Sustainable Design and Manufacturing

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Sustainable Design and Manufacturing

Dr Atanas Ivanov

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Foreword

The world is changing rapidly, with a trend towards globalisation, international supply

chains and widely dispersed design and manufacturing teams. Engineering products

and the processes by which they are created are becoming increasingly complex. It

is essential that engineers address the whole life cycle of the systems and products

they create to ensure they meet the long-term needs of society. At the same time

they must use natural resources wisely and produce the minimum impact on the

environment.

1. Introduction

Sustainabilityis the capacity to endure. In ecology the word describes how biological

systems remain diverseand productive over time. For humans it is the potential for long-

term maintenance of well being, which in turn depends on the maintenance of the natural

world and natural resources.

Sustainability has become a wide-ranging term that can be applied to almost every facet of

life onEarth, from local to a global scale and over various time periods. Long-lived and

healthywetlands andforests are examples of sustainable biological systems.

Invisible chemical cyclesredistribute water, oxygen, nitrogen and carbon through the world's

living and non-living systems, and have sustained life since the beginning of time. As the

earths human population has increased, naturalecosystems have declined and changes in

the balance of natural cycles have had a negative impact on both humans and other living

systems.Paul Hawken has written that "Sustainability is about stabilizing the currently

disruptive relationship between earths two most complex systemshuman culture and the

living world.

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1.1 Definition

Definitions of sustainability often refer to the "three pillars" of social, environmental

and economic sustainability.

A representation of sustainability showing how both economy and society areconstrained by environmental limits.

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The word sustainability is derived from the Latin sustinere (tenere, to hold; sus, up).

Dictionaries provide more than ten meanings forsustain, the main ones being to

maintain", "support", or "endure. However, since the 1980s sustainabilityhas been

used more in the sense of human sustainability on planet Earth and this has resulted

in the most widely quoted definition of sustainability and sustainable development,

that of the Brundtland Commission of the United Nations on March 20, 1987:

sustainable development is development that meets the needs of the present

without compromising the ability of future generations to meet their own needs.

At the 2005 World Summit it was noted that this requires the reconciliation

ofenvironmental, socialand economic demands - the "three pillars" of

sustainability. This view has been expressed as an illustration using threeoverlapping ellipses indicating that the three pillars of sustainability are not mutually

exclusive and can be mutually reinforcing.

The UN definition is not universally accepted and has undergone various

interpretations. What sustainability is, what its goals should be, and how these goals

are to be achieved is all open to interpretation. For many environmentalists the idea

of sustainable development is an oxymoron as development seems to entail

environmental degradation. Ecological economist Herman Daly has asked, "whatuse is a sawmill without a forest?" From this perspective, the economy is a

subsystem of human society, which is itself a subsystem of the biosphere, and a gain

in one sector is a loss from another. This can be illustrated as three concentric

circles.

A universally accepted definition of sustainability is elusive because it is expected to

achieve many things. On the one hand it needs to be factual and scientific, a clear

statement of a specific destination. The simple definition "sustainability is improving

the quality of human life while living within the carrying capacity of supporting eco-

systems", though vague, conveys the idea of sustainability having quantifiable limits.

But sustainability is also a call to action, a task in progress or journey and therefore

a political process, so some definitions set out common goals and values. The Earth

Charterspeaks of a sustainable global society founded on respect for nature,

universal human rights, economic justice, and a culture of peace.

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To add complication the word sustainabilityis applied not only to human

sustainability on Earth, but too many situations and contexts over many scales of

space and time, from small local ones to the global balance of production and

consumption. It can also refer to a future intention: "sustainable agriculture" is not

necessarily a current situation but a goal for the future, a prediction. For all these

reasons sustainability is perceived, at one extreme, as nothing more than a feel-

good buzzword with little meaning or substance but, at the other, as an important but

unfocused concept like "liberty" or "justice". It has also been described as a

"dialogue of values that defies consensual definition".

1.2 Principles and concepts

The philosophical and analytic framework of sustainability draws on and connects with many

different disciplines and fields; in recent years an area that has come to be

called sustainability science has emerged. Sustainability science is not yet an autonomous

field or discipline of its own, and has tended to be problem-driven and oriented towards

guiding decision-making.

1.3 Scale and context

Sustainability is studied and managed over many scales (levels or frames of reference) of

time and space and in many contexts of environmental, social and economic organization.

The focus ranges from the total carrying capacity (sustainability) of planet Earth to the

sustainability of economic sectors, ecosystems, countries, municipalities, neighbourhoods,

home gardens, individual lives, individual goods and services, occupations, lifestyles,

behaviour patterns and so on. In short, it can entail the full compass of biological and human

activity or any part of it. As Daniel Botkin, author and environmentalist, has stated: "We see

a landscape that is always in flux, changing over many scales of time and space."

1.4 Consumption population, technology, resources

The overall driver of human impact on Earth systems is the destruction

ofbiophysicalresources, and especially, the Earth's ecosystems. The total environmental

impact of a community or of humankind as a whole depends both on population and impact

per person, which in turn depends in complex ways on what resources are being used,

whether or not those resources are renewable, and the scale of the human activity relative to

the carrying capacity of the ecosystems involved.

Historically, humanity has responded to a demand for more resources by trying to increase

supply. As supplies inevitably become depleted sustainable practices are

encouraged throughdemand managementfor all goods and services by promoting

reduced consumption, using renewable resources where possible, and encouraging

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practices that minimise resource intensity while maximising resource productivity. Careful

resource management can be applied at many scales, from economic sectors like

agriculture, manufacturing and industry, to work organisations, the consumption patterns of

households and individuals and to the resource demands of individual goods and services.

One of the initial attempts to express human impact mathematically was developed in the

70's and is called the I PAT formula. This formulation attempts to explain human

consumption in terms of three components: population numbers, levels of consumption

(which it terms "affluence", although the usage is different), and impact per unit of resource

use (which is termed "technology", because this impact depends on thetechnology used).

