in Vol. 5 - July Issue - Year 2004
Beyond the Surface
Paul S. Prevey, President and Director of Research, Lambda Technologies
Lambda Technology engineers confer on a finite element model of residual stress distribution in a turbine component
LPB caliper tool processing a turbine engine blade
Single point LPB tool in operation
Interview with Paul S. Prevey, President and Director of Research, Lambda Technologies
(?) MFN: Since we began talking about this interview, the name of the company has changed. Would you care to elaborate on this?
(!) P.P.: Yes. Lambda Research and our affiliate company, Surface Enhancement Technologies, have fallen under the Lambda Technologies umbrella. We’ve chosen Lambda Technologies because our expansion into surface enhancement has led us into a broader market than we’ve traditionally pursued.
(?) MFN: Lambda Research is a long-standing entity in the field of x-ray diffraction and residual stress measurement, how do the capabilities of Lambda Technologies differ from those of Lambda Research?
(!) P.P.: The capabilities of Lambda Technologies go beyond x-ray diffraction. What we’re actually doing in the case of Lambda Technologies is developing custom solutions to the distribution of beneficial surface residual stress within a component. Our goal is to impart compressive residual stress in a component to make it more resistant to traditional damage mechanisms through the most effective method. Sometimes this involves using a Lambda developed process such as Low Plasticity Burnishing or LPB. In other cases, it may mean shot peening. The other aspect is the integration with the manufacturing area. We provide seamless integration of the selected processes into the customer’s facility. We believe it’s a much broader undertaking involving interfacing traditional design and engineering talents with production engineering to implement this approach.
(?) MFN: So you are still actively involved in the x-ray diffraction area?
(!) P.P.: Absolutely. We are still actively involved in x-ray diffraction and residual stress measurement using both diffraction and mechanical methods. We operate a world-class laboratory facility and are the pre-eminent source of residual stress measurement and analysis. Lambda Technologies will continue to provide those services through Lambda Technologies - Laboratory Services.
(?) MFN: You mentioned LPB, would you describe the process and its applications?
(!) P.P.: LPB is a method of imparting deep compressive residual stress in a component. Our initial method for doing this involves rolling a high modulus ball under pressure across the surface. The unique thing about our approach is that the design of the compressive zone and the engineering to best locate the equilibrating tensions falls within Lambda Technologies. We see a number of applications for LPB in aircraft. We’ve identified a wide range of applications including some for ships and trucks, nuclear and electric power generation, and surgical implants. We feel this technology will touch all of us within the not too distant future.
(?) MFN: How does this tie to the new organizational structure?
(!) P.P.: Many of the engineering and scientific disciplines required for the design of beneficial residual stress distributions are more closely aligned with the research activities of the company. A good example is contracted research and development such as our Small Business Innovation Research. We’ve also developed new capabilities in finite element analysis and linear elastic fracture mechanics. Lastly, the introduction of manufacturing related disciplines are all new growth areas for Lambda. We have three functional organizations: Laboratory Services to perform our traditional x-ray diffraction and residual stress measurements, Research And Engineering to design and develop residual stress solutions, and Surface Enhancement to field and support our processes. We feel it’s a strong move forward.
(?) MFN: Let’s talk specifically about LPB, What are the differences between LPB and other surface enhancements?
(!) P.P.: Perhaps the easiest comparison is in terms of shot peening that provides excellent compressive residual stress on the surface - usually to a maximum of .010 or .015 of an inch. In addition, shot peening also entails a high degree of cold working percentage often 50 to 60% and as much as 100%. LPB provides a depth of compression that can easily achieve .080 to .100 of an inch depending on the material. At the same time, the amount of cold working is very low in the 3-5% range, providing thermal and mechanical stability of the compressive layer. So there is a substantial difference.
The other issue that we look at is how LPB integrates into a manufacturing operation. Being a one-pass machine shop process, it is possible to LPB a component on the same machine as other production operations without the need for multiple set-ups. Compared to laser shock peening that requires a unique facility and an extensive capital outlay, LPB’s much easier to integrate. At the same time, I have to caution you that LPB will never be as inexpensive as shot peening. On the other hand, the benefits are far greater when there are potential damage mechanisms that may affect component life.
(?) MFN: What are the relative costs?
(!) P.P.: The great thing about LPB is that the same technical skills used to machine a part are the same skills necessary to LPB it. So you’re not looking at a work force training issue. In addition, LPB is a machining process that is compatible with existing technologies in a manufacturing setting.
