presentation general design

8/14/2019 Presentation General Design

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Machine Design

UET, Taxila

Lecture: Introduction to Design &Uncertainty


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1- General Design

To design is either to formulate a planfor the satisfaction of a specified needor to solve a problem.

The designed product must be functional,safe, reliable, competitive, usable,could be manufactured, and

marketable.


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Design is an original, cyclic and adecision-making process.

(e.g. Screw Jack)

Decisions sometimes have to be madewith too little information, occasionally

with just the right amount ofinformation, or with an excess ofpartially contradictory information.


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Decisions are sometimes madetentatively (uncertainly), with the rightreserved to adjust as more informationbecomes known.

The point is that the engineeringdesigner has to be personally familiar

with a decision-making, problem-solving role.


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Design is a communication-intensiveactivity in which: both words andpictures are used, and written and oralforms are employed.

Engineers have to communicateeffectively and work with people of

many disciplines. These are importantskills, and the engineers success willdepend on them.


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A designers personal resourcesof creativeness, communicativeability, and problem solving

skills are intertwined withknowledge of technology andfirst principles.


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Engineering tools (such as mathematics,

statistics, computers, graphics, andlanguages) are combined to produce a planthat, when carried out, produces a product

that is functional, safe, reliable, competitive,usable, manufacturable, and marketable,regardless of who builds it or who uses it.


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2- Mechanical Engineering Design

Mechanical engineers areassociated with the productionand processing of energy and

with providing the means ofproduction, the tools oftransportation, and thetechniques of automation.


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The skill and knowledge base areextensive.

Among the disciplinary bases aremechanics of solids and fluids, massand momentum transport,manufacturing processes, electricalengineering & management.

Mechanical engineering design involvesall the disciplines of mechanicalengineering.


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Real problems needs the knowledge ofmany areas.

A simplejournal bearing involves fluidflow, heat transfer, friction, energytransport, material selection, thermo-mechanical treatments, statisticaldescriptions, and so on.


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Similarly, internal-combustion enginedesign, turbo-machinery design, andjet-engine design are sometimesconsidered distinct entities.

Here, the leading string of wordspreceding the word design is merely aproduct descriptor.


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Also, there are phrases such asmachine design, machine-elementdesign, machine-component design,systems design, and fluid-power

design. All of these phrases aresomewhat more focused examples ofmechanical engineering design.


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They all draw on the same bodiesof knowledge, are similarlyorganized, and require similar

skills. The complete design process,from start to finish, is often

outlined as in Fig. 1.


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The phases in design, acknowledging the

many feedbacks and revisions (Fig. 1).


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The process begins with anidentification of a need and a decisionto do something about it.

After many iterations (repetitive andrevisions), the process ends with thepresentation of the plans for satisfying

the need.


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Depending on the nature of the designtask, several design phases may berepeated throughout the life of theproduct, from setting up to

termination. In the next several subsections, we

shall examine these steps in the design

process in detail.


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A- Identification of need

generally starts the design process.

Detection of the need and phrasing theneed often constitute a highly creativeact, because the need may be

only unclear dis-satisfaction, a feelingof un-easiness, or a sensing thatsomething is not right.


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The need is often not evident at all;identification is usually triggered by aparticular unfavourable circumstance ora set of random circumstances that

arises almost simultaneously.


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For example, the need to do somethingabout a food-packaging machine maybe indicated by:

the noise level,

by a variation in package weight, and

by slight but observable variations inthe quality of the packaging or wrap.


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B- Design Considerations

Sometimes the strength required of anelement in a system is an importantfactor in the determination of thegeometry and the dimensions of the

element. In such a situation we say that strength

is an important design consideration.


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When we use the expression designconsideration, we are referring to somecharacteristic that influences the designof the element or, perhaps, the entire

system.


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Usually quite a number of suchcharacteristics must be considered andordered in priority in a given designsituation. Many of the important ones

are as follows (not necessarily in orderof importance):

1 Functionality

2 Strength/stress

3 Distortion/deflection/stiffness


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4 Wear

5 Corrosion

6 Safety

7 Reliability8 Manufacturability

9 Utility (usefulness, effectiveness &

Convenience)10 Cost


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11 Friction (energy)

12 Weight

13 Life recovery

14 Noise

15 Styling

16 Shape

17 Size


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18 Control

19 Thermal properties

20 Surface

21 Lubrication22 Marketability

23 Maintenance

24 Volume25 Liability

26 Remanufacturing/resource


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Some of these characteristics have to do

directly related with the: dimensions, the material, the processing, and thejoining of the elements of the system.

