Session 37 – Poor Laser Cutting Is Rarely Beam Alignment

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment

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The Concise RDWorks Learning Lab with Russ Sadler.

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Session 37. Poor cutting is rarely due to beam alignment.

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Just get my brain lubricated. Now, in the last session, we talked about cutting.

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We talked about cutting with the tube operating in its rather strange start up mode called pre ionization.

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Now. The problem with cutting is.

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You have to have a tube that is a good tube.

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And today, what we’re going to talk about is what a good tube really means, because without a good tube, you’ll be able to cut,

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but you won’t be able to cut very well. If you want to do what you really expect to do with this machine.

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I’ve got to show you what a good tube really looks like and how you can test it for yourself. Because,

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well, as I will show you in a few moments. There’s a lot of rubbish out there.

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Either supplied with your machine or that you can buy as a replacement for the rubbish that you bought with your machine.

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There’s not much point in putting rubbish back in to replace rubbish that you had there to start with,

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so you need to understand what the laser tube is and how you can test it.

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Now you will have seen this picture before. This is a picture of what a laser beam intensity looks like.

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I mean it’s not a physical drill. It’s the intensity graph, if you like, of the light.

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And I use the word advisedly light because some purists will say that light is something that you can see.

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You can’t see this laser light because it’s above our ability to see it and perceive it.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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But I think it’s still called light, and I think the best way that you can imagine it is this is intensity.

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OK, the more intense the light, the taller this graph, the less intense the light, the shorter this graph.

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You remember how material works with laser light. We’ve got molecules and atoms which are doing this.

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And if we excite them with light, we can make them vibrate faster.

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But the thing is, the more intense, the light not only will we be able to make them exciting faster, but we’ll be able to make them excite faster, quicker.

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So what we’re trying to do when we’re destroying material is vibrate the material up to the point where it flies apart and it gets hot.

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You think you’re heating the material, but really you’re vibrating the material and the vibration is a measure of its temperature.

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The more intense the light that you could throw at the material, the faster the material will heat up.

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So let’s take that to cutting and say the speed at which you can cut material is very dependent upon the intensity profile within your laser beam.

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That’s what we’re going to talk about to start with, because if you don’t have a good intensity profile,

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you will never be able to cut thick material or even cut material fast.

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Now, before we go onto looking at what this really means, I want to point out to you, you have to buy a good tube to get a good cut.

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It doesn’t matter about engraving as much because engraving doesn’t use the high power output of a tube, but cutting does! So for cutting,

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you must have a good quality to a good quality beam.

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This is a good quality tube. Everybody will tell you that, these are the best tubes on the market,

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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so everybody believes. I’m afraid I’m not one of those believers because these

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guys are a little bit roguish in the way in which they approach laser cutting.

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I think I’ve tackled that in another session about how they over specify their tube.

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But there’s an even bigger problem with, not only these guys, but all laser tube manufacturers.

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During its manufacture, this laser tube has to be very, very precisely manufactured in one particular area.

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And that’s this face here, those two faces have to be absolutely parallel and absolutely perpendicular to each other.

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They then stick a mirror on here and a mirror on here.

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Now those mirrors have to face each other absolutely perfectly.

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But if you go back to the way in which the tube works, one of the earlier sessions that we did,

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you realize that there are photons that are flying backwards and forwards down this tube,

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this central tube, and they are bouncing off this mirror and of this mirror and off this mirror and they’re going backwards and forwards.

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And that’s how we get light amplification.

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But of course, if that mirror is very, very slightly out of position, when these rays come back and hit that mirror, they’re not going to bounce off.

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And get back to this mirror. They’re going to bounce off and go somewhere else.

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Now, I’ve exaggerated that.

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We only need the nearest hint of error between these two faces, and we will not get proper amplification.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)When those two faces are perfectly aligned,

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this is the sort of profile of intensity that Reci claim will come from their tube.

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And this is a Gaussian intensity profile.

