When preparing to laser cut coated stainless steel, it’s first important to select the proper assist gas; and nitrogen is the best choice. Being an inert gas, nitrogen does not produce a chemical reaction thus making it the safest and most reliable choice. Avoid cutting with oxygen as it lacks the predictability of nitrogen. There are too many instances of oxygen catching fire to the PVC and melting the coating to the metal.
Generally speaking coated stainless steel is slightly easier to cut with a fiber rather than a CO2 laser, there’s really not much difference if both are set up properly. What is important, however, is the piercing conditions. When the incorrect pierce sub-routine is selected the finished part results can be poor and inconsistent.
Turning the assist gas on too fast / too high can cause bubbles which in turn will affect the height sensing of the laser head and throw the laser cutting off. Consequently, it’s vital to get pierce sub routines correct. Be sure to take the time to communicate with the machine manufacturer and run some cutting tests in order to get the optimum settings. It is recommended that you set up a cutting condition library for PVC coated materials. This is a one-time step that’s well worth the effort. Do it once and you’re finished; from that point on it’s an automatic function.
Still some laser operators try to shortcut the process and pre-melt the coating. In doing this the laser head is generally positioned anywhere from 0.100” to 0.600” above the material and used to melt the coating prior to initiating a pierce point. While it’s true that most lasers come with this pre-melt functionality, its recommended to avoid this practice. Pre-melting introduces an opportunity for excessive melting and creates a mess generating dust and debris which is bad for a fiber laser. Take the time to set the machine up properly and make sure that you utilize a quality coating specifically made for laser applications and there’s no need for employing this risky tactic.
Sometimes you may get a bad sheet or batch of metal from the customer or supplier where the PVC coating is not tacky/sticky enough. As mentioned earlier, this may cause the coating to lift or bubble when cutting. In this instance you can peel the PVC off of the material prior to cutting. This might also be a last resort if you struggle with piercing or pre-melt. Again, this isn’t recommended as it introduces an opportunity for damaging the metal. However, if you choose to do this and were able to navigate cutting without damaging the surface, be sure to prepare the cut surface prior to any secondary operations. There is a special tape that can be placed on the stainless steel or on your press brake punches and dies, in lieu of coating which protects the material from scratching or marring during bending and other secondary operations.