Process control during LSP is complicated by variations in the thickness and even turbulence of the water tamp, or debris in the beam path, that affect the power of the shock wave produced. As a result, quality control of the process is difficult, no matter how controlled the laser is. Studies have shown internal cracking on laser-treated components caused by superposition of echoing shock, so treating thin sections like engine blades and vanes can prove to be fairly difficult. Make sure the processed parts are inspected closely to ensure that processing hasn’t inadvertently caused damage to the same part you were trying to improve.
Low plasticity burnishing
LPB, currently available through Delta TechOps and PAS Technologies, uses hydrostatic ball and roller tools to produce the plastic deformation necessary to create the desired compression for the work piece. LPB has even been shown to have the ability to produce through-thickness compression in blades and vanes, greatly increasing their damage tolerance more than 10-fold, effectively mitigating most FOD and reducing inspection requirements.
The LPB process uses either CNC machines or industrial robots in the MRO shop or manufacturing environment along with the patented tools to create a deep layer of residual compression that mitigates surface damage. LPB has been documented to create compression as deep as 12 mm into the component in a single treatment (average is 1-7+ mm), leaving the surface superior to what it was before and actually rendering the component, in most cases, better than new. The cold work produced from this process is less than 5 percent, although it can be adjusted for varying needs, making it widely applicable throughout the aerospace industry. LPB has already been successfully applied to engines, propellers, propeller hubs, and landing gear.
The LPB process can be performed on-site in the shop or insitu on aircraft using robots, making it easy to incorporate into everyday maintenance and manufacturing procedures. The method is applied under continuous closed loop process control (CLPC), creating accuracy within 0.1 percent and alerting the operator and QA immediately if the processing bounds are exceeded. The limitation of this process is that different CNC processing codes need to be developed for each application, just like any other machining task. The other issue is that because of dimensional restrictions, it may not be possible to create the tools necessary to work on certain geometries, although that has yet to be a problem.
Treating the components of your aircraft with any of these surface enhancement fatigue and damage tolerance strengthening techniques can save huge amounts of maintenance and inspection time and money, more than offsetting the initial cost of implementation. With the current weak economy and maintenance-related accident rates going up, surface enhancement processes are invaluable and need to be looked into by everyone. Surface enhancement may not fix all problems, but at least you won’t have to worry about stress corrosion cracking or fatigue failures of critical components, and your aircraft can spend more time on wing rather than in the shop.
This article was submitted by Julia Prevey from Lambda Technologies. For more information visit www.lambdatechs.com.
LPB uses residual compression by design to increase damage tolerance in metallic components, greatly extending their service life
Pacific Propeller International has begun robotically processing aircraft components for the US Navy, using Lambda Technologies' patented low plasticity burnishing (LPB).