Laser Engraving Powdercoat woes

[Shannon Galway]

I'm having some issues engraving powdercoat over stainless reliably. I understand the vast potential differences in color, thickness, quality, etc. I'm mostly just curious if others have run into the same walls as me, and if they found a workaround.

From the attached photos its clear that I have the settings for red and white mostly dialed in. The only issue I'm still having is the slight lines in the direction of the laser travel. My big problem is the blue. I have read that blue is always a major pain, but dang, I wouldn't think it would be this tough. I can get through the coating, but at the power settings needed to remove the coating I am leaving burn marks on the stainless (ironic).

I have found that the following settings seem to work well:

- Ozark trail coated water bottles, blue, red, and matte white
-100w CO2 chinese laser

Red and white -- 19 watts power, 300mm/s travel, 0.03mm scan, 0.05" out of focus. Final wipe down with clorox wipes.

Blue -- 24 watts, 300mm/s travel, 0.03mm scan, 0.05" out of focus. Leaves the linear burn marks in the direction of laser travel.
22 watts, 300mm/s travel, 0.03mm scan, 0.05" out of focus. Leaves minor burn marks and some blue haze remains in the small details. Xylol to remove.
20 watts, 300mm/s travel, 0.03mm scan, 0.05" out of focus. Leaves a blue haze, Xylol will remove most of the haze but dulls the finish of the remaining coating.

I have tried so many different variations of speed, power, scan and focus I am going crazy. The above settings seem to work the best, but aren't even close to acceptable.

So, a few questions:

1.) How to stop the burning?
2.) How to get rid of the faint lines? (I'm guessing 1 & 2 are related)
3.) Why does everyone refer to power settings as percent instead of watts? Everyone has different wattage machines, % doesn't seem to relate. Power stated in watts is universal, isn't it?

Photos are here. http://mylocalmaker.com/photo-drop

Thanks,
Shannon

[Kev Williams]

you're running at .03mm LPI, which means your line spacing is only .0011", which IMO just wastes time, and in the case of powdercoating, is just overcooking it...

I run the same bottles as you on my 30w GCC, I run in-focus and at either 300 or 380 LPI, which is .0033" and .0026" line spacing respectively, 30% speed, which if linearly correct comes to 24" per second/600mm/second-- and always at least 2 passes, sometime 3 on the thick stuff-- but even at 3 passes, in comparison to your settings I'm running twice as fast in the X axis and 3x as fast in the Y axis, so my 3 passes will take less time than your 1 pass...

What I've found with powdercoating is that "less is more"- every time I've tried to slow the machine and/or up the resolution to get done in one pass, the result is a gooey mess that even a second pass has a hard time cleaning out. At my settings, the first pass doesn't even make it to the metal, usually just small areas of metal show thru. But the second pass takes it right down to the metal, and a quick alky or lite-acetone wipe is all that's needed. There are a few anomalies, such as white coated flasks always end up gray, like yours, and some colors or coatings will be finicky....

My advice, run at 500 or 600mm/second, run your power at about 12%, set your scan gap at .007, and get in focus. Try to get the first pass to just barely hit metal, and hopefully the second pass will vaporize the remaining coating rather than melting it down! :)

As for 'power in watts', I have an 80w Chines machine, but you enter power in %, not watts- and also, 70% power as I enter it is 100% power 'actual'... so, do it however suits you! ;)

[Shannon Galway]

Kev, thanks for the feedback. I'll try multiple passes again in focus and at a faster speed. I tried once already but it didn't seem to do any different. Of all the testing I've done it seems on the blue color there is just a wall at 22 watts. If I take two light (15watts) passes prior to this I am left with a light blue haze, if I take one light pass (anywhere from 17-20watts), I am still left with the same light blue haze. The haze will not remove with Xylol, clorox wipes, acetone (without screwing up the rest of the coating). To get through the haze I have to up the power and then it seems to immediately go to burning as shown in the pictures linked.

I suppose a more fundamental question, on the blue bottle is that burning the coating or is it the metal?

[John Lifer]

I run my 80watt at 60% power, 225mm/s and at .08 scan gap. And I clean with Simple Green and a white magic eraser and DNA depending on the powder coating. If the Simple green won't cut it, then I hit with DNA. Be aware the alcohol CAN discolor some PC. So it is second choice.
I NEVER run mine twice. Don't trust my rotary that much... Just me I guess. And some coating is more difficult. Black on RTICS is thick.

It does take a bit of extra cleaning some times.

[Mike Null]

Switch your cleaner to ZEP Fast 505 and use a magic Eraser with it. It makes a difference. I can do most colors with one pass but I'm also familiar with having to do two. Green was my worst color to date.

[Shannon Galway]

I run my 80watt at 60% power, 225mm/s and at .08 scan gap. And I clean with Simple Green and a white magic eraser and DNA depending on the powder coating. If the Simple green won't cut it, then I hit with DNA. Be aware the alcohol CAN discolor some PC. So it is second choice.
I NEVER run mine twice. Don't trust my rotary that much... Just me I guess. And some coating is more difficult. Black on RTICS is thick.

It does take a bit of extra cleaning some times.

