CO2 Lens Failure Causes Part 1: Lens Build-Up



Over the next few laser blogs, I’ll define some of the causes for lens failure and reasons for the occurrences.

Lens failures are a vexing problem in the laser market. Downtime, replacement optics and machine repairs can be expensive and time consuming. Due to the extreme operating environment of a CO2 laser, all laser lenses and manufacturers are susceptible to these problems. Two primary levels of lens failure are:

  • A small amount of absorbed heat may affect the geometry of the lens, changing the focal position or resulting in inconsistent cutting.
  • Too much absorbed heat may eventually burn the lens coating or ultimately reach a point of thermal runaway. The temperature point at which the zinc selenide in the lens actually becomes less transmissive. As the lens continues to heat the zinc selenide passes less and less energy, overheating the lens until it cracks or shatters. Such lens “blow-ups” are not uncommon for most laser systems.

There are many contributory factors for lens failures, which often makes the diagnosis difficult, especially after-the-fact. Still, one of the common reasons for lens failure is lens build-up, which can be frequently attributed to the following causes:

 

  • Splatter – Aluminum and stainless are “high splatter” materials, which will stick to any lens, especially if proper nozzle heights and gas pressure aren’t maintained. A recent customer found that his operator was lowering the nozzle to blow off more dross, which resulted in excess splatter and a shortened lens life.
Lens with excess splatter

Lens affected by high splatter materials like Aluminum and Stainless

  • Vaporized Material Contaminating Lenses – Coatings on the metal or the metal itself may vaporize, causing premature lens failure. For instance, many galvanized products may off-gas zinc and other compounds that are detrimental to the lens coating. Some customers use metal with protective plastic coating. Without proper gas flow, the plastic vapors can lodge on the lens coating and shorten its life. Even P&O sheet steel can cause vapor buildup on the lens from the oil by-products if sufficient gas flow is not used. If aluminum is overheated to the point of vaporization by cutting too slowly or with too much power, it can vaporize and deposit on the lens.
Lens with vaporized contaminant deposit.

Lens with vaporized contaminant deposit.

  • Scratched or Mishandled Optics – Scratches like contaminants provide a “target” for the laser energy on the lens surface that can result in uneven heat absorption and negative thermal effects.
Scratched lens resulting in negative effect.

Scratched lens resulting in negative effect.

  • Improper or Inadequate Maintenance –OEMs recommend that lenses should be cleaned daily. The coating on the lens is very fragile so it can scratch easily. Contact Mate or your Mate sales engineer to learn more about proper cleaning procedures.
 

 

In the next laser blog we’ll cover Part ll: Machine Power and Cooling System Problems.

Blog Author

Cindy Hallas

Cindy Hallas is the Laser Product Specialist at Mate Precision Tooling.