The Fiber Laser Learning Lab Series with Russ Sadler
In this Series, Lotus Laser have lent Russ a MOPA 20 watt fiber laser to “play with”. Although Russ has a moderate understanding of laser technology (his words) and how constant power glass tube systems work, pulsing fiber laser marking machines are shrouded in a deeper mystery than the glass tube machines.
They have been designed for high speed marking and the technology has been well tried and proven. There are limited “tricks” that the pulsing laser technology can perform. You enter predefined parameters for each marking “trick” you wish the machine to deliver , then stand back in amazement. Most correspondents tell Russ that they have bought their machine direct from China and received a machine and EZCAD software, preloaded with a few default parameters. No other instructions beyond the EZCAD manual are forthcoming.
Russ states “I am neither a teacher or expert in this field so you join me in my learning adventure with the warning that I have a simple but inquisitive mind and will probably make mistakes on my way to discovering the truth. I WILL oversimplify and maybe distort the scientific detail in my quest to build a simple picture of why and how this technology works. I am not trying to reverse engineer anything, just to break through the seemingly impenetrable ‘techno cotton wool’ that surrounds this amazing piece of science.”
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Transcript for Fiber Laser Marking: Is this Fools Gold?
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0:00 welcome to another fiber laser learning lab
0:02 that last time we built a foundation on laser fiber
0:06 the color gold today we’re going to try
0:10 and consolidate that foundation a little
0:12 bit more because we can’t really build
0:15 up all the walls of the house until
0:16 we’ve got a good foundation and there
0:20 are a couple of big questions that I
0:23 would like to answer before I go forward
0:25 I’ve heard that there are three major
0:27 problems with putting color on to
0:30 stainless steel there’s a fairly narrow
0:32 range of parameters for each color well
0:35 I think last time we discovered that
0:37 there was a very wide range of
0:39 opportunity for gold now I only tried it
0:45 for nanosecond pulses but within that
0:47 four nanosecond pulse there was a huge
0:50 range of possibilities that existed for
0:52 finding gold but I want to look at the
0:54 other possible problems today as well
0:56 one of them is the thickness or the if
1:00 you like the thermal conductivity of the
1:02 material which will pull heat away from
1:04 the actual work surface and it will
1:07 change the color so unwarned and
1:09 unrelated to that thermal conductivity
1:12 is air temperature in other words if
1:15 it’s a hot environment you will get
1:17 different color results to have it’s a
1:19 cool environment so we’re going to test
1:22 the stability of the Gold’s that I found
1:24 was it fool’s gold or is it the real
1:27 thing that will resist changes of
1:30 temperature and changes of thermal
1:32 conductivity in the material as we saw
1:34 last time there are many types of gold
1:38 those that are gold but don’t show up
1:41 only in a certain light and there are
1:45 those sorts of gold here and here which
1:48 are pretty good at being viewed in all
1:52 sorts of lighting conditions now these
1:54 are the goals that I want to look at
1:56 today I’ve searched through the color
1:58 swatch that I produce last time and
2:00 identified or highlighted here those
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
2:03 colors that were sparkling six or seven
2:07 of them which are what I call good
2:11 quality gold what I want to find out is
2:13 are there
2:13 any common factors that give us some
2:15 clues as to what produces what type of
2:18 gold I think the answer is yes there’s a
2:21 bit of an odd one there at twelve
2:23 hundred and fifty millimeters a second
2:24 but most of the sparkly ones if you
2:26 notice are up here in the sixteen
2:28 hundred to two thousand millimeters a
2:30 second range and then we start taking a
2:34 look at the gold we had a light gold and
2:37 then we had the slightly coppery colored
2:39 what I would call rose gold so we’ve got
2:42 four three and two point five which
2:44 produces light gold and if you remember
2:47 when we looked at the pulse per square
2:50 millimeter density we’ve got numbers
2:53 here which are in that which are a
2:54 hundred K now when we went to rose gold
2:58 the parameters have tightened up quite a
3:01 bit although we had fifteen ninety seven
