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moving focus point

moving focus point

moving focus point


i have a big problem with my Trumpf L4030 machine, with 4 kW resonator.
since last december, the focus point is moving from a moment to another.
this strange behavior began in december. suddenly i could not cut thick material, above 5mm.
a service engineer came to us, and we could restore the cutting quality by adjusting the water pressure at the rear telesacope, on the base machine, from the original 2,9 bar to 2,25 bar. everything was OK for a while.
at the end of february, we was cutting 8 mm steel. we cut a table, the quality was very nice. barely began the second table, i observed that at a specific place of every piece, it does not cut trough, it was blowing back the melted steel in the kerf. i stopped the program, checked everything that i could. i could set the machine to be able to finish that table, by adjusting the focus point. but the the cutting edge of the pieces at one side were beautiful, at the opposite side were rough and there wasn't that 1/3 smooth surface of the cutting edge. the lines were from the top to the bottom. this sign is obviously the sign of incorrect focus point as far as i know.
so 2 or 3 days i was not cutting thicker material, and than i was testing to adjust the focus (cleaning the AutoLas water filters and throttles). it seemed, that the quality was restored. i was able to cut again thicker material.
after that a few days without thick material, and again 8mm steel. i put the 7,5 inch head, and i couldn't cut at all. i was trying again to adjust the focus, and ~1,2 mm above the -5 my test circles almost have been falling out, but again that rough surface at one specific place. i tried everything that i could, even cleaning the filters and throttles, without success. the third day came the service engineer, and the machine began to work more better at the same settings that the day before. he made nothing else that i tried too, but the quality was restored.
today, i started the machine to cut a singe ~2,5 m long contour from 5mm steel. the piece was very nice. than i stopped the machine, and after ~3-4 hours later I strated again the machine to cut some more 5mm steel. i was not able even to cut trough the material. again cleaning the filters and throttles, nothing better. i adjusted the focus point in the technology table by ~2mm higher and increased the power. now i can cut 5mm steel at 80-85% feedrate.

as a summary, my problem is that
- it looks like the focus is suddenly moving, time to time, and by lifting up the focus point the quality can be restored by ~80%.
- after a few days the quality is getting better.

i'm tying to figure it out what could be the reason.
the truth is that the machine work in average ~3-6 hours a day. there are days that it worked 15 hours, but there were days that we did not start it. maybe there is something with the temperature. this is our first winter, our company began it's activity in the last summer. in december the outside temperature fall below 0 Celsius. inside we kept permanently 10 Celsius.

it could have something to do with the cooling and warming temperature?
it could be the dirty water ( as a matter of fact, it is, we have to change the water) ?

i'm trying to think about the reason.
does anybody share his opinion, please?


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