Which color laser?

I must be looking in the wrong places because I have not yet been able to find out which metals absorb which frequencies of light best. I am
looking at heating various metals with a laser so I need to know which laser will work best for which metal. Anybody here have any pointers? Thanks, Eric
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On 19/10/16 21:22, snipped-for-privacy@whidbey.com wrote:

I don't know if it'll be much help but my local laser profiling company mentioned that they had been warned off cutting copper based alloys because the main mirrors in the laser cutter were highly polished copper and cutting copper based alloys could send enough energy back to overheat the mirrors and damage them. They do cut copper based alloys but limit the thickness cut to something that doesn't threaten the mirrors. I was in the past involved with a laser activated optical emission spectrometer so will have a look to see if I have any details that might be useful but don't hold too much hope as I recall the project worked but was abandoned due to issues such a short laser longevity etc. .
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On Wed, 19 Oct 2016 13:22:48 -0700, snipped-for-privacy@whidbey.com wrote:

Eric, I was reading an article the other day in a signmaking mag about an engraving/cutting laser, and they were mentioned using a coating to assist in this. It wasn't detailed, but you might do a search re: this.
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wrote:

Could that be coating the metal so that it didn't reflect the energy instead of absorbing it? I seem to recall having seen that sort of thing a few times when watching How Its Made.
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On Wednesday, October 19, 2016 at 4:19:24 PM UTC-4, snipped-for-privacy@whidbey.com wrote:

Heating to how hot? ~60-100 C or heating to 1000 C, or laser melting and cutting?
George H.
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On Thu, 20 Oct 2016 07:22:11 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

Up to about 200 C. Thanks, Eric
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On 10/20/2016 11:47 AM, snipped-for-privacy@whidbey.com wrote:
...

And what volume of a specimen of what size do you intend to heat? Lasers are quite local in their application of energy, "not so much" when it comes to bulk effects.
Applications like surface heat-treating rely on scanning a laser over the surface and surface heating the local area to a very shallow depth leaving the bulk material temperature essentially unchanged. It's self-quenching into that cool reservoir that's the hardening mechanism as opposed to bulk immersion of a heat-treated part in conventional heat treatment.
What's the end objective here, really???
And, what specific materials?
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I dunno which metals yet, It depends on which ones can be easily heated. Steel, copper alloys, zinc, and tin are ones I want to try though.The laser will be scanned. Thanks, Eric
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wrote in message

Up to about 200 C. Thanks, Eric ==================================================================== Eric, if you have access to a good library look for books by W. W. Duley. He wrote a few on the effects of lasers on solids. I have his "Co2 Lasers: Effects and Applications (Quantum electronics--Principles and applications)" because that's the best if you want to build a CO2 laser (and I did, :-)), but he wrote a few and they do a great job of covering the physics of laser heating (heat capacity, thermal diffusivity, absorbance, thermal conductivity, etc). I know at least one of his books had some nice data on a list of different metals that should give you what you need but it has been 20+ years since I was up on that stuff so I can't recommend a specific book, sorry. Amazon has a pretty good selection, too. They date from the 1970's to maybe 2000 so they don't include all the great solid state high power lasers available now on the laser side, but the target side was well covered.
----- Regards, Carl Ijames
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On Thu, 20 Oct 2016 14:23:10 -0400, "Carl Ijames"

Thanks Carl, I'll head to Seattle soon and check to see if they have these books, Eric
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On Thursday, October 20, 2016 at 12:44:55 PM UTC-4, snipped-for-privacy@whidbey.com wrote:

It's not anything I know much about. Most metals are reflective, which makes it not only hard to heat but scary if you are bouncing a high power laser off it. I quick google search found this
http://www.me.mtu.edu/~microweb/GRAPH/Laser/SPECMET.JPG
from here, http://www.me.mtu.edu/~microweb/chap4/ch4-0.htm
So how about iron and ~800 nm - 1.1um... on issue with the near IR is you can't see it which makes it more dangerous for your eye... no blink reflex.
George H.
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On Thu, 20 Oct 2016 12:51:24 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

I remember seeing a CO2 gas laser used to machine threads into a ceramic bolt. They kept that monster in a separate room and no one was allowed inside the room when it was working. there were occasions the beam reflected around the room and damaged things.
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On Thursday, October 20, 2016 at 9:13:48 PM UTC-4, snipped-for-privacy@nowhere.com wrote:

I've no idea what Eric is doing, but my cast iron frying pan looks like it absorbs pretty well in the visible too. CO2 is useful because you can get a lot of power. George H.
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On Thu, 20 Oct 2016 12:51:24 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

