Assure the experience of a few process designing of CNC Machining precision

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  • source:MACKINNON CNC Machining
In machine program work out, method, skill is used proper, to assure and improving the treatment of numerical control machine tool precision has important sense. The author is in long-term practice, accumulated experience of a few process designing, the introduction is as follows. A lot of dimension of the 1 influence part that removes tolerancepublic errand to take the place are tagged have noncombatant duty, and the place that tolerancepublic errand takes agrees impossibly, and numerical control program weaves by spare parts outline commonly, press the basic measure work out of the spare parts namely, oversight the effect that tolerancepublic errand takes the place. Such, although the precision of numerical control machine tool is very tall, the part that treatment gives does not accord with its dimension public errand likely also to ask. If the graph shows a part 1 times, Ø40 dimension is made for basic shaft, Ø35 dimension is base aperture makes transition fit, Ø25 dimension is base aperture has been made be filled with cooperate, the public errand of 3 dimension takes the position to differ, if process designing still presses his basic measure Ø40, Ø35 and Ø25, and the influence that takes no account of tolerancepublic errand to take the place, make treatment of a certain dimension does not accord with a requirement possibly. The method that solves a problem has 2 kinds: Graph 1 graph 3 graphs 2 graphs 4 graphs 5 graphs 6 graphs 7 press basic measure process designing, with radius compensation consideration public errand takes the position to still press a spare parts namely basic measure computation and process designing, use same lathe tool to machine everywhere outside round, and when machining different public errand to take positional measure, use different cutting tool radius to compensate a value. With this kind of method, should know radius of circular arc of point of a knife first (contrail of treatment of this spare parts and X axis, Z axis is parallel, but need not know) of radius of circular arc of point of a knife, use inconvenience so, and can apply to system of partial numerical control only. Change basic measure and public errand to take the position to be namely below the premise that makes sure size of spare parts maximum is changeless, adjust basic measure and public errand to take the place. Adjust by belt of symmetrical public errand commonly, if the basic measure after adjusting and public errand pursue 2. The basic measure after adjusting is pressed when process designing undertake, use when finish machining so same lathe tool, identical knife fills value (this exemple treatment contrail and X axis, Z axis is parallel, but not knife filling) , can assure to machine precision. Of course, if the part is final even finish machining (grind) like essence of life, to make sure grinding surplus is abundant, also can increase basic measure in a way (right now, tolerancepublic errand is taken with respect to asymmetry) . The reason that the 2 effects that remove machine tool clearance are used for a long time when numerical control machine tool or goes up as a result of construction of system of its itself transmission, put in error of retrorse dead band likely. At this moment, a few step can be taken when numerical control process designing and treatment, in order to eliminate error of retrorse dead band, raise treatment precision. The repetition that is close to numerical control machine tool when the precision of spare parts dimension that is machined especially locates when precision, more important. If the graph is shown 3 times, outline of finish machining workpiece is D of → of C of → of A → B, the line of cutting tool shift that if if pursue,use 4,shows is inappropriate, because the athletic way from ① → ② and ③ → ④ are contrary, can generate backlash, the line of cutting tool shift that like instead the graph shows 5 times, the cutting tool when finish machining maintains dimension to increase by degrees continuously in radial shift trend, measure maintains in the shift of axial trend of successive towards the left, removed the effect of the backlash of the machine tool so. If the graph is shown 6 times, the pitch requirement of aperture of the ① of workpiece, ② , ③ , ④ is accurate, setting process designing coordinate is origin in work center, nod to the knife (program start) also be same point. Like cutting tool mobile course is: Aperture of ④ of → of ③ of → of ② of → of ① of origin O → , can generate backlash, be like instead: ④ of → of ③ of → of ② of → of ① of → of A of origin O → , the dimension of X direction and Y direction keeps successive and degressive or increase by degrees namely trend, if keep successive,increase by degrees and degressive process designing has difficulty. Should add transfer dot, if pursue,7 medium B are nodded, cutting tool shift is ④ of → of ③ of → of ② of → of A → ① , can eliminate machine tool backlash. The systems of 3 influence numerical control that reduce numerical control system to accumulate an error are in the operation process that has sudden shift and interpolation, meeting generation accumulates an error, when it reachs fair value, can make the machine tool produces shift and fixed position error, the influence machines precision. The following measure can decrease what fraction controls a system to accumulate an error. Use very kind process designing as far as possible very kind process designing secures a place with some (workpiece coordinate origin) for fiducial, each paragraphs of program and whole treatment process are with this fiducial. And increment means process designing, it is before was fiducial, carry out continuously multistage the program arises necessarily accumulate an error. When inserting a reference point to dictate the machine tool winds reference point, can make each coordinate to clear, eliminated operation of numerical control system so accumulate an error. Insert a reference point instruction to be beneficial to appropriately in longer program assure to machine precision. When having the demand that change a knife, can answer reference point to change a knife, such kill two birds with one stone. CNC Milling