3:03 there that’s basically the same as 1600
3:05 and they’re both the same so you would
3:07 expect those two to be the same but then
3:09 we’ve got this one here at two thousand
3:11 with a slightly smaller pitch one point
3:14 six microns and that gave rose gold as
3:16 well and again when we looked at the
3:18 pulses per square millimeter these are
3:20 in the hundred and fifty six K so there
3:22 appears to be a color difference that we
3:25 can identify from pixels per square
3:27 millimeter and tie that in with the
3:29 microns that we’re using it gets us a
3:32 nice rose gold color so we’re gonna
3:34 start off today by just reproducing this
3:37 result here which should be a nice rose
3:40 gold okay so we’ve got a nice solid gold
3:43 there okay so the first test I’m going
3:46 to carry out is using my thermocouple
3:48 here my k-type thermocouple which is
3:51 sitting directly under the heated area
3:54 now
3:58 this will just basically check the
4:00 thermal conductivity of the heat zone
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
4:03 through this very thin point five or 0.7
4:06 thick stainless steel so probably my
4:09 hand heat has pushed the temperature up
4:11 a little bit the air temperature in here
4:13 is around about probably 10 degrees C so
4:16 I’m a few degrees higher than the
4:18 ambient but let’s not get too concerned
4:21 about that
4:29 and hey you saw what the temperature
4:31 went up to 70 degrees C okay so let’s
4:36 turn this little cold workshop into
4:38 summer should we turn this piece of
4:41 metal into something about 40 degrees C
4:45 it’s a pretty
4:52 there we go one warm summer’s day
5:05 warder 65 color change what do you think
5:14 so there’s myth number two blown out the
5:16 water it’s not very temperature
5:18 sensitive at all
5:19 let’s go myth number three which is
5:23 thickness of material now haven’t got
5:25 any really thick stainless steel but for
5:27 the purpose of this very very small test
5:29 we’ve gone from 0.5 to something like
5:32 about 1.6 so we’re more than three times
5:35 the thickness and what I’m going to do
5:37 I’m going to do the test right in the
5:38 middle right in the middle of the piece
5:40 of material so I’ve got the maximum
5:42 amount of heat being sucked away this is
5:44 basically the heat being pulled away
5:46 from the surface by a much larger
5:48 thermal mass so let’s see whether this
5:51 has an effect on the color that I’m
5:53 producing it’s also a mechanically
5:55 polished stainless steel this time as
5:58 opposed to a piece of bright annealed
6:00 maybe slightly redder than these first
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
6:03 two so it is possible that there is some
6:06 small degree of variation with
6:10 temperature or with heat sinking so
6:14 we’re not going to dismiss it completely
6:17 but what I would say is it looks as
6:19 though it’s fairly resilient to the two
6:21 extremes that I’ve just tested so it
6:24 takes my fear away from the possibility
6:27 that I may have discovered fool’s gold
6:30 now I think it’s pretty real and that we
6:33 can work with general workshop
6:35 parameters and not worry too much about
6:37 the color and we have just shown that at
6:39 2 microns it’s a pretty durable color
6:43 resisting both heat sinking and
6:46 temperature rise but what these results
6:50 seem to indicate sparkle over here and
6:54 color over here because here we’ve got
6:58 the first four results between four
7:00 three and two and a half giving us a
7:02 light gold and then we’ve got these
7:05 second three results here which are
7:08 giving us a rose gold two and 1.6 micron
7:13 pitch so the indication here is that if
7:15 we go from say
7:17 – which is what we’ve seen our nice rose
7:20 gold s 2.05 in other words half a micron
7:26 pitch that’s a fairly significant change
7:28 in the heating effect that we’re going
7:30 to see into the material are we going to
7:33 push this rose gold towards a purple or
7:35 a moe let’s give it a try that’s a
7:38 pretty nice powder blue sparkly powder
7:44 blue
7:44 so my first shot will be to calculate
7:47 quickly how many pulses per square
7:49 millimeter it took to achieve that and
7:52 then we’ll try a few more variables to
7:56 see whether we can repeat that color
7:57 with different parameters I’ve just
8:00 calculated post density for powder blue
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
8:02 and it’s six hundred twenty-five
8:04 thousand so I’ve done a quick
8:06 calculation and to check the extremes of
8:09 what we found before for spark cleanness
8:11 roughly two thousand and twelve hundred
