06 – The Search for Colour Part 1 (32:08)

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. So let’s learn about Fiber Laser Color Marking.

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.

Fiber laser color marking: steel heat affected zone
Fiber Laser Color Marking: Steel Heat Affected Zone

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 The Search for Colour

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00:00

well welcome to another fiber laser learning lab

00:02

to start off with I’m

00:06

sitting here in my office because it’s

00:08

nice and warm we’ve got quite a lot to

00:10

talk about technically and look at some

00:11

results before we go out and jump on the

00:14

machine and do one or two quick tests

00:17

it’s a very unexcited machine and really

00:21

what we’ve got to do is try and

00:22

understand what it’s doing because it

00:26

does a lot without looking very

00:28

spectacular now what we’ve got here is

00:32

the results of the laser matrix test that I

00:36

carried out last time and what I’ve done

00:38

I’ve broken these down into frequencies

00:40

every one of these patterns on here

00:42

relates to this maximum peak power chart

00:45

that I was given we run from one known a

00:48

second to 350 nanoseconds and there are

00:50

16 of these patterns and we tested all

00:53

these at frequencies which do not

00:55

necessarily tally with this chart as we

00:58

look through these results I will make a

01:00

note roughly of where these maximum

01:02

power numbers tally up with my chart so

01:05

we’ve got nothing that tallies on this

01:07

front sheet here because we’re running

01:09

too fast over a thousand at a thousand

01:12

kilohertz these two you might look like

01:14

black-and-white images trust me these

01:16

are coloured pictures and if we look

01:20

very carefully we can pick up the yellow

01:22

hue that we saw on the screen when we

01:26

looked at some of these results last

01:27

time and there’s definitely yellow hue

01:29

there and there on my results there

01:32

might even be a hint down here at this

01:34

one which is rather strange so when we

01:37

move on now to 900 kilohertz again we’ve

01:43

got these definite yellow hues up here

01:46

at 2 and 4 nanoseconds even though we’re

01:49

not at the frequency for peak power now

01:51

the frequency for peak power is

01:53

appearing on this page it’s supposed to

01:56

be 850 but here we’ve got 800 so we’ve

01:59

got more than enough time to promote all

Transcript for the Search for Fiber Laser Color Marking (Cont…)

02:02

the electrons up to their excited state

02:05

before we put the pulse through and then

02:07

we put them when we put on out to now in

02:09

a second pulse through that’s when we’re

02:11

supposed to get our max

02:12

and we can definitely see here again

02:15

look we’ve got a yellow hue to here and

02:17

a yellow here even at four seconds for

02:19

nanoseconds so yeah we’ve got a

02:23

relationship at the moment where we see

02:26

peak power yellow we’re still seeing

02:30

peak power yellow at two nanoseconds

02:32

even at 700 kilohertz which is not one

02:35

of the preferred numbers 600 here we are

02:38

again definite yellow pattern 500 now

02:45

500 is the peak power for 4 nanoseconds

02:49

and sure enough look at four nanoseconds

02:52

we’ve definitely got that yellow hue and

02:54

maybe at five nanoseconds at six no no

02:57

seconds as well now we come to 400

03:00

kilohertz and there’s not supposed to be

03:03

much happening there at fall killer 400

03:06

kilohertz but look which still got here

03:10

there is a very there is a very dark

03:13

pattern there and it is quite yellow

03:15

here we’ve got a definite yellow pattern

03:18

and some of these here are yellow as

03:21

well so it looks as though we’ve got

03:24

quite a lot of power in this region here

03:27

even at 400 kilohertz and now we drop

03:30

down to 300 kilohertz where we’re

03:32

supposed to come across peak power for 6

03:34

nanoseconds and sure enough look there

03:37

it is bright yellow along with the one

03:40

above it at 4 nanoseconds and even the

03:42

one below at 8 nanoseconds has got a

03:44

brown a yellow hue to it as well and

03:46

even 13 in a second so we’ve got power

03:50

in this region here and here we are at 2

03:53

kilohertz where we’re supposed to

03:55

encounter the max power for 8

03:56

nanoseconds and sure enough there it is

03:58

look yellow there’s yellow at 6

Transcript for the Search for Fiber Laser Color Marking (Cont…)

