Trouble with dirty optics (mirrors) on Mazak 3D laser

For starters, the machine is a Mazak SpaceGear U44 2.5kW CO2 laser. I'm absolutely losing my mind with this thing because we recently had the machine serviced by two different companies (one being Mazak), and we still can't seem to get the power up to what it should be - which is about 2350 W considering losses from all of the 11 mirrors the beam has to hit.

We just had our 4,000-hour pm and all of the mirrors were replaced and cleaned as needed. A complete alignment and spot check was also done and the power was about 2,200 when the technician left. Both technicians that came mentioned that we could be having a beam purge air quality issue (dry air in the beam path not being clean/dry enough leading to beam distortion). To see if that was the issue, we got a few bottles of ultra-high purity nitrogen and hooked that up directly to our beam path using the compression fitting near the z mirror. After a few hours of nitrogen being hooked up, we saw barely a noticeable difference in the power. This leads me to think that our shop air, which is cleaned/dried in the three-stage dryer inside the chiller, is just fine. I'm also a little nervous about putting undried nitrogen directly into the bellows without going through the dryer in the chiller unit.

Where I'm at now is I am thinking there's an issue with debris of some kind in the beam path. We recently cleaned the bellows and what mirrors we could reach just the other day, and now we have dirty mirrors again (see photo). Our power is slowly dropping and making it so we can't cut 1/4" stainless anymore, which is the majority of what we cut. Another important fact is that we also had our laser tubes replaced in the recent pm. The technician measured the power at the resonator and it was right at 2500 W, so we're losing power somewhere between the resonator and the torch.

Has anyone had any issues like this before? The technicians from Mazak that I talked to said that it was likely dirty bellows, but we cleaned them and they really didn't seem that dirty in the first place.

Thanks in advance!

Could you have some form of organics in the beam line that are evaporating out and depositing on the mirrors? Can you have the mirror deposits analysed to see what the actual material is?

How is the system cleaned, such that water or other contaminants aren't allowed in?

I'm not really sure other than the atmospheric air in our shop. We've made no significant changes this year and we've never had this problem before. Typically, after a pm or refurb, we get 2350 W. This time the highest we got was 2258 W. We have highly trained operators that were trained by Mazak to clean mirrors etc., and we cleaned the bellows by taking them off, covering the mirror openings, and lightly shaking them in a vertical position (and nothing visible came out). I spoke with a tech tonight and he thinks it might be the z axis bellows rubbing against the tube that goes through it since none of the other mirrors upstream in the path are dirty. We're going to remove the a mirror tomorrow to get a view of the tube and z bellows to see what's going on. I'll report back on what we find.

The huge bummer about doing this is having to realign a and b as well as spot check since it takes 2-3 hours to do.

Could the bellows have holes or openings where it can suck in debris from outside? Thoroughly check them. Rapid movement could do that if the purge air can't fill up the bellows quick enough when expanding.

And you might try removing them and cleaning in water to get everything out.

I've seen lenses blow up a time or two and make a mess of bellows. In that case we completely removed and washed them.

Is there such a thing as a "leak down test" with this type of laser? I'm thinking plumbing in a vacuum/pressure gauge and a valve, pumping the system to a little over atmosphere, and checking pressure after shutting off the valve to see if it remains constant or drops.

If it drops it may indicate a leak, which could also be an entry for contaminants.

Not super-knowledgeable about this type of laser, so if I'm off base on how the gas system works just ignore...

Your bellows are likely the source of the contamination. I have seen this on Mitsu lasers when the bellows get old and the "rubbery" coating on them gets cracks from the constant flexing. Then the bellows material releases particles when flexing which would contaminate mirrors and lens. Also have seen where "laser dust" settled into the exterior folds of the bellows and wore away the material until the bellows had physical leaks of dust into the beam path. In those cases, the only long term fix was to replace the bellows.

So I tore into the z-axis bellows today, and we found that it was the tube inside the bellows that was scraping against the laser path bore every time the nozzle would/rapid up or down. The tube itself had a huge burr on its OD and the bore was pretty tore up looking. There was metal dust all over inside the bellows but from the tube and bore and not the bellows themselves. We cleaned the bellows, polished the bore and laser tube, and reassembled. After everything was put back together, we were at 2300 watts!

In this style of laser, the bellows are lightly pressurized to keep moist atmospheric air and contaminants out. Day and night, it is constantly positively pressurized for this reason.

Thanks for the tip. I never thought of this, but it makes sense. Our machine gets covered in dust, and we constantly have to clean it. We don't clean the bellows though, so I'll add that to our cleaning schedule.

As an outsider that has never run a laser, it's very interesting to read through this thread! I had no idea PM for a laser was so involved!

aarongough said:

As an outsider that has never run a laser, it's very interesting to read through this thread! I had no idea PM for a laser was so involved!

Click to expand...

There's a lot to be said for fiber lasers for this reason...

aarongough said:

As an outsider that has never run a laser, it's very interesting to read through this thread! I had no idea PM for a laser was so involved!

Click to expand...

CO2 cutting lasers are really complex machines. The resonator has a special gas, water cooling and a very fancy power supply. The beam path mirrors are very very fancy first surface mirrors with water cooling. The beam path is often sealed.

Fiber is much simpler.

I totally agree. Our SpaceGear U44 is a 5 axis and has 11 mirrors total. If one mirror gets a microscopic piece of dust on it, it causes power absorption, and you lose power in a cascading effect all the way to the torch. Our machine is a 2.5kw, but we never got more than 2300 watts at the torch. You also have alignment, which is insanely complex, and if not done properly, the beam can clip the bellows and easily cause a fire.