电子教案统一模板(数控)Unit7.ppt

Unit 7 Computer-aided Part Programming,7.1 Lesson 13 Development of Computer - aided CNC Programming,In the past programming was performed manually. The program was written in word address and was tailored to run on a particular controller.1 Trigonometry was a must for determining tool path.2 The CNC machine needed to be halted while the operator keyed the program into the machine control unit. The CNC machine was further tied up for program verification, which involved machining a test part and inspecting the results.,The digital computer, however, has changed the way programs are written, checked, and run. Some of the most dramatic improvements provided by the computer include off-line programming, the use of computer-aided programming languages, and the application of CAD/CAM to programming.,CNC machines operate at optimum when running part programs and machining parts.3 This goal is achieved when new programs are written and tested at an off-line computer terminal. The program can be composed directly in word address (G and M codes) with the aid of text editing software. It can be tested and then stored on punched tape, diskette, zip diskette or CD-ROM media. If the remote computer has a communication line to the CNC machine, the program can be downloaded directly to the machines controller. This technique is known as off-line programming.,7.2 Lesson 14 Computer-aided Part Programming,CAD/CAM stands for Computer-aided Design and Computer-aided Manufacturing. Experienced programmers use this powerful tool to simplify the task of writing and testing part programs. CAD/CAM can dramatically boost the productivity of CNC shops. The CAD/CAM approach is superior to the technique of using a computer-aided programming language to prepare part programs. Some of the advantages of using CAD/CAM are:,1. The system can be used for off-line checking of the program. Resulting tool paths can be graphically displayed on the computer screen. The user can zoom in and view the tool paths at various orientations. The system can generate real time material removal displays and flag tool breakthrough or part violation problems. 2. Time and cost of machining the part can be quickly determined. 3. The system can determine optimum tooling, speeds and feeds for the material selected.,7.3 Reading Materials 13 Conversational Programming,There are several computer programming languages that developers use to create CNC programming software. They are conversational logical in their approach and user-friendly. The programmer uses English-like conversational statements or source code to select the machine and tools and to describe a tool path. The programming software accepts these statements, makes calculations if needed, and then translates a source code into appropriate code.,Once the program is written, the programmer needs an output file in order to use it on the CNC machine. To enable the CNC machine control to read and execute the prepared program, the output file must be compatible with the tape format of one particular machine, including the G and M codes. However, in the CNC field, there are variations in tape format from one machine combination to another. The answer is a postprocessor.,The postprocessor is a set of instructions used to transform tool centerline data into machine tool motions in a computer numerically controlled system. The postprocessor produces an output file, including feed rates, spindle speeds, and auxiliary functions, that may be printed, punched, or downloaded directly to the machine control via a communication channel.,Two of the more common general programming languages for numerical control programming are APT and COMPACT . They both process information in four phases: （1）Reading input files and scanning for errors. （2）Performing arithmetic operations to define a tool path on a two or three dimensional surface. （3）Editing to apply coordinates of a tool path to different machining sequences. （4）Postprocessor producing NC codes acceptable to the particular machine control combination.,7.4 Reading Materials 14 Computer-aided Programming Languages,The controller of a CNC machine can only operate on word address (G and M) codes. Furthermore, these codes must be entered according to a specific format acceptable to the particular controller. By now the reader has also discovered that word address programming can require trigonometric computations.,A computer-aided programming language is meant to address some of these problems. A computer-aided programming language allows the programmer to write the program using English-like commands, not G and M codes. Because the tool path is described in terms of these commands, trigonometric computations are not needed. All tooling parameters such as tool diameters, tool speeds, and feeds are easily specified. Furthermore, the programmer need not be concerned with tailoring the program to a particular controller.,A program known as a postprocessor can be used to automatically translate the program written in a compute-aided programming language into a corresponding word address program. Special postprocessors have been written for each machine controller. This allows a single program written in a computer-aided programming language to be applied to many different types of machine controllers.,The most popular computer-aided programming language still in use today is APT. APT is short for Automatically Programmed Tools. It was the first and still is the most powerful computer programming la