Cnc machining nm09/2
Exercise 9 — section 4 — lathe programming
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Exercise 9 — section 4 — lathe programmingProgramming practiceStudents instructions
Exercise 9 — CNC lathe programming
Worksheet Exercise 9 — Hand written programNC lathe program Programmer’s notes (as requested) 4.26 Quality controlThere may be many ways in which a program can be checked for errors, but a program can only be proved 100% by running the machine and producing a part. Error checking can be performed in a variety of ways: Verification: Read through the print-out (NOT the handwritten manuscript) carefully— sometimes mistakes can be seen easily. Trialing: This involves the execution of the program without actually cutting the part of may be carried out in several ways depending on the philosophy of the person in charge. Adhere to the latter unless you can put up good reasons for alteration. Trialing usually consists of running the machine with the single block switch active —that is, each block will only be executed by pressing cycle start -in conjunction with the program being displayed on the screen. Quite often the dry run mode is switched -in to hasten proceedings. Dry Run' results in all machine motion being executed at a preset rate, usually in the region of 50% to 80% of the rapid traverse capability of the machine. The actual axis velocity can be overridden from 0% to 100%. The disadvantage of dry running a program is that feed rates will be masked, and attention must be paid to determining the actual programmed feed rate for each block. This may be displayed on the screen. Every movement the machine makes during program trialing should be expected and accountable to the programmer, if not, those motions should be checked for viability, and if necessary a more thorough understanding of the machine operation should be sought. Editing: Wherever errors are found, they should be corrected and rechecked, be it on the machine or at the programming station. Whenever a program is edited on the machine, a note should be made on the print-out so the matter or original program can also be corrected. A better method is to punch out a program from the control after successfully producing a component. 4.27 Canned cyclesCanned cycles may be defined as a set of preprogrammed instructions stored away in the computers memory. The word ‘canned’ has probably been borrowed from canned goods which one usually stores away for later use. Because the instructions represented a set of routine like repetitive patterns, the word cycle was found to best express what was taking place. These canned cycles are filed away under a ‘G’ code address. To a large extent the G¬codes are standardised. As an example (see sketch below), a G84 code, usually representing right-hand tapping in a machining centre and will consist of the following steps:
Figure 4.65 CNC mills, drills and machining centres are all equipped with cycles to perform drilling, reaming, counter boring, boring and tapping operations. Some others have pocketing cycles, slot cutting cycles, hole pattern cycles etc, all of which are designed to save programming time and effort. CNC lathes usually have cycles to cover drilling, grooving/parting, screw cutting, repetatives cut (automatic roughing) operations and others. Each cycle has its own G code to control the sequence of motions and an accompanying set of words to define the parameters of those motions. These words have addresses such as: R,P,Q,D,E,I,K,H,B etc.
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