Laser tube selection,control and more importantly purchasing

[ali_asadzadeh]

Hi
I wanted to build my own Laser machine, it would be used for hobby work, I wanted to know how the tube works? how we could control the output power(are they controllable by PWM dimming or should we lower their tube voltage?  how much power do we need to cut a 0.5mm maximum steel sheet? how do you calculate it? And finally where we can get the Tubes cheaply from china?

Note this project is for gaining more experience and a hobby work.

[Gyro]

Without wanting to discourage you, cutting sheet steel is going to require serious power. You're talking about a CO2 laser which emits an infra-red beam. This definitely isn't "hobby" territory, you could blind yourself or a family member just with an instant of accidental reflection (without even seeing the danger coming).

[mikeselectricstuff]

For cutting steel you;re talking about a minimum of several hundred watts, flowing gas ( pre-mix or seperate gases - from memory I think high-purity CO2 Nitrogen and either helium or Argon)  with gas regeneration, oxygen for assist and a vacuum pump.
Take a look at this  video I made on an old industrial CO2 laset to get an idea of what's involved



I'd suggest that maybe a plasma cutter might be a more realistic solution.

[ali_asadzadeh]

Thanks for your concerns and feedback. One purpose of the job would be to make stencils for my PCB's too, so I should be able to cut accurately? I do not think the Plasma cutter would have such an accuracy,my rough estimate for the laser beam would be 10-50 micro meter so it could be used for the job,

Also Do you suggest any manufacturer in china? and how to control the laser power?

[mikeselectricstuff]

Thanks for your concerns and feedback. One purpose of the job would be to make stencils for my PCB's too, so I should be able to cut accurately? I do not think the Plasma cutter would have such an accuracy,my rough estimate for the laser beam would be 10-50 micro meter so it could be used for the job,

Also Do you suggest any manufacturer in china? and how to control the laser power?

Stencil cutters don't use CO2 - I think they use YAG or fibre. You're talking 5 figure pricetags.
You can cut plastic stencils on the cheap Chinese CO2 lasers, but if you want metal, the only option is going to be photochemical etching. EDM might be an option, though electrode erosion is going to be a problem for small details
But you can buy stencils pretty cheaply nowadays so unless you really need fast turnaround, it's just not worth DIYing 

[CJay]

You can cut plastic stencils on the cheap Chinese CO2 lasers, but if you want metal, the only option is going to be photochemical etching. EDM might be an option, though electrode erosion is going to be a problem for small details
But you can buy stencils pretty cheaply nowadays so unless you really need fast turnaround, it's just not worth DIYing

To jump in on this thread, do you think it'd be possible to etch a working stencil in copper or brass?

Might the OP being in Iran have some bearing on the availability of cheap Chinese stencils?

[mikeselectricstuff]

You can cut plastic stencils on the cheap Chinese CO2 lasers, but if you want metal, the only option is going to be photochemical etching. EDM might be an option, though electrode erosion is going to be a problem for small details
But you can buy stencils pretty cheaply nowadays so unless you really need fast turnaround, it's just not worth DIYing

To jump in on this thread, do you think it'd be possible to etch a working stencil in copper or brass?

Might the OP being in Iran have some bearing on the availability of cheap Chinese stencils?

I think copper may be too soft & creases too easily. Brass may well be an option for using existing PCB ecthing chemistry. Been meaning to try sometime as I have some photoresist brass sheet somewhere.

[Gyro]

Hmm, higher thermal conductivity than steel versus lower melting point. 

[ali_asadzadeh]

Thanks.
Ok, you got the point. I will remove the metal cutting option from the job, I would only go to the plastic cutting till 10mm, so I can make stencils with fast turn arounds and also can cut the plastic case for our quick and quality prototypes.

what's the minimum power laser tube should I choose? any brand or company in china? and how to control the output power of the laser, so I can hack on the case "Designed in shiraz"   with out cutting the case

[MagicSmoker]

Hi
I wanted to build my own Laser machine, it would be used for hobby work, I wanted to know how the tube works? how we could control the output power(are they controllable by PWM dimming or should we lower their tube voltage?  how much power do we need to cut a 0.5mm maximum steel sheet? how do you calculate it? And finally where we can get the Tubes cheaply from china?

