Budynas-Nisbett:Shigley's I.Basics 1.Introduction to ©The McGraw-Hfil Mechanical Engineering Mechanical Engineering Companies,2008 Design,Eighth Edition Design Introduction to Mechanical Engineering Design Chapter Outline 1-1 Design 4 1-2 Mechanical Engineering Design 5 1-3 Phases and Interactions of the Design Process 5 1-4 Design Tools and Resources 8 1-5 The Design Engineer's Professional Responsibilities 10 1-6 Standards and Codes 12 1-7 Economics 12 1-8 Safety and Product Liability 15 1-9 Stress and Strength 15 1-10 Uncertainty 16 1-11 Design Factor and Factor of Safety 17 1-12 Reliability 18 1-13 Dimensions and Tolerances 19 1-14 Units 21 1-15 Calculations and Significant Figures 22 1-16 Power Transmission Case Study Specifications 23 3
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design © The McGraw−Hill 9 Companies, 2008 3 Chapter Outline 1–1 Design 4 1–2 Mechanical Engineering Design 5 1–3 Phases and Interactions of the Design Process 5 1–4 Design Tools and Resources 8 1–5 The Design Engineer’s Professional Responsibilities 10 1–6 Standards and Codes 12 1–7 Economics 12 1–8 Safety and Product Liability 15 1–9 Stress and Strength 15 1–10 Uncertainty 16 1–11 Design Factor and Factor of Safety 17 1–12 Reliability 18 1–13 Dimensions and Tolerances 19 1–14 Units 21 1–15 Calculations and Significant Figures 22 1–16 Power Transmission Case Study Specifications 23 1Introduction to Mechanical Engineering Design
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 Design Mechanical design is a complex undertaking,requiring many skills.Extensive relation- ships need to be subdivided into a series of simple tasks.The complexity of the subject requires a sequence in which ideas are introduced and iterated. We first address the nature of design in general,and then mechanical engineering design in particular.Design is an iterative process with many interactive phases.Many resources exist to support the designer,including many sources of information and an abundance of computational design tools.The design engineer needs not only to develop competence in their field but must also cultivate a strong sense of responsibility and professional work ethic. There are roles to be played by codes and standards,ever-present economics,safety, and considerations of product liability.The survival of a mechanical component is often related through stress and strength.Matters of uncertainty are ever-present in engineer- ing design and are typically addressed by the design factor and factor of safety,either in the form of a deterministic (absolute)or statistical sense.The latter.statistical approach,deals with a design's reliabiliry and requires good statistical data. In mechanical design,other considerations include dimensions and tolerances, units,and calculations. The book consists of four parts.Part 1,Basics,begins by explaining some differ- ences between design and analysis and introducing some fundamental notions and approaches to design.It continues with three chapters reviewing material properties, stress analysis,and stiffness and deflection analysis,which are the key principles nec- essary for the remainder of the book. Part 2.Failure Prevention,consists of two chapters on the prevention of failure of mechanical parts.Why machine parts fail and how they can be designed to prevent fail- ure are difficult questions,and so we take two chapters to answer them,one on pre- venting failure due to static loads,and the other on preventing fatigue failure due to time-varying,cyclic loads. In Part 3,Design of Mechanical Elements,the material of Parts I and 2 is applied to the analysis,selection,and design of specific mechanical elements such as shafts, fasteners,weldments,springs,rolling contact bearings,film bearings,gears,belts, chains,and wire ropes. Part 4,Analysis Tools,provides introductions to two important methods used in mechanical design,finite element analysis and statistical analysis.This is optional study material,but some sections and examples in Parts I to 3 demonstrate the use of these tools. There are two appendixes at the end of the book.Appendix A contains many use- ful tables referenced throughout the book.Appendix B contains answers to selected end-of-chapter problems. 1-1 Design To design is either to formulate a plan for the satisfaction of a specified need or to solve a problem.If the plan results in the creation of something having a physical reality,then the product must be functional,safe,reliable,competitive,usable,manufacturable,and marketable. Design is an innovative and highly iterative process.It is also a decision-making process.Decisions sometimes have to be made with too little information,occasion- ally with just the right amount of information,or with an excess of partially contradictory information.Decisions are sometimes made tentatively,with the right reserved to adjust as more becomes known.The point is that the engineering designer has to be personally comfortable with a decision-making,problem-solving role
