39 – Photo Laser Engraving Anodized Aluminium – Part 1 (31:03)

The Lightblade Learning Lab with Russ Sadler

The Lightblade Learning Lab is a series of videos that Russ did for Thinklaser Limited based on using the Lightblade 4060 Laser Cutting and Engraving Machine. Thinklasers Lightblade 4060 has a 400 x 600mm bed size and was supplied with a 60W EFR laser tube. In this session, Russ has a go at laser engraving anodized aluminium.

Laser Engraving Anodized Aluminium - The Dot Test
Laser Engraving Anodized Aluminium – The Dot Test

Contents

  • Damage thresholds.
  • The test pattern drawing (you can download this here).
  • Setting and running tests to identify the damage threshold of a sheet of red paper.
  • Trying the same settings on white card and adjusting the settings.
  • Testing the same settings on black Perspex.
  • Getting black dots on a material.
  • Looking at anodised aluminium.
  • Plain aluminium as a reflector.
  • The anodising process producing a surface of aluminium oxide.
  • 2- and 3- stage anodising process and the use of dyes.
  • Evaporating the dye in the anodizing leave the white oxidized surface behind.
  • Viewing the engraved anodized aluminium under a microscope.
  • Trying different types of anodised aluminium.
  • Running at different speeds and powers and looking at the results.
  • Trying a 1000 pixel/inch test graphic at different speeds and powers.
  • Using RDWorks on a PC connected to the machine.
  • Using the ‘Read’ command to copy the machine settings from the machine to the PC.
  • Changing the Scan Mode, Facula Size and Engraving Factor.
  • Looking at the ammeter during a test.
  • Looking at a graph of power versus current.
  • Keeping the machine at very low power keeping it in the pre-ionization zone.
  • Using the machine in ‘Special’ mode and looking at an oscilloscope trace of power and the
  • switching on and off relative to the dots being engraved – seeing how ‘Special’ mode breaks
  • each dot into 20 kHz signals. Facula sets the amount of time that the signal is on.
  • Effect of varying Facula.
  • Relationship between power and time.
  • Comparing photos engraved on aluminium at different speeds.

My thanks go out to Tom at Thinklaser for giving permission to embed these videos on this site. If you are looking for a new laser machine from a quality supplier, then I would suggest you check out their website: www.thinklaser.com.

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Transcript for Laser Engraving Anodized Aluminium

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0:10Well welcome to another Lightblade learning lab.

0:20Today we’re going to carry on with the theme that we started last time and that is, we’re going to start off by looking at damage to materials and a quick

0:30examination of this concept that I tried to explain to you last time, about damage

0:35threshold. Now you may remember this very simple little test pattern, we used this when

0:41we were developing speeds for engraving onto wood and card or

0:47organic materials. Now we’re going to use this same pattern again today because at

0:52254 pixels per inch it gives us a point 1 dot and a point 1 space along the

1:00bottom here and it gives us an opportunity to work out just what size dots we’re getting. Now with paper and card we found that we couldn’t get much

1:07better than about 0.15 dot size and the dot size was the thing that basically

1:13limited us to the speed and the resolution of picture that we could work

1:18with. I’ve got some red paper here, I’m going to use this as a starting point so

1:25the first thing we need to do is to set the focus to the to the correct height, 5,

1:306, 7, there we go so we’re going to run this at 13% Max and Min power because

1:3613% is in that pre-ionization zone before the tube gets fully

1:42powered-up. Now that gives us a very high frequency, very high power

1:48pulses and we can do quite a lot of damage at this low power.

1:56We’re running this at 250 millimetres a second, but the dots are showing that

2:02because they are tending to run into each other, they’re not very clear,

Transcript for Laser Engraving Anodized Aluminium (Cont…)

2:07they’re probably nearly 0.2 sausages by 0.10 ~ 0.15 maybe now the problem is if

2:15I slow it down to make the sausages correct I shall probably start burning

2:21a hole through the paper. Can I reduce the power a little bit more? Well we’ll

2:26try, I could probably take it down as low as maybe 9% for this machine.

2:37Hardly any marks and this also demonstrates just how sensitive the

2:44power setting is at this very low range. We’ve eventually got a perfect set of

2:49dots; at 9.5% max and min power and 120 millimeters a second. So we’ve had to

2:58slow it down to get the right amount of power to give us a good shaped dot.

3:04What we’ve done, we’ve found the damage threshold, the perfect damage threshold

3:09for this particular piece of material, a piece of finished paper. Around the

3:15outside here, we’re not producing burn marks we’re actually producing white marks and what we’re really doing is pulling the dye out of the paper.

