Neil Sheward - Metal Improvement Company, Technical Service ...
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Neil Sheward Technical Services Manager Fatigue Enhancement of Critical Components by Controlled Shot-Peening & Laser-Peening
Transcript of Neil Sheward - Metal Improvement Company, Technical Service ...
Neil Sheward
Technical Services Manager
Fatigue Enhancement of Critical Components by
Controlled Shot-Peening & Laser-Peening
CW Flow Control MIC Material Treatments CW Motion Control
MIC International Facilities
USA
Sweden
China
UK France
Spain
Germany
Italy Belgium
Canada
China
3 facilities
Europe
3 facilities
Singapore
1 facility
Austria
A Global Organisation
Over 60 Divisions in 11 Countries
Metal Improvement Company UK Divisions
Controlled Shot-Peening
Super-Finishing
Site Work
Laser-Peening
Peen Forming
Peenflex Protective Mouldings
“Improving the fatigue life of critical components”
Aircraft superstructures
Aero engine components
Landing gear
Fasteners and fittings
“When the work is too big for our site .... our site goes to the work” Aircraft superstructures
Vessels
Power stations
Industrial applications
“CASE isotropic and vibratory polishing”
Gears
Shafts
Turbine blades
“Using the latest technology to achieve very deep levels of residual stress”
Discs
Drums
Blisks
Turbine blades
“Using Shot peening technology to provide form and fatigue strength”
Wing skins
Wing struts
Stringers
“Design and manufacture of bespoke mouldings”
Peen masking
Damage protection
Work-holding
The effects of peening have been long known
2700 BC Peening of
Gold Helmets and Weapons
1200 AD Peening of armour and
swords during crusades
1945 John Almen – Effects of Shot
Blasting on Mechanical Properties of Steel
1949 METAL IMPROVEMENT
COMPANY formed
Shot peening is the bombardment of a metallic surface with spherical media
The primary benefit of Shot-Peening is an increased resistance to fatigue
Progressive localised damage from cyclic loads of less than the material UTS
Crack initiation site
Slow crack growth
Sudden fracture
Stage 1 HPT Disc Fatigue failure
The consequences of fatigue can
be catastrophic
Cast steel shot
Cut wire shot
Glass bead
Ceramic bead
Media Impact Creates a Surface Dimple
Optimum peening conditions are achieved by selecting appropriate media and intensity
0-45deg
SUB-SURFACE YIELDS
IMPACT
COMPRESSION
IMPACT
Compressive forces attempt to restore the deformed layer to its original condition
Stretched Surface is restrained by mass below
METAL FATIGUE CRACKS WILL ONLY OCCUR WHERE THE METAL IS IN TENSION
NEVER WHERE THE METAL IS IN COMPRESSION
TENSION
COMPRESSION
Therefore by introducing a compressive stress to the area in tension.....
…..an increased resistance to metal fatigue is achieved
COMPRESSION
COMPRESSION
METAL FATIGUE CRACKS WILL ONLY OCCUR WHERE
THE METAL IS IN TENSION
NEVER WHERE THE METAL IS IN COMPRESSION
COMPRESSION
COMPRESSION
METAL FATIGUE CRACKS WILL ONLY OCCUR WHERE
THE METAL IS IN TENSION
NEVER WHERE THE METAL IS IN COMPRESSION
COMPRESSION
COMPRESSION
METAL FATIGUE CRACKS WILL ONLY OCCUR WHERE
THE METAL IS IN TENSION
NEVER WHERE THE METAL IS IN COMPRESSION
COMPRESSION
COMPRESSION
Sources of Stress
Vibration Pressure Thermal Bolting Dead Load
Welding Punching Riveting Machining Heat Treat EDM Grinding
Shearing Crimping Laser Cut
Residual Stresses
Applied Stresses
Tension Compression
Typical Residual Stress Profile following Machining, Grinding etc
0
The residual tensile manufacturing stresses are
added to the applied stresses effectively reducing the
fatigue strength of the part
Actual Stress or Load
Planned Stress or Load
The surface stress ss and the depth of compression so will vary with the material properties and the peening
parameters
ss
s0
Compressive residual stresses are balanced by low magnitude and deep tensile stress
Magnitude of compressive stress s
max is at least one-half
of the material UTS.
