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Low Plasticity Burnishing
Abstract
Low Plasticity Burnishing (LPB) is a state-of-the-art method of surface enhancement,
which raises the burnishing to next level of sophistication and that can provide deep,
stable surface compression for improved surface integrity characteristics. This paper
reports an innovative approach, which was used to design and develop a new LPB tool.
The performance of the LPB tool has been assessed on surface roughness and surface
microhardness aspects of steels. This type of design has certain inherent advantages in
terms of flexibility in controlling the process. Low cold work, better finish, improved
surface hardness, enhanced fatigue life, corrosion resistance, improved dimensional
control, etc., are some of the all-round benefits that can be obtained from the current
apparatus. This technology could be very useful, ranged from common small-scale
industries to hi-tech applications, as the tooling and fixturing were developed with a
vision to process varieties of materials for versatile applications and the process can be
readily accommodated in an existing machine shop environment. The process could be
applied to critical components effectively, as it has significant process cycle time
advantage, lower capital cost and suitability to adapt existing machine layout and high-
speed machining concepts.
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Outl ine
(Abstract) ............................................................................................................................ii
Acknowledgements ...........................................................................................................iii
Outline ...............................................................................................................................iv
List of Figures ....................................................................................................................v
List of Tables ......................................................................................................................v
Commonly Used Variables .................................................................................................v
Chapter 1..........................................................................................................................1
Introduction...................................................................................................... ................1
1.1 Need of surface enhancement ...................................................................................1
1.2 Surface enhancement processes...................................... ............................................1
1.3 Scope of the Work Which of the most beneficial process3
Chapter 2..........................................................................................................................4
Low plasticity Burnishing............................................................................................................
2.1 Introduction.........................................................................................................................4
2.2 History..................................................................................................................................4
2.3 Description..........................................................................................................................5
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2.4 How it works.......................................................................................................................6
2.5Cold working........................................................................................................................7
Chapter 3...................................................................................................................................8
Overview................................................................................................................................8
3.1 Benefits............................................................................................................................9
Chapter 4................................................................................................................................11
4.1Process..............................................................................................................................11
4.2 Design..............................................................................................................................13
4.3 Effect of LPB on HCF Performance and FOD Tolerance ...........................................14
4.4 Process Design Protocol ...............................................................................................17
4.5 Quality Control Process Monitoring ..........................................................................19 Chapter 5...............................................................................................................................
Advantages and Benefits ...................................................................................................22
Chapter 6................................................................................................................................
Use & application................................................................................................................24
6.1 Aircraft Propulsion Application.........................................25
6.2 Aircraft Structures Application...26
6.3 Engineering Application............................................................................................27
6.4 Medical Implants Application27Chapter 7.28
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Conclusion..28
Referances.
Lis t ofFigures
Fig 1.1 LPB uses a patented constant volume hydrostatic tool
Fig 2.1 LPB
Fig 4.1 Single point tool LPB processing of the dovetail of Ti -6-4 compressor blade.
Fig 4.2 Finite Element Analysis
Fig 4.3 Residual Stress
Fig 4.4 Residual Stress & Cold work Profile for IN718
Fig 4.5LPB Processing Control System
Fig 6.1Industrial Robot
List of Table
Table 1 summarizes the processing speed, depth of compression, amount of cold work
produced, and relative cost for the different surface enhancement methods available
Commonly Used Variables
LPB-low plasticity burnishing
FOD- foreign object damage
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SCC- stress corrosion cracking
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Chapter1
Introduction
Introduction:
1.1Need ofSurface enhancement
Surface enhancement is the introduction of a surface layer of compressive residual
stress to minimize sensitivity to fatigue or stress corrosion failure mechanisms,
resulting in improved performance and increased life of components. Surface
enhancement methods include:
Shot Peeni ng Deep Roll ing
Contr ol led Coverage Peening Low Plasticity Burn ishing
(LPB)
Laser Shock Peening (LSP) Controll ed Plastici ty
Burnishing
With the exception of simple overload, failures initiate from the surface of a part by some
combination of fatigue, stress corrosion cracking, or corrosion fatigue. Failures are often
exacerbated by a crack initiating damage mechanism such as fretting, corrosion pitting,
intergranular corrosion, or foreign object damage (FOD). The surface of a component is
inherently weaker than the interior because the free surface lacks the constraint imposed
by fully surrounding material. Therefore, as is generally observed, fatigue cracks will
initiate at the surface. Internal fatigue crack initiation requires high internal residual
tensile stress and/or a discontinuity such as an inclusion, void, or other internal flaw to
act as a surface for initiation.
