Budynas-Nisbett:Shigley's I.Basics 1.Introduction to T©The McGraw-Hill Mechanical Engineering Mechanical Engineering Companies,2008 Design,Eighth Edition Design Mechanical Engineering Desigr Design Considerations Sometimes the strength required of an element in a system is an important factor in the determination of the geometry and the dimensions of the element.In such a situation we say that strength is an important design consideration.When we use the expression design consideration,we are referring to some characteristic that influences the design of the element or,perhaps,the entire system.Usually quite a number of such charac- teristics must be considered and prioritized in a given design situation.Many of the important ones are as follows(not necessarily in order of importance): 1 Functionality 14 Noise 2 Strength/stress 15 Styling 3 Distortion/deflection/stiffness 16 Shape 4 Wear Size 5 Corrosion 18 Control 6 Safety 19 Thermal properties 7 Reliability 20 Surface 8 Manufacturability 21 Lubrication 9 Utility 22 Marketability 10 Cost 23 Maintenance 11 Friction 24 Volume 12 Weight 25 Liability 13 Life 26 Remanufacturing/resource recovery Some of these characteristics have to do directly with the dimensions,the material,the processing.and the joining of the elements of the system.Several characteristics may be interrelated,which affects the configuration of the total system. 1-4 Design Tools and Resources Today,the engineer has a great variety of tools and resources available to assist in the solution of design problems.Inexpensive microcomputers and robust computer soft- ware packages provide tools of immense capability for the design,analysis,and simu- lation of mechanical components.In addition to these tools,the engineer always needs technical information,either in the form of basic science/engineering behavior or the characteristics of specific off-the-shelf components.Here,the resources can range from science/engineering textbooks to manufacturers'brochures or catalogs.Here too,the computer can play a major role in gathering information. Computational Tools Computer-aided design(CAD)software allows the development of three-dimensional (3-D)designs from which conventional two-dimensional orthographic views with auto- matic dimensioning can be produced.Manufacturing tool paths can be generated from the 3-D models,and in some cases,parts can be created directly from a 3-D database by using a rapid prototyping and manufacturing method(stereolithography)paperless manufac- turing!Another advantage of a 3-D database is that it allows rapid and accurate calcula- tions of mass properties such as mass,location of the center of gravity,and mass moments of inertia.Other geometric properties such as areas and distances between points are likewise easily obtained.There are a great many CAD software packages available such An excellent and comprehensive discussion of the process of"athering information"can be found in Chap.4,George E.Dieter,Engineering Design,A Materials and Processing Approach.3rd ed.. McGraw-Hill,New York,2000
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design 14 © The McGraw−Hill Companies, 2008 8 Mechanical Engineering Design Design Considerations Sometimes the strength required of an element in a system is an important factor in the determination of the geometry and the dimensions of the element. In such a situation we say that strength is an important design consideration. When we use the expression design consideration, we are referring to some characteristic that influences the design of the element or, perhaps, the entire system. Usually quite a number of such characteristics must be considered and prioritized in a given design situation. Many of the important ones are as follows (not necessarily in order of importance): 1 Functionality 14 Noise 2 Strength/stress 15 Styling 3 Distortion/deflection/stiffness 16 Shape 4 Wear 17 Size 5 Corrosion 18 Control 6 Safety 19 Thermal properties 7 Reliability 20 Surface 8 Manufacturability 21 Lubrication 9 Utility 22 Marketability 10 Cost 23 Maintenance 11 Friction 24 Volume 12 Weight 25 Liability 13 Life 26 Remanufacturing/resource recovery Some of these characteristics have to do directly with the dimensions, the material, the processing, and the joining of the elements of the system. Several characteristics may be interrelated, which affects the configuration of the total system. 1–4 Design Tools and Resources Today, the engineer has a great variety of tools and resources available to assist in the solution of design problems. Inexpensive microcomputers and robust computer software packages provide tools of immense capability for the design, analysis, and simulation of mechanical components. In addition to these tools, the engineer always needs technical information, either in the form of basic science/engineering behavior or the characteristics of specific off-the-shelf components. Here, the resources can range from science/engineering textbooks to manufacturers’ brochures or catalogs. Here too, the computer can play a major role in gathering information.2 Computational Tools Computer-aided design (CAD) software allows the development of three-dimensional (3-D) designs from which conventional two-dimensional orthographic views with automatic