3:23But when we look carefully under the microscope you’ll see that we’re actually still burning holes through the paper. So what we’ve now got here is a

3:32piece of white card, which has got quite a lot of china clay in it and we’ll just

3:39see what those same settings of 9.5% can do on this piece of paper and the answer

3:46is not very much. Let’s try 10%, now 10% is not bad….

3:58Okay, so now here we have a piece of black perspex and I shall just have to just set the focus

Transcript for Laser Engraving Anodized Aluminium (Cont…)

4:04up again and we’re using black perspex because it will show up the marks a little bit better. So we’ll run the ten and a half percent at 120

4:15millimeters a second and see what damage we can do. Yeah, we can do something, we

4:21shall see that under the microscope so that’s the same damage threshold as white card two completely different materials with the same damage threshold.

4:30Now would you have believed that, this rather stringent dot test that I use

4:37will tell us the sort of speeds and feats (power) that we can use for doing dot

4:43pictures. Now with some of those materials it may well be that we can run at a slightly faster speed but the problem is we’re running at a slow speed

4:51to get perfect dots but we’re not getting a very good colour, we’re not getting a very good burn. If we put the power up, we shall make the dots bigger

5:01and what we should be doing if you remember back to our last session, the brown halo around the hole is the thing that we shall be seeing as our dot. Not

5:11the actual dot, the powerful dot itself. So that’s why there isn’t too much control over the dot size as we increase the power. We’ve got to deal with another

5:20problem of somehow decreasing the power so that we don’t burn a hole, but we do

5:28produce a brown mark. So it all comes back to this thing about energy density

5:33and time that we talked about last time. Remember when we were burning the wood

5:38in an unfocused beam, how it took a long time to burn, but we were able to put a

5:44mark on the surface of the wood with very low unfocused power. But once we

5:50took it to the other side of the lens all of a sudden that same power was able to burst through. So you’ve got to keep those those facts in mind, power density

6:02and the time that you allow the high density mark to sit in one place or you decrease the density of that mark and that’s something we shall

Transcript for Laser Engraving Anodized Aluminium (Cont…)

6:12have to play with in a future session. The next thing that I want to look at, it’s the main part of today’s session is anodised aluminium. I suspect that some

6:22of you guys won’t really understand what anodised aluminium is. You’ll have heard of it and you will recognize it when you see it because understanding about

6:31anodised aluminium is going to help you understand how and why we damage it.

6:39Okay, now what I’ve got here is a piece of ordinary aluminium, this is a piece of

6:44aluminium extruded bar and as you can see the surface finish on it is not particularly good. It’s raw aluminium and on the other side I’ve polished it. Now

7:02if I put that in front of the laser beam I should get about 98% of the beam

7:07bouncing back at me it will act just like a mirror. Polishing the surface has

7:15a small effect and it may well increase the reflectivity by 1% up to 99%. Now I

7:22say that sounds a really strange property because aluminium is a very good transmitter of heat what we’ve got to remember is and I keep reinforcing this,

7:31the laser beam itself is not hot. It’s only when the laser beam stimulates the

7:38atoms in this surface that we get an energy transfer. If we get reflection off

7:44the surface there is no heating effect. Well that’s why you wouldn’t want to use naked aluminium for any of the parts inside this machine. My other machine

7:53over there for example first came to me with an aluminium bed. The first thing I

8:00did was to cover it with a piece of mild steel which has only got a 60%

Transcript for Laser Engraving Anodized Aluminium (Cont…)

8:05reflectivity and as it reflects it causes the Rays to diverge and the

8:11energy density gets dissipated. Anodising is a process that you can put onto this material you dip this into a bath with some chemicals and some electrical

8:19contacts and it will convert the surface of this material into a

8:24nonmetallic oxide. If you could imagine sprinkling salt on the surface granular,

8:32well that’s what this surface gets converted into it’s not loose salt that you can shake off obviously but it’s a granular surface that this metal gets

8:40converted to by a chemical reaction. Bear in mind this granular structure that’s on the surface is non metallic it is no longer aluminium it’s an aluminium oxide.

