Fiber Laser: Polished Brass Starting Point?

[Matt Schrum]

Does anyone have a good starting point for engraving or annealing polished brass tags?

Our church has some brass tags on their oil decanters that look fairly terrible. I've done some raw/scrap brass on my 30W before and figured it wouldn't be much of a problem so I volunteered to make some new ones before the holiday season. Anywho, I got the polished brass tags in last night and I was only able to run a few tests (100mm/s, 100% power, tried at 30 and 80 kHz with a 0.01 hatch or thereabouts. Tried slightly out of focus initially for annealing, but didn't pan out) and I was surprised at how faint of a marking the laser left at those settings. The polished surface sure makes a big difference from the scrap brass I ran a while back. For kicks and grins I also Sharpie-d the surface and gave it another go, but same result-- faint markings.

I do plan on running through a proper test grid when I get a chance tonight or later this week (my "day job" keeps getting in the way), but I wanted to reach out and see if anyone here had past experience or tips as I move forward. I did have the foresight to purchase a spare tag-- so I do have the real estate to run some tests.

Thanks!

[vic casware]

Hi Matt,
I am sure someone here posted a link to permanentmarking.com a while ago
i downloaded the Laser Marking settings pdf and that has some very helpful
info and setting for engraving brass, it has worked for me.

[John Lifer]

On my 20 Watt, I use 2 or three passes, 200mm/s speed, 100% and 125kHz and .02 hatch at 90 and 270, That should blacken you can reduce distance to get it darker.
I've also done decent getting an engraving giving a white mark at 2000 speed, 100% and 60khz, .02 hatch. You might start off a bit lower on power with the 30W

[Matt Schrum]

Vic,
I do have the Tykma settings PDF tucked in a folder somewhere, I'll see if they have any good tidbits in there for this application.

John,
I appreciate it, thanks. I have a plain-Jane laser that maxes out at 80kHz-- but good to know you're running at a high frequency. At least I have plenty of time to experiment and they're not a paying customer! :)

[Kev Williams]

First of all, you can't 'anneal' brass, 'annealing' by fiber consists of, and results in, oxidizing the carbon at the surface of metal. Can't turn brass black that way, no carbon! ;)

I have 3 'black' settings for brass that work for me:

Using a 150 lens on leaded engravers brass:
.006 line space (yes, tight), single hatch
100 power
600 speed
80 freq

Same brass but using a 220 lens,
.006 line space, single hatch
100 power
700 speed
42 freq...

--some frequency settings notes... with the 220 lens (which engraved totally different from the 150), I played with the frequency in 1kh increments until 42 proved to work best. Also for what it's worth, doing this testing I found that with all 3 of my machines set at 300 speed, 37 freq was optimal for deep engraving. And, with fiber lasering keep in mind that frequency and cutting speed work in tandem with each other; increasing cut speed decreases the actual cutting frequency, and vice-versa, because unlike the X-axis dots per inch on a C02 gantry machine is a measurement of space that doesn't change, the firing frequency of a fiber laser is a measurement of time - the faster a 1" line engraves at 30kh, the less firing pulses occur within that inch...

My 3rd setting involves engraving plain brass dog tags; I've never been able to get these to go 'black', all I've gotten is a very dark brown. But since these are for utilitarian use- just need to be visible- rather than aesthetic use, it works for my customers, thankfully. Using a 150 lens:

.15 line space (not a misprint!), cross hatched
60 speed (also not a misprint),
100 power
37 freq

-the wide hatch and low speed gets the job done pretty quick. Tags are hot as Hades when done with six characters ;) -- I probably could've hit on a better black with some different numbers, like a much tighter hatch spacing, but with a 1300 tag order, fast rather than 'pretty' was a necessity ;)

Lens choice and frequency seem to be the most critical adjustments...

[Matt Schrum]

I have 3 'black' settings for brass that work for me:
...


Kev, you're fantastic. I'll run through your notes and give it a shot hopefully tonight. Thank you!

[Kev Williams]

OK, so my last settings I listed for plain brass dog tags, I'm pretty sure they were from earlier testing, because I'm running another small job of brass tags, and the settings I found earlier didn't EVEN match the newest saved job I just found! So I did a test of the newer settings, made a quick tweak, and I got a really nice black burn using a 220 lens on my ebay1 machine!

So I shot a quick vid, showing the settings I used, and burned one tag :)


https://youtu.be/6SA-aErMQtw

--and because GoPro's are crap for close-ups (and I'm a lousy cameraman), a couple of pics, diff lighting angles...

http://www.engraver1.com/work/brstag1.jpg http://www.engraver1.com/work/brstag2.jpg http://www.engraver1.com/work/brstag3.jpg

---------
all 3 of my machines are 30 watt, in case that matters ;)

[Matt Schrum]

Alright, so I have a giant telecentric lens on my machine at the moment (and a 150 on deck I can switch to... and two other focal lengths on the way) and used Kev's settings above (600mm/s, 99%, 0.006 cross hatch) and you're right, it was really quite interesting how just 1kHz made a difference. I ran 2mm squares on polished (almost mirror like) brass tags from 80 to 30 kHz at 1kHz apart and found:

60-80kHz: Not much of anything. Very faint and inconsistent marking
mid 50's kHz: some nasty, patchy, tar black on the first pass that mostly got cleaned up when the cross hatch came through
43 kHz: Actually a pretty good frosted/matte white
30-39kHz: Tans, with 32kHz being the darkest tan

I've got a bit more poking and prodding to do-- but this is fantastic progress and I appreciate everyone's help!

[Matt Schrum]

Ha, I should note that I just realized my laser was ever so slightly out of focus to get the whites. I dropped it back into focus and everything is brown now. I'm going to blame forgetting to check the focus on the newborn robbing me of sleep, but it's a good data point to have to get white!