Several characteristics may be inter-related, which affects the configurationof the total system.

The Design Engineers Professional


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The Design Engineer s Professional

Responsibilities

In general, the design engineeris required to:

satisfy the needs of customers(management, clients,consumers, etc.)

and is expected to do so in acompetent, responsible, ethical,and professional manner.


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Much of engineering coursework and practical experiencefocuses on competence, butwhen does one begin to develop

engineering responsibility andprofessionalism? To start on theroad to success, you should

start to develop thesecharacteristics early in youreducational program.


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You need to cultivateyour professional workethic and process skills

before graduation, so thatwhen you begin yourformal engineering career,

you will be prepared tomeet the challenges.


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You can start to develop yourcommunication skills by keeping a neatand clear logbook of your activities,entering dated entries frequently.

(Many companies require theirengineers to keep a logbook for patentand liability concerns.) Separate

logbooks should be used for eachdesign project (or course subject).


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When starting a project or problem, inthe definition stage, make logbookentries quite frequently. Others, as wellas yourself, may later question why

you made certain decisions.Good chronological records will make iteasier to explain your decisions at a

later date.


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Many engineering students expectthemselves after graduation aspracticing engineers for designing,developing, and analyzing products and

processes. However, they consider the need of

good communication skills, either oral

or writing, as secondary. This is farfrom the truth.


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Most practicing engineers spend a gooddeal of time communicating withothers, writing proposals and technicalreports, and giving presentations and

interacting with engineering and non-engineering support personnel.


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You have the time now to sharpen

your communication skills. When givenan assignment to write or make anypresentation, technical ornon-

technical, accept it actively, and workon improving your communicationskills.

It will be time well spent to learn theskills now rather than on the job.


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When you are working on a designproblem, it is important that youdevelop a systematic approach.

Careful attention to the following actionsteps will help you to organize yoursolution processing technique.


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Understand the problem

Problem definition is probably the mostsignificant step in the engineeringdesign process. Carefully collect allinformation from all involved persons.

After that: read, understand, and refinethe problem statement.


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Identify the known

From the refined problem statement,describe concisely what information isknown and relevant.

Identify the unknown and formulate the


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Identify the unknown and formulate the

solution strategy

State what must be determined, in whatorder, so as to arrive at a solution tothe problem


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Sketch the component or system underinvestigation, identifying known andunknown parameters.

Create a flowchart of the steps

necessary to reach the final solution.


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The steps may require the use of free-body diagrams; material propertiesfrom tables; equations etc. from firstprinciples, textbooks, or handbooks

relating the known and unknownparameters; experimentally ornumerically based charts; specific

computational tools


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State all assumptions and decisions

Real design problems generally do nothave unique, ideal, closed-formsolutions.

Selections, such as choice of materials,

and heat treatments, require decisions. Analyses require assumptions related

to the modelling of the real

components or system. All assumptions and decisions should

be identified and recorded.


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Analyze the problem

Using your solution strategy in

conjunction with your decisions andassumptions, execute the analysis ofthe problem.

Reference the sources of allequations, tables, charts, softwareresults, etc. Check the reliability of

your results. Check the order of magnitude,

dimensionality, trends, signs, etc.


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Evaluate your solution

Evaluate each step in the solution,

noting how changes in strategy,decisions, assumptions, and executionmight change the results, in positive

or negative ways.

If possible, incorporate the positivechanges in your final solution.


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Present your solution

Here is where your communication

skills are important. At this point, you are selling yourself

and your technical abilities. If you

cannot capable of explaining what youhave done, some or all of your workmay be misunderstood and

unaccepted.

Know your audience.


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As stated earlier, all design processes

are interactive and iterative. Thus, itmay be necessary to repeat some or allof the above steps more than once if

less than satisfactory results areobtained.


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In order to be effective, all

professionals must keep current in theirfields of enterprise.


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attending meetings, conferences, and

seminars of societies, manufacturers,universities, etc.; taking specificgraduate courses or programs at

universities; regularly reading technicaland professional journals; etc.


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An engineers education does not end

at graduation.


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To give the utmost of performance;

To participate in none but honestenterprise;

To live and work according to the lawsup to the highest standards of

professional conduct;


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To place service before profit, the

honour and standing of the professionbefore personal advantage, and thepublic welfare above all other

considerations.

In humility and with need for Gods

Guidance, I make this pledge.

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