The equation is expressed:

I = P A T

Where: I = Environmental impact,P = Population,

A = Affluence,

T = Technology

1.5 Measuring Sustainability

By establishing quantitative measures for sustainability it becomes possible to set goals,

apply management strategies, and measure progress. The Natural Step (TNS) framework

developed byKarl-Henrik Robrt examines sustainability and resource use from

its thermodynamicfoundations to determine how humans use and apportion natural

capital in a way that is sustainable andjust. The TNS framework's system conditions of

sustainabilityprovide a means for the scientifically based measurement of

sustainability. Natural capitalincludes resources from theearth's crust (i.e., minerals, oil),

those produced by humans (synthetic substances), and those of the biosphere. Equitable

access to natural capital is also a component of sustainability. The energy generated in use

of resourcesreferred to as energycan be measured as the embodied energy of a

product or service over itslife cycle. Its analysis, using methods such as Life Cycle

Analysis orEcological Footprint analysis provide basic indicators of sustainability on various

scales.

There are now a vast number of sustainability indicators, metrics,benchmarks, indices,

reporting procedures, auditsand more. They include environmental, social and economic

measures separately or together over many scales and contexts. Environmental factors are

integrated with economics through ecological economics, resource economics andthermo-

economics, and social factors through metrics like the Happy Planet Index which measures

the well-being of people in the nations of the world while taking into account their

environmental impact. Some of the best known and most widely used sustainability

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measures include corporatesustainability reporting, Triple Bottom Line accounting, and

estimates of the quality of sustainability governance for individual countries using

the Environmental Sustainability Index and Environmental Performance Index.

At the global level, and from the equation I = PAT, it is clear that measuring sustainabilityrequires a knowledge of the world's expected population. We also need estimates of how

many people the Earth can support. This is a tall order but for many years now scientists

have been refining models of the carrying capacity of planet Earth by measuring key human

impacts, especially those that relate to biodiversity.

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2. Design and Manufacturing

The relationship between design and production is one of planning and executing. In theory,

the plan should anticipate and compensate for potential problems in the execution process.

Design involves problem-solving and creativity. In contrast, production involves a routine or

pre-planned process. A design may also be a mere plan that does not include a production

or engineering process, although a working knowledge of such processes is usually

expected of designers. In some cases, it may be unnecessary and/or impractical to expect a

designer with a broadmultidisciplinary knowledge required for such designs to also have a

detailedspecialized knowledge of how to produce the product.

Design and production are intertwined in many creative professionalcareers, meaning

problem-solving is part of execution and the reverse. As the cost of rearrangement

increases, the need for separating design from production increases as well. For example, a

high-budget project, such as a skyscraper, requires separating (design) architecturefrom

(production) construction. A Low-budget project, such as a locally printed office party

invitationflyer, can be rearranged and printed dozens of times at the low cost of a few

sheets of paper, a few drops of ink, and less than one hour's pay of adesktop publisher.

This is not to say that production never involves problem-solving or creativity, nor that design

always involves creativity. Designs are rarely perfect and are sometimes repetitive. The

imperfection of a design may task a production position (e.g.production artist, construction

worker) with utilizing creativity or problem-solving skills to compensate for what was

overlooked in the design process. Likewise, a design may be a simple repetition (copy) of a

known pre-existing solution, requiring minimal, if any, creativity or problem-solving skills from

the designer.

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2.1 Sustainability in Product Design

What does it mean to have a sustainable design?

First what is to design something?

No generally-accepted definition of design exists, and the term has different

connotations in different fields (see design disciplines below). Informally, a design

(noun) refers to a plan for the construction of an object (as in architectural

blueprints, circuit diagrams and sewing patterns) and to design (verb) refers to

making this plan. However, one can also design by directly constructing an object

Substantial disagreement exists concerning how designers in many fields, whether

amateur or professional, alone or in teams, produce designs. Dorst and Dijkhuis

argued that there are many ways of describing design processes and discussed

two basic and fundamentally different ways, both of which have several names.

The prevailing view has been called The Rational Model, Technical Problem

Solving and The Reason-Centric Perspective. The alternative view has been

called Reflection-in-Action, co-evolution and The Action-Centric Perspective.

2.2 Design and engineering

Engineeringis often viewed as a more rigorous form of design. Contrary views suggest that

design is a component of engineering aside from production and other operations which

utilize engineering. A neutral view may suggest that design and engineering simply overlap,

depending on the discipline of design. TheAmerican Heritage Dictionary defines design

as: "To conceive or fashion in the mind; invent,"and "To formulate a plan", and defines

engineering as: "The application of scientific and mathematical principles to practical ends

such as the design, manufacture, and operation of efficient and economical structures,

machines, processes, and systems.". Both are forms of problem-solving with a defined

distinction being the application of "scientific and mathematical principles". How much

science is applied in a design is a question of what is considered "science". Along with the

question of what is considered science, there is social science versusnatural science.

Scientists at Xerox PARC made the distinction of design versus engineering at "moving

minds" versus "moving atoms".

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2.3 Process design

"Process design" (in contrast to "design process" mentionedabove) refers to the planning of

routine steps of a process aside from the expected result. Processes (in general) are treated

as a product of design, not the method of design. The term originated with the

industrial designing ofchemical processes. With the increasing complexities of

the information age, consultants and executives have found the term useful to describe

the design of business processes as well as manufacturing processes.

2.4 Importance of engineering design

The decisions made by engineers have a widespread and long-lasting effect on the

quality of life and on the quality of the environment. The results of the work they do

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can improve life and living conditions in many ways and give people the opportunity

to develop fuller roles in society and to shape its future direction. Decisions of such

importance should be based upon the accumulated and carefully considered

experience of generations of engineers. Those making such decisions need to have

a deep understanding of the natural laws and the societal context of their work, and

to base their judgements upon this understanding. Because of the wide impact of

many of their decisions, engineers need integrity, independence, impartiality,

responsibility and competence, and, frequently, discretion. They are trusted by

society to make wise and fruitful decisions, occasionally on a global scale,

acknowledging cultural differences and limitations of resources human and

material.

