Grinding

Manufacturing Processes for Engineering Materials, 5th ed. Kalpakjian Schmid 2008, Pearson EducationISBN No. 0-13-227271-7

Grinding Wheel


FIGURE 9.1 Schematic illustration of a physical model of a grinding wheel, showing its structure and grain wear and fracture patterns.

Bond fracture

Microcracks

Attritious wear Wheel surface

PorosityBond

Grain

Grainfracture

Grindingwheel

Workpiece

Common glass 350-500 Titanium nitride 2000Flint, quartz 800-1100 Titanium carbide 1800-3200Zirconium oxide 1000 Silicon carbide 2100-3000Hardened steels 700-1300 Boron carbide 2800Tungsten carbide 1800-2400 Cubic boron nitride 4000-5000Aluminum oxide 2000-3000 Diamond 7000-8000

TABLE 9.1 Knoop hardness range for various materials and abrasives.


Grinding Wheel Types

FIGURE 9.2 Some common types of grinding wheels made with conventional abrasives (aluminum oxide and silicon carbide). Note that each wheel has a specific grinding face; grinding on other surfaces is improper and unsafe.

(a) Type 1straight (b) Type 2 cylinder

(c) Type 6straight cup (d) Type 11flaring cup

(e) Type 27depressed center

(g) Mounted

Grinding face

Grinding face

Grinding faces Grinding faces

Grinding face

Grinding face

(f) Type 28depressed center


Superabrasive Wheels

FIGURE 9.3 Examples of superabrasive wheel configurations. The rim consists of superabrasives and the wheel itself (core) is generally made of metal or composites. Note that the basic numbering of wheel types (such as 1, 2, and 11) is the same as that shown in Fig. 9.2. The bonding materials for the superabrasives are: (a), (d), and (e) resinoid, metal, or vitrified; (b) metal; (c) vitrified; and (f) resinoid.

(a) (b) (c)

(d) (e) (f)

Type1A1

1A1RSS

2A2

11A2

DW DWSE


Grinding Wheel Marking System

FIGURE 9.4 Standard marking system for aluminum-oxide and silicon-carbide bonded abrasives.

Prefix Grade Structure Bondtype

Manufacturer!srecord

Abrasivetype

Abrasivegrain size

51 A 36 L 5 V 23

Manufacturer!s symbol

(indicating exacttype of abrasive)(use optional)

Manufacturer!sprivate marking

(to identify wheel)(use optional)

Example:

Medium

30

36

46

54

60

Fine

70

80

90

100

120

150

180

Very

fine

220

240

280

320

400

500

600

Coarse

8

10

12

14

16

20

24

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

etc.

(Use optional)

Dense

Open

B Resinoid

BF Resinoid reinforced

E Shellac

O Oxychloride

R Rubber

RF Rubber reinforced

S Silicate

V Vitrified

A Aluminium oxide

C Silicon carbide

Soft

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Medium Hard

Grade scale


Diamond and cBN Marking System

FIGURE 9.5 Standard marking system for diamond and cubic-boron-nitride bonded abrasives.

Manufacturer!ssymbol

(to indicate typeof diamond)

A letter or numeralor combination

(used here will indicatea variation fromstandard bond)

B Cubic boron nitride

D Diamond

20

24

30

36

46

54

60

80

90

100

120

150

180

220

240

280

320

400

500

600

800

1000

B Resinoid

M Metal

V Vitrified

1/16

1/8

1/4

25 (low)

50

75

100 (high)

Prefix Abrasivetype

Grit size Grade Diamondconcentration

Bond Bondmodification

Diamonddepth (in.)

M D 100 P 100 B 1/8

A (soft)

Z (hard)

to

Example:

Absence of depthsymbol indicatessolid diamond


Abrasive Grains

FIGURE 9.6 The grinding surface of an abrasive wheel (A46-J8V), showing grains, porosity, wear flats on grains (see also Fig. 9.7b), and metal chips from the workpiece adhering to the grains. Note the random distribution and shape of the abrasive grains.

FIGURE 9.7 (a) Grinding chip being produced by a single abrasive grain. Note the large negative rake angle of the grain. Source: After M.E. Merchant. (b) Schematic illustration of chip formation by an abrasive grain. Note the negative rake angle, the small shear angle, and the wear flat on the grain.

(a) (b)

Grain

VChip

Wear flat

Workpiecev

F

Chip

A

Workpiece

Abrasive grain

F

10 Mm


Grinding Variables

FIGURE 9.8 Basic variables in surface grinding. In actual grinding operations, the wheel depth of cut, d, and contact length, l, are much smaller than the wheel diameter, D. The dimension t is called the grain depth of cut.

VGrinding wheel

Grains

Workpiece

t

d

v

l

D

Chip length, external grinding

Chip length, internal grinding

Chip length, surface grinding

l =

Dd

1+(D/Dw)

l =

Dd

1 (D/Dw)

t =

4vVCr

dD


Grinding Parameters

FIGURE 9.9 Chip formation and plowing (plastic deformation without chip removal) of the workpiece surface by an abrasive grain.

