building a small, cheap laser system to cut thin metals

[Jonathan Brown]

I have built a few CO2 laser cutters in the past, using either old medical lasers or more recently Synrad lasers I repaired (had faulty MRF150 fets in one...bitch to desolder!) Recently I have purchased a used IPG Ytterbium fiber laser which outputs a 1064nm beam of 10 watts average power in a 20khz to 100khz pulse stream of 100ns 0.1mJ per pulse (5000 watts). 10 watts does sound tiny, but the beam quality is excellent...might be something like M^2 = 1.2 or lower.

I have not had a chance to do much with it except verify the average power using a Synrad Powerwizard thermal meter and verify the pulse stream using a Agilent DSO and a reverse biased photodiode. I did lathe up a quick mount for a scrap ~25mm plano convex optic and fired a few rough focus test shots at a razor blade. For two of the shots I managed to find the focus and the laser punched a hole all the way through (maybe a 20um hole). I have some real lenses on order from Thorlabs. I am going to try a achromat cemented doublet 1 inch diameter 40mm focal length, AR coated for 1050 to 1620nm. I calculated the focus spot could be as small as 11um and the Rayleigh number would be 75um with this lens.

My goal is experimenting with micromachining....or really I just want to be able to cut things I cannot easily do on my cnc bedmill or my co2 laser cutter. Plus these little fiber lasers are so compact and power efficient....50,000 hour lifetime not bad either.

I am not sure what I should do about the gas nozzle. Most likely I will want/need oxygen, but I have read that the velocity out of the 0.02" orifice on a typical nozzle is supersonic at pressures of just a few bar. I have not found a lot of info on nozzle design. Plenty of stuff on lens choices, not a lot on cutting heads/nozzles.

Do any of you have a similar system and can maybe offer some hints or sources of reading material?

Here is a shot of the razor blade under a microscope (blurry photo as I do niot have the appropriate camera system yet). The black line is a human hair of maybe 25 to 40um. I illuminated the holes from the back also for visibility.

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[Bruce Boone]

My fiber laser has a LaserMech head. They have copper nozzles that screw into the laser head. The inside of the nozzle is a simple polished cone going all the way to the tip. They also have drawer type holders for the lens and lens protection glass. The area below the lens is pressurized. I use 250 psi argon when cutting titanium. I had to source high pressure lines and selonoids in order to handle the pressure. I also got crash protection. This is a special connection to the machine column that has a detent to hold it in place, and if it gets bumped, it will deactivate the laser and machine axes circuits. I don't need it often, but it does come in handy when you least expect it.

[Jonathan Brown]

Ok, wow, a 4500 watt fiber laser....I was thinking a bit smaller. :-) My laser is the size of a small box of cereal, runs on a bit more than 100 watts and is air cooled.

I am somewhat familiar with the LaserMech head after reading this excellent phd paper on fiber laser micromachining: http://research-archive.liv.ac.uk/12...295_part_1.pdf

In this the author used a IPG 50 watt laser (but I think no high peak power pulses like mine) to cut stainless steel stents using a LaserMech cutting head probably similar to yours. FineKerf or something.

I am guessing that cutting head would cost significantly more than I paid for the fiber laser. It does sound like there is not too much special about the nozzle though...I should be able to cut that out on my cnc lathe...or at least cut something out for testing.

I have some uncoated BK7 glass windows but that would leave me with an 8% power loss. The Thorlabs achromat doublet is only $90, so I might start my tests without worrying about protection glass.

I don't have anything specific right now I want to cut...I am just fascinated with miniaturization of things. Speed and job time are non-issues for me.

Edit: Mmmm, yeah, I just checked Thorlab's price on the 1 inch diameter BK-7 windows v-coated for 1064nm...$172.90 lol. With my optic costing only $90 it would be more cost effective to protect the lens protector glass with the lens instead of the other way around :D

[Bruce Boone]

To be fair, mine is a quasi continuous 450/4500, so is continuous to 450 watts and pulsed to 4500. Mine is air cooled too! They are insanely efficient. The Laser Mech head was indeed major bucks. I got it with a confocal setup where I could use two different focal length lenses, and I wanted to get as fine a spot size as possible. With some fanagling, I got a spot size of 50 microns. The 11 microns is insane! I might get a laser like that just to experiment with selective laser welding or sintering.