04:01

nanoseconds but not much else down this

04:04

chart then this one was a little bit of

04:06

a puzzle because we’re supposed to come

04:07

across peak power here for 13 and 20

04:12

nanoseconds but these don’t look

04:14

particularly yellow now between 13 and

04:18

100 nanoseconds will looks as though

04:20

we’re beginning to develop this broader

04:25

d part of the pulse up to now 2 4 6 8

04:29

these have been very sharp peaky poses

04:33

so let’s just see what happens 2:30

04:35

we’ve got no distinct yellowness there

04:38

and here we are again look there’s lots

04:40

of these max powers that fall into this

04:42

category here and really when we look at

04:46

these none of them are really very

04:48

yellow they’ve lost that punch let’s

04:51

call it that that probably still got

04:53

quite a lot of power in them but they

04:55

don’t any longer burn the material and

04:58

then the rest of them which are hundred

05:01

and fifty up to 350 150 up to 350 all of

05:06

them occur on this page here and if we

05:09

take a look it’s rather interesting that

05:11

first of all they’re all lines which is

05:13

rather strange we’ve lost our pattern

05:15

but all these lines have got a slight

05:18

yellow hint to them so we’ve got I think

05:22

heat coming from a different direction

05:24

we’ve got sustained heat this time as

05:28

opposed to peak heat so I think when we

05:34

look at these lower pulses we’ve got to

05:36

consider that we’ve got a different way

05:38

in which we’re heating up the material

05:41

now that’s as low technically as I

05:44

should have gone but of course I went

05:46

lower than that and I’ve gone right the

05:49

way down to 5 kilohertz where basically

05:52

I’ve got rubbish results it’s a bit

05:55

expected because I’ve dropped off the

05:56

bottom of I’ve dropped off the bottom of

05:58

their chart there and serves me right so

06:01

there are interesting correlations in

06:03

those results to these patterns and

06:05

pulse Peaks

06:07

which we will be able to use and refer

06:09

to as we discovered last time one of the

06:13

most important things is try to work out

06:17

how we’re going to get heat down into a

06:19

specific spot now look here’s what we’re

06:23

trying to decode what’s going on here

06:26

and if you remember in the last session

06:30

I did mention to you that even though

06:32

the hole of this center section here

06:34

which finishes up as a blue went

06:37

red-hot

06:38

up at 800 900 degrees see it settled

06:42

back down to this blue when it got to

06:46

something like about 300 degrees C so

06:50

regardless of how high the temperature

06:52

went the oxide layer formed at a certain

06:56

temperature where I suspect the oxide

07:01

layer had reached a maximum thickness

07:03

because regardless of how hot we made it

07:05

we still got blue so the interpretation

07:09

of that is because these are refraction

07:12

colors coming off of the under neath and

07:15

you can see that even though it’s blue

07:19

we can see the image of that little

07:23

pointer on the surface underneath there

07:25

so this blue color is completely

07:29

transparent so our goal is to try and

07:33

find a way of thickening this oxide

07:38

layer that’s just here which is fully

07:40

transparent to a different thickness

07:44

that gives us these colors now as I said

07:49

it does look as though we’ve got a

07:50

maximum thickness we can make it up too

07:52

which gives us this blue and everything

07:55

else in between

07:56

now this clear layer that we’ve got here

07:59

is only somewhere in the region of about

Transcript for the Search for Fiber Laser Color Marking (Cont…)

