Was Laser Engraving. . .question regarding reflectivity issue

This is a how did they do that. . .

I am curious about the reflection issue. In the mid 90s I had many parts
cut from stainless sheet that had been prestamped with a pattern--it was
somewhat reflective, and was about 18 gauge. I mention the stamping,
because not only was it reflective in its finish, it was variably shaped.
We only re-finished the edges after cutting. Although a few cutters sent
me away, the one I used had absolutely no problem, and claimed they could
even cut mirror finished stainless. This was probably about 1996 or 97 at
the latest. Wondering how they got around the reflection issue. Is
Aluminum more reflective than stainless in the required wavelengths? Did
they use some sort of exotic laser? I wish I had asked more questions when
I was there, but I was just happy to get my parts. . . the machines were
enormous.

Peter

> [Original Message]
> From: Graham Stabler <eexgs@...>

> I think once you are past the dark layer you are back to square one.
> In general trying to cut AL is just not worth it and I think Jon's
> estimated power may be on the small side for a decent cut quality
> although I am not so sure for YAG.
>
> It is strange that steel which is usually something we might shy away
> from prefering instead aluminium is actually much easier to cut with a
> laser. The gas that pushes out the molten metal is normally oxygen
> which essentially causes the steel to burn, the burn-extringuish-burn
> cycle is what produces the striations seen on laser cut steel edges.
>
> If you are just interested in marking then you may consider one of the
> special compounds that allows marking of metals with low power CO2
> lasers. You will have to google these I am afraid. You may get
> somewhere by using a 50W Co2 and a short focal length lens, this
> reduces spot size and increases intensity.
>
> Graham
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
> >
> > Carl Boudreau (pressenter) wrote:
> >
> > >How much power is needed to cut thru 1/8" aluminum?
> > >
> > >
> > I'd start thinking around 1000 Watts, very generally. Aluminum
> > is pretty reflective down into the IR wavelengths, and is one of
> > the best heat conductors. That makes it hard to weld, too.
> > So, aluminum and copper are a BEAR to cut with laser. It might
> > be possible to improve the reflection situation with a dark coating
> > on the face of the aluminum.
> >
> > Jon