Chapter01-Introduction-机械零件设计英文全套教案课件

1、Design of Machine ElementsDesign of Machine ElementsChapter 1 IntroductionThe Meaning of DesignEngineeringMechanical EngineeringDesignMachine design Chapter 1 IntroductionEngineering is concerned with the conversion of energy from one form to another with the objective of extracting useful work.Mech

2、anical engineering has the more specific objective of designing machinery to this purpose in the most suitable manner possible.“Engineering” is the art of directing the great sources of power in nature for the use and convenience of human beings / utilizing the existing resources and natural law to

3、benefit humanityEngineering is concerned with Chapter01-Introduction-机械零件设计英文全套教案课件Chapter01-Introduction-机械零件设计英文全套教案课件1) Definition of Machine A machine is a combination of mechanisms and other components that transforms, transmits, or uses energy, load, or motion for a specific purpose.A machine

4、is a combination of components which can transmit power in a controlled manner by converting energy from one form to another and eventually producing useful work.1) Definition of Machine A mIn terms of basic manufacturing unit, a machine is composed by machine elements/components.In terms of the fun

5、ctions of the sub-system of a machine, it is comprised of the source-power, transmission, execution and control/manipulation parts.For the convenience of kinematic or dynamic analysis of a machine, a machine can be decomposed into mechanisms.2) Composition of MachineIn terms of basic manufacturin3)

6、Classification of Machine ElementsNormal load transmitter: sliding bearings, rolling-element bearingsTorque tramsmitter: gears, traction drives, chain drives, belt drives, power screwsEnergy absorber: brakes and dampersSupporting elements: shafts, springs, sealsConnection and joints: thread fastener

7、s, keys, couplings3) Classification of Machine E2. Machine Design A Discipline-blending Human EndeavorMachine design involves many decision-making, including engineering ones and non-engineering ones.Engineering decisions: loading, kinematics, materials; strength, reliability, deformation, tribology

8、, space, weight, etc.Non-engineering decisions: cost, marketability, product liability, ethics, politics, etc. 2. Machine Design A DiscipliFundamental Design Considerations1 Strength 2 Reliability 3 Thermal effect4 Corrosion 5 Wear 6 Friction 7 Processing 8 Utility 9 Cost 10 Safety 11 Weight 12 Nois

9、e13 Styling 14 Shape 15 Size16 Flexibility 17 Control 18 Stiffness19 Surface finish 20 Lubrication 21 Maintenance22 VolumeFundamental Design Considerati3. Basic Requirements for Machine DesignEconomics and functionality are always pressing concerns, and good design inherently means safe, economical,

10、 and functional design.A primary responsibility of any mechanical designer is to ensure that the proposed design will function as intended, safely and reliably,for the prescribed design lifetime and, at the same time, compete successfully in the marketplace.3. Basic Requirements for Mac1) Functional

11、 Requirements The machine to be designed should fulfill specified functions. This requires:Fundamental decisions regarding loading, kinematics, and the choice of materials must be made properly during the design of a machine. Besides, strength, reliability, deformation, tribology (friction, wear, an

12、d lubrication), also need to be considered.1) Functional Requirements The2) Economic DemandsThe objective is to produce a machine that not only is to function properly for a reasonable time but is also economically feasible.The economic requirements need to be addressed over the entire life circle o

13、f design, manufacturing and operation of the product.2) Economic DemandsThe objecti3) Other Demands Safety and space requirements, convenience in transportation also need to be considered. Nonengineering decisions regarding marketability, product liability, ethics, politics, etc., must be integrated

14、 into the design process early. 3) Other Demands Safety and s4. Contents and Purpose of the CourseFundamental design principles of various machine elements.Even the design of a single bolt or spring needs the designers thorough understanding of the principles and methods of machinery design and more

15、. Master the basic knowledge, methods and procedures and gain the competence in applying them into practical design.4. Contents and Purpose of theOther Purposes Develop competence of creative design and solving practical problemMechanical system design requires considerable flexibility and creativit

16、y to obtain good solutions. Creativity seems to be aided by familiarity with known successful designs of related systems, components or elements. Other Purposes Develop competeGeneral Procedure of Machine Design1) Recognition of the need, market analysis, specification; 2) Definition of the problem

17、(original concept), conceptual design.3) Synthesis, design analysis and optimization, (detail design)4) Production drawings5) Evaluation and presentationGeneral Procedure of Machine Two Approaches of Machine DesignTwo Approaches of Machine DesiConceptual design of configuration 1) Suggest feasible c

18、onfigurations and alternatives 2) Analyse and synthesize them by decomposing the consisting units, evaluate their functional parameters and other requirements. Detailed technical design 1) Complete a number of assembly and component drawings which reflect detailed design by presenting structural det

19、ails, materials, geometric/dimensional tolerances. 2) Complete design calculations and detailed technical documents.Conceptual design of configuraSuggestionsDesign engineers can no longer work alone and must participate in group discussions and design reviews. They need good communications skills. D

20、esign engineers cannot merely focus on their discipline and rely on experts for the rest. They need to know other disciplines, at least from a linguistics standpoint. Improve your presentation skills.SuggestionsDesign engineers ca1) Selecting a suitable type of machine element from consideration of

21、its function2) Estimating the size of the machine element that is likely to be satisfactory3) Evaluating the machine elements performance against the requirements4) And then modifying the design and the dimensions until the performance is near to whichever optimum is considered most important5. Desi

22、gn of Machine Element5. Design of Machine Element1) About the First Two StepsRequire some creative decisions, represent the most difficult part of designAfter a suitable type of machine element has been selected for the required function, the specific machine element is designed by analyzing kinemat

23、ics, load, and stress coupled with proper material selection enable a stress-strain-strength evaluation in terms of a safety factor 1) About the First Two StepsRe2) Failure Prevention the Basis for Successful Design of Machine ElementDesigner must have a good working knowledge of analytical and/or e

24、mpirical techniques for predicting potential failures at the design stage.These predictions must then be transformed into selection of a material, determination of a shape, and establishment of the dimensions for each part to ensure safe, reliable operation throughout the design lifetime. 2) Failure

25、 Prevention the Ba Improper functioning of a machine or machine part constitutes failure.When it becomes completely inoperableWhen it is still operable but is unable to perform its intended function satisfactorilyWhen serious deterioration has made it unreliable or unsafe for continued use.3) Failur

26、e of Machine Elements Improper functioning of a mac4) Failure ModesFailure of a machine part might be brought about by any one or a combination of many different responses to loads and environments while in service.Force and/or temperature induced elastic deformationYielding plastic deformation Brit

27、tle fracture; fatigue fracture Surface failureWear, Fatigue, Galling, Seizure, ductile rupture, Creep, Brinnelling, Corrosion, spalling, Fretting Violation of its intended functionoverall slip of belt, Buckling of spring 4) Failure ModesFailure of a mFailure Modes of a ShaftFatigue fracture/ for com

28、mon shaftExcessive elastic deformation/ for precision shaft Resonant vibration / for rotating shaft at high speedFailure Modes of a ShaftFatigu5) About Design AnalysisDesign analysis attempts to predict the strength or deformation of a machine element so that it can safely carry the imposed loads fo

29、r as long as required. An analysis by itself should not be looked on as an absolute and final truth. An analysis is limited by the assumptions imposed and by its range of applicability. 5) About Design AnalysisDesign6. Some Terminology Concerning Machine Design1) Codes and Standards2) Reliability3) Safety and Product Liability6. Some Terminology Concerning1) Codes and StandardsA standard is a set of specifications for part