Need Help!- Undershooting problem on TOYODA VMC/FANUC 11M

[jstkatz]

I don't know if anyone would consider this HSM, but it seems to be a problem that is related. I'm trying to machine some 35 2 inch cubes of aluminum and needing to remove quite a lot of material from them, I went out and found a 1/2 SC Zirconium coated end mill and was set to more or less max out my TOYODA 45V at 9000rpm and around 140 ipm. However, when I try to run a cut that fast, the cutter seems to undercut, as in cut a sharper concave curve than it is programmed for, this is very obvious on the piece because the EM is followed by a roundover on the same cutpath. My first thought was deflection or backlash, however running the path twice in a row dosen't fix it so it is not an issue of cutting forces, its almost like the control is overcompensating for the acceleration it needs to do around that U shaped contour, the problem goes away only when I lower the feedrate. I apologize if this is a no-brainer, we are not a machine shop and I am not a machinist, just the guy who runs the machines

Any thoughts would be very appreciated

[Cmailco]

Your lowered-feed observations pretty much confirm your suspicion. Most likely a toolpath issue; ie, fine step-over, lots of 90º changes in direction over short distances. 140 IPM isn't necessarily fast, especially in aluminum. How old is the machine and more importantly, when was the last time it was put through a ballbar contouring test?

[jstkatz]

Thanks for the response, It is a rather old machine, 1983-85 I think. We're not a production shop and do a lot of one off parts so mostly the machine works well for us. I've included the gcode for a contour, I don't think it is an issue there because its pretty simple and not a large number of moves. I'm not sure what a ball bar test is, we got the machine at least second hand. It came with a couple of CAT40 probes of some sort but no documentation for them.I could take some pictures if you might know what they are.




G01 X1.33944 Y2.37041
G03 X1.60401 Y2.21253 I0.17939 J0.
G02 X1.813 Y2.265 I0.20774 J-0.38503
G02 X2.25 Y1.8275 I-0.00125 J-0.43825
G01 X2.25 Y0.2025
G02 X1.8125 Y-0.235 I-0.4375 J0.
G01 X0.1875 Y-0.235
G02 X-0.25 Y0.2025 I0. J0.4375
G01 X-0.25 Y1.8275
G02 X0.1875 Y2.265 I0.4375 J0.
G01 X0.47807 Y2.265
G02 X0.85696 Y1.60875 I0. J-0.4375
G01 X0.76675 Y1.4525
G03 X0.75496 Y1.35514 I0.10825 J-0.0625
G03 X0.81654 Y1.28021 I0.11811 J0.0343
G01 X0.86109 Y1.25382
G03 X0.97769 Y1.24466 I0.06718 J0.10839
G03 X1.05083 Y1.33593 I-0.04751 J0.11301
G02 X1.10167 Y1.47261 I0.42973 J-0.08207
G01 X1.43286 Y2.04625
G02 X1.60401 Y2.21253 I0.37889 J-0.21875

G01 X1.33944 Y2.3965

[Cmailco]

This should explain a bit about the ballbar test: http://www.moldmakingtechnology.com/...es/040306.html

I think the answer – for that particular machine – is to keep the feedrates down in whatever range is necessary to produce a good part. Probably still a good machine for general work and the occasional prototype with fine-step 3D toolpaths but not a good candidate for hi-speed production-level work.

Any pictures you could provide would be great.

Best regards.