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design 10 © The McGraw−Hill Companies, 2008 4 Mechanical Engineering Design Mechanical design is a complex undertaking, requiring many skills. Extensive relationships need to be subdivided into a series of simple tasks. The complexity of the subject requires a sequence in which ideas are introduced and iterated. We first address the nature of design in general, and then mechanical engineering design in particular. Design is an iterative process with many interactive phases. Many resources exist to support the designer, including many sources of information and an abundance of computational design tools. The design engineer needs not only to develop competence in their field but must also cultivate a strong sense of responsibility and professional work ethic. There are roles to be played by codes and standards, ever-present economics, safety, and considerations of product liability. The survival of a mechanical component is often related through stress and strength. Matters of uncertainty are ever-present in engineering design and are typically addressed by the design factor and factor of safety, either in the form of a deterministic (absolute) or statistical sense. The latter, statistical approach, deals with a design’s reliability and requires good statistical data. In mechanical design, other considerations include dimensions and tolerances, units, and calculations. The book consists of four parts. Part 1, Basics, begins by explaining some differences between design and analysis and introducing some fundamental notions and approaches to design. It continues with three chapters reviewing material properties, stress analysis, and stiffness and deflection analysis, which are the key principles necessary for the remainder of the book. Part 2, Failure Prevention, consists of two chapters on the prevention of failure of mechanical parts. Why machine parts fail and how they can be designed to prevent failure are difficult questions, and so we take two chapters to answer them, one on preventing failure due to static loads, and the other on preventing fatigue failure due to time-varying, cyclic loads. In Part 3, Design of Mechanical Elements, the material of Parts 1 and 2 is applied to the analysis, selection, and design of specific mechanical elements such as shafts, fasteners, weldments, springs, rolling contact bearings, film bearings, gears, belts, chains, and wire ropes. Part 4, Analysis Tools, provides introductions to two important methods used in mechanical design, finite element analysis and statistical analysis. This is optional study material, but some sections and examples in Parts 1 to 3 demonstrate the use of these tools. There are two appendixes at the end of the book. Appendix A contains many useful tables referenced throughout the book. Appendix B contains answers to selected end-of-chapter problems. 1–1 Design To design is either to formulate a plan for the satisfaction of a specified need or to solve a problem. If the plan results in the creation of something having a physical reality, then the product must be functional, safe, reliable, competitive, usable, manufacturable, and marketable. Design is an innovative and highly iterative process. It is also a decision-making process. Decisions sometimes have to be made with too little information, occasionally with just the right amount of information, or with an excess of partially contradictory information. Decisions are sometimes made tentatively, with the right reserved to adjust as more becomes known. The point is that the engineering designer has to be personally comfortable with a decision-making, problem-solving role
Budynas-Nisbett:Shigley's I.Basics 1.Introduction to T©The McGraw-Hill Mechanical Engineering Mechanical Engineering Companies,2008 Design,Eighth Edition Design Introduction to Mechanical Engineering Design Design is a communication-intensive activity in which both words and pictures are used,and written and oral forms are employed.Engineers have to communicate effec- tively and work with people of many disciplines.These are important skills,and an engineer's success depends on them. A designer's personal resources of creativeness,communicative ability,and problem- solving skill are intertwined with knowledge of technology and first principles. Engineering tools (such as mathematics,statistics,computers,graphics,and languages) are combined to produce a plan that,when carried out,produces a product that is fumnc- tional,safe,reliable,competitive,usable,manufacturable,and marketable,regardless of who builds it or who uses it. 1-2 Mechanical Engineering Design Mechanical engineers are associated with the production and processing of energy and with providing the means of production,the tools of transportation,and the techniques of automation.The skill and knowledge base are extensive.Among the disciplinary bases are mechanics of solids and fluids,mass and momentum transport,manufactur- ing processes,and electrical and information theory.Mechanical engineering design involves all the disciplines of mechanical engineering. Real problems resist compartmentalization.A simple journal bearing involves fluid flow,heat transfer,friction,energy transport,material selection,thermomechanical treatments,statistical descriptions,and so on.A building is environmentally controlled. The heating,ventilation,and air-conditioning considerations are sufficiently specialized that some speak of heating,ventilating,and air-conditioning design as if it is separate and distinct from mechanical engineering design.Similarly,internal-combustion engine design,turbomachinery design,and jet-engine design are sometimes considered dis- crete entities.Here,the leading string of words preceding the word design is merely a product descriptor.Similarly,there are phrases such as machine design,machine-element design,machine-component design,systems design,and fluid-power design.All of these phrases are somewhat more focused examples of mechanical engineering design. They all draw on the same bodies of knowledge,are similarly organized,and require similar skills. 