Jon,
Thanks for the reply. Any time I get above 20-24w I get distinct lines on the metal. You can see the beginning of these in the white bottle shown in the link above. I guess that's the second question I am trying to get answered, I hear everyone talk about these high power numbers, but anytime I try to go that high I just mark up the metal with lines. 20w at 300mm/s is the sweet spot for for the red bottles, basically perfect finish after cleaning. I just can't understand what is so different about my machine that others claim to be running at 30-40w and not leaving a mark on the metal.

I am new to all this if you couldn't tell, trying to learn as quickly as I can though.

[Doug Fisher]

What lens are you using? That will make a difference.

>>3.) Why does everyone refer to power settings as percent instead of watts? Everyone has different wattage machines, % doesn't seem to relate. Power stated in watts is universal, isn't it?<<

I agree with you. I am guessing the main reason is that most laser users have never done an accurate measurement test and graphing of the power curve for their tubes so they are unable to talk in terms of actual watts. Most tube output is not linear so even if two people are using the same wattage tube the percentages likely won't match up.

[Shannon Galway]

What lens are you using? That will make a difference.


I am using a 1.5" focal length lens. I am currently running about 0.05" out of focus.

[Kev Williams]

Ozark trail- I've never engraved PC'd Ozarks, only the SS versions...

I took your pics and downloaded them, the red & blue anyway, didn't need to download the white, in the thumbnail you can see it's a nice matte finish...

The red & blue isn't matte, more of a semi-high-gloss. Your pics are big, and I resampled them a bit larger and zoomed in--

The red here, the coating is very thick, but quite smooth, and your laser got right thru it nicely.
385060

The blue on the other hand, the finish isn't very smooth at all, lots of 'grain', and there's shouldn't be grain, the coating should cover any grain in the metal... and the coating looks more like paint than PC..?
385061
- And hard to say if you're burning the metal, but in my experience, you're not going to burn stainless with less than 60 or 70 watts, and that's running very slowly. My best guess is the coating they're using just isn't laser friendly at all, and I do believe your laser IS burning it...

Last resort, paint it 70% black, change it to a 200dpi bitmap and run it, using YOUR original power settings, but .07 gap... the dithering might help get to at least look consistent. And most customers would be happy with consistent...

[Nick Hale]

I have a 100w co2 and do every color the same, 40pwr, 500mms, and .08 line distance. Everytime I finish a cup, i give it a quick scrub with magic eraser and 80% alcohol. havent had a problem with it yet. Candy colors i only scrub lightly with alcohol and microfiber cloth. The last step is really where it makes the cup shine.

[Trey Tull]

I find that the blue cups give me trouble as well. I always make two passes on PC cups but some of them take 3. I'll clean with a magic eraser and water after lasering and they come out good.

[Shannon Galway]

Wow! I want to thank you all for the tips and guidance. I've come up with a workable solution thanks to a magic eraser and some gelcoat tricks. I originally suspected this blue wasn't powdercoat and now I am convinced of that.

tldr; Engraving Ozark Trail Blue coating on stainless, process that works great 21w power, 300mm/s speed, 0.05 scan gap, magic eraser to remove haze, rubbing compound to bring gloss back.

Photos: http://mylocalmaker.com/photo-drop

The sort of collective suggestion was to bring the laser back in focus, up the power, and increase the scan gap. I will address one at a time.

Focus: No problem. I am running a 1.5" lens and this really makes stuff sharp. Ties into the next point though.

Scan gap: I did runs at 0.08mm scan gap, the results were not great. There were faint slices where I wasn't removing the material (see photos). Decreasing the scan gap to 0.06mm finally makes them disappear. I have some long diagonal lines in the graphic which is turning into a sort of saw tooth at high scan gaps as well. I've settled on 0.05mm (increased from 0.03mm). Under a magnifying glass you can see a difference between the two, but its not obvious unless you are looking for it. 0.05mm seems to be the good comprimised. I think the short focal length lens is not allowing a larger scan gap since the focus is so tight.

Power: I tried runs at 50w and 60w power 225mm/s and 300mm/s, neither worked well. Still had very prominent vertical scan lines (see photos). Nothing was taking the lines off, they are burned in the metal. I dropped the power back down to 20w and 300mm/s and there was still a very blue haze left on the test graphic. Nothing was taking the haze off, DNA, goo gone, 505, Simple Green, Clorox wipes, nothing. But 10 seconds of decent pressure rubbing with a magic eraser and the blue haze is gone and the stainless under looks gorgeous. The problem is now the magic eraser is leaving the coating dull due to the abrasives in the eraser. Luckily, some 3M rubbing compound takes the dullness away with about 30 seconds of work.

Thanks again for the awesome help. What a PITA this color has been!

[Bill George]

I would put the OEM 2 inch lens back in and since nearly all the folks posting speed and power settings use that one their suggestions would be more relevant. You would be less likely to be burning the metal also.

[Kev Williams]

^^ what Bill just said- or even a 2.5" if you have one. And with 100 watts handy a 3" lens may work well. The wider beam spot will clear more of a path per swipe with less tendency to burn. Only time I've ever used a 1.5 lens is when I need the narrower beam spot for tiny lettering and detail...

[Shannon Galway]

Thanks guys, I will try that out after this run is finished. I've got a workable solution for now though.

[Mike Dowling]

My first post here. Been following along for over a year. Great info from this site. One of the best tips I’ve gotten here if not the best is the use of the “magic eraser”. Makes any of our jobs that need cleanup go from good looking to great looking. Usually use it with dna.