Black marking on aluminium without cer/thermark

[Jeff Woodcock]

Thanks Arjen,

We built and installed the 445nm LD engraving systems on two of our CNC routers. Both are 4 axis machines.

[Arjen Abbestee]

4.5 Watt seems like a lot for a Laser Diode. Where did you get it and how much did you spend?

[Jeff Woodcock]

We are using two 2.25W 9mm Nichia LD's focused to the same intersecting focal point and it's mounted on our servo CNC router. The Nichia 9mm LD came from DTR on eBay for $99 each already pressed into a copper module and included a 3 element glass lens. The analog modulation driver is a Flexmod P3 and is around $35. On our first build, the mini CNC router is only a 1W and it uses a Flexmod P3 also.

Here is a video of our dual LD engraver shading a 3D spindle engraving. We were only using 2/5 of the full output power on this project.

[Arjen Abbestee]

Good idea to combine two lasers in the same focal point. Should have thought of that myself. The price of laser diodes seems to rise exponentially with power, and since I don't want to spend a fortune on an experiment this is just what I was looking for. Now that I know that 445nm will blacken aluminium I guess other wavelengths between 445 and 1064 (fiber/yag) nm will also work. Lots of possibilities to play with now!
Good video by the way. I love how the vertical axes is used to retain focus. Halfway through the video is a shot of a motor driving something. Is that a mechanical laser-power-control?

[Jeff Woodcock]

Actually Arjen, the 445nm whitened the black anodizing with high power and at lower power it stays black. The servo motor down below (4th axis) drives a US Digital MA3 magnetic shaft encoder. It gives us 0-5 varied analog voltage output to the Flexmod P3 LD driver based on a 0-360 degree rotation to vary the power. We power it with the 5v from the USB port on my PC.

This spindle/laser process takes two same size images, one is a greyscale height map image for the 3D spindle engraving and the second is a color or 8bit greyscale image for the shading. We use Mach3 for the controller program which is gcode driven and it's an open source option so we don't have the restraints of a proprietary program. We generate two gcode files with Picengrave image to Gcode program we use and then combine the two files into one. X,Y & Z from the height map image file and A from the other image file for varying the laser diodes power. It gives us X,Y,Z & A movements in one file so the LD's focal point follows the contours of the spindle engraving. The gcode we generate is 40,000 PPSI (Positions Per Square Inch).

Since the MA3 encoder has 10bit resolution, even at a half power setting, there are 512 incremental voltage changes to the analog modulation input on the LD driver with a A.0000 to A-.0256" full depth setting (8bit). To set the max power for the LD, we just change the Steps Per. in Motor Tuning in Mach3 for the A axis servo motor.

Our servo CNC router's spindle mount excepts both the spindle and Laser engraver so it eliminates alignment issues like when using two different machines.

[Arjen Abbestee]

I'm impressed! Very nice combination of techniques.
I'm shopping for a 2W laser now. I'll attach it to the X carriage of my CO2 laser so I will use all the electronics and mechanics from that machine. That means the laser + mount has to be as lightweight as possible, it's not a heavy CNC milling machine capable of carrying 'lots' of extra weight.
Then it's a matter of finding the right speed/power combination. This will only be for black marking of anodised aluminium (read iPads/phones etc.). For all other purposes the CO2 tube does everything I need.

[Jeff Woodcock]

Thanks Arjen,

It has been allot of fun with these builds. I like figuring out multitasking ways to use my CNC router. I have even thought about a 3D printer attachment to go on it in the future. I would post some links to the components you may need, but that is not allowed on this forum. Just search on the net based on my description. I would also recommend a Lasorb for ESD protection for the LD.

[Arjen Abbestee]

You could pm me, but there are so many sellers for this kind of stuff I won't have a problem finding it.
Thanks for all the info.

[Dan Hintz]

I'm impressed! Very nice combination of techniques.
I'm shopping for a 2W laser now. I'll attach it to the X carriage of my CO2 laser so I will use all the electronics and mechanics from that machine. That means the laser + mount has to be as lightweight as possible, it's not a heavy CNC milling machine capable of carrying 'lots' of extra weight.
Then it's a matter of finding the right speed/power combination. This will only be for black marking of anodised aluminium (read iPads/phones etc.). For all other purposes the CO2 tube does everything I need.

