数控英文翻译.docx

1、数控英文翻译 英 文 翻 译 2013届 机械制造设计及自动化 专业 130696 班级姓 名 学号 130 指导教师 职称 教授 二 一五 年 三 月 二十七 日Chapter lIntroductionWith the advent of computers, the promise of fast, accurate and automatic machining of parts was born. Pioneering research into numerically controlled (NC) machining in the late 1940s and early 195

2、0s, MITs Servomechanism Labs developed a language for specifying geometry and cutting movements, called APT. This gave NC programmers a consistent interface to NC milling machines.a consistent interface to NC milling machines.窗体顶端窗体底端APTs geometrical formatting has been supplanted as CAD systems hav

3、e developed to allow more refined and interactive surface definition and editing. Generating cutting tool movements has also been simplified, allowing significant increases in NC programming productivity. However, the basic process of machining is still similar. A designer creates a part description

4、 and then an experienced NC programmer generates cutting tool paths. They are then checked for accuracy, often by cutting models out of wood or plastic, a time-consuming and error-prone method.窗体顶端窗体底端 Despite this, automated machining has resulted in improved efficiency and economic benefit. Ultima

5、tely, however, the complete automated NC machining process, from the input of a part specification to the fabrication and checking of correctness of the final part, would be a completely automatic sequence of operations, requiring no intervention. This would free up human designers to do the creativ

6、e work without worrying about the details necessary to implement it.窗体底端1.1 The goal of an automated machining systemA complete automated NC machining system would be one that takes a part description and does everything required to manufacture the desired part. The chain of steps needed to accompli

7、sh this is not insignificant and each step is an involved procedure, calling for complex, interrelated decisions. The system must be able to make decisions about such things as methods for clamping a block of material while machining is going on as well as determining the different position the bloc

8、k should be held and in what order. It has to select the cutting tools to use and how to use them most effectively.窗体顶端窗体底端Let us take a closer look at what is involved in the machining process. 20 offers an effective breakdown of the sequence of events:窗体顶端Part Design Design of the part is usually

9、accomplished within a CAD system today. These systems are widely available and have interactive capabilities that make them relatively simple to use.Surface evaluation The part description must be analyzed to locate features that will significantly affect the machining process. For example, this sta

10、ge should detect slots, bosses and large changes in surface orientation so that they can be compensated for during the generation of the NC program.Machining Planning To cut the part from a piece of stock requires answers to several questions. For example, the system must decide how to clamp the par

11、t and how many different positions are necessary to allow machining of the complete product. The types and sizes of cutting tools must be selected, as well as the overall sequence of events. This requires knowledge and reasoning about a large number of details concerning the particular milling machi

12、ne.窗体顶端窗体底端Tool Movement Generation Once the strategy has been plotted, the actual cuts to be made must be calculated. This means that an NC program must be created that will carve the desired surface. In actuality, the goal will be to machine a part that is within some tolerance of the desired resu

13、lt when everything is finished.窗体顶端窗体底端Simulation and Verification The NC program should be checked to guarantee that it produces the desired surface to within acceptable tolerance limits. Geometric correctness of the cutting program must be verified. Allowing the body of the milling machine to hit

14、the stock or itself during the cutting could result in very expensive damage to both machine and stock. If the final result is out of tolerance or there is forbidden contact between surfaces, the generator can then replan the NC program. The loop of generation and simulation may repeat until everyth

15、ing is satisfactory.窗体顶端窗体底端窗体底端Dynamic Simulation The previous step verifies the geometric accuracy of the program. This one analyzes the forces involved. The more material removed in a given time, the more force between the material and the tool. These forces cause deflections in both surfaces, an

16、d the result is further deformed. However, faster feedrates (speed of material removal) result in less machining time, reducing the costs. These factors must be balanced and feedrates set accordingly.窗体顶端窗体底端Determine Cost Once the feedrates have been determined, calculation of cutting time is strai

17、ghtforward. Once the costs of machining have been calculated, a go ahead or stop command can be issued.Execute Machining Program Ideally, the machining equipment could sense the actual forces and adjust the feedrates to keep within tolerance.Evaluate Final Result The part that has just been cut shou

18、ld be checked to make sure that it meets the requirements set out at the beginning of the manufacturing process.As we can see, building a system that can do everything is a fairly formidable assignment. Each step poses challenges of its own. We will examine geometric verification in more detail.1.2

19、VerificationThe goal of verification is straightforward. Given a part description, an NC program of tool movements, and a workpiece that is to be shaped, determine if the NC program shapes the workpiece into a copy of the part description, and where it fails to do so. This of course is a simplistic

20、statement of the problem. In manufacturing, the question is really how close is the final product to the desired part, as opposed to are they the same. Usually, the manufacturing process introduces small errors into the desired surface. Therefore, verification must actually determine if the machined

21、 product is within some small tolerance of the part, inside or out, for all points on the surface. In addition, verification must be prepared to identify the locations where gouging has occurred and where too much excess material has been left behind, if we wish to correct the tool program.Another o

22、bjective of verification is to check that the tool doesnt gouge the mounting hardware or other parts of the mill. In addition, detection of any tool movement that causes the non-cutting surfaces to hit workpiece material is desirable. Otherwise, an expensive repair may be in order. We may also like

23、to know the volume of material that a tool movement removes to allow for later dynamic simulations. These last desired features call for simulation of the cutting process, not just determining the final product of the milling.To accomplish these goals, we must represent the components involved in th

24、e actual cutting process. First, the part description is needed. We must have a representation for the workpiece to be machined. The swept volume of each tool movement must be available in some usable representation (some representations are much more useful than others for certain purposes). And if

25、 we wish to examine interference of surfaces that should not come into contact such as the machine body, we must have representations of those surfaces as well. Given this information, we must provide a method for removing the swept volume of each tool movement from the workpiece model. The tool mov

26、ements have to be processed in order if we wish to do simulation of the workpiece and environment at any time, as opposed to just the finished product. Lets take a closer look at the means developed for performing verification.1.2.1 Methods of VerificationThere are several ways one can go about perf

27、orming verification. A commonly available technique is to display the tool paths on top of the part surface. This has the advantage of being quite simple to implement, as well as being easy on the computer. Then verification could be performed by visually comparing tool paths and the part surface. H

28、owever, only gross errors are likely to be found in this manner. It is also time intensive. Since manufacturing often requires tight tolerances, something better is needed. It also makes sense to have the computer doing the work, both for the sake of speed and reliability. Increasing the computers i

29、nvolvement in the verification process, we can check for interference between the part surface and the swept envelope of each tool movement. This will locate tool movements that gouge the part surface, but has several disadvantages. Since no model of the workpiece is kept, it is inconvenient to comp

30、are the machined result to the desired part surface. Each tool movement can keep track of its impact on the surface, but the overall effect is not known. In addition, since this is not a simulation, material removal cannot be determined.The two methods mentioned above are not really simulations of t

31、he machining process. To perform all of the tasks of verification, a geometric model of the machining process must be maintained. Solid Modeling and Discrete Modeling are the two major methods of simulating machining.Solid modelingSolid modeling was developed as a way of representing complex surface

32、s built up as boolean combinations of simple objects. The machining operation is just this an object (the workpiece) from which other objects (the tool movement envelopes) are subtracted. An accurate model of the current state of the workpiece is maintained at all times, and material removed by each tool movement can be determined. Solid modeling systems for NC simulation and verification were investigated by voelcker and Huntin 34 and 17 and by Frishdalin 12.Using solid modeling to do simulation and verification has a down side, however.Simulation require