VOL. 7 November ISSUE YEAR 2006
in Vol. 7 - November Issue - Year 2006
Laser Peening – An Affordable Solution to Metal Fatigue
Jeff Dulaney, President and CEO of LSP Technologies
Jeff Dulaney with one of LSP Technologies production laser peening systems
Production laser peening cells at LSP Technologies
LSP Technologies production facility in Dublin, OH USA
Laser peening is a relatively new technology that has a number of advantages. MFN wanted to know more details about this process and was pleased that Jeff, Dulaney, President and CEO of LSP Technology, agreed to take time for this interview.
(?) MFN: What is LSP Technologies, Inc.’s primary business?
(!) J. D.: LSP Technologies provides laser peening services under the trademark LaserPeen® brand of processing services. We also provide customized laser peening systems for government and industry customers. We have been providing LaserPeen® brand services and equipment to our customers for more than 10 years.
(?) MFN: What is LaserPeen® processing?
(!) J. D.: LaserPeen® processing is an innovative surface enhancement technology that is used to increase the fatigue resistance of metal parts by the introduction of compressive residual stresses like shot peening. It uses high-power pulsed lasers to generate a shock wave on the surface of the part. This shock wave cold works the surface of the metal surface. LaserPeen® processing is also known as laser shock peening, or more simply, laser peening.
(?) MFN: How is this treatment different from metal shot peening?
(!) J. D.: LaserPeen® processing creates beneficial compressive residual stress in the surfaces of parts that results in improved resistance to metal fatigue and improved damage tolerance. It creates residual stress five to ten times deeper than those achievable with conventional shot peening. Consequently, the improvements in resistance to metal fatigue are also much greater than can be achieve d with shot peening.
(?) MFN: How does LaserPeen® processing work?
(!) J. D.: The equipment drives a high amplitude shock wave into a material surface using a high energy pulsed laser. The effect on the material being processed is achieved through the mechanical "cold working" effect produced by the shock wave, not a thermal effect from heating of the surface by the laser beam. The surface of the metal part is not heated by the process. Essentially, the part is "micro forged", spot by spot in critical areas using high intensity laser light.
Before processing, an opaque overlay (typically black paint or tape) and a transparent overlay (typically flowing water) are applied to the surface to be processed. The laser pulse passes through the transparent overlay and strikes the opaque overlay, causing it to begin to partially vaporize. The vapor absorbs the remaining laser light and produces a rapidly expanding plasma plume. The expanding plasma plume is confined between the surface of the part and the transparent overlay, and a rapidly rising, high-pressure shock wave propagates into the material. When the peak stress of the shock wave is above the dynamic yield stress of the metal, the metal yields, and the surface of the metal is "cold worked" or plastically deformed.
The plastic deformation caused by the shock wave results in compressive residual stresses in the surface of the part. The depth and magnitude of the residual stresses depend upon the material and the processing parameters. Compressive residual stresses typically extend as deep as 0.040” to 0.100” (1.0 to 2.5 mm) below the surface and can approach the yield strength of the material at the surface of the part. These deep compressive residual stresses increase the resistance of materials to surface-related failures such as fatigue, fretting fatigue, and stress corrosion cracking.
LaserPeen® processing should not be viewed strictly as an alternative to conventional shot peening methods for creating surface compressive residual stresses. Laser peening is well suited for precisely controlled treatment of localized problem areas, whereas shot peening may be better suited for broad area coverage. Laser peening and shot peening may be used in combination beneficially and economically to treat parts requiring deep compressive residual stress in critical areas and having less stringent requirements in other areas.
(?) MFN: What markets or industries does LSP Technologies serve?
(!) J. D.: The initial applications for LaserPeen® processing have been for gas turbine engine blades and components used in the aerospace industry, because of the critical need for better fatigue performance and damage tolerance. New applications are emerging for LaserPeen® processing of helicopter components, which are especially susceptible to metal fatigue. LSP Technologies maintains AS-9100 quality system certification for processing parts for the aerospace industry.
Many other industries also have applications where metal fatigue is a significant problem, and LSP Technologies is developing numerous applications for customers in the automotive/truck, medical device/orthopaedic implant, and industrial machinery industries.
(?) MFN: Does LaserPeen® processing work on all metals?
(!) J. D.: This treatment has been used successfully on a wide variety of engineering materials. The initial applications have focused on titanium and aluminum alloys used in the aerospace industry, but laser peening also works very well on all types of steels, and nickel-base and copper-base alloys.
(?) MFN: Is laser peening affordable?