Global economic developments are changing the industrial world rapidly and involve

increasingly challenging international and cross-cultural needs, along with ever

tighter regulations. Products are often designed by multi-disciplinary teams that are

no longer co-located, placing great reliance on sophisticated IT systems. Products,

and the processes by which they are created, are getting ever more complex. In

order to achieve shorter lead times, several of the traditional product creation

processes now have to be undertaken in parallel, an approach referred to as

Concurrent Engineering. New technologies such as biotechnology, nanotechnology

and photonics are having an increasing impact, as are the many new materials and

production processes. With companies moving from simply providing products to

providing total service packages, the importance of whole life modelling, right

through to the decommissioning, recycling and disposal of products, is constantly

increasing. It is clearly impossible to include all such developments in undergraduate

engineering courses, so the emphasis must be on providing students with a solid

grounding in engineering fundamentals and their context, and preparing them to

work adaptably and across disciplines throughout their lives.

2.5 Nature of engineering design

Design can be described briefly as: (1) identifying the needs a new project has to

address; (2) having the vision to conceive solutions to those needs; and (3)

delivering the solutions (Armstrong, 2002). The design process begins with the

identification of a new idea, a specific market need or a new technology. The design

team then has the challenge of conceiving a solution to that need, which may fall into

one or more of the following categories:

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Major one-off project, e.g. hydro-electric scheme, large bridge, shopping complex

Consumer product, e.g. kitchen kettle, motor vehicle, personal computer

Process, e.g. chemical plant, traffic management, food distribution, or

System, e.g. computer software, telecommunications system, mail delivery.

2.6 Educating Engineers in Design

It is critical to identify and formulate needs accurately. The perceived wants of

clients and customers are not always what they need in reality. Part of the

professional skill of engineers is the ability to recognise these differing requirements,

and to reconcile them.

After formulating the needs, the significant creative process of design begins. This

involves meeting the requirements of fitness for purpose, safety, quality, value for

money, aesthetics, constructability, ease of use, efficiency of production etc. It is vital

throughout the design process, and the subsequent delivery of solutions, to respect

the quality of life in an emerging global society and to give high priority to reducing

environmental impact and increasing sustainability.

2.7 What is Engineering Design?

Engineering design is the process of converting an idea or market need into the

detailed information from which a product or system can be made to satisfy all the

requirements safely, economically and reliably.

In order to explain the design process effectively, it is helpful to have an overall

framework. Design methods and guidelines can then be described within the context

of this framework, and their application in practice demonstrated through projects. A

starting point is provided by James Armstrong in his booklet Design Principles The

Engineers Contribution to Society (Armstrong, 2002). Armstrongs high-level model

of product development encompasses three key stages of realisation:

Need all design begins with a clearly defined need

Vision all designs arise from a creative response to that need

Delivery all designs result in a system or product that meets that need.

The need might arise from a good idea, a new technological development or a

carefully researched market requirement. In order to turn this proposal into a

concrete system or product, a design team with vision must be established to

undertake the complex sequence of activities necessary to define what is to be

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produced. If delivery of the system or product is to be timely and cost effective, then

the design team must be provided with adequate resources, including finance,

facilities, tools and information.

A slightly more detailed model of product development is shown in the figure below.

After a need has been defined, the creative activity of design is supported by inputs

from other key functions such as production, marketing, research, development,

quality assurance, sales and customer service. Progress depends on making

decisions. During the design stage the aim is to ensure that the proposed product

will be economical to produce, that it will operate to specification safely, reliably

and economically, and that it will be possible to recycle it at the end of its useful life.

Where recycling is not possible, careful consideration should be given to safe

decommissioning and environmentally benign disposal. Decisions depend on the

accuracy of forecasts, ranging from broad customer requirements to detailed

engineering stresses in a component. The design team as many solutions as

possible and analyses them to predict how these solutions will perform if realised.

Forecasts, and the decisions based on them, often turn out to be in error and

corrective actions have to be taken. Simple models, such as that shown in Figure 37,

mask the complex iterative nature of the product development process. The stages

often merge and because of errors and unknowns many steps have to be returned to

and repeated. For complex products, extensive development programmes involving

costly prototype testing are necessary before they can be released for production.

Large quantities of information, obtained from repositories and specialists in many

different fields, must be handled during the design process.

Since large, widely dispersed design teams are often required, communication

becomes a major issue. Continual feedback from all stages of the process provides

essential information for improving the system or product.

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Design problems are often described as being open-ended. By this it is meant that

they do not have correct solutions, though some solutions will clearly be better than

others. Several solutions must be developed before the best can be selected through

evaluation against the criteria. This is an iterative process involving many feedback

loops during which information is updated to improve both the criteria and the

solutions.

A general strategy for tackling complex problems is to break them down into smaller,

more manageable sub-problems and to tackle each sub-problem in turn. In line with

this strategy, the design process can be split into a number of main phases and each

phase then broken down into a number of steps.

Details of the phases and steps, which often have to be undertaken concurrently,

along with appropriate methods and guidelines to tackle each step, can be found in

standard texts on engineering design (Pahl & Beitz, 1998; French, 1999).

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The model of the design process can give the impression that each phase of the

design process is completed before the next one is started. This is seldom so. The

phases merge and are frequently repeated. The detail design of long-lead time items

will have to be undertaken and the sourcing of materials and production started

before the design of other, less critical, items has been completed. In the past

designs tended to be passed to the production department without careful

consideration having been given to process planning and the procurement of

materials and bought-in items. Also, at times, little attention was given to how easily

a product could be maintained in service and then disposed of and recycled at the

end of its useful life. It is therefore vital to emphasise the importance of starting to

plan for production, materials procurement, maintenance and disposal early in the

design process.

Although a systematic approach to design is advocated, it is important to emphasise

that such an approach must be applied flexibly and adapted to suit the particular

project being undertaken. It is not intended to replace intuition, inventiveness or

insight, but rather to support and enhance these qualities by disciplining thinking and

helping to focus on important aspects of the problem.