[Jonathan Brown]

I lathed a quick and dirty copper nozzle today...or at least something that looks like a nozzle. I managed to taper it on the inside fairly smooth, drilled a 0.045" hole, and tapered the outside a little bit.

I found a old CO2 laser fitting in the junk box which had a damaged 0.75" znse lens in it, which was cool because the lens I am testing with the fiber laser is also 0.75" dia. I swapped the lenses then press fit the copper nozzle into a cutoff piece of aluminum threaded tube with the correct threads (my lathe is manual and doesn't have threading...I could do cnc thread on my mill, but the setup time would be long and I have the fiber laser on there now for testing.

Anyway, the completed setup should at least keep the sparks and backsplash off the lens and maybe it will provide a cleaner cut. I used about 40 pounds to press fit the copper nozzle into the aluminum tube, so I am guessing it would handle about 100psi before it goes shooting out llike a bullet :-) Perhaps I should swage it in or drill a setscrew.

Tommorow going to try running it with a mix of 75% argon 25% co2 from my mig welder. That mixture does a good job when welding non-stainless...I am curious what it will do with the laser. I don't have a bottle of oxygen to test with. I do have a bottle of nitrogen though...

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[Joe Hillmann]

Jonathan,

I have no experience with building laser systems but I somewhere I read that when using a cone air assist if you use more then 35psi you run the risk of breaking your lens and the larger the lens the lower the max pressure it can withstand.

[Jonathan Brown]

Good point. Most of the fiber laser systems seem to be running around 6 bar (90 psi?). A 1 inch dia lens would have an area of 0.5^2 * 3.14 = .785 inches^2

At 90psi that would be a pressure on the lens of around 70 pounds.

Does sound like a lot. Perhaps I will keep it below 35 psi for now :-)

[Bruce Boone]

That looks like it should work. I imagine the argon/co2 mix should work for just about anything. The trick in cutting is you need to dwell for a fraction of a second while piercing, then do your feed move. I program my dwell in milliseconds, and for most stuff I do around 400 or so. If I do less, sometimes the beam won't get through, and the cut won't happen. I imagine you will be doing very thin stock, as the power will greatly ramp down as you get out of focus. Also, having such a tight focus will mean that your thin kerf itself will block a lot of power as you go deeper. It should do some wicked graphics on thin stainless though.

[Jonathan Brown]

Some success. I bought a set of (non-stainless) feeler gauges to get some different thickness than the 0.009" standard razor blades.

Mounting up the 0.005" thick feeler gauge, I set the 75% argon/25% CO2 gas feed to 30 PSI. I then cut some rectangles that are 0.02" wide by 0.03" high. I tried feedrates of 0.6 IPM, 1 IPM and 2 IPM. The 2 IPM actually seemed to leave the best cut. I have not tried faster yet.

There is still some brownish/red smudge around the cuts and some dross on the top and bottom side, but definitely less than when I was running with no nozzle or gas. These tests are all with a cheapy plano convex single lens of about 30mm FL. I will be getting the hopefully much better achromat doublet from Thorlabs this Monday.

The pictures show the rectangles cut out next to a 0805 resistor for a sense of scale. There were three pieces but I sneezed and one went flying somewhere. The last pic is the very comical setup I have for this on my Shizuoka cnc bedmill. Imagine a 7000 pound cnc mill being used to cut out a square that is 0.02" by 0.03" by 0.005"! I do plan on building a xyz stage out of some NSK linear robot modules very soon. Always being safe, I am in a closed room wearing OD10+ goggles and not staring at the beam. Until this gets into a closed box system I am being extra cautious.

I would like to try some variables to see if I can get an even better cut. I did all of these at 20khz rep rate....perhaps going to 40khz or even higher might improve things. Suggestions?

