I don't think you could possibly make an observation on what was the cause of this "Fanuc controlled" CNC test cut, without seeing. Mechanical factors could not account for the inaccuracies we saw. There was nothing wrong with the program, fixturing, cutter etc. This brings us back to the control that creates the inaccurate motion. This motion I am refering to is circular interpolation. It is disappointing how bad a lot of controls are at doing arcs. This kind of feature is easilly inspected on a machined part. Say a slot .200 wide with full radius of .1 at each end and 1.000 long. The code to produce the R.100 "depending on the end mill used" would be pretty small arcs, say R.0375 for a .125 end mill. On this test cut the programmed feed rate was F78. The material was 6061-T6 .125 thick, the .125 end mill, a 2 flute stub carbide end mill. Now, to most of you this feed rate would be way too high. But we use this "programmed" feed rate all the time and sometimes over F100. for small features on a Fadal CNC with a Rubicon control. The important thing to know is the programmed feed rate is F78. but a good control does not go any faster "than it can" in small radii or at a sharp corner. In this case "the Fanuc" control did have some feed reduction depending on geometry but, lost accurate control of motion due to either tuning, or lack of feedback loop resolution. True, there are many things to go wrong in a CNC machine but, this was a new CNC. I am sure, that a well tuned Fanuc controlled CNC machine could perform well but, I don't believe Fadal Engineering would be qualified to fine tune a Fanuc, they are not all that successful with their own control. Seimens, same thing, Fadal has not shown me the ability to develope a high performance set up. One thing I have learned lately, it is a lot more difficult at the higher performance end of HSM.
Our next test cut: Mori Seiki, Kitamura then ?
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Scott_bob |