Grinding Process

• Workpiece brought into contact with revolving grinding wheel

• Each small abrasive grain on periphery of wheel acts as individual cutting tool and removes chip of metal

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

4. If wheel appears too soft or wears rapidly, decrease speed of work or increase speed of 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

6. If wheel wears too quickly, cause may be any of the following:

1. Wheel too soft2. Wheel speed too slow3. Work speed too fast4. Feedrate too great5. Face of wheel too narrow6. Surface of work interrupted by holes or

grooves

Surface Grinding• Refers to production of flat, contoured, and

irregular 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

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

Parts of a Hydraulic Surface Grinder

• Base– Generally heavy cast-iron construction– Usually contains hydraulic reservoir and pump to

operate 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

• Column– Mounted on back of frame– Contains ways for spindle housing and

wheelhead– Wheelfeed handwheel provides means of

moving wheelhead vertically to set depth of cut• Table traverse handwheel or hydraulic

control valve lever– Means to control manually the reciprocating

action of table

• 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

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Guidelines for Grinding Wheel Care

1. When not in use, store properly2. Should be tested for cracks prior to use3. Select proper type wheel for job4. Should be properly mounted and operated

at recommended speed

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Procedure for Mounting a Grinding Wheel

1. Test wheel to see that it is not cracked by ring testing with handle of screwdriver

2. Clean grinding wheel adapter3. Mount adapter through wheel and tighten

threaded flange1. Place blotter on each side prior to mounting2. Should be good fit on adapter or spindle3. Diameter of flanges not less ½ wheel diameter

4. Tighten adapter flanges so holds firmly

Two Methods of Balancing a Wheel

1. Static balancing• Wheel balance off machine with use of

balancing stand and arbor• Counterweights in wheel flange must be

correctly positioned in order to balance2. Dynamic balancing

• Automatically balanced wheel while revolving using ball-bearing balancing devices on machine

Procedure To Balance a Grinding Wheel

1. Mount wheel and adapter on surface grinder and true wheel with diamond dresser

2. Remove wheel assembly and mount special tapered balancing arbor in hole of adapter

3. Place wheel and arbor on balancing stand that has been leveled

4. Allow wheel to rotate until it stops5. 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 mark

7. Check wheel in four positions (Steps 4, 5)

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

Grinder Safety

1. Use the right wheel2. Ring test the wheel before mounting3. Always use mounting blotters4. Tighten clamping nuts only enough to

prevent wheel from slipping5. Be sure flanges are flat and free from

burrs and gouges

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

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

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

Procedure To True and Dress a Grinding Wheel

1. Check diamond for wear and if necessary, turn it in holder to expose sharp cutting edge

2. Clean magnetic chuck thoroughly with cloth3. Place piece of paper on left-hand end of

magnetic chuck4. Place diamond holder on paper and energize

chuck

5. Raise wheel above height of diamond6. Move table longitudinally so diamond

is offset approximately ½ in. to left of centerline of wheel

7. Adjust table laterally so diamond is positioned under high point on face of wheel

8. Start wheel revolving and carefully lower wheel until high point touches diamond

9. Move table laterally, using crossfeed handwheel to feed diamond across face of 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

Helpful Ideas When Truing or Dressing Grinding Wheels

1. To minimize wear on diamond, rough-dress with abrasive stick

2. If coolant to be used during grinding, use coolant 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

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

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

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 for lubrication

• 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 180º to off position

• Moves bars and inserts out of line so work not held

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 ¼ in.)

• Magnetic chuck blocks provide means of extending flux paths to hold workpieces that cannot be held securely on chuck face

How to Make Magnetic Chuck Blocks Last Longer

1. Clean thoroughly before and after use2. Store in covered wooden box3. Check frequently for accuracy and burrs4. If regrinding necessary to restore

accuracy, take light cuts with dressed wheel

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

More Work-Holding Devices• Magna-vise clamps

– Used when workpiece does not have large bearing area on chuck or work nonmagnetic

– Consist of comblike bars attached to solid bar by piece of spring steel

– Work placed on chuck surface between toothed edges

• Special fixtures– Used to hold nonmagnetic and odd-shaped work

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

Types of Grinding Fluids

1. Soluble oil and water• Milky solution applied by flooding surface

2. Soluble chemical grinding fluids and water

• 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

Methods of Applying Coolants• Flood system

– Coolant directed onto work by nozzle and recirculated through system

• Through-the-wheel cooling– Fluid pumped and discharged into dovetailed groove in

wheel flange (with holes), fluid forced through wheel by centrifugal force

• Mist cooling system– Atomizer principle: air passes through line, as passes

reservoir draws coolant and discharges it in vapor form directed at point of contact

Factors Affecting Surface Finish

• Material being ground• Amount of material being removed• Grinding wheel selection• Grinding wheel dressing• Condition of machine• Feed