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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.

References[1] Legarth JB. Sustainable metal resource management

the need for industrial development: efficiency

improvement demands on metal resource management to

enable a (sustainable) supply until 2050. Journal of Cleaner

Production. 4 (2) (1996) 97-104

[2] Veleva V and Ellenbecker M. Indicators of sustainable

production: Framework and methodology. 9(2001) 519-549

[3] Johansson G. Success factors for integration of Eco-

design in product development. Environmental

Management and Health. 13(1) (2002) 98-107.

[4] Randall T and Ulrich K. Product variety supply chain

structure and firm performance: Analysis of the US bicycleindustry. Management Science. 47 (12) (2001) 1588-1604.

[5] Emilsson S and Hjelm O. Implementation of

standardised environmental management systems in

Swedish local authorities: reasons, expectations and some

outcomes. Environmental Science and Policy 5(6)(2002)

443-448.

[6] Tang E and Yam R. Product Variety Strategy An

Environmental Perspective. Integrated Manufacturing

Systems 7(6) (1996)24-29.

[7] Berry WL and Cooper MC. Manufacturing flexibility:

method for measuring the impact of product variety on

performance in process industries. Journal of operation

management. 17 (1999) 163-178.

[8] Swift KG and Booker JD (Ed.). Process selection:

From design to manufacture. 2nd edition. Butterworth

Heinemann, Oxford, 2003,pp 13-105.

[9] Costa CE, Zapata WC and Parucker ML.

Characterization of casting iron powder from recycled

swarf. Journal of Materials Processing Technology 143-144

(2003) 138-143.

[10] Velasco F, Ruiz-Roman JM, Cambronero LEG,.

Torralba JM and Ruiz-Prieto JM. P/M Steels manufactured

from cast iron swarf to powder. Journal of the Japan

Powder and Powder Metallurgy Association,41 (10) (1994)

1282-1287

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