Chapter01 Introduction 机械零件设计英文教案 课件Design of Machine Elements

1、Design of Machine ElementsChapter 1 IntroductionThe Meaning of DesignEngineeringMechanical EngineeringDesignMachine design Engineering is concerned with the conversion of energy from one form to another with the objective of extracting useful work.Mechanical engineering has the more specific objecti

2、ve 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 benefit humanityDesign requires significant crea

3、tivity, practice, and vision to be done well. Machine design is the fundamental practice in engineering; is the transformation of concepts and ideas into useful machinery. Machine design is the application of science and technology to devise new or improved products for the purpose of satisfying hum

4、an needs. Design problems are, almost without exception, open-ended problems combining hard science and creativity. Definition of MachineComposition1. About Machine1) Definition of Machine A machine is a combination of mechanisms and other components that transforms, transmits, or uses energy, load,

5、 or motion for a specific purpose.A machine 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.In terms of basic manufacturing unit, a machine is composed by machine elements/components.In

6、terms of the functions 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 Machine3) Classification

7、 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 fasteners, keys, coupl

8、ings2. 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, space, weight, etc.Non-engineering decisio

9、ns: cost, marketability, product liability, ethics, politics, etc. Fundamental Design Considerations1 Strength 2 Reliability 3 Thermal effect4 Corrosion 5 Wear 6 Friction 7 Processing 8 Utility 9 Cost 10 Safety 11 Weight 12 Noise13 Styling 14 Shape 15 Size16 Flexibility 17 Control 18 Stiffness19 Sur

10、face finish 20 Lubrication 21 Maintenance22 Volume3. Basic Requirements for Machine DesignEconomics and functionality are always pressing concerns, and good design inherently means safe, economical, and functional design.A primary responsibility of any mechanical designer is to ensure that the propo

11、sed design will function as intended, safely and reliably,for the prescribed design lifetime and, at the same time, compete successfully in the marketplace.1) Functional Requirements The machine to be designed should fulfill specified functions. This requires:Fundamental decisions regarding loading,

12、 kinematics, and the choice of materials must be made properly during the design of a machine. Besides, strength, reliability, deformation, tribology (friction, wear, and lubrication), also need to be considered.2) Economic DemandsThe objective is to produce a machine that not only is to function pr

13、operly for a reasonable time but is also economically feasible.The economic requirements need to be addressed over the entire life circle of design, manufacturing and operation of the product.3) Other Demands Safety and space requirements, convenience in transportation also need to be considered. No

14、nengineering decisions regarding marketability, product liability, ethics, politics, etc., must be integrated into the design process early. 4. Contents and Purpose of the CourseFundamental design principles of various machine elements.Even the design of a single bolt or spring needs the designers t

15、horough understanding of the principles and methods of machinery design and more. Master the basic knowledge, methods and procedures and gain the competence in applying them into practical design.Other Purposes Develop competence of creative design and solving practical problemMechanical system desi

16、gn requires considerable flexibility and creativity to obtain good solutions. Creativity seems to be aided by familiarity with known successful designs of related systems, components or elements. General Procedure of Machine Design1) Recognition of the need, market analysis, specification; 2) Defini

17、tion of the problem (original concept), conceptual design.3) Synthesis, design analysis and optimization, (detail design)4) Production drawings5) Evaluation and presentationTwo Approaches of Machine DesignConceptual design of configuration 1) Suggest feasible configurations and alternatives 2) Analy

18、se 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 details, materials, geometric/dimensional

19、tolerances. 2) Complete design calculations and detailed technical documents.SuggestionsDesign engineers can no longer work alone and must participate in group discussions and design reviews. They need good communications skills. Design engineers cannot merely focus on their discipline and rely on e

20、xperts for the rest. They need to know other disciplines, at least from a linguistics standpoint. Improve your presentation skills.1) Selecting a suitable type of machine element from consideration of its function2) Estimating the size of the machine element that is likely to be satisfactory3) Evalu

21、ating 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. Design of Machine Element1) About the First Two StepsRequire some creative decisions, represent the mos

22、t 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 kinematics, load, and stress coupled with proper material selection enable a stress-strain-strength evaluation in terms of a safety fa

23、ctor 2) Failure Prevention the Basis for Successful Design of Machine ElementDesigner must have a good working knowledge of analytical and/or empirical techniques for predicting potential failures at the design stage.These predictions must then be transformed into selection of a material, determinat

24、ion of a shape, and establishment of the dimensions for each part to ensure safe, reliable operation throughout the design lifetime. 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 inten

25、ded function satisfactorilyWhen serious deterioration has made it unreliable or unsafe for continued use.3) Failure of Machine Elements4) 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.F

26、orce and/or temperature induced elastic deformationYielding plastic deformation Brittle 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 sp

27、ring Failure Modes of a ShaftFatigue fracture/ for common shaftExcessive elastic deformation/ for precision shaft Resonant vibration / for rotating shaft at high speed5) About Design AnalysisDesign analysis attempts to predict the strength or deformation of a machine element so that it can safely ca

28、rry the imposed loads for 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. 6. Some Terminology Concerning Machine Design1) Codes and Standards2) Reliability3) Safety and Product Liability1) Codes and Stand