Those of you laser cutting metals have likely experienced the disheartening feeling of opening up a lens assembly and finding pits or a complete rupture of your focusing lens. These special optics can be an expensive maintenance item, especially when processing materials that tend to generate high levels of back splatter.
That’s why our friends over at Kern Laser Systems are offering advice on how to reduce back splatter. While completely eliminating splatter is not possible, these tips will certainly help to reduce it.
Proper Pierce
The majority of splatter is generated during the piercing process. Generally, the thicker the metal, the more splatter generated, the more likely the lens is affected — so it’s important to pierce with the smallest hole possible to reduce the amount of splatter generated.
When piercing reflective metals such as aluminum, brass and copper a high power and moderate assist gas pressure, results in a nice small pierce point. When cutting thick mild steel, the ideal pierce is generally achieved with a lower power, lower assist pressure, along with a longer pierce dwell. For example, when processing 4.5mm mild steel on our 400W CO2 laser, we generally use a 3 second pierce, 35% power and 40 PSI oxygen.
Invest in a Cover Lens
A cover lens is a protective barrier that is specially designed to fit between the nozzle and focusing lens. Kern’s covers lens for their CO2 laser systems is called the K-Lens. The K-Lens are accessed by unscrewing the lens holder from the ceramic isolator. This allows for easy replacement without having to remove the focusing lens.
Nozzle Selection
A variety of nozzles are available for Kern’s laser systems. The standard nozzle on Kern’s CO2 metal cutting assemblies have a 1.5mm diameter opening. If you find yourself replacing your optics more frequently than you like, try switching to a 1mm nozzle. The beam alignment through this smaller nozzle becomes more critical and will need to be re-calibrated. However, the smaller opening drastically reduces that amount of splatter reaching the optic.
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Gap Distance
A larger gap between the nozzle and material being cut reduces the amount of splatter that successfully makes its way back into the nozzle.
A general rule of thumb is to set your gap at the same thickness as the material being cut. It generally goes without saying that the thicker the material, the more splatter — so the larger the gap you need.
Non-Metals
When piercing plastic, wood, foam and other non-metals, splatter is not generally an issue. However, smoke and residue are created during the piercing and cutting process. A vacuum system will remove a majority of the smoke and residue, although some lingering traces may collect on the focusing optics.
To help combat smoke and residue from getting into the nozzle, a knife air should be used. The knife air is installed on Kern’s laser shroud and injects compressed air perpendicular to the cut, pushing the smoke and residue away from the nozzle opening.
