Laser cutting problem on a JD 6090

[MillieA]

Hi Guys,

Hope you can help ...

We have a JD 6090 60W laser, purchased new, about 15 months ago. For some time now (last 6-9 months), the cutting power seems to have been reducing until I am now having to cut 3mm acryilc 3 TIMES, on a speed of 3 (really, really slow ... was 20 earlier in the year) and a power setting of 100% in order to cut right through, and even then there are some areas of the cut that don't go right through and need breaking out.
Engraving is fine ... crisp and quick (engraves happily on 300, power of 20).
It has already had a replacement PSU (power unit) this year and a new driver on the X axis, and it has had the mirrors and lens regularly cleaned - not that they seem to get that dirty. Z axis set every time.

Any suggestions gratefully received :-)
MillieA

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[Signmaker]

Have you checked the beam alignment?

You say you've changed the mirrors... did you check the beam alignment straight after? If the beam is only giving a glancing "blow" on your mirrors and/or lens this would explain the lack of cutting power. The little adjustment screws on the mirror assemblies only need to be tweaked a fraction of a turn and the beam will "walk" across or off the next mirror.

Coolant temperature is important- the "pond pump in a bucket" solution that comes with most Chinese laser machines is pretty cr@p. We run all our machine using chilled deionsed water which is held between 10- 15 degress celcius. A nicely cooled laser tube gives good power for longer.

If your coolant and mirrors are fine then your glass laser tube is probably starting to fail

[MillieA]

Hi Signmaker,
many thanks for the quick reply ... I checked the laser route / alignment earlier in the week thinking that might be the problem, it was ever so slightly out, so I realigned it back to the centre, didn't make any difference so can't have been far out. We do have a chiller connected, doesn't run as low as yours though, typically 25, not 15 ... I hear what you say about chilled de-ionised water though and will check levels and temperature parameters next week when I'm back in work. I'm afraid you're probably right about the tube, I'll investigate prices etc and go from there. Huge thanks again :-)
Millie

[wmgeorge]

Replace the tube, chiller should be set at about 20 DegC. Warmer temps will shorten life of the tube.

[SignWave]

Hi Millie,
Here's another test you can try... Probly take you an hour or so, over all, to get a possible result.

Generate a rectangle/square shape in your software. Try to make it at least 90 % of the length of your X axis. It only needs to be about a 1/4 to 1/2 inch wide(tall). once created, engrave that shape into a material that will allow your beam to cut evenly to at least a 1/4 inch deep into the material.

Let 'er rip! Once the file has been cut measure the depth of the cut at both ends. If there is any difference in the depth of the cut. Your mirrors are out of alignment and you will have to readjust them.. As Signmaker has mentioned... it is very easy to throw them out.. and even though you think that they are aligned,,, they may not be. check and recheck. Google out (on youtube) how to align mirrors on a laser.
Its worth a shot. You may need to create a big square that is about the same size as your table.. it doesn't need to be full fill in the middle.. just a 1/4 - 1/2 square "box" if there is any misalignment it will show on one of the corners as a shallow spot or a deeper than expected spot.

If your tube is old.. like 3 years plus old and you've used it more than say 200 or more hours in that time... It may be time for a replacement, but I doubt this.. Check out the simple things first before investing in a new tube you may or may not need. Your tube losing power like you are describing does not sound normal to it "burning out" My 80 watt has 1000plus hours on it over a 3 year term and at varying power levels. Over that time i have had to adjust my power by about 10-30% depending on the material...At one point I skewed my mirrors and the cutting power went right down the drain, but it still engraved very well. The giveaway was the unevenness of the gravure I created.

Cheers!

[MillieA]

Hi to all of you who have taken time out to reply ...

I really appreciate the time taken in your replies and suggestions and will try out Sign Waves suggestions first, but have also got a quote for a new tube as per wmgeorgs's suggestion, and I will try and adjust the chiller setting to bring down the temperature.
thanks again :-) ... I'll let you know how I get on.