1-3 Phases and Interactions of the Design Process What is the design process?How does it begin?Does the engineer simply sit down at a desk with a blank sheet of paper and jot down some ideas?What happens next?What factors influence or control the decisions that have to be made?Finally,how does the design process end? The complete design process,from start to finish,is often outlined as in Fig.1-1. The process begins with an identification of a need and a decision to do something about it.After many iterations,the process ends with the presentation of the plans for satisfying the need.Depending on the nature of the design task,several design phases may be repeated throughout the life of the product,from inception to termi- nation.In the next several subsections,we shall examine these steps in the design process in detail. Identification of need generally starts the design process.Recognition of the need and phrasing the need often constitute a highly creative act,because the need may be only a vague discontent,a feeling of uneasiness,or a sensing that something is not right. The need is often not evident at all;recognition is usually triggered by a particular
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design © The McGraw−Hill 11 Companies, 2008 Introduction to Mechanical Engineering Design 5 Design is a communication-intensive activity in which both words and pictures are used, and written and oral forms are employed. Engineers have to communicate effectively and work with people of many disciplines. These are important skills, and an engineer’s success depends on them. A designer’s personal resources of creativeness, communicative ability, and problemsolving skill are intertwined with knowledge of technology and first principles. Engineering tools (such as mathematics, statistics, computers, graphics, and languages) are combined to produce a plan that, when carried out, produces a product that is functional, safe, reliable, competitive, usable, manufacturable, and marketable, regardless of who builds it or who uses it. 1–2 Mechanical Engineering Design Mechanical engineers are associated with the production and processing of energy and with providing the means of production, the tools of transportation, and the techniques of automation. The skill and knowledge base are extensive. Among the disciplinary bases are mechanics of solids and fluids, mass and momentum transport, manufacturing processes, and electrical and information theory. Mechanical engineering design involves all the disciplines of mechanical engineering. Real problems resist compartmentalization. A simple journal bearing involves fluid flow, heat transfer, friction, energy transport, material selection, thermomechanical treatments, statistical descriptions, and so on. A building is environmentally controlled. The heating, ventilation, and air-conditioning considerations are sufficiently specialized that some speak of heating, ventilating, and air-conditioning design as if it is separate and distinct from mechanical engineering design. Similarly, internal-combustion engine design, turbomachinery design, and jet-engine design are sometimes considered discrete entities. Here, the leading string of words preceding the word design is merely a product descriptor. Similarly, there are phrases such as machine design, machine-element design, machine-component design, systems design, and fluid-power design. All of these phrases are somewhat more focused examples of mechanical engineering design. They all draw on the same bodies of knowledge, are similarly organized, and require similar skills. 1–3 Phases and Interactions of the Design Process What is the design process? How does it begin? Does the engineer simply sit down at a desk with a blank sheet of paper and jot down some ideas? What happens next? What factors influence or control the decisions that have to be made? Finally, how does the design process end? The complete design process, from start to finish, is often outlined as in Fig. 1–1. The process begins with an identification of a need and a decision to do something about it. After many iterations, the process ends with the presentation of the plans for satisfying the need. Depending on the nature of the design task, several design phases may be repeated throughout the life of the product, from inception to termination. In the next several subsections, we shall examine these steps in the design process in detail. Identification of need generally starts the design process. Recognition of the need and phrasing the need often constitute a highly creative act, because the need may be only a vague discontent, a feeling of uneasiness, or a sensing that something is not right. The need is often not evident at all; recognition is usually triggered by a particular
