In August 2000, an article about laser transformation hardening as performed at Caterpillar appeared in this magazine. The article, "Hitting pay dirt with lasers," told of the production challenges the company faced in the manufacture of its earthmoving equipment. Operating in the most severe environments, Caterpillar customers depend on their equipment running 6 to 7 days per week with very high uptime, for well over 40,000 hours. The article noted that, because of such severe operating conditions, the company continually searches for ways to alter and improve surface properties of its equipment in order to give more value to its customers. However, due to the enormous size of its equipment, traditional surface modification procedures are often cost prohibitive. This factor provided the company with opportunities to incorporate laser transformation hardening into its production operations.
Initially, laser hardening at Caterpillar was performed with a 6kW CO2 laser, an integrating optic, and a proprietary absorptive coating. Then, with the arrival of reliable, multi-kilowatt Nd:YAG lasers, the process was switched to the higher absorptive 1.64-µm laser, because it produced tremendous cost saving in the reduction of operations needed to heat treat. The absorbent paint preparation and removal procedures were eliminated, the optical cleaning and alignment were greatly simplified, the disposal of waste paint and used air filters was eliminated, and the process itself generated far less suspended particulate.
Diode laser solves maintenance problems for transformation hardening at Caterpillar
However, there were drawbacks; long cycle times required for heat treatment with Nd:YAG pushed the laser's limits. Special cooling had to be designed because some larger components required continuous beam-on time in excess of 30 minutes at full power in order to cover the required surface area. Nevertheless, laser transformation hardening using the Nd:YAG laser became a well-established production process, allowing the intelligent use of energy and resources to modify surfaces on an "as needed basis." The article ended with the comment, "It is no wonder that lasers are being looked upon with favor by manufacturing at Caterpillar and its customers."
Fast-forward and lasers are still very much in favor at Caterpillar. But today it is a much more versatile, more powerful laser, the direct-diode laser (DDL), that has taken center stage. Ways to control excessive costs get primary attention in today's extremely fast-moving, highly competitive manufacturing environment. And, after more than a year of research and testing, the company believes DDLs are up to the challenge. This time though, the challenge has to do with controlling the prohibitive maintenance costs inherent with the use of Nd:YAG lasers in the heat-treating process.
Not too long after Caterpillar introduced the Nd:YAG laser into its manufacturing process, it became evident that there was a problem in controlling maintenance costs. Excessive, time-consuming maintenance on Nd:YAG lasers had become a serious problem that begged a solution. Personnel were spending an inordinate amount of downtime on maintenance that primarily involved flashlamp change-out, water leakage and realignment.
In the interim, staffers at Caterpillar's Tech Center had begun to research diode laser technology and called upon Nuvonyx Inc. (Bridgeton, MO), a pioneer in the manufacture of DDLs, to determine what role its technology could play in helping to enhance Caterpillar's manufacturing productivity. Could DDLs improve performance and, at the same time, reduce the considerable costs associated with the maintenance required by Nd:YAG lasers?
In June 2000, Caterpillar's production management began to work with its technology people and engineers from Nuvonyx, who were selected for their experience in the development and production of DDLs, as well as for their knowledge of industrial materials processing applications.
One advantage of the diode laser was obvious from the start: its smaller size created a space advantage on the manufacturing floor. However, would it be durable enough to perform reliably in Caterpillar's manufacturing environment? In addition, would the company's operating and maintenance costs compare favorably with the Nd:YAG laser's? It would take the better part of a year to learn the answers.
During this time, the two companies put the diode laser through rigorous testing.
Initially, there were technical problems due to the power distribution across the beam width. Up until this time, almost all applications with DDLs had been with plastic welding, heat treating, and welding. Caterpillar was Nuvonyx' first production customer to heat treat, and both parties learned from the experience. The power distribution problem was soon corrected with a drop-in lens that produces a steep profile on the wings of the heat treat spot so that they are at focus in the lateral axis and the top hat profile and at defocus in the transverse axis.
Caterpillar discovered a situation with power degradation while putting the laser through long duty cycles in a production environment. Working together, the companies were able to solve the problem and, as a result, were able to bring the production performance of the laser to a consistently higher level.
The rigorous testing of the diode laser also did away with skepticism about the laser's durability and reliability under actual manufacturing conditions. For example, at this writing, Caterpillar has now logged more than 650 trouble-free hours operating its diode laser. During this period, it was noted that a significant decrease in downtime occurred: maintenance hours were reduced by 85 percent. And cycle times decreased anywhere from 10 to 25 percent due to the increased bandwidth and faster speed of the diode laser. Additionally, it was learned that the diode laser provided greater flexibility in power output. With the Nd:YAG laser, the power was basically on or off, and could not be varied. Such positive results with the diode laser led management to conclude that the diode laser technology was the next logical successor to its Nd:YAG lasers. With these improvements in production performance and cost reduction, it is no wonder that (diode) lasers are being looked upon with favor by Caterpillar and its customers.
John Haake (jhaake@nuvonyx) is vice president-market development with Nuvonyx Inc. Check out the company's high-power diode products on its Web site www.nuvonyx.com.