Machinery's Handbook, 31st Edition
1354 CNC PROGRAMMING specific type of formatting, unique to a particular machine and control. The majority of post processors are customizable by the users who have thorough knowledge of manual programming methods, as well as a various machine and control systems. The major advantage of computer based program generation is elimination of tedious calculations, minimizing errors, and providing a program in much shorter time than using the manual approach. Graphical interfaces quickly allow obvious errors to be detected visually. For more on this topic, see CAD/CAM on page 1390. Shop-floor Programming: Shop-floor programming, sometimes called conversational programming, is performed at the machine by the CNC operator using programming soft ware built into the control system. Using the keyboard and control display screen, the pro grammer/operator interactively defines tools, material, setup, toolpath, cutting conditions, etc. Virtually all work is completed at the display screen. The resulting program can be stored externally, to be used at another time. Although relatively fast, visual, and easy to edit, the built-in programming software adds to the overall cost of the machine. If not managed efficiently, it does not offer the same flexibility in toolpath control as other methods. It may also tie up the machine from production and is not as portable as some alternatives. Depending on the control system, conversational programming software ranges from some software having only minimum basic features to others with very advanced features. In addition to defining points, lines, and arcs, typical features include various patterns of holes, pocketing cycles, automatic roughing, corner rounding and chamfering, threading, and other operations. Typically, the programming method selected is also the most convenient programming method available. Type and complexity of the job is always a major factor. The choice between manual and computer based programming has become rather narrow. Complex parts always benefit from a computer generated programs, while simple parts will typi cally benefit from a manual program. Macro Programming: Macro programming is the highest level of manual programming. It requires thorough knowledge of manual programming concepts at all levels. In princi ple, the single purpose of a macro program is to develop a generic toolpath or other activity for a particular purpose. Once the macro program is stored in the control memory, it can be used many times in the future—with variable data supplied for a specific job. Typical examples include a bolt circle or a rectangular pocket—in both cases the basic input features remain the same, but the actual dimensions change from part to part. All basic shapes of a bolt circle or pocket are retained while their sizes change—the macro itself does not change. See page 1377 for detailed information on macro programming. Control System.— The control system, the actual computer controlling a CNC machine, is the main core of any CNC machine activity. It has many features that are important not only to the machine operator, but to the programmer as well. Some features are unique to a particular type of control system (mill, lathe, wire, etc.), while others are optional and may not be available on all controls. Typical features of various CNC systems include: ON / OFF switch: Power switch for the main power and the control unit. Cycle start: Starts program execution or an MDI command. Emergency stop: Stops all machine activity and turns off power to the control unit. Feedhold: Temporarily stops motion of all axes. Single block: Allows program to run one block at a time. Optional stop: Temporarily stops the program execution (requires M01). Block skip: Ignores blocks preceded with a forward slash ( / ) in the program. Dry run: Enables program testing at fast feed rates (without a mounted part). Spindle override: Overrides programmed spindle speed within 50–120% range. Feed rate override: Overrides the programmed feed rate, within 0–200% range. Chuck clamp: Displays current status of chuck clamping (Outside / Inside).
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