Etching stainless steel... & warping

[Ian Stewart-Koster]

Hi Folks,
I'd done a little etching on stainless using Cermark, with our ULS M-300 and found it was great.
But the problem that plagued me 6 months ago is back: y axis movement issues.
I found a ULS V400 very inexpensively on Fleabay, so bought it for spare parts, to hopefully get around the problem. It has 2 dead tubes, and no lens (they're keeping that) but otherwise worked fine.

IN the meantime I tested out engraving stainless on our 130 watt Golden Laser, and found the stainless warped quite a bit, even to the point of lifting, and hitting the nozzle which was the required 3mm above the substrate.

Just wondering if I'm the only one to have this problem, or if there are comments that might help me!

I wanted to laser some bigger plaques, but can't if I have this issue.
Thanks!

[Scott Anders]

A wider scan gap and a damp cloth beneath the job will help. I bought some large heat sinks that have also been helpful.

[Mike Null]

The thickness matters. I do some .020" tags and they always warp.

[Ian Stewart-Koster]

Thanks, Mike and Scott.
Scott, what's the biggest stainless panel you've 'etched' ?

[Scott Anders]

I've done 600 x 400mm panels before. 0.9mm ss. Magnets also help (remove your nozzle) like Mike said, thicker ss = less warping

[Kev Williams]

I engrave a crapload of stainless, I just bought my 3rd 500gram bottle of Cermark this year about a month ago. I engrave 24" x 28" x 1/8" thick stainless panels regularly, along with many various smaller sizes in 1/8", like 8" x 11", 14" x 10", 4" x 15", etc. While the smaller sizes don't warp much, the large ones do, mostly because the company logo takes up nearly 12 x 7", seven 3" high very bold characters. Plus the panel and some sections are outlined 1/4" wide, and there's plenty of words too. When I'm done with the logo and unclamp the plate, the sides are over 1/4" above the table. Some warp worse than others, but they all warp, it's simply a heat thing, and I use the bare minimum amount of heat required to fuse the Cermark good. Even not enough power will still warp them.

There's nothing you can do to stop it, but the wet rag thing does help with the smaller plates. Another thing you can do if you have time and patience, is to flip the plate around and dry-run the laser over the back side, the heat will reverse the warp and flatten the plate back out. I did this not long ago with a bunch of 7/8" diameter SS disks I was inserting into the grips of some pistols. Fiber lasering the parts turned them into shallow cereal bowls! Because I needed a slight concave on the bottom and not the top, I drew up a 1/2" diameter spiral to fiber etch onto the other side. The spiral cut provided something for the glue to grab onto, and perfectly re-warped the disks just how I wanted.

[Ian Stewart-Koster]

Thanks again for the useful replies, Scott & Kev.

I had an idea to etch in stainless, for some interpretive signage museum plaques, and then digitally print colour aspects in optically clear film, and stick that to the back of acrylic, in places, then mount the acrylic over the stainless, for a unique anc 'contemporary' effect.
The whole thing still needs mounting vertically then, between posts 4 ft apart, so we'd need a backing behind the stainless to hide any warped effect - unless the warpage is going to be too much be able to level out.

(I'm talking about a dozen such panels... 6 double-sided - still in the thinking & sleeping-on-it & designing stage, but it needs to be modern, clever, and 'cool', and can have 3D and/or layered elements. Just not to be plain boring & flat.)


Any ideas or cautions are welcome! :)

P.S. The final sign to go in the project will be a big one - 4 metres wide is the space betwen the posts.
I'm thinking of a plasma or waterjet-cut steel background with trees etc, and basically an oval shaped hole in most of the middle of the area.
In that will be a lasered acrylic picture in reverse on clear acrylic, and then I'd vectorise elements and cut them out in clear actylic, and stick them on top, to build the picture up. Thinking of an old steam train going over a railway bridge. Included in the detail though is it needs to be a local style of train, but that's do-able.
It's to be a subtle but unique background element, the whole thing.

[Ian Stewart-Koster]

Back to the warpage question...
now that ULS have repaired the notherboard!

I Cermarked a piece of stainless steel 24" x 12" two days ago, and the warp was an upwards cupping, as if the face being etched was actually contracting, not expanding.

I was tempted to flip it over and do the back to counteract the warp - but we'll fold the sides in the end, to make it more rigid.

Because the ULS has the lens so high above the substrate, it's no big deal except losing focus.
However our Chinese laser had the nozzle hit the stanless when I tried on it, as the stainless steel warped up and into the path of the travelling air-assist nozzle...

Do many others here laser cermark with Chinese systems?
What power, please?

[Gary Hair]

You have to use the power necessary to adhere the Cermark, so changing your settings will only cause problems. What you can change, however, is how much of an area you laser and where on the piece you laser. You may have to break up your design into small sections and move around the piece a bit to let the previously lasered area cool down a bit. You can also direct compressed air at the piece and also have your exhaust directed at the piece, both can help to keep it cooler. I have some thin aluminum I'm cutting with my fiber and I can only take 5 passes per section then place it on a large block of aluminum to cool it down otherwise it bows up about 1/4" in the middle.

[Ian Stewart-Koster]

Thanks - this was cupping or contracting, though, rather than bowing up in the middle- it bowed up in the edges.
What I did to help, was vector engraved the perimeter of every letter and panel, to help define them, then I rasterised the lot - black, greyscale dithered, and photos edited & converted to BMP.
The final test image overall was good, except for 2 pale areas that perhaps I didn't scrub well enough with metho first... I'll ise IPA next time, and a scourer.

