Re: Lasers - my $.25 worth ( thats 2 cents adjusted for inflation...)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "skykotech" <rick@...> wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "skullworks"
> <skullworks@> wrote:
> >
> > Hi All;
> >
> > I have been using a Nd-YAg 60W 1064Nm since 1990. At this point

the

> > machine is a functional dinosaur.
> >
> > It uses a full height enclosed 19" rack mount to house all the
> driver
> > subsystems. The rack is cooled by a water to air intercooler and
> the
> > De-ionized water is run thru a water to water intercooler. The
> main
> > computer is a Motorola 68000 ( 8 whole MHz! ) on a VME chassis
> with
> > 2Mb ram... (Wow!)
> >
> > The beam exiting the laser cavity is a 8x6mm ellisp - in some
> > applications we use a tunsten apature to trim the edges of the
> beam
> > to a perfect circle. The laser mirrors (99.5% and 100%) are
> > watercooled and are outside the laser cavity. There is a high
> speed
> > shutter before the 100% mirror which is used to modulate beam
> pulse
> > freq up to 32KHz.
> >
> > The beam that exits the 99.5% mirror is run thru a beam expander -

> > there are many reasons for a beam expander but the most important
> one
> > is that you now have a up to 60Watts hitting within a 8mm circle.
> > This system uses mirrors on highspeed Galvos to direct the beam
> > within the lense marking field. - If the beam was not expanded
> these
> > mirrors would be burned thru in a few seconds.
> >
> > The beam now goes thru the final lense group and at the proper
> focal
> > length is focused to a dot .1mm or less (about .0027") The galvos
> can
> > move the beam up to 999mm/sec.
> >
> > I have a program that draws sheet music - and plays the tune as

it

> > draws the notes. - People think thats neat. Its really simple, I
> am
> > hitting an object with energy - and can control the freq of the
> > impact - works like an adjustable tuning fork.
> >
> > Back in 1990 the proper filtered safety glasses cost $640 each.
> (They
> > have dark green lenses resembling a #5 welding lense but with a
> much
> > more complex makeup - DON'T USE WELDING GOGGLES - THEY DO NOT
> PROVIDE
> > PROPER PROTECTION. )
> >
> > I've worked with HeNe, Nd-YAg, and some diode lasers. I still
> > consider myself a rank amature... But I'm game if someone decides
> > Lasers need there own forum.
> >
> > GAB
> >
>
>
> A few things to note:
>
> Nd:Yag is 1064nm which most glass and plastics are transparent to
> (it passes right through them)

Acrylics and glass are transparent - Polycarbonate (Lexan) IS
reactive.

> CO2 lasers are 10,600nm, almost like a infrared heat ray. Glass

and

> plastics absorb almost all or totally all of this energy (little or
> no laser light gets through unless it melts).
>
> Nd:Yag goggles therefore have to have special coatings to allow
> visible light (which is relatively close in wavelength 450-700nm)
> where CO2 lasers you can use glass or plastic goggles from Home
> Depot.
>
> Your Nd:Yag laser is not actually 60 watts, but is more likely 10s
> of kilowatts peak power (60 watts is the average power...but that

is

> high..most of them are like 20-30 watts average power). Most CO2
> lasers are not q-switched like yag and therefore do not have such
> extreme high power pulses. This is why you can't mark some metals
> with CO2 but you can with YAG...other than the shorter wavelength
> which is absorbed more readily by some metals, the high peak power
> of the q-switched yag overcomes the surface reflectivity of the
> metal.

60 Watt is peak power - to get this we are feeding 400V @22.5A to the
flash lamp - the power cables going into the cavity are 10mm and are
inside the Deionized water lines to keep from melting. System was
once tested with a fresh lamp and new DI filter and put out 67W peak.
Lasers are lousy for power economy - you get so little for what you
put in, its just that for what you do get you can put it to good use.

BTW for those that have never seen a YAg setup - the laser is a
crystal rod in a elliptical gold cavity that has a high pressure Xeon
flash lamp as a driver - this entire cavity has Deionized water
flowing thru it - think a light bulb in an aquarium since De-I water
is almost non conductive.

>
> On CO2 lasers you use beam expanders not so much to protect the
> mirrors but because the formula for focus spot size depends on the
> beam diameter...larger diameter can be focused to smaller spot
> (sorta..more complicated that that really). Some people call these
> optics "cut enhancers" or something.

This system was intended for part marking - but will do some light
cutting, it just has no provision for air blast or other jet.