35 – Thermal Laser Marking Stainless Steel (25:11)

The Lightblade Learning Lab with Russ Sadler

The Lightblade Learning Lab is a series of videos that Russ did for Thinklaser Limited based on using the Lightblade 4060 Laser Cutting and Engraving Machine. Thinklasers Lightblade 4060 has a 400 x 600mm bed size and was supplied with a 60W EFR laser tube. In this session, Russ uses his CO2 Laser machine for the purpose of Thermal Laser Marking Stainless Steel.

Thermal Laser Marking Stainless Steel
Thermal Laser Marking Stainless Steel

Contents

  • Looking at the example of marking a tall, stainless steel key press.
  • Don’t laser raw stainless steel – it may damage the lens.
  • A beam of light hitting a surface and changing to heat energy.
  • Reflective materials versus non-reflective materials.
  • Effect of focusing the beam.
  • Reflections causing damage to the lens.
  • Thermark products from the US for coating metals and the way they work.
  • DM-90 – a cheaper alternative (Molybdenum Disulphide MoS2) for placing black letters on stainless steel.
    • Shake the can thoroughly and apply.
    • Drying with a hot air gun.
  • Testing the marking – outline lettering and then full letters.
  • Use of acetone to clean off the excess DM-90.
  • Scratch-testing the resulting letters.
  • Using RDWorks and ensuring that a graphic is lined up with the job properly.
  • Moving the green dot to a different part of the image.
  • Setting the parameters and saving to a memory stick.
  • Putting a long sheet of steel through the machine and out of the back.
  • Setting the sheet square.
  • Creating a program in RDWorks to engrave letters.
  • Discovery that the machine will only pass-through 500mm sheets.

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

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Video Resource Files

Thermark

DM-90

Cermark

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External Resource Links

www.thinklaser.com

www.rdworkslab.com

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Transcript for Thermal Laser Marking Stainless Steel

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0:14Welcome to another Lightblade Learning Lab today we’re going to do a real task

0:21that involves marking of stainless steel now stainless steel can be marked with a

0:29proper metal cutting laser and I have managed to mark stainless steel with one

0:36of these lasers as well but not very successfully and at the risk of damaging

0:41the lens so please don’t do raw stainless steel let me first of all show

0:49you what we’re going to try and do on this piece of metal behind me which is

0:55stainless steel it’s 1,800 millimeters tall and it’s 600 millimeters wide which

1:01is just about the capacity of this machine now I’m hopeful that I’m going

1:07to be able to slide this through the machine because it is a pass-through

1:10machine and I’m going to be able to mark numbers and letters on this grid of

1:16slots that we’ve got here this is basically a key cabinet that

1:21I’ve designed now the bunches of keys are various sizes they can be anything

1:27from the size of my fist here down to just a simple bunch of keys like mine

1:36you can’t have all these keys at the same pitch so I’ve designed some special

1:42hooks that actually fit into these slots in a solid manner we pop them in the

1:49slot and then you just gently tap them down and they then remain

1:56permanently fixed in the slot I say permanently, but you can knock them out. But then

2:02what we need to do is to mark this sheet up, that’s already happened across the top

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

2:07here with a laser a proper metal laser engraver and you’ll see that it’s been

2:12numbered across the top so all these slots just like a spreadsheet I’ve got a

2:16reference to them so it’s ABC down the side and numbers across the top so every

2:22bunch of keys can have its own reference the problem is these numbers in this

2:28light you could just about see them but to be honest they’re not very distinct

2:33when they’re in a dark cupboard what I’ve decided to do is to overwrite these

2:38numbers somewhere else with itched solid black numbers and letters and that’s

2:45what I’m going to show you today now before we start that process we need to

2:49go through a little bit of theory now there are some fundamental things about

2:53the laser beam which in a way I’ve been slightly misleading you about up to now

2:59Our laser beam is a parallel beam of and this is the important thing

3:06sorry I can’t write sideways and all the light is traveling in one direction and

3:14it runs completely parallel it’s what they call a coherent monochromatic light

3:21it is a light beam but it’s invisible I’ve been referring to it up to now as a

3:27beam of heat that’s where I’ve been misleading you because it isn’t really a

3:33beam of heat it is a beam of light and it’s only when that light hits a surface

3:40and gets absorbed into the surface that it turns from one energy form to another

3:48so it turns from light energy to heat energy when it gets absorbed by a

3:55surface if you can understand that simple principle it will give you a much

4:00clearer understanding of how and why the laser beam works when our infrared beam

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

4:06hits a suitable reflective material and most

4:10metals are a reflective material to some degree there are some metals which are