8:51Now what is aluminium oxide? Well you can see aluminium oxide in sandpaper or

8:58emery paper or things like that, it’s a very very hard material it’s used for

9:03grinding wheels in industry. So the surface of this material has now been converted into a very hard material, but it’s got an open pore structure. They dip

9:12this product into a sealant which seals up all the pores and stops the outside atmosphere and anything else from going

9:22through the pores and attacking the raw aluminium that’s still underneath. Okay

9:27now that’s a two-stage anodising process, you can go for a three-stage anodising

9:34process and that’s what this piece of material has been through. After the

9:41first stage of oxidation on the surface, instead of dipping it into a clear

9:47sealant, what they’ve done is they’re dropped this into a bath of dye. You can

9:52get all sorts of coloured anodized aluminium but it’s only the dye that they do for the second operation that’s giving the anodised aluminium its colour

10:02and then after the dye has gone into the surface and sat between all the granules

Transcript for Laser Engraving Anodized Aluminium (Cont…)

10:08they then put the sealing coat on top so now we’ve got a coloured anodized

10:14aluminium product. We’re not going to burn through the very hard oxide coating,

10:20we’re just going to put enough heat into it to evaporate the dye that’s in the

10:28product so this is yet another damage mechanism, we’re not attempting to damage

10:33the material. We want just enough energy to evaporate the dye so this might be

10:39quite a delicate balancing operation to get the dye out without damaging the

10:45material. Now until I had these little sample squares made, so that I could do some demonstrations for you guys. The only product that I had that was

10:54anodized was a piece of channel section and this has got gold anodise on it, but

11:00this has been industrially produced in bulk and I suggest that probably this is

11:09a very very thin anodizing process that’s taking place in here. Whereas this

11:15has been done by a small plating company where they specialize in high-quality

11:20plating rather than let’s call it high-volume industrial plating. We will test this and see whether this performs differently to

11:30this. Okay, so here we’ve got our piece of black acrylic, we were in the pre-

11:36ionization region and we were able to damage this at 10.5% power .10.5% power

11:44is down at probably something like about 3 or 4 watts coming out onto the job. So it was a very small amount of power but running at

11:55slow speed that we were able to damage this, so it’s the

12:00apportionment of power over time that gives us damage to a product and we’re

Transcript for Laser Engraving Anodized Aluminium (Cont…)

12:06gonna start off with those same numbers on this piece of gold anodizing and see what sort of results we get. Well it’s interesting we’ve got some damage.

12:36I’m going to run the same test on this black anodize because I’ve got a half a

12:44suspicion that I shall not be able to damage this at these settings.

12:52Well my half a suspicion is wrong, it’s actually done quite a nice job so that’s

12:59at 10.5% / 120 millimetres a second they are really very clean little dots in

13:08fact I would say the gold anodizing needs more power to burn through. Okay so

13:13now I’m going to run 120 millimetres a second at 13%. It’s the upper of those

13:24two sets they don’t look any different just because we’ve increased the power, we’ve more than doubled the power. We also run a test on the gold anodizing at 120

13:33millimetres a second and 13% power. Well they’re also now beginning to look very

13:43nice between these two products there’s something in common…. the white background.

13:52We’re just drawing the dye out of the material and we’re leaving the white

13:57oxidised surface behind, that’s the key to this process so we’re down at very

Transcript for Laser Engraving Anodized Aluminium (Cont…)

14:06very low powers at the moment. I’m just going to carry on with the black one, because it’s the black one that I want to demonstrate. We’ll just set this to

14:14seven millimeters, eight, seven, click, done!

14:21I’m sorry I don’t use the autofocus on this machine because it is so much quicker to set it by hand. Now I’m going to try something really silly and that

14:31is we’re going to double the speed so we’ve found the threshold where it looked very very good and we found that at 13%.

14:41And 13% is about as high as this machine works in its pre-ionisation mode,

14:49its high-frequency pulsing and that’s why we’re getting I think quite good

14:55resolution on these dots. Right we’ve now gone to 250 millimeters a second same power

15:0213%

15:14and I think you can see we’re beginning to lose it a little bit, we’ve lost the centre line of dots. The dots are actually still quite nice dots but

15:23they’re not as dark as they were in this one, because we’re not allowing quite

15:29enough time for the dots to form properly at 250 millimeters a

15:35second. We’ve doubled the speed, we’ve basically allowed half the amount of time. At 13% we’re running at about 12 watts, so after we take let’s just say we

15:44take 20% off we’re down to probably about 9 or 10 watts here. So let’s double

15:53that up to 18 or 20 watts which means we need maybe 30 watts coming out of the

16:01tube. So we need to go up to about 22 or 23 percent power. In other words what

16:07we’re doing, we’ve halved the amount of time which means we halved the amount of

16:12power that we’re putting into every dot. So if we double the power we should be

16:18back to where we were here. And there we go, we’ve gone from that to that

16:28and now we’ve doubled the power but also doubled to speed we’re back to this and