12 Budynas-Nisbett:Shigley's I.Basics 1.Introduction to T©The McGraw-Hil Mechanical Engineering Mechanical Engineering Companies,2008 Design,Eighth Edition Design Mechanical Engineering Design Figure 1-1 Identification of need The phases in design, acknowledging the many feedbacks and iterations. Definition of problem Synthesis Analysis and optimization Evaluation Iteration Presentation adverse circumstance or a set of random circumstances that arises almost simultaneously. For example,the need to do something about a food-packaging machine may be indi- cated by the noise level,by a variation in package weight,and by slight but perceptible variations in the quality of the packaging or wrap. There is a distinct difference between the statement of the need and the definition of the problem.The definition of problem is more specific and must include all the spec- ifications for the object that is to be designed.The specifications are the input and out- put quantities,the characteristics and dimensions of the space the object must occupy, and all the limitations on these quantities.We can regard the object to be designed as something in a black box.In this case we must specify the inputs and outputs of the box, together with their characteristics and limitations.The specifications define the cost,the number to be manufactured,the expected life,the range,the operating temperature,and the reliability.Specified characteristics can include the speeds,feeds,temperature lim- itations,maximum range,expected variations in the variables,dimensional and weight limitations,etc There are many implied specifications that result either from the designer's par- ticular environment or from the nature of the problem itself.The manufacturing processes that are available,together with the facilities of a certain plant,constitute restrictions on a designer's freedom,and hence are a part of the implied specifica- tions.It may be that a small plant,for instance,does not own cold-working machin- ery.Knowing this,the designer might select other metal-processing methods that can be performed in the plant.The labor skills available and the competitive situa- tion also constitute implied constraints.Anything that limits the designer's freedom of choice is a constraint.Many materials and sizes are listed in supplier's catalogs, for instance,but these are not all easily available and shortages frequently occur. Furthermore,inventory economics requires that a manufacturer stock a minimum number of materials and sizes.An example of a specification is given in Sec.1-16. This example is for a case study of a power transmission that is presented throughout this text. The synthesis of a scheme connecting possible system elements is sometimes called the invention of the concept or concept design.This is the first and most impor- tant step in the synthesis task.Various schemes must be proposed,investigated,and
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design 12 © The McGraw−Hill Companies, 2008 6 Mechanical Engineering Design adverse circumstance or a set of random circumstances that arises almost simultaneously. For example, the need to do something about a food-packaging machine may be indicated by the noise level, by a variation in package weight, and by slight but perceptible variations in the quality of the packaging or wrap. There is a distinct difference between the statement of the need and the definition of the problem. The definition of problem is more specific and must include all the specifications for the object that is to be designed. The specifications are the input and output quantities, the characteristics and dimensions of the space the object must occupy, and all the limitations on these quantities. We can regard the object to be designed as something in a black box. In this case we must specify the inputs and outputs of the box, together with their characteristics and limitations. The specifications define the cost, the number to be manufactured, the expected life, the range, the operating temperature, and the reliability. Specified characteristics can include the speeds, feeds, temperature limitations, maximum range, expected variations in the variables, dimensional and weight limitations, etc. There are many implied specifications that result either from the designer’s particular environment or from the nature of the problem itself. The manufacturing processes that are available, together with the facilities of a certain plant, constitute restrictions on a designer’s freedom, and hence are a part of the implied specifications. It may be that a small plant, for instance, does not own cold-working machinery. Knowing this, the designer might select other metal-processing methods that can be performed in the plant. The labor skills available and the competitive situation also constitute implied constraints. Anything that limits the designer’s freedom of choice is a constraint. Many materials and sizes are listed in supplier’s catalogs, for instance, but these are not all easily available and shortages frequently occur. Furthermore, inventory economics requires that a manufacturer stock a minimum number of materials and sizes. An example of a specification is given in Sec. 1–16. This example is for a case study of a power transmission that is presented throughout this text. The synthesis of a scheme connecting possible system elements is sometimes called the invention of the concept or concept design. This is the first and most important step in the synthesis task. Various schemes must be proposed, investigated, and Figure 1–1 The phases in design, acknowledging the many feedbacks and iterations. Identification of need Definition of problem Synthesis Analysis and optimization Evaluation Presentation Iteration