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[matthew knott]

Sounds like you having a great time Jon, good results, speed seems very slow for cutting so be interesting to see what happens when you ramp the speeds up, most used pulsed IPG would be the .5mJ(10 watt) version normally run from 20khz to 80 khz, great little lasers, normally pretty reliable but I have know them fail and IPG charge lots or refuse to fix depending on where the laser came from, lots were out of Telesis marking lasers and IPG won't fix them and insist they go back to Telesis who also aren't interested. Your laser has the built in anti back refection protector so no worries there which is good.
We have some of IPG'S newer lasers and you can program the pulse widths and run much higher/lower frequencies, never really find them much use, there are way to many variables you can adjust as it is. Do you have any real plans for this or is it just for fun?
Matt

[Jonathan Brown]

Sounds like you having a great time Jon, good results, speed seems very slow for cutting so be interesting to see what happens when you ramp the speeds up, most used pulsed IPG would be the .5mJ(10 watt) version normally run from 20khz to 80 khz, great little lasers, normally pretty reliable but I have know them fail and IPG charge lots or refuse to fix depending on where the laser came from, lots were out of Telesis marking lasers and IPG won't fix them and insist they go back to Telesis who also aren't interested. Your laser has the built in anti back refection protector so no worries there which is good.
We have some of IPG'S newer lasers and you can program the pulse widths and run much higher/lower frequencies, never really find them much use, there are way to many variables you can adjust as it is. Do you have any real plans for this or is it just for fun?
Matt

Hi Matt. It sounds like you have some experience with these little fiber lasers. Mine is indeed the 0.5MJ 10 watt average power model YLP-0.5/100/20/10 with a range of 20khz to 100khz rep rate. It was made in may 2009 so is fairly recent...I think it came from a bankrupt solar cell scribing company auction (as many as 45 were sold in that auction). It was pretty inexpensive and I found out that they really are not that expensive even when new. I don't see the option on the 10 and 20 watt current versions for varying the length of the pulse though.

I don't have any particular plan or use for it at the moment, but rather I wanted to experiment with micro machining without breaking the bank. Even the crude parts I have already cut are beyond what I could do on my cnc mill, lathe or with my CO2 laser engraver, so that might come in handy. I am always building and tinkering, so any tool that helps me make parts is always nice. I will use it until it breaks :-)

Do you think it would be detrimental to the laser to test what it can do to a 35um thick copper layer on a bare pcb? I usually get my boards made by a board house, but if this laser could remove copper and create isolated traces, I could see that being usefull for late night prototyping.

[matthew knott]

They must have upped the frequency range at some point before 2009, the YLP's are their basic pulsed laser, they do some more special and expensive ones where the frequencies go much higher (200khz), just used one on a project as the customer wanted black marking with no material removal, (annealing) and the higher frequency helped as at 100khz there is still a decent peaks of power.

No reason why it should break, but if (and it rare) they do people are disappointed as they expected 50'000 hours, but this is a pretty much made up figure, its an extrapolated figure from for the pump diode life. At my old company we purchased lots of them, they sometimes failed after 5 hours, others lasted 1-2 years, most never had a problem and are still running. The real clue is in the warranty, no more than 2 years, and extending it is pricy so the manufacturers know there is a liability, even my TV has a 5 year warranty.

I'm a massive fan of fibre lasers and think it almost all circumstances better than old yag lasers, except on copper, I make the odd prototype pcb with the lasers, and thought our new 30 watt fibre would be the perfect tool, I actual thought the laser had broken till i took the pcb material out and stuck in stainless steel and got a plume of sparks. I suspect its the lack of energy per pulse, a small yag will have way higher energy in a pulse, small fibers lack the joules but great peak powers at high frequencies. It might be much better with your short lens, and i can see no harm in trying. You might get back reflection warnings, but it has protection, go for it, the fibreboard stinks a bit when you get past the copper!

