifugal casting,closed die forging, cold forming, powder metallurgy,
electrochemical machining, electron beam machining,
laser beam machining, chemical machining. Potential
processes are identified from the capable processes
by correlating the product attributes to the
performance characteristics of respective process.
Processes such as cold forming and shell moulding
are eliminated as they do not meet the product
attribute criteria. Preferred processes are selected
based upon the correlation of economic,
environmental, technical, facility requirements and
capabilities, production rate etc. The potential
processes are selected using a process knowledgebase and preferred processes are selected based upon
the importance of each requirement to the company.
The final preferred process alternatives are
centrifugal casting, powder metallurgy and
machining.
By utilising the powder metallurgy
technology, the component could be manufactured to
a near net shape. The process of producing the
product by powder metallurgy consists of pressing,
dewaxing, sintering and machining. The powder is
first pressed into shape by a press and then de-waxed
to remove the binding agents. The product is then
sintered at very high temperatures. The facingoperations of the traditional process have been
replaced by a high-volume grinding operation to save
machining costs. Finally the turning operations are
performed to achieve the specific dimensions.
Therefore, by generating products with a near net
shape before machining by powder metallurgy
process, significant material can be saved for each
component which otherwise would have been
disposed of in to the environment. In this case, apart
from general powder waste during pressing or
Fig. 3. Process selection stage of manufacturing system design.
Fig. 4. Variable sizes for product X.
Process selectionProduct characteristicsProduction environment capabilitiesFacility tasksHierarchy prioritiesManufacturing constraintsEnvironmental issues (material waste,
equipment energy consumption,
landfill costs, waste disposal costs,by-product material reuse and by-
product material contamination)
Capable processesPotential processesPreferred possesses
Process sequenceProduction device matrix
Capacity planningProduct designMSD
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scrapping of the part due to defect (as opposed to
entire bar as in casting), the waste generated during
the machining process is shown in Table 2.
By utilising the powder metallurgy process,
there is a significant reduction in material waste. By
comparing the material waste generated from twodifferent processes (see Table 1 and Table 2), it is
evident that powder metallurgy process produces
76% less waste than the casting process. Furthermore,
it was also suggested that by reducing the material
waste, the tool life on the machining centres would be
increased, thus reducing the need for frequently
disposing worn out tools. However, due to the high
cost of powder metal and the sintering process, the
cost price per piece of product 'X' was found to be
three times higher than cast material. This process
was favourable from an environmental (material
waste) viewpoint. However, in the current economic
condition, the new piece price was too high to justify.
4. Discussion
For company 'A', the business decision-
making factors and steps taken to introduce product
variety in the company were essential to penetrate
newer markets and to gain competitive advantage.
Similarly, in todays competitive manufacturing
scenario, environmental considerations are also
essential to yield intangible benefits and to add
credibility to the business. An increase in product
variety levels would mean more waste would be
generated by the increase in raw material usage, more
machining operations and high levels of wastegenerated to produce the final product. The high
manufacturing cost of the powder metallurgy process
is due to cost of raw powder material, cost of mixing
the powder to the correct specification, cost of
carbide tooling for pressing and cost of running the
de-wax and sintering furnace (highly significant). The
total cost of the product includes the manufacturing
cost, waste disposal cost, raw material cost and
holding cost. With uncertainty in demand and high
product variety in place, the company has to stock
more raw material variety and volume with the
traditional process. However, with the suggested
powder metallurgy process, the total variety of raw
material (material composition) is less. Furthermore,
the rising cost of landfill poses a stiff challenge to
control the total cost of the products, however with
the powder metallurgy process, waste powder is
sieved and reused, while the volume of swarfgenerated is substantially lower.