4:16extremely reflective things like silver gold aluminium copper there are other

4:24metals such as this piece of metal that I have here which is a piece of

4:29stainless steel which is about probably 90 to 95% reflective so when we fire

4:37this beam at any organic material such as wood leather card any of those sorts

4:44of materials what happens is the surface of the material absorbs the energy and

4:50therefore it starts to heat up and if you heat it up enough it will burn and

4:56that is the process by which cutting takes place with organic materials now

5:03with acrylic the absorption into the surface creates heat but immediately the

5:10material evaporates it doesn’t burn if you fire it into water water absorbs the

5:18energy within the first probably less than a millimeter and it heats the

5:23surface of the water up so much that it boils and creates steam now you’ve seen

5:28me demonstrating that probably in some of my earlier videos so all I’m doing is

5:32trying to reinforce the fact that this beam is totally innocuous until it gets

5:39absorbed by an absorbing surface so when we looked at creating marks on our piece

5:44of stainless steel we were doing damage to the surface of the stainless steel so

5:50stainless steel melts at about fourteen hundred and fifty degrees C we’re going

5:55to need a lot of heat to cause damage to the surface of our stainless steel and

6:03we’re not going to get that out of a 60 watt parallel beam like this well two

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

6:10things are going to work in our favour first of all the light in this beam is

6:15not uni.. uniformly distributed across it we’ve talked about it before

6:21and we’ve said that the energy distribution in this beam is what they

6:24call Gaussian in other words it looks something like this

6:27where the center of the beam is very intense light and the light dissipates

6:32towards zero as we get further towards the edge of the beam here I’ve got a

6:38lovely little magic pen and it’s a great demonstrator of that principle if we

6:44look at that light there you’ll see that it is very intense in the middle and it

6:48gets weaker and weaker as it goes to the edge well that’s exactly what this beam

6:53of light is doing as well it is not a uniform puddle of energy when I tried to

6:59measure with a thermocouple the temperature in the middle of this beam

7:03here I know that it is more than 1300 degrees C because I’ve melted the

7:09thermocouple and that is in the standard raw beam as I call it but what we would

7:14then do is pass this beam through a lens where it would come down to a very very

7:19small area something that we’ve previously called the spot size a two inch

7:24lens has got a spot size of about naught point one of a millimeter this

7:31concentration of the light becomes greatly amplified and we get very very

7:36high temperatures now at this spot of light because the energy density has

7:41been increased tremendously so now we can do damage to the surface of

7:47stainless steel but of course remember what I said to you, stainless steel is

7:52in fact reflective so whatever you fire at the stainless steel most of it will

7:57be firing back at your lens and this time it will be at a very high

8:01temperature a very high energy density because it’s firing off of a flat

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

8:06surface and so consequently what will happen is it’ll come back up here and

8:10it’s likely to damage the surface of your lens now if I shine my light on

8:15that lens there you can see that little black spot there well look I’ve removed

8:20the coating from the surface of the lens by doing just that reflecting the beam

8:25back onto the lens surface and so that lens is now being completely destroyed

8:29so if I can’t mark the metal surface by firing the laser at it as we do in

8:37most products you know we just fire the laser at it and etches the surface well

8:41we can’t do that with metal because of this reflective property so what we’ve

8:45got to do is adopt a different procedure and the procedure that has normally been

8:50adopted as to buy some expensive chemicals this is a product called CERMARK

8:55this one’s called a metal marking material and this one a glass marking

9:01material and you can normally only get this stuff in the States if you try and

9:05buy in the UK it’s even more expensive because it has to be transported under

9:11very special conditions and those transport conditions hike the price up

9:15even more so from being maybe 10 or 12 pound in the States

9:19it may be real as much as 50 or 60 pounds to buy that same bottle of

9:23material here in the UK now how does this material work well basically you

9:29paint it onto the surface of your steel your stainless steel in particular and

9:33then you fire your laser beam at it as though you’re engraving normally now

9:38although you’ve got a very thin layer of this material sitting on the surface of

9:42your stainless steel this material will absorb all the energy and convert it

9:48into heat and so this material is the thing that heats up and in heating up it

9:55transmits some of its heat quite a lot of its heat into the surface of the

9:59stainless steel underneath and the combination of heating this material on

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

10:03the top surface and the stainless steel beneath causes a bonding action between

10:09some of this material and the stainless steel that’s basically the principle

10:13that we’re going to be using today to mark this stainless steel instead of

10:20this little bottle of material which would have cost me 60 pounds in the UK

10:25I’m going to be using some of this spray which cost me about 10 or 12 pounds now

