,机电技术专业英语,2,Lesson Sixteen,Text,As you are beginning to see, the conventional CNC control requires a rather cryptic form of CNC program. Without previous exposure to CNC programming, the beginner will find even the simplest CNC program rather difficult to understand. For this reason, there are those in the industry who feel that manual programming is a thing of the past. They contend that there are alternatives to manual programming that eliminate the need to learn it. Admittedly, there are alternatives to manual programming. Though this is the case, the beginning programmer must grasp a basic understanding of manual programming in order to continue on to the alternatives. There are three important points we want to make related to the alternatives to manual programming.,Why Learn Manual Programming,Lesson Sixteen,Compression Moulding Compression moulding is the least complex of the moulding processes and is ideal for large parts or lowquantity production. For lowquantity requirements it is more economical to build a compression mould than an injection mould. Compression moulds are often used for prototyping, where samples are needed for testing fit and forming into assemblies. This allows for further design modification before building an injection mould for highquantity production. Compression moulding is best suited for designs where tight tolerances are not required. A compression mould is simply two plates with cavities cut into either one or both plates. Additional plates between the top and bottom plates can be included to create cavities in the moulded part. Figure B.15 shown below is an example of a basic twoplate single cavity mold. The mould does not require heater elements or temperature controllers. The moulding temperature is fully controlled by the pressure it is running in.,Lesson Sixteen,First, there is a form of CNC control called a conversational control. This newer form of CNC control allows the operator to input programs right at the machine in a more understandable and graphic manner than with manual programming. However, there is quite a controversy in the industry dealing with whether conversational controls should be used. Many companies, for example, do not wish their CNC operators to be creating CNC programs. This, coupled with the fact that conventional CNC controls requiring manual programming currently outnumber conversational controls by at least ten to one, means the well versed programmer must have a good understanding of how manual CNC programs are prepared. Second，even conventional CNC controls need not be programmed manually.,Lesson Sixteen,There are many excellent Computer Aided manufacturing (CAM) systems available to help the manual programmer develop programs. These CAM systems eliminate much of the drudgery of manual programming. However, the experienced programmer must be well acquainted with manual programming techniques even if he or she is using CAM system to develop programs. There are many times when a good working knowledge of manual programming will help, especially when CAM generated CNC programs must be modified at the machine when the program is to be run. The better the programmers understanding of manual programming techniques, the faster and better they will be at correcting mistakes and optimizing programs during the programs verification. Without a good knowledge of manual programming the CAM program must go back to the computer to fix even simple mistakes. This wastes precious machine time.,Lesson Sixteen,Third, CNC as we know it today has evolved over thirty years of development and constant change. The machine tool and control builders have constantly strived to offer new features that make the usage of CNC equipment easier to work with and more cost effectiveness. For example, many techniques available today were not even possible as little as five years ago. Many of these improvements have been related to how the manual program is developed. Older NC and CNC controls are quite inflexible. The programs format had to be just so. Newer CNC controls are much more forgiving with regard to how the program must be prepared. Also, many of the special techniques currently allowed in manual programming rival even a good CAM system or conversational control. For this reason, and because this evolution is still occurring, it is wise for the beginner to understand manual programming. With these programming enhancements, and especially with simper applications, it is getting to the point that an experienced manual programmer can be out of perform the CAM system programmer.,Lesson Sixteen,New Words and Expressions,Lesson Sixteen,参考译文,首先你应该明白，传统的CNC控制器要求相当透明的CNC编程形式。没有前面对CNC编程内幕的揭露，初学者会发现即使是最简单的CNC程序也很难理解。 基于这个原因，有些业内人认为手工编程已经成为过去。他们认为既然有替代手工编程的方法，所有完全没有必要学习它。 应当承认，手工编程是可供选择的办法而已。 即便如此，为了继续学习各种替代的方法，初学者也必须对手工编程有基本的了解。手工编程与其他替代方法之间有三个重要关系。 首先，有一种CNC控制器称为对话式控制器。在这种新型的CNC控制器上，操作员可以直接在机床上输入程序。这种方式要比手工编程法更容易理解，图示性更强。 然而，对会话式控制器是否应该在工业领域使用还是很有争议的。比如，许多公司不希望他们