Determining the Correct Laser Lens
It seems like OEMs are introducing new laser machines into the market at a faster pace. When it’s time to replace the lens, customers can be confused, resulting in the frequently asked question: what lens is the correct one? Here are some ways to check:
What type of laser is the lens for? CO2 or Fiber laser
What is the diameter of the lens? This is easily determined by measuring the outside diameter of the lens. The most common diameters are 1.1”, 1.5”, 1.75” or 2.0”; Trumpf has a 1.96” lens.
What is the lens shape or cross-section? Generally there are only two shapes: Plano-Convex and Meniscus. Both are rounded up (convex) on the top. If the bottom lens facing the work surface is flat, it is a Plano-Convex; if concave, it is a Meniscus.
What is the edge thickness? This can easily be measured with a micrometer. In absence of an edge thickness, you can also ask the maximum pressure of cutting gas that will be used. Edge thickness requirements vary because higher pressure cutting will cause thinner lenses to break due to pressure on one side of the lens.
What is the focal length? Focal length is typically 3.75, 5 or 7.5 inch, and is specific to the machine parameters. If the focal length is unknown, use the following method to approximate it: hold a lens above a printed surface and move the lens up or down until the print is in focus. The distance between the bottom of the lens and the focused print is the approximate focal length.
What power will the lens be cutting at and what type of material? A low absorption PEAK lens is recommended if you will be cutting at 4kW and higher. For lower power cutting, a standard PERFORMAX lens is sufficient, although an experienced operator will see improvement with the PEAK Lens. BLACK MAGIC lenses work well for cutting aluminum, stainless steel and in certain climates. Fused Silica lenses are for fiber lasers.