Tricks for laser engraving black anodize

[bryan henderson]

Morning all

Does anyone have any trade secrets that they could share in regards to getting the best whiteness from laser rngraving black anodized aluminum. I am currently using 5005 AQ MX aluminum H34. I was jsut wondering if someone had a chemical or something that they might spray or wipe on this to make it look the best.

Bryan Henderson

[Mike Null]

Bryan

do a little testing and you will easily find the sweet spot. The trick is not to use so much power that you remove the anodized surface. I would work at no more than 500 dpi.

[bryan henderson]

Mike

I know you have a 40W Trotec but I have a 30W and it is set up for 500 dpi and full power, do you think I should try lower and around what.

Bryan

[Mike Null]

I run mine at about 50 power and 80 speed. that's 112 ips.

[Dave Johnson29]

I am currently using 5005 AQ MX aluminum H34.


In my experience, you will get the whitest results from the harder grades of Aluminum like 6061/60663 or even better 7075.

I have only been marking anodized for a short time but in my other business I have been using it for 12+ years and had been getting the laser work done outside. I opt for 6061-T6 as it has the best all round characteristics for strength and laser results although 6063 is good too if you can live with the reduced strength.

[Michael Hunter]

I do a lot of black anodised aluminium (sorry - don't know what grade : some is sheet and some machined solid).

With my 60W Epilog I use 75% speed, 25 to 30% power and 1200dpi for doing very small text (about 1mm high [3/64"?]).
On larger areas and bigger text, that power is enough to blow away the anodising completely, so I reduce to 22% power and it comes out nice and white.

I find 1200dpi necessary to prevent horizintal lines in the engraving. Lower dpi, higher power and slight defocus might make the jobs quicker, but I get paid well for doing them so I'm prepared to go slow!

Hope this helps

[Rodne Gold]

There is no secret - barring trying to use minimal power.
The reason is that the lasering of anodised ally just leaches the dye used - anodising is a sort of natural white and it is dipped in dye which soaks into the anodising which is then "sealed".
Lasering will firstly have to vaporise the seal and then leach the dye - the problem is you have no idea of how or what was used to seal it , what the dye composition is and how thick the anodised layer is - there is no standard amongst anodising plants unfortunately.

[Dave Johnson29]

Rodney,

I can't really agree with you. There are 3 common types of Anodizing. Type I, Type II and Type III.

Type I is a soft anodizing and does not do black very well at all. It comes out looking a smutty-gray. I doubt Type I is used much at all these days.

Type II, by far the most common is 0.0004" to 0.0007" thick and it does all colors well. It increases the surface hardness dramatically and the surface is no longer conductive.

The anodizing process creates millions of little tubes standing on end at the surface. The coloring dye leaches into those tubes by capillary action.

It is then sealed by immersion in boiling water for 20+ minutes which seals over the small tubes created in the aluminum surface by the anodizing process and that traps the color dye inside.

The laser boils the dye inside the tubes and it expands and opens the sealed tube end and then evaporates the dye leaving the aluminum visible.

If you use minimal power, the tubes remain open and can be re-dyed and resealed if desired. I posted some pics of multiple colored anodized things some time back. Too much power and the visual effect is still very similar but the tubes get mangled and will not re-fill and seal at all well.

Type III is very very hard and I am only aware of it being in black. Not saying "only" it is just I have never seen it in another color. It is between 0.0025" and 0.005" thick and used used for high wear and tear items like aluminum rifle breeches.

[Rodne Gold]

Sheesh...
All anodisng plants do not use the same dye , they do not always anodise the same time , current etc and they do not all seal by boiling , some use other methods.
Apart from that , anodised plates can have various finishes, like brushed , matte , less matte and so forth. I speak from expereince here and stand by my statement that there is no standard AMONGST ANODISING PLANTS in this regard.
There is only one way to get the best whiteness on anodised material , and that is to suck it and see - IE trial and error , and what works well on one batch or plate or plants output might not work as well on anothers.

[Mike Null]

Dave

I also disagree with your premise that the laser removes the anodic coating and reveals bare aluminum. It does that if you use too much power but that is not the proper way to engrave anodized aluminum.

I have been doing various types of anodized aluminum for nearly 10 years and I agree with Rodney. The only thing consistent is inconsistency.

The fly in the ointment is not the process but how the process is managed and whether it is contaminated.

[Peter Meacham]

Well, I'm befuddled here - I have always engraved to remove the anodized layer down to the bare metal. And my customers like what they get.

Naturally, I have an important job due out today - but half the job is already done and installed using my "bare metal" approach - too late to change my method on this job.

I have not tried to reduce power to produce another look - I guess I have to try it.

[Dave Johnson29]

I stand corrected.

[Mike Null]

Dave

Let me add that my experience, limited though it is, is the same as yours on what you refer to as Type 3.

[Michael Hunter]

I'd go further than Rodne on type 2 "decorative" anodising - even the same shop anodising the same grade of aluminium produces different results every time. A good shop will be reasonably consistent, but a bad one can be dramatically different from batch to batch.
Fortunately, the settings needed to engrave remain pretty constant for the same colour.

The batch of machined items I did this morning have a glorious glossy finish and engraved to a startling white which looks amazing.
Last month's batch were a nice velvety matte and engraved to a very light grey (which also looked pretty neat).
The aluminium was the same grade, from the same supplier and machined at the same shop. The same anodising shop did the blacking. (And this is the **good** anodiser). Go figure!


Type 3 or "hard" anodising is usually black or dark coloured, but can be any colour from straw through brown to black - the anodising shop has little, if any, control. The colouring is caused by chemical reactions on the metal surface and adding dye to the bath makes no difference to the outcome. Type 3 is hard because it is not porous.