dimensioning can be produced. Manufacturing tool paths can be generated from the 3-D models, and in some cases, parts can be created directly from a 3-D database by using a rapid prototyping and manufacturing method (stereolithography)—paperless manufacturing! Another advantage of a 3-D database is that it allows rapid and accurate calculations of mass properties such as mass, location of the center of gravity, and mass moments of inertia. Other geometric properties such as areas and distances between points are likewise easily obtained. There are a great many CAD software packages available such 2 An excellent and comprehensive discussion of the process of “gathering information” can be found in Chap. 4, George E. Dieter, Engineering Design, A Materials and Processing Approach, 3rd ed., McGraw-Hill, New York, 2000
Budynas-Nisbett:Shigley's I.Basics 1.Introduction to ©The McGraw-Hil Mechanical Engineering Mechanical Engineering Companies,2008 Design,Eighth Edition Design Introduction to Mechanical Engineering Design 9 as Aries,AutoCAD,CadKey,I-Deas,Unigraphics,Solid Works,and ProEngineer,to name a few. The term computer-aided engineering (CAE)generally applies to all computer- related engineering applications.With this definition,CAD can be considered as a sub- set of CAE.Some computer software packages perform specific engineering analysis and/or simulation tasks that assist the designer,but they are not considered a tool for the creation of the design that CAD is.Such software fits into two categories:engineering- based and non-engineering-specific.Some examples of engineering-based software for mechanical engineering applications-software that might also be integrated within a CAD system-include finite-element analysis (FEA)programs for analysis of stress and deflection (see Chap.19),vibration,and heat transfer (e.g.,Algor,ANSYS,and MSC/NASTRAN);computational fluid dynamics(CFD)programs for fluid-flow analy- sis and simulation (e.g.,CFD++,FIDAP,and Fluent);and programs for simulation of dynamic force and motion in mechanisms(e.g..ADAMS,DADS,and Working Model). Examples of non-engineering-specific computer-aided applications include soft- ware for word processing,spreadsheet software (e.g.,Excel,Lotus,and Quattro-Pro), and mathematical solvers(e.g.,Maple,MathCad,Matlab,Mathematica,and TKsolver). Your instructor is the best source of information about programs that may be available to you and can recommend those that are useful for specific tasks.One caution,however: Computer software is no substitute for the human thought process.You are the driver here: the computer is the vehicle to assist you on your jourey to a solution.Numbers generated by a computer can be far from the truth if you entered incorrect input,if you misinterpreted the application or the output of the program,if the program contained bugs,etc.It is your responsibility to assure the validity of the results,so be careful to check the application and results carefully,perform benchmark testing by submitting problems with known solu- tions,and monitor the software company and user-group newsletters. Acquiring Technical Information We currently live in what is referred to as the informnation age,where information is gen- erated at an astounding pace.It is difficult,but extremely important,to keep abreast of past and current developments in one's field of study and occupation.The reference in Footnote 2 provides an excellent description of the informational resources available and is highly recommended reading for the serious design engineer.Some sources of information are: Libraries(community,university,and private).Engineering dictionaries and encyclo- pedias.textbooks,monographs,handbooks,indexing and abstract services,journals, translations,technical reports,patents,and business sources/brochures/catalogs. .Government sources.Departments of Defense,Commerce,Energy,and Transportation; NASA;Government Printing Office;U.S.Patent and Trademark Office;National Technical Information Service;and National Institute for Standards and Technology. Professional societies.American Society of Mechanical Engineers,Society of Manufacturing Engineers,Society of Automotive Engineers,American Society for Testing and Materials,and American Welding Society. Commercial vendors.Catalogs,technical literature,test data,samples,and cost information. Internet.The computer network gateway to websites associated with most of the categories listed above.3 Some helpful Web resources,to name a few.include www.globalspec.com,www.engnetglobal.com. www.efunda.com,www.thomasnet.com,and www.uspto.gov
