Well welcome to another Lightblade learning la.
Today 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
examination of this concept that I tried to explain to you last time, about damage
threshold. Now you may remember this very simple little test pattern, we used this when
we were developing speeds for engraving onto wood and card or
organic materials. Now we're going to use this same pattern again today because at
254 pixels per inch it gives us a point 1 dot and a point 1 space along the
bottom 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
better than about 0.15 dot size and the dot size was the thing that basically
limited us to the speed and the resolution of picture that we could work
with. I've got some red paper here, I'm going to use this as a starting point so
the first thing we need to do is to set the focus to the to the correct height, 5,
6, 7, there we go so we're going to run this at 13% Max and Min power because
13% is in that pre-ionization zone before the tube gets fully
powered-up. Now that gives us a very high frequency, very high power
pulses and we can do quite a lot of damage at this low power.
We're running this at 250 millimetres a second, but the dots are showing that
because they are tending to run into each other, they're not very clear,
they're probably nearly 0.2 sausages by 0.10 ~ 0.15 maybe now the problem is if
I slow it down to make the sausages correct I shall probably start burning
a hole through the paper. Can I reduce the power a little bit more? Well we'll
try, I could probably take it down as low as maybe 9% for this machine.
Hardly any marks and this also demonstrates just how sensitive the
power setting is at this very low range. We've eventually got a perfect set of
dots; at 9.5% max and min power and 120 millimeters a second. So we've had to
slow it down to get the right amount of power to give us a good shaped dot.
What we've done, we've found the damage threshold, the perfect damage threshold
for this particular piece of material, a piece of finished paper. Around the
outside 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.
But 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
piece of white card, which has got quite a lot of china clay in it and we'll just
see what those same settings of 9.5% can do on this piece of paper and the answer
is not very much. Let's try 10%, now 10% is not bad....
Okay, so now here we have a piece of black perspex and I shall just have to just set the focus
up 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
millimeters a second and see what damage we can do. Yeah, we can do something, we
shall see that under the microscope so that's the same damage threshold as
white card two completely different materials with the same damage threshold.
Now would you have believed that, this rather stringent dot test that I use
will tell us the sort of speeds and feats (power) that we can use for doing dot
pictures. 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
to 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
and 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
the 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
problem of somehow decreasing the power so that we don't burn a hole, but we do
produce a brown mark. So it all comes back to this thing about energy density
and time that we talked about last time. Remember when we were burning the wood
in an unfocused beam, how it took a long time to burn, but we were able to put a
mark on the surface of the wood with very low unfocused power. But once we
took 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
and 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
have 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
of 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
anodised aluminium is going to help you understand how and why we damage it.
Okay, now what I've got here is a piece of ordinary aluminium, this is a piece of
aluminium 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
if I put that in front of the laser beam I should get about 98% of the beam
bouncing back at me it will act just like a mirror. Polishing the surface has
a small effect and it may well increase the reflectivity by 1% up to 99%. Now I
say 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,
the laser beam itself is not hot. It's only when the laser beam stimulates the
atoms in this surface that we get an energy transfer. If we get reflection off
the 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
over there for example first came to me with an aluminium bed. The first thing I
did was to cover it with a piece of mild steel which has only got a 60%
reflectivity and as it reflects it causes the Rays to diverge and the
energy 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
contacts and it will convert the surface of this material into a
nonmetallic oxide. If you could imagine sprinkling salt on the surface granular,
well 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
converted 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.