[Jonathan Brown]

Similar thing with Synrad lasers. I hear of people who have them go bad after 1 year but then I have two 48 series units from 1997 and 2000 that are still putting out spec power. Lasers are a crapshoot.

Still, if the pump diodes don't die I would have to guess any failure would be in the electronics, which *might* be possible to fix. I wouldn't think the doped fiber would just decide to break. The nice thing about buying this gently used unit is I could probably get back 50% to 60% of my purchase price selling it as a parts machine if it breaks and I can't fix it.

I tried a few more cuts at a faster feedrate, higher repetition rate, and higher gas pressure. It was still cutting all the way through at 10IPM+ and 100khz rep rate, but even with 80psi of the argon/co2 mix the steel seems to be reforming behind the cut...or the cut is clogged with dross. It is a much thinner, cleaner looking cut but it is filled and you have to press on the part quite hard to snap it out.

Perhaps I made the hole in my nozzle too big? I went with 0.045 because it seemed a size that wouldn't break in the gummy copper on my lathe. I might be able to change the order of machining ops and get a smaller hole, say 0.025.

It may also be that with the size of the cut (about 20um wide by my estimation) it is just hard to get the vaporized metal to blow out through the 127um thickness. Or I need oxygen for this non-stainless steel...

[Bruce Boone]

I would say not to try the copper. I just cut some .040" brass on mine, and it took 4000 wats and about 20ipm to get through. It wasn't a great cut and I had to snap the parts out. That means tons of reflection. I could have gotten through about 1/4" of titanium with that power. I think the dross issue is simply that your beam is so fine that you can't evacuate all the molten metal. Try faster still, maybe around 40 ipm and higher pressure if you think the parts can handle it. I do get dross on the back of my titanium cuts, but noticed that the hardened dross knocks right off with a pointy tool, and the cut itself is clean. I've been trying to chase the dross thing for a long time and finally realized that I probably can't completely eliminate the problem partly due to my fine beam width. My nozzle is .062", but I'm running 250 psi. I run the nozzle about .030" from the surface and focus the beam on the bottom of the sheet being cut.

[Dave Sheldrake]

Hi Jonathan,

http://www.iiviinfrared.com/resources/pressure_loading.html

II-VI's resource for pressure loading,

http://www.boconline.co.uk/internet.lg.lg.gbr/en/images/laser-cutting410_39553.pdf

Page 10 for nozzle standoff details.

best wishes

Dave

[Jonathan Brown]

Thanks Dave, those are good links. I have had the pressure up to 90 psi now with no damage but I will try to calculate what might be the breaking point.

I hooked up a gas solenoid and a laser on/off line from my cnc controller so I could run some standard g-code programs for testing. I created a 16 tooth spur gear and generated the g-code for it. At first I made the gear less than 0.03" in diameter but that was too small for this lens and also I forgot my cnc has 0.0015" backlash in the x-axis ballscrew (not worth replacing for most of my work). When trying to cut teeth in a 0.03" diameter gear, 0.0015" of backlash just kills you.

In the larger gears (about 0.07" in diameter) you can see the effects of the backlash in some of the poorly formed teeth. There are a few good teeth and all of the gears of a size have the same defects in the same area which confirms that the culprit is backlash and not the laser or lens. It will be nice to get the achromat doublet for a signicantly tighter beam but I need to switch from my cnc metal bedmill to the Adept ballscrew linear robot modules I happen to have. These have zero backlash and 1um position. The cnc mill was just faster to do a proof of concept of the fiber laser being able to cut thin, small stuff.

I wonder if I want to keep moving the workpiece when I build with the Adept modules or if I want to do sort of a flying optic arrangement. Or maybe move the workpiece in x and the optics in Y, Z...

So many fun things to try, and I haven't even started trying to play with micro welding or soldering or sintering or scribing...

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[Dave Sheldrake]

That's some very impressive stuff Jonathan, there are some commercial machines that can only dream of holding those resolutions ;)

best wishes

Dave

[Bruce Boone]

Real metal laser cut parts for a couple thousand bucks is pretty big time. It will be fun to see where the limits are.