08:01

two nanometers thick if you can imagine

08:05

such a thickness to billionth of a meter

08:09

and to billionths of a meter maybe only

08:12

10 or 20 depending on the size of the

08:15

atoms 10 or 20 atoms thick this chromium

08:18

oxide layer that’s on the top here and

08:20

is invisible is going to start melting

08:25

at about 3,000 degrees C and it’s going

08:29

to boy off at 4,000 degrees C now

08:34

although this stainless steel will

08:35

actually melt at around about probably

08:37

14 1500 degrees C it’s actually got to

08:42

get up to something in the region of

08:43

about maybe 3,000 degrees C before it

08:46

boils ie vaporizes and disappears

08:50

now if we’re going to engrave this

08:52

material at some stage in the future

08:54

which I believe we can and will then

08:56

we’ve got to actually start vaporizing

08:59

the material underneath but that’s a

09:03

long way off let’s deal with this

09:05

problem to start with now as I said

09:08

we’ve got a very thin layer here and it

09:11

looks as though we’re going to have to

09:13

add heat to it to get these colors but

09:16

we only want to add heat to this layer

09:20

we don’t want to go through that layer

09:22

and damage the material that’s

09:23

underneath so we’ve got our very

09:26

accurate control of temperature to try

09:28

and manipulate the thickness of this

09:30

very thin film that’s on here now we

09:33

started to investigate this problem last

09:35

time when we decided that we got a beam

09:38

which was this size and we could inject

09:44

a small pulse of energy into it and do

09:47

some damage the problem is if we use one

09:51

of these very short pulses here we can

09:56

put something like 10 or 11 kilowatts of

09:59

energy into the peak power of that pulse

Transcript for the Search for Fiber Laser Color Marking (Cont…)

10:01

and we have seen that yes we are able to

10:05

do quite significant damage here because

10:08

we’ve got this yellowing effect so that

10:10

indicates that we are producing quite a

10:12

bit of heat but with this test I was

10:15

only running at 250 millimetres a second

10:18

we were just doing single little pulses

10:21

now there are many strategies that we

10:23

can adopt to improve the heating of a

10:28

particular spot one of the first things

10:31

we can do is to increase the frequency

10:33

of these pulses so that we get the next

10:36

pulse just here and the next pulse just

10:40

here and the next pulse just here so

10:43

that first pulse has been heated several

10:45

times before the pulse has moved off

10:47

into new pastures so by overlapping the

10:51

pulses like this we can build up heat in

10:53

one particular area even though they’re

10:55

very very small amounts of energy and

10:59

heat provided we keep the heat in the

11:01

same spot we can

11:02

probably some damage now that’s one

11:05

strategy that we can adopt I’ve drawn up

11:08

a chart here for each one of my pulses 2

11:12

4 6 8 sound so to give me an idea of the

11:16

number of pulses per millimeter that

11:18

running at different speeds will produce

11:21

four different kilohertz for different

11:24

frequencies we will hit the job eight

11:27

thousand five hundred times per

11:28

millimeter with that pulse so that’s

11:33

what this chart shows and it’s a useful

11:36

chart because it does give us an idea

11:39

that if we’re burning too much with this

11:41

particular setting at a hundred

11:43

millimeters a second we can increase the

11:46

speed and as we increase the speed look

11:48

we can go from eight thousand five

11:50

hundred down to 850 of course we’ve also

11:53

got power as well that we can play with

11:55

so we could leave this at 8,500 pulses

11:59

per second and reduce the power because

Transcript for the Search for Fiber Laser Color Marking (Cont…)

