Non-MOPA on raw aluminum?

[Bert McMahan]

I have the potential to do some logos on raw aluminum pieces and am looking at buying a laser to do this.

From what I read, you can make black marks on anodized aluminum with a MOPA fiber laser, but not with a standard fiber. What kind of marks CAN you get with a standard, non-MOPA laser? The cost difference is several thousand dollars and I'm not sure it's worth it.

Can you do any marking on raw aluminum without a MOPA?

[Kev Williams]

No black on aluminum with a standard fiber. And the catch-22 with a MOPA is the slow speeds required to get the colors. Time is money, and you have to charge for it...

--Can you do any engraving on raw aluminum? Of course- when you get thru the anodizing you're engraving raw aluminum--

I fiber engrave these things, this is the 'poker chip' model-
sppc.jpg
Note the dark gray engraving... That's the darkest I've been able to get (on 6061). But, it's also an illusion, the same exact engraving on natural color aluminum appears many shades lighter, it's all a matter of contrast. And the same is true with the "white" engraving. The engraving looks like it's painted white, even on raw aluminum, but look at it with a 15x loupe and you can see it's aluminum colored, not white ... The hatch filled engraving creates more exposed surface and reflects more ambient light. (that's my theory anyway)

Another issue with MOPA's and aluminum--I'm not all that knowledgeable about them, but it seems that the only color a MOPA will do on aluminum is black--?

While these blades aren't aluminum, you can see what a few adjustments can do to change between engraving to the bare metal and everywhere in between...

bkknfs.jpg

-several shades of dark/light on an SS plug in a gun grip
TB2.jpg

and this is opaque black plex.
BPL3.jpg

These machines amaze me every day -- but personally, I've never felt the need for a MOPA...

[Bert McMahan]

Thanks for the pictures Kev. The only color I'd need for these parts is black, and even that's not necessarily a requirement. I just know the customer would prefer black.

I think as long as I could get some sort of contrast it would be fine. The part is a raw aluminum bracket (think an extruded aluminum channel) that needs a logo. As long as it's somewhat visible it should be acceptable, but a nice high-contrast black would definitely be the preferred way to go.

Unfortunately these parts can't be marked with Cermark or similar due to engineering material restrictions which means a very long run through their quality assurance program. Marking on the surface of the material or a thou or so deep would be allowable, but not introducing another material to the product.

Anyone else done anything on just a plain ol' piece of scrap aluminum, non-anodized? I'd like to give them a "Here's what your part would look like" if possible.

[Matt Schrum]

I don't have pictures, but with my 150 lens (well, that's what it's closest to, long story) on my 30W non-MOPA I used 1500 mm/s, 99% power, 35kHz, 0.002 (yes, tiny) hatch and got a fairly decent black mark on raw aluminum.

[John Lifer]

I've a low end mopa, I can go from 1 to 400 kHz. Zero true black on aluminum. I've tried, but no go. I only can get black using cermark with my CO2 and only some aluminum there.
I wouldn't buy a mopa with the intention of doing a black on aluminum engraving. It doesn't work. No one I've seen really claims black on aluminum excepting Matt above.

[Kev Williams]

I just ran some tests on a probably 50 year old piece of 5051, all grunge still intact

Here's 3 pics I took at different lighting angles, using a piece of paper to shade the overhead lights...
I ran 4 tests, at the hatch, power, speed and freq settings as it says.
The 4th test, I stopped after the ".0" because at that speed and hatch distance, it took 34 seconds just for the 0, that would've been a 7-minute run!
I didn't catch the times of the first 2 tests, but line 3, the darkest, took 39 seconds for the line.
Text height is 3.6mm, and it's a rather thick font...

AB1.jpg
AB2.jpg
AB3.jpg

also about line 4, it didn't go dark at all, is simply engraved, which isn't surprising

with a couple of fine-tuning tweaks, in particular the freq settings, a bit darker might happen, but line 3 here is about as dark as I've ever seen. And lighting angle is a factor... And I'm not sure what would happen on 6061 or other varieties..
Final note, the results- all of them- are NOT babybutt smooth, there IS a bit of slag so it feels a teeny bit rough...

<<< E D I T >>>

ok so I decided that since "some sort of contrast would be fine", I decided to run a 'white' pass:

AB4.jpg

--as you can see, good contrast! BUT, my 5050 isn't particularly shiny or light-colored, so it DOES show up good.
And I just copied the last line, the settings I used are my basic anodized settings,
which are: .07 crosshatch @ 45°, at 100p, 1500sp, 37 freq,
and a .07 @ 90° single 'cleanup' hatch, at 60p, 2000sp, 60 freq. And, it really didn't need the cleanup pass, it was brighter before

The best part? Line 3 took 39 seconds, the bright line only took 3.9 seconds... yup, 10x faster

[Bert McMahan]

Kev you are *awesome*. Thanks so much for running those tests. Looks great to me... hopefully I'll have a laser soon enough and can start giving back as well!