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发动机零件及其工作原理模具设计与制造外文翻译

时间:2013-1-11 16:15:28  作者:鸿禾娱乐官网注册-鸿禾娱乐怎么注册  来源:www.92bylw.com  查看:32  评论:0

原 文 标 题 Engine Parts and Operation and Mould Design and
 Manufacturing
译 文 标 题 译文标题 发动机零件及其工作原理和模具设计与制造
原文标题 Engine Parts and Operation and Mould Design and Manufacturing
作    者  译  名  国 籍 中国
原文出处 机电工程专业英语
    译文:
   汽车要始终根据使用者的要求进行设计。汽车上使用的发动机必须要重量轻并且燃料损耗少,这是工程师设计各种类型发动机时主要考虑的两个因素。
   汽车发动机可以是单缸的,单缸发动机只有一个气缸,而多缸发动机有多个气缸,所有气缸内的活塞都和曲轴相连,因此发动机可以是:
   单缸——气缸可能直列也可能水平;
   多缸——气缸可能直列也可能倾斜。
   如今大多数的汽车使用火花点火、四冲程、往复式汽油发动机。
   往复式汽油发动机每个气缸内都有一个圆形的活塞、一个连杆和一个曲轴。它的工作原理很简单,活塞在气缸内向上移动,压缩它上面的空气和燃油的混合气。压缩使空气和燃油非常易燃,当活塞到达它行程的顶端时燃油混合气被点燃。活塞在气缸内被膨胀气体向下推,它又推动连杆使得曲轴旋转,曲轴回转产生能量推动汽车。伴随曲轴转动,活塞又返回到气缸顶部再一次重复循环,活塞持续上下运动,这就是发动机被称作往复式发动机的原因。
   燃烧的混合气被气缸盖和气缸垫密封在气缸的顶部,如图26.2 所示。气缸盖上有进气口和排气口,进气口允许空气燃油混合气流入气缸,排气口允许燃烧后的废气排出,每个口都有一个气门密封,它由凸轮轴上的凸轮打开,被气门弹簧关闭,如图26.2 所示。活塞靠活塞环在气缸里密封,当活塞上下运动时,活塞环沿着气缸壁滑动。
   图 26.1 气缸组成示意图                      图26.2 气缸气门操作示意图
   