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This is a 3-D version of what I’ve just drawn on here.

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If you fire this beam, this perfect Gaussian distribution beam into a piece of acrylic.

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Then here is what you should get. Here’s a perfect laser spot on acrylic.

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This is from a different company called SPT, who manufacture super quality tubes.

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Reci produce super quality tubes, but they’re not quite as super as people imagine because they’re over specified,

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and a lot of the tubes that you find out there at the moment are what they call B-grade tubes.

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I call them B-grade tubes. Now, why do I call them B-grade tubes?

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Because look, they’ve got this little QR code on here, which, if you put it into your phone,

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will come back and tell you, Yes, this is a genuine Reci tube. And sure enough, it is.

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It isn’t a fake. This manufacturing process, because it is so sensitive, only yields a certain percentage of A-grade tubes.

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This process, which you cannot correct once the tube is made, it’s made.

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And so what they have to do with any tube that fails their final test.

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And the reason why it will fail their final test is because it doesn’t supply the output quality that’s required.

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It may supply Watts, but Watts of output from here is not a measure of the beam quality.

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And that’s what we’re going to talk about during this session. The quality of the beam and the relationship between this and Watts. Because, you

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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can buy a 150 watt tube that won’t cut 3mm plywood if it’s not the correct shape.

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Here we’ve got some product parameters for the Reci tubes.

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Let’s just take a look at this tube here, for example, which is a W8 tube.

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So it’s got a rated maximum output of 180 watts, and it’s got a nominal working output of 150 watts.

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This is a genuine Reci tube, and it comes from the Reci factory and

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it’s not warranted by Reci. Because it failed to make

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the peak specification of 180 watts.

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Now, because it didn’t make that 180 watts. There’s a problem of some sort. It’s most likely the mirrors being very slightly out of line.

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And so instead of having a nice sharp Gaussian distribution,

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a good intensity where we’ve got high amplification because the beam is going back, absolutely true. If the beam goes back very slightly,

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missing the centre of that mirror and then missing the centre of this mirror.

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We’re going to get a degradation of power. And we’re also definitely going to get a degradation of the shape of the beam.

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And so consequently, if we take a look at this, as I said, it should have made a 180 watts at final test when it was tested against maximum output.

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You are not allowed to use that maximum output, by the way, that is technically just a test specification. 175 watts.

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You see, this particular tube didn’t make the 180 watts that was claimed in the specification.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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It did make one hundred and fifty watts, which is what they promised it would work at nominally.

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Technically, I suppose they’re legally OK to sell this because it did make one hundred and fifty watts,

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which is what they claim. But because it didn’t make 180 watts,

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it’s not necessarily an A-grade tube that they will warrant.

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They will throw that tube away or sell it onto a grey market where machine builders will pick up this tube,

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happily claim that they’re selling you a top quality Reci tube when in fact it’s a B-grade tube,

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that didn’t make the specification and is not warranted by Reci.

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They will sell that tube. But the person that you buy that tube from is the person that’s going to pick up the tab

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if you find something wrong with that tube. Now, I’m not picking on Reci as a particularly bad example.

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All manufacturers will suffer with this manufacturing problem.

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Here we have a company that’s selling a range of laser tubes, anything from 150 to 40.

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Now, it’s rather interesting to note as you work your way down in this product range.

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Those three there, are different to these four here. Now these look like they could be SPT or EFR tubes originally.

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But this company specializes in buying up junk tubes and relabelling them after they’ve tested them to make sure that they work “in some way”.

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Now we don’t know what “in some way” means until you try and cut with it.

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Maybe it will be reasonable. Maybe it will be absolutely junk. I can’t say.

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But what we can say is that this product name, KH Laser guarantees that you’re not buying an A-grade, tube.

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Now there is another tube out there that you might come across, which is labelled up SP laser.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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That’s interesting, SP Laser look at the shape and the size and style of that label as opposed to KH Laser.

