Laser engraving anodised aluminium medical device – the application
This below knee prosthetic component uses laser engraving on two opposite sides. The branding element, the components brand name, is placed across the top of the component while a scaling alignment mark is placed around the through hole area as a single pass process. The component is turned over and the laser marking process repeated using a new job file. Tooling is a very important part of the process, due to the dimensional accuracy required for the scale alignment. The combined precision of the beam placement along with our tooling design, means the part and laser marking are precisely aligned every time we set up a new batch.
Anodised Aluminium
Anodising is an important form of finishing in the world of aluminium components. It is cost effective, widely available and is suitable across a whole host of applications. The wide range of colours available provides a very aesthetic finish strengthening its popularity. Laser engraving anodised aluminium has become an acceptable process across many industry sectors.
This electrolytic passivation process changes the microscopic texture of the aluminium by modifying the crystal structure near the surface. The range of available colours and the very aesthetic finishes make it a popular finish for both industrial and non-industrial products. Out of the three general forms of anodising, sulphuric acid anodising is probably the most widely used. When coloured anodising is required this process is the preferred option.
The passivation thickness will be between 10 and 25 microns, generally between 10 and 15 microns where colouring is used. This makes laser engraving 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. This exposes the host material below. Where a darker dye colouring is used the contrast levels are good. The laser is used to, in this case, place information radially onto the component. The software provides the capability to mix and match both alphanumeric characters and logos.
The laser engraving of anodised aluminium, in the case, was performed by Nd:YAG laser. The process is to vaporise the top surface to remove the area affected by the anodising process exposing the host material. Where a darker dye colouring is used the contrast levels remain high between the two contrasting surface areas.
Aluminium corrosion
The general consensus is that as the laser removes the anodised layer an oxide layer forms to the surface providing protection to the material beyond the oxide layer thickness preventing corrosion.
Laser engaving anodised aluminium using CO2 lasers
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”. The result is a fuzzy edge to the mark image. Not as crisp as with Nd:YAG or Fibre. The main advantage is that no material is removed leaving the anodising closer to its original state. Per unit cost will be slightly higher with CO2 due to the process time being slower.
To achieve consistent white marks on aluminium the correct laser power, repetition rate, marking speed and image fill ratio must all be made. With most aluminium’s a slight deviation, either way, from your standard settings should be enough to pull back any variation you see. In some cases it may also be worthwhile considering a second pass with much lower power settings to lightly skim the image removing any burning caused by the initial process pass.
The combined precision of the beam placement along with our tooling design means the part and mark are precisely aligned every time we set up a new batch. Your files are saved and held for as long as you wish to work with us.
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
