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.