Session 36 – How to Laser Cut Thin Materials

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The Concise RDWorks Learning Lab with Russ Sadler.

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Session 36 Cutting Thin Materials. Well, in previous sessions, we dealt with the basic principles of cutting. As I explained,

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then, there is some, there are some very serious difficulties associated with cutting quite a lot of understanding.

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You can just cut stuff without any problem at all. You can make it fall out.

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But is it neat? Is it tidy? Is it efficient? Those are the sorts of things, the skills that you’ve got to really start practicing and learning.

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Now I can never teach you those skills. I can only show you the principles.

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And today we’re going to start off with the easy end of the cutting spectrum, very thin material.

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In fact, not only thin material, but very flimsy and weak material.

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We’re going to deal with paper and card. What can be difficult about that?

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Okay, look, we’ve got some it’s a slightly thicker than inkjet printer paper.

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It’s about 110 grams this. So yeah, it stays fairly level and I can support it on these little bars that I’ve got here.

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The first thing I’m going to do is find out what the correct focus is for this paper.

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Now, if you remember, I’ve got a little automatic test in here,

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which because I’ve got a programable z on this machine, allows me to test the focus point at various depths.

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So I’ve set it to three millimetre gap under there to start with.

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And then we’ll drop the table one millimetre at time and we’ll try and find the correct gap.

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For the ideal focus. Now, this is a standard focus test that I’ve got set up on here, and it’s running at cutting speeds of typically 20mm a second,

Transcript for How to Laser Cut Thin Materials (Cont…)

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which is not an unreasonable cutting speed and 15 percent power.

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Ideally we’re looking for the thinnest line.

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Now, remember, I said, I set this to roughly three millimetres to start with,

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so that’s three four five six seven eight nine mm, looks to be about the ideal gap that we have for the thinnest possible cutting line. ow 20mm

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a second is pretty slow, so we want to find out how quickly and efficiently we can cut this paper.

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So if you remember the basic rules that I described to you in the previous session, maximum power.

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We’re going to do some test squares because that’s the quickest and the easiest way to try and find out our cutting parameters.

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But our first test will be twenty five millimetres a second at

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Ninety five percent power, full power basically. It’s done a reasonable job, it’s cut it out,

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but it’s also done a lot of scorching around the outside. And look what the heat has done, it has caused distortion on the edge of the paper.

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Such a thin material. We should be able to rip through this very quickly.

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So let’s put the speed up to one hundred. OHOH. So in case you didn’t see that look.

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Several things seem to have happened here. We’ve got terrible reflection off of something.

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I think it must be off the back of our grid.

Transcript for How to Laser Cut Thin Materials (Cont…)

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So let’s move my supports out the way and we’ll do the same thing again. A-ha!

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So now it’s clean and we don’t have any burn marks.

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So it just shows you, doesn’t it? What

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reflection off of things can do for your cuts, especially on thin materials like this, which are very sensitive.

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Now there is some browning around the edge here if we look. It’s not exactly perfectly clean and is that on the back or the front?

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Well, the front looks reasonably clean when we look around here, and so does the back.

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Although there is just a hint there on the back of some sort of scorch mark just there.

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So maybe high power and high speed is not the right approach for paper.

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I can turn my air assist on or I can regulate it back with this ball valve to just the merest whisper to protect the lens from getting smoked up.

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You can hear how silent things are at the moment, except for that small amount of air that you can hear in the background.

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Let me turn that down a little bit more. There we go. Now you can hardly hear any air at all.

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So let’s just run that cut again. The cut is absolutely silent.

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It just dropped out. I’m going to change the settings on this machine.

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We’re still going to leave it at 100mm a second.

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And now listen very carefully and compare what you hear this time with what you heard last time.

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Can you hear that noise? Listen again. It’s no longer silent.

Transcript for How to Laser Cut Thin Materials (Cont…)

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It’s what I like to call hissy. Listen and hear what I mean.

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Did you hear it? Now, I’m still using 100mm a second.

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But I’m only using 15 percent power. I’m probably down at something like about 20 watts.

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And if we take a look at my ammeter while I’m running that cut. We’ll notice that it probably only goes up to maybe four, six, five milliamps. Four milliamps.

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I mean, that’s half of nothing. So what’s going on?

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The quality of the cut is superb. There’s no smoke marks or damage to it, either on the top or the underneath.

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How am I able to get such a clean cut at such a low power and such a high speed?

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This is a calibration graph for typically this sort of machine.

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And what we’ve got here is 0 to 100 percent power.

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And up here, we’ve got 0 to 90 watts and this happens to be in this machine, about an 80 watt tube.

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And what happens is when you select zero to 100 percent power, you’re actually selecting milliamps, the current that flows through the tube.

