1. How does designed compression work?
Lambda induces designed compression by mechanically stretching the surface just enough to produce a deep stable layer of beneficial residual stress with minimal cold working. Unlike previous surface enhancement techniques, the depth, magnitude and distribution of compression are designed for the component and application. Lambda’s CNC-controlled processes, like LPB®, have patented closed-loop process control exceeding six-sigma, ensuring uniform, repeatable production.
2. Why are Lambda’s surface enhancement processes beneficial?
The layer of beneficial compression stops fatigue crack initiation and growth caused by a wide variety of surface damage, such as corrosion pitting, fretting and foreign object damage (FOD). Because the designed compression can be deeper than other surface treatments, like shot peening, Lambda’s processes provide superior damage tolerance. Stress corrosion cracking, common in high strength materials, is eliminated entirely because the surface in contact with the corrosive environment is not in tension. Lambda’s processes introduce minimal cold work, while shot peening and deep rolling typically cold work the surface over 50%. Low cold work means the yield strength and dislocation density of the treated surface are not altered significantly during the creation of the compressive layer. Therefore, the beneficial compressive layer is much more stable at elevated temperatures and is not prone to mechanical relaxation in the event of a momentary tensile overload.
3. What surface problems has designed residual compression been proven to improve?
Through extensive laboratory testing, designed residual compression has been proven to mitigate fatigue crack initiation and propagation from a wide variety of surface damage mechanisms, including foreign object damage (FOD), corrosion pitting, fretting induced microcracks, and local regions of high tension that are due to stress concentrations inherent in design. In addition, stress corrosion cracking can be virtually eliminated by rendering the surface in compression and the related corrosion fatigue with propagation concurrent is greatly improved.
4. Do Lambda’s processes change material properties?
Unlike shot peening, which commonly cold works the surface over 50%, Lambda’s CNC-controlled processes, like LPB® create minimal cold work. The yield strength, hardness, ductility, and other properties altered by plastic deformation then are not significantly affected. Therefore, the compression induced by Lambda’s CNC-controlled processes is not only deeper than shot peening, but also far more stable at elevated temperatures. Because the yield strength is uniform through the compressive layer and on into the substrate, the beneficial compression does not relax in the event of tensile overload. Metallographic examination at 500x reveals no damage to the grain structure following treatment.
5. Can Lambda’s processes be performed at the customer’s facility or only at Lambda Technologies?
Our surface enhancement techniques are some of the most logistically adaptable surface enhancement processes ever developed. Unlike shot peening and laser shock peening (LSP), Lambda’s processes do not require shipping the components to a remote facility. For example, LPB® is performed in the production shop on conventional CNC machine tools (or by robots) during manufacturing or overhaul. Lambda Technologies develops the LPB® solutions for a specific component geometry and material using our process and materials engineering, fatigue design, and residual stress measurement capabilities. Lambda then provides a CNC turnkey process that is installed at the customer’s facilities, usually on the very CNC machine tools used in manufacturing. Installation and training may occur at the OEM or at the supplier sub-licensed by the OEM. Lambda Technologies does provide LPB® processing for small lots and for low rate initial production (LRIP) prove-out, but the preferred business model is to insert LPB® processing directly into manufacturing in the way that most efficiently and economically benefits our customers.
6. What equipment is required to perform Lambda’s surface enhancement processes?
Lambda’s processes are performed on conventional CNC machine tools or robots in the manufacturing shop environment. Tooling, designed and manufactured by Lambda, is adapted to the tool holders of the CNC machines to be used for processing, usually on the customer’s existing machines that are currently used for machining their parts. Machining often continues to be performed using the same machines used for our processes, such as LPB®, with only a tool change. A computerized control is interfaced with a single digital input to the CNC machinery to synchronize the pressure applied to the work pieces as the tool is positioned under CNC control. Lambda Technologies provides the control system and the tooling required along with the CNC code and pressure files that will create the designed residual stress distribution that optimizes the performance of the customer’s part.
7. What is the process if a company is interested in imparting designed residual compression during production for certain parts?
Customers contact Lambda with a potential application, and an NDA is usually signed to allow discussion of technical details, such as failure modes, component geometry, material, manufacturing methods, etc. If both technical and business cases exist for any of Lambda’s patented surface enhancement processes, Lambda provides a quotation for the nonrecurring engineering (NRE) required to develop production processing. The NRE and any equipment costs depend upon the processing details and the location of processing. All costs can be covered initially or over time under a piece-price license during production, as may be negotiated to meet the needs of the customer and the application.
8. Does Lambda’s surface enhancement processing require a license?
Processing performed at Lambda Technologies does not require a license. Processing at the customer’s facilities or at the customer’s manufacturer does require licensing of Lambda’s patented and proprietary technologies. Licenses can be issued to an OEM who in turn sub-licenses to their suppliers, providing complete control of their supply chain.
9. Can Lambda’s surface enhancement equipment be leased to minimize capital costs or for temporary applications?
Lambda’s surface enhancement tooling and control systems can be provided under lease to minimize the capital costs with royalties paid on a piece-price basis per component produced. The lease includes the control system and the license for the control system software and the proprietary CNC and processing files developed for the customer’s applications. The lease includes support for both the surface enhancement equipment and software. An annual visit provides maintenance and calibration of the Lambda surface enhancement systems in the field. Both hardware and software upgrades are provided as improvements are made.
