Tube cutting with Mazak U-44 SpaceGear 4kw

[Bigums]

We have been having the machine for a little over a year now and have been able to reach our machining capabilities for the most part. Most of our jobs consist of .375"-.380" thick stainless round tubing varying from 2.0" - 4.0" I.D. We have been having the same problem from day one and we have yet to improve on it because I just can't seem to find help anywhere. I see videos of other laser machines cutting the same thickness of stainless tubing and NOT using a sacrificial rod of any sort inside the part. Then they proceed to not have any burn marks on the bottom of the reverse side of the cut and their cuts are extremely clean.

--Our most common operation in these tubes are 3/16" slots going around the OD in varying lengths and spacing--

Now I don't know if it's an issue with our setup, or maybe we are just doing something completely wrong. I have just always been told to max the power and dip the focus to -.280 and go for it. We have only ever resulted in burning the opposite side of the material until we put a bar in the part to prevent that from happening. The problem is while the bar is in the part it takes up a lot of room and stops the metal slugs and spray from the slots we are cutting out from vacating the part. So they end up getting stuck underneath our cut sometimes which causes a blowout and makes it extremely hard to get the bar out of the part.

If we had a way to cut these pipes without needing a bar we would definitely up our productivity almost two-fold. Most of our time is spent cleaning the parts out and hammering the now "welded" sacrificial bar out from the inside of our part.

If anyone has any tips or if they actually run a machine similar to ours with a similar application your opinions would be greatly appreciated. I have been scratching my head over this for entirely too long and it would be much appreciated to get some help.

 

[Foostrap]

I don't know this machine, but I have done some tube cutting. The key is to get enough power to cut through, but not too much to burn the other side of the tube. You may want to experiment with the power. The edge quality may not be as nice, but it should get better on the other side. Another tricky part of this is the piercing. You'll have to get your pierce time set as low as possible; again, it needs to be just enough to pierce through, but not too long or it could start burning/piercing the other side.

 

[Bigums]

I have no problem throwing a bar in there for the pierce cycle (I always run full pre-pierce cycles due to the feathers left by them causing auto-gaps like crazy). We usually use a different bar for piercing than we do for cutting because of the actual power of the pierce and dwell time. I might try toying with the power and feed a bit to see if that changes things, but I'm pretty sure I'll have to keep the frequency and duty at max in order to actually cut the material. I am using a 7.5 lens which I failed to mention earlier if that would have anything to do with it.

Also for some reason we are only able to achieve a -.280 focal point. The book recommends -.320 in some cases, but when we put our depth that low we can't fit the lens back in the machine. We had a tech come out and try and figure that out, but he said we were missing some sort of component from the initial setup of the laser that would allow us to get a deeper focus.