disturbance focal point

[nidbe]

when I make the cut on a piece of sheet metal of 10mm! I observe that the focal point that varies in the four face part is ... it depends on what lens (lens I use 7.5 ')?

 

[HenryRollins]

You are leaving out some details, we need to know what machine you are using and what wattage resonator. Some other details would help like power, feed rate, gas pressure and focal position so that we may help you with your problem. Thanks.
-HR

 

[IRstuff]

I don't see why that's surprising. Laser systems tend to have very low f/numbers in order to get the energy concentration needed to cut materials. A 10mm change in object distance seems rather drastic for a low f/number optic.

TTFN
faq731-376

 

[nidbe]

I use as a machine (AMADA FO from 3015 to 4000 watt) and thick in some difficulty I found a little to get a good focal point because I'm a beginner can: (

 

[Foostrap]

Are you saying that when you cut a square in 10mm mild steel, you can see a change of edge quality in the 4 faces? If so, this could be as simple a bad nozzle alignment, bad nozzle, bad lens, bad optical path alignment, problem with polarizing mirror, or more complex problem with the mode quality (internal optics alignment).
Try to cut something thinner, like 6mm (1/4). Your focal for that should be around 0.5mm above the plate. To cut 10mm, your focal should then be a little higher than that, for example 1mm above the plate surface.

 

[nidbe]

merci monsieur je vais le voir

 

[nidbe]

thank you sir I will see

 

[nidbe]

thank you sir I will see

 

[nidbe]

thank you sir I will see

 

[nidbe]

thank you sir I will see

 

[krugtech]

What footstrap said proly alignment. Also do a long cut and see if the focal changes, stop, let it cool and try again and see if the focal moves w heat load.

Does that machine purge the beampath w air? We had a machine do something like this whenever they left the forklift running near their air compressor, the compressor sucked in the fumes and pumped it into the laser. in other words, make sure you have clean beam path air. Another customers machine stopped cutting when they used their paint booth, the air compressor was on top of the booth. Purge w N2

Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[LASERNINJA]

Not to spit hairs or anything but the focal point should be negative on this machine. -1mm for 6mm, the same for 10mm or maybe -2mm. Its they way they set up the A/O.

Also. Post some pictures. It helps.

 

[nidbe]

in my opinion it is because of the alignment ... ! I'll put some pictures

 

[Foostrap]

Hard to see, but it seems that one of the 2 sides you see on the picture looks OK. Is this the first side cut? If so, try to cut the side that looks bad first. If that side now becomes better, then you know this is not an alignment issue; but would be heat related. Maybe the material is bad quality and it is heating up over time, or you have an optic overheating or stressed and it is affecting the beam.
You could try to move your focus a little bit higher and see if that gets better. Or lower the gas pressure or power a little bit.
Not sure how much power you were using; but try to cut with less power, like 2500W (you may have to slow down the speed a bit). If it becomes more consistent at lower power, then it's probably an optic issue (maybe stressed output coupler?). How many hours do you have since last optics change?

 

[LASERNINJA]

If I were there, In your shop, I would use
4000w 2000hz 100%duty 0.06Mpa 1.5mm gap at 70 inches per minute 1750mm / minute. Check the setting in the upper left of the control and make sure its on THICK. Make sure your beam purge or nitrogen purge is on and working.

Make sure your lens is clean top and bottom (for now, and the sake of argument, no spots at all). Make sure you have a good nozzle and it is centered properly.

Read the document I posted / attached.

Start out by adjusting the focus in the upper right of the cutting condition page. Line E1 if you have a 160i or the spot where it says focal if you have a NT.

Cut a hole and square, mark on it your focal position, move up 1mm, cut another one, mark it, move up another mm, ......


You should see a range where the cut gets worse and worse. If that is the case, stop when you get one that will not come out of the sheet. Ideally, you would see a complete range, from bad, to good to great to good to Turmph part.

Your focal point you want to cut with should be right in the middle of that range.

To be more specific, for example, you cut a part it will not come out of the blank at -6mm. You keep moving it up (-5mm -4mm -3mm -2mm....) until you get to -1mm part looks good. Keep going until you get a part that does not come out of the sheet. Go all the way. it may be at +4mm before you get one that does not come out of the sheet. (-6 mm + 4 mm)/2 = -1mm (pretty good, even for an engineering website). The point you want to cut with is in the middle of the range.

 

[nidbe]

thank you ...

 

[FOSTERLASER]

We have found that a mirror can look perfectly clean and have coating that is failing. If you clean a reflector and there are tiny gold specs on the lens paper, the coating has failed.

 

[IRstuff]

Yeah, we generally don't recommend using anything resembling lens paper on lenses or mirrors.

TTFN
faq731-376

 

[FOSTERLASER]

IRstuff-what do you use?

 

[JayMaechtlen]

Laserninja - interesting file.

I worked on that doc (mainly to make it semi-usable) while I was at Amada.
It's kind of scary that nobody has reworked it since then!

regards
Jay


Jay Maechtlen

http://www.laserpubs.com/techcomm