16:35maybe a little bit better. Those blocked dots there look as though they may well have merged, we’ve got a lovely row of dots along the centre and yes what we’ve

16:45got here now we’ve got dots that are more or less touching. So they’re sausages, they’re little oval shape pieces which are just about touching so

16:56they’re about 0.15 or 0.12 wide and almost maybe 0.19 long but we are

17:03running at 250 millimeters a second. As well as trying to demonstrate what the

17:09damage threshold for materials is, because this is a very special type of engraving material. What the limits are that we can go to, we can certainly go to

17:19250 millimeters a second and probably get a reasonable picture. This is a

17:26resolution of 250 pixels per inch as well, 254 to be exact so we’re already

17:35able to go probably two times faster with twice the resolution than we could

17:44do with wood or with card. I have heard that you can actually run at a thousand

17:51pixels per inch and get good quality pictures, now that’s quite a long way to

17:56go at the moment. A thousand pixels per inch. I’ve developed a thousand pixels

18:02per inch pattern here that we can run, to see whether we can

Transcript for Laser Engraving Anodized Aluminium (Cont…)

18:09succeed in getting any sort of results for a thousand pixels per inch because

18:15that would be some mighty resolution if we could, we’d be able to produce almost

18:21perfect photographic representations on black anodized surfaces. Because the

18:27surface is black and the background is white, whereas when we do it with paper

18:34we’ve got brown, various types of brown whereas here we’ve only got two colours.

18:40We know we’ve only got two colours to start with black and white. We’re going

18:46to run this thousand pixels per inch test at the ideal speed that we found

18:51when we were running the 250 pixel test ie 13% power and a hundred twenty

18:59millimetres a second. So we’ll use it as our starting point.

19:07I’m actually staggered to say that we do look as though we’ve got individual

19:15pixels running along there, but whether there is I think it’s a hundred pixels

19:20that I had along there we’d have to count them underneath the microscope because I certainly can’t do it with my, with my little eye glass here. Let’s

19:30change the speed up to 240 and let’s double the power up to 23%.

19:42There’s virtually nothing that I can pick out by way of an individual pixel,

19:47that probably is because we are now running the power in solid beam mode ie

19:58the beam is on all the time and it takes a finite amount of time for the beam to

Transcript for Laser Engraving Anodized Aluminium (Cont…)

20:04die off and come back on again. Whereas when we were doing this, at 13% the

20:12beam was switching on and off incredibly quickly and it was probably punching

20:18these. If I got it synchronised correctly it would be punching these at the same

20:23speed as the dots were passing by. What I’m going to do now is something which

20:29would not normally be done for photo engraving. Now I’m going to go into

20:36RDWorks which is connected up to the Machine and press the read button across

20:42the bottom there and make sure that I’m reading into this table here what’s

20:49actually in the machine. So I’ve got the Machine settings here now available to me on this screen. I’m now going to look down these settings and somewhere I

20:59should find a scanning mode and there it is there, look, scan mode / common mode

21:08and this strange word underneath Facula size 50 to 99 percent. Change from

21:15common mode and I get a choice here I get this thing called special mode. I’m

21:23going to set the Facula size to 50% and I’ll explain what I’m doing

21:28shortly, an engraving factor hundred. So now I’ve got to write that information

21:35back to the machine, which I’ve now done. So now I’ve set the Machine up into

21:40something called special mode and let’s go and see what effect it has on my results. Now I’ve not changed anything with the settings and previously we had

21:5223 percent power 230 millimeters a second and we were producing a solid

21:58block, let’s see what happens now. We’ve got lots of individual dots there but

Transcript for Laser Engraving Anodized Aluminium (Cont…)

22:06I’m not so sure we’ve got as many dots, so what we can do we can push the power up a little bit. Let’s go from 23% to 50% special mode.

22:18Well I would say we have not got individual pixels anymore

22:24we’ve got something which are sort of pixely you can see that there are blobs

22:31that are joining together so you know it may well work. We’re currently at 230

22:40millilitres a second and 50% power

22:47now that is quite phenomenal let’s be silly shall we and drive it up to 400 millimeters a second and see what we

22:56get. Now we’re being really silly, 400 millimeters a second and 70% power.

