Fatigue Enhancement of Critical Components by Controlled Shot-Peening & Laser-Peening. Neil Sheward Technical Services Manager

Transcription

1 Fatigue Enhancement of Critical Components by Controlled Shot-Peening & Laser-Peening Neil Sheward Technical Services Manager

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3 CW Motion Control MIC Material Treatments CW Flow Control

4 MIC International Facilities Canada UK France Sweden Germany Austria USA Spain A Global Organisation Over 60 Divisions in 11 Countries China China 3 facilities Belgium Italy Europe 3 facilities Singapore 1 facility

5 Metal Improvement Company UK Divisions

6 Controlled Shot-Peening Super-Finishing Site Work Laser-Peening Peen Forming Peenflex Protective Mouldings

7 Improving the fatigue life of critical components Aircraft superstructures Aero engine components Landing gear Fasteners and fittings

8 When the work is too big for our site... our site goes to the work Aircraft superstructures Vessels Power stations Industrial applications

9 CASE isotropic and vibratory polishing Gears Shafts Turbine blades

10 Using the latest technology to achieve very deep levels of residual stress Discs Drums Blisks Turbine blades

11 Using Shot peening technology to provide form and fatigue strength Wing skins Wing struts Stringers

12 Design and manufacture of bespoke mouldings Peen masking Damage protection Work-holding

13 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

14 Shot peening is the bombardment of a metallic surface with spherical media The primary benefit of Shot-Peening is an increased resistance to fatigue

15 Progressive localised damage from cyclic loads of less than the material UTS Sudden fracture Slow crack growth Crack initiation site

16 The consequences of fatigue can be catastrophic Stage 1 HPT Disc Fatigue failure

17 Media Impact Creates a Surface Dimple 0-45deg Optimum peening conditions are achieved by selecting appropriate media and intensity Glass bead Cast steel shot Cut wire shot Ceramic bead

18 IMPACT SUB-SURFACE YIELDS

19 IMPACT Compressive forces attempt to restore the deformed layer to its original condition COMPRESSION

20 Stretched Surface is restrained by mass below

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28 METAL FATIGUE CRACKS WILL ONLY OCCUR WHERE THE METAL IS IN TENSION TENSION COMPRESSION NEVER WHERE THE METAL IS IN COMPRESSION

29 Therefore by introducing a compressive stress to the area in tension... COMPRESSION COMPRESSION..an increased resistance to metal fatigue is achieved

30 METAL FATIGUE CRACKS WILL ONLY OCCUR WHERE THE METAL IS IN TENSION COMPRESSION COMPRESSION NEVER WHERE THE METAL IS IN COMPRESSION

31 METAL FATIGUE CRACKS WILL ONLY OCCUR WHERE THE METAL IS IN TENSION COMPRESSION COMPRESSION NEVER WHERE THE METAL IS IN COMPRESSION

32 METAL FATIGUE CRACKS WILL ONLY OCCUR WHERE THE METAL IS IN TENSION COMPRESSION COMPRESSION NEVER WHERE THE METAL IS IN COMPRESSION

33 Sources of Stress Applied Stresses Vibration Pressure Thermal Bolting Dead Load Residual Stresses Welding Punching Riveting Machining Heat Treat EDM Grinding Shearing Crimping Laser Cut

34 Typical Residual Stress Profile following Machining, Grinding etc Planned Stress or Load Actual Stress or Load 0 The residual tensile manufacturing stresses are added to the applied stresses effectively reducing the fatigue strength of the part Tension Compression

35 Typical Shot-Peening Residual Stress Profile Tension The surface stress ss and the depth of compression so will vary with the material properties and the peening parameters d is the depth of s max below the surface and is proportional to the radius of the contact area 0 d Magnitude of compressive stress s max is at least one-half of the material UTS. ss Compression s max Compressive residual stresses are balanced by low magnitude and deep tensile stress s0 Stress ( s )

36 Hoop stress MPa Replacing Tensile Residual Stresses from machining with Compressive Shot Peening Stresses MACHINED Depth m 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 MACHINED & PEENED Machining stresses typically lie within 100 microns of the surface these can be completely removed and replaced by compressive peening stresses

37 COMPRESSION TENSION STRESS AMPLITUDE MEAN STRESS + CYCLE Fatigue life is affected by the stress amplitude and the mean stress UN-SHOT PEENED 0 _ TIME Compressive Stresses close fatigue cracks over part of the cycle reducing the cycle amplitude SHOT PEENED

38 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

39 Plating

40 Mould Texturing

41 Prevents Stress Corrosion Cracking

42 Peen form correction

43 Prevents Galling of threads Prevents Cavitation erosion

44 Anodised Aluminum Bending fatigue Test Hard anodising can reduce the fatigue strength of the base material by up to 47%,

45 Forming of Wing skins Peen forming Machine Form Checking Fixture

46 Stress, MPa Unpeened Shot peened Number of cycles

47 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.

