【正文】 o produce the best product for the society today． It is natural that designing engineers give first consideration to the functional and economic aspects of new products or devices． Machinery design needs to ensure safety and reliability in a prescribed lifetime． To address such a problem conventionally， the technical consideration of the mechanical ponent design is largely centered around two main areas of concerns： (1) strengthstiffnessstability criteria involving the bulk of a solid member and (2) surface phenomena including friction， lubrication， weal7， and environmental deterioration． However， in parison with such relatively straightforward putations as stress and deflection， the design determination of safety and reliability is likely to be an elusive and indefinite matter， plicated by psychological and sociological factors． It must be kept in mind that safety and reliability are inherently relative to each other， and the value judgments must be made with regard to trade—offs between safety， reliability， cost， weight，and so forth． On the other hand， a practical design needs to reflect clearly manufacturability and economy to make sure of the lowest cost as well as the least consumption of energy and materials． Otherwise， the products or devices designed will be of no further engineering or mercial interests． Nowadays， the simultaneous considerations of 中英文資料 4 manufacturing and assembly factors phases including design， manufacturing，inspection， as assembly and other is considered in such a parallel fashion that the quality and cost are best satisfied concurrently． In addition to these traditionally technological and economic considerations fundamental to the design and development of mechanical ponents and systems， the modern engineers have bee increasingly concerned with the broader considerations of sustainability， ecology， aesthetics， ergonomics， maintainability，and overall quality of life． It is clear that a greater than ever engineering effort is being recently devoted to broader considerations relating to the influences of engineered products on people as well as on the environment． The following is a list of general factors for engineers to consider in the design process， which from a different viewpoint shows us a panoramic picture with regard to the designrelated activities and tasks． (1) Cost of manufacturing． Will the selling price be petitive? Are there cheaper ways of manufacturing the machine? Could other materials be used? Are any special tools， dies, jigs， or fixtures needed? Can it easily be inspected? Can the workshop produce it? Is heat treatment necessary? Can parts be easily welded? 第 4頁 Cost of operation． Are power requirements too large? What type of fuel will be used? Will operation cost be less expensive? (3) Cost of maintenance． Are all parts easily accessible? Are access panels needed? Can mon tools be used? Can replacement parts be available? (4) Safety features． Is a suitable factor of safety used? Does the safety factor meet existing codes? Are fuses， guards， and／ or safety valves used? Are shear pins needed? Is there any radiation hazard? Any overlooked ”stress raiser”? Are there any dangerous fumes? (5) Packaging and transportation． Can the machine be readily packaged for shipping without breakage? Is its size suitable to parcel post regulations, freight car dimensions， or trailer truck size? Are shipping bolts necessary? Is its center of gravity in a desirable location? (6) Lubrication． Does the system need periodic checking? Is it automatic? Is it a sealed system? (7) Materials． Are chemical， physical， and mechanical properties suitable to its use? Is corrosion a factor? Will the materials withstand impact? Is thermal or electrical conductivity important? Will high or low temperatures present any problem? Will design stress keep parts reasonable in size? (8) Strength． Have dimensions of ponents been carefully calculated? Have all the load cases be taken into account? Have the stress concentrations been carefully considered? Has the fatigue effect be puted? (9) Kinematics． Does it provide necessary motion for moving parts? Are rotational speeds reasonable? Could linkages replace cams? What will be the best 中英文資料 5 choice， the belts， chains or gears?