12:01

we’ve got control of percent power as

12:03

well so there’s another variable that we

12:06

can use to play with the amount of power

12:08

that we’re going to dispense now the

12:10

other thing that we can also take a look

12:12

at is this ratio down here now it’s the

12:16

ratio of on to off and basically it’s on

12:21

one and off 588 whatever right so the

12:29

ratio of on to off is very very large

12:31

which means that even though we put a

12:34

little pulse of energy in there and

12:35

heating we’ve got a huge amount of time

12:38

for it to cool or to radiate the heat

12:41

away through adjacent atoms so that’s

12:45

not good and another reason why we need

12:50

to keep the frequency as high as

12:51

possible so that we can keep the heat in

12:55

the same spot almost and I’ll probably

12:57

be doing a test square like this all

13:00

right it’ll only be a small one maybe

13:02

five millimeters square so the first

13:05

thing that we can do is fill in this

13:07

square with pulses at 8500 per

13:11

millimeter and we can go across like

13:14

this with a line

13:16

we can fly back or we can come back with

13:19

another line we can fly back we can come

13:23

back with another line that’s one of the

13:25

options that we’ve got another option

13:27

that we’ve got is to come across and

13:30

then go back come across and go back so

13:35

we can either do single scan like this

13:39

or we can do double scan like this now

13:43

which one of those do you think would be

13:45

a better strategy for keeping the heat

13:48

into the inter into this area that we’re

13:51

working with well my belief is that

13:54

probably it’s this first one we’ve

13:57

heated this line up so here we’ve got t1

Transcript for the Search for Fiber Laser Color Marking (Cont…)

14:01

and by the time we get to the end here

14:03

we’ve got T Max right because t1 is now

14:07

cooled off so if we now jump back to the

14:11

beginning of this line again we will

14:13

have T Max against T 1 and this one will

14:16

be cooling down while this moves along

14:19

so we shall get a much more even flow of

14:21

heat across these lines whereas if we go

14:24

this way like this we’ve got T Max here

14:27

and then we’ll immediately turn round

14:29

and we’ll have 2 T Max’s here and then

14:31

we’ll be running back this way where

14:33

we’ve got t1 and we’ll have t1 again now

14:36

there are other things that I found out

14:37

that you can do in the software you can

14:40

make you can define a little circle for

14:42

example so although we’ve got a point 6

14:44

dot like that we can make that point 6

14:48

dot do things like this it can work its

14:52

way across the job in a spiral so

14:55

there’s another way that we can create

14:57

heat over lapping heat and then we’ve

15:00

got all these various pulses with their

15:02

spread of power so we’ve got an infinite

15:06

number of possibilities for trying to

15:11

solve this problem where do we start now

15:15

we’ve had a little bit of a fail of the

15:16

power based on aluminium test but of

15:20

course stainless steel is going to be

15:21

completely different maybe that would be

15:23

a good strategy to see just what happens

15:26

when we run this same pattern on

15:28

stainless steel perhaps I’ll give me a

15:31

little bit of a pointer as to where we

15:33

should start our tests where you might

15:36

even magically get some colors of midair

15:39

without even trying so I think it’s off

15:41

to the Machine in the cold workshop

15:43

after all okay now what I’ve got here is

15:45

a piece of 304 L first of all it’s low

15:50

in carbon and secondly it’s bright

15:52

annealed now it might look like a mirror

15:55

finish on there but in fact it’s been

15:58

prepared in a vacuum furnace with argon

Transcript for the Search for Fiber Laser Color Marking (Cont…)

16:02

and hydrogen I believe to exclude oxygen

16:07

particularly during the process and it

16:11

then has to be quenched and it comes out

16:13

with this nice clean mirror looking

16:15

finish even though it’s not been

16:17

polished so there’s no built-in oxide

16:22

within the surface what’s actually

16:25

happening here is as soon as it gets

16:27

exposed to the air you’ve got this thin

16:29

film of oxide that builds up on the

16:31

surface itself so there’s a controlled

16:34

amount of oxide there on this particular

16:36

type of product

17:06

[Applause]

17:22

things that we’re gonna have to deal

17:24

with the longer function

17:27

they’re the only ones in synchrony

17:32

the good news is without even trying

17:36

here in this daylight we’ve got quite a

17:40

few sort of colors so we’ve even gotten

17:43

a hint of a blue there so yeah we’ve got

17:49

a bit of a starting point here for some

17:50

of the colors now up this end here I’ve

17:55

got virtually no fail at all it’s just a

Transcript for the Search for Fiber Laser Color Marking (Cont…)