Note this project is for gaining more experience and a hobby work.

CO2 lasers are gas plasma devices - not unlike, say, a neon sign - so require a constant current (high voltage) power source. Output power can be varied over a limited range by adjusting the current through the tube. Tube life is drastically reduced when operating above rated current (conversely, tube life can be greatly extended - especially if the tube is sealed - by operating at reduced current).

All of the CO2 lasers from China are complete crap, but they are also really cheap so perhaps worth a flier for hobby work.

You won't be cutting even 0.5mm stainless steel with any kind of precision/speed with less than 100W continuous (usually abbreviated as "CW", btw), and above about 60W CW the lasing gas mixture is usually pumped continuously through the tube which is considerably more expensive than a sealed tube laser.

Generally speaking, Nd:YAG (older technology) and diode-pumped solid state (DPSS) or fiber lasers are preferred for cutting thin stainless steel. The wavelength is a better match for the job (near infrared - 1.064um vs. the deep infrared of CO2 - 10.6um) and efficiency of the diode types is much higher (note: Nd:YAG has terrible electrical efficiency, especially the old flashlamp-pumped style). Off the top of my head I would say a laser capable of cutting stainless steel stencils will cost at least $15000US, and maybe as much as $75K. So, not even remotely practical for even a medium sized business unless you need to make dozens of stainless steel stencils per month, minimum.

[mikeselectricstuff]

The cheap Chinese laser cutters start at 40W.
They are useable, and would do stencils ( not sure to what resolution - 0.5mm qfp is probably a stretch) but do need a certain amount of tweaking & fiddling.
You basically get what you pay for.

[CJay]

You can cut plastic stencils on the cheap Chinese CO2 lasers, but if you want metal, the only option is going to be photochemical etching. EDM might be an option, though electrode erosion is going to be a problem for small details
But you can buy stencils pretty cheaply nowadays so unless you really need fast turnaround, it's just not worth DIYing

To jump in on this thread, do you think it'd be possible to etch a working stencil in copper or brass?

Might the OP being in Iran have some bearing on the availability of cheap Chinese stencils?

I think copper may be too soft & creases too easily. Brass may well be an option for using existing PCB ecthing chemistry. Been meaning to try sometime as I have some photoresist brass sheet somewhere.

Oh handy, I didn't realise you could buy it ready sensitised, I was thinking I would need to apply film or spray it. (I think etching is used to make  a lot of model engineering brass kits)

[LaserSteve]

Salt Water plus a little hydrochloric acid is actually fairly good at electrochemical etching of certain stainless steels...  There was a guy etching shutters  for home made jet engines using a crude car battery, carbon rod, and salt water system.   If you can  keep the stainless  steel stretched taunt,  electrochemical etching might be an answer.

Chinese CO2 tubes are very much on/off devices. Some power supplies idle them and then pulse the tube current up to a set point when they want to cut, with a very high frequency PWM.  Varying DC current for modulation can be very damaging to the Hochuli cathodes (1970s technology) used in Chinese tubes. It is wise to buy the power supply from the same vendor who sells you the tube. The factory power supplies are quite inexpensive

Large lasers used for cutting steel are in a class of their own, and while you might get a very thin sheet of 306 steel sheet pierced  with a tightly focused CO2 laser at 40-60 watts..., cutting would be extra-ordinarily slow. I tried it with a 300 watt gantry system and was very disappointed..

As other posters have explained, low power Co2 is not the choice for thin steel,  rapidly pulsed ND:YAG or Nd:fiber  lasers are.  Most laser steel cutting is done with lasers in the Kilowatt and above class. My friend's shop uses two to four Kilowatts. Even then, you need an inert  assist gas to either remove material from the cut, or  an active one to assist in burning through the material/

Steve

[ali_asadzadeh]

I managed to find a 2.5W laser in our local shop for 30$(Supper cheap, if it could be used for my job ), can it be used for cutting 0.5mm plastic for making stencil? as I see in this kickstarter project they used a 2.5W laser too and could cut 3mm wood!!!


https://www.kickstarter.com/projects/pineconerobotics/xplotter-desktop-plotter-laser-cutter-and-engraver?ref=nav_search

another one

https://www.kickstarter.com/projects/mrbeam/mr-beam-ii-the-desktop-laser-cutter-and-engraver?ref=nav_search

what's your Idea? Do we have a cheap 10W small tube?