10:33these two materials are not really the same material but there is sufficient of

10:39this material in this product that it’s probably the active material

10:46we can use this dry film molybdenum disulphide lubricant to actually perform

10:52almost the same task if we get the combination of speed and power correct

10:58we shall get a very good black bond on this surface. Ok, just like any normal spray paint, you have to make sure this

11:08stuff is thoroughly mixed before you spray it and then what we need to do is

11:14just spray the surface fairly liberally

11:28got a reasonably thick coating as you can see and we just get rid of the

11:35excess and there because I’m very impatient I shall use my hot-air gun

11:47that doesn’t need to be rock-hard it just needs to be dry we’ve now got a

11:55nice matte gray surface and that is the surface very thin surface that will more

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

12:03or less 100% absorb the energy from the laser beam I’ve set this up to the

12:09correct focal distance I’ve got a 2-inch lens in there and I’m gonna run this

12:14initially at about 100 millimetres a second but I’ve got maximum power coming

12:20through the lens and what we’ve got to try and do is to develop enough heat in

12:25a single spot to produce this chemical bond if we run too fast we shan’t get

12:31enough heat into a single spot to produce that bond so I may well have to

12:35slow it down if I don’t succeed in the first pass I’m gonna close the lid down

12:41because this stuff produces some rather strange smelling fumes and I’m not sure

12:47what they are so I want to make sure that I will extract them safely into my

12:52Purex unit now for this first attempt I’ve just done outline letters so that

12:58we can see the relative density of the letters themselves okay now for the

13:04second test I’ve rearranged the programme

13:07so I’ve got a small amount of air assist on there so that it doesn’t come up and

13:11damage the lens the fumes don’t come up and damage the lens and you can see 100

13:16millimeters a second is actually quite a leisurely speed we’ve got our letters

13:20that have been hopefully chemically bonded into the surface of the stainless

13:26steel the next process is a bit like magic painting

13:34we need some of this stuff Acetone and today I’m wearing my protective PVC

13:42gloves

13:49we just go for a final cleanup

13:56and there we go you can see how nice and crisp and clean those letters are and

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

14:01now well what I want to show you is this

14:13yeah I’ve scratched the surface but I’ve not taken the letters off those letters

14:19are chemically bonded into that surface okay so I’ve scratched the surface but I

14:25haven’t erased the letter but it produces nice crisp black letters that

14:32was just a test now before I start on this rather large

14:37wide sheet of material I’ve got some slightly narrower sheets here that are

14:44probably only about 300 millimeters wide requires the same type of lettering

14:49different lettering different numbers but I’m going to do this easy one first

14:55because if I make a mistake on here I can turn it over and I can use the other

15:02side

15:05because this sheet is not yet bent when it’s bent there’ll be a front and a back

15:10but at the moment both sides are exactly the same so I have two shots at getting

15:16this job correct to be honest I’m very confident I should

15:20do it in one but there is an escape route that makes me more comfortable now

15:26it’s all very well me showing you what I’m going to do and how I’m going to get

15:31these numbers and letters into exactly the right place against the slots in

15:37both planes well obviously I’m not going to do it all in one go because there’s

15:42no way that I can make the unit pass through the machine but what I’m going

15:47to do now is we go back to RDWorks and I’ll show you how I program these

15:51numbers this is how I’ve imported my sets of numbers as you can see I’ve got

15:57two sets of numbers here well we don’t need both those sets of numbers and I’ve

16:01also shown you the slots that I’ve imported as well so what the first thing

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

16:08I’ll do we’re going to do let’s just say we’re going to do 21 to 29 to start with

16:12I would delete that set there and we’ll work on this set here now the first

16:19thing I need to do is make sure I can I know where I’m going to put my head to

16:24start with the important thing for me to do is to accurately position these

16:28numbers relative to my slots and the way that I plan to do that is to mess around

16:33with this green dot so we’re go into config and system setting and here we’ll

16:41change the position of the green dot which is the start point for the head to

16:45the bottom center, close. Now watch what happens to the green dot now it goes

16:53down to there but look what happens when I remove the slots

17:04so that basically means the head is sitting at the top of the center slot

17:09and that’s where I’ve got to locate the head to get my letters into the correct

17:16position and the reason why I’ve drawn a rectangle around the letters like that is so

17:20that I can put that particular feature onto a different layer and let’s put it

17:24onto a blue layer and on this blue layer up here we’ll set is output no in other

17:33words I don’t want that rectangle to print but I do want the green square on

