[dcas1]

Hi all,
we're trying to cut shapes out of 1 mm thick silver sheet. The machine we're using is a brand new Beamer, middle power range, model 50 I think. The machine is intended primarily for laser marking and it uses high speed galvos for beam steering. The engraving performance is acceptable but the cutting or blanking out is still not working.
We're testing the cut trhrough performance by cutting out a 1/2" square.
It is supposed to cut clean trhough a .040" thick silver sheet, but it requires about 25 passes around in order to cut through, and there is a small amount of recast on the underside edge. It will cut through .030" thick with 15 passes. The metal workpiece sheet (skeleton) gets extremely hot. It was supposed to go to 2MM thickness.
The sides of the cut are smooth, but the recast or slag is disappointing because it will require some post production cleanup.
The control software and machine control is custom. There is no gcode, you can import vector graphics bu the scaling appears to be off. From what I know, the manufacturer says the laser has to cut a series of tiny circles as it moves along the cutting path.
Would anyone have any experience with this machine or in general cutting silver, gold, copper and brass with a pulsed fiber laser? Please note that these materials can't be cut with CO2 lasers, I think because of the heat conduction of these metals. These materials require extremely short duration, high energy laser pulses to ablate, or phase change the base metal into plasma, in so brief a period of time that the metal never has enough time to get hot.
We were under the impression that this machine would cut the blanks out in one pass. I'm wondering if the laser source is correct for our application. Perhaps our problem is caused by the settings we've entered. We have control over these 3 variables, cutting speed, power, and frequency.
My thinking is that if we were to increase the power setting but reduce the duty cycle, we'd get better performance because we'd be ablating more, thereby changing the material state to plasma, and heating less, as opposed to a longer duration and lower power laser pulse heating up the part. Less recast too perhaps.
Would anyone care to comment?

[Litografa]

Forget about cutting even thin metals with this laser - I spent 2 months with different tips like adding O2 to laser zone but result was the same -multi pass cutting with extremely bad edge You need much powerful laser with flying optics, like GCC C290 at least

[dcas1]

Hi Litografa,
thanks for the reply. I got a bit more information on the fiber laser machine that may help clarify things.
Machine is made by Ultra Dex Tooling Systems,
model is a Beamer FS-50 Fiber Laser
Laser source is:
Manufacturer IPG, type is Ytterbium Fiber Laser,
model # is YLP-1/120/50/50-HC manufacured in 11/2008
Do you think that this laser source is underpowered for the cutting 1 MM thick silver sheet? Would the source need more power because it uses flying optics/galvos, or is the laser source just underpowered?
Would it be possible to make adjustments to cutting speed, frequency, and power to get a cleaner cut?

[Litografa]

My suggestion use for this application powerful (more than 200 Wt) CO2 laser with oxygen addition to lasering area.

[zax15uk]

Yitterbium lasers are excellent for marking metals, and cheaper than Nd:YAG.

I have a 20W Yb system as well as several 60A Nd:YAG's for engraving, but unfortunately I don't have experience on silver and no where near 1mm thick.

I suggest having the laser checked out and power output measured, maybe it's time to replace the pump diode.

Zax.

[dcas1]

Thanks Zax
unforturnately it's a brand new machine, but you are right getting the laser checked out is a good start. I'll contact the manufacturer
cheers,
Denis

[dcas1]

Hi Litografa,
have you been able to succeed at cutting 1 mm thick sterling silver with this CO2 laser?
I was told that C02 wouldn't do it because the metal conducts the heat too fast and the whole sheet just heats up and melts and boils, instead of ablating. Something about the pulse duration being too long.
This laser heats up the sheet so hot that it tarnished, and discoloured. It took 15 passes to cut .030" thick sheet
cheers,
Denis

My suggestion use for this application powerful (more than 200 Wt) CO2 laser with oxygen addition to lasering area.

[Litografa]

Yes, I do tests on different materials including silver. Check Synrad site for more information www.synrad.com

[LaserWeld&Cut]

Hi,

I read the original post and the replies with interest. We manufacture laser cutting machines in the UK and silver is difficult to laser cut due to high reflectivity and high thermal conductivity. To cut 1mm thickness with satisfactory quality and speed there is no real alternative to a pulsed YAG laser with a gas nozzle using Oxygen at fairly high pressure. See the YouTube video : http://www.youtube.com/rofinbaasel#p/u/26/MyB9IDU-m6Q
In this case the laser has a small spot size (maybe 0.05mm) and a high peak power for each short duration pulse (maybe a millisec). If you use a laser with a bigger spotsize (CO2 laser for example is typically 0.1-0.2mm or larger) you will not have enough power density to get through the surface. The Yitterbium fiber laser you mentioned is capable of engraving - and if you engrave with multiple passes you will go all the way through. But, as mentioned there is a lot of heat input and edge damage - this technique works better in gold, but will never match the speed or quality of a system with a gas nozzle. If you were sold this system as being suitable for cutting 2mm thick silver, then the company selling it did not give you all the available facts.

Hope this is helpful.

Dave

[junee]

Check out A-1 Laser International... It's free to ask questions from there as well.