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You’re not actually selecting watts. The Watts are related to the milliamps in a very non-linear way.

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It’s all to do with the physics, but it’s not linear. And as you can see here, we get the power coming up in a strange, non-linear fashion.

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And so consequently, we’ve got an 80 watt tube. You might think that 25 percent a quarter of 80 watts would be roughly 20 watts.

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Well, look, here is 25 percent. Power takes us up here to nearly 50 watts, so that’s nowhere near what you might expect.

Transcript for How to Laser Cut Thin Materials (Cont…)

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And 50 percent power 40 watts. Well, 50 percent power is up here, nearly 70 watts.

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So there is totally no sense in looking at watts in terms of percent power.

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You have to understand how your machine works because this scale is not related to Watts, and I can’t stress that enough.

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If we look at this red graph, you’ll see that it drops down to here and stops.

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This might not be exactly the right number that I’ve drawn on this graph, but somewhere down here below, these are millliamps remember, as well.

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And we’ve just seen that at 4 milliamps, we’re getting tremendous power out of this machine.

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We were able to cut the paper at 100 millimeters a second.

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That that just doesn’t make sense because this graph says that there’s virtually no power down here at all.

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What is going on now? The laser tube is something called a gas discharge tube.

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If you’re very old like me, you remember them as valves in radio, in steam radio.

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If you’re younger, you still know what a gas discharge tube is, even if you don’t know.

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I’ll show you that you do know. OK, now hiding under one of my cabinets here in my workshop we’ve got one of these things it’s a fluorescent tube.

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This is a gas discharge tube. And it’s quite an old tube now, and it takes a little bit of time to kick into action.

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Let me just show you. So there we go, Look, it’s glowing at this end here and then all of a sudden “Ping” it jumps into life now that glow at the end there.

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Is something called a ray discharge? It took a little bit of time for that beam to come on completely.

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The same mechanism operates in our gas discharge tube, the laser tube.

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So we’re just going to set up a little demonstration to show you the relationship between this missing bit

Transcript for How to Laser Cut Thin Materials (Cont…)

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of data or this very strange bit of information at the bottom here and the fluorescent tube starter that you’ve just seen.

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I’ve found a very useful job for my cup of coffee.

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I’m going to run this machine and I’m going to fire the laser beam into my cup of coffee, but for safety reasons,

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because firing it down into that coffee, all the energy will be absorbed into my cup.

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So that’s all it’s going to do. OK, so I’ve set the power now to eight percent.

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Technically, that’s almost off the scale, and maybe we shall find that

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we’ve got zero cutting ability. But we can just check that, we’ll just run that program onto my piece of paper there.

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My cup is underneath remember. It’s just about scorching the paper.

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If we look, it’s certainly not cutting through the paper.

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So as near as, damn it, zero power, so this is the output end of the tube.

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And what we’re going to do, we’re going to study what’s happening just here at the cathode.

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Remember, the fluorescent tube? The end of the tube was the bit that lit up first before the whole of the tube illuminated.

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And look, can you see the merest little glow in here?

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So I’m now going to change that to 10 per cent. We’re going to go up in two per cent power steps.

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Now you can see it’s a lot brighter. That length, of the glow has got a little bit longer.

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Now we’re at 12 percent. The glow is traveling further along the tube.

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It’s not all the way along the tube, but you’ll notice how unstable that glow is.

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Now we’ll go to 14. Now we can see the glow is beginning to creep along the tube a bit more.

Transcript for How to Laser Cut Thin Materials (Cont…)

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It’s certainly not all the way along. Now we go to 16 per cent.

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It’s still not a really powerful beam, but it’s getting brighter just here, as you can see.

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And it is beginning to go along the tube a bit.

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Let’s just stop there and you watch when the tube goes out, it’s very, very faint and then it disappears.

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But the whole thing is that this tube, this beam is continuously fluttering.

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If you look, it’s misty. It’s very random in its motion and 22 percent.

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Well the beam is starting to travel along the tube now, but look how fluttery and unstable that beam is.

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It’s nearly along the whole length of the tube now. And this is 24 percent.

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This is 26 percent. No, we’ve still got lots of instability in the beam, even at 26 percent. Now look at 28 percent.

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That beam is completely stable, but the current is still only four milliamps.

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So lets go up to 30 per cent. It’s a pretty stable beam.

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You can hear my cup of coffee crackling away in the front of the machine as the power increases.

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We’re at 30 percent at the moment, and I’m going to drop this down to say 24 percent.

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And you can definitely see the fluttery nature of the beam, the difference between 24 percent and 30 percent.

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OK, now that’s the difference between pre ionization and full ionization.

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This current control is managed by the high voltage power supply.