It is important to recognise that because of the time constraints on their studies, and

consequently the limited time they spend on engineering design, students can still

fail to appreciate two important characteristics of new product creation even if this

framework is used.

The first characteristic is that in order to deal with the complexity of many products,

they evolve incrementally. Experienced designers have a large repertoire of past

design solutions to draw upon and have a wide knowledge of and feel for standard

parts, material properties, and production and assembly processes. Undergraduates

do not have this repertoire.

The second characteristic is that attention to detail is critical. What distinguishes a

safe and reliable product is often not its conceptual design but its detail design.

Undergraduates often consider the detail design phase to be less important than the

others. It should be pointed out that many excellent concepts fail in the market

though lack of attention to detail. Because of time constraints in undergraduate

courses, it is seldom possible to undertake the full detail design of a product of

significant complexity.

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2.8 The four phases of the design process can be summarised as:

Clarification of the Task

The starting point for the design process is an idea or a market need, often stated in

vague, and sometimes contradictory, terms. Before the subsequent design phases

start, it is important to clarify the task by identifying the true requirements and

constraints. The result of this phase is a design specification (design brief or

requirements list), which is a key working document that should be continually

reviewed and updated as the design develops.

Conceptual Design

In this phase, concepts with the potential of fulfilling the requirements listed in the

design specification must be generated. The overall functional and physical

relationships must be considered and combined with preliminary embodiment

features. The result of this phase is a concept model (drawing).

Embodiment Design

In this phase, the foundations are laid for detail design through a structured

development of the concept. In the case of a mechanical product, the result of this

phase would be a detailed layout model (drawing) showing the preliminary shapes

and arrangement of all the components, along with their materials (Ashby, 2005).

Detail Design

Finally, the precise shape, dimensions and tolerances of every component have to

be specified, and the material selections confirmed. There is a close interrelationship

between the shape of a component, its material and the proposed method of its

manufacture. The result of this phase is a set of detailed manufacturing instructions.

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2.9 Design Engineering and Sustainability

The aim of education in Design Engineering is to simply formalize the

approach and in doing so, identify new methods and research opportunities

similar to the way it occurs in other fields of engineering.

Design Engineering focuses on defining customer needs and required

functionality early in the development cycle, documenting requirements,

then proceeding with design synthesis and system validation while

considering the sustainability issue.

2.10 The Idea!

Design can be described briefly as: (1) identifying the needs a new project

has to address; (2) having the vision to conceive solutions to those needs;

and (3) delivering the solutions (Armstrong, 2002).

BUT:

Every design always ends with drawings on which there is information about only

two things:

Materials & Dimensions

So every design can be regarded as a binary translation of the complexity of the

designed product or system

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2.11 Materials and dimensions

Materials - are selected based on Engineering Analysis methods and nominal

of dimensions are determined to satisfy the strength and rigidity requirements

of the system

Dimensions are represented by:

- Nominal

-Deviation (Tolerance)

-Position of the deviation (position of the Tolerance)

(- Distribution function)!!!

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2.12 Quantifying the quality:

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3. Quality Chains

Quality chains theory has no alternative at present for determining in a scientific

manner the needed accuracy and guarantee the workability, therefore the

sustainability, of the engineering designs and manufacturing settings from the first

attempt (iteration).

1. Basic definitions:

Quality chain - Sequence of dimensions in a closed loop (each part

contributes with only one dimension) expressing the dependence of a specific

functional criteria (closing element of the chain; distance, clearance,

interference etc.) This definition determines two conditions for assistance of a

Quality Chain (QC). 1 It is a closed loop contour; 2 in the contour are included

only dimensions whose change, brings a change to the element of the QC for

which the QC is created and called the closing element or accumulator.

In the schematics of the QC the closing elements are marked with a capitol

letter and index , (e.g. A , B , ). The rest of the elements of the QC are

marked with the capital letter and index i, which denotes the number of the

element.

Elements of the QC can be linear, marked with capital letter and index

showing their number in the particular QC (A1, B5, D3) and angular, marked

with Greek letters 1, 4 etc, but not using , , and .

The elements of the QC can be:

-Increasing When this element increases the closing element of the QC

(the accumulator) also increases. It is marked with right pointing arrow on the

top of the letter denoting the element;

-Decreasing- When the element increases the closing element

of the QC (the accumulator) decreases. It is marked with left pointing arrow on

the top of the letter denoting the element;

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-Compensator- This is a selected in advance element of the QC whose

change guarantees the desired accuracy. It is marked with letter and index c

(Bc, Dc, etc);

-Common is an element which belongs to two or more QCs

at the same time.

There are two stages of Quality Chain analysis.

a) Creation of the QC with graphic representation on the assembly drawing, process

planning drawing;

b) Calculating the needed elements using numerical values.

Some examples of QC and methods of determining the type of the structural element

whether increasing or decreasing:

2. Graphical representation of the QC elements

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- Linear dimensions with fairly big nominal are represented with

a line and two arrows;

- Dimensions which are very small like clearance, interference

are graphically represented by rotating the axes of those surfaces

and marking for which surface the axes line belong to and then

giving the dimension.

-Angular dimensions are marked as shown below

Quality Chains can be independent or connected when two or more chains are

dependent on each other.

Parallel linked chains. (At least one common element should be present). In

the example below there are 2 common elements. In this case first have to

be calculated the chain requiring higher accuracy!

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Serially linked QC. These are Chains which have common datum.

These chains do not influence each other but they only show the sequence of the

assembly.

There is also third type of linked QCs where they share elements and common

datum. They are called combined linked chains.

3.3 Types of Quality Chains

1. Depending on the position in the space they can be 2D and 3D. 2D chains

can be with parallel elements or non parallel elements.

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2. According to the application QC can be: Design QCs, Manufacturing QCs

and Metrology QCs

3. Parts design QCs In this case the closing element of such QCs are the

missing from the drawing dimensions. In the fig. below the dimensions from A1

to A5 are sufficient linear dimensions for the shaft to be fully determined. The

number of these dimensions should be equal to the number of the face

surfaces minus one. All the rest of the dimensions shown on the figure below

are closing elements of some QCs, e.g. A is resultant from A3, A4 and A5.

