1. Polycrystalline Cutting Tools
Unit 33

2. Objectives
Explain the manufacture and properties of polycrystalline tools
Select the proper type and size of polycrystalline cutting tools
Set up a tool and machine for cutting with polycrystalline tools

3. History
Bessemer invented commercial method of making steel in 1860 (carbon steel)
Late 1800 saw high-speed steel cutting tools
Then came more productive cemented-carbide and coated carbide cutting tools
General Electric Company produced manufactured diamond in 1954
Today, polycrystalline layer composed of small diamond nitride particles fused to base

4. Manufacture of Polycrystalline Cutting Tools
Two distinct types
Polycrystalline cubic boron nitride
Polycrystalline diamond
Manufacture of blanks basically same
Layer of polycrystalline diamond or cubic boron nitride (.020 in. thick) fused on cemented-carbide substrate by high temperature (3275ºF), high pressure (1 million psi)

5. Polycrystalline Mass
Created from substrate composed of tiny grains of tungsten carbide cemented tightly together
Cobalt binder
High-heat, high-pressure conditions
Cobalt liquefies, flows up and sweeps around diamond or cubic boron nitride abrasive
Serves as catalyst that promotes intergrowth

6. Polycrystalline Cubic Boron Nitride Tools
Structure of cubic boron nitride feature nondirectional, consistent properties
Resist chipping and cracking
Provide uniform hardness
Abrasion resistance in all directions
Qualities built into turning and milling butting-tool blanks and inserts
Can operate at higher cutting speeds, and take deeper cuts

7. Types and Sizes of PCBN Tool Blank Insert Shapes Available
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8. Four Main Properties of PCBN
Hardness
Impact resistance, high strength, hardness in all directions (random orientation of tiny CBN crystals)
Abrasion Resistance
Maintain sharp cutting edges much longer
Compressive Strength
Maximum stress in compression material will take before ruptures
Thermal Conductivity
Allow greater heat dissipation or transfer

9. Types of PCBN Tools Tipped inserts Full-faced inserts
Available in most carbide insert shapes
Usually most economical
Only one cutting edge (can be reground)
Full-faced inserts
Layer of PCBN bonded to cemented-carbide
Available as triangles, squares and rounds
Can downsize repeatedly
Brazed-shank tools
Made by machining pocket in proper-style of tool shank and brazing PCBN blank in place
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10. Four General Types of Metal Cut
Hardened ferrous metals ( >45 Rc)
Hardened steels
Cast irons
Abrasive ferrous metals ( Brinell)
Pearlistic gray cast iron and Ni-Resist
Heat-resistant alloys
Superalloys (jet engine parts)

11. Advantages of PCBN Cutting Tools
High Material-Removal Rates
Cutting speeds (250 to 900 ft/min) and feed rates (.010 to .020 in.) result in removal rates three time carbide tools with less tool wear
Cutting Hard, Tough Materials
Capable of machining all ferrous materials with Rockwell C hardness of 45 and above
Also used to machine cobalt-base and nickel-base high temperature alloys (Rockwell c 35)

12. More Advantages High Quality Products Uniform Surface finish
Wear very slowly
Uniform Surface finish
Surface finishes in range of 20 to 30 µin. possible during roughing operations
Finishing surfaces in single-digit micro-inches
Lower Cost per Piece
Reduced Machine Downtime
Increased Productivity

13. Polycrystalline Diamond Tools
Polycrystalline diamond (PCD) layer fused to cemented-carbide substrate
.020 in. thick
Highly efficient cutting tool
Increased production when machining abrasive nonmetallic, nonferrous materials

14. Types and Sizes of PCD Tools
Catalyst-bonded PCD available in three microstructure series
Coarse PCD blanks
Medium-fine PCD blanks
Fine PCD blanks
Basic difference between types is size of diamond particle used to manufacture blank

15. Coarse PCD Blanks Made of coarse diamond crystals
Designed to cut wide variety of abrasive nonferrous, nonmetallic materials
Highly recommended for machining cast aluminum alloys
Especially those containing more than 16% silicon
More durable than other types

16. Medium-Fine PCD Blanks
Composed of fine to medium-fine crystals
Greater size distribution than coarse blanks
Used for machining highly abrasive nonferrous and nonmetallic materials
Short cutting edges acceptable

17. Fine PCD Blanks Made from fine diamond crystals
Fairly uniform in size
Have extremely sharp cutting edges
High finishes on rake and flank sides
Recommended for very fine surface finishes and long cutting edges

18. Properties of PCD Tools
Composite materials found in base provide mechanical properties
High thermal conductivity and low coefficient of thermal expansion
Diamond layer
Hardness, abrasion resistance, compressive strength, and thermal conductivity
Compressive strength highest of any tool
Thermal conductivity highest of any tool

19. Advantages of PCD Tools
Offset their higher initial cost
Long tool life
Cuts tough, abrasive material
High quality parts
Fine surface finishes
Reduced machine downtime
Increased productivity

20. Types of Material Cut Five general categories Nonferrous metals
Typically soft but have hard particles dispersed
Silicon-aluminum alloys
Copper alloys
Tungsten carbide
Advanced composites
Ceramics
Wood composites

21. Diamond-Coated Tools
Early 1980s brought new process of chemical vapor deposition (CVD)
Produce diamond coating few microns thick
Process
Elemental hydrogen dissolved in hydrocarbon gas around 1330º
Mixture contacts cooler metal, carbon precipitates in pure crystalline form and coats metal with diamond film (slow 1-5 microns/hr)

22. QQC Process developed by Pravin Mistry in mid 1990s
Eliminated problems of adhesion, adjusting to various substrates, coating thickness and cost
Process creates diamond film through use of laser energy and carbon dioxide as source of carbon

23. QQC Process
Laser energy directed at substrate to mobilize, vaporize and reate with primary element (carbone) to change crystalline structure of substrate
Conversion zone created beneath substrate surface
Changes metallurgically to composition of diamond coating on surface
Diffusion bonding of diamond coating to substrate
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24. Major Advantage of the QQC Process
Superior bonding and reduced stress form metallurgical bond between diamond and substrate
Diamond-coating process can be carried out in atmosphere (no vacuum needed)
Parts do not require pretreatment or preheating to be coated

25. More Advantages
Only carbon dioxide primary or secondary source for carbon; nitrogen acts as shield
Diamond deposition rates exceed 1 micron per second
Process can be used for wide variety of materials
Tool life up to 60 times better than tungsten carbide and 240 times better than high-speed steel