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Stress corrosion cracking (SCC) under static load, and its dynamic cousin corrosion
fatigue, which combines cyclic crack growth with stress corrosion cracking, also
necessarily originate at the surface. Only at the surface do the combination of susceptible
material, a corrosive environment, and tension exceeding the threshold stress level for
SCC occur.
Surface enhancement is the introduction of a surface layer of compressive residual
stress to minimize sensitivity to fatigue or stress corrosion failure mechanisms, resulting
in improved performance and increased life of components. The presence of a stable
compressive layer with a depth and magnitude of compression and cold work designed
for the service stresses and environment can dramatically improve the effective material
properties. The improvements in life and performance can far exceed those achieved by
alloy substitution. If the compressive layer is of sufficient depth, damage mechanisms
such as corrosion pits, FOD, and fretting can be completely mitigated. The effective
strength improvement achieved by surface enhancement can allow substitution of less
expensive materials, reduction in cross sections and weights, and mitigation of failure
mechanisms. Component life and performance can be increased, avoiding the expense of
changing either material or design.
Surface enhancement is not a new idea. A classic 1959 example of four-foldimprovement in fatigue strength resulting from shot peening with different preloads. In
the high cycle fatigue regime, with design lives exceeding a few thousand cycles, the
presence of a shallow layer of compression dominates the fatigue performance. The
fatigue strength is effectively increased from 50 ksi to over 200 ksi by a layer of residual
compression only 0.010 in. deep. The lower linear plot of endurance limit as a function of
maximum compressive stress is essentially an empirically determined Goodman diagram
confirming the four-fold increase in fatigue strength achieved by introducing a layer of
residual compression on the surface. Lambdas patented fatigue design methods allow
surface enhancement to be optimized for the material and application.
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The fatigue benefits shown in result from retardation of crack nucleation and microcrack
growth. Damage from corrosion pitting, FOD, and fretting can penetrate through the shot
peening induced compressive layer. Deepercompression achievable with laser shock
peening (LSP) and low plasticity burnishing (LPB), is sufficient to completely mitigate
many of the common damage mechanisms that dramatically reduce fatigue performance.
Shot peening, introduced into the automotive industry in the late 1920s, has been widely
used to ensure the fatigue performance of a wide variety of automotive, aerospace and
other mechanical components. Other surface enhancement methods have since been
developed and are commercially available. These are briefly described here. Interest in
surface enhancement has increased as performance improvement through alloy
development has encountered cost and material limitations. Lambdas unique
combination of residual stress and cold work measurement, fatigue design, processing
and testing capabilities provide the means to select and design surface enhancement
processes for optimal component performance.
1.2 Scope of workWhich is most beneficial process
Table 1 summarizes the processing speed, depth of compression, amount of cold work
produced, and relative cost for the different surface enhancement methods available
Surface Treatment Speed Coldwork Depth
Shot Peening Fast High 15-50% 0.2 mm
Gravity Peening Fast Lower 10-20% 0.5 mm
Low Plasticity Burnishing
(LPB)
Moderate Low 2-5% 1mm 7+mm
Deep Rolling Moderate High 10-50% 1 mm+
Laser Shock Peening (LSP) Slow Low 5-7% 1-2 mm
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Table 1: Relative processing speed, depth of compression, amount of cold work produced
and cost of surface enhancement methods.
Chapter 2
Low Plasticity Burnishing (LPB)
2.1 Introduction
Low plasticity burnishing (LPB) is a method of metal improvement that provides deep,
stable surface compressive residual stresses with little cold work for improved damage
tolerance and metal fatigue life extension. Improved fretting fatigue and stress corrosion
performance has been documented, even at elevated temperatures where the compression
from other metal improvement processes relaxes. The resulting deep layer of compressive
residual stress has also been shown to improve high cycle fatigue (HCF) and low cycle
fatigue (LCF) performance.
2.2 History
Unlike LPB, traditional burnishing tools consist of a hard wheel or fixed lubricated ball
pressed into the surface of an asymmetrical work piece with sufficient force to deform the
surface layers, usually in a lathe. The process does multiple passes over the work pieces,
usually under increasing load, to improve surface finish and deliberately cold work the
surface. Roller and ball burnishing have been studied in Russia and Japan, and were
applied most extensively in the USSR in the 1970s. Various burnishing methods are used,
particularly in Eastern Europe, to improve fatigue life. Improvements in HCF, corrosion
fatigue and SCC are documented, with fatigue strength enhancement attributed to
improved finish, the development of a compressive surface layer, and the increased yield
strength of the cold worked surface.
