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 Cutting Tools Unit 29

2. 29-2 Objectives Use the nomenclature of a cutting-tool point Explain the purpose of each type of rake and clearance angle Identify the applications of various types of cutting-tool materials Describe the cutting action of different types of machines

3. 29-3 Cutting Tools One of most important components in machining process Performance will determine efficiency of operation Two basic types (excluding abrasives) –Single point and multi point Must have rake and clearance angles ground or formed on them

4. 29-4 Cutting-Tool Materials Lathe toolbits generally made of five materials –High-speed steel –Cast alloys (such as stellite) –Cemented carbides –Ceramics –Cermets More exotic finding wide use –Borazon and polycrystalline diamond

5. 29-5 Lathe Toolbit Properties Hard Wear-resistant Capable of maintaining a red hardness during machining operation –Red hardness: ability of cutting tool to maintain sharp cutting edge even when turns red because of high heat during cutting Able to withstand shock during cutting Shaped so edge can penetrate work

6. 29-6 High-Speed Steel Toolbits May contain combinations of tungsten, chromium, vanadium, molybdenum, cobalt Can take heavy cuts, withstand shock and maintain sharp cutting edge under red heat Generally two types (general purpose) –Molybdenum-base (Group M) –Tungsten-base (Group T) Cobalt added if more red hardness desired

7. 29-7 Cast Alloy Toolbits Usually contain 25% to 35% chromium, 4% to 25% tungsten and 1% to 3% carbon –Remainder cobalt Qualities –High hardness –High resistance to wear –Excellent red-hardness Operate 2 ½ times speed of high-speed steel Weaker and more brittle than high-speed steel

8. 29-8 Cemented-Carbide Toolbits Capable of cutting speeds 3 to 4 times high- speed steel toolbits Low toughness but high hardness and excellent red-hardness Consist of tungsten carbide sintered in cobalt matrix Straight tungsten used to machine cast iron and nonferrous materials (crater easily) Different grades for different work

9. 29-9 Coated Carbide Toolbits Made by depositing thin layer of wear-resistant titanium nitride, titanium carbide or aluminum oxide on cutting edge of tool –Fused layer increases lubricity, improves cutting edge wear resistance by 200%-500% –Lowers breakage resistance up to 20% –Provides longer life and increased cutting speeds Titanium-coated offer wear resistance at low speeds, ceramic coated for higher speeds

10. 29-10 Ceramic Toolbits Permit higher cutting speeds, increased tool life and better surface finish than carbide –Weaker than carbide used in shock-free or low- shock situation Ceramic –Heat-resistant material produced without metallic bonding agent such as cobalt –Aluminum oxide most popular additive –Titanium oxide or Titanium carbide can be added

11. 29-11 Cermet Toolbits Cutting-tool insert made of ceramics and metal Most made from aluminum oxide, titanium carbide and zirconium oxide compacted and compressed under intense heat Advantages –Exceed equivalent tool life of carbides –Can be used for machining at high temperatures –Produce improved surface finish –Used to machine steels up to 45 Rc hardness

12. 29-12 Diamond Toolbits Used mainly to machine nonferrous metals and abrasive nonmetallics Single-crystal natural diamonds –High-wear but low shock-resistant factors Polycrystalline diamonds –Tiny manufactured diamonds fused together and bonded to suitable carbide substrate

13. 29-13 Polycrystalline Cutting Tools Offer greater wear Greater shock resistance Greatly increased cutting speeds Improved surface finish Better part-size control Up to 100 times greater tool life than carbide tools Increased productivity

14. 29-14 Cubic Boron Nitride Toolbits Borazon next to diamond on hardness scale Cutting tools made by bonding layer of polycrystalline cubic boron nitride to cemented-carbide substrate Exceptionally high wear resistance and edge life Used to machine high-temperature alloys and hardened ferrous alloys

15. 29-15 Cutting-Tool Nomenclature Cutting edge: leading edge of that does cutting Face: surface against which chip bears as it is separated from work Nose: Tip of cutting tool formed by junction of cutting edge and front face Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

16. 29-16 Cutting-Tool Nomenclature Nose radius: radius to which nose is ground –Size of radius will affect finish Rough turning: small nose radius (.015in) Finish cuts: larger radius (.060 to.125 in.) Point: end of tool that has been ground for cutting purposes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

17. 29-17 Cutting-Tool Nomenclature Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Base: Bottom surface of tool shank Flank: surface of tool adjacent to and below cutting edge Shank: body of toolbit or part held in toolholder

18. 29-18 Lathe Toolbit Angles and Clearances Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

19. 29-19 Lathe Cutting-tool Angles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Positive rake: point of cutting tool and cutting edge contact metal first and chip moves down the face of the toolbit Negative rake: face of cutting tool contacts metal first and chip moves up the face of the toolbit