             图 26.3 四冲程循环示意图
   四冲程循环
   
在这里用单缸发动机来描述四个冲程的循环。如图26.3 所示。汽车发动机实际上由多个气缸。活塞从行程顶端到行程底端的运动叫做一个冲程,每个循环要求燃烧空气燃油混合气有四个冲程,因此,叫做四冲程循环。
       在进气冲程,活塞被旋转的曲轴向下拉,在它上方产生一个真空,因为在活塞向下移动时进气门打开,空气燃油混合气通过进气门进入气缸,混合气是由燃油系统提供给气缸的。当一部分汽油和15 倍的空气混合后尤其易燃,雾化使得混合气体成雾状。
   压缩冲程,活塞在气缸内返回,压缩混合气体,使它更加易燃。当活塞接近它行程的顶端时,火花塞点燃混合气。
   做功冲程,燃烧后的混合气体迅速膨胀,迫使活塞在气缸内向下移动,当活塞接近行程底部终点时,排气门打开使得燃烧的气体可以在活塞再一次在气缸内向上运动之前排出。排气冲程,活塞向上运动,通过排气门把气缸内残留的废气挤压出去,随着曲轴的连续转动,活塞在气缸内上下运动,重复四冲程的循环。
   模具设计与制造
   CAD 和CAM 广泛用于模具的设计和制造中。CAD 允许你在屏幕上画出模型,然后采用三维动画从各个角度进行察看,最后通过在数字仿真模型上引入各类参数(压力、温度、冲力等)进行测试。而CAM,从另一方面来说,能够控制制造质量。这些鸿禾娱乐官网注册技术的优点是很多的:设计时间短(可用鸿禾娱乐官网注册的速度进行修改)、费用低、制造快,等等。这种新的方法还允许进行小批量生产,可以在最后一分钟对某个特定零件的模具进行改动。最后这些新工艺还可用来制造复杂的零件。
    模具的鸿禾娱乐官网注册辅助设计
   一直以来模具的制图是一项费时的任务,它不属于创造性工艺过程的一部分。制图不是工艺过程所要求的部分,但对工艺组织不说是必需的。
   鸿禾娱乐官网注册辅助设计(CAD)是指采用鸿禾娱乐官网注册及其外围装置来简化和提高设计过程。CAD 系统提供了一种高效的设计方法,并且当它和坐标测量机器和其他检验设备结合使用时可用来创立检验程序。在选择工艺顺序时CAD 数据将发挥关键的作用。
   一个 CAD 系统由3 个基本的部件组成:硬件、软件、用户。一个典型的CAD 系统的硬件部分包括一个处理器、一个系统显示器、一个键盘、一个数字转换器和一个绘图仪。而CAD 系统的软件部分由允许其完成设计和画图功能的程序组成。用户是模具的设计者,他采用硬件和软件来完成设计过程。
   在产品的三维数据的基础上,应首先对模芯和型腔进行设计。通常设计人员先进行零件的预设计,这意味着可以改变围绕模芯和型腔所进行的工作。现代CAD 系统可支持该设计,先针对确定好的画图方向计算出一条分模线,将零件分成模芯和型腔两侧,并生成出流表面和截流表面。在计算出零件的最佳设计草案后,再确定型腔、滑道和嵌件的位置和方向。然后在初步设计阶段,粗略地定出模具部件的位置和几何形状——例如滑动装置、喷出系统等。有了这些信息,便可确定板的大小和厚度,并从产品标准目录中选取相应的标准模具。如果没有一个标准的模具能满足需要,则选择和要求最接近的标准模具并做相应修改——通过调整限制和参数使得任意数量的任意尺寸的板子都能用于设计中。对功能部件进行细化,并加入标准部件完成整个模具的设计(图23.1)。这一切均在三维空间中进行。此外,模具系统还提供了对零件进行检查、修改和细化的功能。早在这个阶段,就可以自动生成图纸和材料清单了。
   通过运用模具设计系统的三维设计及功能,可在开始阶段就消除二维设计中的典型错误——例如冷却系统和部件/型腔间的碰撞或孔的位置错误。在任何阶段都能生成材料和图纸的清单——从而能够准时定购材料,并且总是具备实际的文件可用来与客户进行探讨,或者对模具制造商来说总是能给出报价。
   一个特定的三维模具设计系统的使用能缩短研发周期。提高模具质量,增进团队合作,使设计人员从沉闷的日常工作中解脱出来。但经济上的成功主要取决于工作流程的组织。只有采取了适当的组织方法和人员评估策略才能缩短研发周期。零件设计、模具设计、电气设计以及模具制造部门必须紧密合作,协同工作。
模具的鸿禾娱乐官网注册辅助制造
   减少制造费用和研发周期的一个方法是建立能够充分发挥设备和人员潜能的制造系统。这类制造系统的基础是采用CAD 数据来帮助对主要工艺做出决策,使得最终能够提高机器精度并减少不直接从事生产的时间。这就被称为鸿禾娱乐官网注册辅助制造(CAM)。CAM 的目的是,如果可能的话,通过从鸿禾娱乐官网注册工作站启动机器运作,从而直接生产出模具断面而不需要经过中间步骤。
   对于一个好的 CAM 系统,自动化不仅仅体现在某个独立的细节上。加工工艺的自动化还体现在组成一个零件的各个侧面之间,最终导致方法路径的最优化。当你要产生多种特征时,CAM 系统会为你构建一个工艺规划。它会在系统分析的基础上指定操作步骤以减少工具的变动以及所采用的工具的数目。
   在 CAM 方面,发展趋势是新技术和新工艺,例如微研磨,以支持带复杂三维结构和高表面质量的高精度注塑模具的制造。CAM 软件将继续在软件本身固有的智能化加工的深度和广度上发展,直至鸿禾娱乐官网注册数值控制(CNC)编程工艺变成完全自动化。对于要求加工操作步骤能更灵活地组合在一起的先进的多功能加工工具来说尤其如此。CAM 软件在保持机械师所需要的控制的同时,将继续使冗余的制造工艺逐渐自动化,使其通过鸿禾娱乐官网注册更快且更精确地进行操作。
   在强调模具制造业在维持质量的同时还要以最高效的方式制造模具的今天,模具制造商们需要紧跟最新的软件技术包,以便使他们能够快速地规划并制造出复杂的模具,从而减少模具生产时间。简言之,模具制造业正朝着提高CAD 和CAM 之间以及CAM 和CNC之间数据交换的质量方向发展,并且CAM 软件在涉及加工工艺方面变得更为智能化——从而减少了生产周期和总的加工时间。同时五轴加工已作为“必须有的”加工方式出现在车间工场上——尤其是在涉及型腔较深的场合。随着电子数据处理(EDP)被引入模具制造业,模具制造出现了新的发展机会,从而可以缩短生产时间、提高成本效率并获得更好的质量。