8:14 the pitch becomes naught point four
8:17 microns and naught point six six microns
8:20 we’ll try those two numbers and see
8:22 whether we can replicate powder blue now
8:25 that is weird because that’s sixteen
8:28 hundred millimeters a second half a
8:31 micron two thousand millimeters a second
8:34 point four of our on twelve hundred
8:38 millimeters a second point six sixth of
8:41 a micron a thousand millimeters a second
8:44 point eighth of a micron nine hundred
8:48 millimeters a second twenty nine of a
8:51 micron and eight hundred millimeters a
8:54 second one micron the rule seems to hold
8:58 up except that one there’s nothing wrong
9:01 with my calculations these are all done
9:03 with exactly the same calculation in a
9:05 spreadsheet I really don’t understand
9:07 why that should be different the
9:09 principle involved here is very simple
9:11 we’ve got exactly the same number of
9:14 pulses per square millimeter which
9:17 technically means we should have exactly
9:20 the same heating effect per square
9:22 millimeter the only difference is we’ve
9:25 changed the relationship between the
9:28 pulses across
9:29 and the lines down in general it looks
9:33 as though it doesn’t make any difference
9:35 but in this particular instance for some
9:37 strange reason it does
9:40 that’s a bluey green that’s a nice
9:41 powdery blue I suppose and these are I
9:45 suppose edging towards a green rather
9:48 than a blue I can see clearly that that
9:51 one has got a smoother effect to it as
9:55 we decrease the speed we’re putting more
9:57 pulses in in the horizontal direction
9:59 and we’re producing a smoother effect it
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
10:02 would appear that the roughness or the
10:04 texture on the surface comes from
10:06 running at the higher speeds as I
10:08 anticipated before I mean to get blue
10:10 we’ve got actually got to drive right
10:12 through this color range here to get
10:15 towards the hotter part of the spectrum
10:18 and obviously by closing up the pitch
10:20 we’re putting more heat into the
10:22 material I mean logically it does make
10:24 sense that I should move from here to
10:27 blue although I didn’t didn’t think that
10:30 it was going to be as Extreme as that I
10:31 thought it would move from there from
10:34 that to rate first as we start moving in
10:36 towards the hot razón we won’t know
10:38 until we really go and have a look at
10:39 these under the microscope okay so
10:42 here’s a puzzling image it’s a sort of a
10:44 a purpley gold so that was when we
10:48 changed to say point five five look a
10:53 half a micron and there’s no apparent
10:57 difference so let’s go down half a
11:00 micron it looks like the same picture
11:02 because that’s what the color is on the
11:04 surface it’s it’s exactly the same
11:06 colour when you look at it in normal
11:08 light okay so let’s go back to this
11:12 image which is the starting image and
11:15 this time instead of changing the pitch
11:18 we’re going to reduce the speed to 1900
11:21 which means we’re going to reduce the
11:23 number of pulses in this horizontal
11:25 direction we’re giving a little less
11:28 mode and a little more blue so now we
11:32 reduce it to 1800 though we’re getting a
11:36 lot more blue and a lot less pink
11:39 although the yellow hasn’t changed very
11:40 much
11:41 so now we reduce it to 1600 a little
11:44 less pink we’ve got some green coming in
11:47 a bit now but it’s still rough as you
11:51 could see from the texture now we’re at
11:53 1600 and we’ve virtually lost all the
11:56 yellow and we’re just in two shades of
11:58 blue and green now and sure enough the
12:01 color is coming out as a very nice blue
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
12:03 now we’re at 1500 still a nice sparkly
12:07 texture more green less blue no yellow
12:12 now we’re going out to 1400 ah now look
12:16 what’s happening now 1400 can you see
12:20 all these sort of blotches coming in and
12:24 these blobs we’re getting much more of a
12:28 flatter surface now this is what this
12:30 indicating although we’ve still got some
12:32 spark cleanness in there we’ve got areas
12:35 where the surface is basically flat and
12:39 now we come down to the final test which
12:42 is 1,300 still got a moderately rough
12:45 surface there it is sparkly now what you
12:50 must remember is there is no green in
12:53 these temporary colors so these colors
12:59 that we’re seeing here there must be a
13:01 combination of light rays which are
13:03 creating colors that are not really