Now what is aluminium oxide? Well you can see aluminium oxide in sandpaper or
emery paper or things like that, it's a very very hard material it's used for
grinding 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
this product into a sealant which seals up
all the pores and stops the outside atmosphere and anything else from going
through the pores and attacking the raw aluminium that's still underneath. Okay
now that's a two-stage anodising process, you can go for a three-stage anodising
process and that's what this piece of material has been through. After the
first stage of oxidation on the surface, instead of dipping it into a clear
sealant, what they've done is they're dropped this into a bath of dye. You can
get all sorts of colored anodized aluminium but it's only the dye that
they do for the second operation that's giving the anodised aluminium its colour
and then after the dye has gone into the surface and sat between all the granules
they then put the sealing coat on top so now we've got a colored anodized
aluminium product. We're not going to burn through the very hard oxide coating,
we're just going to put enough heat into it to evaporate the dye that's in the
product so this is yet another damage mechanism, we're not attempting to damage
the material. We want just enough energy to evaporate the dye so this might be
quite a delicate balancing operation to get the dye out without damaging the
material. 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
anodized was a piece of channel section and this has got gold anodise on it, but
this has been industrially produced in bulk and I suggest that probably this is
a very very thin anodizing process that's taking place in here. Whereas this
has been done by a small plating company where they specialize in high-quality
plating rather than let's call it high-volume industrial
plating. We will test this and see whether this performs differently to
this. Okay, so here we've got our piece of black acrylic, we were in the pre-
ionization region and we were able to damage this at 10.5% power .10.5% power
is 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
slow speed that we were able to damage this, so it's the
apportionment of power over time that gives us damage to a product and we're
gonna 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.
I'm going to run the same test on this black anodize because I've got a half a
suspicion that I shall not be able to damage this at these settings.
Well my half a suspicion is wrong, it's actually done quite a nice job so that's
at 10.5% / 120 millimetres a second they are really very clean little dots in
fact I would say the gold anodizing needs more power to burn through. Okay so
now I'm going to run 120 millimetres a second at 13%. It's the upper of those
two 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
millimetres a second and 13% power. Well they're also now beginning to look very
nice between these two products there's something in common.... the white background.
We're just drawing the dye out of the material and we're leaving the white
oxidised surface behind, that's the key to this process so we're down at very
very 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
seven millimeters, eight, seven, click, done!
I'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
is 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%.
And 13% is about as high as this machine works in its pre-ionisation mode,
its high-frequency pulsing and that's why we're getting I think quite good
resolution on these dots. Right we've now gone to 250 millimeters a second same power
13%
and 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
they're not as dark as they were in this one, because we're not allowing quite
enough time for the dots to form properly at 250 millimeters a
second. 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
take 20% off we're down to probably about 9 or 10 watts here. So let's double
that up to 18 or 20 watts which means we need maybe 30 watts coming out of the
tube. So we need to go up to about 22 or 23 percent power. In other words what
we're doing, we've halved the amount of time which means we halved the amount of
power that we're putting into every dot. So if we double the power we should be
back to where we were here. And there we go, we've gone from that to that
and now we've doubled the power but also doubled to speed we're back to this and
maybe 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
got 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
they're about 0.15 or 0.12 wide and almost maybe 0.19 long but we are
running at 250 millimeters a second. As well as trying to demonstrate what the
damage 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
250 millimeters a second and probably get a reasonable picture. This is a
resolution of 250 pixels per inch as well, 254 to be exact so we're already
able to go probably two times faster with twice the resolution than we could
do with wood or with card. I have heard that you can actually run at a thousand
pixels per inch and get good quality pictures, now that's quite a long way to
go at the moment. A thousand pixels per inch. I've developed a thousand pixels
per inch pattern here that we can run, to see whether we can
succeed in getting any sort of results for a thousand pixels per inch because
that would be some mighty resolution if we could, we'd be able to produce almost
perfect photographic representations on black anodized surfaces. Because the
surface is black and the background is white, whereas when we do it with paper
we've got brown, various types of brown whereas here we've only got two colours.
We know we've only got two colours to start with black and white. We're going
to run this thousand pixels per inch test at the ideal speed that we found
when we were running the 250 pixel test ie 13% power and a hundred twenty
millimetres a second. So we'll use it as our starting point.
I'm actually staggered to say that we do look as though we've got individual
pixels running along there, but whether there is I think it's a hundred pixels
that 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
change the speed up to 240 and let's double the power up to 23%.