This dimension can be given on the drawing in brackets meaning for

reference. It is important not to over-dimension the parts.

4. Assembly QCs help to analyse the quality links in the whole assembly. On

the figure below the quality requirement for mismatch of the axes of the head

and tailstock of a lathe is denoted as B. The element B3 comes as a result

from the assembly of the headstock where it was the closing element of

another assembly QC, and B1 comes as a result of the assembly of the

tailstock. Therefore, the QCs are linked with the sequence of creating of the

new design and the elements may change their role during this process.

5. Manufacturing QCs are used to guarantee the accuracy during the

manufacturing operations. On the fig below is shown automated lathe. The

dimension B is achieved by automatic switch off of the feed rate. As it can be

seen from the figure in the QC take part elements from the machine tool, jigs

and the tools.

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6. Metrology QCs helps to analyse the accuracy with which the parts will be

measured. On the fig below the measured dimension G is the closing

element of a QC as the micrometer reading will depend on the dimensions Gi.

3.4 Rules for creating Quality Chains:

1. Preliminary condition is availability of a drawing (part, assembly, process

planning etc.)

2. Defining the functional parameters (see above the quantifying the quality) for

which the QC will be created. They will be the closing element (accumulator)

of the QC. Most often these are distances between surfaces or axes,

clearances, angular deviation between surfaces and axes.

3. Creation of the QC starts from the one end of the closing element and involve

only dimensions which influence directly the closing element of the chain till

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the other end of the closing element is reached. This should be the shortest

distance.

4. In the assembly QCs one part can participate in one QC with only one

dimension. If this is not achieved, either is a mistake or a parallel chain is

influencing the first one. On figure below is given an example of assembly of

two plates with a dowel pin and the functional characteristic is to ensure that

there is a clearance A. The two parts participate in the QC with only one

dimension A1 and A2. The designer has not given the dimension A2 but the

dimensions B1 and B2 for part1. In this case first has to be determined the

dimension B=A2.

5. The elements of the QCs can change their meaning as it was mentioned

above depending on the stage of the preparation, manufacturing or assembly

of the final product or system.

6. Parts assembled with clearances will count as separate parts as it allows

moving of one part relative to the other. Parts assembled with interference fits

will count as one part as for example the axes of the shafts and the bushes

cannot be misplaced during the exploitation of the product and it is irrelevant

to the value of the interference fit whether it is 3 micrometers or 30

micrometers.

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AA3

A2 A1

A4

3.5 Defining the characteristics of the closing element (accumulator) of a QC

Each element of the QC, including the closing element, is characterised by

three components:

1. Nominal dimension A;

2. Tolerance T or field of variation ;

3. Position of the middle of the tolerance EM.

) Calculation of the nominal dimension ofA

From the examples shown till now for the liner QCs can be seen that the nominal of

the closing element is a sum of the structural elements taken with the corresponding

sign depending on whether they are increasing or decreasing.

,

In general

,

or

,Where: i is the nominal value of i

-th element;

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m number of the increasing elements;

n the total number of the structural elements;

i Ratio, showing the influence of the i-th element onto the

closing element.In this case i could be +1 or -1, respectively for

increasing and decreasing structural element.

In QCs with non parallel elements the task can be resolved

in two ways: 1 By projecting the structural elements onto

the direction of the closing or by projecting of all elements

onto coordinate system.

Example of such QC is shown on the figure above.

b) Calculation of the Tolerance T or the fields of variation .

According to the calculation of the nominal the closing element is afunction of all structural elements of the QC e.g.

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In principle, the tolerances have values which are very small in comparison to the

nominal (e.g. 80-0.03). This allows the deviations within the tolerances to be

presented as small changes of the nominal Ai.

Therefore:

In this case is the ratio and shows the effect of the ith element onto

the closing element of the QC and should be taken as absolutevalue. The design QCs, use the prescribed value of the variation of adimension which is the tolerance Ti. The Manufacturing QCs use thevariation of the processes .

For QCs with parallel elements:

c) Calculating the position of the middle of the tolerance EM.

EM in general or for a specific QC EMA, gives the position of the middle of the

tolerance according to the nominal (see the fig below).

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A

Amin

AmaxEM

A

TA

AA3

A2 A1

A4

Therefore in general

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*********************************************************************

********************

The 3 equations to remember!!!

1.

2.

3.

*********************************************************************************************

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3.6 Tasks to be solved with the QCs:

1. When the characteristics of the closing element are known and

the characteristics of the structural elements are needed Ai, Ti,

Ei. This task usually takes place during the design process.

2. When characteristics of the structural elements are known and the

characteristics of the closing element are needed , , and M .

3.7 Improving the accuracy of the closing element of the chain

To increase the accuracy of the closing element of a QC, means to

reduce the tolerance and the variability of this element. Having in

mind the formulae above, there 3 ways of doing that:

1. Decreasing the fields of variation of the construction elements of

the chain; this is very often applied method but unjustifiable

decrease of the Ti will make the product more expensive and not

sustainable on the market because requires more manufacturing operations

and the production will be more expensive.

2. Decreasing the number of the construction elements in the QC

(n); this is an effective and economically viable method. Example is

given on the fig below.

The accuracy of the closing element in the first variant is guaranteed

by 4 structural elements and in the second with 2 structural elements. If , for example

the ==0,4 mm, the average tolerances of the structural elements will be

respectively for the first variant 0.1 mm and for the second 0.2mm. This means that

the parts in the second variant will have twice the tolerance than the parts in the first

variant (e.g it will be cheaper).

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3. Decreasing the ratio .

This can be achieved by positioning of the structural elements

which have severe contribution to the accuracy of the closing

element on angle close to 90 in relation to the closing

element. Then In design QCs this method has limited

application. It is widely used in the Manufacturing QCs where

the closing element can be made invariant to the errors

brought by some structural elements. The example below

shows the diminished influence of the positioning of the tool on

the turret on a lathe onto the achieved machined diameter.