s max
„d‟ is the depth of s max below
the surface and is proportional to the radius of the contact area
Tension Compression
Stress ( ) s
d
Typical Shot-Peening Residual Stress
Profile
0
-1500
-1000
-500
0
500
1000
1500
2000
2500
0 50 100 150 200
Depth m
Ho
op
str
ess M
Pa
50/0.15/20 machined
40/0.15/10 machined
50/0.12/23 machined
50/0.15/20 peened
40/0.15/10 peened
50/0.12/23 peened
Machining stresses typically lie within 100 microns of the surface – these can be completely removed and replaced by compressive peening stresses
MACHINED
MACHINED & PEENED
Replacing Tensile Residual Stresses from
machining with Compressive Shot
Peening Stresses
Fatigue life is affected by the stress amplitude and the mean stress
STRESS
CO
MPRESSIO
N
TEN
SIO
N
0
_
+
AM
PLIT
UD
E
MEAN
STRESS
Compressive Stresses close fatigue cracks over part of the cycle reducing the cycle amplitude
CYCLE
TIME
UN-SHOT PEENED
SHOT PEENED
Removes manufacturing stresses Superimposes compressive stresses Combats fatigue failure Improves damage tolerance Allows higher stress levels Enhances lubrication Enables lighter design Textures surfaces Forms and corrects form errors Closes porosity in coatings and substrates Resists fretting and galling
Plating
Mould Texturing
Prevents Stress Corrosion Cracking
Peen form correction
Prevents Galling of threads
Prevents Cavitation erosion
Hard anodising can reduce the fatigue strength of the base
material by up to 47%,
Anodised Aluminum Bending fatigue Test
Forming of
Wing skins
Peen forming Machine Form Checking Fixture
0
100
200
300
400
500
600
1000 100000 10000000
Str
es
s,
MP
a
Number of cycles
Unpeened
Shot peened
→ →
→
There are no Non-Destructive tests available to verify that Shot Peening has been done correctly! Positive control of the process is essential to ensure repeatability and reliability of the part.
1. Media 2. Intensity 3. Coverage 4. Equipment
Control Parameter 1 – Media
•size •shape •material •hardness
SHAPE Shape is essential to repeat stress profile and avoid stress raisers SIZE Size consistency is essential for maintaining the depth of compressive stress
Media Shape Grading
Sieved Media Distributed 360 degrees „Helter Skelter‟ Good Media Retained
The Media must be inspected every:-
8 hours - steel shot
4 hours - ceramic
2 hours - glass beads
Out of specification media is removed and re-graded
Control of Shot Quality
Maximum Media Size
If media is too large the radius of the part will not be protected
Diameter of media should be less than half of the minimum radius
Controlled Shot Peening
Control Parameter 2 - Intensity Almen Strip System Saturation
Intensity Control Almen Strips
N Strip
A Strip
C Strip
0.78 MM(0.031ins)
1.30 MM(0.051ins)
2.38 MM(0.0938ins)
Arc Height
Hardened Ball Supports Shot Stream
Almen Block
Almen Test Strip
Peening Nozzle
The Almen Strip System
Almen Strip Removed - Residual Stress Induced Curve
Digital or Dial Display
Almen blocks are positioned on a dummy part or fixture in areas where intensity is to be measured
Almen strip arc height is measured at time based intervals
5 SECS
Height
12 SECS
15 SECS
19 SECS
22 SECS
7 SECS
Saturation Curve
T 2T
Exposure Time
Arc
He
igh
t
10% Increase
Saturation Point
~ 80% YS
Constant for material
Light SP
Effect Of Peening Intensity
Medium SP
Heavy SP
Too Heavy SP
Peenstress Residual Stress
Profile Prediction Software
Controlled Shot Peening
Control Parameter 3 - Coverage Peenscan Visual
Visual Coverage
Partial Complete
Establishing coverage on flat surfaces and soft metals can be easily achieved under 1 x 10 magnification
Peenscan Coverage
For complex shapes and hard metals the surface can be analysed by coating the surface with a flourecent tracer liquid and examining under UV (Black) light.
