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 Surface Grinding Operations Unit 82

2. 82-2 Objectives Set up various workpieces for grinding Observe the safety rules to operate the grinder Grind flat, vertical, and angular surfaces

3. 82-3 Surface Grinding Primarily for grinding flat surfaces on hardened or unhardened workpiece Perform operations such as form, angular, and vertical grinding Good results depend on several factors: –Proper mounting –Proper wheel selection for job

4. 82-4 Mounting Workpiece for Grinding Flat Work or Plates 1.Remove all burrs from surface of work 2.Clean chuck surface with clean cloth 3.Place piece of paper slightly larger than workpiece in center of magnetic chuck face 4.Place work on top of paper, and be sure to straddle as many magnetic inserts as possible 5.If workpiece warped, shim work to prevent rocking 6.Turn handle to on position 7.Check work to see it is held securely

5. 82-5 Thin Workpieces Tend to warp because of heat created during grinding –Minimize by mounting workpiece at angle of 15º to 30º from side of chuck Reduces length of time wheel in contact with work Use adapter if available and mount work at an angle

6. 82-6 Short Workpieces Work that does not straddle three magnetic poles generally not held firmly enough for grinding Advisable to straddle as many poles as possible –Set parallels or steel pieces around work to prevent it from moving Parallels should be slightly thinner than workpiece

7. 82-7 Grinder Safety 1.Before mounting a grinding wheel, ring test wheel to check for defects 2.Be sure grinding wheel properly mounted on spindle 3.See wheel guard covers at least one-half wheel 4.Make sure magnetic chuck has been turned on by trying to remove work

8. 82-8 5.See that grinding wheel clears work before starting grinder 6.Be sure grinder operating at correct speed for wheel being used 7.When starting grinder, always stand to one side of wheel 8.Never attempt to clean magnetic chuck or mount and remove work until wheel has stopped completely 9.Always wear safety glasses when grinding

9. 82-9 Procedure to Grind a Flat (Horizontal) Surface 1.Remove all burrs and dirt from workpiece and face of magnetic chuck 2.Mount work on chuck, placing piece of paper between chuck and workpiece 3.Check to see that work held firmly 4.Set table reverse dogs so center of grinding wheel clears each end of work by 1 in.

10. 82-10 5.Set crossfeed for type of grinding operation – roughing cuts,.030 to.050 in.; finishing cuts,.005 to.020 in. 6.Bring work under grinding wheel by hand, having about 18 in. of wheel edge over work 7.Start grinder and lower wheelhead until wheel just sparks work 8.Wheel may have been set on low spot of work.

11. 82-11 Cutting fluid should be used whenever possible to aid grinding action keep cool 9.Start table traveling automatically and feed entire width of work under wheel to check for high spots 10.Lower wheel for every cut until surface is completed – roughing cuts,.001 to.003 in.; finishing cuts,.0005 to.001 in. 11.Release magnet and remove workpiece by raising one edge to break attraction

12. 82-12 Table 82.1: Surface grinding problems, causes, and remedies Grinding ProblemCausePossible Remedy Burning orWheel is too hard. Use a softer, free-cutting wheel. discoloration Decrease wheel speed. Increase work speed. Coarse-dress the wheel. Take lighter cuts and dress the wheel frequently. Use coolant directed point of contact between wheel, work Burnished Wheel is glazed. Dress the wheel. work surface Use a coarser-grit wheel. Use a softer wheel. Portion of table taken from text

13. 82-13 To Grind the Edges of a Workpiece Edges ground square and parallel so edges may be used for further layout or operations Flat surfaces ground first, permits them to be used as reference surfaces for setups Clamp work to angle plate so two adjacent sides ground square without moving workpiece

14. 82-14 Setting Up the Workpiece 1.Clean and remove all burrs from workpiece, angle plate, and magnetic chuck 2.Place piece of paper slightly larger than angle plate on magnetic chuck 3.Place one end of angle plate on paper 4.Place flat-ground surface of workpiece against angle plate so top and one edge of work project 12 in. beyond edges of angle plate

15. 82-15 5.Hold work firmly against angle plate and turn on magnetic chuck 6.Clamp work to angle plate and set clamps so they will not interfere with grinding operation 7.Turn off magnetic chuck and carefully place base of angle plate on magnetic chuck 8.Carefully fasten two more clamps on end of workpiece to hold work securely

16. 82-16 Grinding Edges of Workpiece Square and Parallel 1.Raise wheelhead so it is about 12 in. above top of work 2.Set table reverse dogs so each end of work clears grinding wheel by about 1 in. 3.With work under center of wheel, turn crossfeed handle until about 18 in. of wheel edge overlaps edge of work

17. 82-17 4.Start grinding wheel and lower wheelhead until wheel just sparks work 5.Move work clear of wheel with crossfeed handle 6.Raise wheel about.005 to.010 in. in case wheel has been set to low spot on work 7.Check for high spots by feeding table by hand so entire length and width of work passes under wheel