Thanks for the links George. I'll check them out this wekend. Eric
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On Wednesday, October 19, 2016 at 4:19:24 PM UTC-4, snipped-for-privacy@whidbey.com wrote :

I've done some looking into laser etching circuit boards. Apparently, it re flects so much IR that it's virtually impossible with IR or visible lasers. There ARE machines that do it, but insanely expensive (quarter-million dol lar range) with UV lasers. I have not looked much further other than to hav e read various dire warnings about the dangers of UV lasers - "you'll shoot your eye out" sort of things. One day, I'll find the time to get back to t his.
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How big a board are you talking about ? Will a cnc machine do the job - there are companies that make enclosed lasers. Martin
On 10/22/2016 9:50 AM, rangerssuck wrote:

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On Sunday, October 23, 2016 at 9:27:13 PM UTC-4, Martin Eastburn wrote:

No particular size, though my work usually fits in 8" x 10" or so. This was more of an exploration into the practicality of producing quick protos in my shop rather than sending them out and paying big bucks or waiting a long time for them to come back.
when you say "cnc" I assume you mean milling machine. That would work for s ome boards, but I don't know what kind of resolution you can get that way, I find it hard to imagine 6 mil traces and 6 mil spaces from a milling mach ine, though I haven't looked in that direction recently.
Another possibility is using a laser to remove a resist layer applied to th e board. People are getting promising results that way, but it's not easy t o control a chemical etching process with such small features. It would see m (to my uneducated mind) that it would be easier and more repeatable to di al in the parameters for a laser etch than for chemicals.
The machine I saw a price for was from LPKF. I did not find an online price , but I did find a public record contract from a college in the Pacific Nor thwest to purchase one. Delivered and installed, with a day or two of train ing, the prices was around $250K. A bit out of my price range.
I do have access to a 40W laser cutter at the local makerspace, and I may t ake a whack at the etching of a chemical resist (most likely black Krylon) when I get some free time.
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On Sunday, October 23, 2016 at 9:27:13 PM UTC-4, Martin Eastburn wrote:

No particular size, though my work usually fits in 8" x 10" or so. This was more of an exploration into the practicality of producing quick protos in my shop rather than sending them out and paying big bucks or waiting a long time for them to come back.
when you say "cnc" I assume you mean milling machine. That would work for some boards, but I don't know what kind of resolution you can get that way, I find it hard to imagine 6 mil traces and 6 mil spaces from a milling machine, though I haven't looked in that direction recently.
Another possibility is using a laser to remove a resist layer applied to the board. People are getting promising results that way, but it's not easy to control a chemical etching process with such small features. It would seem (to my uneducated mind) that it would be easier and more repeatable to dial in the parameters for a laser etch than for chemicals.
The machine I saw a price for was from LPKF. I did not find an online price, but I did find a public record contract from a college in the Pacific Northwest to purchase one. Delivered and installed, with a day or two of training, the prices was around $250K. A bit out of my price range.
I do have access to a 40W laser cutter at the local makerspace, and I may take a whack at the etching of a chemical resist (most likely black Krylon) when I get some free time. ======================================== I used these with generally acceptable results: http://www.t-techtools.com/store/
At the time, the 1990's, 6 mils was difficult but possible for them, IIRC 10 mils was easy. The Z height adjustment of the tapered engraving cutter relative to an adjacent foot that pressed the board against the platen set the space width. It was capable of milling a GPS receiver. I used Mentor's PADS for PCB design .
--jsw
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On Monday, October 24, 2016 at 6:13:41 PM UTC-4, Jim Wilkins wrote:

interesting. They say they do 4mil trace/space, which is pretty damned good. I'll be contacting them for system pricing, though I'm guessing it aint cheap.
But still, I'm thinking about this more as a diy project.
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Mechanically the T-Techs I used consisted of a smal high-speed motor plus 1/8" shank engraving cutter on an X-Y bridge mount. The head was spring-loaded down and located in Z by a foot resting on the board, which compensated for warpage, until a dull cutter began raising burrs. A solenoid raised it. Blank boards were located with dowel pins, so they could be accurately flipped, and held with masking tape.
To some extent you could do the same job manually on a mill with the high speed motor or Dremel spring-loaded below the spindle. I think the main difficulties would be translating the PC artwork vectors and adjusting the cutter depth to the intended width of cut precisely enough.
A Gerber file consists of line endpoint pairs with an associated track width, originally meant to be photoplotted with light through a round aperture. You could have undercutting at corners if you only made the tool paths the track centerline plus/minus half the track + space width.
--jsw
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