Control Parameter 4 - Equipment Machine type Nozzles / Lances Controls (Feeds / Pressures / Flow)
• Centrifugal Wheel
• Nozzle
– Gravity
– Vacuum
– Pressure
Sieving Apparatus Dust Control Enclosure Control and monitoring Robotic Nozzle Manipulation
TYPICAL EQUIPMENT
Lance Tooling for Narrow Slot
Deflector for small holes
Rotating Lance for Larger Bores
Reciprocating and rotating Peening lance
Peening of Hard to Reach Areas
Shot Peening Callouts
• MI 230 H, 6-10A, 200%
• S 230 R, 0,15-0,25A, 200%Almen
• AF Glass, 4-6N, 100%
• Z300, 8-12A, 400%
Typical Aerospace Peening Applications......
3 Worldwide Facilities
• Livermore, USA
• Frederickson, USA
• Earby, UK
Support Facilities:
Livermore, CA
– Provides research & development on laser systems and programs
Laser source - 600 watts Pulse – 10 - 200 nanoseconds Repetition - 6Hz Short Bursts - 2.7Hz Continuous Temperature at surface 70
oC
Ablative Layer
Laser
Peening
Conventional
Shot Peening
Tamping
Layer
Plasma
Contact Time
= micro-seconds
Cold Work
10 to 50%
Contact Time
= nano-seconds
Cold Work
1 to 2%
Advantages
•Greater depths of residual compressive stress
•Less surface roughening
•Less cold work – relaxation advantages
•Targeted
•Media free
Development of Square Laser beam allows the fastest possible coverage of the area. The efficiency of each individual spot is monitored in real time and can be reworked if parameters are not met.
Square spots provide uniform
coverage
• Square spots provide efficient
coverage in a single treatment
layer
• Constant flat-top beam profile
provides highly uniform stress
Laser peened area (both sides) Laser peening significantly extends the
fatigue lifetime of metal components
-2000
-1500
-1000
-500
0
500 0 0.5 1.0
Laser Peening Shot Peening
CASE Isotropic and vibratory polishing
Gears
Shafts
Bearings
Turbine blades
Micro-pitting Progression
Typical Macro-pitting
C.A.S.E.
SHOT PEENED SURFACE PROFILE
SHOT PEENED AND CASE POLISHED SURFACE PROFILE
C.A.S.E.
Different Profiles with Same Ra Value
Ground Grd+Peen Grd+Peen+CASE
Negative
Skew
Positive
Skew
ROUGHNESS PARAMETER
Material: Case hardening Steel EN 36 (DIN : 15NiCr13 )
Surface after grinding Grinding + C.A.S.E.
C.A.S.E.
Shot-Peened
C.A.S.E
Shot-Peened
+ C.A.S.E.
Extended
Process Time
Shot-Peened
+ C.A.S.E.
C.A.S.E.
C.A.S.E.
Shot Peening
Induces compressive residual stresses from a few microns up to 0.5mm Increases fatigue strength and fatigue life Offers resistance against many fatigue failure modes Economical and well proven technology
Laser Peening
Induces 5-10 times greater depths of residual stresses than shot peening Far less cold working Less surface roughness Suitable for critical components where stresses are localised
C.A.S.E.
Reduces contact stress (micro / macro pitting) Removes surface asperities Lowers friction (reduced operating temperature and mechanical loss)
Neil Sheward- Technical Services Manager
Metal Improvement Company
www.metalimprovement.co.uk