17:38the center of that rectangle for location and so now what we’ve got to do

17:43is go to the black letters which is the parameters up here is output yes speed

17:50100 is blowing yes scan and max power that’s all we need so now I shall output

17:58that to a memory stick and now we can be a little bit clever save yourself some

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

18:04time by pressing by pressing ctrl + Z several times and there we go we’re back

18:11to our original so now we can delete this one and we can delete these we can

18:26call that

18:29a blue layer and it should already contain the properties that we want just

18:36check output no that’s all we need to worry about all the rest is unimportant

18:42okay and we’ve got our position in the center and now we’ll just check the

18:46black parameters hundred output yes blowing yes scan yes maximum power okay

18:55now we can save that to an output file back to the machine

19:02okay well I’ve set myself up the easy one to deal with which is a set of numbers

19:08right across the middle of the sheet but that means I’ve got to hang one end right

19:13out of the machine and to support it to stop it drooping I’ve had to use one of

19:17my tripods now what I’ve also done is set the table so that it’s completely

19:22level with this and I can pass right through the machine so I’ve removed the

19:28plate on the back so that this material can pass through the machine okay now if

19:33you remember the idea was to line the head up with the top of this slot so

19:39we’ll do that now because that’s where we’ve got to set the origin point what

19:41I’ve also done is I’ve made sure that my sheet is running square to the edge of

19:47the machine set that to 5.5 I’ve got air assist on, we don’t want too much air

19:57because we’re not trying to cool the surface down we basically want to keep

20:01as much heat in the job as we can extraction on and we’re ready to go

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

20:15but now you may think we’re going to do these letters individually but as you

20:19can see I’ve copied a slot with a letter beside it now I don’t need the slot

20:24other than I’m going to use the slot as a means of setting up this rectangle and

20:30the rectangle will then be where I start from in other words I shall start

20:35putting my letter from the top of a slot so to do that what I shall need to do is

20:40first of all where should we start we can start at the end s and work our way

20:47up the sheet yeah let’s do that so I shall remove those slots and I shall

21:00remove those then I come up here to config system setting and I’ll change my

21:08location for The Head now to top right

21:15okay so that’s where my head will start on a slot and then I shall basically

21:23engrave four letters in one program so the first thing we’ve got to do if we

21:30remember is to get rid of the we don’t get rid of it we need it there so we

21:35change it onto a different layer and then we’ll make that blue layer if it’s

21:39probably still there is output no that’s okay that’s good and then P well if we

21:47look at the black letters we should find the black layer it’s still set output

21:55yes engraving at 100 millimetres a second is it blowing yes scanning yes

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

22:02maximum power fine and we’ll have an interval of 0.15 so we can save that to

22:09a Ufile control Z and we’ve got everything back again we can delete that

22:17hold down the shift key and delete those and at the same time we can delete those

22:26slots delete we’ve already got our little

22:31green square at the top right hand corner all we’ve got to do is to mark

22:36the outside shape put it onto a blue layer and hopefully the job is OK

22:42let’s go and do those and here we are with the program working four letters at

22:48a time

22:51that’s not too tedious just got to keep loading the program

23:04okay well now I’m stumped because here we’ve got a 600 wide sheet on a 600 wide

23:12machine which I thought was a 600 millimeter pass through machine it turns

23:17out not to be the case

23:21the aperture at the back is 600 over 600 the bridge

23:28is only 560 and there are pillars in the way that hold up the backplane that

23:36limit you to something around about 500 so in reality this is only a 500 pass

23:43through machine so the maximum you can get is 560 if you were to take the

23:49pillars out that basically means I can’t engrave the letters down the side the

23:54best that I can do is engrave the letters at the top and turn my program

23:59round and run them upside down from the bottom and just run with two sets of

Transcript for Thermal Laser Marking Stainless Steel (Cont…)

24:05numbers well we are managing to do the letters across the top and I’ve now

24:10turned the sheet around and we’re doing the doing the bottom row numbers upside

24:15down as you can see so yeah, we’ve 20% done the second part of the job

24:23there’s a central row there’s a central row of numbers that are missing and all

24:27the letters down the side but hey I’m sure we’ll make do without them because

24:32we’ve got adjacent doors with the numbers on and the letters on as well

24:38well it’s sad that we couldn’t complete the job because as you can see behind me

24:42here this stuff does a very good job of producing black letters very durable

24:50black letters on stainless steel without any fear of damaging your machine well

24:56thanks for your attention I hope that’s been of some interest to your practical

25:01demonstration of something that’s real and not just an experiment and I’ll see

25:06you next session so bye for now

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