Most workstation format fiber laser marking machines have the functionality of using interchangeable lenses the extent of which will be determined by the maximum travel distance of the Z-axis. If the Z-axis is longer then the variety of focal length lenses that can be used with the laser engraving machine is greater.
It’s very important to understand how the different characteristics between lenses influence the performance of the laser marking machine and the results it produces. We cover in detail the characteristics of f-theta lenses in a separate article. Here we outline why certain lenses should be used instead of others.
The majority of laser engraving machine operators will only ever use a single focal length (f/l) lens for all of their work.
Most commonly this will be 163mm f/l, which provides for a marking area of approximately 110mm. For most applications this is a good all-round lens.
The next most popular would be a lens with 254mm f/l delivering a work area of 175mm and the third most popular would be a lens with 100mm f/l providing for a work area of 70mm
Other commonly used but less popular lenses would be 330mm f/l providing for a work area 220mm and 420mm f/l providing for a work area of 300mm. These very long f/l lenses are generally only effective when used with lasers >30w.
As the focal length increases, aside from the scan (work) area increasing so too does the size of the focal point and the depth of focus
When choosing which lens to use there are five main fundamentals to consider:
- Resolution, energy density and marking speed.
A lens with a shorter focal length will provide for a smaller focal point (laser spot), which in turn can achieve a higher resolution and a higher degree of energy density. This is useful for marking very high levels of detail and/or where the power of the laser source is low and the application requires maximum material ablation
Conversely, some applications do not require high resolution so can benefit from a longer focal length and a larger focal point because the marking process can be much faster with a wider spaced hatch fill
Using a lens with a longer focal length also requires shorter mirror movement, which again can make the marking process much faster
- Clearance between the lens and the material being marked.
Some components require marking inside them. For example, to the bottom of a bowl and here it’s important that there is sufficient clearance between the lens and the highest point of the part that is being marked to avoid any collision.
- Depth of focus
This means the effective distance from the perfectly focused focal point to the point where the laser is not marking desirably (because it is too far out of focus).
This is only an issue for parts being marked that are not flat; for example, the surface of a pen. In this example it is sometimes better to use a 254mm f/l lens rather than a 163mm f/l lens because with the longer focal length lens the height of the mark can be larger
- Mark area
A lens with a longer focal length provides for a larger effective marking area. This is especially useful where a single mark is very large or where a single part must be marked in numerous locations
Some applications can generate corrosive fumes that can contaminate and deteriorate the lens. A longer focal length will place the lens further away from the surface of the material making it unlikely to become contaminated
At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your application.