机械设计外文文献

Mechanical Design John Ernst Abstract A machine is a combination of mechanisms and other components which transforms transmits Examples are engines turbines vehicles hoists printing presses washing machines and movie cameras Many of the principles and methods of design that apply to machines also apply to manufactured articles that are not true machines The term mechanical design is used in a broader sense than machine design to include their design The motion and structural aspects and the provisions for retention and enclosure are considerations in mechanical design Applications occur in the field of mechanical engineering and in other engineering fields as well all of which require mechanical devices such as switches cams valves vessels and mixers Keywords Mechanical Design Mechanisms Design Process Application 1 The Design Progress Designing starts with a need real Existing apparatus may need improvements in durability efficiency weight speed or cost New apparatus may be needed to perform a function previously Done by men such as computation assembly or servicing With the objective wholly or partly In the design preliminary stage should allow to design the personnel fully to display the creativity not each kind of restraint Even if has had many impractical ideas also can in the design early time namely in front of the plan blueprint is corrected Only then only then does not send to stops up the innovation the mentality Usually must propose several sets of design proposals and then perform the comparison Has the possibility very much in the plan which finally designated has used certain not in plan some ideas which accepts When the general shape and a few dimensions of the several components become apparent analysis can begin in earnest The analysis will have as its objective satisfactory or superior performance plus safety and durability with minimum weight and a competitive cost Optimum proportions and dimensions will be sought for each critically loaded section together with a balance between the strengths of the several components Materials and their treatment will be chosen These important objectives can be attained only by analysis based upon the principles of mechanics such as those of static for reaction forces and for the optimum utilization of friction of dynamics for inertia acceleration and energy of elasticity and strength of materials for stress and deflection of physical behavior of materials and of fluid mechanics for lubrication and hydrodynamic drives The analyses may be made by the same engineer who conceived the arrangement of mechanisms or in a large company they may be made by a separate analysis division or research group Design is a reiterative and cooperative process whether done formally or informally and the analyst can contribute to phases other than his own Product design requires much research and development Many Concepts of an idea must be studied tried and then either used or discarded Although the content of each engineering problem is unique the designers follow the similar process to solve the problems Product liability suits designers and forced in material selection using the best program In the process of material the most common problems for five a don t understand or not use about the latest application materials to the best information b failed to foresee and consider the reasonable use material may such as possible designers should further forecast and consider due to improper use products In recent years many products liability in litigation the use of products and hurt the plaintiff accused manufacturer and won the decision c of the materials used all or some of the data data especially when the uncertainty long term performance data is so d quality control method is not suitable and unproven e by some completely incompetent persons choose materials Through to the above five questions analysis may obtain these questions is does not have the sufficient reason existence the conclusion May for avoid these questions to these questions research analyses the appearance indicating the direction Although uses the best choice of material method not to be able to avoid having the product responsibility lawsuit designs the personnel and the industry carries on the choice of material according to the suitable procedure may greatly reduce the lawsuit the quantity May see from the above discussion the choice material people should to the material nature the characteristic and the processing method have comprehensive and the basic understanding Finally a design based upon function and a prototype may be built If its tests are satisfactory the initial design will undergo certain modifications that enable it to be manufactured in quantity at a lower cost During subsequent years of manufacture and service the design is likely to undergo changes as new ideas are conceived or as further analyses based upon tests and experience indicate alterations Sales appeal 2 Some Rules for Design In this section it is suggested that applied with a creative attitude analyses can lead to important improvements and to the conception and perfection of alternate perhaps more functional economical and durable products To stimulate creative thought the following rules are suggested for the designer and analyst The first six rules are particularly applicable for the analyst 1 A creative use of need of physical properties and control process 2 Recognize functional loads and their significance 3 Anticipate unintentional loads 4 Devise more favorable loading conditions 5 Provide for favorable stress distribution and stiffness with minimum weight 6 Use basic equations to proportion and optimize dimensions 7 Choose materials for a combination of properties 8 Select carefully stock and integral components 9 Modify a functional design to fit the manufacturing process and reduce cost 10 Provide for accurate location and noninterference of parts in assembly Machinery design covers the following contents 1 Provides an introduction to the design process problem formulation and safety factors 2 Reviews the material properties and static and dynamic loading analysis Including beam vibration and impact loading 3 Reviews the fundamentals of stress and defection analysis 4 Introduces fatigue failure theory with the emphasis on stress life approaches to high cycle fatigue design which is commonly used in the design of rotation machinery 5 Discusses thoroughly the phenomena of wear mechanisms surface