Preventing Fires in a Laser Cutting Machine

Some suppliers include warning devices within their laser cutting machines designed to indicate the presence of a fire and would have you believe that material flaming during laser cutting of potentially flammable materials, such as laser cutting acrylic, laser cutting wood or laser cutting card is a normal part of the process.

Nothing could be further from the truth.

Allowing the material to flame is at best an incorrect use of a laser cutting machine and at worst a very dangerous risk of causing a major fire. Flaming during the laser cutting process will damage the material as well as deteriorate the system optical components leading to wasted time, wasted materials and expensive repairs.

Allowing the flaming to develop into igniting the material is extremely dangerous and nothing short of user negligence.

If the material is flaming it indicates a serious fault in the process that could relate to a misguided use of the equipment (incorrectly specified machine and/or inappropriately trained operator), incorrect parameters being used, incorrect focus or optical configuration (lens) and a variety of other common user errors.

In most cases flaming during laser cutting can be related to two specific causes:

1) An inadequate rate of laser fume extraction and/or air assist. If the vapours generated during the laser cutting process are not quickly and effectively removed from the path of the laser beam they can combust. In vapour form the material will ignite much easier than it will as a solid.

The best way to remove these fumes is by way of aggressive extraction from the underside of the material combined with a targeted delivery of high pressure through a small bore nosecone. This keeps the vapours away from the cutting point, preventing flaming.

2) An inappropriate use of the laser cutting machine. Some suppliers would have you believe that it is perfectly safe for a 30w laser to cut 20mm thickness acrylic. Just because the machine can do such a thing doesn’t mean it should. Using a laser of very low power to cut thick materials requires a very slow feed rate and sometimes multiple passes.

Also, using a lens with a short focal length (anything less than 127mm or 5” f/l) to cut thick material (>12mm or ½”) means that even for waveguide materials, such as acrylic, the majority of the material is being cut with a beam significantly out of focus. This maximises the heat absorbed by the edge of the material and in so doing brings closer the flash-point where the material ignites.

It is therefore more important that when using a lower power laser to cut thicker material, the user is even more vigilant with their supervision of the process.

Whenever the machine is laser cutting, no matter what the materials are in terms of type or thickness, the laser cutting machine should NEVER be left unattended for more than a few moments at most. We train operators to have a constant ‘line of sight’ to the machine at all times that it is laser cutting. In the event that flaming appears the process must be stopped and the system configuration and/or parameters adjusted accordingly. In the event that flaming still occurs our advice is not to continue with the process. If the user has no option but to continue while the material is flaming then we advise to do so with a great degree of caution and a real understanding of the risks being taken.

At Lotus Laser Systems we manufacture a wide range laser, marking and engraving solutions and we pride ourselves on the quality and depth of knowledge of our support staff. Our experts would be happy to advise you on this or any other aspect of your laser system operation.