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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine.

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Presentation on theme: "Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine."— Presentation transcript:

1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany Krar Gill Smid Technology of Machine Tools 6 th Edition Diamond, Ceramic, and Cermet Cutting Tools Unit 32

2 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 32-3 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 32-4 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 32-5 "Belt" Furnace

6 32-6 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 32-7 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 32-8 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 32-9 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 32-10 Advantages of Diamond Cutting Tools 1.Can be operated at high cutting speeds, and production increased to 10 to 15 times that of other cutting tools 2.Surface finishes of 5 min. (0.127 m m) or less can be obtained easily 3.Very hard and resist abrasion

11 32-11 Advantages of Diamond Cutting Tools 4.Closer tolerance work can be produced 5.Minute cuts, as low as.0005 in. (0.012 mm) deep, can be taken from the inside or outside diameter 6.Metallic particles do not build up (weld) on cutting edge.

12 32-12 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 20-50 times that of carbide tools! Increase production 10-15 times that of any other cutting tool!

13 32-13 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 32-14 Diamond Cutting-Tool Data Cutting SpeedFeed (per Rev.)Depth of Cut Materialft/ Metallic (nonferrous)250–10,000.0008–.004.0005–.024 Nonmetallic 250–3300.0008–.024.0008–.060 Table 32.1 from Text – Metric included in text.

15 32-15 Hints on the Use of Diamond Tools 1.Diamond-tipped points designed with maximum included point angle and radius for added strength 2.Always handle with care – cutting edges should never be checked with micrometer 3.Stored in separate containers, with rubber protectors over tips

16 32-16 4.Machine tool should be as free of vibration as possible 5.Use very rigid setup with diamond tip set exactly on center 6.Work should be roughed out with carbide tool 7.Diamond tools should always be fed into work while work revolving – never stop machine during cut 8.Interrupted cuts will shorten tool life

17 32-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Diamond-tipped Cutting Tool Angles and Clearances

18 32-18 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 32-19 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 32-20 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 32-21 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 32-22 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, sharp edge can be obtained by indexing (turning) insert in the holder

23 32-23 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 32-24 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 32-25 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

26 32-26 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

27 32-27 Factors for Optimum Results From Ceramic Cutting Tools 1.Accurate and rigid machine tools essential 2.Machine tool equipped with ample power and capable of maintaining high speeds 3.Tool mounting and toolholder rigidity important as machine rigidity 4.Overhand of toolholder kept to minimum: no more than 1 ½ times shank thickness

28 32-28 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

29 32-29 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 32-30 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 32-31 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 32-32 Ceramic Tool Geometry Material to be machined Operation performed Condition of machine Rigidity of work setup Rigidity of toolholding device

33 32-33 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 32-34 Clearance Side –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 32-35 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 32-36 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 32-37 Cutting Edge Chamfer Small chamfer (radius) on cutting edge recommended especially on heavy cuts and hard materials –Strengthens and protects cutting edge Use.002- to.008-in. radius for machining steel Use.030- to.060-in. radius for heavy roughing cuts and hard materials

38 32-38 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 32-39 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 32-40 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 32-41 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 32-42 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 32-43 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 32-44 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)

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