Workpiece

Groove

RidgesChip

TABLE 9.2 Typical ranges of speeds and feeds for abrasive processes.

Process Variable Conventional Grinding Creep-Feed Grinding Buffing PolishingWheel speed (m/min) 1500-3000 1500-3000 1800-3600 1500-2400Work speed (m/min) 10-60 0.1-1 - -Feed (mm/pass) 0.01-0.05 1-6 - -


Specific Energy in Grinding

Specific EnergyWorkpiece Material Hardness W-s/mm3 hp-min/in3

Aluminum 150 HB 7-27 2.5-10Cast iron (class 40) 215 HB 12-60 4.5-22Low-carbon steel (1020) 110 HB 14-68 5-25Titanium alloy 300 HB 16-55 6-20Tool steel (T15) 67 HRC 18-82 6.5-30

TABLE 9.3 Approximate Specific-Energy Requirements for Surface Grinding.

Temperature rise:

Temperature rise D1/4d3/4(Vv

)1/2


Residual Stresses

FIGURE 9.10 Residual stresses developed on the workpiece surface in grinding tungsten: (a) effect of wheel speed and (b) effect of type of grinding fluid. Tensile residual stresses on a surface are detrimental to the fatigue life of ground components. The variables in grinding can be controlled to minimize residual stresses, a process known as low-stress grinding. Source: After N. Zlatin.

mm

0 0.05 0.10 0.15

0

80

60

40

20

220

240Co

mp

ressio

nTe

nsio

n

Re

sid

ua

l str

ess (

psi x 1

03)

400

200

0

2200

MP

a0 0.002 0.004 0.006

Depth below surface (in.)

4000 ft/min (20 m/s)

3000 (15)

2000 (10)

(a)

mm

0 0.05 0.10 0.1540

20

0

220

240

260

280

2100

Co

mp

ressio

nTe

nsio

n

0 0.002 0.004 0.006

Depth below surface (in.)

200

0

2200

2400

2600

2800

MP

a

Re

sid

ua

l str

ess (

psi x 1

03)

(b)

Soluble oil (1:20)

Highly sulfurized oil

5% KNO2 solution


Dressing

FIGURE 9.11 (a) Methods of grinding wheel dressing. (b) Shaping the grinding face of a wheel by dressing it with computer-controlled shaping features. Note that the diamond dressing tool is normal to the wheel surface at point of contact. Source: OKUMA America Corporation.

(a)

Diamond dressing tool

Grinding face

Grinding wheel

(b)

Single-pointdressing diamondfor dressing formsup to 608 on bothsides of the grindingwheel

Precision radius dresser for single- and twin-track bearing production

Rotary dressing unit for dressing hard grinding wheels or for high-volume production

Silicon carbide or diamond dressing wheel for dressing either diamond or cBN grinding wheels

Dressing tool

Grinding wheel

Formed diamond roll dressing for high-volume production

Dressing tool

Fixed-angleswivelling dresserto dress forms up to 908 on bothsides of the grindingwheel60


Surface Grinding

FIGURE 9.12 Schematic illustrations of surface-grinding operations. (a) Traverse grinding with a horizontal-spindle surface grinder. (b) Plunge grinding with a horizontal-spindle surface grinder, producing a groove in the workpiece. (c) Vertical-spindle rotary-table grinder (also known as the Blanchard-type grinder).

(a) (b)

Horizontal-spindle surface grinder: Traverse grinding

Workpiece

Wheel

Horizontal-spindle surface grinder: Plunge grinding

Workpiece

Wheel

(c)

Wheel

Rotary table

Workpieces

Work table

FIGURE 9.12 Schematic illustration of a horizontal-spindle surface grinder.

Wheel guard

Wheel head

Column

Bed

Workpiece

Saddle

Worktable

Feed


Thread and Internal Grinding

FIGURE 9.14 Threads produced by (a) traverse and (b) plunge grinding.

(a) (b)

Grinding wheel

FIGURE 9.15 Schematic illustrations of internal-grinding operations.

(a) Traverse grinding (b) Plunge grinding (c) Profile grinding

WorkpieceWheel

Wheel

Workpiece

Wheel

Workpiece


Centerless Grinding

FIGURE 9.16 (a-c) Schematic illustrations of centerless-grinding operations. (d) A computer-numerical-control centerless grinding machine. Source: Cincinnati Milacron, Inc.

(d)

Through-feed grinding Plunge grinding

Internal centerless grinding

Workpiece(revolves clockwise)

Regulatingwheel

Pressureroll

Grinder shaft

Support roll

Grindingwheel

Feed

Work-rest blade

Regulating wheel

!

