Reprinted from Industrial Laser Review November 1996
Copyright ©1996 PennWell Publishing Company
By: Joy Rockwell
Cutting and welding spatter and contaminated assist gases are continually hammering away at the weakest link in the chain. As CO2 lasers pour thousands of watts through their focusing lenses, back spatter chips away at the anti-reflective (AR) coating and even pits the surface of the lens. The delicate AR coating prevents energy absorption within the zinc selenide (ZnSe) lens and increases energy transmission to more than 90 percent. Damage to this coating reduces beam power transmission resulting in increased heating of the lens leading to performance degradation and eventual failure. Even the use of assist gases canít completely prevent this damage from occurring. Disposable protective windows such as those supplied by International Crystal Laboratories (ICL-Garfield, NJ) block spatter from contacting the focusing lens of CO2 lasers. As shown in the photo, these low-cost windows attach to the front of the laser optics between the lens and the source of the back spatter keeping the energy throughput of the lens from being altered by damage to the lens or AR coating.
The life of a lens depends, in great part, on the material that is being cut and, of course, the quantity. Stainless steel and aluminum can cause the most mess and the most spatter, and machines cutting these materials tend to go through lenses faster than other machines. The thicker the material, the more opportunity for spatter. New lenses can cost as much as $500 and regrinding and recoating can cost half as much as the original lens. A protection window such as ICLís Lens Saver is less than one tenth the cost of a new lens, and just one can extend the life of a lens by more then two or three times depending on the frequency of use and application. Further, no recoating, regrinding, or replacing of the lens is necessary due to spatter. ICL customers report the life of their lenses increased from a few weeks to a few months. The average is at least twice the life of an unprotected lens. At $500 for a new lens, a shop going through two lenses a month will save nearly the entire cost of a new lens every month for each machine. One shop reports a savings of around $50,000 per year.
The Hogan story
Mark Lopez, a supervisor at Hogan Manufacturing (Escalon, CA), a company with two locations and 220 employees, claims they are the largest manufacturer of wheelchair lifts for buses in the United States. Hogan runs six high-powered CO2 laser systems ranging from 1 to 2 kW. Four of these, from Mazak Nissho Iwai (Schaumburg, IL), are new to Lens Saver® windows, having had them mounted for just the last three months.
A low-cost solution to prevent lens damage
Hogan’s production is hard on their optics, cutting steel up to 0.375-in. thick as well as some aluminum and stainless. So far they’ve only had to replace three lenses over the last three months. Lens Saver windows are used because of the ease of use. “We were quick to use them on the Mazaks, because the way the mount is designed leaves space where you can just pull out an adapter and slip the Lens Saver® in its place,” says Lopez.
The Central Cal story
Joe Alandt of Central Cal Metals (Fresno, CA) owns a shop running 12 Mazak laser systems ranging in power output from 1 to 2 kW. Nine of these are equipped with Lens Saver® windows. They were replacing ZnSe lenses every two weeks at a cost of $350-400 for each machine before using the lens protectors. Now they go through about one Lens Saver® per week at a cost of $30 each, and one lens per month. This works out to a cost reduction from their previous expense of from $38,000 to $43,000 annually down to around $19,000 annually, a 50 percent savings.
Alandt says the only reason they lose a lens now is contamination internal to the laser. “Lasers have some contamination internally. There is still a life on these things, but it is substantially longer when you use the Lens Saver.”