Budynas-Nisbett:Shigley's I.Basics 1.Introduction to ©The McGraw-Hil 13 Mechanical Engineering Mechanical Engineering Companies,2008 Design,Eighth Edition Design Introduction to Mechanical Engineering Design quantified in terms of established metrics.As the fleshing out of the scheme progresses, analyses must be performed to assess whether the system performance is satisfactory or better,and,if satisfactory,just how well it will perform.System schemes that do not survive analysis are revised,improved,or discarded.Those with potential are optimized to determine the best performance of which the scheme is capable.Competing schemes are compared so that the path leading to the most competitive product can be chosen. Figure 1-1 shows that synthesis and analysis and optimization are intimately and iteratively related. We have noted,and we emphasize,that design is an iterative process in which we proceed through several steps,evaluate the results,and then return to an earlier phase of the procedure.Thus,we may synthesize several components of a system,analyze and optimize them,and return to synthesis to see what effect this has on the remaining parts of the system.For example,the design of a system to transmit power requires attention to the design and selection of individual components (e.g.,gears,bearings,shaft) However,as is often the case in design,these components are not independent.In order to design the shaft for stress and deflection,it is necessary to know the applied forces. If the forces are transmitted through gears,it is necessary to know the gear specifica- tions in order to determine the forces that will be transmitted to the shaft.But stock gears come with certain bore sizes,requiring knowledge of the necessary shaft diame- ter.Clearly,rough estimates will need to be made in order to proceed through the process,refining and iterating until a final design is obtained that is satisfactory for each individual component as well as for the overall design specifications.Throughout the text we will elaborate on this process for the case study of a power transmission design. Both analysis and optimization require that we construct or devise abstract models of the system that will admit some form of mathematical analysis.We call these mod- els mathematical models.In creating them it is our hope that we can find one that will simulate the real physical system very well.As indicated in Fig.1-1,evaluation is a significant phase of the total design process.Evaluation is the final proof of a success- ful design and usually involves the testing of a prototype in the laboratory.Here we wish to discover if the design really satisfies the needs.Is it reliable?Will it compete successfully with similar products?Is it economical to manufacture and to use?Is it easily maintained and adjusted?Can a profit be made from its sale or use?How likely is it to result in product-liability lawsuits?And is insurance easily and cheaply obtained?Is it likely that recalls will be needed to replace defective parts or systems? Communicating the design to others is the final,vital presentation step in the design process.Undoubtedly,many great designs,inventions,and creative works have been lost to posterity simply because the originators were unable or unwilling to explain their accomplishments to others.Presentation is a selling job.The engineer, when presenting a new solution to administrative,management,or supervisory persons, is attempting to sell or to prove to them that this solution is a better one.Unless this can be done successfully,the time and effort spent on obtaining the solution have been largely wasted.When designers sell a new idea,they also sell themselves.If they are repeatedly successful in selling ideas,designs,and new solutions to management,they begin to receive salary increases and promotions:in fact,this is how anyone succeeds in his or her profession. An excellent reference for this topic is presented by Stuart Pugh,Total Design-Integrated Methods for Successful Product Engineering.Addison-Wesley,1991.A description of the Pugh method is also provided in Chap.8,David G.Ullman,The Mechanical Design Process,3rd ed.,McGraw-Hill,2003
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design © The McGraw−Hill 13 Companies, 2008 Introduction to Mechanical Engineering Design 7 quantified in terms of established metrics.1 As the fleshing out of the scheme progresses, analyses must be performed to assess whether the system performance is satisfactory or better, and, if satisfactory, just how well it will perform. System schemes that do not survive analysis are revised, improved, or discarded. Those with potential are optimized to determine the best performance of which the scheme is capable. Competing schemes are compared so that the path leading to the most competitive product can be chosen. Figure 1–1 shows that synthesis and analysis and optimization are intimately and iteratively related. We have noted, and we emphasize, that design is an iterative process in which we proceed through several steps, evaluate the results, and then return to an earlier phase of the procedure. Thus, we may synthesize