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Tool Wear Detection and Quantitation by Digital Microscopy

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Outline

1. Tool wear
- Economic impact
- Types of wear

2. Characterization techniques
- Scanning electron microscopy
- Optical microscopy

3. Digital microscopy applied to tool wear quantitation
- Illumination modes
- 3D imaging

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Tool Wear Detection and Quantitation by Digital Microscopy

  1. 1. Tool Wear Detection and Quantitation by Digital Microscopy Olympus Scientific Solutions Americas 2018 ASNT Annual Conference Marcel Lucas
  2. 2. 1. Tool wear − Economic impact − Types of wear 2. Characterization techniques − Scanning electron microscopy − Optical microscopy 3. Digital microscopy applied to tool wear quantitation − Illumination modes − 3D imaging Outline
  3. 3. • U.S. market for cutting tools estimated at $5 billion in 2017 • U.S. market for indexable milling tools estimated at $1.2 billion in 2017 Cutting tools Source: McKinsey & Company Drill bit Center drill Indexable milling insert
  4. 4. • Industrial machinery/equipment • Automotive • Construction machinery • Aerospace • Oil and gas field machinery • Utilities/telecommunications • Farm machinery • Pumps/valves • Dies/tools, fixtures, molds • Cutting tools • Screw machine products • Medical devices Cutting tools: major consuming industries Sources: Modern Distribution Management, MDM Analytics, McKinsey & Company
  5. 5. • Growing demand for indexable tools, including indexable milling inserts Milling Feed Tool holder Insert Workpiece Face milling Insert cutting edge Insert Workpiece Chip
  6. 6. 1. Negative impact on quality − Reduced dimensional accuracy for workpieces − Increased roughness of machined surfaces − Increased residual stresses in workpieces 2. Negative impact on productivity − Scrapped parts − Downtime to replace tools − Increased cutting forces and power consumption Tool wear impact
  7. 7. • Tools typically used for only 50 to 80% of their expected life • Tools not used at rated cutting speed in 42% of applications • Downtime due to cutting tool breakage on an average machine tool is between 7% and 20% • Tooling cost accounts for approximately 25% of total machining cost Tool wear economic impact Sources: Wiklund, Quality and Reliability Engineering International 14, 303 (1998); Karandikar et al., Int. J. Adv. Manuf. Technol 77, 1613 (2015); Ivester et al., Machining Science and Technology 4, 511 (2000); Ghosh et al., MATEC Web of Conferences 192, 01017 (2018)
  8. 8. Types of wear Insert cutting edge Crater wear Flank wear Built-up edge Fracture
  9. 9. • Flank wear is commonly used to characterize cutting tool wear Flank wear Cutting time or distance Flankwear Break-in Steady-state wear Failure
  10. 10. • Flank wear is commonly measured by SEM • Mean and maximum flank wear measurements compared with requirements Scanning electron microscopy (SEM) Insert cutting edge Flank face Max. Mean
  11. 11. 1. Uncertainty for in-plane distance: − Interaction volume − Edge effect − Calibration under different conditions − Aberrations 2. Uncertainty for out-of-plane height: − No NIST-traceable 3D calibration standard − Large depth of field Scanning electron microscopy (SEM) Edge effect Sources of secondary electrons Edge Flat surface Chamber Sample Electron beam
  12. 12. • Distance over which the image is in reasonably sharp focus • Affected by working distance, aperture size, and magnification Depth of field Aperture Depth of field Convergence angle Sample
  13. 13. • Depth of field of SEM is significantly larger than that of optical microscopy Depth of field Source: Hessler-Wyser, Centre Interdisciplinaire de Microscopie Electronique Magnification Depthoffield 102 10 103 104 105 0.1 μm 1 μm 10 μm 100 μm 1 mm 10 mm Optical SEM
  14. 14. • Significantly smaller depth of field for optical microscopy • Aberrations can be compensated in optical microscopy Comparison between SEM and optical microscopy SEM Optical microscopy Electron source 1st condenser 2nd condenser Aperture Scan coils Objective lens Detector Sample Light source Condenser Sample Objective Eyepiece
  15. 15. • Observation with brightfield illumination − Glare from a metallic surface − Limited depth of field Conventional optical microscopy Fractured insertSharp insert Light source Sample Eyepiece Objective Beamsplitter Brightfield illumination
  16. 16. • Ring light for darkfield illumination − Reduces glare significantly − Highlights scratches and indents Darkfield illumination Darkfield illumination Sample Eyepiece Objective Ring light Brightfield image Darkfield image
  17. 17. • MIX illumination is a combination of brightfield and darkfield illumination − Significantly reduces glare − Shows details in dark and bright areas MIX illumination MIX illumination Darkfield imageSample Eyepiece Objective Ring light Light source MIX image
  18. 18. • Ring light for side illumination − Available for darkfield and MIX illumination − Reduces glare and highlights scratches and indents Side illumination Front Back Left Right Ring light configuration All quadrants on Front and left quadrants on
  19. 19. • Image processes to increase dynamic range and reduce glare Digital microscopy: WiDER® and High Dynamic Range (HDR) HDRWiDER Original image
  20. 20. • Extended focus image (EFI) of uneven samples • 3D image with height data Digital microscopy: 3D imaging 3DEFI 2D image
  21. 21. • Extended focus and 3D images generated from a stack of 2D images Digital microscopy: 3D imaging Height Extended focus image
  22. 22. Digital microscopy: EFI imaging of tool wear Insert cutting edge Crater wear Flank wear Built-up edge Fracture
  23. 23. • Flank wear measured on the height profile from a 3D image • Measurement accounts for the orientation of wear and flank face Digital microscopy: length measurement Insert cutting edge Position (μm) Height(μm) 4000 200 400 600 0 800 250 μm
  24. 24. • Comparison of sharp and worn cutting edge height profiles Digital microscopy: area measurement Position (μm) Height(μm) 0 1000 500 0 500 1000 Sharp Worn 28,100 μm2 Sample Area(μm2) 300000 200000 100000 0 Lightly worn Worn Fractured
  25. 25. • Integration of the cross-sectional area to measure volume Digital microscopy: volume measurement Volume of material loss: 3.14 × 106 μm3 for 100 μm long section = Sharp edge Worn edge 0 200 350 190
  26. 26. • Measure wear rate: − As a function of: Ø Cutting conditions (speed, feed rate, depth of cut) Ø Temperature − For different: Ø Tool geometry (rake angle, flank angle, edge preparation) Ø Tool coatings, workpiece materials Ø Coolant Applications
  27. 27. 1. The combination of brightfield and darkfield illumination significantly reduces glare from the tool cutting edge 2. Digital microscopy can generate fully focused images of rough and uneven cutting edges (extended focus and 3D images) 3. From 3D images, the length, cross-sectional area, and volume were measured to quantify tool flank wear Conclusions
  28. 28. Olympus and WiDER are registered trademarks of Olympus Corporation.

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