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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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Obj185
Obj186
Obj187Obj188
Obj189
Obj190
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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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