Recently, though, several military facilities have been testing a new repair technique developed to save expensive parts from the scrap heap. The technique, known as Laser Engineered Net Shaping (LENS™), produces far less heat than conventional repair techniques–so little that the manufacturer says it won't damage small, thin components such as turbine blades, vanes, and impellers. In early tests the technique has fixed a variety of unweldable parts, resulting in millions of dollars of projected annual savings for the U.S. military.LENS machines also automate the process of adding material to a worn or fractured surface. Guided by original CAD data, a CNC interface, or simplified teach and learn software, LENS machines deposit metal features one layer at a time in a fast, repeatable manner that also boosts repair quality.Commercial LENS Invented at Sandia National Laboratories, LENS has been developed and commercialized by Optomec Inc., a supplier of additive manufacturing systems.To start the repair process, a high–powered laser beam strikes a small spot (approximately 0.02 inch wide) on a damaged metal component, producing a molten pool (see Figure 1). A nozzle blows metal powder into the pool to increase its volume. The nozzle positions the material so accurately that there's no need for masking. This process is repeated within a plane to create a single metal layer.
Then another layer is deposited on top of that. The machine deposits layer upon layer until it has produced a metal version of the CAD model.LENS is a computer-controlled, layer-by-layer deposition process that uses a high-powered laser beam to strike a small spot on a damaged metal component, producing a molten pool. A nozzle blows metal powder into the pool to increase its volume, allowing the system to give new life to damaged metal parts that can't stand up to igh-temperature welding.In most cases, the tiny molten pool produced by the LENS system cools at a rate of 1,000 to 5,000 degrees C per second. Rapid material cooling and solidification produce fully dense features with greater strength and ductility than those made by other welding techniques. In some cases, the LENS repair even exhibits mechanical properties that are superior to the original material. This means parts may stay in service longer after repair than before.LENS produces small, uniform grain structures, which enhances repair quality. The technique can even replicate the single–crystal structures required for some applications. LENS repairs also exhibit no sink or undercut, further increasing the range of repair possibilities.Two years ago the U.S. Department of Defense (DOD) launched a $3 million program to establish LENS as a viable repair option. During the program, now viewed by the DOD as a major success, users were expected to recoup their LENS investments in as little as six months.LENS tehnology saves money by fixing parts for a fraction of the cost of a new part.
Consider a compressor made of thin INCONEL alloy 713LC. LENS repairs to the compressor cost $2,000, compared to the $8,300 purchase price of a new compressor. The bottom line: Military facilities save $6,300 by fixing damaged compressors that used to be scrapped.The National Center for Manufacturing Sciences (NCMS), its member companies, and the DOD conducted a collaborative research project to employ the LENS system for repair and overhaul techniques at the Anniston Army Depot (ANAD) in Anniston, Ala. Unable to take the heat from conventional welding methods, small, thin metal parts in the gas turbine engines of ANAD's M1 Abrams tanks used to be classified as irreparable and were replaced with new parts. Now a LENS machine fixes them for a fraction of the replacement cost, which is projected to generate more than $6.3 million in savings annually for the DOD –13.5 percent more than original projections.Completing the first project phase of technology assessment and validation, the NCMS–led team has proven not only that LENS technology meets critical performance demands, but initial results also indicate that the projected annual savings will be more than $747,000 over the initial target goal of just less than $5.6 million. Based on NCMS's initial findings, the U.S. Army Tank–Automotive Armaments Command (TACOM) already has approved military use of LENS for seven of the repair operations tested in phase I. With one of the methods, TACOM now will have the ability to complete fourth–stage seal runner restoration at one–third the cost of replacement.In addition to these welding–type fixes, LENS machines can make unconventional repairs beyond the capabilities of any welding system. In one case, several welding procedures failed to fix a crack in a 11in.–diameter mold tool made of 420 stainless steel. The repeated welding attempts also ruined the material in the area of the crack (HAZ). Finally workers cut off the cracked half of the tool and replaced it with a new half deposited by a LENS system.The newest LENS machines feature a vision system that lets users see the damaged part on a monitor. Crosshairs appear on top of the part image" users map the repair area by moving the crosshairs with a computer mouse. Then they enter process parameters, such as the length and width of the repair. Using the map and entered data, special software generates the repair file that directs the operation of the LENS machine. Then the system stores this information for future use. If a similar repair is needed, the operator can use the stored file rather than create a new one.
Other uses of LENS technology center on low–volume manufacturing, in which CAD files drive LENS to create parts that were thought to be impossible to fabricate with conventional techniques. This opens the door for LENS to fabricate replacement components for parts that are not repairable at the time they are needed.