Why would you do this?

You still seem to be under the impression the laser Jeff mentions marks bare aluminum. It does not, it only bleaches the black anodizing already on it, just like the CO2 laser you already own.

Strapping another laser to your CO2 carriage would be like tying a Ferrari on top of a Yugo because the Yugo has wheels.

[Arjen Abbestee]

Good catch Dan, thanks! Yes, I was under the impression that the 445nm laser leaves a black mark on clear anodized aliminium. Now I see that in the image Jeff posted it is a black anodized sheet where the image is lasered by removing the black. Bummer.
So I'm back to where I started. The only way to get black marking on clear anodized aluminium is to use a YAG laser. And that's too expensive for the amount of work I'd do with it...
Though I still don't get why only a 1064nm laser can leave a black (or at least very dark) mark on aluminium. I get why my CO2 with the 10 times longer wavelength won't work, but wouldn't a 808nm work as well?

[Jeff Woodcock]

Strapping another laser to your CO2 carriage would be like tying a Ferrari on top of a Yugo because the Yugo has wheels.

Dan,

I do appreciate the compliment of your comparison of my 445nm LD build to a Ferrari, considering Ferrari's are mostly hand built too, but why do you have to insult Arjen with comparing his CO2 machine to a Yugo on wheels? Sometimes you just are not very nice in your comments, especially anywhere I have posted. The term a$$hole comes to mind.

Arjen, I did point out that the 445nm whitened the black anodize at higher power in post #20 and I thought you understood that.

[Dan Hintz]

Good catch Dan, thanks! Yes, I was under the impression that the 445nm laser leaves a black mark on clear anodized aliminium. Now I see that in the image Jeff posted it is a black anodized sheet where the image is lasered by removing the black. Bummer.
So I'm back to where I started. The only way to get black marking on clear anodized aluminium is to use a YAG laser. And that's too expensive for the amount of work I'd do with it...
Though I still don't get why only a 1064nm laser can leave a black (or at least very dark) mark on aluminium. I get why my CO2 with the 10 times longer wavelength won't work, but wouldn't a 808nm work as well?

There is a peak in the absorption of aluminum at the mid-800's, but you'll want more than a couple of Watts to do much with it. Fiber/YAG is on the other side of that peak (and surprisingly far down) from visible, but it's usually in the 20W+ range for marking. Just as a CO2 can cut metal when you throw in enough power (kW levels), if you throw enough power at it in the near-visible, it will be absorbed.

[Dan Hintz]

Dan,

I do appreciate the compliment of your comparison of my 445nm LD build to a Ferrari, considering Ferrari's are mostly hand built too, but why do you have to insult Arjen with comparing his CO2 machine to a Yugo on wheels? Sometimes you just are not very nice in your comments, especially anywhere I have posted. The term Stalking comes to mind.

Sorry, Jeff, but I was not comparing your machine to a Ferrari, nor was I comparing his to a Yugo. I was making an analogy... tacking a low-power laser of one wavelength (Yugo) underneath a high-powered laser of a perfectly usable wavelength (Ferrari) is adding an unnecessary step.

[Scott Shepherd]

Dan,

I do appreciate the compliment of your comparison of my 445nm LD build to a Ferrari, considering Ferrari's are mostly hand built too, but why do you have to insult Arjen with comparing his CO2 machine to a Yugo on wheels?

I didn't read it like that at all Jeff. I didn't read it like he said your machine was a Ferrari either. I read it as saying that "You already have a C02 laser that will engrave anodized aluminum the Ferrari in the equation), why would you strap on a 2W laser (the yugo in the equation) to do something slower than you can already do with what you have must faster".

Seemed like a point well stated to me, and didn't mention you or even remotely talk about anything you did at all. I think you may have read his comments wrong.

[Arjen Abbestee]

My mistake completely. Sometimes one reads what one wants to read. I assumed from the start that your 445nm laser marked black, because that was what I wanted to read. And as you know, assumption is the mother of all f••k-ups...
But I still enjoyed reading about your CNC-mill/laser-engraver.