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Nature of Mechanical Machine Design - Mechanical Engineering ...

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Adoptive <strong>Design</strong>• Adoptive design is the use <strong>of</strong> existing/knownscientific principles and technical information fordevelopment <strong>of</strong> systems or device with suitablemodifications/changes. Very <strong>of</strong>ten only minoralterations or modifications are made in the existingdesigns (based on the feed back from manufacturing,service or marketing departments). This type <strong>of</strong>design needs no special knowledge or skill andattended by first level designers with ordinarytechnical training.UPRM –Spring 2005 INME 4011 - Lecture 1 3


Development <strong>Design</strong>• This type <strong>of</strong> design involve modifying anexisting design into a new product withappropriate changes in size, shape, form,material, power range etc. This requiresconsiderable scientific training and designability.UPRM –Spring 2005 INME 4011 - Lecture 1 4


Creative design• Creative design on the other hand is development <strong>of</strong>an unusual or novel solution to meet an exiting need.Very <strong>of</strong>ten it results in or needs further scientificunderstanding. This type <strong>of</strong> design needs creativethinking, higher technical ability and can beattempted by only experienced designers who havepersonal qualities <strong>of</strong> sufficiently high order.UPRM –Spring 2005 INME 4011 - Lecture 1 5


What is <strong>Machine</strong> <strong>Design</strong>• <strong>Machine</strong> design is one aspect <strong>of</strong>engineering design. The ultimate goal inmachine design is to size and shape theparts (machine elements) and chooseappropriate materials and manufacturingprocesses so that the resulting machinecan be expected to perform its intendedfunction without failure.UPRM –Spring 2005 INME 4011 - Lecture 1 6


<strong>Machine</strong> Element <strong>Design</strong>• This course on machine element design is first basic course in‘real engineering’ and primarily concerned with the basicscientific principles related to design and analysis <strong>of</strong> commonmachine elements and devices or more specifically generalpurposecomponents or elements <strong>of</strong> a machine or mechanicaldevice.• General-purpose elements: Components/elements <strong>of</strong> various(kinds) machines, which are identical in shape or geometryand carry out same or similar function. Example: Shafts,bearings, springs, fasteners, gears brakes, clutches etc.• <strong>Machine</strong> is a combination <strong>of</strong> certain general purpose andspecial purpose elements which can transmit power (ormotion) in a controlled manner and which is capable <strong>of</strong>performing some useful work or task.UPRM –Spring 2005 INME 4011 - Lecture 1 7


<strong>Nature</strong> <strong>of</strong> <strong>Machine</strong> Element <strong>Design</strong>• To design machine element and deices, youmust be competent in the design <strong>of</strong> individualelements that comprise the system. But youmust also be able to integrate severalcomponents and devices into a coordinated,robust system that meets your customer’s need.• <strong>Design</strong> <strong>of</strong> machine elements is an integral part<strong>of</strong> the larger and more general field <strong>of</strong>mechanical design. <strong>Design</strong>s and designengineering create devices or systems to satisfyspecific needs.UPRM –Spring 2005 INME 4011 - Lecture 1 8


<strong>Nature</strong> <strong>of</strong> <strong>Machine</strong> Element <strong>Design</strong> - Iteration• At the initial stages <strong>of</strong> machine design, we face a dilemma. Thedesigner can not predict with accuracy what environmental loads theuser will subject the machine to. The dilemma can be resolved onlyby iteration, which means to repeat, or to return to a previous state.We must assume some trial configuration for each part; use the massproperties <strong>of</strong> that trial configuration in dynamic force analysis todetermine the forces, moments, and torques acting on the part, andthen use the cross-sectional geometry <strong>of</strong> the trial design to calculatethe resulting stresses.• Most likely, on the first trial, we will find that our design failsbecause the materials cannot stand the levels <strong>of</strong> stresses presented.We must then redesign the part by changing shapes, size, materials,manufacturing processes, or other factors in order to reach anacceptable design. It is generally not possible to achieve a successfulresult without making several iterations through this design process.UPRM –Spring 2005 INME 4011 - Lecture 1 9


A <strong>Design</strong> Process1. Identification <strong>of</strong> need– The chief objective <strong>of</strong> an enterprise that produces a product is to satisfythe customer. It is essential that you know your customers’ desiresbefore beginning a product design2. Background research– background information is necessary to fully define and understand theproblem.3. Goal statement– after background research it is possible to restate the goal in a morereasonable and realistic way than in the original problem statement.4. Task specification– task specification bound the problem and limit its scope5. Synthesis– as many alternative possible design approaches are sought, usuallywithout regard for their values or quality. In this step, the largestpossible number <strong>of</strong> creative solutions are generated.UPRM –Spring 2005 INME 4011 - Lecture 1 10


A <strong>Design</strong> Process6. Analysis– the possible solution from the previous step are analyzed and eitheraccepted, rejected, or modified.7. Selection– the most promising solution is selected.8. Detailed design– once an acceptable design is selected, the detailed design can be donein which all the loose end are tied up, complete engineering drawingmade, manufacturing specification defined etc.9. Prototyping and testing– the actual construction <strong>of</strong> the working design is first done as a prototype10. Production– finally in quantity in productin• note that iteration is require within the entire process, moving anystep back to any previous step, in all possible conbmbinations, anddoing this repeatedly.UPRM –Spring 2005 INME 4011 - Lecture 1 11