The traditional casting process also has an
implication on field failures due to density
imperfections and it has also generated huge amount
of material waste during casting, which increases the
raw material cost. Although the powder metallurgy
process results in reduced material waste, the energy
consumed in the sintering process is significantly
high. However, when the production volume of the
product X and its varieties are significantly higher,
the economics of scale allows operating sintering
equipment of larger capacities to reduce the energy
cost per product. To further reduce the cost of thepowder metallurgy process a proposal was made to
convert the swarf generated by company A to a useful
powder material after reprocessing. As the swarf is
processed and converted as a powder material the
alternative process has low material waste per
product when compared with the traditional process.
There have been many applications of use of
metal swarf for producing metal components and
blanks using the powder metallurgy process [9, 10].
The advantage of powder metallurgy is generation of
the part to its near net shape. It is estimated that 50%
of the production cost is spent on geometric shaping
which also involves large material wastes such asswarf, defects, rework, though the parts produced by
the powder metallurgy requires machining to achieve
the final dimensions, the volume of machining is
substantially less which makes powder metallurgy a
prospective manufacturing technology. As the swarf
is contaminated with oil and other metals, the value
of the swarf is very low. To improve the value of
swarf recovered, strategies such as improved swarf
management by reducing contamination with other
metals, breaking up into small fragments, conveying
and cleaning swarf have been developed.
Table 1
Machining waste in traditional process
Operation Material waste x103
mm3
Parting 8.3
Boring 6.6
Turning 1 1.35
Turning 2 1.1
Total material waste per part 17.35
Table 2
Machining waste in powder metallurgy process
Operation Material waste x103
mm3
Grinding 0.216
Boring 3.534
Turning 0.392
Total material waste per part 4.142
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Due to the availability of limited data, a
detailed cost analysis was not carried out to determine
the optimal production volume required by thesintering process which has an equivalent unit price
that of the traditional process. Furthermore it is
highly difficult to compare the process based on the
environmental impacts, because the material waste
generated in the traditional process is replaced by
high energy consumption in dewaxing and sintering.
However, with the availability of modern equipment,
heat loss can be substantially minimised. Moreover
with the increasing landfill cost, the company may
sooner choose this process as a viable option.
5. Conclusion
This paper focussed on a case study from aBritish company and demonstrated how a company
can move towards sustainable manufacturing by
looking into alternative processes. As the described
case study goes beyond the current industrial best
practices and approaches, it is also necessary to look
at the barriers which hinder a company in moving
towards sustainable manufacturing. First of all there
has always been a trade-off between environmental
impact and other factors such as quality, cost,
performance, etc. Generally companies favour cost as
a predominant factor unless the environmental impact
of the product or the process is regulated by
legislation. It is clearly evident there is less scope forimproving sustainability (reducing environmental
impact, cost etc.) once the process has been selected
and the manufacturing system has been designed. For
instance, the case study outlined that the traditional
manufacturing process produces high material waste
and with the total production volume of all the
varieties is expected to be in millions per annum, the
material waste is highly significant in terms of
sustainability. There are process models that exist in
practice and literature to analyse the trade-offs such
as volume, cost, defects, etc. but these models lack
the analysis between the environmental impacts,
energy, cost, etc. The study also indicates thattechnological capabilities and economic r isk are the
two main factors which prevent a company to adopt
sustainable manufacturing.
An environmental oriented methodology to
process selection has been shown in the case study.
The powder metallurgy generates low material waste
but the production cost is significantly higher
compared to the casting process which makes this
alternative impracticable in current economic
conditions. Although in this case, it is not economic
to use the powder metallurgy process; this would
need to be reviewed against anticipated increase in
energy and landfill cost. It is also anticipated that athigh volumes (either due to individual product
volume or cumulated volume of all the varieties) and
with the use of energy efficient sintering equipment,
the cost of the powder metallurgy process can be
significantly reduced.
The proposed sustainable manufacturing
system design method forces manufacturing
engineers to consider additional environmental
factors in process selection such as material waste,
tool change or disposal, raw material consumption,
landfill costs, waste storage and disposal costs, by-
product material reuse and by-product material
contamination.
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