several components of a system, analyze and optimize them, and return to synthesis to see what effect this has on the remaining parts of the system. For example, the design of a system to transmit power requires attention to the design and selection of individual components (e.g., gears, bearings, shaft). However, as is often the case in design, these components are not independent. In order to design the shaft for stress and deflection, it is necessary to know the applied forces. If the forces are transmitted through gears, it is necessary to know the gear specifications in order to determine the forces that will be transmitted to the shaft. But stock gears come with certain bore sizes, requiring knowledge of the necessary shaft diameter. Clearly, rough estimates will need to be made in order to proceed through the process, refining and iterating until a final design is obtained that is satisfactory for each individual component as well as for the overall design specifications. Throughout the text we will elaborate on this process for the case study of a power transmission design. Both analysis and optimization require that we construct or devise abstract models of the system that will admit some form of mathematical analysis. We call these models mathematical models. In creating them it is our hope that we can find one that will simulate the real physical system very well. As indicated in Fig. 1–1, evaluation is a significant phase of the total design process. Evaluation is the final proof of a successful design and usually involves the testing of a prototype in the laboratory. Here we wish to discover if the design really satisfies the needs. Is it reliable? Will it compete successfully with similar products? Is it economical to manufacture and to use? Is it easily maintained and adjusted? Can a profit be made from its sale or use? How likely is it to result in product-liability lawsuits? And is insurance easily and cheaply obtained? Is it likely that recalls will be needed to replace defective parts or systems? Communicating the design to others is the final, vital presentation step in the design process. Undoubtedly, many great designs, inventions, and creative works have been lost to posterity simply because the originators were unable or unwilling to explain their accomplishments to others. Presentation is a selling job. The engineer, when presenting a new solution to administrative, management, or supervisory persons, is attempting to sell or to prove to them that this solution is a better one. Unless this can be done successfully, the time and effort spent on obtaining the solution have been largely wasted. When designers sell a new idea, they also sell themselves. If they are repeatedly successful in selling ideas, designs, and new solutions to management, they begin to receive salary increases and promotions; in fact, this is how anyone succeeds in his or her profession. 1 An excellent reference for this topic is presented by Stuart Pugh, Total Design—Integrated Methods for Successful Product Engineering, Addison-Wesley, 1991. A description of the Pugh method is also provided in Chap. 8, David G. Ullman, The Mechanical Design Process, 3rd ed., McGraw-Hill, 2003
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
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 11 from first principles,textbooks,or handbooks relating the known and unknown parameters;experimentally or numerically based charts;specific computational tools as discussed in Sec.1-4;etc. State all assumptions and decisions.Real design problems generally do not have unique,ideal,closed-form solutions.Selections,such as choice of materials,and heat treatments,require decisions.Analyses require assumptions related to the modeling of the real components or system.All assumptions and decisions should be identified and recorded. Analyze the problem.Using your solution strategy in conjunction with your decisions and assumptions,execute the analysis of the problem.Reference the sources of all equations,tables,charts,software results,etc.Check the credibility of your results. Check the order of magnitude,dimensionality,trends,signs,etc. Evaluate your solution.Evaluate each step in the solution,noting how changes in strategy,decisions,assumptions,and execution might change the results,in positive or negative ways.If possible,incorporate the positive changes in your final solution. Present your solution.Here is where your communication skills are important.At this point,you are selling yourself and your technical abilities.If you cannot skill- fully explain what you have done,some or all of your work may be misunderstood and unaccepted.Know your audience. As stated earlier,all design processes are interactive and iterative.Thus,it may be nec- essary to repeat some or all of the above steps more than once if less than satisfactory results are obtained. In order to be effective,all professionals must keep current in their fields of endeavor.The design engineer can satisfy this in a number of ways by:being an active member of a professional society such as the American Society of Mechanical Engineers (ASME),the Society of Automotive Engineers (SAE),and the Society of Manufacturing Engineers (SME);attending meetings,conferences,and seminars of societies,manufacturers,universities,etc.;taking specific graduate courses or programs at