13:07 there and these are the colors that we
13:09 can see at high magnification once they
13:13 get drawn away and get to your eye
13:15 these colors don’t exist what you see is
13:18 an amalgam of these colors I haven’t
13:20 done the calculations at the moment to
13:22 see what degree of variation we’ve got
13:24 in the pulses per square millimeter
13:26 count across this range of colors I will
13:30 go and do that shortly
13:31 we’ve just come across coppery gold
13:34 again okay so let’s run again with two
13:39 microns or I have to say it’s a bit
13:42 difficult to say what that color is it’s
13:45 it’s almost just a blank brown it’s
13:49 certainly not sparkly
13:52 so I think we’ll try and put some
13:53 Sparkle into that by increasing the
13:55 speed which is the formula for spark
13:58 leanness so far we’ll push the speed up
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
14:03 to 1600
14:04 okay now by pushing the speed up we’ve
14:09 decreased the heat and we’ve got our
14:14 copper color back again which is
14:17 virtually the same as these two here
14:20 let’s see if we can lighten the gold by
14:22 putting the speed up leaving the picture
14:25 2 microns well yeah we’ve gone lighter
14:28 and we’ve also gone spark Leah and those
14:32 two there were done with a for
14:35 nanosecond pulse but this time we’ve got
14:37 our nice coppery gold rose gold at 6
14:42 milliseconds as opposed to 4 nanoseconds
14:44 so I wonder what happens if we go two
14:48 thousand and something like point five
14:54 point five of the micron well the answer
15:00 is it gets us back to this strange brown
15:03 color that we had here it’s not sparkly
15:07 it’s it’s a dull brown so I’m not
15:11 interested in that really I mean it’s
15:12 obviously part of the color spectrum
15:14 it’s going to take a long time to
15:15 produce it at point zero at point five
15:19 of a micron so I’m trying to see if I
15:21 can get nice color and relatively high
15:25 speed let’s jump up to another power
15:27 band let’s try eight nanoseconds which
15:31 will be at two hundred and fifty
15:32 kilohertz and we’ll start off again what
15:36 should we say 1200 let’s say 8 microns
15:41 well we got a a sparkly coffee color
15:46 there that’s nearly gold but not quite
15:48 it’s like a a white coffee and we’ll do
15:53 two things we’ll first of all put the
15:55 speed up to 2000 and see what happens
15:59 so we’re decreasing the power which
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
16:01 means we might move too
16:03 – sparkly gold again yeah
16:06 that’s actually not bad that’s even more
16:10 that’s a bit of a copy but this one or
16:12 some of these here and these down here
16:16 so we found rose gold again at another
16:20 set of parameters yeah we’ll take the
16:23 vertical lines down to 6 micron 6 micron
16:26 spacing so we’re adding some heat now
16:31 which might drive us towards blue yeah
16:36 there’s definitely a blue tinge in there
16:37 it’s no longer copper so let’s push it
16:41 one more down to 4 microns which
16:46 increases the power permit per square
16:48 millimeter and that’s done something
16:50 really weird we’ve got a sort of a green
16:54 on the ends and a gold in the middle now
16:58 that must create that must be created by
17:00 some really weirds heating effects
17:02 because we are scanning like this so it
17:09 means we’re getting double a heating
17:11 effect at each end like that hot there
17:18 turn round hot there so this is very hot
17:21 this area and then as we scan across
17:23 this middle area here we’ve got a cooler
17:26 zone and that’s exactly what that
17:31 pattern there seems to be showing I’m
17:32 sure you could see that in this light
17:34 let’s just zoom in on that
17:35 there we go look you can see that
17:37 clearly there now gold in the middle and
17:39 green at the ends so does that mean if I
17:42 go down to 2 microns I might be finding
17:45 a sort of a peppermint green well the
17:48 answer to that question is no we’ve
17:50 we’ve gone to a very nice coffee color a
17:55 very nice sort of a but you’ll notice
17:58 something else in here as well look
18:00 we’ve got the same effect that we had
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
18:02 here we’ve got the ends which are a
18:06 different color to the center well
18:10 although this is very interesting and
18:11 we’re getting further and further away
18:13 from gold but we are
18:15 effectively trying to see if there are
18:18 any patterns in the data that we’re
18:21 getting I’m still trying to see whether
18:23 or not there are any rules for colors