LPB was developed and patented by Lambda Technologies, a small family-owned
company from Cincinnati, Ohio, in 1996. Since then, LPB has been developed to produce
compression in a wide array of materials to mitigate surface damage, including
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fretting, corrosion pitting, stress corrosion cracking (SCC), and foreign object
damage (FOD), and is being employed by such companies asDelta TechOps and PAS
Technologies, as well as NAVAIR, to aid in their daily MRO operations. To this day,
LPB is the only metal improvement method applied under continuous closed-loop
process control and has been successfully applied to turbine engines, piston engines,
propellers, aging aircraft structures, landing gear, nuclear waste material containers,
biomedical implants and welded joints. The applications involved titanium, iron, nickel
and steel-based components and showed improved damage tolerance as well as high and
low cycle fatigue performance by an order of magnitude.
2.3 Descri ption
Low Plasticity Burnishing (LPB) differs from conventional ball or roller burnishing,
also known as deep rolling, in using theminimal amount of plastic deformation (or
cold working) needed to create the level of residual stress to improve fatigue or stress
corrosion performance. Low cold working provides both thermal and mechanical
stability of the beneficial compression. LPB uses a patented constant volume
hydrostatic tool design to float the burnishing ball continuously during operation,
regardless of the force applied. This provides indefinite tool life and eliminates the
possibility of dragging the ball and damaging the surface.
LPB can be performed in the direction chosen to most-favorably develop the desired
state of residual stress (U.S. Patent 6,415,486). For blade edges, the tool path is
commonly either parallel or perpendicular to the blade edge (span-wise or cord-wise in
the terminology of blade designers) to which the pressure is applied and; therefore, the
burnishing force generated is varied as a function of position both cord-wise and span-
wise to achieve the desired magnitude of compression, typically through-thickness on
blade leading edges. LPB can produce compression ranging from a few thousandths ofan inch (comparable to shot peening) to over a full centimeter for nuclear weld
applications. Wheel-type tools are also available for tight radii and restricted geometries,
such as splines and fillets.
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Schematic
LPB uses a patented constant volume hydrostatic tool
design to "float" the burnishing ball continuously during operation, regardless of the
force applied.
LPB is a patented, mature, proven surface treatment for improving High-Cycle
Fatigue (HCF), Stress Corrosion Cracking (SCC) and damage tolerance performance.
This metal improvement technique was first used in applications in 1996 by Lambda
Technologies and has been in commercial production since 2004. It is available through
Lambda Technologies, industrial OEM's and through select third party providers for
commercial and military aircraft maintenance applications. The LPB process can be
applied during initial manufacture or during maintenance and repair operations. LPB
is a practical, cost-effective, shop floor logistically compatible process that provides
reliable performance improvement without altering either the material or design.
2.4 How it works
The basic LPB tool is a ball that is supported in a spherical hydrostatic bearing. The tool
can be held in any CNC machine or by industrial robots, depending on the application.
The machine tool coolant is used to pressurize the bearing with a continuous flow of fluid
to support the ball. The ball does not contact the mechanical bearing seat, even under
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load. The ball is loaded at a normal state to the surface of a component with a hydraulic
cylinder that is in the body of the tool. LPB can be performed in conjunction with chip
forming machining operations in the same CNC machining tool.
The ball rolls across the surface of a component in a pattern defined in the CNC code, as
in any machining operation. The tool path and normal pressure applied are designed to
create a distribution of compressive residual stress. The form of the distribution is
designed to counter applied stresses and optimize fatigue and stress corrosion
performance. Since there is no shear being applied to the ball, it is free to roll in any
direction. As the ball rolls over the component, the pressure from the ball causes plastic
deformation to occur in the surface of the material under the ball. Since the bulk of the
material constrains the deformed area, the deformed zone is left in compression after the
ball passes.
2.5 Cold working
The cold workproduced from this process is typically between 2-5%, a great deal less
than shot peening, laser peening, gravity peening ordeep rolling. Cold work is
particularly important because the higher the cold work at the surface of a component, the
more vulnerable to elevated temperatures and mechanical overload that component will
be and the easier the beneficial surface residual compression will relax, rendering the
treatment pointless. In other words, a component that has been highly cold worked will
not hold the compression if it comes into contact with extreme heat, like an engine, and
will be just as vulnerable as it was to start. The reason LPB produces such low
percentages of cold work is because of the aforementioned closed-loop process control.
