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ME364_NC_programming - 166 Part Programming for NC Systems...

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Part Programming for NC Systems 166 Valery Marinov, Manufacturing Technology 9.2 PART PROGRAMMING FOR NC SYSTEMS NC program A program fo NC consists of a sequence of directions that causes an NC machine to accomplish a certain operation. The NC program describes the sequence of actions of the controlled NC machine. These actions include but are not limited to v component movements, incl. direction, velocity and positioning; v tool selection, tool change, tool offsets, and tool corner wear compensation; v spindle rotation and spindle rotation speed, incl. possibility to change it to keep constant v cutting speed for different diameters in turning; v application of cutting fluids. A part program is simply an NC program used to manufacture a part. Part programming for NC may be performed manually ( manual part programming ) or by the aid of a computer ( Computer-aided part programming ). Many programming languages have been developed for part programming. The first that used English- like statements and one of the most popular languages is called APT (for Automatically Programmed Tools ). Many variations of APT have been developed, including ADAPT (ADaptation of APT), EXAPT (a European flavor of APT), UNIAPT (APT controller for smaller computer systems), etc. NC programming for complex parts are generated using advanced computer programs (CAD/CAM programs), which create automatically the machine code (so called G-code ) in a graphic environment. Machine code is also largely used for manual part programming of simple shapes and is covered in the present section. Structure of a NC program. NC program block consists of a number of program words. The NC program is executed block by block: each next block is entered in the system and executed only after entirely completing the current block. Each program word is an ordered set of characteristics, letters and numbers, to specify a single action of the machine tool. Program words fall into two categories, modal , which are active in the block in which they are specified and remain active in the subsequent blocks until another program word overrides them; non-modal , which are only active in the block in which they are specified. Machine code The structure of a NC program written in machine code is standardized and for a two-axis NC system has the following format:
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Part Programming for NC Systems 167 Valery Marinov, Manufacturing Technology Some of the most important program words are as follows v
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