Anodising has become a dominant form of finishing for aluminium. This is largely due to its cost effectiveness, availability and suitability, across a whole host of applications and industrial sectors. Laser marking anodised aluminium, has also become an accepted process across these industrial sectors.
Anodising is an electrolytic passivation process. It changes the microscopic texture of the aluminium by modifying the crystal structure near the surface. The passivation thickness will be between 10 and 25 microns, generally between 10 and 15 microns where colouring is used. This makes laser marking anodised aluminium very cost effective, as the layer can be removed easily and quickly. The laser is used to vaporise the top surface, removing the area affected by the anodising, and this exposes the aluminium material below. When a darker dye colouring is used, the contrast levels are very good.
The quality of the finish on the aluminium relies heavily on the material quality. With poor quality materials (high levels of alloys), the grain structures have a tendency to tear leaving rough surfaces and edges. The higher the quality of the base material, the higher the quality of the mark result, and the closer to white the mark will appear.
In this example, the equipment front panels have corporate branding details added as well as some contact information. Because the images are quite large, the panels are processed using high power to start. Then we finish off using a second pass, with lower power effectively skimming the image.
Aluminium corrosion: The general consensus is, as the laser removes the anodised layer, an oxide layer forms on the surface providing protection.
CO2 lasers can also be used to process anodised aluminium. In this case, it is the dye that is directly affected rather than the material. The energy from the laser creates a heating action that removes the dye from the surface. The use of CO2 is generally not as well received as Nd:YAG or Fibre due to the lower quality created by the mark process. This is directly related to the fact that the heating effect is difficult to control, due to “heat creep”. Although, per unit cost will be slightly higher with CO2 due to the process time being slower.
If you would like further information on this laser marking application, or any other application, please request a call back, or talk to one of our laser marking specialists on 01737 826902