机械零件设计英文PPT教案.ppt
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1、Design of Machine Elements,Chapter 1 Introduction,The 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 objec
2、tive 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 humanity,Design requires significant
3、creativity, 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
4、 human needs. Design problems are, almost without exception, open-ended problems combining hard science and creativity.,Definition of MachineComposition,1. About Machine,1) Definition of Machine A machine is a combination of mechanisms and other components that transforms, transmits, or uses energy,
5、 load, 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/compone
6、nts.In 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 Machine,3) Class
7、ification of Machine Elements,Normal 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, k
8、eys, couplings,2. 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-engineer
9、ing decisions: cost, marketability, product liability, ethics, politics, etc.,Fundamental Design Considerations,1 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 Sti
10、ffness19 Surface finish 20 Lubrication 21 Maintenance22 Volume,3. Basic Requirements for Machine Design,Economics 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
11、 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.,1) Functional Requirements,The machine to be designed should fulfill specified functions. This requires:Fundamental decisions re
12、garding loading, 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 Demands,The objective is to produce a machine that not only
13、 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 of design, manufacturing and operation of the product.,3) Other Demands,Safety and space requirements, convenience in transportation also need t
14、o be considered. Nonengineering decisions regarding marketability, product liability, ethics, politics, etc., must be integrated into the design process early.,4. Contents and Purpose of the Course,Fundamental design principles of various machine elements.,Even the design of a single bolt or spring
15、needs the designers thorough 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 problem
16、,Mechanical system design 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 Design,1) Recognition of the need, market analysis,
17、specification; 2) Definition of the problem (original concept), conceptual design.3) Synthesis, design analysis and optimization, (detail design)4) Production drawings5) Evaluation and presentation,Two Approaches of Machine Design,Conceptual design of configuration 1) Suggest feasible configurations
18、 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 details, materia
19、ls, geometric/dimensional tolerances. 2) Complete design calculations and detailed technical documents.,Suggestions,Design 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 th
20、eir discipline and rely on experts 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 like
21、ly 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 important,5. Design of Machine Element,1) About the First Two Steps,Require some creat
22、ive 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 kinematics, load, and stress coupled with proper material selection enable a stress-strain-strength ev
23、aluation in terms of a safety factor,2) Failure Prevention the Basis for Successful Design of Machine Element,Designer 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 se
24、lection of a material, determination 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 b
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