【正文】 r method, called quality function deployment or QFD, seeks to identify all of the features and performance factors that customers desire and to assess the relative importance of these factors. The result of the QFD process is a detailed set of functions and design requirements for the product.It is also important to consider how the design process fits with all functions that must happen to deliver a satisfactory product to the customer and to service the product throughout its life cycle. In fact, it is important to consider how the product will be disposed of after it has served its useful life. The total of all such functions that affect the product is sometimes called the product realization process or PRP.Skills needed in mechanical design Product engineers and mechanical designers use a wide range of skills and knowledge in their daily work, including the following:（1）Sketching, technical drawing and puteraided design.（2）Properties of materials, materials processing, and manufacturing processes. （3）Applications of chemistry such as corrosion protection , plating , and painting.（4）Statics, dynamics, strength of materials, kinematics, and mechanisms.（5）Oral munication, listening, technical writing, and teamwork skills. （6）Fluid mechanics, thermodynamics, and heat transfer. （7）Fluid power, the fundamentals of electrical phenomena, and industrial controls. （8）Experimental design and performance testing of materials and mechanical systems. （9）Creativity, problem solving, and project management. （10）Stress analysis. （11）Specialized knowledge of the behavior of machine elements such as gears, belt drives, chain drives, shafts, bearings, keys, splines, couplings, seals, springs, connections (bolted, riveted, welded, adhesive), electric motors, linear motion devices, clutches, and brakes.It is expected that you will have acquired a high level of petence in multidisciplinary knowledge and skills that are developed continuously throughout your academic study and through experience.Functions, design requirements, and evaluation criteria In order to emphasize the importance of carefully identifying the needs and expectations of the customer prior to beginning the design of a mechanical device, you can formulate these by producing clear, plete statements of functions, design requirements, and evaluation criteria:Functions tell what the device must do, using general, nonquantitative statements that employ action phrases such as to support a load, to lift a crate, to transmit power, or to hold two structural members together.Design requirements are detailed, usually quantitative statements of expected performance levels, environmental conditions in which the device must operate, limitations on space or weight, or available materials and ponents that may be used.Careful preparation of function statements and design requirements will ensure that the design effort is focused on the desired results. Much time and money can be wasted on designs that, although technically sound, do not meet design requirements. Design requirements should include everything that is needed, but at the same time they should offer ample opportunity for innovation.Evaluation criteria are statements of desirable qualitative characteristics of a design that assist the designer in deciding which alternative design is optimum—that is, the design that maximizes benefits while minimizing disadvantages.Evaluation criteria should be developed by all members of a product development team to ensure that the interests of all concerned parties are considered. Often weights are assigned to the criteria to reflect their relative importance. Safety must always be the paramount criterion. Different design concepts may have varying levels of inherent safety in addition to meeting stated safety requirements as noted in the design requirements list. Designers and engineers are legally liable if a person is injured because of a design error. You must consider any reasonably foreseeable uses of the device and ensure safety of those operating it or those who may be close by. Achieving a high overall performance should also be a high priority. Certain design concepts may have desirable features not present on others.Together these elements can be called the specifications for the design.Most designs progress through a cycle of activities as outlined in Figure . You should typically propose more than one possible alternative design concept. This is where creativity is exercised to produce truly novel designs. Each design concept must satisfy the functions and design requirements. A critical evaluation of the desirable features, advantages, and disadvantages of each design concept should be pleted. Then a rational decision analysis technique should use the evaluation criteria to decide which design concept is the optimum and, therefore, should be produced.Example of the integration of machine elements into a mechanical design Mechanical design is the process of designing and/or selecting mechanical ponents and putting them together to acplish a desired function. Of course, machine elements must be patible, must fit well together, and must perform safely and efficiently. The designer must consider not only the performance of the element being designed at a given time but also the elements with which it must interface.Identify customer requirementsDefine functions of the deviceState design requirementsDefine evaluation criteriaPropose several alternativeDesign conceptsEvaluate each propose alternativeRate each alternative againsteach evaluation criterionSelect the optimum design conceptComplete detailed design of theselected conceptDefine SpecificationsCreate Design ConceptDecision MakingDetailed DesignFigure Steps in the design processTo illustrate how the design of machine elements must be integrated with a larger mechanical design, let us