Changing the head lense? 4

[sjclaser]

Hi All,
I have recently started using my first laser, a Bysprint 2.2Kw machine. I am looking for some advice on how often the lense in the head should be changed. Bystronic say take it out and clean it every shift and if there are ANY marks which do not come of then you should change the lens! At £200 each, i dont want to change them unnecessarily so is this true - or can you get away with the odd mark, or light scratch if it is still cutting well? Are lens really that fragile that a scratch can make them heat up and brake?

Thank you for all advice given, much appreciated!
Simon.

 

[HenryRollins]

Clean the lens after 8-12 hours of use. Follow the procedure specified during your training. This will differ in method depending upon what office gave you your training. make sure you go to a clean area away from anything that throws off dust to clean the lens.
-HR

 

[krugtech]

What Henry said. Save the crappy lens for o2 cutting, n2 cutting will blow a lens up a lot faster. also use a polarizer to check your kens, you wont see much for a while but one day you'll have a lens that looks fine but the machine dont cut this will find it. I posted this a while back-

If anyone uses polarizing filters to check their lens, here's an easier way to do it. Normally you would lay a polarizer on a diffuse light source, lay a lens on top of it and place another polarizer on top of the lens. Rotate one of the polarizers until all the stress in the lens appears.

easier way- open notepad on a computer with an LCD screen. The white LCD screen is an excellent polarized diffuse light source and you probably have an LCD screen on the laser anyway. Then get one ploarizing filter or even a pair of polarized sunglasses and hold the lens between the light source and polarizer filter. Rotate the polarizer and if there's any stress in the lens you'll see it clear as day.

My customers will try this and not see anything, maybe they'll see some clovers where the lens clamp ring was pressing on the lens. Then they'll find a lens that looks fine but the polarizer shows all hell breaking loose inside. As you rotate the polarizer the amount of light coming through should change, if it doesn't then you don't have an LCD screen or the polarizer isn't a polarizer.

Chris Krug

http://krugtech.com/

Maximum Up-time, Minimum BS

 

[Tasa75]

Don´t have much experience with lenses, because I am working for two years with laser,but here it is :
I have lens on the 7.5" head that has mark on the lower side in the middle of it and it is not mark as something is burnt on the lens,it looks like thermal damage on the lens it self.It cuts like that for almost a year now.It cuts like new.
On the 5"head for 2 years I have changed 2 lenses, both of them, when they had a mark from the lower side, that looks like there was a piece of plastic foil (from the sheet burned while it was attached on the lens) and has damaged the lens coating surface. Cutting with that lens is poor.There is one thing you should beware of : catastrophic lens brake- if lens brakes ,it goes to many tiny pieces and than you must clean thoroughly whole beam path.If it brakes it is very toxic.. There is also a big difference depending on the power of the laser.Lenses last longer on less power transfer.I think that as soon you notice cutting quality change due to the lens you should change it. Missing energy that causes bad quality cut is transferred in a heat on the lens itself.
As for the cleaning, I clean my lenses on about 8 hours of cutting, almost every day, as it takes only few minutes to do that.
More experienced guys are welcome to correct my statements.

 

[sjclaser]

Hi All,
Thanks for the replys! I hope to reduce the number of lenses i am using. I've only had the laser about 2 months and it started with a new 5" lens. After 2months, running 3-4hrs a day (5days/wk) i am on the third lens which seems like too many. Apparently a new install may cause you to get through more lenses because any dirt in the gas lines may come though to the lens, but once this is out of the system the will not require changing so often. On lense supplier says i should be able to get around 6 weeks out of a lens, does this sound right or should i get more?

Thanks all, sjclaser!

 

[HenryRollins]

Dirt in your gas lines? Wow, you really need to address that as soon as humanly possible or you will have bigger problems to go with it like blowing a lens up and taking out a few mirrors in the process. Lens life may vary with cutting gas. Example, if you are cutting with N2, you require more power to perform the cut and your lens will heat up faster. Every time it heats up, it must cool down and this will cause microcracks/thermal distortion to form over time. So you may experience shorter life with
if you cut with N2 because the beam does the cutting and the gas pushes the material out of the kerf. O2 is the opposite because the gas does the cutting and most materials require less energy to perform the cut. The heat build up will be there in your lens but may not kill the lens as quickly. Just be sure that you clean the lens after 8-12 hours of cutting and be sure to correct your gas issue. Also, careful of your piercing parameters and debris build up on the nozzle. Bad piercings may spatter up your lens because your gas for piercing may be higher than that of the cut and when that is the case, you can cause a venturi effect that will draw debris into the nozzle and on to the lens. use the nozzle cleaning feature often, say every 100-150 pierces.
-HR

 

[sjclaser]

Thank you Henry for your reply!