PDA

View Full Version : What gas can I use with hardwood to minimise charing



Mark Simons
02-24-2006, 1:05 PM
I am cutting hardwood ply that needs a lot of energy:
uls 120w @ power 100 - speed 5 - ppi 100 - quality 4
Can anyone advise which gas to use with my gas assist to further decrease charing?

Thanks

Shaddy Dedmore
02-24-2006, 2:45 PM
I don't know about gas, sorry (although nitrogen comes to mind).

Can you reduce the PPI or possibly make 2 faster passes? I haven't had much luck with multiple passes myself though. But I have noticed a difference with reducing the PPI in my Epilog 45w with some wood.

Shaddy

Brent Perkinson
02-24-2006, 3:04 PM
We have an open 4' x 8' table with an overhead gantry instead of an enclosed machine so this may not be good advise for you, but we use argon in place of our normal air assist in a situation such as you describe to eliminate combustion.

Brent Perkinson
02-24-2006, 3:10 PM
We have an open 4' x 8' table with an overhead gantry instead of an enclosed machine so this may not be good advise for you, but we use argon in place of our normal air assist in a situation such as you describe to eliminate combustion.

Ed Lang
02-24-2006, 3:10 PM
CO2 or Argon are used in MIG welding as a shield gas. I expect it will also work as a shield gas in laser work. CO2 is available at my local Farm supply store so it is easy to get and try. Remember you will need a regulator on the gas bottle!

Let us know how you get this solved.

Joe Pelonio
02-24-2006, 3:37 PM
I'd check with the laser manufacturer and see if they have a suggestion or whether you could have a warranty problem using something other than air. I'll sometimes increase my air supply to 35 lbs instead of the usual
25 for thick wood. Also, it may be that you could make up a longer tip with smaller opening to attach to the air assist too blow it out better.

Mike Mackenzie
02-24-2006, 3:46 PM
Mark,

Try turning up the air pressure at the cone try going up to 25-40 psi. This may work better.

Ed Lang
02-24-2006, 4:27 PM
I would sure listen to Mike.

Now think about this. What happens when you blow on a fire or embers?

What happens when you flood a fire with CO2?

Would the laser still cut wood if the area was flooded with CO2?

Brent Brod
02-25-2006, 7:26 AM
I did a little research into this, but never actually tried it. Nitrogen would probably be the least costly inert gas, but you are going to need quite a bit if you intend to do much cutting. You could buy a bottle for experimentation.

I saw some photos of laserwork cutting fiber composites with and without inert gas shielding. There was a definate difference. The issue I never sorted out for myself was whether or not the ventilation flow through the machine would simply overwhelm the small air assist stream. I think the people doing the work above were on an open table and quite a bit of flow.

Joe Pelonio
02-25-2006, 10:51 AM
Apparently people with yag lasers cutting metals use gasses all the time
instead of air but I've not been able to find anyone using it on a C02. If I were to try it I think rather than flooding the box I'd "T" it into the air assist line so you could use either but only at the head.

Roy Brewer
02-27-2006, 4:23 PM
Can anyone advise which gas to use with my gas assist to further decrease charing?

Mark,

While I don't recall my chemistry that well, I took my local air supply company rep's advice "definitely Nitrogen..." and on numerous occasions it has worked very well.

My application was cutting PCBoards where tolerance was critical and the kerf was reduced by over .002"
Since I have the set up, we've found it very useful for cloth and a few other applications.

Roy Brewer
02-27-2006, 4:41 PM
Now think about this. What happens when you blow on a fire or embers? What happens when you flood a fire with CO2?
Would the laser still cut wood if the area was flooded with CO2?

Ed,

One thing that is not commonly understood is that the laser does not burn the wood.
The laser vaporizes the wood. What is combusting is the rising vapors.
If we can get rid of the vapors (high power air as Mike Mac suggested) then less combustion and less charring.
If we can both evacuate *and* reduce the available Oxygen, then we have still further reduction of combustion/charring.

This is not in disagreement with Rodney's (sometime past) post that under some circumstances we can cut deeper by blowing Oxygen directly onto the working laser. This is certainly true if we can live with the "blowtorch" effect and a few other risks --- no potty breaks recommended during this exercise {;<)

Rodne Gold
02-27-2006, 5:32 PM
At the point of contact or when power density is high enough , the burn is a "vaporization". When the laser fires a pulse at something , if the heat dispersal of that object cannot wick energy away fast enough it gets thermally shocked and does vaporise , there is however the HAZ (heat affected zone) adjacent to the vaporization where the material "burns". Using an inert gas (I use nitrogen) will minimise the oxidation at the HAZ leading to less charring , this is not to say the area is NOT heat affected , it is , but the products of oxidation are minimised.
For steel and metal cutting , O2 is often used to promote the vaporisation as it significantly elevates temps and thus aids vaporisation.
Reducing char can also be as simple as running your laser much quicker with less pulses per inch into the material if you can Its highly unlikely you are going to significantly reduce char on ply by that much as a lot of the char has to do with the bonding glues and resins in the wood that enter gaseous state and "resolidify" on the edges etc
A significant increase in power would reduce char , coupled with a lens that gives greater depth of focus if the ply is thickish.

Ed Lang
02-28-2006, 11:15 AM
Glad I said something on this thread.... I was corrected, and learned a bit!

Gotta love SMC and the folks who post here.