18:00

smooth surface whereas as I get down

18:02

here down at this end we’ve definitely

18:06

got damage to the surface I can feel

18:09

engraving so that again is another

18:13

useful and we’ve got engraving in this

18:16

middle area here as well so I think

18:18

we’re gonna have to start up at this

18:19

into the range here with small posters

18:22

so that we don’t do any damage to the

18:24

material we’re trying to thicken the

18:26

oxide film remember where as definitely

18:28

here we’re burning right through the

18:30

material so all these lovely pastel

18:32

colors but because these are not real

18:34

colors are said before yes it depends on

18:37

the frequency of the light that’s

18:38

hitting the job and we’ve got a very

18:40

restricted range of frequencies with

18:42

this white LED light I had half a dozen

18:44

attempts at trying to do something

18:46

earlier with the artificial light to be

18:49

honest I was wasting my time because the

18:53

way that light interacts with these

18:54

colors it’s got to be daylight to get

18:57

some sort of idea of whether I’m making

18:58

any progress so here I am another day

19:02

and another piece of material this is

19:04

stainless steel 304 L and as you can see

19:08

it’s been protected by a plastic film so

19:11

I’m taking the plastic film off never

19:14

been touched by human hand except to

19:17

hold that corner those colors that we

19:20

produced on there even though this was

19:22

red-hot it didn’t damage the surface and

19:26

I’ve still got a reflection in that blue

19:29

and all the colours around the outside

19:31

this is transparent this colour that’s

19:34

what I’m basically trying to achieve on

19:36

this surface here if I get through the

19:38

film then I think I’m probably not

19:41

succeed using my colour chart here that

19:43

I produce yesterday

19:45

which you can’t see in this light I’ve

19:47

chosen a speed to try and get me a blue

19:52

now technically blue was produced when

19:56

we got the hottest color if you remember

19:59

it glowed red hot and then when it

Transcript for the Search for Fiber Laser Color Marking (Cont…)

20:01

cooled down it cooled down to blue my

20:04

first attempt is still going to be at

20:06

the speed of 250 millimeters a second

20:08

I’m going to be running at a frequency

20:09

of 400 kilohertz 100% power and a pulse

20:14

width of 6 nanoseconds and just one pass

20:20

it’s definitely a navy blue hue it’s

20:24

almost black and in fact to be honest

20:27

whichever way I look at it in the light

20:29

as I turn it round it remains black so

20:33

hey at our first attempt we found a way

20:36

of producing a black mark on stainless

20:38

steel now black would imply that we’ve

20:43

got complete destructive interference

20:46

between the light waves we’re sending

20:49

white light in and we’re getting nothing

20:51

out now this seems a bit

20:53

counterintuitive but I’m going to see

20:56

what happens when I do nothing other

20:59

than increase the number of passes so

21:02

we’re going to run the program twice

21:06

[Applause]

21:09

well that’s a little unexpected going

21:13

twice as actually

21:16

created a lighter blue well on that

21:20

basis logic says if I do it three times

21:22

I should get an even lighter blue

21:25

[Applause]

21:31

there’s any significant difference in

21:33

the color there so it looks as though

21:36

two passes is a good starting point

21:38

established the surface to such an

21:40

extent that I haven’t got a reflection

21:43

let’s go back to two passes at this time

21:48

I’m going to reduce the power by 50%

21:54

[Applause]

21:56

well it’s a paler blue but it’s a pretty

21:58

washed out pale blue so we’re going back

Transcript for the Search for Fiber Laser Color Marking (Cont…)