3.8 Methods for achieving the accuracy required for A

1. Method of full interchangeability;

2. Method of partial interchangeability (probability);

3. Method of group interchangeability (selection);

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4. Method of compensation;

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3.9 Method of full interchangeability

This method applies when is needed 100% guarantee for the parameters of the QC.

It has the following advantages: very easy and economically viable assembly;

additional adjustment and additional work is not needed; fairly low qualification from

the workers is required; good conditions for automation. The major drawback is that

it is required high accuracy and the tolerances of the structural elements are the

smallest compare to the other methods. Thats why it applies only for short QCs with

up to 5 structural elements.

The task for the designers is interesting. For the 3 characteristics of the structural

elements the task is mathematically undetermined as there are 3 equations (for

nominal, tolerance and middle of the tolerance of the closing element) and n

structural elements.

1. Determining of the nominal dimensions of Ai. They have to satisfy the

equation ;

2. Calculation of the tolerances of the structural elements

The problems here can be resolved in two ways:

a) Equal tolerances. It is accepted that all structural elements have the same

tolerance . This is possible only if the nominals of the structural

elements are similar. Additionally tolerances can be adjusted to

satisfy the equation

;

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b) Equal tolerance grades (based on BS EN 20286-1; ISO system)

Empirically it is established that the field of variation of the manufacturing

processes can be described by the following equation:

V=cxd

V the zone of variation

c- proportionality coefficient

d- nominal dimension

The Tolerances are calculated depending on the nominal size and the assumption is

that all structural elements have equal tolerance grades. The solution is based on

the interpretation of the ISO system for the calculation of the tolerance, depending

on the tolerance factor i and the number of the tolerance units .

D=D1D2

The first part 0.453D accounts for the error of the manufacturing process

And the second part 0.001D accounts for the errors in the measuring

D - geometric mean for the standard range

av number of tolerance units which will be equal for all structural elements of the

QC

i- Standard tolerance factor.

All structural elements will have the same tolerance grade

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, or .

If there are known tolerances of standard parts C they have to be taken away

For QC with parallel elements:

c) Calculating of the position of the middle of the tolerance EMi

To avoid the mathematical uncertainty in this case few assumptions are made:

- For the standard elements (bearings, screws etc), the manufacturer EMi are

taken into account;

- For external dimensions (e.g. shafts) it is adopted to use

- For internal dimensions (e.g. holes) it is adopted to use

- For other type of dimensions (e.g. linear dimensions) it is adopted to use

symmetrical tolerance

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EM

EM

A

A

T

A

A3A2

A1

A4

A1 (1) A2 (2) A3 (3) A4 (4) A ()

?

A ()

Then for the closing element it is possible to calculate

REFLECTION:

With this method the quality of A is guaranteed 100% for all extremes of the

structural elements and thats why it is called min-max method

Recommended for the most important quality characteristic of the system

Defence systems

Short Quality Chains (max 5 elements)

CONDITION! to be completely within T ( T )

QUESTION:

What is the probability function of and how this will affect the life performance of

the product?

3.10 Method of partial interchangeability (probability method)

This method is used for longer (n>5) QCs but the sequence of calculations is the

same as with the full interchangeability method (Ai,Ti, EMi). The difference is in the

approach for calculating the tolerances. This method does not cover all extreme

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P %

scrap

0.01 0.10 0.27 1.0 2.0 3.0 4.0 4.5 5.0 10

t 3.89 3.29 3.00 2.57 3.32 2.17 2.05 2.00 1.96 1.65

situations and do not guarantee 100% accuracy of the closing element of the QC but

at the same time the probability of such extreme situations is very low and decreases

with the increase of the number of the elements in the QC. Thats why with this

method is assumed certain percentage scrap but structural elements of the QC have

bigger tolerances.

The structural elements of the QC are regarded as random variables having certain

distribution function. Most often is used normal distribution but its use must be

justified. In the case that the distribution is not normal but there are number of

structural elements with different distribution, the compound distribution of the

closing element will be close to normal distribution.

On the figure below is the mathematical expectation; standard deviation; P -

probable percentage scrap; t - risk factor.

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i

Normal distribution 1/9

Uniform distribution 1/3

Triangular distribution 1/6

To determine the is used a theorem from the probability theory. The variance of a

sum of independent random variables is equal to the sum of variances of the randomvariables. The structural elements of the QC are independent random variables.

From the figure above we can express , than

and from here we can express

In this case we have to consider the distribution functions of the structural elements

which is given by

For QCs with non parallel structural elements we have to include as for each

element is has a constant value.

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For QCs with parallel structural elements and normal distribution (,) the tolerance is

calculated with the following equation:

a) Method of equal tolerances

The average tolerance can be calculated

And for QCs with parallel elements

b) Method of equal tolerance grades (BS EN 20286-1; ISO system)

In this case the difference is only in calculating of av

Using the ISO standard for calculating the tolerance we can calculate:

For QCs with parallel elements

The probability method is very effective with QCs with higher number of structural

elements. This can be demonstrated by the following example:

EXAMPLE:

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AA1

A2 A3 A4

A5

Ac

If we have , , parallel elements, normal distribution i=1/9 and we assume scrap of

0.27% ( 6)

The full interchangeability method will give and the probability method will give ,

which is 3 times more. This means that the structural elements will be manufactured

cheaper and the probability of scrap is only 0.27% .

REFLECTION:

With this method the quality of A is NOT guaranteed 100%

Recommended for the majority of the QCs

Quality Chains with more than 5 elements (n>5)

CONDITION to be completely within T ( T )

To remember and

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EM

EM

A

A

T

QUESTION:

What is the probability, all structural elements to come with their extremes (all

increasing in their max and all decreasing in their min values or vice versa) for a QC

with 9 structural elements?

