Laser cutting help 2

[bssharpy]

I have just started work at a new company that has recently about six months ago purchased a new MAZAK HYPERGEAR 4 KW laser.

I have worked with two Mazak MKII machines A 2.5 KW and a 4 KW for around 4 years at my previous employer running lights out in an FMS cell.

The HYPERGEAR machine has had a bad history since the installation. The machine only has around 700 HRS on it and it has had the external optics replaced 4 times because of contamination problems. Mazak service is telling me that the external optics are only lasting around 1000 hrs on other installed machines?
Last week Mazak replaced the external optics and we are now getting around 3900 watts at the head. As the optics where contaminated again and we where only getting 1200 watts at the head. With the fresh set of mirrors I have no trouble cutting light gage HRS.
I can cut 0.250 HRS at 100 IPM at 4KW, 0.6KG oxygen, 500HZ, With a 7.5 IN convergence lens at -0.04 focus with a near glass like edge finish. When cutting 0.375 I can get the edge quality acceptable but only at a very slow feed “around 40 to 50 IN a minute at around 3kw.

(Question 1)
Does external optics replacement at 1000 hrs sound normal for a flying optics machine?

(Question 2)
If you have a flying optics machine “TRUMPF, BYSTRONIC, ETC” how long are your external optics lasting?
The MKII machines would go around 4000 hrs or more before optic or resonator service.

(Question 3)
I am trying to cut 0.75 HRS with good edge finish to reduce a machining step. I can get 0.750 to cut but with occasional thermal runaway. I suspect that the thermal runaway is material related as the material is just plain old A36 structural. Any advice as what to look for in thick plate that would attribute laser cutting problems would be helpful. Have you found a specific type of thick plate that cuts well on a laser. Any advise related to cutting A36 thick plate on a laser would be helpful.

 

[1plus1]

When you talk about external mirrors I am guessing you mean the x and y reflective mirrors. Replacing mirrors 4 times in 750 hours is a major problem, especially with the newer machines out there. Are you using nitrogen as a purge gas or shop air? Nitrogen is much better. Try increasing purge gas pressure a bit to see if this helps. Check the inside of the focal lens to see if it has particles burned in the lens. This could be a sign of contamination. The other possibility you have is the mode of the beam. If the beam does not have a proper "cool spot" that is centered and shaped properly it can prematurely end the life of the mirrors. Do the mirrors have a noticeable "burn" look to them? Usually installers will have a piece of plexiglass to show the mode burn. I don't have experience with 4kw lasers, only 2.5kw and lower. The extreme wattage could be a problem that your mirrors can't handle. Check with the manufacturers of mirrors, there are some good ones out there, and see what they have to say. If you have to change mirrors frequently, you should consider training individuals in beam alignment and minor maintenence. This will save you thousands of dollars. Shop around for mirrors, lens, tips, etc. This can save you money also.

 

[bssharpy]

Thank you for your reply. This week we had a Mazak Tech come out and he tried to cut the .750 also with the same results. The tech replaced the output coupler the rear mirror and readjusted the mode. He also realigned the external mirrors and checked for contamination. It cuts .750 real nice now.
I have always had the techs do the mirrors and mode adjustments. But I normally buy Convergence lenses and nozzles from IIVI or MATE Tooling. For the past 4 years I have been using chrome plated double nozzles for Mild steel on the MKIIs. They work great! You can get better feed rates and less freeze lines. They don’t work as good for cutting stainless or aluminum as you need way to high of a flow rate for that.
As for the Mazak HYPERGEAR I would not recommend this laser to anyone at this time. Most of the supposedly intelligent features don’t work that well. The torch changer and auto blue flame works fine but the nozzle changer works some times at best. The nozzle grinder is just a bad idea “A wire brush bolted to the table works much better”. The pallet shuttle needs something to stop debris from falling on top of a fresh sheet in the lower station. The double sheet detector needs to be able to read in inches and not only in metric. Last but not least the beam quality of the machine is poor. The feed rates for mild steel are around 40 to 50 percent faster on a fixed beam MK2 machine.

 

[bklauba]

One of the Q's I have is: Do you see more distortion (Z axis) when cutting the thicker materials?

BK

 

[bssharpy]

I normally check for proper alignment before the tech leaves the shop “learned from past experiences”. I check the alignment using the hole in tape method at each corner of the machine and the lowest and highest of the z axis.
I have noticed that the distortion gets globally worse as you start hitting the 3800 watt range.
The acrylic mode shot looks pretty jagged to me but the tech insisted on telling me that you will not get a mode shot as nice as the MKII off the HYPERGEAR?
But we are up and cutting now at least.

 

[bklauba]

What I was wondering is how "live" the material you are cutting might be. One problem that a number of laser users have related to me is that if the material is prone to distortion during laser cutting, that the cleanliness of the cut starts to suffer, and can even get extreme enuff to cause laser shutoff.

So, does the problem you are seeing vary not just with thickness of the material, but with lot??

BK

 

[bssharpy]

The 0.75 A36 plate is a little rusted on the edges and is not the best stuff around but it is all from the same lot. Just 4 days ago we had the same steel cutting really nice at 3600 watts,+0.04 focus, 4 nozzle to work, 0.4 KG O2, at 27 ipm and a 3.0 MM nozzle with a slow step pierce of 35 seconds. Today I had to cut more of the same 0.75 plate. And with the same setup I was getting bad edge quality again? After checking the nozzle, Lens, and centering, I could only get it to cut decent at 3000 watts, +0.06, 17 nozzle to work, 0.4 KG O2, at 26 ipm, with a 3mm nozzle and a slow step pierce of 55 seconds? The only thing that significantly had to be changed was the focus the power and the peirce time. Why in 4 days would there need to be that big of a change?

 

[bklauba]

The variable might be the material, not your tool. Start looking at the material (uniformity of flatness, thickness) and see if you can select the oldest material to cut, rather stuff you get in fresh (more likely to be "green").

If you cut an "ugly" plate, see what the next one does.

If the problem seems to vary from plate to plate, then expose some plates to some mechanical / thermal excitation, which, combined with time (tuff to find in these days of JIT), so as to give the plates some chance of becoming less live. Putting them on or adjacent to a truck dock, and/or placing them outside on the west side of a building, so they are cool in the morning and stay in the shade during the AM, but then get smacked with the PM sunlight is one of my favorite methods. Cheap too!

You could also have a few pcs stress relieved (perhaps too-rich-for-the-room for production) and run those, to see if the problem is residual stress. You wouldn't believe how live raw plate stock, bar stock, tubing or pipe is, fresh from the mill.

BK