universities;regularly reading technical and professional journals;etc.An engineer's education does not end at graduation. The design engineer's professional obligations include conducting activities in an ethical manner.Reproduced here is the Engineers'Creed from the National Society of Professional Engineers(NSPE): As a Professional Engineer I dedicate my professional knowledge and skill to the advancement and betterment of human welfare. I pledge: To give the utmost of performance; To participate in none but honest enterprise; To live and work according to the laws of man and the highest standards of pro- fessional conduct; To place service before profit,the honor and standing of the profession before personal advantage,and the public welfare above all other considerations. In humility and with need for Divine Guidance,I make this pledge Adopted by the National Society of Professional Engineers,June 1954."The Engineer's Creed."Reprinted by permission of the National Society of Professional Engineers.This has been expanded and revised by NSPE.For the current revision,January 2006.see the website www.nspe.org/ethics/ehl-code.asp.or the pdf file,www.nspe.org/ethics/code-2006-Jan.pdf
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design © The McGraw−Hill 17 Companies, 2008 Introduction to Mechanical Engineering Design 11 from first principles, textbooks, or handbooks relating the known and unknown parameters; experimentally or numerically based charts; specific computational tools as discussed in Sec. 1–4; etc. • State all assumptions and decisions. Real design problems generally do not have unique, ideal, closed-form solutions. Selections, such as choice of materials, and heat treatments, require decisions. Analyses require assumptions related to the modeling of the real components or system. All assumptions and decisions should be identified and recorded. • Analyze the problem. Using your solution strategy in conjunction with your decisions and assumptions, execute the analysis of the problem. Reference the sources of all equations, tables, charts, software results, etc. Check the credibility of your results. Check the order of magnitude, dimensionality, trends, signs, etc. • Evaluate your solution. Evaluate each step in the solution, noting how changes in strategy, decisions, assumptions, and execution might change the results, in positive or negative ways. If possible, incorporate the positive changes in your final solution. • Present your solution. Here is where your communication skills are important. At this point, you are selling yourself and your technical abilities. If you cannot skillfully explain what you have done, some or all of your work may be misunderstood and unaccepted. Know your audience. As stated earlier, all design processes are interactive and iterative. Thus, it may be necessary to repeat some or all of the above steps more than once if less than satisfactory results are obtained. In order to be effective, all professionals must keep current in their fields of endeavor. The design engineer can satisfy this in a number of ways by: being an active member of a professional society such as the American Society of Mechanical Engineers (ASME), the Society of Automotive Engineers (SAE), and the Society of Manufacturing Engineers (SME); attending meetings, conferences, and seminars of societies, manufacturers, universities, etc.; taking specific graduate courses or programs at universities; regularly reading technical and professional journals; etc. An engineer’s education does not end at graduation. The design engineer’s professional obligations include conducting activities in an ethical manner. Reproduced here is the Engineers’ Creed from the National Society of Professional Engineers (NSPE)4 : As a Professional Engineer I dedicate my professional knowledge and skill to the advancement and betterment of human welfare. I pledge: To give the utmost of performance; To participate in none but honest enterprise; To live and work according to the laws of man and the highest standards of professional conduct; To place service before profit, the honor and standing of the profession before personal advantage, and the public welfare above all other considerations. In humility and with need for Divine Guidance, I make this pledge. 4 Adopted by the National Society of Professional Engineers, June 1954. “The Engineer’s Creed.” Reprinted by permission of the National Society of Professional Engineers. This has been expanded and revised by NSPE. For the current revision, January 2006, see the website www.nspe.org/ethics/ehl-code.asp, or the pdf file, www.nspe.org/ethics/code-2006-Jan.pdf