   
   
原文:
   Automobiles are designed keeping in view the requirements of users.Significantly, the engines used in automobiles must be light in weight and their fuel consumption must be minimum. These are the two main considerations which have led engineers to develop various types of automobile engines.
   An engine may be a single-cylinder engine. In a single-cylinder engine there is only one cylinder, whereas in a multi-cylinder engine there is more than one cylinder. The pistons of all the cylinders are connected to the commoncrankshaft. Therefore engines may be:
   Single-cylinder  Cylinder may be vertical or horizontal
   Multi-cylinder   Cylinder may be vertical or inclined to vertical plane
   Most of today!ˉs automobiles use spark-ignitedfour-stroke reciprocating gasoline engines. 
   A reciprocating gasoline engine has a round piston in a cylinder, a connecting rod, and a crankshaft. The principle of its operation is simple.   The piston moves up in the cylinder, compressing a mixture of air and fuel in front of it. Compressing the air and fuel makes it very flammable. When the piston reaches the top of its travel, the air-fuel mixture is ignited.As the piston is pushed down in the cylinder by the expanding gases, it pushes on the rod, forcing the crankshaft to rotate.
   Power is taken from the rotation of the crankshaft to propel the car. As the crankshaft turns, the piston is returned to the top of the cylinder to repeat the cycle again. The continuing up-and-down motion of the piston is why the engine is called a reciprocating engine.
   The burning mixture is sealed into the cylinder on the top end by a cylinder head and a head gasket (Fig.26.1). The cylinder head hasintake and exhaust ports. The intake port allows the flow of the air-fuel mixture into the cylinder. The exhaust port allows the escape of the exhaust gases after the mixture has been burned. Each port is sealed by a valve that is opened by a lobe on the camshaft and closed by a spring (Fig.26.2). The piston is sealed to the cylinder with piston rings that slide against the cylinder wall as the piston moves up and down.
   Four-Stroke Cycle
   The four-stroke cycle is described here using a single cylinder engine (Fig.26.3). Automobile engines actually have multiple cylinders. The movement of the piston from the top of its travel to the bottom of its travel is called a stroke. Each cycle required to burnthe air-fuelmixture has four strokes. Hence the name, four-stroke cycle.

                            
   
       Fig.26.1EngineParts     Fig.26.2 The Valve Is Operated by a Lobe                                  
                                              
   
            Fig.26.3 The Four-Stroke Cycle
     
     
     During the intake stroke, the piston is pulled down by the turning crankshaft, creating a vacuum above it. Because the intake valve is open while the piston is moving down, the air-fuel mixture is drawn into the cylinder through the intake valve port. The mixture is supplied to the cylinder by the fuel system. Gasoline is especially combustible when one part of it is atomized with about 15 parts of air. Atomization makes the mixture like fog.
     The piston moves back up in the cylinder on the compression stroke,   compressing the air-fuel, making it far more combustible. As the piston approaches the top of its travel, a spark plug ignites the mixture.
     During the power stroke the burning fuel expands rapidly, forcing the piston to move back down in the cylinder. The exhaust valve opens as the piston approaches the bottom of its travel.This is so that burning gases can escape before the piston begins to move upward in the cylinder once again.
     
