外文翻译--对机械设计的认识

Knowledge of machine design The machine design is an application technical science which designs the new product or improves the old product to meet the human need. It involves all domains of the project technology , which mainly studies basic idea of the size, the shape and the detailed structure of products. And it also studies the questions of manufacture, sale and usage.The goal of the machine design is to produce the product which meets the human need. The invention, discovery and technical knowledge are not necessarily bringing the advantages to humanity, which take benefits when they are applied on the product. So , it should be realized that if the product is needed or not before a special design carrying on . Its a good opportunity for machine designer to use creative ability on the product design, system analysis and a formulation product manufacture technology. Grasps the project elementary knowledge is more important than memorize some data and the formula. The merely service data and the formula is insufficient to the completely decision which makes in a good design. On the other hand, it should be earnest precisely all operations. For example, a decimal point position wrongly can cause the correct design to false. In the preliminary stage of design, its allowed to display the creativity for designers fully, none of restraint will be take. Even if having many impractical ideas, these can be correct in the early design, before the blueprint drawings are drawed . Only then, the mentality on innovation will be not stop up. Usually, several sets of design proposals will be proposed and compared. May be some thoughts will be used in the last proposal from the other proposals which are not accept . Usually, some problems will happen in the manufacture process. Such as making some modifies on components size or the common to make the components production easily. But, the project change must be authorized by designer to guarantee the products function not to be damaged. Sometimes, some kinds of design flaws founded before product assembling or in the experiment before packing. These instances exactly showed the design is a dynamic process. There is always a better method to complete the design work. Designers should be supposed unceasingly diligently, to seek these better methods. Recent year, the engineering material choice appeared more important. In addition, the choice process should be a continuously and reappraisal process. The new materials unceasingly appear, and some original materials keep reducing. The environmental pollution, material recycling, workers health and security will attach the new limiting condition to the choice of materials. In order to reduce the weight or save energy, it should be requested to use different material. The competition from domestic and international, the request enhancement for product service maintenance and convenience , customers aspect and so on will feedback pressure and urge the people to carry on the material reappraising. Because of the materials wrong selected , which cause the product responsibility lawsuit, has already had the profound influence. In additional, its clear that the material and the material processing interdependence. Therefore, in order to get the satisfy result under the reasonable cost and quality guarantee, project engineer have to choose, determine and use the materials carefully. The first step of product manufacturing is design . Design usually divide into several explicit stages: (a) preliminary design； (b) functional design； (c) production design. In the preliminary design stage, the designer emphatically consider the function of product. They always conceive and consider several plans, then decide if the thought is feasible； If it is feasible, they should make the further improvement to one or several plans. In this stage, the question of choice of material is: Is there a material which can conform the performance to be supplied for choice； If no, whether has a bigger assurance to develop a kind of new material in limit of the cost and the time. In the functional design and the engineering design stage, it needs to make a practical feasible design. The quite complete blueprint must be drew up in this stage, and choose, determine the materials for each kinds of components. Usually, the prototype or the working model must be manufactured , and carries on the experiment to it, appraises products function, reliability, the outward appearance and the service maintenance and so on. Although this kind of experiment will indicate that some materials will be replaced , before the product sending into the production line. But, this point is absolutely not a excuse to take not earnestly choice of the material. The outward appearance, the cost and the reliability of the product should be carefully considered, unified with the function of product. Its best for a successful company to use the same materials which are used in the