Industrial CO2 Lasers. RF vs DC.

[revdode]

Has anyone experience of recent DC and RF resonators in sheet metal cutting applications?

I've used RF lasers in the past but for our next machine I have selected a DC laser, largely for reasons of purchase cost and better service coverage. From my point of view as long as I get power and an acceptable level of control frm the machine the method of excitation in the resonator is irrelevant. I'd be interested, without starting a religious war, if anyone had positive or negative experience with either technology.

TIA

Rev Doh'd

 

[jdsewell]

pardon my ignorance. i have worked with a co2 laser for many years, but i don't recall the terms rf and dc. please clarify for my own education.

 

[revdode]

I'm no expert in this field but the following is I believe a suitably accurate over simplification.

Industrial CO2 resonators employ one of two basic methods of excitation of the lasing gases. Either a high DC voltage (8kV~20kV) passed between a cathode and anode in the resonator glassware or a radio frequency (RF) applied across two electrodes usually located outside the glassware.
RF has some advantages for low power control, less contamination of glassware and lower voltages. DC has the advantage that the electronics are simpler and more reliable and they generally cost less.

As I said in my original post as far as I can tell this is somewhere between a holy and marketing war. Currently companies such as Trumpf and LVD (Fanuc) use RF lasers, Bystronic and Prima (PRC) use DC.

 

[jdsewell]

i feel better. that's what i thought dc and rf stood for. however i have not heard of an industrial grade laser utilizing rf for laser excitation. i knew it was theoretically possible. is the effeciency higher for rf? dc munches a lot of power.

 

[crgopal]

RF stands for radio frequency and Dc means direct current.
the electrical excitation of the laser medium i.e the gas mixture (CO2, N2 & He)is done by RF or DC. Both have merits and demerits. As far as the user is concerned, it matters in the efficiency of the machine only, since DC excitation consumes lot of power because of the use of ballast resistances whereas RF is not. since the output power of the laser matters to the user as well as the application, you need not worry about the RF or DC.But, in general RF excited lasers are currently marketed everywhere.

Hope this would suffice to your doubts.

 

[dror]

It is very simple RF lasers has positive dinamic resistance
DC has negative

DC has high constant power and bad short poulse preformance
RF has 5% less but good short poulse preformance

 

I FEEL RF LASERS ARE MORE STABLE OVER A LONGER PERIOD OF TIME. THEY ALSO TAKE MUCH SHORTER TIME TO START AFTER COMPLETE SHUTDOWN. THEY CONSUME LESS GASES. RF LASERS ARE MORE COMPACT. MAINTAINANCE REQUIREMENTS ARE LESS.

 

[revdode]

Following up my original post with a few notes, these are my observations based on my experience of RF and now DC laser in the last four years.

I've found the low power control of the DC to be poorer than that on the RF laser I've used in the past. This is only noticeable in extreme fine profiles and switching rapidly from etching to cutting.

The CO2 laser seems to use slightly more resonator gasses than the RF machine, but this may be a feature of the way we are running the machine.

The stability of the cut on the CO2 laser is better particularly at the limits of the machines capability. I've found it possible to obtain a good cut in most cases cutting Zintec material with O2 at speeds I couldn;t have achieved on the RF machine I used previously. As we cut a lot of Zintec this has proved to be a great saving.

Thats after six months, and apart from these notes I haven't found many real differences. If this thread is still around in anotehr six months I'll post an update.

 

[kbowers]

What about at high wattages? say 5kw or 6kw are there differences in the benefits of RF and DC? I assume from the power stand point the DC is still better and usually with 5 or 6 no one needs to control the power down to 10% of teh 5 or 6. I would guess though gas consumption becomes a problem.

 

[mikeelms]

When you put more current into your DC-Tube, it will tend to arc instead of maintaining the desired glow discharge.
With RF you can have a higher Powerinput/Volume but with less efficency than the DC-Tube==> RF-Tubes can be smaller.
when the spacing between the electrodes is small,it is possible to cool the electrodes with water and the heat is removed from the gas just by heat-conduction, => you need >>MHz. This goes up to 100W sealed system waveguide laser.
for normal discharge Tubes with fast gas flow, you can use ~13MHz. I don't remember the industrial-band frequencies at the moment...
DC-Tubes have electrodes inside which sputter metall and cover the tube. => maintainance required.
RF-Systems feed the power "evenly" distributed into the discharge-tube and there are no electrodes inside.

If you want to cut, then you will need a small focal spot DC/RF is up to you...

 

[JayMaechtlen]

unless you intend to design and build a laser, you really need to just research the units commercially available.

There are good RF units available (1kw to 4kw for sure) and good DC units (to 6kw+)

for power level, it depends on what you mean by "sheet metal". If you will integrate your own machine, pay HUGE attention to power control, pierce routines, cutting parameter control, gas switching and pressure control, beam stability, consistancy of beam size at the focus lens, etc, etc.

look at published power consumption, gas consumption, etc.
cost of resonator gas is trivial compared to everything else!

look at service and parts support from the vendor(s)

let us know how you make out

Jay
(at Amada America, Inc)