48 1. Media 2. Intensity 3. Coverage 4. Equipment

49 Control Parameter 1 Media size shape material hardness

50 SHAPE Shape is essential to repeat stress profile and avoid stress raisers SIZE Size consistency is essential for maintaining the depth of compressive stress

51 Media Shape Grading Sieved Media Distributed 360 degrees Helter Skelter Good Media Retained

52 Control of Shot Quality 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

53 If media is too large the radius of the part will not be protected Maximum Media Size Diameter of media should be less than half of the minimum radius

54 Controlled Shot Peening Control Parameter 2 - Intensity Almen Strip System Saturation

55 Intensity Control Almen Strips 0.78 MM(0.031ins) Digital or Dial Display Peening Nozzle Shot Stream N Strip A Strip C Strip Almen Test Strip 1.30 MM(0.051ins) 2.38 MM(0.0938ins) Hardened Ball Supports Arc Height Almen Block Almen Strip Removed - Residual Stress Induced Curve The Almen Strip System

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64 Almen blocks are positioned on a dummy part or fixture in areas where intensity is to be measured 5 SECS 7 SECS 12 SECS 15 SECS 19 SECS 22 SECS Height Almen strip arc height is measured at time based intervals

65 Arc Height Saturation Curve 10% Increase Saturation Point T 2T Exposure Time

66 Light SP Medium SP Heavy SP Too Heavy SP ~ 80% YS Constant for material Effect Of Peening Intensity

67 Peenstress Residual Stress Profile Prediction Software

68 Controlled Shot Peening Control Parameter 3 - Coverage Peenscan Visual

69 Visual Coverage Partial Complete Establishing coverage on flat surfaces and soft metals can be easily achieved under 1 x 10 magnification

70 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.

71 Control Parameter 4 - Equipment Machine type Nozzles / Lances Controls (Feeds / Pressures / Flow)

72 Centrifugal Wheel Nozzle Gravity Vacuum Pressure

73 Sieving Apparatus Dust Control Enclosure Control and monitoring Robotic Nozzle Manipulation TYPICAL EQUIPMENT

74 Peening of Hard to Reach Areas Lance Tooling for Narrow Slot Deflector for small holes Rotating Lance for Larger Bores Reciprocating and rotating Peening lance

75 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%

76 Typical Aerospace Peening Applications...

77 3 Worldwide Facilities Livermore, USA Frederickson, USA Earby, UK Support Facilities: Livermore, CA Provides research & development on laser systems and programs

78 Laser source watts Pulse nanoseconds Repetition - 6Hz Short Bursts - 2.7Hz Continuous Temperature at surface 70 o C

79 Advantages Greater depths of residual compressive stress Less surface roughening Less cold work relaxation advantages Plasma Ablative Layer Tamping Layer Targeted Media free Contact Time = micro-seconds Cold Work 10 to 50% Conventional Shot Peening Contact Time = nano-seconds Cold Work 1 to 2% Laser Peening

80 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.

81 Square spots provide uniform coverage Square spots provide efficient coverage in a single treatment layer Constant flat-top beam profile provides highly uniform stress

82 Laser peening significantly extends the fatigue lifetime of metal components Laser peened area (both sides)

83 Shot Peening Laser Peening

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86 CASE Isotropic and vibratory polishing Gears Shafts Bearings Turbine blades

87 Micro-pitting Progression

88 Typical Macro-pitting

89 C.A.S.E. SHOT PEENED SURFACE PROFILE SHOT PEENED AND CASE POLISHED SURFACE PROFILE

90 C.A.S.E. Negative Skew Positive Skew Different Profiles with Same Ra Value ROUGHNESS PARAMETER Ground Grd+Peen Grd+Peen+CASE

91 C.A.S.E. Surface after grinding Grinding + C.A.S.E. Material: Case hardening Steel EN 36 (DIN : 15NiCr13 )

92 C.A.S.E Shot-Peened Shot-Peened + C.A.S.E. Shot-Peened + C.A.S.E. Extended Process Time

93 C.A.S.E.

94 C.A.S.E.

95 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)

96 Neil Sheward- Technical Services Manager Metal Improvement Company