contact stresses and surface fatigue 6 Investigates shaft design using the fatigue analysis techniques 7 Discusses fluid film and rolling element bearing theory and application 8 Gives a thorough introduction to the kinematics design and stress analysis of spur gears and a simple introduction to helical bevel and worm gearing 9 Discusses spring design including compression extension and torsion springs 10 Deals with screws and fasteners including power screw and preload fasteners 11 Introduces the design and specification of disk and drum clutches and brakes The complete design of a machine is a complex process The machine design is a creative work Project engineer not only must have the creativity in the work but also must in aspect and so on mechanical drawing kinematics engineering material materials mechanics and machine manufacture technology has the deep elementary knowledge One of the first steps in the design of any product is to select the material from which each part is to be made Numerous materials are available to today s designers The function of the product its appearance the cost of the material and the cost of fabrication are important in making a selection A careful evaluation of the properties of a material must be made prior to any calculations Careful calculations are necessary to ensure the validity of a design In case of any part failures it is desirable to know what was done in originally designing the defective components The checking of calculations and drawing dimensions is of utmost importance The misplacement of one decimal point can ruin an otherwise acceptable project All aspects of design work should be checked and rechecked The computer is a tool helpful to mechanical designers to lighten tedious calculations and provide extended analysis of available data Interactive systems based on computer capabilities have made possible the concepts of computer aided design CAD and computer aided manufacturing CAM How does the psychologist frequently discuss causes the machine which the people adapts them to operate A design personnel s basic responsibility is diligently causes the machine to adapt the people This certainly is not an easy work because certainly does not have to all people to say in fact all is the most superior operating area and the operating process Another important question project engineer must be able to carry on the exchange and the consultation with other concerned personnel In the initial stage designs the personnel to have to carry on the exchange and the consultation on the preliminary design with the administrative personnel and is approved This generally is through the oral discussion the schematic diagram and the writing material carries on If front sues the machine design goal is the production can meet the human need the product The invention the discovery and technical knowledge itself certainly not necessarily can bring the advantage to the humanity only has when they are applied can produce on the product the benefit Thus should realize to carries on before the design in a specific product must first determine whether the people do need this kind of product Must regard as the machine design is the machine design personnel carries on using creative ability the product design the system analysis and a formulation product manufacture technology good opportunity Grasps the project elementary knowledge to have to memorize some data and the formula is more important than The merely service data and the formula is insufficient to the completely decision which makes in a good design needs On the other hand should be earnest precisely carries on all operations For example even if places wrong a decimal point position also can cause the correct design to turn wrongly Good design personnel should dare to propose the new idea moreover is willing to undertake the certain risk when the new method is not suitable use original method Therefore designs the personnel to have to have to have the patience because spends the time and the endeavor certainly cannot guarantee brings successfully A brand new design the request screen abandons absolutely many knows very well the method for the people Because many person of conservativeness does this certainly is not an easy matter A mechanical designer should unceasingly explore the improvement existing product the method should earnestly choose originally the process confirmation principle of design in this process with has not unified it after the confirmation new idea Human life can not be separated from the machinery it is everywhere but for the mechanical manufacturing production and its development and future we know little about After this semester I have more knowledge and understanding of the profession of the mechanical From the primitive society of early human use such as axes knives and other simple tools to a simple lever pulley human bicycles animal Kip Shum car tools developed to a more complex hydraulic drive wind driven Shuinian and windmills morecomplex machinery After the 18th century British Industrial Revolution the steam engine internal combustion engines electric motors mechanical power source for the rapid development of manufacturing transport human beings began to enter the modern civilized society The 20th century the computer issuing automatic control technology information technology infectious organic combination of technology so that the machinery is fully modernized phase Robotics CNC machine tools high speed delivery vehicles heavy machinery and the large number of advanced machinery and equipment to accelerate the prosperity and progress of human society humans can travel into space landing on the moon you can explore the vast depths of the sea to live and pass below the surface all of which can not be separated from the machinery the development of the machinery into the intelligent stage Machinery has become one of the five elements of production and services of modern society The history of the development of the mechanical history of the development of human civilization In ancient Chinese mechanical engineering invention and creativity is very brilliant such as grinding technology metal smelting technology China s machinery manufacturing industry developed after 1949 After the founding of new China the tremendous achievements of China s economy are inseparable from the progress of the manufacturing sector After decades of struggle China s manufacturing components with considerable scale an