3.11 Method of the group interchangeability

This method applies for very short QCs where extremely high

accuracy is required and its achieving is either technologically

impossible or economically not viable to achieve (examples

bearings, fuel injection pumps etc.) Calculated using full

interchangeability method tolerances Ti are increased ktimes so that

the new tolerances are technologically possible or economically

viable. After machining, the parts are measured 100% and partsaccording to the dimensions achieved are split in kgroups. Parts are

assembled only from the same groups.

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This method is applicable when the following conditions are

considered:

1. Quality of the assemblies in all groups should be the same

otherwise the assemblies will have different performance. Most

often this method is used for QC with 3 elements, 2 structural

and one closing. The tolerances of the two structural elements

must be equal. On the figure above are given the tolerances of

the two structural elements TA and Tar and the extended k times

tolerances and . Let Ji denotes the average clearance in the ith

group. Equal quality will be achieved if :

According to the figure above:

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-------------------------

Therefore:

Initial condition of the method was k2

Therefore:

or

QCs with more than 3 elements requiring this method can be

transferred into 3 elements QC if we combine all increasing

elements into one and all decreasing element into one element.

For example we can show guaranteeing the clearance in a ball bearing

shown on the figure below. A1 and A3 are the diameters of the internal and

the external rings; A2 and A4 and the diameters of the balls. Lets assume

that we have to guarantee clearance of. In this case the only increasing

element is A1 and it is the most difficult to manufacture. Let give to

this element a tolerance of . This way already half of the tolerance of

the closing element is gone. The 5 micrometers left have to be

distributed among the decreasing elements . The balls have more

accurate manufacturing process and they will have . For the

tolerance of the internal ring we have left. This means that the two

tracks on the internal and the external rings will be manufacturedwith different tolerances.

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2. Distribution functions of the extended tolerances must be the

same otherwise the groups will have different number ofproduced parts which cannot be assembled. On the figure

below this is demonstrated where the amount of produced

parts which cannot be assembled is proportional to the

hatched area.

3. Number of the groups kshould be kept to a minimum and must not

exceed 3-5 as the efficiency of the method decreases.

4. Tolerances for the shape and position should not be extended and

kept according to Ti as they will affect the final accuracy of the closing

element of the QC.

5. Parts need to be measured 100% and stored separate.

3.12 Method of compensation

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This method applies as an alternative of the method of the partial

interchangeability, when the latter cannot guarantee the accuracy of the closingelement of the QC. With this method is possible to guarantee high accuracy of

the closing element but decision to apply this method should be taken early at the

design stage. In the design of the product is included a special element called a

compensator. And through change of its dimensions the final accuracy is

achieved. Some of the calculated tolerances using the probability method still

may not be economically viable Ti and they are extended to economically viable

tolerances .

Then the new closing element tolerance will be: . The difference is called

tolerance for compensating and should be covered by the special new element

the compensator.

Apart from the possibility of producing the parts more economically viable

(sustainable) this methods allows in the process of exploitation of the product the

accuracy of the closing element to be recovered after certain time. The method

has few possible realisations depending on the type of the compensator element:

fixed, adjustable, deformable, automatic (self adjustable).

On the figure below are shown two examples of fixed and adjustable

compensator. The advantage in the latter case is that the accuracy can be

restored without disassembling the unit. Typical example for this is adjusting the

clearance in the valves in the internal combustion engines.

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c

B

B

BB Bc

Calculations for a fixed compensator.

The tolerance for compensating is splint into N groups. In each group should be

compensated tolerance within -com, where Tcom is the tolerance of the

compensator itself and not to be mixed with the tolerance for compensating Tk.

Tcom should be much smaller than Tk.

It is necessary to calculate the number of the groups N and the dimensions Aki of

the compensators in each group. The dependencies can be derived from the

figure given below:

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From here we can calculate the number of the groups needed

N

According to the above formula, the smaller the Tcom is the les

groups will be used. The number of the needed compensators in

each group will be determined according to the distribution

function of A. When compensating for long QCs it is very likely

that this will be normal distribution.

Calculations for a number of equal fixed compensators

(shims)

This method is widely spread as it uses cheap compensators. The thickness of

the compensator has to be equal (the best) or proportional to the

not considering the Tcom, , where (integer).

Here also is very important how to determine the nominal

dimension of the first compensator (all the rest will be equal). In

this case is need to be produced a special part. It would be the

best if the Ak1 is:

The number of the compensators (shims) are determined similarly tothe number of the compensator groups with a fixed compensatorelement.

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In practice N is not calculated but the approach is similar to the

adjustable compensator where the dimension A is measured and

compensated till within the allowable range.

Compensating with deformable compensator

Deformation can be elastic and plastic.

In the first case springs are used and the deformable length of the spring should

cover for the tolerance to be compensated and the min force on the spring should

be bigger than the working force in the assembly.

As a plastically deformable compensator usually are used soft

materials like copper, aluminium, plastics. Example of such

compensator is shown on the figure below.

Major advantage of this method is that it is quick, there is no

need of special compensators to be manufactured, there is no

need of any measurements, and can work well in automatic

assemblies. The drawback is that if the unit is disassembled it will

require fresh deformable compensator.

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4. Put all this to practice

Tasks:

1. Create QCs for all shafts guaranteeing a clearance in the bearings (3 QCs)

2. Create QCs guaranteeing clearance in all gear engagements (2 QCs)

3. Create QCs guaranteeing gears not to touch inside of the gear box ( (2QCs)

4. Create QCs guaranteeing keys not to be out of the gear hubs (2 QCs)

5. Create QCs for mismatch of the gears (aligning of the gears) (2QCs)

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Some examples of QCs

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5. Classification of the parts surfaces

After the conceptual design where the structure of the new product will be

created as shown on the figure below, the next step is to go through strength and

rigidity calculations which will allow calculating the initial nominal dimensions ofthe new product. At this stage is clarified the shapes and dimensions of the most

of the parts involved. The shape of the parts surfaces should reflect their

function, as the aim is to use the simplest possible shapes.

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QUESTION:

During the Detailed design stage, when dimensioning the parts, does it matter which

dimensions will be given on the detailed drawing?

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Based on the QCs theory now we can extract rules for classification of the surfaces

and dimensioning of the parts.

