low plasticity burnishing

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Low Plasticity Burnishing

DYPCOE Akurdi Page 1


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


(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)
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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

low plasticity burnishing

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