Other processes have some guesswork involved and are not exact at all, causing the
procedure to have to be performed multiple times on one component. For example, shot
peening, in order to make sure every spot on the component is treated, typically specifiescoverage of between 200% and 400%. This means that each spot was impacted 2-4 times
on the component. The problem is that one spot will be hit four times while the one next
to it is hit only twice, leaving uneven compression. This uneven compression results in
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the whole process being easily "undone", as was mentioned above. LPB requires only
one pass with the tool and leaves a deep, even, beneficial compressive stress.
The LPB process can be performed on-site in the shop orin situ 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% 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.
Chapter 3
Overview
3.1 Benefits:
Surface enhancement offers a variety of benefits ranging from increased life to cost
reduction when properly designed and optimized for the material and application.
Strength and life can be increased without changing either the material or the component
design. Common service damage can be completely mitigated by placing the damaged
layer in compression. Whether it is optimizing conventional shot peening for maximum
production at minimal cost, or developing novel LPB solutions for improved damage
tolerance, Lambdas extensive experience and unique combination of applied stress
modeling, residual stress measurement, surface treatment design, and performance testing
capabilities are applied to each project to realize these benefits for our clients
applications. Some of the benefits of surface enhancement to introduce a deep stable
surface layer of residual compression are as follows:
Fatigue L if e ExtensionLocal stress concentrations at fatigue critical features such as fillets and bolt holes can be
effectively strengthened by introducing residual compression. Fatigue damage too small
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for NDT detection can be completely arrested, allowing components removed from
service to be fully restored to full service life.
Low Plasticity Burnishing (LPB)
Damage Tolerance ImprovementSurface damage introduces local stress concentrations, greatly reducing fatigue strength.
Holding the damage entirely in compression can eliminate failure from the damaged
surface, removing the fatigue debit. All common damage mechanisms including foreign
object damage (FOD), corrosion pitting, fretting micro-cracking, erosion and wear have
been mitigated by LPB in a wide variety of alloys.
Manufacturing DamageManufacturing damage such as machining marks and shallow handling damage can be
mitigated like FOD. Phase transformations and residual tension from grinder burn and
EDM recast layers can be eliminated at fatigue initiation sites by surface enhancement.
Stress Corrosion Cracking and Corr osion F atigueA deep layer of stable high compression can completely eliminate static stress corrosion
cracking (SCC) and suppress the corrosion component of corrosion fatigue. SCC simply
cannot occur if the surface is in compression to sufficient depth. LPB has completely
eliminated SCC in high strength landing gear steels, and in aluminum propellers and
structural components in salt water environments. LPB restores the corrosion fatigue
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performance of friction stir welded aluminum and eliminates SCC in stainless steel
nuclear piping welds subject to SCC.
Weight ReductionCompressive stress fields designed to offset service induced tensile stresses can be used
to reduce sections, and therefore weight in some components. Critical locations can be
effectively reinforced by introducing compression at critical features such as fillets and
bolt holes.
Materi al Substituti onSubstitution of a new material to improve fracture toughness, fatigue strength or SCC
resistance of existing components can be prohibitively expensive and provide only
incremental benefit. Depending upon the applied stress, designed surface enhancement
can often improve performance even more than material substitution at greatly reduced
cost. Less expensive alloys can be used with surface enhancement to provide superior
performance.
Performance ImprovementSignificant improvements in the load carrying capacity of fatigue limited components can
be achieved through surface enhancement. Controlled shot peening has been widely used
for years to extend the load range of automotive gearing. Critical components can be
operated at higher loads and for longer design lives through the introduction of designed
residual compression at critical locations without changing either the component material
or design.
Examples of the use of surface enhancement to minimize cost and improve performance
are included in our publications. Lambdas engineers will be pleased to draw upon their
extensive experience to assist in achieving the benefits of surface enhancement in your
application.
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Chapter 4
Process
4.1 Pr ocess
LPB is unique among surface enhancement processes in that the force applied to the
tool is synchronized with the CNC tool positioning, using either CNC machine tools or
industrial robots. The process is a highly repeatable surface treatment, as repeatable as
CNC machining. The burnishing force can be synchronized to the burnishing tool
positioning within milliseconds, producing unprecedented definition of the residual stress
distribution produced. Combining the CNC control with Lambdas patented design
method allows the creation of the ideal residual stress distribution required for the
application. Patented closed-loop CNC control technology provides immediate
conformation of the processing, giving assurance that the desired residual stress was, in
fact, achieved in the component, and that a data file was created documenting the
processing details by component serial number. Instrumented smart fixturing, also
patented at Lambda, provides independent confirmation that the residual stresses were
induced in the component.