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design © The McGraw−Hill 15 Companies, 2008 Introduction to Mechanical Engineering Design 9 as Aries, AutoCAD, CadKey, I-Deas, Unigraphics, Solid Works, and ProEngineer, to name a few. The term computer-aided engineering (CAE) generally applies to all computerrelated engineering applications. With this definition, CAD can be considered as a subset of CAE. Some computer software packages perform specific engineering analysis and/or simulation tasks that assist the designer, but they are not considered a tool for the creation of the design that CAD is. Such software fits into two categories: engineeringbased and non-engineering-specific. Some examples of engineering-based software for mechanical engineering applications—software that might also be integrated within a CAD system—include finite-element analysis (FEA) programs for analysis of stress and deflection (see Chap. 19), vibration, and heat transfer (e.g., Algor, ANSYS, and MSC/NASTRAN); computational fluid dynamics (CFD) programs for fluid-flow analysis and simulation (e.g., CFD++, FIDAP, and Fluent); and programs for simulation of dynamic force and motion in mechanisms (e.g., ADAMS, DADS, and Working Model). Examples of non-engineering-specific computer-aided applications include software for word processing, spreadsheet software (e.g., Excel, Lotus, and Quattro-Pro), and mathematical solvers (e.g., Maple, MathCad, Matlab, Mathematica, and TKsolver). Your instructor is the best source of information about programs that may be available to you and can recommend those that are useful for specific tasks. One caution, however: Computer software is no substitute for the human thought process. You are the driver here; the computer is the vehicle to assist you on your journey to a solution. Numbers generated by a computer can be far from the truth if you entered incorrect input, if you misinterpreted the application or the output of the program, if the program contained bugs, etc. It is your responsibility to assure the validity of the results, so be careful to check the application and results carefully, perform benchmark testing by submitting problems with known solutions, and monitor the software company and user-group newsletters. Acquiring Technical Information We currently live in what is referred to as the information age, where information is generated at an astounding pace. It is difficult, but extremely important, to keep abreast of past and current developments in one’s field of study and occupation. The reference in Footnote 2 provides an excellent description of the informational resources available and is highly recommended reading for the serious design engineer. Some sources of information are: • Libraries (community, university, and private). Engineering dictionaries and encyclopedias, textbooks, monographs, handbooks, indexing and abstract services, journals, translations, technical reports, patents, and business sources/brochures/catalogs. • Government sources. Departments of Defense, Commerce, Energy, and Transportation; NASA; Government Printing Office; U.S. Patent and Trademark Office; National Technical Information Service; and National Institute for Standards and Technology. • Professional societies. American Society of Mechanical Engineers, Society of Manufacturing Engineers, Society of Automotive Engineers, American Society for Testing and Materials, and American Welding Society. • Commercial vendors. Catalogs, technical literature, test data, samples, and cost information. • Internet. The computer network gateway to websites associated with most of the categories listed above.3 3 Some helpful Web resources, to name a few, include www.globalspec.com, www.engnetglobal.com, www.efunda.com, www.thomasnet.com, and www.uspto.gov
Budynas-Nisbett:Shigley's I.Basics 1.Introduction to T©The McGraw-Hill Mechanical Engineering Mechanical Engineering Companies,2008 Design,Eighth Edition Design 10 Mechanical Engineering Desigr This list is not complete.The reader is urged to explore the various sources of information on a regular basis and keep records of the knowledge gained. 1-5 The Design Engineer's Professional Responsibilities In general,the design engineer is required to satisfy the needs of customers(man- agement,clients,consumers,etc.)and is expected to do so in a competent,responsi- ble,ethical,and professional manner.Much of engineering course work and practical experience focuses on competence,but when does one begin to develop engineering responsibility and professionalism?To start on the road to success,you should start to develop these characteristics early in your educational program.You need to cul- tivate your professional work ethic and process skills before graduation,so that when you begin your formal engineering career,you will be prepared to meet the challenges It is not obvious to some students,but communication skills play a large role here, and it is the wise student who continuously works to improve these skills-even if it is not a direct requirement of a course assignment!Success in engineering (achieve- ments,promotions,raises,etc.)may in large part be due to competence but if you can- not communicate your ideas clearly and concisely,your technical proficiency may be compromised. You can start to develop your communication skills by keeping a neat and clear journal/logbook of your activities,entering dated entries frequently.