Standards and Standardization• Once upon a time there were no standards or even uniformity among the sameproducts, for example, bolts, nuts and screw threads. Finding a replacement was notan easy task. This lack <strong>of</strong> standards and uniformity was costly and ineffective for agreat variety <strong>of</strong> reasons.• Standardization is the term applied to the obligatory norms to which variousindices <strong>of</strong> a product should correspond. These indices are types, grades, parameters(dimensions), and quality characteristics, test methods, rules <strong>of</strong> marking, packingand storage <strong>of</strong> products, raw materials and semi-manufactured goods.• Standardisation is the key to ‘cost effectiveness’ and ‘quality’. Standardisations <strong>of</strong>specifications for machine elements promote their quality and increase their servicelife. It curtails the time needed for their designing, quickens their entry into serviceand simplifies repairs as new standard ones easily replace worn or damaged parts.• An important feature <strong>of</strong> standardization, in present day mechanical engineering isthe principle <strong>of</strong> interchangeability without which lot and mass production isimpossible.UPRM –Spring 2005 INME 4011 - Lecture 1 12


Standards and Codes• A standard is a set <strong>of</strong> specifications for part, materials, or processesintended to achieve uniformity, efficiency and a specified quality. One <strong>of</strong>the important purposes <strong>of</strong> a standard is to place a limit on the number <strong>of</strong>items in the specifications so as to provide a reasonable inventory <strong>of</strong>tooling, sizes, shapes and varieties.• Code: A code is a set <strong>of</strong> specifications for the analysis, design,manufacture and construction <strong>of</strong> something. The purpose <strong>of</strong> a code is toachieve a specified degree <strong>of</strong> safety, efficiency, and performance or quality.• Interchangeability is the property <strong>of</strong> machine parts or units making itpossible to utilize them in assembly (or replace them during repair/service)without any additional machining (fitting) while preserving the technicalrequirements for the given unit, mechanism or machine functioning.• For parts to be interchangeable their dimensions need not ideally coincide.It is enough that the actual size <strong>of</strong> each part lies within the assigned limits.UPRM –Spring 2005 INME 4011 - Lecture 1 13


Standards and Codes• In mechanical engineering the following is standardized:– <strong>Design</strong>ation <strong>of</strong> general engineering quantities, rules forconstruction <strong>of</strong> drawings; series <strong>of</strong> numbers applied to lineardimensions.– Structural elements <strong>of</strong> the majority <strong>of</strong> machine components, bar,beams, angle, channels, plates rounds etc.– Accuracy (Fits and tolerances) and surface finish <strong>of</strong> parts.– Materials, their chemical compositions, basic mechanicalproperties and heat treatment– Shape, size <strong>of</strong> most common parts and units: bolts, screws,studs, nuts, washers, cotton pins, rivets, dowels, keys, forms anddimensions <strong>of</strong> spline joints etc.– Belts chains, diameter and width <strong>of</strong> pulleys; couplings andclutches and antifriction bearings. Modules <strong>of</strong> gears and wormwheels etc.UPRM –Spring 2005 INME 4011 - Lecture 1 14


Engineer’s Responsibility• Essence <strong>of</strong> machine design is to define and calculate motions,forces, and changes in energy in order to determine the size, shape,and materials needed for each <strong>of</strong> machine element.• Engineer’s responsibility is to calculate and predict the mode andconditions <strong>of</strong> failure for each element and then design it to preventthat failure.• A good design engineer would provide a foolpro<strong>of</strong> solution to aproblem, obtained at an economical cost and comprising <strong>of</strong>minimum number <strong>of</strong> parts. To be a successful designer, theengineer must use the best available scientific understandingtogether with empirical information, a good judgement and <strong>of</strong>ten adegree <strong>of</strong> imagination or ingenuity. Then only best products suitableto a welfare society and marketable in a competitive economy couldbe turned out.UPRM –Spring 2005 INME 4011 - Lecture 1 15


The Criteria for Evaluating <strong>Machine</strong> <strong>Design</strong> Decisions• In approaching a design, the designer should establish criteria that will guide thedecision-making processes inherent in any project. Because each design problemhas many alternative solutions, each can be evaluated in terms <strong>of</strong> the list <strong>of</strong> criteria.There may not be a single best design, but designers should work toward anoptimum design, that is design should maximize benefits and minimizedisadvantages. The following are general criteria for machine design– Safety– Performance (the degree to which the design meets or exceeds the design objectives)– Reliability (a high probability that the device will reach or exceed its design life)– Ease <strong>of</strong> manufacture– Ease <strong>of</strong> service or replacement <strong>of</strong> components– Ease <strong>of</strong> operation– Low initial cost– Low operating and maintenance costs– Small size and low weight– Low noise and vibration, smooth operation– Use <strong>of</strong> readily available materials and purchased components– Prudent use <strong>of</strong> both uniquely designed parts and commercially available components– Appearance that is attractive and appropriate to the application.UPRM –Spring 2005 INME 4011 - Lecture 1 16


Skills Needed in <strong>Machine</strong> <strong>Design</strong>• technical drawing and CAD• properties <strong>of</strong> materials• manufacturing processes• statics, dynamics, and strength <strong>of</strong> materials• kinematics and mechanismsBuilding on these skills, and using this book, youshould now be ready to learn design <strong>of</strong> machineelement and mechanical design.UPRM –Spring 2005 INME 4011 - Lecture 1 17

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