Figure .. Single point tool LPB processing of the
dovetail of Ti -6-4 compressor blade.
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LPB offers a logistical advantage of incorporation directly into the manufacturing
environment. Machining and LPB can be performed in the same machine tool, with
only a simple tool change. The CNC tool positioning file and the associated tool pressure
file ensure precise reproduction in the manufacturing environment, minimize operator
interaction, and processing accuracy within 0.1% for production process control
exceeding six-sigma.
Finite Element Analysis
Lambda provides the design of the optimal residual stress
field and the range of compression allowable in production, along with the necessary
tooling for LPB processing as
part of the non-recurring engineering supporting each
LPB application.
During the design process of a metallic component, applied stresses are generally
determined using finite element analysis (FEA) to ensure the part can withstand the
applied loads either in yielding or fatigue. To reduce the applied stresses, designers can
modify the geometry by adding material in critical regions or by using a material with
more desirable properties. Utilizing the FDD method, the designer can reliably use
compressive residual stresses (RS) to offset the applied stresses thereby improving
performance. Incorporating compressive RS in metallic components has long been
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recognized to enhance fatigue strength. However, credit is seldom taken for RS in design
because RS may not be stable or reproducible and a reliable method of including RS in
design has not been available.
4.2 Design
Lambda has created and patented a unique Fatigue Design Diagram (FDD) method of
designing the residual stress field appropriate for a given application. Knowing the
applied stress state, material properties, and failure locations, Finite Element (FE) models
of the applied stress are input into Lambdas FDD code to determine the amount of
residual compression required at each element in the FE model to achieve the desired
fatigue performance, or to mitigate damage defined by the stress concentration,
kt. Lambda provides the optimal residual stress field design and the range of
compression allowable in production along with the necessary tooling for LPB
processing as part of the non-recurring engineering supporting each LPB application
Residual Stress
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Lambdas unique combination of residual stress and
cold work measurement, fatigue design, processing and
testing capabilities provide the means to select and design surface enhancement processes
for optimal component performance.
4.3 Effect of LPB on HCF Performance and FOD Tolerance:
The thick section HCF results for IN718 presented in Figure 5 show a substantial
increase in the HCF endurance limit, or fatigue strength at 2x106 cycles for LPB over
shot peening for either 525C or 600C exposure for 100 hrs. The similar fatigue
performance for shot peening followed by either 525C or 600C exposure is attributed to
the near uniform relaxation of the surface compression seen in Figure 3 after exposure to
either temperature. The endurance limit is typically associated with surface residual
compression governing the initiation of fatigue cracks while fatigue strength in the finite
life regime is dominated by crack growth through the depth of the compressive layer left
by surface enhancement.The difference in the ability of the two surface enhancement
methods to resist FOD either in the form of a single indentation or a sharp notch is shown
in Figure 6. The endurance limit is reduced from nominally 700 to 300 MPa (101. to 43.5
ksi) by either form of damage. The deep compressive layer produced by LPB is more
effective in retarding crack growth, even after thermal exposure, because of the minimal
thermal stress relaxation and the greater depth of the compressive layer. Although
considerable scatter is evident in the LPB + FOD data (which is attributed to variability
in the FOD damage) all of the specimens treated by LPB have fatigue strengths and lives
superior to that of shot peening even without FOD.
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HCF data for thick section Ti-6Al-4V shows similar trends in Figure 7. The HCF results
presented in this figure show a 38% increase in the endurance limit for LPB (>620 MPa
(>90ksi)) compared to shot peening (~448 MPa (~65 ksi)) after exposure to 425C
(795F) for 10 hrs. The increased endurance limit after surface enhancement is generally
associated with surface compression delaying the initiation of fatigue cracks at the
surface. The reduced HCF strength of the highly cold worked shot peened condition is
attributed to the complete loss of surface compression after even a brief elevated
temperature exposure.
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4.4 Process Design Protocol
Total Engineeri ng Soluti ons
Turn Key solution for fati gue and stress corrosion cracking problems.
Lambda Technologies offers complete solutions for fatigue and stress corrosion cracking(SCC) problems through the design and creation of compressive residual stress fields to
offset applied tension and mitigation of surface damage. The exclusive design protocol
results in a turn key production solution providing our customers with state of the art
residual stress measurement, fatigue modeling, and CNC production technology in a
single comprehensive package.