To develop an LPB application, we have a systems approach that goes through three phases. Phase 1 analyzes and determines the qualities and the characteristics of the material that we’re working with. The 2nd phase designs a custom residual stress distribution for the customer. In Phase 3, we take it to the manufacturing floor. There are some initial costs relative to design and integration. But in the long run, the enhancement to the material performance in high cycle fatigue or other potential damage mechanisms is a relatively modest investment. Our approach is to license our customers to process components in their own facility. That way, processing falls under their quality control and keeps their workforce busy.
(?) MFN: Can you be more specific about the applications?
(!) P.P.: Many of the components we’re working with are proprietary. There are a couple of broad applications that we can discuss that provide insight. The first is the use of LPB to overcome fretting fatigue damage. In that case, the depth of compression gets below the micro-cracking associated with fretting. Even though the components may continue to fret, there is no potential for structural or fatigue failure from the fretting. Another major application in the aircraft area is in overcoming stress corrosion cracking in the hardened steels used for aircraft landing gear.
(?) MFN: How does LPB overcome Stress Corrosion Cracking (SCC) in high strength steels?
(!) P.P.: As I’m sure you are aware, the phenomenon of stress corrosion cracking requires three conditions to occur. The first is a susceptible material such as the hardened steels used in landing gear components such as 300M, 4340, or 4350 steels. The second condition is the introduction of a corrosive environment. The third, and final, condition is the existence of tensile stresses. Without those tensile stresses, stress corrosion cracking simply cannot take place. By imparting deep compressive residual stress, LPB eliminates the potential for stress corrosion cracking. In this regard, we developed some rather spectacular results that have been confirmed by the Department of Defense.
(?) MFN: So it makes for a safer, more robust landing gear?
(!) P.P.: Considering that SCC can render one of the most robust designs in an aircraft susceptible to failure, we feel that it will provide for safer aircraft operations in take-offs and landings. This is particularly true in military operations from aircraft carriers or other environments where aircraft are exposed to more aggressive environments.
(?) MFN: How is the process controlled?
(!) P.P.: LPB is controlled in a number of ways. Through our controller, we’re able to implement very tight quality assurance standards and use statistical process control to measure the performance. We provide that information to our clients as part of our ongoing service arrangements. That enables them to have a high degree of confidence in the kind of pressures and compressive stresses that are generated in their components.
(?) MFN: It’s too bad that the residual stress distribution can’t be part of the design process. Landing gear are the heaviest structures in an aircraft and a great opportunity for weight reduction…
(!) P.P.: The long term goal of Lambda Technologies is to develop residual stress design methods. We believe there are ways in which the benefits of compressive residual stress can be quantified and used in the design process. As you pointed out, landing gear are the heaviest components on an aircraft. If in the future, we can begin attacking these problems in the design process, it will make it easier to employ lighter structures in aircraft.
(?) MFN: Let’s change the topic and talk about engines…
(!) P.P.: Certainly they are the main area of concern for potential failures and LPB has clearly been shown to provide superior enhancement to turbine components by mitigating traditional damage mechanisms such as foreign object damage (FOD), fretting, or high cycle fatigue.
(?) MFN: Are you under contract for any specific applications?
(!) P.P.: As a matter of fact, we are under contract to Rolls-Royce to develop a specific engine enhancement.
(?) MFN: This process is also applicable to aircraft structures?
(!) P.P.: We think of LPB as widely applicable to aircraft structures. This is particularly true for ageing aircraft in which parts may be out of production and very difficult to procure. The damage mechanisms of fretting, corrosion, and corrosion pitting are mitigated through the use of LPB. We think it’s a great opportunity to avoid extensive overhaul or reclaim previously condemned parts using the process. We’ve actually looked at providing in situ type tools for field repairs.
(?) MFN: We’ve really talked a great deal about aircraft, is LPB useful in other industrial segments?
(!) P.P.: Yes, we’re in the running for the use of LPB on the Yucca Mountain Project. We have clearly proven that LPB can be used to provide superior stress relief in the weldments that seal the waste containers used to store nuclear waste. Not only do we impart the highest degree of compressive stress, we are also the most cost effective approach of doing that.
(?) MFN: It sounds like events are moving rapidly on the LPB front, is Lambda Technologies pursuing other capabilities?
(!) P.P.: We’re always on the lookout for other technologies and openings where we feel our unique capabilities will apply, and we’ll be talking about those - hopefully in the near future.
MFN: Paul, thank you for taking the time to speak with us.
P.P.: My pleasure, and my thanks to the Metal Finishing News for taking the time to visit with us today.
Dave Butler, Director of Research,
5521 Fair Lane, Cincinnati, Ohio 45227, USA
Tel.: +1.513.561 0883
Fax: +1.513.561 0886