Unit82 Surface Grinding Operations

8/13/2019 Unit82 Surface Grinding Operations

1/49

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

PowerPoint to accompany

Krar Gill Smid

Technology of Machine Tools6thEdition

Surface Grinding

Operations

Unit 82


2/49

82-2

Objectives

Set up various workpieces for grinding

Observe the safety rules to operate thegrinder

Grind flat, vertical, and angular surfaces


3/49

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


4/49

82-4

Mounting Workpiece for Grinding

Flat Work or Plates1. Remove all burrs from surface of work

2. Clean chuck surface with clean cloth

3. Place piece of paper slightly larger thanworkpiece in center of magnetic chuck face

4. Place work on top of paper, and be sure tostraddle as many magnetic inserts as possible

5. If workpiece warped, shim work to prevent rocking6. Turn handle to on position

7. Check work to see it is held securely


5/49

82-5

Thin Workpieces

Tend to warp because of heat created

during grinding

Minimize by mounting workpiece at angle of

15 to 30 from side of chuck

Reduces length of time wheel in contact with work

Use adapter if available and mount work atan angle


6/49

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


7/49

82-7

Grinder Safety

1. Before mounting a grinding wheel, ring

test wheel to check for defects

2. Be sure grinding wheel properly mountedon spindle

3. See wheel guard covers at least one-half

wheel4. Make sure magnetic chuck has been

turned on by trying to remove work


8/49

82-8

5. See that grinding wheel clears work

before starting grinder6. Be sure grinder operating at correct speed

for wheel being used

7. When starting grinder, always stand toone side of wheel

8. Never attempt to clean magnetic chuck ormount and remove work until wheel hasstopped completely

9. Always wear safety glasses whengrinding


9/49

82-9

Procedure to Grind a Flat

(Horizontal) Surface1. 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.


10/49

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 overwork

7. Start grinder and lower wheelhead until

wheel just sparks work8. Wheel may have been set on low spot of

work.


11/49

82-11

Cutting fluid should be used whenever

possible to aid grinding action keep cool9. Start table traveling automatically and feed

entire width of work under wheel to check

for high spots10. 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


12/49

82-12

Table 82.1: Surface grinding problems,causes, and remedies

Grinding

Problem Cause Possible Rem

Burning or Wheel is too hard. Use a softer, free-cutting whe

discoloration Decrease wheel speed.

Increase work speed.Coarse-dress the wheel.

Take lighter cuts and dress

the wheel frequently.

Use coolant directed point ofcontact between wheel, wor

Burnished Wheel is glazed. Dress the wheel.

work surface Use a coarser-grit wheel

Use a softer wheel.

Portion of table

taken from text


13/49

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


14/49

82-14

Setting Up the Workpiece

1. Clean and remove all burrs fromworkpiece, angle plate, and magnetic chuck

2. Place piece of paper slightly larger thanangle plate on magnetic chuck

3. Place one end of angle plate on paper

4. Place flat-ground surface of workpieceagainst angle plate so top and one edge ofwork project 12 in. beyond edges of angleplate


15/49

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

chuck8. Carefully fasten two more clamps on end

of workpiece to hold work securely


16/49

82-16

Grinding Edges of Workpiece

Square and Parallel1. 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


17/49

82-17

4. Start grinding wheel and lower wheelhead

until wheel just sparks work5. Move work clear of wheel with crossfeed

handle

6. Raise wheel about .005 to .010 in. in casewheel has been set to low spot on work

7. Check for high spots by feeding table by

hand so entire length and width of workpasses under wheel


18/49

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


19/49

82-19

12. Place angle plate (with attached

workpiece) on end, with surface to beground at top

13. Fasten two clamps to right-hand side of

workpiece and angle plate14. Remove original clamps from top of setup

15. Repeat steps 1 to 8 and grind second edge

16. Remove assembly from chuck and removeworkpiece from angle plate


20/49

82-20

Grinding the

Third and Fourth Edges

First two edges used as reference surfaces

to grind other two sides1. Clean workpiece, angle plate, and

magnetic chuck thoroughly and remove

any burrs2. Place clean piece of paper on magnetic

chuck


21/49

82-21

3. Place ground edge of workpiece on paper

If work 1 in. thick and long enough to spanthree 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 4thedge


22/49

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

82 23


23/49

82-23

Conditioning CBN Wheels

For best performance, important they areconditioned (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 abrasivecrystals and allow wheel to cut

82 24


24/49

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

82 25


25/49

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 lessrunout

2. Tighten flange nut securely

82 26


26/49

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 nibabout 12 in. to left of wheel centerline

