Metal Cutting Challenges: Coated Materials

What are the challenges and risks associated with laser processing coated materials? While it’s true that each presents unique challenges in their own rite, there is some common ground that many share.

Coatings

Often materials arrive with a surface protective coating. Examples may include a stainless steel appliance, a part designated for a medical or aerospace application, a decorative art piece, and so on. The material may be coated with a variety of finishes including paint, polyvinyl chloride (PVC), Nitto, Laser Film, and so on.  To reduce the likelihood of scratches or other damage, these finishes are intended to remain on the materials during processing and shipping. It is therefore important to learn how to effectively laser cut coated materials while keeping the protective surface intact. The trick is to produce quality cuts without removing, scratching, melting or otherwise damaging the coating.

Coated Stainless Steel

When preparing to laser cut coated stainless steel, it’s important to select the proper assist gas. Nitrogen is generally 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.

While 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.  Some 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, this practice is not recommended. 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.