[MagicSmoker]

...
Chinese CO2 tubes are very much on/off devices. Some power supplies idle them and then pulse the tube current up to a set point when they want to cut, with a very high frequency PWM.  Varying DC current for modulation can be very damaging to the Hochuli cathodes (1970s technology) used in Chinese tubes. ...

Interesting... I knew that using RF to excite the gas mixture results in much longer operational life, but I did not know that adjusting the current away from an ideal value could damage the cathode. Is that because of partial ionization of the electrode or what?

[LaserSteve]

Twenty-five Watts of Co2 Laser  would have you slowly cutting light plastic sheet to 5 mm, wood to say 4-5 mm, the ability to engrave organic materials.   So then you need  a fold mirror (30$) a fold mirror mount (30-40%) , an air assist nozzle, a focusing lens, a focusing lens mount and focus servo,  an aiming laser (red or green), an aiming laser combiner, a fume extractor fan and hose (NEVER use a carbon dioxide laser without a fume extractor)  etc,,, I'm not even at the motion stage or work hold down yet...

Even with a low cost laser, these things add up.

A really tightly focused 2.5 Watt blue might cut carbon loaded (black) plastic of 0.25 mm,,,  You will need a pair of cylindrical lenses to correct the diode laser beam shape, which is elliptical,  and a focus lens.  The plastic fumes will quickly give you headaches and kill you eventually if you do that in a confined space.


Steve
 

[LaserSteve]

The issue is the ratio of current emitting area to current density. At very high densities the cathode gets poisoned by decomposition of the organic gasses and if the pressure is low, the gas ions "knock" the emissive material off of the cathode, a process called sputtering.  That metal finds its way to the optics and glass, and buries more gas in the process.

There are catalyst driven reactions going on in the tube to cause oxygen and carbon to re-unite in the gas mixture. If the tube  current is too low, you may not get catalysis and may also end up damaging the electrode surface. Very tiny amounts of Water, and/or a few percent of  Xenon, and Carbon monoxide are often added to tubes to create recombination of the gas and better energy transfer.

I haven't worked with this in years, but there is a very specific regime of pressures, temperatures and materials where all this works. If you get outside that window or band where the physics works, tubes can die fairly quickly.

Hochuli cathodes are a combination of some metals that can be oxidized during processing to form a stable electron emissive surface with far more emission then a bare metal. ,  Exactly how they work and what materials are best for long lifetime or power density  are proprietary matters for tube makers. There is quite a bit published on the matter, but a lot of it is a trade secret...

Overdriving a tube will kill it fairly quickly.

  RF is a different regime, I haven't worked with that, and it gets rid of a lot of electron emission issues due to more uniform plasmas and capacitive or inductive  coupling of energy into the discharge.  I was given a few tiny RF waveguide tubes when I was a kid, but they were already dying.  You can get a lot more energy in when your electrodes are not limited to a few hundred microamps (or whatever) per square cm..

Steve

[LaserSteve]

Removed double post.

Steve

[ali_asadzadeh]

Thanks for the update, now a days every thing is manufactured cheaply in china...ranging from our very old friend NE555 to 16nm xilinx SOC's, even apple phones
Does anyone know some china manufacturer to sell a complete laser kit with 40W power or less? so we could only attach it to the CNC, and make the life a hacker easier? Do we have chines friends in here? so maybe they could help us and shed the light upon us

[Mr.B]

I have a VersaLaser made by Universal Laser Systems USA.
https://www.ulsinc.com/

It is a 50W model. Bed size 600mm x 300mm.
It has the following capabilities:
Cut max 12mm acrylic.
Cut max 5mm hard wood.
Cut max 7mm soft wood.
Cannot cut steel, copper, alloy, etc.

It can etch the surface of almost anything.

Cost: NZD32k about 10 years ago.
It is very well designed and made from high quality components.
I would not even dream of trying to DYI one, just wouldn't go there.