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OK, now KH is a factory called Kehui and they manufacture e-Bay machines,

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so they’re very happy to put these substandard tubes into eBay machines and ship them to you.

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Because you’re naive about this technology, you’re buying a machine because you want to get into the technology.

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It’s a jungle out there. This may have sufficient power and capability to do some engraving. To do some serious cutting?

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No. So at some stage, you’re going to have to buy a decent tube.

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Now there is a manufacturer on the market, which I personally trust a great deal. A company called SPT Laser.

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Now they manufacture super quality tubes, and I’ve got one in this machine, one in my other machine over the other side there.

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I’ve got one in the little K40 that I’m working on at the moment. These are top grade tubes that will produce a shot like that.

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I’ll show you how we go about testing that shortly. They have a whole range of tubes, which you can buy from the factory.

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But the most reliable source to buy it from, to be honest, is Cloudray.

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I’m not being paid any money by cloudray to use their name,

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but I have tried to work with Cloudray to make sure that they understand what these B-grade tubes are.

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And that they put in test procedures to make sure that the manufacturers that they deal with are not palming off B-grade tubes to them, to sell to you.

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Anything that you buy from Cloudray can virtually be guaranteed to be an A-grade tube.

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You go and look on the cloud ray website at how they test their tubes, and they test their tubes in many different ways before they ship them to you.

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They’re one of the few companies that I will trust and will point you towards if you want to buy a proper A-grade tube.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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There is a product range that Cloudray sell, which is their own labelled Cloudray tube.

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Now I’m very distrustful of relabelled tubes, as I pointed out to you here.

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I know that Cloudray have got their own relabelling arrangement with SPT and SPT allow them to sell their product under the Cloudray badge.

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These are A-grade products, and they are very competitively priced.

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So you need to go and look at the CR range of metal ended tubes when you come to replace your tube.

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OK, let’s go about showing you how we do a test of what your beam actually is.

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I’ve got a block, a twenty five millimetre block of acrylic here, which I’ve placed in front of mirror three.

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And I’m going to fire the laser beam at this block and we’re going to watch what happens as it burns in.

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Now I’ve got an air assist tube here, which is blowing air,

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and I want to blow it onto the face here, because with the high watts that I’m putting into this face,

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the fumes will catch fire. They will reignite unless I blow them away with this

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air assist. Zero one two three four five six.

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So that took six seconds to burn through there. And I think you’ll see that compares pretty favorably with what the manufacturer promised.

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So bear in mind that is after two mirrors. Now one of the most vulnerable mirrors is this one here.

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Number three, especially for me because I do a lot of messing around without air assist on sometimes.

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So what we’ll do, we’ll compare what comes out of three with what comes out of two.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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There should really be any significant differences, about a three per cent power loss, but it really depends on the shape of the beam more than the power.

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So let’s see what we got. Zero one two three four five six seven. I think that one is slightly bigger than that one.

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And because it’s slightly bigger, it’s probably going to have slightly less penetration, not much difference between them,

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which is good news because that means we’re not getting losses, we’re not getting any loss across Mirror three.

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And that is most important that we’ve got a fairly constant shaped beam across the whole of the machine.

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Now I’m taking you on to another one of my machines. This is an RF driven machine as opposed to a constant current driven machine.

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Still, a CO2 machine, still does exactly the same job.

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This is 30 watts this machine? I’ve got this machine very specially set up at the moment.

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Because I’m doing some experiments with it,

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but it very easily and clearly demonstrates the principle that I want to show you about cutting and the shape of the beam.

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Remember, this was seven seconds to burn through there with 70 watts.

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Zero one, two three four five.

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With less than half the amount of power we got through there in five seconds.

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Can you see the obvious difference there? The size of the beam, the beam diameter is smaller.

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Therefore, we’ve got a much higher light intensity in that beam, because it is a smaller diameter.

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I’ve just done one on its own. I’ve moved the test to the back corner of the machine and we’ll do the same test again.

