surface grinders
TRANSCRIPT
-
7/29/2019 Surface Grinders
1/38
Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display.
PowerPoint to accompany
Krar Gill Smid
Technology of Machine Tools6th Edition
Surface Grinders and
Accessories
Unit 81
-
7/29/2019 Surface Grinders
2/38
81-2
Objectives
Name four methods of surface grinding
and state the advantage of each
True and dress a grinding wheel
Select the proper grinding wheel to be
used for each type of work material
-
7/29/2019 Surface Grinders
3/38
81-3
Grinding
Important part of machine tool trade
Applied extensively to production of
unhardened parts where high accuracy and
surface finish required
Has eliminated need for conventional
machining
Modern grinding machines permits faster
manufacture of intricate parts
-
7/29/2019 Surface Grinders
4/38
81-4
Grinding Process
Workpiece brought into contact withrevolving grinding wheel
Each smallabrasive grain onperiphery of
wheel acts asindividual cutting tooland removes chipof metal
Copyright The McGraw-Hill Companies, Inc.
Permission required for reproduction or display.
-
7/29/2019 Surface Grinders
5/38
81-5
General Rules for Grinding
1. Use silicon carbide wheel for low-tensile-
strength material and aluminum oxide
wheel for high-tensile-strength materials
2. Use hard wheel on soft materials and soft
wheel on hard materials
3. If wheel too hard, increase speed of work
or decrease speed of wheel to make it act
as softer wheel
-
7/29/2019 Surface Grinders
6/38
81-6
4. If wheel appears too soft or wears rapidly,
decrease speed of work or increase speedof wheel
5. Glazed wheel will affect finish, accuracy,
and metal-removal rate. Main causes of wheel glazing are:
Wheel speed too fast
Work speed too slow Wheel too hard
Grain too small
Structure too dense
-
7/29/2019 Surface Grinders
7/38
81-7
6. If wheel wears too quickly, cause may be
any of the following:
1. Wheel too soft
2. Wheel speed too slow
3. Work speed too fast
4. Feedrate too great
5. Face of wheel too narrow
6. Surface of work interrupted by holes or
grooves
-
7/29/2019 Surface Grinders
8/38
81-8
Surface Grinding
Refers to production of flat, contoured, andirregular surfaces on piece of work
Passed against revolving grinding wheel Four distinct types of surface grinding
machines
Horizontal spindle grinder, reciprocating table
Horizontal spindle grinder, rotary table
Vertical spindle grinder, reciprocating table
Vertical spindle grinder, rotary table
-
7/29/2019 Surface Grinders
9/38
81-9
Horizontal Spindle Reciprocating
Table Surface Grinder
Most commonly used
Either hand or hydraulically operated EZ-SURF Grinder
TEACH mode: operator can teach and program
up to 100 points for X and Z coordinates "Intelligent DRO": helps increase productivity,
improve accuracy and simplify grinding
operations
-
7/29/2019 Surface Grinders
10/38
81-10
Parts of a Hydraulic
Surface Grinder Base
Generally heavy cast-iron construction
Usually contains hydraulic reservoir and pump tooperate table and power feeds
Saddle
Moved in or out across ways, manually or auto
Table
Mounted on top of saddle
Ways for table at right angles to those on base
-
7/29/2019 Surface Grinders
11/38
81-11
Column
Mounted on back of frame
Contains ways for spindle housing and
wheelhead
Wheelfeed handwheel provides means ofmoving wheelhead vertically to set depth of cut
Table traverse handwheel or hydraulic
control valve lever Means to control manually the reciprocating
action of table
-
7/29/2019 Surface Grinders
12/38
81-12
Stop dogs
Mounted on side of table
When strike table traverse reverse lever the
direction of table reversed
Crossfeed handwheel Manual means for table to be fed toward or
away from column
Power crossfeed control Automatic means for table to be fed toward or
away from column
-
7/29/2019 Surface Grinders
13/38
81-13
Guidelines for
Grinding Wheel Care
1. When not in use, store properly
2. Should be tested for cracks prior to use
3. Select proper type wheel for job
4. Should be properly mounted and operated
at recommended speed
-
7/29/2019 Surface Grinders
14/38
81-14
Procedure for Mounting a