18:26 and this one here again it’s a color
18:30 that’s at two microns
18:32 that’s a nice coincidence that we’ve
18:34 come across many times before and at two
18:38 thousand millimeters a second with a
18:40 different pulse now we came across this
18:44 lovely but very positive meter brown and
18:48 if we take a look here look at the
18:50 texture of the surface we’ve got all
18:52 these little blobs on the surface here
18:54 little raised portions so let me just
18:57 bring one of them into clear focus and
19:02 that’s 41 microns let’s just see how
19:07 that relates to the background right
19:09 there and that’s 39 38 so that’s about a
19:16 three micron difference in depth which
19:22 is substantially more than the thickness
19:25 of the film itself so we must be
19:27 disrupting the surface of the metal to
19:30 make that amount of distortion so I did
19:34 the calculations for that mid Brown and
19:35 found it was sixty-two thousand five
19:37 hundred pulses per square millimeter now
19:41 I changed from two thousand at two
19:45 microns to one thousand at four microns
19:50 okay now that looks like a modern
19:54 artwork but even though that is
19:59 different it still comes out looking the
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
20:03 same mat made of brown now is a huge
20:08 change in terms of the speed going from
20:11 two thousand two one thousand and the
20:14 line width from two microns to four
20:17 microns we get no apparent change of
20:19 color even though you can see that it is
20:22 significantly different down at this
20:24 level so here we are at three microns
20:27 and thirteen hundred and thirty three
20:30 millimeters a second again that we’ve
20:33 got these little raised blobs here but
20:36 they’re not as pronounced as they were
20:37 in the first one but we still got lots
20:39 of yellow in the background and we’ve
20:42 still got the same apparent meat brown
20:45 despite this different slightly
20:46 different surface texture so we up the
20:50 speed again to sixteen hundred
20:51 millimeters a second and dropped the
20:54 pitching to 2.5 microns
20:57 we’ve got blocks here with modes and
21:00 browns and we’ve got yellow in the
21:03 background and gold and red the net
21:07 result of this is still a meat brown so
21:12 we’ve got a very very wide range of
21:15 opportunity to get this lovely meat
21:18 Brown blank color I think I’m going to
21:21 have to produce a separate swatch with a
21:23 record of each one of these colors on it
21:26 so that we can see what our progress is
21:28 and what the lovely range of colors that
21:31 I should be able to put onto this
21:33 palette so although I’ve been supplied
21:35 with a recipe of colors from Lotus laser
21:39 I have to say I’ve not opened the files
21:41 at all I’m going my own way at finding
21:45 colors with my method because I’m
21:48 looking for a different sort of color
21:50 that normally you see on these pallets
21:53 now I’m feeling fairly happy with that
21:56 swatch because even in this white LED
21:59 light we’ve got some nice colors this is
Transcript for Fiber Laser Marking: Is this Fools Gold? (Cont…)
22:03 not daylight this is this is a thing
22:05 that was defeating other systems that
22:09 should be green those should be I think
22:15 that’s pink and that one’s gold
22:19 that one’s gold I think these are
22:24 supposed to be a pub a purple and I
22:27 think these are silver this one is
22:29 supposed to be like a sky-blue and it’s
22:32 come out as a sort of a bit of a grey
22:33 here the color recipe that I’ve been
22:36 given is nothing like the recipe that
22:40 I’m
22:40 yet here no we accidentally came across
22:45 this setting doesn’t look particularly
22:48 different to some of the golds that
22:50 we’ve seen you know it’s it’s got like
22:53 pieces in it yellow pieces a little bit
22:56 of pink in it some blue what color do
23:00 you think that’s gonna come out to look
23:02 at that isn’t that beautiful
23:04 cuz look I can get that I can get the
23:07 top of that lock into focus now let’s
23:10 call that 90 well the bottom is just
23:13 here somewhere I’ll just bring that
23:15 little bit of brown into focus there and
23:18 that’s only 88 so that’s only 2 microns
23:22 difference what color would you think
23:24 that that is going to come out at okay
23:32 you’ve had enough time the answer is
23:34 matte black don’t ask me why just
23:42 mention it in your prayers tonight see
23:44 if you get an answer so thanks again for
23:48 your time and patience and I’ll catch up
23:50 we’re doing the next session
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