Doosan DNM 750/50 Spindle Load Meter

I've recently been assigned at my workplace to operate a Doosan vertical machining center, a 750/50. All I do with it is face milling, nothing else. I keep an eye on the spindle load meter, which is marked in segments of blue (below 100%), yellow (100% to 200%) and red (above 100%).

At what I take to be reasonable RPM (350) and feed-rate (45) and depth of cut (.09 to .06) using a six-inch shell mill, the load meter is almost always in the 140% to 180% range.

Is that too much load on the spindle to sustain all day long, day after day? Am I running the risk of damaging the spindle?

Thanks

Are you sure the load meter is marked like you say it is? Your description contradicts itself.

You have two things- The spindle and the spindle motor. The spindle isn't going to be harmed by a steady low RPM load. The spindle motor has a torque curve and time ratings that are always described in detail in the machine manual. That's where you need to look for a definitive answer.

All the machines I have owned (Japanese) are rated to where 100% on the load meter is the continuous 24/7 rating. 100-150% on the load meter is the 30 minute rating. Usually meaning you can run it at 150% load for 30 minutes continuously provided there's a short cooldown period, like 5-10 minutes after the 30 minutes of heavy load. The 150% and up red area is momentary loads.

In my experience, going past the 150% load for more than a few seconds it just won't do it. The spindle will bog down until it stops, usually breaking the tool or it will trigger an overload alarm.

IMO, the spindle 30 minute ratings are based on the spindle chiller and spindle motor cooling fan's ability to remove heat and the is affected by the ambient temperature. You can run it harder on a 50 degree day than a 90 degree day kinda deal.

If its not alarming out your probably fine.

If it bothers you switch to smaller face mill. It will run at a higher rpm where the machine likely has much more HP available. Usually a smaller face mill at a higher rpm will have same metal removal rate as a bigger one going slower.

nicholasfreres said:

I've recently been assigned at my workplace to operate a Doosan vertical machining center, a 750/50. All I do with it is face milling, nothing else. I keep an eye on the spindle load meter, which is marked in segments of blue (below 100%), yellow (100% to 200%) and red (above 100%).

At what I take to be reasonable RPM (350) and feed-rate (45) and depth of cut (.09 to .06) using a six-inch shell mill, the load meter is almost always in the 140% to 180% range.

Is that too much load on the spindle to sustain all day long, day after day? Am I running the risk of damaging the spindle?

Thanks

Click to expand...

You're just under the torque range of the spindle. Hence the higher numbers. As said by others, running at 100% is not an issue. You're approaching 140%, you may want to either increase speed a little, or decrease feed, just a little. The fact that the machine hasn't stalled out or alarmed means you're not really hurting it, again, as said by others.

When I worked at Doosan we ran test loads in the showroom up to about 180% before the machine slammed to a halt, but I would really NOT recommend doing that, as it did wreck the inserts and the test part we were using.

Thanks, everyone, for the responses. Those were helpful and informative. I really appreciate your feedback.

Garwood, you're right, I contradicted myself. I meant to write that the red area of the load meter is reached at 200%, not 100%.

My cut times rarely exceed 17 or 18 minutes with another 15 or 20 minutes in between for flipping the part or loading a new one. I've adjusted speed and feed to remain below 150%, often I'm cutting at no more than 80% or 90%.

Thanks, everyone.
Nick

Is there a specific reason to use a 6" cutter?
You could very likely remove a lot more material a lot quicker with a 3" or 4" and higher RPM/feed and keep the spindle in a better power/torque range, easier on the machine too.