22:01

to the success will blue – passes so now

22:05

what we’re going to do is try and change

22:07

the frequency and see what effect the

22:08

frequency has technically the frequency

22:11

is going to only increase the amount of

22:15

repetitions that we get so we’re going

22:18

to actually be putting in more power if

22:21

I increase the frequency so let’s go

22:24

from 400 up to 600 to start with well

22:33

that hasn’t worked is it so let’s go the

22:36

other way

22:36

and go down from 400 to 200 if anything

22:40

I would say is are sort of slightly

22:42

Goldie it’s almost a coffee color latte

22:46

actually that does remind me it’s bit

22:49

frosty outside this morning and a cup of

22:52

coffee would certainly help me warm up a

22:55

little bit so at this time let’s change

22:57

the pulse width to 4 nanoseconds

23:06

it’s nothing like these here is it so

23:08

it’s amazing how sensitive it is to

23:10

various factors so let’s go back to that

23:15

and let’s try and change the speed a

23:18

little bit so by increasing the speed

23:21

from 250 to 400 in fact I’ll tell you

23:24

what we do a double it will go up to 500

23:27

which means that my dots are now twice

23:31

as far apart so every millimeter is now

23:34

receiving half as much power and this is

23:37

a very good comparison because we found

23:39

that reducing the power to 50%

23:41

completely destroyed the color so it

23:44

does reducing the speed cause the same

23:48

issue I think the answer is no because

23:51

we’ve got the same power in each dot so

23:55

it’s a different way of taking the power

23:58

away something that’s a much brighter

Transcript for the Search for Fiber Laser Color Marking (Cont…)

24:02

light when we put half as much power in

24:05

by playing with the speed we get a gold

24:10

when we reduce the power by 50% we get a

24:15

pale-blue reducing the power one way is

24:18

not the same as reducing the power the

24:20

other way so I think we ought to start

24:21

making a note of the parameters for

24:24

getting all of these colors these are

24:27

all very very close to each other in

24:30

parameter settings and you’ve got this

24:33

whole range of fairly weak colors it has

24:36

to be said at the moment well I’ve had

24:38

to give in a little bit of heating might

24:41

allow me to carry on in here because my

24:44

hands are just about to drop off we’ve

24:46

go back to our base parameters which we

24:48

found and this time we’ll change the

24:51

speed from 250 down to 200

24:54

[Applause]

24:58

so reducing the speed there’s not had a

25:02

great deal of effect so we’re still

25:04

running at 200 millimeters a second and

25:07

we’re doing a single pass and well we’re

25:15

almost back to that that subtract one

25:17

pass at 150 well the bad news is I can’t

25:25

record any of these colors under my

25:27

microscope because it is a white LED

25:31

light and it completely destroys all the

25:34

colors that you can see here I’ve tried

25:37

to look at my best blue swatch under the

25:41

microscope

25:41

now this is under the microscope in

25:44

daylight when I turn on the white LED

25:47

light just in a few places mmm we’ve got

25:52

the little flashy hint of Blues now as I

25:56

said this is a an LED light which has

25:59

obviously got a limited color range and

Transcript for the Search for Fiber Laser Color Marking (Cont…)