18. 82-18 8.Engage table reverse lever and grind surface until all marks removed Depth of cut for roughing cuts.001 to.003 in. Depth of cut for finishing cuts.0005 to.001 in. 9.Stop machine and remove clamps from right-hand end of work 10.Turn off magnetic chuck and remove angle plate and workpiece as one unit 11.Clean chuck and angle plate

19. 82-19 12.Place angle plate (with attached workpiece) on end, with surface to be ground at top 13.Fasten two clamps to right-hand side of workpiece and angle plate 14.Remove original clamps from top of setup 15.Repeat steps 1 to 8 and grind second edge 16.Remove assembly from chuck and remove workpiece from angle plate

20. 82-20 Grinding the Third and Fourth Edges First two edges used as reference surfaces to grind other two sides 1.Clean workpiece, angle plate, and magnetic chuck thoroughly and remove any burrs 2.Place clean piece of paper on magnetic chuck

21. 82-21 3.Place ground edge of workpiece on paper If work 1 in. thick and long enough to span three magnetic poles on chuck, and no more than 2 in. high, no angle plate required If work less than 1 in. thick and does not span three magnetic poles, fastened to angle plate Place ground edge on paper and place angle plate no higher than workpiece against workpiece Turn on chuck and clamp work to angle plate 4.Grind third edge to required size 5.Repeat operations 1 to 3 and grind 4 th edge

22. 82-22 Grinding a Flat Surface with a CBN Wheel Grind hardened tool and die steels more efficiently than aluminum oxide wheels Increase productivity, improve work quality, and reduce grinding costs –Wear slow, uniform and life long –Not necessary to dress wheel frequently Grind cool so stay sharp longer

23. 82-23 Conditioning CBN Wheels For best performance, important they are conditioned (trued and dressed ) properly Truing –Operation of making grinding wheel round and concentric with spindle axis –Usually leaves grinding surface smooth Dressing –Operation of removing some of bond material from surface of trued wheel to expose abrasive crystals and allow wheel to cut

24. 82-24 Properties of a Trued and Dressed Wheel Produce accurate workpieces and good surface finish Use minimum of grinding power Produce work without burn, surface damage, or chatter marks Increase material-removal rates and lower grinding costs

25. 82-25 Procedure for Truing a CBN Wheel Example assumes use of an impregnated diamond wheel to true SBN resin-bond (100% concentration) wheel 1.Mount CBN wheel on grinder, snug up flange nut, and indicate wheel circumference to within.001 in. or less runout 2.Tighten flange nut securely

26. 82-26 3.Clean magnetic chuck and place diamond holder on left-hand side of chuck Cover as many magnetic inserts as possible Energize chuck 4.Adjust grinder table to locate diamond nib about 12 in. to left of wheel centerline Lock table in position 5.Lower wheelhead by hand until just touches piece of paper held between wheel and diamond

27. 82-27 6.Turn grinder crossfeed handle so diamond clears edge of wheel 7.Lightly coat wheel surface to be trued with wax marking crayon 8.Start grinder spindle and feed wheelhead down in.0004 in. increments until contact made with diamond 9.Direct coolant to wheel-diamond interface 10.Feed diamond across wheel face at 3 to 12 in./min 11.Continue truing until crayon removed

28. 82-28 Dressing a CBN Wheel After truing, surface smooth, no abrasive grains sticking out –Wheel cannot cut Wheel bond must be partially removed or lowered to expose abrasive crystals –Simplest, least expensive and most popular method of dressing is with aluminum oxide dressing stick or block

29. 82-29 Procedure For Dressing a CBN Wheel 1.Select 200 grit, C-grade aluminum oxide dressing stick 2.Hold dressing stick in vise so half of thickness above vise jaws 3.Mount vise on magnetic chuck so dressing block parallel to table travel 4.Lower stationary wheel until just touches top of dressing stick

30. 82-30 5.Use crossfeed handle to bring edge of dressing stick even with edge of wheel 6.Move table so wheel just clears right-hand end of dressing stick 7.Start grinder spindle and coolant Feed wheel down about.020 in. 8.Using slow but steady feedrate ( 5 to 10 ft./min) take one pass lengthwise along dressing stick

31. 82-31 9.At end of pass, index table slightly less than width of grinding wheel 10.Repeat procedure until width of dressing stick ground 11.Downfeed wheel after full surface of dressing stick has been ground 12.When grinding wheel appears to be cutting dressing stick freely, stop and inspect wheel face Surface feels rough – dressing complete

32. 82-32 Grinding a Flat Surface Job used to show procedures is a piece of die steel (AISI M-4) Rc-62 that must be reground 1.Select 100-concentration CBN resin-bond wheel to grind M-4 steel 2.Mount CBN wheel securely on grinder spindle 3.True and dress wheel

33. 82-33 Mounting the Workpiece 4.Remove burrs from magnetic chuck and workpiece and thoroughly clean chuck 5.Place piece of smooth paper between work and magnetic chuck; energize chuck Setting Speeds and Feeds 6.Adjust table reverse dogs so center of grinding wheel clears each end of work to be ground by 1 in.