Grinding Wheel1. Test wheel to see that it is not cracked by ring
testing with handle of screwdriver
2. Clean grinding wheel adapter
3. Mount adapter through wheel and tighten
threaded flange
1. Place blotter on each side prior to mounting
2. Should be good fit on adapter or spindle
3. Diameter of flanges not less wheel diameter
4. Tighten adapter flanges so holds firmly
-
7/29/2019 Surface Grinders
15/38
81-15
Two Methods of
Balancing a Wheel
1. Static balancing
Wheel balance off machine with use ofbalancing stand and arbor
Counterweights in wheel flange must becorrectly positioned in order to balance
2. Dynamic balancing Automatically balanced wheel while revolving
using ball-bearing balancing devices onmachine
-
7/29/2019 Surface Grinders
16/38
81-16
Procedure To Balance a
Grinding Wheel
1. Mount wheel and adapter on surfacegrinder and true wheel with diamonddresser
2. Remove wheel assembly and mountspecial tapered balancing arbor in hole of
adapter3. Place wheel and arbor on balancing stand
that has been leveled
-
7/29/2019 Surface Grinders
17/38
81-17
4. Allow wheel to rotate until it stops
5. Rotate wheel and stop it at three positions:
one-quarter, one-half, and three-quarters
of a turn to check balance
6. Loosen setscrews in wheel
counterbalances, in grooved recess of
flange, and move counterbalances
opposite chalk mark7. Check wheel in four positions (Steps 4, 5)
-
7/29/2019 Surface Grinders
18/38
81-18
8. Move counterbalances around groove
equal amount on each side of centerline
and check for balance again
9. Continue to move balances away from
heavy side until wheel remains stationary
at any position
10. Tighten counterbalances in place
-
7/29/2019 Surface Grinders
19/38
81-19
Grinder Safety
1. Use the right wheel
2. Ring test the wheel before mounting
3. Always use mounting blotters
4. Tighten clamping nuts only enough to
prevent wheel from slipping
5. Be sure flanges are flat and free from
burrs and gouges
-
7/29/2019 Surface Grinders
20/38
81-20
6. Check arbor holes wheel should slip
freely, not loosely, onto spindle arbor
7. Do not exceed maximum speed
8. Always use wheel guard supplied
9. Stand to one side whenever wheel started
10. Always wear safety glasses when grinding
-
7/29/2019 Surface Grinders
21/38
81-21
Truing a Grinding Wheel
Process of making grinding wheel round
and concentric with its spindle axis and
producing required form of shape on wheel
Involves grinding of a portion of the abrasive
section of grinding wheel
-
7/29/2019 Surface Grinders
22/38
81-22
Dressing a Grinding Wheel
Operation of removing dull grains and metal
particles
Exposes sharp cutting edges so cuts better Reasons for dressing wheel
Reduce heat generated between work and wheel
Reduce strain on grinding wheel and machine Improve surface finish and accuracy of work
Increase rate of metal removal
81 23
-
7/29/2019 Surface Grinders
23/38
81-23
Procedure To True and Dress a
Grinding Wheel1. Check diamond for wear and if necessary,
turn it in holder to expose sharp cutting edge
2. Clean magnetic chuck thoroughly with cloth
3. Place piece of paper on left-hand end of
magnetic chuck
4. Place diamond holder on paper and energize
chuck
81 24
-
7/29/2019 Surface Grinders
24/38
81-24
5. Raise wheel above height of diamond
6. Move table longitudinally so diamondis offset approximately in. to left ofcenterline of wheel
7. Adjust table laterally so diamond ispositioned under high point on face ofwheel
8. Start wheel revolving and carefullylower wheel until high point touchesdiamond
81 25
-
7/29/2019 Surface Grinders
25/38
81-25
9. Move table laterally, using crossfeed
handwheel to feed diamond across faceof wheel
10.Lower grinding wheel about .001 to
.002 in. per pass
Rough-dress face of wheel until flat and
dressed all around circumference
11.Lower wheel .0005 in. and take several
passes across face of wheel
81 26
-
7/29/2019 Surface Grinders
26/38
81-26
Helpful Ideas When Truing or
Dressing Grinding Wheels1. To minimize wear on diamond, rough-
dress with abrasive stick
2. If coolant to be used during grinding, usecoolant when dressing wheel
3. Loaded wheel indicated by discoloration
