> What power CO2 laser do you need for cutting 3mm
steel/brass/aluminium?
> I've got a two-stage pump that can go to 10^-4 torr. I'm designing a
> cnc x-y table...
I had a Mitsubishi CNC Laser for several years and have some
knowledge of how they work. This machine was a model 1212HC with a
3000 watt resonator and 48" x48" cutting table. The entire machine
installation was the size of two pickup trucks.
We used this machine mainly for cutting small stainless steel and
acrylic plastic parts. When cutting .060" stainless steel the power
levels would vary between approximately 400 and 700 watts depending
on cutting speeds. The CNC program would change power levels when
needed. Lower power and table speed is used for fine cuts with higher
power and feed rates for everything else.
A coaxial beam of cutting gas is always used with CNC CO2 lasers. We
used oxygen for most steel and stainless and sometimes nitrogen for
stainless cutting since it leaves a cleaner cut edge. Clean
compressed air or nitrogen was used for cutting plastics.
Acrylic plastic cuts well with compressed air and 75 to 150 watts for
up to .125" thick and around 200 watts for .250" thick. The power
level, frequency, duty cycle and gas pressure was fully adjustable
(even while cutting) and allowed precise control of the cut quality.
Since most of our work was small parts with fine detail we used short
focal length lenses. A 5" focal length lense was used for most work
and a 2" lens was used for super fine cutting on thin materials. A
7.5" lens was used on materials over .25" thick and up to .5" thick.
The longer focal length gave a straight cut through thicker materials
but had a wider kerf (cut width) in the material being processed.
One time we tried cutting some FR-4 double sided laminate and it
didn't work very well. It took about 900 watts to pierce through the
top copper layer and then the glass epoxy exploded into a blob since
the power level was so high and was also being reflected back from
the bottom copper layer while piercing it.
Non-ferrous metals such as aluminum, copper and brass take much
higher powers levels to pierce and cut on a CO2 laser. My experience
was that the same power level to cut .375" steel could not even
pierce through the copper on a circuit board. I don't think the CO2
laser is the best choice for cutting PWB laminates. Maybe the YAG
machines will do a better job on circuit boards.
Tom