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Zero one two three four five.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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It’s the same beam, the same power. That’s five seconds, and that’s five seconds.

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So look how I’ve strangled the cutting capacity here.

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But you notice the difference of the beam diameter, the beam diameter is big.

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So it doesn’t cut as deep and I’ve got the same power in that smaller beam.

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I want to go back and look at the session where I spoke about how beam power and intensity are related.

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Let’s go back and have a quick summary. That’s 20 watts, 30, 40, 50, 60, 70 watts. Right now,

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I never want you to lose sight of the fact that I am not teaching you in these sessions how to run your laser machine.

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My goal is to teach you the principles of what lies behind this laser machine.

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You can use those principles to try and understand why your cutting is not correct.

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So I’m going to try and decode those mode burns in a way that I hope everybody will be able to understand.

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Now I’m going to start off at a very simple level. So that you can associate something real with what’s happening here.

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I purposely filled these with W now W could stand for water, it could stand for watts, or it could stand for a volume

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W. Well, in this instance, let’s assume it’s W volume.

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Now, if I tip this volume w into this container here, look what happens.

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It fills it to a much higher level. And all I’ve done is change the size of the container.

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Now, I could turn this into a completely different scenario and say,

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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this is our laser beam and we’ve got a laser beam that happens to be, say, six millimetres diameter.

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And this laser beam here happens to be three millimetres diameter.

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Now, that means that this particular watts.

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And let’s make that equal, say, 50. And that one equal to 50. 50 watts of power in our laser tube. This one

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is a six mm diameter beam. And this one is a three millimetre diameter beam.

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And this here, is intensity.

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Look at the intensity in this one. It’s twice as much as the intensity in this one.

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We got the same volume. We got the same watts. We’ve got a different size beam.

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And because the beam is a different size, we’ve squashed the same watts into a smaller size beam and it’s got a much higher intensity.

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Remember, intensity is the speed at which we can damage material. More intense light, faster damage.

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So instead of water in tubes. Here, we’ve got our intensity varying, but it’s not in a square tube,

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it’s in a Gaussian shape, a mathematical shape called Gaussian distribution.

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So transferring this across to this picture here, here we’ve got our volume under this graph of 50 watts.

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But because we’ve kept the beam size the same, when we put 100 watts into there, what we’re actually doing, to get the same intensity as that beam.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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We’ve actually got a 100 watts.

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So the principle is that if you want to increase the intensity for any given size beam, you have to increase the watts.

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So we go from 10 to 20 to 30, 40, 50, 60, 70, 80 and as we go up and increase the watts, so we increase the intensity.

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And so here’s our 70 watt beam, and it’s doing exactly what this picture shows. A nice, long, thin burn.

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But, look at the diameter. The diameter of these is around about seven or eight millimetres diameter.

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So this is equivalent to this situation here.

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OK, so we’ve managed to burn through. To the same level depth as this one.

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Because what we did, we kept the dimension of burn the same, the depth, the burn the same.

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But what we did was monitor the time. So this one took round about seven seconds to burn this deep.

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This one here, which is smaller, did the same amount of burn in less time.

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But remember, not only was it less time, it was also less power.

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So even though I’ve got these equivalent here in terms of intensity,

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this one still beat this one in terms of time. Because this one took around about five seconds.

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These took around about six or seven seconds.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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OK, so here it clearly shows that the beam diameter, which is dropped to around about three or four millimetres diameter,

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as opposed to seven or eight millimetres diameter.

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So we’ve done the same amount of damage because we’ve got intensity which is capable of doing that damage.

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But that intensity has worked faster on this smaller beam than it has on the bigger beam.

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Plus the fact that this beam is less than half the power of this beam.

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So effectively that smaller beam has actually got an effective intensity, which is probably up here somewhere in relation to this one.

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It’s much more efficient at cutting. Now, this, remember, is exactly the same beam as that one.

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All I did was move the beam, move this to a different position along the beam, where the beam has changed diameter.