Analysis of different products and systems show that according to its function, parts

surfaces can be classified as follows:

1. Main Datums (MD) number of surfaces which determine the position of the

part in the product or system;

2. Auxiliary Datums (AD) - number of surfaces which determine the position of

other parts according to the regarded part;

3. Working surfaces (WS) number of surfaces through which the regarded part

does its function;

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MD MD

CS WS

AD CS AD

WS CS

AD

4. Connecting surfaces (CS) number of surfaces which connect the first 3

types of surfaces, ensuring the needed distances and rigidity of the part.

On the figure below is given an example of the above classification.

5.1 Method of dimensioning of the parts:

There is no problem with dimensioning diameters and distance between axes as

their nominal are calculated from strength and rigidity calculations as well as

kinematic accuracy and their tolerances are calculated from the Design QCs.

The problem is with functional linear dimensions. There are different variants due

to different considerations and different approaches.

The most rational and technologically correct should be considered this solution

which can guarantee the functionality of the designed product or system with the

biggest possible tolerances given to the parts. This will be also the most

sustainable solution as it will guarantee the functionality of the product at the

minimum price.

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On that ground and on the basis of the above classification of the parts surfaces

and the QCs theory, can be formulated the following algorithm for dimensioning

of the parts.

1. Clarify the functionality of the product or unit, the role of each part in it and the

quality criteria of the product which this part is involve in.

2. Determine the design datum of the product or unit in the selected direction

(the products are 3D!)

3. Clarified the role of each part in the designed product or system;

4. Select the Main Datum of the part in this direction.

5. Give dimensions from the MD to the ADs

6. WS are dimensioned to the closest MD or AD

7. Give dimensions to the own lengths of the MDs

8. Give dimensions to the own lengths of the ADs

9. Give dimensions to the own lengths of the WSs

This algorithm is applied for axial dimensioning of the shaft from the figure above.

These dimensions are sufficient for the functional dimensioning of the shaft. The

dimension A12 is given in brackets meaning for information, but can be omitted. As it

is seen from this dimensioning, only the connecting surfaces are not given with their

own lengths.

When dimensioning using the above algorithm, there is a hesitation which dimension

to be given, the best criteria would be the QCs theory. It should be given the

dimension which has smaller tolerance calculated according to the above described

methods.

This method for linear dimensioning of the parts assigns dimensions based on the

functionality of the part and it is expected that if two parts have the same geometry

but different functions in two different products, they will be dimensioned differently.

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The method guarantees the biggest possible tolerances for the assigned

dimensions, which will reflect in the cost of the manufacturing of those parts.

Dimensioning of the parts according to the above algorithm also guarantees better

and cheaper manufacturing not only because of the biggest tolerances assigned to

the dimensions but also because it gives much less problems associated with stack

up tolerances and process planning which will be demonstrated in the next chapter.

Sustainable Manufacturing

1. What is manufacturing?

Manufacturingis the use ofmachines,toolsand labour to produce goods for use or

sale. The term may refer to a range of human activity, from handicraft to high tech, but is

most commonly applied toindustrial production, in whichraw materials are transformed

into finished goodson a large scale. Such finished goods may be used for manufacturing

other, more complex products, such as aircraft,household appliances orautomobiles, or

sold to wholesalers, who in turn sell them to retailers, who then sell them to end users the

"consumers".

Manufacturing takes turns under all types ofeconomic systems. In a free market economy,

manufacturing is usually directed toward the mass production of productsfor saleto consumers at a profit. In acollectivist economy, manufacturing is more frequently directed

by the state to supply a centrally planned economy. In free market economies,

manufacturing occurs under some degree of government regulation.

Modern manufacturing includes all intermediate processes required for the production and

integration of a product' components. Some industries, such as

semiconductorand steelmanufacturers use the term fabrication instead.

The manufacturing sector is closely connected with engineering andindustrial design.

Examples of major manufacturers in theNorth America include General Motors

Corporation,General Electric, and Pfizer. Examples in Europe include Volkswagen

Group, Siemens, and Michelin. Examples in Asia include Toyota, Samsung,

andBridgestone.

2. Economics of Manufacturing

According to some economists, manufacturing is a wealth-producing sector of an economy,

whereas a service sector tends to be wealth-consuming.Emerging technologies have

provided some new growth in advanced manufacturing employment opportunities in the

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Manufacturing Belt in the United States. Manufacturing provides important material support

for nationalinfrastructure and fornational defence.

On the other hand, most manufacturing may involve significant social and environmental

costs. The clean-up costs ofhazardous waste, for example, may outweigh the benefits of a

product that creates it. Hazardous materials may expose workersto health risks. Developed

countries regulate manufacturing activity with labour laws and environmental laws. In

the U.S, manufacturers are subject to regulations by the Occupational Safety and Health

Administration and the United States Environmental Protection Agency. In Europe, pollution

taxes to offset environmental costs are another form of regulation on manufacturing

activity. Labour Unions and craft guilds have played a historic role negotiation of worker

rights and wages. Environment laws and labour protections that are available in developed

nations may not be available in thethird world. Tort law and product liability imposeadditional costs on manufacturing.

Manufacturing requires huge amounts offossil fuels. The construction of a single car in the

United States requires, on average, at least 20 barrels of oil.

3. The Key Role of Sustainable Manufacturing in Achieving Sustainable

Development

The main enabler of global sustainable development is a new paradigm: competitive

sustainable manufacturing. Therefore, sustainable manufacturing is explored from

different aspects which encompass products and services, processes and business

models.

In order to have a comprehensive approach towards examining the sustainable

manufacturing, three main levels need to be considered. Those three levels were

defined by Jovane at al (2008, p.646-647) and are discussed below:

Macro: macro economics.

Meso: production and consumption paradigms.

Field level: products/services, processes, business models.

Sustainability at the macro level is concerned with a global strategy to protect the

environment while economical development improves social life. It is at this level

where sets of indicators have been developed at international level to monitor the

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Sustainable Design and Manufacturing