of periphery or face remove completely
4. If rapid removal of metal more important
than surface finish, do NOT finish-dress
81 27
-
7/29/2019 Surface Grinders
27/38
81-27
Work-Holding Devices
Work must be held in vise, held on V-blocks
or bolted directly to table for some surface-
grinding operations
Most of ferrous work ground on surface
grinder held on magnetic chuck Clamped to table of grinder
81 28
-
7/29/2019 Surface Grinders
28/38
81-28
Two Types Magnetic Chucks
Electromagnetic chuck
Uses electromagnets to provide holding power
Advantages Holding power may be varied to suit area of contact
Special switch neutralizes residual magnetism in
chuck
Permanent magnetic chuck
Holding power provide by means of permanent
magnets
81 29
-
7/29/2019 Surface Grinders
29/38
81-29
Permanent Magnetic Chuck
Construction Base plate
Provides base for chuck and means of
clamping it to table of grinder Grid (magnetic pack)
Houses magnets and grid conductor bars
Moved longitudinally by handle
Case Houses grid assembly, permits longitudinal
movement, and provides oil reservoir forlubrication
81 30
-
7/29/2019 Surface Grinders
30/38
81-30
Top plate
Contains inserts or pole pieces separated
magnetically from surrounding plate by means
of white metal
Necessary to conduct magnetic lines of flux Work place on face of chuck (top plate) and
handle moved to on position, grid conductors
bars and inserts in line
Permits magnetic flux to pass through work
Handle rotated 180 to off position
Moves bars and inserts out of line so work not held
81 31
-
7/29/2019 Surface Grinders
31/38
81-31
Magnetic Chuck Accessories
Holding power of magnetic chuck
dependent of size of workpiece, area of
contact, and thickness of workpiece Adapter plate used to securely hold thin
work (less than in.)
Magnetic chuck blocks provide means ofextending flux paths to hold workpieces that
cannot be held securely on chuck face
81 32
-
7/29/2019 Surface Grinders
32/38
81-32
How to Make Magnetic Chuck
Blocks Last Longer
1. Clean thoroughly before and after use
2. Store in covered wooden box3. Check frequently for accuracy and burrs
4. If regrinding necessary to restore
accuracy, take light cuts with dressed
wheel
81-33
-
7/29/2019 Surface Grinders
33/38
81-33
More Work-Holding Devices
Sine Chuck
Use when required to grind angle on work
Form of magnetic sine plate
Double-faced tape
Used for holding thin, nonmagnetic pieces on
chuck for grinding Two adhesive sides: places between chuck and
work
81-34
-
7/29/2019 Surface Grinders
34/38
81-34
More Work-Holding Devices
Magna-vise clamps
Used when workpiece does not have large bearingarea on chuck or work nonmagnetic
Consist of comblike bars attached to solid bar bypiece of spring steel
Work placed on chuck surface between toothed
edges Special fixtures
Used to hold nonmagnetic and odd-shaped work
81-35
-
7/29/2019 Surface Grinders
35/38
81-35
Four Purposes of
Grinding Fluids
1. Reduction of grinding heat
2. Lubrication
3. Removal of swarf from cutting area
Small metal chips and abrasive grains
4. Control of grinding dust
81-36
-
7/29/2019 Surface Grinders
36/38
81 36
Types of Grinding Fluids
1. Soluble oil and water Milky solution applied by flooding surface
2. Soluble chemical grinding fluids andwater Used with "through-the-wheel" systems
Contains rust inhibitors and bactericides
3. Straight oil grinding fluids Applied by flood system and used for high
finish, accuracy and long wheel life
81-37
-
7/29/2019 Surface Grinders
37/38
81 37
Methods of Applying Coolants
Flood system
Coolant directed onto work by nozzle and recirculatedthrough system
Through-the-wheel cooling Fluid pumped and discharged into dovetailed groove in
wheel flange (with holes), fluid forced through wheelby centrifugal force
Mist cooling system Atomizer principle: air passes through line, as passes
reservoir draws coolant and discharges it in vapor formdirected at point of contact
81-38
-
7/29/2019 Surface Grinders
38/38
81 38
Factors Affecting Surface Finish
Material being ground
Amount of material being removed
Grinding wheel selection
Grinding wheel dressing
Condition of machine Feed