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The beam has changed from three millimetres to about six millimetres,

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and all of a sudden we’ve lost cutting ability. Because using this same equation, look, we’ve gone from small back to big and we’ve lost our intensity.

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We’ve gone from an intensity there to an intensity here, half the intensity, and we’ve done a lot less damage.

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So I hope they clearly explains to you why you must have a very clean, sharp, crisp burn. If you don’t have it,

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you will get a stunted, cutting capability like that.

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What does this mean for you? Well, the chances are you’re going to be very disappointed when you test your machine and find that it’s not like that.

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As I explained to you earlier in this session, the chances are that you’ve got a dud tube.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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It might not be terrible, but it might not be anything like this.

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You have two choices you can either say, well, yeah, but by the time I put it through a lens, it’s going to cut.

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So bear in mind that this is the crude unfocused laser beam.

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This point is not a point of focus. This is a point of intense light.

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This is not the same as what you do when you focus a beam down.

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This is what hits your lens, this diameter here, and that diameter is then focused down in a different way to the way in which this burn takes place.

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The lens has only got a certain amplification factor, depending on what lens you’re using.

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They will focus and intensify the light by a different amplification factor, whatever factor it is that you use.

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You will eventually finish up with a burn on your product. If you’ve got a big blunt beam.

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There’s not much intensity there to start with. So you can’t amplify what’s not there.

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You will amplify what’s there and you will be able to cut. That’s why you’re looking for beams that look like this.

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Two things you need to understand about laser tubes. Number one, they do not just fail. Out of my thousands of correspondents.

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I’ve only ever heard of one tube failure that just mechanically collapsed.

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Every other situation that I’ve come across has been people moaning and groaning about the quality of their cut.

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And saying that they can’t get the machine to cut properly. They’ve tried everything.

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Trust me, fiddling with the lens, fiddling with your mirrors, fiddling with your beam alignment will not fix this problem.

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If you’ve got a blunt beam, you’ve got a blunt beam.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment (Cont…)

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And that’s something that most people fail to recognize. They blame themselves because they believe what the manufacturer has told them.

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You’ve got a 50 watt tube. No! You may have 50 watts worth of power, but you’ve got 50 watts worth of power in a blunt beam.

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Remember this beam and that beam are the same power.

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The only difference between them is the diameter. As I just mentioned tubes will not just fall over and die.

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So, yes, I could keel over with a heart attack tomorrow. A tube won’t. A tube

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would do the other thing which I hope I shall do? Well, I’ve already started to grow grey, fat and ugly and slow down.

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And that’s what your tube will do. It will slow down.

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You will know when your tube is beginning to die because whereas you used to be able to cut, say,

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three millimetre birch plywood at 30 mm a second, it’ll drop to twenty five or 20 or 15. Then is the time to go out and buy a new tube.

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You will get time to buy a new tube, the other clues that will tell you that your tube is beginning to die is the colour of the beam.

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The beam itself will start changing from a nice, lovely purplish colour.

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If you watch your tube, you’ll see exactly what I mean. And it will start turning to an almost white beam.

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That means that you virtually depleted all your carbon dioxide in the tube and you changed some of the nitrogen into nitrous oxide.

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Which has a different colour of plasma. So there are two clues that you’re going to look for say, Yeah, my tube is on the way out.

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I better get a new one. I had a brand new tube with my first machine that was already dead.

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It had a white plasma and it wouldn’t cut at all. I didn’t know that because I was naïve.

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I’m not naïve now, and I understand a lot more about the technology and I’m trying to pass that

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experience onto you guys so that you don’t struggle like I did. In the next session,

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we will start putting this lovely beam through different lenses and show you the effect of different lenses and cutting.

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But for this session,

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I think we’ve done enough to hopefully explain to you why it’s so important that you understand what your laser beam intensity profile is.

Transcript for Laser Beam Cutting Performance: Poor Cutting Is Rarely Laser Beam Alignment