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But as you saw with that beam, it was very flaky, it was very misty.

Transcript for How to Laser Cut Thin Materials (Cont…)

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It was very wispy. The current flow was effectively out of control.

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And what was actually happening there? We were getting little bursts of current there, very high bursts of current for maybe a few nanoseconds.

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So effectively, we may well have more power down here than we have up here.

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But this is stable power and down here, it’s incredibly high and totally random frequency and amount of power.

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So we’ve got this very weird power zone down at the bottom here.

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And because, as I said, it’s very, very high power. When we get weak material, thin, weak material like paper,

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these very high power pulses are able to burst through our paper and do damage without any burning. It just instantly evaporates

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the paper and the carbon. Now it doesn’t work when you’re starting to do things like thick or three millimetre thick, acrylic or 3mm thick.

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And the way that you can tell is you can hear this hissy mode and the hissy mode is,

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in fact, this very high frequency, pulsing hitting the paper and causing damage.

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As I say, cutting is quite a complex process.

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And this pre ionization zone is also the zone that we tend to use for things like photo engraving, which I’ve probably mentioned before.

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This pulsing mode is a very powerful mode. So really,

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what you need to do is work out on your tube, identify between what percentage and what percentage

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you get this pre ionization and then use towards the top end of the zone that you identify.

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We’ve identified 30 as being stable and 25 is definitely being hissy.

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And that’s where I would tend to set the optimum cutting if I wanted to do paper or card.

Transcript for How to Laser Cut Thin Materials (Cont…)

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So here I’ve got some white card. This is really about probably half millimetre thick,

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and the reason why it’s shiny and smooth is because it’s got a lot of Kaolin or China cray built into the paper that makes it stiff and smooth.

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Now, China clay is a mineral material which doesn’t burn,

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and this does not have the same burn properties as that paper that you just saw. We’re already set to 30 percent.

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We’ll just run a test square. And we’ve done that at 100 mm a second.

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And it’s a thick up paper. And so consequently, it might not drop out.

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I think you can see how smoky it is around the cuts.

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As you can see, 30 percent power hasn’t really cut out.

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It’s got those Ferrari effects that I was telling you about look dark in the corner, but missing along the center.

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So we’re going to leave the head at exactly the same position. And all I’m going to do now is to change the power from 30 down to 24, lower power

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technically. It didn’t cut at 30, remember?

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So what’s it going to do at 24, it must by default cut even worse.

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So listen and watch.

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And sure enough, a little less power means we’ve actually not made it quite as dark in the center of the cut.

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But what we have done is probably got a little bit further into the cut.

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Away from the corners, we’ve now dropped the speed from 100 to 80, very noisy, and that is hanging in by the merest thread.

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So we drop the speed to 70. And there we go.

Transcript for How to Laser Cut Thin Materials (Cont…)

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It drops out completely, OK? On each of the corners where the beam runs away from the corner, it’s leaving a little trail behind it.

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That’s the smoking effect of this Kaolin that’s in this card. That’s why I don’t use this card.

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I bought this card originally because I thought it was an amazing, lovely piece of material to make Christmas cards or birthday cards with.

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No, it’s rubbish at actually cutting,

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as you can see. This is a creamy, much softer.

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This is not as dressed with Kaolin as the other one.

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There may be a very small amount in it, but it’s negligible and this time – the cuts are virtually clean.

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Although I use this for cards, what I normally do use it the wrong way round.

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In other words, I will reverse my images and cut them from the back.

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Now, here’s what I’ve found is one of the best materials for cutting when I do my cards.

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It’s a fairly thick 200 gram, but it’s you can see, it’s a watercolour paper and it’s a bit like a very,

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very thick cartridge paper that’s probably again half a millimeter thick.

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But it’s got none of the sort of additives in it. It’s a beautifully flat piece of paper, cuts without a mark.

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And here we are, cutting at 170 millimetres a second.

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This is a sort of job that I would do with this setting.

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Now, I don’t need to turn my air assist on, but I normally turn it on so that, let’s just stop that, I normally turn it on so that any of the pieces blow away.

Transcript for How to Laser Cut Thin Materials (Cont…)

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It’s not for any other reason than just blowing the pieces cleanly out the bottom of the work.

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I transferred this file from my other machine.

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So it’s totally the wrong way round because the datum on this machine is the opposite corner to the other machine.

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But really, this is just a demonstration to show you the sort of thing that you can do with this sort of mode.

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So I’m not going to I’m not going to take that through to conclusion,

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but that’s just an idea of the sort of stuff you can do. Now that was done at 100 millimetres a second.

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Remember, don’t leave debris behind because debris can catch fire, and this time we’ll run it at 200mm a second.

