Laser engraving bitmap images has been difficult to create to any great quality or definition. Contrast levels within images along with limitations of the lasers to modify parameter settings on the fly have provided, at best, unattractive results.
Work to develop materials that will absorb differing levels of energy and hardware developments to allow per pulse energy changes to the laser output, have contributed to better results today in certain high profile areas.
Laser engraving bitmap images and vector images.
A bitmap is a series of tiny dots known as pixels. In reality, each pixel is actually a small square that has been asigned a colour. Its colour and position are used to form the overall image you are looking at.
Laser marking system uses a raster scanning technique to travel over the image area placing an energy pulse where each pixel would normally be. Because the laser can not produce colour in each pixel, it requires the image to be less complex. In most cases, the image would be translated to black and white reducing the number of pixels creating a less defined image overall. The laser then pulses on for each black or white pixel depending on how the process setup.
Vector images are not based on the same pixel format. They use a series of lines (vectors) generated from mathematical formulas. The vector image contains much less data than the bitmap, and processes much faster than its bitmap counterpart. The ability to scale vector images much easier than bitmaps makes them much more commercially acceptable.
Personalisation is a growing market
There seems to be a commercial requirement to create photographic images in order to personalise products such as iPhones, iPads etc. The main market being the Far East. The process can by no means be qualified as 100% successful, but with selected materials matched to goods images, the results can be quite stunning. Before you ask, the results will always be monochrome.
To produce the images shown, the laser engraving system was a flash lamped Nd:YAG. Laser engraving bitmap images means we run in a lower mode level. The material used was an anodised aluminium plate which helps provide the contrast levels equating to grey levels. The dot density can be increased or decreased in the conversion software to create the dark and light shade areas.
Laser engraving bitmap images onto 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, 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.
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.
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