20. 29-20 Positive Rake Angle Considered best for efficient removal of metal –Creates large shear angle at shear zone –Reduces friction and heat –Allows chip to flow freely along chip-tool interface Generally used for continuous cuts on ductile materials not too hard or abrasive

21. 29-21 Factors When Choosing Type and Rake Angle for Cutting Tool Hardness of metal to be cut Type of cutting operation –Continuous or interrupted Material and shape of cutting tool Strength of cutting edge

22. 29-22 Negative Rake Angle Used for interrupted cuts and when metal is tough or abrasive Creates small shear angle and long shear zone –More friction and heat created Heat desirable when tough metals machined with carbide cutting tools

23. 29-23 Advantages of Negative Rake Shock from work meeting cutting tool is on tool's face –Prolongs life of tool Hard outer scale on metal does not come into contact with cutting edge Surfaces with interrupted cuts can be readily machined Higher cutting speeds can be used

24. 29-24 Shape of Chip Altered in number of ways to improve cutting action and reduce amount of power required Continuous straight ribbon chip can be changed to continuous curled ribbon –Changing angle of the keeness Included angle produced by grinding side rake –Grinding chip breaker behind cutting edge of toolbit

25. 29-25 Cutting-Tool Life: Reported As Number of minutes tool has been cutting Length of material cut Number of cubic inches or cubic centimeters (cm 3 ) of material removed Number of inches or millimeters of hole depth drilled (case of drills)

26. 29-26 To Prolong Cutting-Tool Life Reduce friction between chip and tool as much as possible –Provide cutting tool with suitable rake angle Allows chips to flow away freely Large rake angle creates large shear angle Small rake angle creates small shear angle –Highly polishing cutting-tool face with honing stone Reduces friction on chip-tool interface Reduces size of built-up edge

27. 29-27 Results of a Large Shear Angle Thin chip is produced Shear zone relatively short Less heat created in shear zone Good surface finish produced Less power required for machining operation

28. 29-28 Results of a Small Shear Angle Thick chip produced Shear zone is long Heat is produced Surface finish not quite as good as with large-rake-angle cutting tools More horsepower required for machining operation

29. 29-29 Tool Life Number of parts produced by cutting-tool edge before regrinding is required Cutting tools must be reground at first sign of dullness Three types of wear –Flank wear (1) –Nose wear (2) –Crater wear (3) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

30. 29-30 Tool Life Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Occurs on side of cutting edge as result of friction between side of cutting-tool edge and metal being machined When flank wear is.015 to.030 in. need to be reground Nose wear occurs as result of friction between nose and metal being machined Crater wear occurs as result of chips sliding along chip-tool interface, result of built-up edge on cutting tool

31. 29-31 Factors Affecting the Life of a Cutting Tool Type of material being cut Microstructure of material Hardness of material Type of surface on metal (smooth or scaly) Material of cutting tool Profile of cutting tool Type of machining operation being performed Speed, feed, and depth of cut

32. 29-32 Turning High proportion of work machined in shop turned on lathe –Workpiece held securely in chuck or between lathe centers –Turning tool set to given depth of cut, fed parallel to axis of work (reduces diameter of work) Chip forms and slides along cutting tool's upper surface created by side rake

33. 29-33 Turning Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Assume cutting machine steel: If rake and relief clearance angles correct and proper speed and feed used, a continuous chip should be formed.

34. 29-34 Planing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Workpiece moved back and forth under cutting tool –Fed sideways a set amount at end of each table reversal Should have proper rake and clearance angles on cutting tool

35. 29-35 Plain Milling Multi-tooth tool having several equally spaced cutting edges around periphery Each tooth considered single-point cutting tool (must have proper rake and clearance angles) Workpiece held in vise or fastened to table –Fed into horizontal revolving cutter –Each tooth makes successive cuts –Produces smooth, flat, or profiled surface depending on shape of cutter

36. 29-36 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nomenclature of a Plain Milling Cutter

37. 29-37 End and Face Milling Multi-tooth cutters held vertically in vertical milling machine spindle or attachment Used primarily for cutting slots or grooves Workpiece held in vise and fed into revolving cutter End milling –Cutting done by periphery of teeth

38. 29-38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nomenclature of an End Mill

39. 29-39 Nomenclature of an End Mill Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

40. 29-40 Inserted Blade Face Mill Consists of body that holds several equally spaced inserts –Required rake angle –Lower edge of each insert has relief or clearance angle ground on it Cutting action occurs at lower corner of insert –Corners chamfered to give strength

41. 29-41 Drilling Multi-edge cutting tool that cuts on the point Drill's cutting edges (lips) provided with lip clearance to permit point to penetrate workpiece as drill revolves Rake angle provided by helical-shaped flutes –Slope away from cutting edge Angle of keeness –Angle between rake angle and clearance angle

42. 29-42 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Characteristics of a Drill Point Cutting-point angles for standard drill Chip formation of a drill