Budynas-Nisbett:Shigley's I.Basics 1.Introduction to T©The McGraw-Hil Mechanical Engineering Mechanical Engineering Companies,2008 Design,Eighth Edition Design 12 Mechanical Engineering Desigr 1-6 Standards and Codes A standard is a set of specifications for parts,materials,or processes intended to achieve uniformity,efficiency,and a specified quality.One of the important purposes of a standard is to place a limit on the number of items in the specifications so as to provide a reasonable inventory of tooling,sizes,shapes,and varieties. A code is a set of specifications for the analysis,design,manufacture,and con- struction of something.The purpose of a code is to achieve a specified degree of safety, efficiency,and performance or quality.It is important to observe that safety codes do not imply absolute safery.In fact,absolute safety is impossible to obtain.Sometimes the unexpected event really does happen.Designing a building to withstand a 120 mi/h wind does not mean that the designers think a 140 mi/h wind is impossible;it simply means that they think it is highly improbable. All of the organizations and societies listed below have established specifications for standards and safety or design codes.The name of the organization provides a clue to the nature of the standard or code.Some of the standards and codes,as well as addresses,can be obtained in most technical libraries.The organizations of interest to mechanical engineers are: Aluminum Association (AA) American Gear Manufacturers Association (AGMA) American Institute of Steel Construction (AISC) American Iron and Steel Institute (AISI) American National Standards Institute(ANSI)> ASM International American Society of Mechanical Engineers(ASME) American Society of Testing and Materials(ASTM) American Welding Society (AWS) American Bearing Manufacturers Association (ABMA)' British Standards Institution(BSI) Industrial Fasteners Institute (IFI) Institution of Mechanical Engineers(I.Mech.E.) International Bureau of Weights and Measures (BIPM) International Standards Organization (ISO) National Institute for Standards and Technology (NIST) Society of Automotive Engineers(SAE) 1-7 Economics The consideration of cost plays such an important role in the design decision process that we could easily spend as much time in studying the cost factor as in the study of the entire subject of design.Here we introduce only a few general concepts and simple rules. SIn 1966 the American Standards Association (ASA)changed its name to the United States of America Standards Institute (USAS).Then,in 1969,the name was again changed,to American National Standards Institute,as shown above and as it is today.This means that you may occasionally find ANSI standards designated as ASA or USAS. "Formally American Society for Metals(ASM).Currently the acronym ASM is undefined. 7In 1993 the Anti-Friction Bearing Manufacturers Association(AFBMA)changed its name to the American Bearing Manufacturers Association(ABMA). Former National Bureau of Standards(NBS)
Budynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition I. Basics 1. Introduction to Mechanical Engineering Design 18 © The McGraw−Hill Companies, 2008 12 Mechanical Engineering Design 1–6 Standards and Codes A standard is a set of specifications for parts, materials, or processes intended to achieve uniformity, efficiency, and a specified quality. One of the important purposes of a standard is to place a limit on the number of items in the specifications so as to provide a reasonable inventory of tooling, sizes, shapes, and varieties. A code is a set of specifications for the analysis, design, manufacture, and construction of something. The purpose of a code is to achieve a specified degree of safety, efficiency, and performance or quality. It is important to observe that safety codes do not imply absolute safety. In fact, absolute safety is impossible to obtain. Sometimes the unexpected event really does happen. Designing a building to withstand a 120 mi/h wind does not mean that the designers think a 140 mi/h wind is impossible; it simply means that they think it is highly improbable. All of the organizations and societies listed below have established specifications for standards and safety or design codes. The name of the organization provides a clue to the nature of the standard or code. Some of the standards and codes, as well as addresses, can be obtained in most technical libraries. The organizations of interest to mechanical engineers are: Aluminum Association (AA) American Gear Manufacturers Association (AGMA) American Institute of Steel Construction (AISC) American Iron and Steel Institute (AISI) American National Standards Institute (ANSI)5 ASM International6 American Society of Mechanical Engineers (ASME) American Society of Testing and Materials (ASTM) American Welding Society (AWS) American Bearing Manufacturers Association (ABMA)7 British Standards Institution (BSI) Industrial Fasteners Institute (IFI) Institution of Mechanical Engineers (I. Mech. E.) International Bureau of Weights and Measures (BIPM) International Standards Organization (ISO) National Institute for Standards and Technology (NIST)8 Society of Automotive Engineers (SAE) 1–7 Economics The consideration of cost plays such an important role in the design decision process that we could easily spend as much time in studying the cost factor as in the study of the entire subject of design. Here we introduce only a few general concepts and simple rules. 5 In 1966 the American Standards Association (ASA) changed its name to the United States of America Standards Institute (USAS). Then, in 1969, the name was again changed, to American National Standards Institute, as shown above and as it is today. This means that you may occasionally find ANSI standards designated as ASA or USAS. 6 Formally American Society for Metals (ASM). Currently the acronym ASM is undefined. 7 In 1993 the Anti-Friction Bearing Manufacturers Association (AFBMA) changed its name to the American Bearing Manufacturers Association (ABMA). 8 Former National Bureau of Standards (NBS)