The problem with the cupping is the loss of focus, unless you follow it and slowly rock/tilt it so the part under the beam is always down... or something.

I'm tempted to flip it and laser the back afterwards to equalise the stresses...

[John Lifer]

Haven't CO2 lasered large flats, but why not take off the front nozzle piece if it is hitting. (yeah focus IS an issue) I altered my 38mm nozzle a while back, moving the lens forward by adding a second ring behind the first. Added about 5 mm more clearance in the front, and then ground off another 3 or so to give me 13mm gap between work and the nozzle. Makes it way easier to work with materials.

[Kev Williams]

my very biased opinion about nose cone/nozzles: these nozzles are a cheap bandaid approach to supply air assist and keeping the lens clean. Air is best supplied from outside the lens thru a smaller orifice at an angle, better use of the air, and the smoke always goes in one direction instead of all over the place. I found right from the getgo with my Triumph, the nozzle was always in the way, of other items on the table, or of the beam itself. I have many 1/2" thick steel bars I had special made, that I use as spacers, mobile fences and weight- like for placing along the edge of stainless that's going to warp :) -- Can't use them with a nozzle. And while experimenting with my 4" lens, I found that even though the beam was centered thru the nozzle hole, nonetheless the beam was hitting the nozzle; with the nozzle on I couldn't cut thru a piece of 3/4" wood, with the nozzle off it cut thru easily. The nozzle hasn't been on since. And FWIW none of the Western machines I've owned ever had a nozzle...

[Ian Stewart-Koster]

Thanks, Kev.
I've found similar oddities - yes, the ULS has no air-assist and works fine.
The chinese unit also cuts well on thinner stuff with no air on, except to keep the lens from getting exhaust onto it, as the air extraction isn't quite as good over the larger area, than the little Universal's extraction is.
Thicker stuff I've tested with no air, and fires are the issue.
I've fiddled with air pressures and flow rates to get a setting that gives me fewest unexpected fires, and clean cuts.

But I'm liking the idea of an air nozzle on an angle, separate from the nose cone, because as you say it crashes into stuff... and into warped stainless steel also! ;)

[Kev Williams]

I still use the air to keep flareups down when cutting, and to move smoke when engraving leather which keeps the lens cleaner longer.
But in my usual Macgyver style, I just added on to the hose a bit and bent up a piece of trophy aluminum to hold it...
376287376288
-most of the time I don't use it and it just dangles like in the first pic. I just have the cheap diaphragm pump that came with the machine, and with the unrestricted hose, it blows a lot of air, but under low pressure. It'll move smoke like crazy, and during cutting it prevents flareups and reduces soot from the cut edges. I have a small piece of copper tubing that I can stick in the end of the tube that will pinpoint a smaller stream of air, but the only time I've used it was just to see if it worked :)

[Ian Stewart-Koster]

Here's an interesting PS to the Etching-with-Cermark story...
I stopped by the SS engineering shop today to get the big plaque cut, so I can laser it.
The owner asked me if I wanted a B4 finish, or the shiny mirror type on top. I said I'd be scuffing it, & rinsing it, before putting Cermark on so the brushed B4 finish would be fine as the top face.

I asked if he has a scrap that I could test out though, since he said it'd be protected with a thick plastic cover till I pulled it off.

He gave me about a 4" square, 1mm thick.
I cut half the plastic off, got IPA and a green scourer and thoroughly scuffed it clean, and rinsed it with IPA.
Then I took the half that was left, cut half that plastic off and just rinsed it and the top half with IPA, and then wiped them clean with a lint-free cloth.
The last quarter was left plain - untouched- and I took the plastic off, and coated it all with Cermark, let it dry, and lasered our logo on both halves. (Using the ULS)

The logo had black, white, grey, and a stochastic background gradient of almost white to almost black - twice. (It might have been the Stucky Corel Photopaint one-I've long since forgotten)>

What's weird is that after cleaning the remaining Cermark off, and then getting a kitchen scourer and soap, and thoroughly attacking it all, the best looking part was the quarter that had NO preparation at all!

The differences are probably imperceptible to a customer, but clear to someone looking to find them, like us.

The best image in every respect was in the 'just remove the plastic and quickly brush on the cermark' quadrant. No prior surgical cleaning, de-oxidising, etc, just remove the factory cover and do it.

Hope this helps someone else...
Before this I'd always been pretty meticulous to wash grease & possible contaminants off, but it appears at least in THIS case here, that I was putting minor contaminants ON instead!

[Bill George]

I always use DNA instead of IPA for cleaning.

[Kev Williams]

I rarely Cermark SS on my Triumph (the big outlines on the SS ski lift operator panels I etch is about it for SS) and never text, because the mark is always a hazy brownish darkish gray, somewhere in the 70% black spectrum, whereas my RF machines produce a nice 90% 'charcoal' black with no hint of brown. The other issue with the Triumph marking is when view at certain angles, the mark almost disappears, my RF marking does lighten up a bit at certain angles, but is always 'there' and legible.

That said, I've always had better luck with cleaning my materal first. Not because of the quality of the "look" of the mark, but because it enhances adhesion and durability of the mark. Virtually every Cermark 'failure' I've every had was due to either a focus issue, or not cleaning the material first. And as for cleaning, in my experience it doesn't matter what I clean with- DNA, IPA, Windex, Fantastic- as long as I DID clean first, I've never had a failure.

Regardless of whether I pre-cleaned or not (Yeti's come to mind ;) ), I've never noticed a difference in the look of the mark.

And then there's aluminum, while the Triumph sucks at stainless, it shines at Cermarking aluminum and brass- which is good, because my lower powered RF machines just don't have the power..