26:03

it seems that yellow is something it’s

26:05

much happier with there’s something

26:08

interesting about that pattern I used a

26:11

point one spacing between my lines but

26:14

obviously burning through the very thin

26:17

oxide layer that’s on the surface so if

26:21

I’ve burned through the oxide layer

26:23

where’s the colour coming from

26:25

it’s amazing what observation and

26:28

accidents can do for you isn’t it you

26:29

know I think that what we’re seeing

26:31

there is a freshly cut groove that’s

26:35

been burnt into the material and then

26:38

the oxide has formed onto the surface of

26:41

the freshly cut material to a specific

26:44

thickness depending on the temperature

26:46

of the cut but it also explains why when

26:51

I touch this material I can fail some

26:54

roughness it’s a different texture for

26:56

the surface and also when I look at the

26:59

reflections in here I can’t see a

27:02

reflection in there so this is not the

27:05

same oxide surface that we had when we

27:09

heated it up very interesting

27:11

observation so I’ve taken a photograph

27:12

for the swatch so that I could annotate

27:15

it to tell me to tell me which settings

27:18

I was getting for each one of these

27:19

colors they they’re not really quite

27:23

what I’m seeing with my eye

27:25

perhaps I would just go in and use Auto

27:27

levels in Photoshop here to just enhance

27:32

the picture a bit they are slightly

27:35

exaggerated from the colors that I can

27:37

see but they are still roughly fortunate

27:40

they give me a good idea of what’s going

27:44

on I think we’ve made a pretty major

27:47

discovery here about how this light

27:50

system works in case I didn’t explain

27:53

myself very well I’m just gonna do a

27:56

quick sketch of what I see in the hope

28:00

that it may well clarify it for you let

Transcript for the Search for Fiber Laser Color Marking (Cont…)

28:03

me hand our burnt patch on here I

28:05

demonstrated to you that you could see

28:07

through the through the patch in other

28:10

words the coloring was transparent here

28:14

the colors are not really transparent so

28:20

that was a bit of a concern what was

28:23

going on why was I getting color but I

28:26

wasn’t affecting the film on the surface

28:28

I was somehow burning through the film

28:30

on the surface and yet I’m still getting

28:33

color so that part didn’t make sense and

28:37

then when I looked through my little

28:38

microscope and a certain circumstances I

28:41

could see when I looked at the lines

28:45

that were on my microscope like this I

28:48

could see little hints of speckles of

28:51

blue or yellow like this in the grooves

28:57

that wasn’t there continuously there

29:00

were just little speckles as I said to

29:02

the white LED light in my microscope is

29:05

distorting the colors it’s a very narrow

29:08

spectrum white light if I take a section

29:10

through the material what I was

29:13

effectively seeing was a little groove

29:17

like this where the beam had gone along

29:21

like this overlapping and caused the

29:28

groove and of course if you look

29:30

carefully you’ll see that there is hints

29:32

of this overlapping beam along the edge

29:36

of the group I have to

29:37

dude that this color that we’re seeing

29:40

in here is not sitting on the surface

29:45

it’s not a change in the thickness of

29:48

the surface as I was worried about

29:50

remember earlier I was saying we’ve

29:52

somehow got to change the thickness of

29:54

this film either up or down that was

29:59

rubbish

29:59

in hindsight but you may well also

Transcript for the Search for Fiber Laser Color Marking (Cont…)

30:02

remember something else that I mentioned

30:05

about one of the properties of stainless

30:07

steel you’ve only got to damage the

30:09

surface and within a few nanoseconds it

30:13

will automatically Hale over with this

30:15

film of chromium oxide so undoubtedly

30:19

that’s what’s happening in here when we

30:22

heat it up I’ll let thin sheet your

30:23

stainless steel this bit in the middle

30:26

got red-hot but when it cooled down it

30:30

cooled down to a blue so it would appear

30:35

that maybe the thickness of this film

30:38

this work is controlled in this groove

30:41

when the temperature cools down so if we

30:47

overheat it it will always be blue and

30:49

if we under heat it maybe it will be a

30:53

different color now with this new

30:55

possible mechanism of how the color

30:59

system works I need to go and have a

31:01

look that the various factors that we

31:06

have been playing with here what does

31:09

this mean in terms of power that’s gone

31:13

into the surface to produce these colors

31:15

so first of all I’m going to put all the

31:18

data onto that picture and to see

31:21

whether or not I can determine whether

31:22

there’s any special factors that will

31:25

allow me to manipulate the color well I

31:30

think it’s a little bit early to say

31:31

we’re having great success but from

31:35

nothing to finding blue and if you are

31:40

the colors um and much deeper

31:44

understanding of how the colors are

31:45

happening is certainly a major step

31:49

forward

31:50

so I think this is a convenient point to

31:51

stop for me to do a little bit more

31:55

documentation and analysis work and then

31:58

we can start off a new session with a

32:00

slightly different sense of direction so

32:03

thanks for your time and I’ll catch up

32:05

with you in the next session

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