cause of focus lens burning in my Fiber laser

[bast64]

Hello everybody

I have one 2 kw fiber laser machine from Ermaksan. In first work day after training I faced with problem in cutting. after around 1 min machine couldn't cut SS at all. one Technician came from Ermaksan and found problem in cutting lens. the focus lens is burned from up side (internal side).You can find a photo of it in attachment. The cutting head of my machine is procutter version of precitec. Technician replaced it under warranty, but he told me this is an effect of back reflection that it make after cutting an nonstandard filmed SS and if it be damaged again it will be out of warranty. I am in doubt about this diagnose and I am worry about repeating this damage.
would you please see the attached photo and answer to my following question:
1- Is it possible that this phenomena make with back reflection?
2- what are other possibilities?
3- I have heard that procutter head can counteract back reflection, is it a true claim or not? and if it is true, how?

PS: I will be more happy if msandoval, tstc and Jeanfreli reply to my question, too.

 

[evans1089]

So you did use a filmed covered sheet? And was the stainless a mirrored finish?

Are you ensuring that before you start every shift that the nozzle and beam is alligned perfectly?

 

[JeanFreli]

Since how long you got your laser? because you have the old version of precitec head which were very bad at my experience with them. I am very surprise he didn't offer you to upgrade the head for the new version of precitec. They did an amazing job with the new one. And with the bluetooth on it you can prevent dammage. It worth the price.
And yes the film of the sheet can cause serious dammage to your lens. You have plenty of film on the market but some are bad for fiberlaser. I always click the filmburning before the cut. Your problem is the dirt or fume from the plastic that goes on your protective lens and dirty it very fast. The problem with this head is the dirt reaching the focus lens and then your are stuck forever with problem until you change again the focus lens. I can predict soon you are going to have to change the fiber cable because of the back reflection. The focus lens of the new head is sealed from the protective lens and it makes a huge difference. You might have more answer here, i learned a lot with these guys. you can contact me if you have more questions at jeanfreli391@gmail.com

 

[Foostrap]

Doesn't your cutting head have a protection window; which will absorb any dirt of spatter, protecting the cutting lens?
Normally you simply replace that protection window and do not have to touch the cutting lens. Unless somehow you have a head with no protection window (which would be very bad as you'll need to constantly change the lens; this also needs to be done in a very clean environment; fiber lasers are very sensitive to dust).