(Many companies require their engineers to keep a journal for patent and liability concerns.)Separate journals should be used for each design project (or course subject).When starting a project or problem,in the definition stage,make journal entries quite frequently.Others, as well as yourself,may later question why you made certain decisions.Good chrono- logical records will make it easier to explain your decisions at a later date. Many engineering students see themselves after graduation as practicing engineers designing,developing,and analyzing products and processes and consider the need of good communication skills,either oral or writing,as secondary.This is far from the truth.Most practicing engineers spend a good deal of time communicating with others, writing proposals and technical reports,and giving presentations and interacting with engineering and nonengineering support personnel.You have the time now to sharpen your communication skills.When given an assignment to write or make any presenta- tion,technical or nontechnical,accept it enthusiastically,and work on improving your communication skills.It will be time well spent to learn the skills now rather than on the job. When you are working on a design problem,it is important that you develop a systematic approach.Careful attention to the following action steps will help you to organize your solution processing technique. .Understand the problem.Problem definition is probably the most significant step in the engineering design process.Carefully read,understand,and refine the problem statement. Identify the known.From the refined problem statement,describe concisely what information is known and relevant. Identify the unknown and formulate the solution strategy.State what must be deter- mined,in what order,so as to arrive at a solution to the problem.Sketch the compo- nent or system under investigation,identifying known and unknown parameters Create a flowchart of the steps necessary to reach the final solution.The steps may require the use of free-body diagrams;material properties from tables;equations
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design 16 © The McGraw−Hill Companies, 2008 10 Mechanical Engineering Design This list is not complete. The reader is urged to explore the various sources of information on a regular basis and keep records of the knowledge gained. 1–5 The Design Engineer’s Professional Responsibilities In general, the design engineer is required to satisfy the needs of customers (management, clients, consumers, etc.) and is expected to do so in a competent, responsible, ethical, and professional manner. Much of engineering course work and practical experience focuses on competence, but when does one begin to develop engineering responsibility and professionalism? To start on the road to success, you should start to develop these characteristics early in your educational program. You need to cultivate your professional work ethic and process skills before graduation, so that when you begin your formal engineering career, you will be prepared to meet the challenges. It is not obvious to some students, but communication skills play a large role here, and it is the wise student who continuously works to improve these skills—even if it is not a direct requirement of a course assignment! Success in engineering (achievements, promotions, raises, etc.) may in large part be due to competence but if you cannot communicate your ideas clearly and concisely, your technical proficiency may be compromised. You can start to develop your communication skills by keeping a neat and clear journal/logbook of your activities, entering dated entries frequently. (Many companies require their engineers to keep a journal for patent and liability concerns.) Separate journals should be used for each design project (or course subject). When starting a project or problem, in the definition stage, make journal entries quite frequently. Others, as well as yourself, may later question why you made certain decisions. Good chronological records will make it easier to explain your decisions at a later date. Many engineering students see themselves after graduation as practicing engineers designing, developing, and analyzing products and processes and consider the need of good communication skills, either oral or writing, as secondary. This is far from the truth. Most practicing engineers spend a good deal of time communicating with others, writing proposals and technical reports, and giving presentations and interacting with engineering and nonengineering support personnel. You have the time now to sharpen your communication skills. When given an assignment to write or make any presentation, technical or nontechnical, accept it enthusiastically, and work on improving your communication skills. It will be time well spent to learn the skills now rather than on the job. When you are working on a design problem, it is important that you develop a systematic approach. Careful attention to the following action steps will help you to organize your solution processing technique. • Understand the problem. Problem definition is probably the most significant step in the engineering design process. Carefully read, understand, and refine the problem statement. • Identify the known. From the refined problem statement, describe concisely what information is known and relevant. • Identify the unknown and formulate the solution strategy. State what must be determined, in what order, so as to arrive at a solution to the problem. Sketch the component or system under investigation, identifying known and unknown parameters. Create a flowchart of the steps necessary to reach the final solution. The steps may require the use of free-body diagrams; material properties from tables; equations