(!) J. D.: Absolutely! We have worked diligently to reduce the cost over the past 10 years. With support from the U.S. Air Force and U.S. Army Manufacturing Technology programs, we have been able to significantly reduce the cost of laser peening and to increase the process throughput. Also, we continue to invest in the technology to further decrease the cost and increase the production throughput. This is allowing us to reach markets which are more cost sensitive. Laser peening is more expensive than shot peening, but it does a superior job of extending part life.
LaserPeen® processing is affordable for most applications where a critical need exists to improve fatigue performance, especially when the full life cycle costs and consequences of catastrophic failures are considered.
(?) MFN: What is the history of LSP Technologies and LaserPeen® processing?
(!) J. D.: I founded LSP Technologies in 1995 in response to an urgent need by GE Aircraft Engines and the U.S. Air Force to build and implement production laser peening systems for laser peening of gas turbine engine blades for the B1-B Lancer. Laser peening technology was invented at Battelle in the early 1970s, but commercialization was slow until a critical need arose, and improved laser systems were developed and hardened for production applications..
In the early 1990s, the B-1B Lancer's F101 engine began experiencing failures of titanium turbine blades due to foreign object damage (FOD) caused by hard objects ingested into the engine. Several catastrophic engine failures occurred from fatigue cracks, which initiated at FOD damage sites along the leading edge of the first stage fan blade. In several cases, chunks of blades broke loose and caused irreparable damage to the engines.
To avoid grounding the B-1 fleet during this time, the Air Force required a manual inspection of all the fan blades. Crew chiefs were required to conduct an inspection of the leading edge of each blade prior to the first flight of the day. These time-consuming leading edge inspections involved rubbing the leading edge with cotton balls, cotton gloves and even dental floss. If a single snag was detected, the blade was replaced prior to the next flight. In 1994, over one million man-hours at a cost of about $10 million per year were required to complete the engine inspections and keep the B-1 flying.
The Air Force ManTech Program, working with General Electric Aircraft Engines (GEAE) and LSP Technologies, Inc. determined that laser peening was the best solution to increase the durability of the titanium fan blades and decrease their sensitivity to FOD. Laser peening was shown to maintain the fatigue performance of damaged blades, to equal to or better than new, undamaged blades.
Members of LSP Technologies’ staff developed the process for this first-ever production application, designed and delivered four laser peening systems for GEAE, and conducted a technology-transfer program to transition laser peening technology into GEAE production operations.
Based on this success, laser peening was also applied to turbine engine blades for the F110 engine used in the F-16 Falcon, which was experiencing problems with FOD-induced fatigue failures.
Laser peening has been cited as a major "success story" by the Air Force. The Air Force has estimated the cost savings benefit of laser peening to be more than $100 million to date, and the total benefit is expected to be in excess of $1 billion when applied to additional aircraft applications.
In 2001 LSP Technologies demonstrated the benefits of laser peening on what would become the world’s first commercial production application; the Trent 800 fan blade for Rolls-Royce.
In 2003, LSP Technologies began production LaserPeen® processing at our Dublin, OH, facility of integrally bladed rotors (IBRs) for Pratt & Whitney’s F119 engine that is used in the F/A-22 Raptor, the nation’s newest fighter aircraft. This application of laser peening avoided a costly redesign, estimated at $10 million, and restored the high cycle fatigue strength and damage tolerance needed for the F119 IBRs. Even more important, the impact on crew safety and mission readiness is very positive.
(?) MFN: What do you predict for the future for LaserPeen® processing?
(!) J. D.: There is a large market for LaserPeen® processing that extends to a variety of industrial arenas. As we drive the cost of the process lower with the introduction of our continuing technology developments, the process will be adopted by those industries that are extremely cost driven, but looking to add value for their customers.
(?) MFN: How important was it to your company to become AS9100 qualified?
(!) J. D.: Our customers depend upon our ability to provide them quality products and services. The AS9100 certification assures them that we adhere to specific rigorous procedures.
(?) MFN: Is LSP Technologies developing any other new technologies?
(!) J. D.: LSP Technologies is developing several technologies which have evolved from laser peening technology.
We are coming to the end of the development cycle for a revolutionary new inspection technology called laser bond inspection (LBI), which can be used for inspecting and assuring the quality of adhesive bonds used in next generation aircraft and unmanned vehicles, as well as repair patches applied to aging aircraft. The integrity of adhesive joints is difficult or impossible to inspect by conventional X-ray or ultrasonic testing, which cannot detect "kissing bonds" or joints where the parts are in intimate contact, but have no structural strength.
We at MFN would like to thank Mr. Jeff Dulaney for this interview!