34. 82-34 7.Set table crossfeed: Rough grinding – ¼ to ½ wheel width Finish grinding – smaller crossfeed increments 8.Set table speed rate from 50 to 100 ft/min 9.Set spindle speed for size and type of CBN wheel used Setting wheel to work surface 10.Set wheel to top of work surface 11.Traverse workpiece under revolving wheel to locate high spot of work surface

35. 82-35 12.Move table so wheel clears edge of work surface to be ground Coolant 13.Use proper grinding fluids to suit wheel and workpiece 14.Stop grinder spindle and adjust coolant nozzle so it is about ¼ in. above work surface and as close to wheel face as possible

36. 82-36 15. Place dummy block, slightly lower than work surface, at right-hand end so entire surface receives coolant at all times Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

37. 82-37 Grinding the Surface 16.Start grinder spindle and lower wheelhead.001 in. for first cut 17.Start coolant flow 18.Start table reciprocating and engage crossfeed to take roughing pass 19.Be sure edge of grinding wheel clears side of work after each pass 20.Take as many passes (.001 in.) as needed 21.Set wheelhead for.0005 in. depth for final pass to improve surface finish

38. 82-38 Procedure to Grind a Vertical Surface 1.Mount proper grinding wheel; true, dress and balance 2.Dress side of wheel to give it slight clearance 3.Clean surface of magnetic chuck and mount work 4.With indicator, align edge of work parallel to table travel

39. 82-39 5.Turn on magnetic chuck and test to see if work held securely 6.Set reversing dogs 7.Bring side of wheel close to vertical surface to be ground 8.Lower wheel to within.002 to.005 in. of flat or horizontal surface finish ground 9.Start table slowly and feed wheel across until just sparks vertical surface

40. 82-40 10.Rough-grind vertical surface to within.002 in. of size by feeding table in.001 in. maximum per pass 11.Redress side of wheel if necessary 12.Finish-grind vertical surface by feeding table approximately.0005 in. maximum per pass

41. 82-41 To Grind an Angular Surface Work may be held at angle by sine bar and angle plate, sine chuck, or adjustable angle vise –Ground with flat-dressed wheel Hold work flat and dress grinding wheel to required angle with sine dresser –Sine dresser not available, parallel set to desired angle by means of sine bar may be clamped to angle plate – setup placed on magnetic chuck

42. 82-42 Form Grinding Production of curved and angular surfaces produced by means of specially dressed wheel Reverse form or contour required on workpiece is dressed on grinding wheel Contours and radii may be produced by means of radius wheel dresser Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

43. 82-43 Procedure to Dress a Convex Radius On a Grinding Wheel 1.Mount radius dresser squarely on clean magnetic chuck 2.Set both stops on radius dresser so it can be rotated only ¼ of turn Two stops 90º apart 3.Fasten diamond height-setting bar in radius dresser Bottom surface of height-setting bar is center of radius dresser

44. 82-44 4.Place gage block buildup using wear blocks on each side, equal to radius required on grinding wheel Between height-setting bar and diamond point 5.Raise diamond until just touches gage blocks then lock in position 6.Move table longitudinally until diamond is under center of grinding wheel 7.Lock table to prevent longitudinal movement

45. 82-45 8.Rotate arm of radius dresser ¼ of turn so diamond is in horizontal position 9.Start machine spindle and bring diamond in until just touches side of grinding wheel Using crossfeed handle 10.Lock table cross-slide in position 11.Stop grinder and raise wheel until clears diamond

46. 82-46 12.Start grinder and lower wheel until it just touches diamond Slowly rotate diamond back and forth through 90º arc 13.Feed wheel down approximately.002 to.003 in. for every rotation of dresser 14.Continue to dress radius until periphery of wheel just touches diamond when it is in vertical position 15.Stop grinder, raise wheel, remove dresser

47. 82-47 Crush-Formed Wheels Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tool-steel or carbide roll having desired form or contour of finished workpiece Forced into grinding wheel Grinding wheel assumes reverse form of crushing roll Wheel then used to grind form or contour on workpiece

48. 82-48 Crush-Formed Grinding Wheels Tolerances as close as ±.002 in. and radii as small as.005 in. depending on grit size and structure of wheel Gradually wear out of tolerance and form must be redressed Not advisable to perform on machine equipped with ball-bearing spindle –Machines equipped with roller bearings proved satisfactory for crush-dressing operations

49. 82-49 Cutting-Off Operations Using thin cutoff wheels to cut off hardened materials using the surface grinder Work clamped in fixture or vise and positioned below wheel Thin, short pieces, wheelhead fed straight down; longer pieces, work mounted and table is reciprocated while wheel fed down Diamond wheels used on carbide