There's virtually nothing that I can pick out by way of an individual pixel,
that probably is because we are now running the power in solid beam mode ie
the beam is on all the time and it takes a finite amount of time for the beam to
die off and come back on again. Whereas when we were doing this, at 13% the
beam was switching on and off incredibly quickly and it was probably punching
these. If I got it synchronised correctly it would be punching these at the same
speed as the dots were passing by. What I'm going to do now is something which
would not normally be done for photo engraving. Now I'm going to go into
RDWorks which is connected up to the Machine and press the read button across
the bottom there and make sure that I'm reading into this table here what's
actually 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
should find a scanning mode and there it is there, look, scan mode / common mode
and this strange word underneath Facula size 50 to 99 percent. Change from
common mode and I get a choice here I get this thing called special mode. I'm
going to set the Facula size to 50% and I'll explain what I'm doing
shortly, an engraving factor hundred. So now I've got to write that information
back to the machine, which I've now done. So now I've set the Machine up into
something 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
23 percent power 230 millimeters a second and we were producing a solid
block, let's see what happens now. We've got lots of individual dots there but
I'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.
Well I would say we have not got individual pixels anymore
we've got something which are sort of pixely you can see that there are blobs
that are joining together so you know it may well work. We're currently at 230
millilitres a second and 50% power
now that is quite phenomenal
let's be silly shall we and drive it up to 400 millimeters a second and see what we
get. Now we're being really silly, 400 millimeters a second and 70% power.
Now we're nearly back to seeing individual pixels there, not quite but
hey 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,
now 70% power should be somewhere up here at about 22 milliamps. What on earth is
going on? Well remember that we got some half-decent results when we were running
down at 13% power, we got nice crisp dots provided we didn't run too fast, but
basically what happens is as the tube starts up it will go through this phase
of high-frequency impact Engraving pre ionization before it settles down to a
constant current. Now it will do this every time we start the tube up. So if if
we're running at 40%, 40% power will be this but for the first few milliseconds
or microseconds after we turn the tube on it will go through this phase of high
frequency before it settles down to a stable current. Now provided we use the
Machine at very very low currents we can keep it in this region and at 13% I was
running it like this so the current never managed to settle down throughout
my 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
the 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
appears black and sometimes it's a group of pixels rather than a single pixel. The
beam will switch on and the current will flow and the beam will switch off when
it gets to the end of a pixel or a block of pixels and it will stop and then it
will 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
that the current flows and it flows continuously.
When we look at the blocks of pixels under the microscope
we'll find that the current has had a chance to build up and burn through
whereas 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
achieve when we were burning Brown pixels onto wood or paper. I've now set
the machine into a special mode and I've done a trace for you of power which is
the red line and the switching on and off which is the blue line. As you can see, there
is my pattern that top line are the continuous lines and they match up with
this 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
special mode it's broken up into 20,000 Hertz signals. I've set the Fukuda to 50%
so that means the signal is only on for 50% of the time so I've divided the
power effectively by 2 but in reality it's a lot less than that because I
don'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
break these continuous signals into smaller pieces.
These are single dots, sometimes we've got signals which break up the dot is on
long enough to produce like 2 or 3 little signals and then at other times
there's not enough for it to only do 1 pulse 2 pulses one and a half one two
one three you know we're getting a strange pattern
along here an aliaising pattern basically where the pulsing does not
coincide with the pixels. We're likely to get varying colours on these pixels
because we haven't got exactly the same signal on each one now I haven't got the
single 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
bit, that dot is broken into two, that dot is broken into two, a dot, a dot, something
funny going on there you know we've got some randomness taking place along here.
So we've got again inconsistency in the power signal for single dots. Now if I
need more colour in my dots I can't increase the powe,r I've got to
decrease the speed to increase the time per dot by decreasing the speed we
shall allow more power per unit of time to burn our dots.
I 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
already 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
information, detailed information about the experimentation that I went through,
but I've had to go through a similar test procedure on this machine to make
sure 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
other 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
this one is a thousand pixels per inch it was still done at 240 millimeters a
second but it was 40% power. Now however you look at that that's pretty damned
amazing, so in the next session I plan to go through the preparation of a
photograph to produce a thousand PPI image. It's not this one
but it'll be a different image and we'll test out how well it works on this
machine now that we've got a set of test parameters which promised to give us a
thousand pixels per inch.....
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