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Why would this work at 200mm a second?

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Well, remember the Ferrari effect when these dimensions are very small, it will never get up to 200 millimetres a second.

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It will only ever get up to 200 millimetres a second on the long, thin strokes,

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but it will achieve the fastest possible cutting speeds it can on those small cuts.

Transcript for How to Laser Cut Thin Materials (Cont…)

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{hissing sound of laser cutter}.

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Large things like this where it’s not going to exceed the damage threshold as I might not be cutting on these very large outer shapes.

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Just about, just about, so 200mm a second is really too fast for that job because it’s not too fast for these,

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but it’s too fast for these straights if you like where you do get up to 200 miles an hour.

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We could reclaim this because it’s basically perforated.

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So I hope you can see that although it hasn’t pierced through completely, it’s actually perforated because of the randomness of the high power pulses.

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Some of it is perforated through. So that’s how we can actually still,

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effectively reclaim that. With the right material and an understanding of what the right settings are.

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You can do some really nice work with thin card and thin materials.

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Two things first of all. Here I’ve got some white card, which is basically what they use for making beer mats.

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It’s a very soft white card, which is basically almost like grainless wood because it is just wood pulp.

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There’s no China Clay or anything in this and I often use this for making cardboard models, which is what we’re going to do today.

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You will notice that I’ve got this stuff on here that I am not very keen on because it normally marks the back of your product.

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There are times, like today, when you can use it with almost zero effect on the back of your product.

Transcript for How to Laser Cut Thin Materials (Cont…)

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If you’re using this pre ionization or hissy mode, you will find that it has virtually no effect on the back of the product.

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I can be lazy because when you see what I’m going to cut out of this piece of paper, it would take me quite a long time to put all the bridges in.

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That would allow me to lift this up, put it on some pins or my strips and prevent the parts from falling out.

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Because if parts fall out, then it’s possible that you’ll get burn marks.

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If the parts overlap, the next cut. So I’ve got this machine set up and what I’ve done, I’ve put my zero point right on the corner of the paper

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there. Now I can check that because all I’ve got to do is go {pulse} and you can see that a little teeny weeny white dot of

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light is right in the corner of the paper. That tells me that I’ve got the correct zero or origin starting point.

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Now I need to put some extraction on for this. This happens to be a nice flat card.

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Sometimes you may well find if you turn it the wrong way, the corners might stick up.

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So make sure that the sticky up corners are down.

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And then there’s a fair chance that the middle will get pulled down by the vacuum that’s underneath here.

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We’ve got most of our air drawing through here. So what we can do, we can improve the suction at this point here by blocking off most of the air.

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So now this card is being very gently pulled down by the vacuum.

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OK, well, we’re going to turn some air on now. So we’ve got air assist on this because we’re cutting.

Transcript for How to Laser Cut Thin Materials (Cont…)

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I’m running this at 35mm/s, but I’m also running at only 25 per cent, which is towards the top end of my pre ionization mode.

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If you remember. Even though this is one point one millimetres thick.

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We’re running at about four milliamps. This is not a continuous cut.

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This is like a perforated cut. You’ve got very high power, for very, very short intervals here,

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which means we’re able to do a lot of damage without doing a huge amount of burning to the product.

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We’re only just using the central power of the laser beam itself, not the outer intensity, low intensity scorching parts of the beam.

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So as you can see, this would be a bit of a challenge.

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I’d have to go round and bridge every one of these pieces, but hopefully now if I’ve done this right.

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And if we take a look at the back, which is the important bit, just a few odd scorch marks here and there,

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but nothing that’s going to cause any real damage to the product, as you can see. Now, these parts are numbered.

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I’ve got another sheet I’ve got to cut. We’ll start in the middle at eight, and we put that through there.

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And we put seven on the back of six, five and five.

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Put that on there like that, and there we’ve got the start of that bird.

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And we’ve got the tail. So that’s the beginning of our Model Bird. We’ll just go and make the other parts of the wings.

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So we’ve got one,

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two and three, which will fit on onto here.

Transcript for How to Laser Cut Thin Materials (Cont…)

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So I think that five goes in front of four and I think four fits behind it and just literally pushes in there to lock everything in.

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And one and there’s our little model bird, so there’s all sorts of things you can do with this machine.

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This was originally designed for two or three millimeter thick material,

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so I had to, I’ve had to go round and modify all the slots and grooves to make things fit.

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This is quite thick card at one millimetre thick, or 1.1 millimetre thick.

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And I’m still catching it with pre ionization power.

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Now I will explain in the next session why I’ve done this little demonstration

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with card, and why we started off with the easy jobs cutting thin paper and card.

Transcript for How to Laser Cut Thin Materials