Step 1: Applied Stresses
Applied stresses are determined by finite element modeling, measurement, or estimated
from the failure history of the component. Finite element models of mean and alternating
stress are prepared to support both the design of the compressive residual stress field and
tool path modeling.
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Step 2: Fatigue Design
Using Lambdasfatigue design diagramtechnology, the amount of residual stress
required at each point in the component is determined to precisely overcome the applied
tension and the stress intensity factors caused by surface damage.
Step 3: Residual Stress Modeling
A residual stress distribution is calculated by application of the fatigue design
methodology, applied stresses, and stress concentration factors caused by damage. The
model is adjusted to minimize equilibrating tension and distortion while achieving justthe level of compression necessary to attain the required performance.
Step 4: Compression Validation
Using Lambdas unique laboratory facilities and measurement techniques, the residual
stresses achieved by LPB or other surface enhancement process are mapped both with
depth and position onto the component to determine whether or not the designed residual
stress distribution has been achieved by surface enhancement.
Step 5: Fatigue Life Verification
Fatigue testing of either feature specimens or actual components, such as fan blades, is
conducted to verify the fatigue performance under the conditions of surface damage,
temperature, corrosion, and environment appropriate for the application.
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Step 6: Processing Tools & Code
LPB tooling and CNC control and pressure codes required to generate the residual
stress distribution in the component are created for integration into the clients
manufacturing operation or to be provided separately as a processing service.
Step 7: Statistical Quality Control
Lambdas unique smart tooling based upon the patented constant volume hydrostatic
bearing tool design provides unique real time quality control monitoring of the forceapplied to the component as a function of CNC tool positioning. Any variation is
immediately identified, recorded, and uploaded to the web for review by the clients QA
system and assessment of system performance by Lambda technicians.
Step 8: Turn-Key Production
A turn-key system consisting of the hydraulic control system, tooling, and proven CNC
and pressure code files required to achieve the designed residual stress distribution is
delivered to the client for integration into their manufacturing operations. The client
receives a completely engineered solution to their fatigue or stress corrosion cracking
problem delivered directly to the manufacturing floor.
4.5 Quali ty Control Process Moni toring
Lambdas patented LPB processing control system is theonly surface enhancement
technology that provides true closed-loop process control. The pressure and force applied
to the burnishing tool and the responding pressure in the patented constant volume
hydrostatic tool design give both independent and dependent confirmation of the
processing at millisecond intervals. Data files documenting the processing force as
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functions of the CNC tool position are recorded for each component by serial number,
date and tooling used, providing a permanent record for quality control process
monitoring. LPB process control is nominally 0.1% within an allowable range of
typically 10%, providing a very robust process easily achieving six-sigma process
control.
Surface Enhancement Technologies Purchase Order Quality Clauses are available in
Adobe PDF format. Click the following link to view the clauses: Surface Enhancement
Technologies Purchase Order Quality Clauses.
ISO 9001:2008 Certified
The Quality Management System applicable to the engineering and
implementation of surface enhancement technologies including patented and
proprietary Low Plasticity Burnishing (LPB) has been assessed and
registered as conforming to the requirements of ISO 9001:2008. (See
Certificate No. US-3920a)
http://www.lambdatechs.com/html/surface/FM-7.4-02_3.pdfhttp://www.lambdatechs.com/html/surface/FM-7.4-02_3.pdfhttp://www.lambdatechs.com/surface-enhancement/documents/US-3920aSurfaceEnhancementTechnologies-1.pdfhttp://www.lambdatechs.com/surface-enhancement/documents/US-3920aSurfaceEnhancementTechnologies-1.pdfhttp://www.lambdatechs.com/surface-enhancement/documents/US-3920aSurfaceEnhancementTechnologies-1.pdfhttp://www.lambdatechs.com/surface-enhancement/documents/US-3920aSurfaceEnhancementTechnologies-1.pdfhttp://www.lambdatechs.com/surface-enhancement/documents/US-3920aSurfaceEnhancementTechnologies-1.pdfhttp://www.lambdatechs.com/html/surface/FM-7.4-02_3.pdfhttp://www.lambdatechs.com/html/surface/FM-7.4-02_3.pdf -
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LPB Processing Control System
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Chapter 5
Advantages and Benef its
LPB has low capitalization costs. As a result of the highly automated design, LPB requires minimal operator
intervention and; therefore, allows fewer chances for human error.
LPB is easily performed on the shop floor, requiring no specialized or remotefacilities.