Lock table in position

5. Lower wheelhead by hand until justtouches piece of paper held between

wheel and diamond

82 27


27/49

82-27

6. Turn grinder crossfeed handle so diamond

clears edge of wheel7. Lightly coat wheel surface to be trued with

wax marking crayon

8. Start grinder spindle and feed wheelheaddown in .0004 in. increments until contactmade with diamond

9. Direct coolant to wheel-diamond interface

10. Feed diamond across wheel face at3 to 12 in./min

11. Continue truing until crayon removed

82 28


28/49

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 popularmethod of dressing is with aluminum oxide

dressing stick or block

82 29


29/49

82-29

Procedure For Dressing

a CBN Wheel1. 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

82 30


30/49

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 10ft./min) take one pass lengthwise along

dressing stick

82 31


31/49

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 ofdressing stick has been ground

12. When grinding wheel appears to be

cutting dressing stick freely, stop andinspect wheel face

Surface feels rough dressing complete

82 32


32/49

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

reground1. Select 100-concentration CBN resin-bond

wheel to grind M-4 steel

2. Mount CBN wheel securely on grinderspindle

3. True and dress wheel

82-33


33/49

82-33

Mounting the Workpiece

4. Remove burrs from magnetic chuck andworkpiece and thoroughly clean chuck

5. Place piece of smooth paper between work

and magnetic chuck; energize chuckSetting Speeds and Feeds

6. Adjust table reverse dogs so center of

grinding wheel clears each end of work tobe ground by 1 in.

82-34


34/49

82-34

7. Set table crossfeed:

Rough grinding to 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 CBNwheel 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

82-35


35/49

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 in. above work

surface and as close to wheel face aspossible

82-36


36/49

82 36

15. Place dummy block, slightly lower than

work surface, at right-hand end so entiresurface receives coolant at all times

Copyright The McGraw-Hill Companies, Inc.

Permission required for reproduction or display.

82-37


37/49

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 engagecrossfeed to take roughing pass

19. Be sure edge of grinding wheel clears sideof work after each pass

20. Take as many passes (.001 in.) as needed

21. Set wheelhead for .0005 in. depth for finalpass to improve surface finish

82-38


38/49

82 38

Procedure to Grind

a Vertical Surface1. 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

82-39


39/49

82 39

5. Turn on magnetic chuck and test to see if

work held securely6. Set reversing dogs

7. Bring side of wheel close to vertical

surface to be ground8. Lower wheel to within .002 to .005 in. of

flat or horizontal surface finish ground

9. Start table slowly and feed wheel acrossuntil just sparks vertical surface

82-40


40/49

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 feedingtable approximately .0005 in. maximum

per pass

82-41


41/49

To Grind an Angular Surface

Work may be held at angle by sine bar andangle plate, sine chuck , or adjustable angle

vise Ground with flat-dressed wheel

Hold work flat and dress grinding wheel torequired angle with sine dresser

Sine dresser not available, parallel set to desiredangle by means of sine bar may be clamped toangle plate setup placed on magnetic chuck

82-42


42/49

Form Grinding

Production of curved and angular surfacesproduced by means of specially dressed

wheel Reverse form or contour

required on workpiece isdressed on grinding wheel

Contours and radii may beproduced by means of radiuswheel dresser



82-43


43/49

Procedure to Dress a Convex

Radius On a Grinding Wheel1. Mount radius dresser squarely on clean

magnetic chuck

2. Set both stops on radius dresser so it canbe rotated only of turn Two stops 90 apart

3. Fasten diamond height-setting bar inradius dresser

Bottom surface of height-setting bar is centerof radius dresser

82-44


44/49

4. Place gage block buildup using wear

blocks on each side, equal to radiusrequired on grinding wheel

Between height-setting bar and diamond point

5. Raise diamond until just touches gageblocks then lock in position

6. Move table longitudinally until diamond is

under center of grinding wheel7. Lock table to prevent longitudinal

movement

82-45


45/49

8. Rotate arm of radius dresser 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 clearsdiamond

82-46


46/49

12. Start grinder and lower wheel until it just

touches diamond Slowly rotate diamond back and forth through

90 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

82-47


47/49

Crush-Formed Wheels



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

82-48


48/49

Crush-Formed Grinding Wheels

Tolerances as close as .002 in. and radii assmall as .005 in. depending on grit size andstructure of wheel

Gradually wear out of tolerance and formmust be redressed

Not advisable to perform on machine

equipped with ball-bearing spindle Machines equipped with roller bearings proved

satisfactory for crush-dressing operations

82-49


49/49

Cutting-Off Operations

Using thin cutoff wheels to cut off hardened

materials using the surface grinder

Work clamped in fixture or vise andpositioned below wheel

Thin, short pieces, wheelhead fed straight

down; longer pieces, work mounted andtable is reciprocated while wheel fed down

Diamond wheels used on carbide

Date post:	04-Jun-2018
Category:	Documents
Upload:	ramesh-panda
View:	234 times
Download:	3 times

Unit82 Surface Grinding Operations

Documents