23:06Now we’re nearly back to seeing individual pixels there, not quite but

23:15hey we’ve got the machine running flat out. Okay we’re going to run that test again and I want you to look what’s happening to the ammeter,

23:29now 70% power should be somewhere up here at about 22 milliamps. What on earth is

23:41going on? Well remember that we got some half-decent results when we were running

23:47down at 13% power, we got nice crisp dots provided we didn’t run too fast, but

23:55basically what happens is as the tube starts up it will go through this phase

24:01of high-frequency impact Engraving pre ionization before it settles down to a

24:07constant current. Now it will do this every time we start the tube up. So if if

24:15we’re running at 40%, 40% power will be this but for the first few milliseconds

24:21or microseconds after we turn the tube on it will go through this phase of high

24:27frequency before it settles down to a stable current. Now provided we use the

24:33Machine at very very low currents we can keep it in this region and at 13% I was

24:42running it like this so the current never managed to settle down throughout

24:47my test it was continuously going up and down. So the dots didn’t have a chance to burn into each other because there was only little pulses of power there all

24:57the time. The photograph that we’re going to work with is going to be broken down into black pixels on a white background and what happens is every pixel that

25:10appears black and sometimes it’s a group of pixels rather than a single pixel. The

25:16beam will switch on and the current will flow and the beam will switch off when

25:23it gets to the end of a pixel or a block of pixels and it will stop and then it

25:29will switch back on again and the current will flow. There’s no current flowing when the beam is switched off so it’s only when the beam is switched on

25:37that the current flows and it flows continuously. When we look at the blocks of pixels under the microscope

25:46we’ll find that the current has had a chance to build up and burn through

25:52whereas when we get a single pixel its hardly had a chance to reach maximum power before it switches off and that’s the balance point that we had to

26:01achieve when we were burning Brown pixels onto wood or paper. I’ve now set

Transcript for Laser Engraving Anodized Aluminium (Cont…)

26:08the machine into a special mode and I’ve done a trace for you of power which is

26:16the red line and the switching on and off which is the blue line. As you can see, there

26:23is my pattern that top line are the continuous lines and they match up with

26:31this pattern under normal circumstances what you’d see is you’d see the signal switching on here, off because it’s blank then back on off on off on off, but with

26:45special mode it’s broken up into 20,000 Hertz signals. I’ve set the Fukuda to 50%

26:57so that means the signal is only on for 50% of the time so I’ve divided the

27:05power effectively by 2 but in reality it’s a lot less than that because I

27:12don’t think the actual physics of the machine through the power supply can respond that quickly, but that’s what the machine is trying to do. It’s trying to

27:22break these continuous signals into smaller pieces. These are single dots, sometimes we’ve got signals which break up the dot is on

27:34long enough to produce like 2 or 3 little signals and then at other times

27:40there’s not enough for it to only do 1 pulse 2 pulses one and a half one two

27:48one three you know we’re getting a strange pattern

27:55along here an aliaising pattern basically where the pulsing does not

28:00coincide with the pixels. We’re likely to get varying colours on these pixels

Transcript for Laser Engraving Anodized Aluminium (Cont…)

28:10because we haven’t got exactly the same signal on each one now I haven’t got the

28:17single dots to match up because I’ve expanded the scale so that you can basically see what’s happening. Look we’ve got a dot a dot a dot a dot and a

28:28bit, that dot is broken into two, that dot is broken into two, a dot, a dot, something

28:35funny going on there you know we’ve got some randomness taking place along here.

28:41So we’ve got again inconsistency in the power signal for single dots. Now if I

28:49need more colour in my dots I can’t increase the powe,r I’ve got to

28:57decrease the speed to increase the time per dot by decreasing the speed we

29:06shall allow more power per unit of time to burn our dots.

29:12I hope I’m getting the message over to you about this relationship between power and time instantaneous amount of energy in a spot to do damage. I’ve

29:24already done quite a lot of experimental work on my other machine over there if you want to go to my RDWorks Learning Lab YouTube channel you’ll find

29:33information, detailed information about the experimentation that I went through,

29:39but I’ve had to go through a similar test procedure on this machine to make

29:44sure that this machine is going to perform the same as my other machine over there and it looks as though this machine may well perform better than the

29:53other machine over there. That’s 400 pixels per inch 240 speed 50/50 power this one is 600 pixels per inch 240 speed 50/50 power and

Transcript for Laser Engraving Anodized Aluminium (Cont…)

30:14this one is a thousand pixels per inch it was still done at 240 millimetres a

30:21second but it was 40% power. Now however you look at that that’s pretty damned

30:31amazing, so in the next session I plan to go through the preparation of a

30:37photograph to produce a thousand PPI image. It’s not this one

30:43but it’ll be a different image and we’ll test out how well it works on this

30:50machine now that we’ve got a set of test parameters which promised to give us a

30:56thousand pixels per inch…..

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