LPB is 100% QA monitored with better than six-sigma quality control, withtypical processing accuracy of 0.1%
LPB causes no surface damage. Other treatments, like certain forms of lasershocking or shot peening, require machining after processing to eliminate dents
and restore the surface.
LPB leaves an improved, mirror-like surface finish on all processed parts. With less that 5% cold working involved, LPB provides beneficial residual
compression that is both thermally and mechanically stable in service.
The LPB process is applicable to arbitrary shapes and directions. LPB leaves a deep compressive layer that ranges between 1 and 12mm. LPB is a rapid process, with greater than 2000 sfm achieved in turning. LPB has the established QA of a mechanical manufacturing system with true
closed-loop servo process control.
LPB has the ability to improve HCF and SCC or mitigate damage withoutchanging the material or design of the component.
LPB produces a high resolution residual stress field using CNC codesynchronized with the tool force pressure file.
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Lambdas FDD method enables the design of the exact compression required forthe component geometry, applied stress field, damage mechanism, and operating
environment.
Because the LPB process cannot produce shock wave superposition, there is nopossibility of internal fracture in any treated component.
Because LPB cannot produce heat, there is no possibility of surface burns andthe resulting tension in treated parts.
No surface coatings are required, so no debris is produced during treatment. LPB requires only one processing cycle to achieve full depth of compression. LPB is capable of achieving a greater depth and magnitude of compression
greater than all other surface treatments (12 mm).
Real time force and pressure monitoring during processing are verified bycontinuous measurement throughout the LPB process.
LPB can reduce inspection requirements, achieving maximum safety at aminimal cost.
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Chapter 6
Uses and Appl ications
LPB has been applied to a broad range of materials, including high-strength steels, stainless steels, titanium, nickel, aluminum, and magnesium
alloys over the last decade. Applications have been developed for the
mitigation of fretting and improving damage tolerance in turbine
engines.Corrosion pitting, SCC, stress concentrations, and Foreign Object
Damage (FOD) mitigation have been addressed in structural aluminum
airframes. SCC mitigation in both high strength steel landing gear and
austenitic nuclear welds have been researched thoroughly. Current
production applications range from turbine engine vanes and blades (both
airborne and ground based), propellers, propeller hubs, landing gear, to
welded nuclear components and medical implants. LPB processing can
be easily integrated into the aerospace, military, medical, nuclear, and oil
industries.
Industrial Robot(The LPB process can be performed in-situ with the use
of industrial robots, as shown above.)
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6.1 Aircraft Propulsion Application
Engine Components: Low Plasticity Burnishing (LPB) improves foreign
object damage (FOD) tolerance and high cycle fatigue endurance limits while
completely mitigating cracking along the trailing edge of the Ti-6Al-4V Alloy
F402 First Stage Low Pressure Compressor (LPC1) Vane used in the U.S. Marine
Corps V/STOL tactical strike aircraft.
Engine Components: Low Plasticity Burnishing (LPB) mitigates pitting, diminishes
foreign object damage (FOD), and improves damage tolerance and high cycle fatigue
(HCF) life while reducing the replacement costs of the 17-4 PH Stainless Steel First
Stage Compressor Blade in the T56 Turboprop Engine.
Engine Components: Mitigation of Fretting Fatigue
Often, turbine engine components are retired from service before full life is reached.
Turbine disks are a typical example. One of the most common reasons for turbine disk
retirement is accumulated fretting damage in the dovetail slots of the disks. Fretting
damage on such components is often difficult to characterize and analyze, but is usually
the result of movement between two metallic surfaces in contact with each other. Assuch, prudence often dictates that the components be removed from service before they
reach their potential design life. Due to the long lead times and the high costs associated
with replacing this hardware, it would be desirable to have proven solutions to avoid,
http://www.lambdatechs.com/publications/documents/AV8BHarrierOverhaulFinal_000.pdfhttp://www.lambdatechs.com/publications/documents/AV8BHarrierOverhaulFinal_000.pdfhttp://www.lambdatechs.com/publications/documents/C130P3OverhaulFinal.pdfhttp://www.lambdatechs.com/publications/documents/C130P3OverhaulFinal.pdfhttp://www.lambdatechs.com/html/documents/LPB_Fret_App_Note_kb.pdfhttp://www.lambdatechs.com/html/documents/LPB_Fret_App_Note_kb.pdfhttp://www.lambdatechs.com/html/documents/LPB_Fret_App_Note_kb.pdfhttp://www.lambdatechs.com/publications/documents/C130P3OverhaulFinal.pdfhttp://www.lambdatechs.com/publications/documents/AV8BHarrierOverhaulFinal_000.pdf -
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minimize or repair fretting damage. One such solution would provide surface treatments
to mitigate the effects of fretting damage by producing a layer of compressive residual
stress that will be retained at high temperatures.
