Anodized Aluminum Over-Engraving on Scan-Direction Lines

[Mikah Barnett]

Hi guys, I just joined but have been lurking here for nearly a year. I bought a G.Weike LC1290 in January for my business and have been having great success with it so far. I have one issue when engraving Anodized Aluminum (which I do a lot of) that I've yet to find a good solution for. I've seen one other thread here about it but no real solution, so thought I'd try again.

You can see in the attached picture (an etch I did on a rare scrap part) that when lines of an image are parallel to the scan direction of the laser, I get more etching than on the lines that are not. I have played around with many different settings but this seems to be there regardless of what I do - from low-power multi-pass etching to high-power one-pass and everything in between.

Has anyone else experienced this and found a solution? The one thing I have not tried is changing the logo file itself from 100% black to being a dark gray on the horizontal lines and fading into black. I suspect this might solve the issue on my logo, but then I'd have to go through a trial/error process with every logo I do. If that's the only answer, so be it. But, if there's something else I can try or change to avoid that - that would be very much preferred.

Can I just re-run or power-up until all the lines look like the horizontal ones, or will I over-etch and ruin the anodize?

IMAG0211.jpg

[Mike Null]

I think you need to reduce your power as you are removing the anodic coating on the horizontal lines. I'm sorry but I can't be of more help with your question.

[Matt Turner (physics)]

I'd guess that this might happen because of changes in the power of the laser depending on how long it's firing. On the horizontal lines, the laser is on for longer, and its power might increase because of that. You could see if this is the case by doing something like a dithered 50% at high DPI and see if this still happens. I'm not familiar with the Weike software, but there might be a setting somewhere to adjust the compensation for this behavior.

[Mikah Barnett]

Thanks for the input guys - both helpful. I share your thoughts, Matt, that it has something to do with "spool up" time of the laser. I can't find any settings that seem to indicate an ability to change that, but I'll keep looking. I think on the next run I'll just plan to do two passes at lower power to see what I get.

[Dave Sheldrake]

It can be changed Mikah in the software settings but remember DC tubes are non polarised so will often pump more (effective) power in one axis than the other. (not an exact explanation but close enough)

best wishes

Dave

[Rich Harman]

...but remember DC tubes are non polarised so will often pump more (effective) power in one axis than the other. (not an exact explanation but close enough)

??? I really doubt that the tube being DC has anything at all to do with a difference in power relating to the axis of travel. Please explain.

[Dave Sheldrake]

Randomly polarized light is exactly what it says; the light is plane polarized, but the direction is unknown, and may vary with time. Random polarization causes problems in optical systems since some components are polarization sensitive. If the polarization state changes with time, then the components’ transmission, reflection, and/or absorption characteristics will also vary with time.

best wishes

Dave

[Mikah Barnett]

Dave - care to give me a hint where in the software? I am using LaserCut 5.3.

It can be changed Mikah in the software settings but remember DC tubes are non polarised so will often pump more (effective) power in one axis than the other. (not an exact explanation but close enough)

best wishes

Dave

[Dave Sheldrake]

File/Machine-options/Work Mode(Engrave)

You can change most of the acceleration figures and distances in there,

best wishes

Dave

[Mikah Barnett]

Okay, that was the only area I saw that I thought might be it. But, since the problem seems related not to head acceleration but laser power on/off, I did not anticipate those settings making any difference. Seems to me (I could well be wrong) that during both the "intermittent" on/off periods where it's engraving vertical/diagonal lines and the steady-on periods where it's doing horizontal lines, all the acceleration should be done and it the head should be moving at constant speed.

Am I off base?

File/Machine-options/Work Mode(Engrave)

You can change most of the acceleration figures and distances in there,

best wishes

Dave

[Dave Sheldrake]

Okay, that was the only area I saw that I thought might be it. But, since the problem seems related not to head acceleration but laser power on/off, I did not anticipate those settings making any difference. Seems to me (I could well be wrong) that during both the "intermittent" on/off periods where it's engraving vertical/diagonal lines and the steady-on periods where it's doing horizontal lines, all the acceleration should be done and it the head should be moving at constant speed.

Am I off base?

Not off base at all but the rise times of Chinese tubes aren't great (to say the least) so the linear distance the head travels in a given time period will affect the amount of power introduced into the workpiece. You may find a shorter acceleration distance helps (so by the time the tube fires on the intermittent) the power has stabilised (power rise / time). Be aware though that setting the accl distance too short may put too much load on the steppers leading to early failure (it will also depend on which of the Leetro cards you have installed)

best wishes

Dave

[Dan Hintz]

I'd guess that this might happen because of changes in the power of the laser depending on how long it's firing. On the horizontal lines, the laser is on for longer, and its power might increase because of that.

Matt has hit it. Reducing the power will get you a nice engraving on long horizontal lines, but it may be too little power for a decent bleaching on the short lines. If your system has a bias setting (a.k.a., "tickle" in Western machines), increase it a bit... this should allow the laser to fire more quickly for short lines. Be careful, however, as too much bias will lead to lasing in areas that shouldn't be touched.

Polarization of the beam really only has an effect when you get up to very high-power machines (kW level)... think of it in terms of a short line rather than a dot. Moving in the direction of the line (like ---------- in a horizontal scan) leads to a higher average power per unit area than if the same beam was scanned vertically.

[Rich Harman]

I don't think that increasing acceleration is going to help, the acceleration happens before it starts firing.

You might try lower power and slower speed rather than lower power with multiple passes, if that doesn't work then widen the vertical lines - that's what I do.

[Dee Gallo]

Isn't this one of those times when you could rotate the image so there are no perfectly horizontal lines? This would avoid the situation of the scan direction lining up with your art.Or am I missing something important?

[Balsanu Gabi]

Hi,

I have that problem - different thickness between horizontal lines and vertical lines. It end up being the tube was not aligned properly. It was a little bit up on the head.
Check that. Just an opinion from experience. It will be nice if manufacturers come with a bullet proof system to align the tube properly. On a CNC machine you have many mechanical parts moving. On a laser....


HTH
Gabi