I had a play this evening with some different materials and cutting speeds so here are some performance figures and results for the 2.5W laser. Most of the trials were performed with outlined text so a "clean cut" meaning the letter fell right out when the piece was picked up and a "intermittent cut" means it was intermittently cut all the way through so the letter could be easily poked out but didn't fall out on its own.
35mm thk foam
The surprise however was powder coated steel.
I initially tried it on a rippled black painted/powder coated steel and was impressed with the results so went looking around for something in a lighter colour to try. Eventually tried it on the inside of a powder coated metal socket set box.
This was on about 100 mm/min so quite slow but the result was quite clear and I can see this being useful to engrave my name, etc onto anything powder coated.
That is a 3cm scale so the line are 1mm apart and about 1mm text height. As this was a bitmap sample image the image was processed with an outline tracing function so each line is actually two passed (down one side and back up the other). I think it would be even sharper if it has been a vector image and each line/number was only burnt in a single pass.
I did also try some aluminum can but it only managed a very fine line which I think was more the paint and internal plastic lining - I don't think 2.5W is powerful enough to mark/engrave the actual metal. Will try some bare aluminium tomorrow (which I assume would be most likely to work due to it low melting temperature), and brass and steel.
I am also trying to source a can of the TherMark locally to give that a try. It is a additive process though, to paint it on, fuse it with the laser and then the excess is wiped off. Reading the product sheet they suggest at least a 10W laser but I would be keen to give it a try anyway - may be slow but I'm not doing production runs so that can be tolerated for one off items.
I would guess the metal, especially aluminum is too reflective. It is light, after all. Do you have any anodized aluminum to try? Something that's darker and not shiny? You've already shown you can mark dark powder coats.
Most materials with high thermal conductivity (copper, aluminum) don't lend themselves to laser cutting, so I kind of doubt they would mark easily. Also if the surface is shiny, the laser will reflect too much. In any case, I hope you and those nearby are wearing the appropriate PPE.
Nice find. This would be great for stencils and gaskets. For metal, you really need the higher peak power of a Q-switched laser. These high peak powers are what allow you to be able to ablate metal. Even the CO2 laser engravers that have maybe 40-50Watts will only engrave metal if a coating is applied to the metal. So it's not really engraving the metal, but rather the coating and some interaction with the metal. Most metal laser engravers that want a direct laser interaction will use a Q-switched fiber laser, YAG laser or similar. The peak powers of these will be in the kW range. Typically also, the beam wavefront or transverse electromagnetic mode are better than nearly all of the multimode diode lasers. This better mode structure allows these lasers to be focused to a very tight beam, increasing the power density.
I used to do a lot of Holography with a 5mW Helium Neon laser. I know 5mW is not much power, but back in the 80's, this laser was $700 and all I could afford. But the beam structure is so clean, it can be focused to a spot that's maybe 10 or 20 microns wide. Even with only 5mW, this laser will burn electrical tape. Just something to keep in mind...
Cutting gaskets was one of the other uses I had thought of for it. Also want to try it with cutting some thick felt I have for way wipers on the lathe. But that is all on hold at present while I get the computer up and running again.
I had some alternative control software I wanted to try but it wouldn't seem to run and I put it down to being an old XP operating system on my laptop. So I installed a copy of Windows 7 I had hoping that would solve the problem but I'm now are having trouble getting all the hardware drivers to install as the Laptop is so old Dell only supply XP and Win200 drivers for it. Will hopefully get it all up and running again over the weekend and have some more trial materials to share results on soon.