Air compressor for laser cutter / engraver

Submitted by kirill on Mon, 03/24/2014 - 11:12

All Laser Cutters need two additional devices which move air: blower which removes air / extracts smoke from machine and air compressor as a source for compressed air for so called air assist.

Why and How

Laser cuts by heat, very high heat focused in tight beam. Side products of high heat are smoke and fire, both are not welcomed addition, smoke disperses laser beam reducint it's efficienty and fire causes charring of material / edges and can even get out of control causing serious emergency.

Fire needs air to burn but it will also die if you blow too hard, think of a candle in the wind. This is essentialy what air assist is for: compressed air is extruded directly at the laser head in a very tight stream and is directed at the place where laser touches material.

Pressure and volume of air

Pressure of air is key variable for air assist efficienty, in our shop we found out that optimal value is between 2 and 3.5 bar (31-50psi).

To achieve required pressure compressor needs to push certain volume of air through air assist opening, exact volume depends on size of the opening and desired pressure. High quality laser cutter heads have small and finely tuned openings while cheaper chinese cutters just blow in general direction via large holes.

Proper compressor

When choosing compressor you need to consider if it will be able to constantly provide desired pressure and volume of air. Small airbrush compressors small compressors boast impressive pressure figures but really poor flow rates sufficient only for airbrush pistols. Even if small compressor would be able to push enough air it will likely overheat in couple of minutes.

Our laser cutter came with small membrane pump (Smallest on the picture), I do not know what specifications it has but stream of air was very weak. It is sufficient if all you want to do is engrave, although even then we got substantial smoke traces around engraved picture.

Second unit we got was AS-48A compressor, it was rated for volume of ~2.4cfm and had a 1 gallon tank which can be filled to 58 PSI. It managed to give us constant 1 bar (14 PSI) of pressure, but it had to run all the time and overheat badly within 5 minutes.

Third and current compressor we got was 6cfm rated belt driven unit with 13 gallon tank which is filled to ~100psi. With this unit we can run at constant ~2bar (31psi) without fear of overheating since compressor engine is not on all the time. Using reserve air in tank we can also push up to 3.5bar (50psi) for short jobs.

The best setup in my opinion would be compressor rated to >6cfm, large 70+ gallons tank rated to 10bar (140psi) and software air control via solenoid valve.

Air Quality

Air which comes out of Air Assist nozzles should be as clean as possible, warer and oil vapors should be removed from it. Proper inline air filers are must have.

Noise

When choosing compressor, please do consider noise, cheap direct driven compressors are terribly noisy! It is one thing to hear noise in the shop and another to have that ratchet around you all the time. Our general advise: Choose belt driven units, they run at lower RPMs and cause much less noise. Our compressor has noise rate of 68dba, we can work without ear plugs when it runs.

Automating air flow

Good laser controller boards come with option to control air flow, it is basically a relays head which is supposed to trigger a solenoid valve when needed (controlled by software), our Ruida controller has this head, we plan to make use of it soon and document it here.