10. Can a company purchase Lambda’s surface enhancement equipment and is a license still required?
Control systems can be either purchased or leased. A license is still required for the control software and component processing files, and to perform any of our patented processes.
11. How long has LPB® been in production?
LPB® has been in commercial production in the field since 2004. The first production LPB® system installed on a CNC lathe is still in operation, having processed hundreds of components, with not a single fault due to the control system or tooling. LPB® has been in commercial production at Lambda Technologies since 2005 with thousands of components processed with production control exceeding six-sigma as documented by continuous real-time SPC.
12. To what materials have Lambda’s processes been applied?
Designed residual compression has been applied to virtually every metallic alloy of interest in airframe, automotive, nuclear and power generation applications. These include a wide variety of titanium alloys and stainless steels used in compressor blades, vanes, and disks, as well as nickel and cobalt alloys used in turbines. High strength steels used for landing gear, shafts, and bearing materials have been thoroughly investigated, as have carburized gear steels. Austenitic alloys and nuclear system welds have been tested for stress corrosion cracking (SCC). Aluminum structural alloys for aircraft of all types have been treated and tested. Structural complexes, such as fastener assemblies and dovetail joints in which fretting, crevice corrosion, and pitting occur, have also been studied. Fretting and galvanic corrosion of dissimilar alloys in contact have been investigated. Simply put:
- The higher the strength of the material, the greater the fatigue benefit of designed residual compression.
- Damage shallower than the depth of compression can be mitigated.
- SCC cannot occur at a surface in deep compression with low cold work.
13. How long do Lambda’s processes take to process a part in a production setting?
Lambda’s processes are essentially CNC machining operations. They require no pre- or post-processing treatment, only a single pass of the tool over the component surface. Production speed is limited only by the speed at which the CNC machine or robot can move the tool. Speeds of 2000 sfm have been achieved in turning. Typical blade processing times are on the order of minutes in a CNC mill. Full IBR/blisks have been processed on leading edge, trailing edge and tip in a few hours. Robotic processing of landing gear cylinders and propeller blades take less than an hour.
14. How are Lambda’s surface enhancement processes, such as LPB®, 100% quality monitored?
Our techniques, such as LPB® are the only surface enhancement processes that are truly closed-loop process controlled. Other surface enhancement processes including shot peening, laser shocking, and deep rolling control the appropriate process parameters (shot flow, air pressure, pulse duration and strength, rolling pressure, etc), but the actual outcome in terms of the plastic deformation of the surface and the residual stress produced is not directly controlled. Lambda’s patented constant volume LPB®tooling allows the exact force with which the tool is pressed into the surface to be monitored at millisecond intervals and adjusted in closed-loop servo control to track the target force as the tool is positioned. The LPB® processing force is controlled to 0.1% and held within high and low processing bounds as the tool moves across the surface. The simple Hertzian surface loading mechanism combined with the uniform CNC tool positioning and force control provide unprecedented quality control. A permanent file of force at each tool position, including the date, tool and processing files used, and component serial numbers is retained whenever the LPB® system operates. The LPB® component processing files are available to the customer’s QA department, and are used for continuous statistical process control (SPC). The LPB®process is very “robust” because the variation in the controlled processing force (~0.1%) is small compared to the processing tolerance. LPB® processing control; therefore, typically exceeds Six Sigma, far superior to any other surface enhancement method.
15. How do Lambda’s patented surface enhancement processes improve safety?
Safety is improved by greatly reducing the chances of component failure. Lambda’s surface enhancement dramatically increases damage tolerance and suppresses stress corrosion cracking. The deep layer of stable high compression produced by Lambda’s patented techniques can virtually eliminate surface failure initiation from common damage mechanisms like FOD, fretting, and corrosion pits. The fatigue strength of processed ex-service components with surface damage can be even greater than untreated new components.
16. How does designed residual compression reduce manufacturing costs?
Lambda’s surface enhancement processes effectively increase fatigue strength and life by introducing a layer of deep surface compression in fatigue critical areas of the component. Using this beneficial compression in design, less expensive materials may be used for a given application, or superior performance or weight reduction may be achieved with the current material. For example, LPB® processed high-strength steels are virtually immune to stress corrosion cracking, making it unnecessary to utilize more expensive alloys. Less expensive alloys can be used in many applications where fracture toughness or sensitivity to stress corrosion cracking would otherwise require greater expense.
17. How does designed residual compression reduce maintenance costs?
By increasing damage tolerance, designed compression may allow significant reductions in the frequency with which inspections are required and parts replaced. For example, LPB® increased the damage tolerance of a titanium fan blade from 0.005in. to 0.10in., a twenty-fold increase. Larger damage tolerance makes inspections easier and more rapid. Because the frequency of FOD decreases exponentially with FOD size, the need to replace components due to damage is reduced by orders of magnitude. In aluminum aircraft structural alloys, designed compression greatly exceeds the maximum depth of corrosion pits, eliminating the need to grind out pits with the associated reduction in section thickness. Much of the routine maintenance of aircraft structures is unnecessary and can be eliminated. Designed residual compression also eliminates fatigue propagation from the microcracks caused by fretting. Elimination of fretting failures reduces the need for engine inspections and blade and disk maintenance saving both operating costs and system down time.