[CLT-Tech]

Has anyone experianced short lens life (particularly when cutting Stainless steel) ? I operate a 4Kw C02 Laser. Whenever i cut .125 SS or thicker. . . . Within 5 parts, my lens is covered in spots, which do not come out of the lens. At this point, the focus is way out, and cut quality is lost.

Anyone else experience this issue?
Got a cure?

Thanks all.

[lamicron]

I have never work with that power of laser but , the pressure air thru the outlet are not protecting the lense from receiveng the dirt>??

[MacGyver]

This is obviously an issue with optics protection, not a failure of the optics itself. Make sure there are no leaks around the gas assist gaskets that would allow dirt in. Make sure the assist pressure is high enough to prevent blow-back. See if you can move to a longer focal length to get the material away from the lens. Try adding in a second air assist that is transverse to the material.

[ImanCarrot]

Zinc Selenide is very prone to thermal shock. You're not heating and cooling it too fast are you? Make sure your optics are coated. Make sure your optics are meticulously clean. Any debris and/ or surface imperfections WILL cause localised concentration of energy (heating) and surface fracture. I've seen this many, many times in high powered laser systems. I've seen lenses actualy fracture at extreme energy concentrations purely due to surface imperfections and/ or dust particles.

Although this was in VERY high energy laser systems using Neodymium doped fused silica, but the principle is the same.

http://www.awe.co.uk/set/Laser_facilities.aspx

[Edit]Just re- read this and I'm certain as others stated, that this is ablated material condensing on the lens. Your loss of focus is caused by diffraction and dispersion as the material affects the optical perfomance of the lens. As stated, a longer focal length will get your lens away from the material being cut. Contamination of lenses in lasers is a big no no.[/Edit]

[KTP]

I thought they used copper parabolic mirrors or something with lasers that powerfull...seems a lot cheaper and easier to polish...

[ImanCarrot]

Hmm how to explain...

Ok, in very rough terms- picture a hypothetical rod of lasing material, say 2 feet long and 1 inch in diameter.

Fire laser light through it and stick more energy into the lasing material by *mumbles* doing something. This "pumps" the valency of the lasing material to give more light out.

Fire this into a bigger one, that into an even bigger one and so on. Build the lot about half the size of a football field 'till you get a really big diameter beam with loads of energy.

Build a second system in tandem so you get two really big beams from different directions. Focus these down to about half a millimeter and you can immagine the energy... albeit over a very small time span.

Now, the interesting thing is what happens to stuff you put at the focus of these beams especialy if it's "interesting" stuff that you put there to begin with hehe

Disclaimer: all this stuff is in the public domain, so I aint giving nothing away.
look at http://www.awe.co.uk/set/Laser_facilities.aspx for more info

[Edit]Off axis parabaloids are used in large aperture systems, polishing them is almost an art form... diamond machining them is too! Copper can be used, but better to have it gold coated or whatever depending on the wavelength of light you're using. Coated Zerodur is about the most stable reflecting material you'll get though, but it's no use in transmission.[/Edit]

[coleong]

Within 5 parts, my lens is covered in spots, which do not come out of the lens

Maybe you should check the cutting parameters especially the piercing distance. i believe it is set too low.

The supplied cutting distance and piercing distance should not be change as per recommended by the machine manufacturer.

[bmak]

Is the material coated in anything that could cause contamination?

Ive only had problems with coated steels such as zinc but i still get a days worth of cutting(50 or so sheets) before the lens needs a clean

[CLT-Tech]

Any coated materials suck as galvanized do tend to add excessive wear and tear to the lens, and requires more frequent cleaning. . . but the coated materials aren't doing any permanent damage to the lens.

It always seems to be .125 304b stainless that destroys my lens.

I haven't cut any recently, but i will be checking my nozzle standoff perameters, and attempt a transverse blowing during piercing.