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... a razor blade is easier to penetrate than much other targets - when optimizing a newly developed disc-laser with max. 0.5J pulsing (avg. 3W CW), I did this regularly to find the optimal focus ... should be a focus diameter around 20 microns then, and penetrated the razor blade with a single pulse ;-)
Viktor
0.5J in a 100ns pulse would be 5 megawatts. I think many materials would bow to that level of peak power. But only 6 pulses per second would make a hell of a dotted line if trying to cut :-)
I really like this laser and the newness of it (just over 3 years old and little run time) but I am going to keep my eyes open for the 1mJ or 2mJ version if it ever comes up for a good price on fleabay and you guys are asleep or something.
Viktor, I found this paper which performed tests using your exact laser (maybe it was even used here):
http://lasers.org.uk/paperstore/Cutting4.pdf
Very interesting. They were cutting 0.1mm stainless with as little as 1 watt average power (but at a much lower rep rate than I can go).
50mm achromatic lens.
On the subject of focusing lenses, what do you think about these V-coated 1064nm N-BK7 plano-convex lenses for experimenting?
LA1540-YAG f = 15.0 mm, Ø1/2", N-BK7 Plano-Convex Lens, 532/1064 nm V-Coat $27.90
LA1074-YAG f = 20.0 mm, Ø1/2", N-BK7 Plano-Convex Lens, 532/1064 nm V-Coat $27.60
LA1304-YAG f = 40.0 mm, Ø1/2", N-BK7 Plano-Convex Lens, 532/1064 nm V-Coat $25.60
on this page: http://www.thorlabs.us/newgrouppage9...tgroup_id=5383
They also have fused silica v-coated plano-convex lenses but they are about $90+ each (which is still $100 cheaper than Edmund or Newport)
15mm to 40mm FL gives me a pretty good range for playing with depth of field vs smallest spot.
They have air spaced v-coated high power doublets, which would probably be the bees knees, but they are $525!
How is N-BK7 vs fused silica? Would I even notice a difference?
Edit: There are also broadband (1050nm to 1620nm reflectance less than 0.5% from each surface) coated cemented achromatic doublets that are reasonably priced.
AC080-010-C f=10.0 mm, Ø8.0 mm Achromatic Doublet, ARC: 1050-1620 nm $45.00
AC080-016-C f=16.0 mm, Ø8.0 mm Achromatic Doublet, ARC: 1050-1620 nm $45.00
AC127-019-C f=19.0 mm, Ø1/2" Achromatic Doublet, ARC: 1050-1620 nm $67.00
AC127-025-C f=25.0 mm, Ø1/2" Achromatic Doublet, ARC: 1050-1620 nm $67.00
Or maybe the Best Form lenses which have a similar 1050nm to 1620nm coating
LBF254-040-C N-BK7 Best Form Lens, Ø1", f = 40 mm, ARC: 1050-1620 nm $52.20
http://www.thorlabs.us/newgrouppage9...tgroup_id=4876
This phd research paper has some excellent information around page 24 to 25 about singlet vs doublet for micromachining.
http://research-archive.liv.ac.uk/12...295_part_1.pdf
It looks like the doublet is very much superior for getting the most energy in the smallest spot.
I think I would like to play with that Thor Labs cemented doublet, perhaps the 25mm FL 1/2 diameter. I am not sure if the 8mm diameter lens would fit my 6mm beam.
... for the actual tests with the 9W-diode I'm using a single plastic lens with 9.6mm diameter and receive a focus of around 0.15mm in 20mm distance to the lens.
Maybe 3 years ago I've tested something similar with a glass lens, comparing a 5W-diode with the fiberlaser - the cut from the diode was around 0.2mm wide (thick cuts @2W), from the fiberlaser around 0.04mm (thin cuts @<1W with 2mm spacing) ... but could be better, when finer tuned ...
Viktor
Some small update:
I turned a copper nozzle, or at least an artist's conception of what a nozzle might look like since I really have not a clue. I drilled a 0.045" hole for the beam exit and tapered the inside and outside. I found a old section of tube in my junk box to press fit the nozzle into, and also a section with a hose input.
I also 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?
Attachment 39279Attachment 39280Attachment 39281Attachment 39282
... the 'magic numbers' are highly depending on your machine - when you'll hit some resonancies, the cut can get 'wavy'.
But I'll recommend going faster with higher rep-rates, powers and gas pressure ...
Viktor
I tried going faster and it does produce a cleaner looking cut that goes all the way through (I only tried up to 10 IPM though). I also tried upping the frequency to 50khz 80khz then max 100khz and perhaps it makes a little bit cleaner cut.Quote:
Originally Posted by VDX
The problem is the cut is filled with melted steel or slag or something and I have to press pretty hard to snap the part out. I think my nozzle design is somewhat of a fail....I went too big with the hole at 0.045" It does protect the lens...there is enough pressure for that, but it does not have the umph to blow the vaporized/melted steel out of the very narrow kerf (maybe 20um right now with this lens, soon to be even smaller) through the thickness of the steel (about 117um). I have tried up to 80psi of the argon/co2 mix...it gets better, with much less brown smudge and dross on the top, but the cut is still filled up with molten metal on the top and bottom side.
I re-read one of the papers I linked and they used a nozzle hole of 0.5mm which is about 0.020" This is way way smaller than my 0.045" hole. Back to the lathe :-)
turned! Turned! TURNED! Lathed is not a work. A lathe is a machine, turning is what you do on a lathe.Quote:
Originally Posted by Skyko
But otherwise, pretty cool!
-Jerry