Low plasticity burnishing (LPB) has been demonstrated to provide deep, controlled
high compression that improves the fatigue life of fret damaged Ti-6Al-4V test
specimens compared with shot peened specimens, even after thermal exposure
6.2 Aircraft Structures Application
Propeller Blades: Low Plasticity Burnishing (LPB) mitigates stress corrosion
cracking and improves corrosion fatigue strength while increasing the service life
and reducing the total maintenance cost of the 7076-T6 Propeller for the U.S.
Navy's maritime patrol aircraft.
Main Landing Gear: Surface treatment program improves the damage tolerance
of a 300M steel main landing gear component by development of an engineered
residual stress (RS) distribution to mitigate stress corrosion cracking (SCC) and
fatigue failure through the use of Low Plasticity Burnishing (LPB) in
combination with conventional shot peening.
Aluminum and Titanium Alloys: Friction Stir Weld Finishing
Aircraft Structures: Aging Aircraft
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6.3 Engineering Application
Fatigue Design: A patented methodology*, the Fatigue Design Diagram (FDD) analysis
provides a means of incorporating compressive residual stress distributions into the
designs of metallic components necessary to achieve optimal fatigue performance and to
mitigate typical damage conditions.
6.4 Medical Implants Application
Medical Implants: Low Plasticity Burnishing (LPB) improves high cycle fatigue
performance and eliminates the occurence of fretting-induced fracture in the Exactech M-
Series Modular Hip Prosthesis by producing beneficial, compressive residual stresses
sufficient to protecting the tapered region of the implant's neck segment.
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Total hip replacement surgery is often required to alleviate pain and improve the
function of hips damaged from disease or fracture. It is estimated that over 300,000 hip
replacement surgeries are performed each year in the United States. Modular total hip
prosthesis (THP) systems afford surgeons the flexibility to choose properly sized
prosthesis subcomponents to treat a wide spectrum of diverse patients with various hip
defects and injuries. However, modular THP subcomponents are vulnerable to fretting at
the tapered connections causing a debit in the fatigue strength and a reduction in the
functional life of the prosthesis.
Chapter 7
Conclusion
From the all study of this , it gives the better understanding of low plasticity burnishing
LPB, and its significance in todays industry.It is most efficient & beneficial suface
enhancement process.Conclusions derived from all above report is listed below:
1.The LPB process includes a unique & patented way of analyzing,desingning & testing
matalic component in order to develope the unique metal treatment necessary to improve
performance & reduce metal fatigue,SCC & corrosion fatigue failures.
2.It is most economical process.
3.Material properties like surface finish,wear resistance,fatigue life,hardness etc.,
increases.
4.Life of component increases.
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Referances
Websites:
www.lambdatechs.com/html/documents/Aa_pp.pdf.
www.sufaceenhancement.com/techpapers/729.pdf
www.grc.nasa.gov
www.techbriefs.com/index.php?option=com_staticxt&staticfile=brief/Aug02/LEW17188
.html.
Books
Machine Design- V.B.Bhandari
Production Technology- R.K.JAIN
http://www.lambdatechs.com/html/documents/Aa_pp.pdfhttp://www.lambdatechs.com/html/documents/Aa_pp.pdfhttp://www.sufaceenhancement.com/techpapers/729.pdfhttp://www.sufaceenhancement.com/techpapers/729.pdfhttp://www.grc.nasa.gov/http://www.grc.nasa.gov/http://www.techbriefs.com/index.php?option=com_staticxt&staticfile=brief/Aug02/LEW17188.htmlhttp://www.techbriefs.com/index.php?option=com_staticxt&staticfile=brief/Aug02/LEW17188.htmlhttp://www.techbriefs.com/index.php?option=com_staticxt&staticfile=brief/Aug02/LEW17188.htmlhttp://www.techbriefs.com/index.php?option=com_staticxt&staticfile=brief/Aug02/LEW17188.htmlhttp://www.techbriefs.com/index.php?option=com_staticxt&staticfile=brief/Aug02/LEW17188.htmlhttp://www.grc.nasa.gov/http://www.sufaceenhancement.com/techpapers/729.pdfhttp://www.lambdatechs.com/html/documents/Aa_pp.pdf