1. Diamond, Ceramic, and Cermet Cutting Tools
Unit 32

2. Objectives
Explain the purpose and application of diamond cutting tools
State the uses of two types of ceramic tools
Describe the types and application of cermet tools

3. Diamond Cutting Tools Diamond hardest known material
Two types of diamonds used in industry
Natural (or mined)
Once widely used for machining nonmetallic and nonferrous materials
Being replaced by manufactured diamonds
Manufactured
Superior in performance in most cases
Used to machine hard-to-finish materials

4. Manufactured Diamonds
1954, General Electric Company produced manufactured diamonds in laboratory
1957, GE began commercial production
First success: carbon and iron sulfide in a granite tube closed with tantalum disks were subjected to pressure 1.5 million psi and temps of 2550º and 4260º
Other metal catalysts and temps high enough to melt metal saturated with carbon to start growth
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5. "Belt" Furnace

6. Manufactured Diamonds
Possible to produce diamonds of size, shape, and crystal structure suited to needs
Can vary temperature, pressure, and catalyst-solvent
Types of manufactured diamonds
RVG Diamond
MBG-II Diamond
MBS Diamond

7. Type RVG Diamond Elongated, friable crystal with rough edges
Used with resinoid or vitrified bond for grinding ultrahard materials
Tungsten carbide
Silicon carbide
Space-age alloys
Used for wet and dry grinding

8. Type MBG-II Diamond Tough, blocky-shaped crystal
Used in metal-bonded grinding (MBG) wheels
Used for grinding cemented carbides, sapphires, ceramics, and electrolytic grinding

9. Type MBS Diamond
Blocky, extremely tough crystal with smooth, regular surface
Used in metal-bonded saws (MBS) to cut concrete, marble, tile, granite, stone, and masonry
May be coated with nickel or copper to provide better holding surface in bond

10. Advantages of Diamond Cutting Tools
Can be operated at high cutting speeds, and production increased to 10 to 15 times that of other cutting tools
Surface finishes of 5 min. (0.127 mm) or less can be obtained easily
Very hard and resist abrasion

11. Advantages of Diamond Cutting Tools
Closer tolerance work can be produced
Minute cuts, as low as in. (0.012 mm) deep, can be taken from the inside or outside diameter
Metallic particles do not build up (weld) on cutting edge.

12. Use of Diamond Cutting Tools
Metallic Materials
Light metals, such as aluminum, duraluminum, and magnesium alloys
Soft metals, such as copper, brass, and zinc alloys
Bearing metals, such as bronze and babbitt
Precious metals, such as silver, gold, and platinum
Nonmetallic Materials
hard and soft rubber
all types of cemented carbides, plastics, carbon, graphite, and ceramics.
Increase production times that of carbide tools!
Increase production times that of any other cutting tool!

13. Cutting Speeds and Feeds
Diamond-tipped cutting tools operate most efficiently with shallow cuts at high cutting speeds and fine feeds
Not recommended for materials where heat generated exceeds 1400ºF
Ideal cutting speed for each type of material-machine combination
Min cutting speed 250 to 300 sf/min

14. Diamond Cutting-Tool Data
Cutting Speed Feed (per Rev.) Depth of Cut
Material ft/min in. in.
Metallic (nonferrous) 250–10, – –.024
Nonmetallic 250– – –.060
Table 32.1 from Text – Metric included in text.

15. Hints on the Use of Diamond Tools
Diamond-tipped points designed with maximum included point angle and radius for added strength
Always handle with care – cutting edges should never be checked with micrometer
Stored in separate containers, with rubber protectors over tips

16. Machine tool should be as free of vibration as possible
Use very rigid setup with diamond tip set exactly on center
Work should be roughed out with carbide tool
Diamond tools should always be fed into work while work revolving – never stop machine during cut
Interrupted cuts will shorten tool life

17. Diamond-tipped Cutting Tool Angles and Clearances
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

18. 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

19. 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

20. 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

21. 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

22. Indexable Insert Most common Fastened in mechanical holder
Available in many styles: square, round, triangular, rectangular
When cutting edge becomes dull, sharp edge can be obtained by indexing (turning) insert in the holder
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

23. 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

24. 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

25. Ceramics Usage
High-speed, single-point turning, boring, and facing operations with continuous cutting
Finishing operations on ferrous and nonferrous materials
Light, interrupted finishing cuts on steel or cast iron

26. Ceramics Usage
Machining castings when other tools break down because of abrasive action of sand, inclusions or hard scale
Cutting hard steels up to hardness of Rockwell c 66
Any operation in which size and finish of part must be controlled and previous tools not satisfactory

27. Factors for Optimum Results From Ceramic Cutting Tools
Accurate and rigid machine tools essential
Machine tool equipped with ample power and capable of maintaining high speeds
Tool mounting and toolholder rigidity important as machine rigidity
Overhand of toolholder kept to minimum: no more than 1 ½ times shank thickness

28. Negative rake inserts give best results
Less force applied directly to ceramic tip
Large nose radius and large side cutting edge angle on ceramic insert reduces its tendency to chip
Cutting fluids generally not required, if required, use continuous and copious flow
As cutting speed or hardness increases, check ratio of feed to depth of cut
Best to use toolholders with fixed or adjustable chipbreakers

29. 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

30. 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

31. 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

32. Ceramic Tool Geometry Material to be machined Operation performed
Condition of machine
Rigidity of work setup
Rigidity of toolholding device

33. Rake Angles Negative rake angles preferred (2º to 30º)
Allows chock of cutting force to be absorbed behind tip, protecting cutting edge
Ceramic tools brittle
Used for machining ferrous and nonferrous metals
Positive rake angles used for nonmetals

34. Clearance Side Front Desirable for ceramic cutting tools
Angle must not be too great
Cutting edge weakened and tend to chip
Front
Angle should be only large enough to prevent tool from rubbing on workpiece
Angle too great – susceptible to chipping

35. End Cutting Edge Angle
Governs strength of tool and area of contact between work and end of cutting tool
Properly designed, remove crests resulting from feed lines and improve surface finish
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

36. Nose Radius Two functions:
Strengthen weakest part of tool
Improve surface finish of workpiece
Should be as large as possible without producing chatter or vibration

37. Cutting Edge Chamfer
Small chamfer (radius) on cutting edge recommended especially on heavy cuts and hard materials
Strengthens and protects cutting edge
Use to .008-in. radius for machining steel
Use to .060-in. radius for heavy roughing cuts and hard materials

38. 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

39. 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

40. 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

41. 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

42. 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

43. 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

44. 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)