     
   During the exhaust stroke the piston moves back up, forcing any remaining exhaust gas from the cylinder through the open exhaust valve. As the crankshaft continues to rotate, the piston goes back down in the cylinder as the four-stroke cycle repeats itself.
   Mould Design and Manufacturing
   CAD and CAM are widely applied in mould design and mould making. [1]CAD allowsyouto draw a model on screen, then view it from every angle using 3-D animation and, finally, to testit by introducing various parameters into the digital simulation models (pressure,  temperature,impact, etc.). CAM, on the other hand,  allows you to control the manufacturing quality.  Theadvantages of these computer technologies are legion: shorter design times (modifications can bemade at the speed of the computer), lower cost, faster manufacturing, etc. This new approach also allows shorter production runs, and to make last-minute changes to the mould for a particular part.Finally, also, these new processes can be used to make complex parts.
   Computer-Aided Design (CAD) of Mould
   Traditionally, the creation of drawings of mould tools has been a time-consuming task thatis not part of the creative process. Drawings are an organizational necessity rather than a desiredpart of the process.
   Computer-Aided Design (CAD)  means using the computer and peripheral devices to simplify and enhance the design process. CAD systems offer an efficient means of design, and can be used to create inspection programs when used in conjunction with coordinate measuring machines and other inspection equipment.  CAD data also can play a critical role in selecting process sequence.
   A CAD system consists of three basic components: hardware, software, users. The hardware components of a typical CAD system include a processor,  a system display, a keyboard, a digitizer, and a plotter. The software component of a CAD system consists of the programs which allow it to perform design and drafting functions. The user is the tool designer who uses the hardware and software to perform the design process.
   Based on the 3-D data of the product, the core and cavity have to be designed first. Usually the designer begins with a preliminary part design, which means the work around the core and cavity could change.  Modern CAD systems can support this with calculating a split line for a defined draft direction, splitting the part in the core and cavity side and generating the run-off or shut-off surfaces. After the calculation of the optimal draft of the part, the position and direction of the cavity, slides and inserts have to be defined. Then, in the conceptual stage, the positions and the geometry of the mould components—such as slides, ejection system, etc. —are roughly defined.  With this information,  the size and thickness of the plates can be defined and the corresponding standard mould can be chosen from the standard catalog. If no standard mould fits these needs, the standard mould that comes nearest to the requirements is chosen and changed accordingly—by adjusting the constraints and parameters so that any number of plates with any size can be used in the mould. Detailing the functional components and adding the standard components complete the mould(Fig.23.1). This all happens in 3-D. Moreover, the mould system provides functions for the checking, modifying and detailing of the part. Already in this early
stage, drawings and bill of materials can be created automatically.

 


         Fig.23.1 3-D Solid Model of Mould


   Through the use of 3-D and the intelligence of the mould design system,  typical 2-D mistakes—such as a collision between cooling and components/cavities or the wrong position of a hole—can be eliminated at the beginning.   At any stage a bill of materials and drawings can be created—allowing the material to be ordered on time and always having an actual document to discuss with the customer or a bid for a mould base manufacturer.
   The use of a special 3-D mould design system can shorten development cycles, improve mould quality,  enhance teamwork and free the designer from tedious routine work.  The economical success, however, is highly dependent upon the organization of the workflow. The development cycles can be shortened only when organizational and personnel measures are taken. The part design, mould design, electric design and mould manufacturing departments have to consistently work together in a tight relationship.
   Computer-Aided Manufacturing (CAM) of Mould
   One way to reduce the cost of manufacturing and reduce lead-time is by setting up
a manufacturing system that uses equipment and personnel to their fullest potential. The foundation for this type of manufacturing system is the use of CAD data to help in making key process decisions that ultimately improve machining precision and reduce non-productive time. This is called as computer-aided manufacturing (CAM). [3]  The objective of CAM is to produce,  if possible, sections of a mould without intermediate steps by initiating machining operations from the computer workstation.
   With a good CAM system,   automation does not just occur within individual features. Automation of machining processes also occurs between all of the features that make up a part, resulting in tool-path optimization. As you create features, the CAM system constructs a process plan for you. Operations are ordered based on a system analysis to reduce tool changes and the number of tools used.
   On the CAM side, the trend is toward newer technologies and processes such as micro milling to support the manufacturing of high-precision injection moulds with complex 3-D structures and high surface qualities. CAM software will continue to add
to the depth and breadth of the machining intelligence inherent in the software until the  CNC  programming process becomes completely automatic. This is especially true for advanced multifunction machine tools that require a more flexible combination of machining operations. CAM software will continue to automate more and more of manufacturing’s redundant work that can be handled faster and more accurately by computers, while retaining the control that machinists need.
   With the emphasis in the mould making industry today on producing moulds in the most efficient manner while still maintaining quality,  mouldmakers need to keep up with the latest software technologies-packages that will allow them to program and cut complex moulds quickly so that mould production time can be reduced. In a nutshell,  the industry is moving toward improving the quality of data exchange between CAD and CAM as well as CAM to the CNC, and CAM software is becoming more “intelligent” as it relates to machining processes—resulting in reduction in both cycle time and overall machining time. Five-axis machining also is emerging as a“must-have”on the shop floor-especially when dealing with deep cavities. And with the introduction of electronic data processing  (EDP)  into the mould making industry,new opportunities have arisen in mould-making to shorten production time,improve cost efficienciesand achieve higher quality.
   


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