1

Ceramic, Cermet, PCBN, and PCD Cutting Tools

2

Ceramic Cutting Tools

• First cutting-tool inserts on market in 1956• Inconsistent: improper use and lack of knowledge

• Uniformity and quality greatly improved• Widely accepted by industry• Used in machining of hard ferrous materials and

cast iron• Gain: lower costs, increased productivity• Operate 3 to 4 times speed of carbide toolbits

3

Manufacture of Ceramic Tools

• Primarily from aluminum oxide• Bauxite chemically processed and converted into

denser, crystalline form (alpha alumina)• Micro sized grains obtained from precipitation of

alumina or decomposed alumina compound

• Produced by either cold or hot pressing• Finished with diamond-impregnated grinding

wheels

4

Manufacturing Process

• Cold Pressing• Fine alumina powder compressed into required form• Sintered in furnace at 2912º F to 3092ºF

• Hot Pressing• Combines forming and sintering with pressure and

heat being applied simultaneously• Titanium oxide or magnesium oxide added for

certain types to aid in sintering and retard growth

5

Ceramic Inserts

• Stronger inserts developed• Aluminum oxide and zirconium oxide mixed in

powder form, cold-pressed into shape and sintered• Highest hot-hardness strength and gives

excellent surface finish• Used where no interrupted cuts and with

negative rakes• No coolant required

6

Indexable Insert

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

• Most common• Fastened in mechanical holder• Available in many styles: square, round,

triangular, rectangular• When cutting edge

becomes dull, sharpedge can be obtained byindexing (turning) insert in the holder

7

Cemented Ceramic Tools

• Most economical• Especially if tool shape must be altered from

standard shape• Bonded to steel shank with epoxy glue

• Eliminates strains caused by clamping inserts in mechanical holders

8

Ceramic Tool Applications

• Intended to supplement rather than replace carbide tools

• Extremely valuable for specific applications• Must be carefully selected and used• Can be used to replace carbide tools that wear

rapidly• Never replace carbide tools that are breaking

9

Ceramics Usage

1. High-speed, single-point turning, boring, and facing operations with continuous cutting

2. Finishing operations on ferrous and nonferrous materials

3. Light, interrupted finishing cuts on steel or cast iron

10

Ceramics Usage

4. Machining castings when other tools break down because of abrasive action of sand, inclusions or hard scale

5. Cutting hard steels up to hardness of Rockwell c 66

6. Any operation in which size and finish of part must be controlled and previous tools not satisfactory

11

Factors for Optimum Results From Ceramic Cutting Tools

1. Accurate and rigid machine tools essential2. Machine tool equipped with ample power and

capable of maintaining high speeds3. Tool mounting and toolholder rigidity

important as machine rigidity4. Overhand of toolholder kept to minimum: no

more than 1 ½ times shank thickness

12

5. Negative rake inserts give best results• Less force applied directly to ceramic tip

6. Large nose radius and large side cutting edge angle on ceramic insert reduces its tendency to chip

7. Cutting fluids generally not required, if required, use continuous and copious flow

8. As cutting speed or hardness increases, check ratio of feed to depth of cut

9. Best to use toolholders with fixed or adjustable chipbreakers

13

Advantages of Ceramic Tools

• Machining time reduced due to higher cutting speeds

• Increased productivity because heavy depths of cut can be made at high surface speeds

• Lasts from 3 to 10 times longer than plain carbide tool and exceed the life of coated carbide tools

• More accurate size control of workpiece

14

Advantages of Ceramic Tools

• Retain their strength and hardness at high machining temperatures [in excess of 2000°F]

• Withstand abrasion of sand inclusions • Better surface finish• Heat-treated materials as hard as Rockwell c

66 can be readily machined

15

Disadvantages of Ceramic Tools

• Brittle and therefore tend to chip easily• Satisfactory for interrupted cuts only under ideal

conditions• Initial cost of ceramics higher than carbides.• Require more rigid machine than is necessary for

other cutting tools• Considerably more power and higher cutting

speeds required for ceramics to cut efficiently

16

Ceramic Tool Geometry

• Material to be machined• Operation performed• Condition of machine• Rigidity of work setup• Rigidity of toolholding device

17

Cutting Speeds

• Use highest cutting speed possible that gives reasonable tool life

• Two to ten times higher than other cutting tools

• Less heat generated due to lower coefficient of friction between chip, work, and tool surface• Most of heat generated escapes with chip