normal production and the same manufacture technology when they are manufacturing the prototypes as much as possible. The function completely prototype cannot be made economically according to the anticipated sales volume, or there are some great different in the quality and the reliable for prototypes and the official production installment , this kind of prototype does not have the great value. Project engineer should complete the analysis, the choice and the determination of the material in this stage , but not remains it to the production design stage . Because, the material replacement in the production design stage is decided by other people, who are inferior to project engineer to all functions understanding of the product. In the production design stage ,it should be completely determined with the material, to make them to adapt with the existing equipment, and to use the existing equipment economically to carry on the processing, moreover, the material quantity can quite be easy to guarantee the supply. In the manufacture process, it will appear the situation to change the material on using. The experience indicated that, use some certain cheap materials to take the substitute. However, in the majority situation, changing the materials after the production process will spend higher than changing the materials before the production process . Completing the choice of materials in the design stage, may avoid the most such situations. The most common reason for changing the materials when the product under manufacturing is that the new material is appeared. Certainly, these new materials possibly reduce the cost or improve the product performance. But, the earnest appraisal to the new material must be carried on , to guarantee its all performance to achieve the purpose. Remember that: the new materials performance and the reliable is not understood by the people. The majority of products expiration and the product accident caused by negligence case is that the selects of the new material not truly understood their long-term operational performance. The product responsibility lawsuit forces designers and the company use the best procedure when they choose materials. In the material choosing process, five most common questions are: (a) did not understand or cannot use the best and the latest information about the material application aspect； (b) has not been able to foresee and to consider the possible and reasonable usage of product (for example: designer is also supposed further to forecast and the consideration when the product used wrong. In recent years, many products responsibilities lawsuit case, because wrongly uses the plaintiff which the product receives the injury to accuse produces the factory, and wins the decision)； (c) the material data are not entire or some data are indefinite, especially its long-term performance data； (d) the quality control plan is not suitable or not confirmed； (e) the personnel who is not competent to choose the material. Through the analysis five questions above , may obtain these questions is does not have the sufficient reason existence the conclusion. It will avoid these questions appearance and indicate the direction after these questions analysis. Although, using the best choice of material will not avoid having the product responsibility lawsuit. Designer and the industry carries on the choice of material according to the suitable procedure, may greatly reduce the lawsuit the quantity. From the above discussion, the choice of material should understand the material nature, the characteristic and the processing method comprehensive and basically. 对 机械设计 的认识 机械设计是一门通过设计新产品或者改进老产品来满足人类需求的应用技术科学。它涉及工程技术的各个领域，主要研究产品的尺寸、形状和详细结构的基本构思，还要研究产品在制造、销售和使用等方面的问题。机械设计的目的是生产能够满足人类需求的产品。发明、发现和科技知识本身并不一定能给人类带来好处，只有当它们被应用在产品上才能产生效益。因而，应该认识到在一个特定的产品进行设计之前，必须先确定人们是否需要这种产品 。 应当把机械设计看成是机械设计人员运用创造性的才能进行产品设计、系统分析和制定产品的制 造工艺学的一个良机。掌握工程基础知识要比熟记一些数据和公式更为重要。仅仅使用数据和公式是不足以在一个好的设计中做出所需的全部决定的。另一方面，应该认真精确的进行所有运算。例如，即使将一个小数点的位置放错，也会使正确的设计变成错误的。 在设计的初始阶段，应该允许设计人员充分发挥创造性，不受各种约束。即使产生了许多不切实际的想法，也会在设计的早期，即绘制图纸之前被改正掉。只有这样，才不致于堵塞创新的思路。通常，要提出几套设计方案，然后加以比较。很有可能在最后选定的方案中，采用了某些未被接受的方案中的一些想法。 通常 ，在制造过程中会出现某个问题。可能会要求对某个零件尺寸或公差作一些更改，使零件的生产变得容易。但是，工程上的更改必须要经过设计人员批准，以保证不会损伤产品的功能。有时，在产品的装配时或者装箱外运前的试验中才发现设计中的某种缺陷。这些事例恰好说明了设计是一个动态过程。总是存在着更好的方法来完成设计工作，设计人员应该不断努力，寻找这些更好的方法。 近些年来，工程材料的选择已经显得重要。此外，选择过程应该是一个对材料的连续不断的重新评价过程。新材料不断出现，而一些原有的材料的能够获得的数量可能会减少。环境污 染、材料的回收利用、工人的健康及安全等方面经常会对材料选择附加新的限制条件。为了减轻重量或者节约能源，可能会要求使用不同的材料。来自国内和国际竞争、对产品维修保养方便性要求的提高和顾客的反馈等方面的压力，都会促使人们对材料进行重新评价。由于材料选用不当造成的产品责任诉讼，已经产生了深刻的影响。此外，材料与材料加工之间的相互依赖关系已经被人们认识得更清楚。因此，为了能在合理的成本和确保质量的前提下获得满意的结果，设计工程师的制造工程师都必须认真仔细地选择、确定和使用材料。 制造任何产品的第一步工作都是设计。设 计通常可以分为几个明确的阶段：（ a）初步设计；（ b）功能设计；（ c）生产设计。在初步设计阶段，设计者着重考虑产品应该具有的功能。通常要设想和考虑几个方案，然后决定这种思想是否可行；如果可行，则应该对其中一个或几个方案作进一步的改进。在此阶段，关于材料选择唯一要考虑的问题是：是否有性能符合要求的材料可供选择；如果没有的话，是否有较大的把握在成本和时间都允许的限度内研制出一种新材料 。 在功能设计和工程设计阶段，要做出一个切实可行的设计。在这个阶段要绘制出相当完整的图纸，选择并确定各种零件的材料。通常要制造出样机 或者实物模型，并对其进行试验，评价产品的功能、可靠性、外观和维修保养性等。虽然这种试验可能会表明，在产品进入到生产阶段之