18

Ceramic Tool Problems

• Tool should be large enough for job• Cannot be too large but easily be too small

• Style (tool geometry) should be right for type of operation and material

• Table 32.4 in text lists tool problems and their possible causes

19

Grinding Ceramic Tools

• Grinding not recommended• May be resharpened with proper care

• Resinoid-bonded, diamond-impregnated wheels recommended

• Coarse-grit wheel for rough grinding• 220-grit for finish grinding

• Hone or lap cutting edge after grinding to remove any notches

20

Cermet Cutting Tools

• Developed about 1960• Made of various ceramic and metallic

combinations• Two types

• Titanium carbide (TiC)-based materials• Titanium nitride (TiN)-based materials

• Cost-effective replacement for carbide and ceramic toolbits• Not used with hardened ferrous metals or nonferrous

metals

21

Characteristics of Cermet Tools

• Great wear resistance (permit higher cutting speeds than carbide tools)

• Edge buildup and cratering minimal• High hot-hardness qualities

• Greater than carbide but less than ceramic• Lower thermal conductivity than carbide

because heat goes into chip• Fracture toughness greater for ceramic but less

for carbide tools

22

Cermet Tool Advantages

• Surface finish better than carbides under same conditions – often eliminates finish grinding

• High wear resistance permits close tolerances for extended periods

• Cutting speeds higher than carbides (same tool life)• Tool life longer than carbine tools (same cutting

speed)• Cost per insert less than coated carbide inserts

and equal to plain carbide inserts

23

Use of Cermet Tools

• Titanium carbide cermets hardest• Used to fill gap between tough tungsten carbide

inserts and hard, brittle ceramic tools• Used for machining steels and cast irons

• Titanium carbide-titanium nitride inserts used for semifinish and finish machining of harder cast irons and steels (less than 45 Rc)

24

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)

25

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

26

High PressureHigh Temp

27

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

28

Types and Sizes of PCBN Tool Blank Insert Shapes Available

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

29

Main Properties of PCBN

• Hardness• Impact resistance, high strength, hardness in all

directions (random orientation of tiny CBN crystals)• Highest Hot Hardness of all tools

• Abrasion Resistance• Maintain sharp cutting edges much longer• Second only to Diamond

30

Main Properties of PCBN

• Compressive Strength• Maximum stress in compression material will take

before ruptures• Thermal Conductivity

• Allow greater heat dissipation or transfer

31

Types of PCBN Tools

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

• Tipped 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

32

Four General Types of Metal Cut

1. Hardened ferrous metals ( >45 Rc)• Hardened steels• Cast irons

2. Abrasive ferrous metals (180-240 Brinell)• Pearlistic gray cast iron and Ni-Resist

3. Heat-resistant alloys4. Superalloys (jet engine parts)

33

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)

34

More Advantages

• High Quality Products• 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

35

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

36

High PressureHigh Temp

37

Types and Sizes of PCD Tool Blank Insert Shapes Available

38

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

39

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

40

Advantages of PCD Tools

Offset their higher initial cost1. Long tool life2. Cuts tough, abrasive material3. High quality parts4. Fine surface finishes5. Reduced machine downtime6. Increased productivity

41

Types of Material Cut

1. Nonferrous metals• Typically soft but have hard particles dispersed• Silicon-aluminum alloys• Copper alloys

2. Tungsten carbide3. Advanced composites4. Ceramics5. Wood composites

42

Disadvantages of PCD Tools

1. Carbon Solubility Potential2. Their higher initial cost3. Their higher initial cost4. Their higher initial cost5. Their higher initial cost6. Their higher initial cost

43

Electro-Plated Diamond Tools

• Process• Polycrystalline Diamond coated with copper or nickel

metal• Copper or nickel mixture electroplated to a metallic

form• Electroplated form then dressed to remove a small

amount of metal to expose PCD within• Form tools can be de-plated and re-plated multiple

times

44

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)

45

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

46

QQC Process

• Laser energy directed at substrate to mobilize, vaporize and reate with primary element (carbone) to change crystalline structure of substrate

• Conversion zone createdbeneath substrate surface• Changes metallurgically

to composition of diamond coating on surface

• Diffusion bonding of diamond coating to substrate

47

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

48

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