Grindingwheel

Regulatingwheel

Workpiece Endstop

(a) (b)

(c)


Creep-Feed Grinding

FIGURE 9.17 (a) Schematic illustration of the creep-feed grinding process. Note the large wheel depth of cut. (b) A groove produced on a flat surface in one pass by creep-feed grinding using a shaped wheel. Groove depth can be on the order of a few mm. (c) An example of creep-feed grinding with a shaped wheel. Source: Courtesy of Blohm, Inc. and Society of Manufacturing Engineers.

d = 16 mm

Low work speed, v

(a) (b) (c)


Finishing Operations

FIGURE 9.18 Schematic illustration of the structure of a coated abrasive. Sandpaper, developed in the 16th century, and emery cloth are common examples of coated abrasives.

Abrasive grains

Size coat

Make coat

Backing

FIGURE 9.19 Schematic illustration of a honing tool to improve the surface finish of bored or ground holes.

Spindle Stone

Nonabrading bronze guide

FIGURE 9.20 Schematic illustration of the superfinishing process for a cylindrical part: (a) cylindrical microhoning; (b) centerless microhoning.

(a) (b)

Workpiece

Oscillation (traverse if necessary)

Stone

Rolls

Motor

Stone

Workpiece

Holder

Rotation


Lapping

FIGURE 9.21 (a) Schematic illustration of the lapping process. (b) Production lapping on flat surfaces. (c) Production lapping on cylindrical surfaces.

(a) (b) (c)

Workpiece

Lap

Before

After

Abrasive Workpiece

Lower lap

Upper lap

Machine pan

Workholding plate

Workpieces Guide rail

Lap position and pressure control


Chemical-Mechanical Polishing

FIGURE 9.22 Schematic illustration of the chemical-mechanical polishing process. This process is widely used in the manufacture of silicon wafers and integrated circuits, where it is known as chemical-mechanical planarization. Additional carriers and more disks per carrier also are possible.

Workpiececarrier

Workpiece (disk)Workpiece carrier

Abrasive slurry

Polishing pad

Polishing table

(a) Side view (a) Top view

Polishingtable

Workpiece


Polishing Using Magnetic Fields

FIGURE 9.23 Schematic illustration of the use of magnetic fields to polish balls and rollers: (a) magnetic float polishing of ceramic balls and (b) magnetic-field-assisted polishing of rollers. Source: After R. Komanduri, M. Doc, and M. Fox.

(a) (b)

Drive shaft

Guide ring

Float

Permanent magnets

Ceramic balls (workpiece)

Magnetic fluid and abrasive grains

N N N N N N S S S S S S

Magnetic fluid

S-pole N-pole Workpiece


Ultrasonic Machining

FIGURE 9.24 (a) Schematic illustration of the ultrasonic-machining process; material is removed through microchipping and erosion. (b) and (c) Typical examples of cavities produced by ultrasonic machining. Note the dimensions of cut and the types of workpiece materials.

(a) (b) (c)

Glass

Holes 0.4 mm (0.016 in.)diameter

1.2 mm(0.048 in.)

Glass-graphiteepoxy composite

Slots 0.64 3 1.5 mm(0.025 3 0.060 in.)

50 mm (2 in.)diameter

Powersupply Transducer

ToolAbrasiveslurry

Workpiece

Contact time:Contact force:

to ! 5rco(cov

)1/5 Fave = 2mvto


Advanced Machining Processes

Process Characteristics Process Parameters and TypicalMaterial Removal Rate or Cut-ting Speed

Chemical machining(CM)

Shallow removal (up to 12 mm) on large flat orcurved surfaces; blanking of thin sheets; low tool-ing and equipment cost; suitable for low produc-tion runs.

0.025-0.1 mm/min

Electrochemicalmachining (ECM)

Complex shapes with deep cavities; highest rateof material removal; expensive tooling and equip-ment; high power consumption; medium to highproduction quantity.

V: 5-25 dc; A: 2.5-12 mm/min,depending on current density.

Electrochemical grinding(ECG)

Cutting off and sharpening hard materials, suchas tungsten-carbide tools; also used as a honingprocess; higher material removal rate than grind-ing.

A: 1-3 A/mm2; typically 1500mm3/min per 1000 A.

Electrical-dischargemachining (EDM)

Shaping and cutting complex parts made of hardmaterials; some surface damage may result; alsoused for grinding and cutting; versatile; expensivetooling and equipment.

V: 50-380; A: 0.1-500; typically300 mm3/min.

Wire EDM Contour cutting of flat or curved surfaces; expen-sive equipment.

Varies with workpiece materialand its thickness.

Laser-beam machining(LBM)

Cutting and hole making on thin materials; heat-affected zone; does not require a vacuum; expen-sive equipment; consumes much energy; extremecaution required in use.

0.50-7.5 m/min.

Electron-beammachining (EBM)

Cutting and hole making on thin materials; verysmall holes and slots; heat-affected zone; requiresa vacuum; expensive equipment.

1-2 mm3/min

Water-jet machining(WJM)

Cutting all types of nonmetallic materials to 25mm (1 in.) and greater in thickness; suitable forcontour cutting of flexible materials; no thermaldamage; environmentally safe process.

Varies considerably with work-piece material.

Abrasive water-jetmachining (AWJM)

Single or multilayer cutting of metallic and non-metallic materials.

Up to 7.5 m/min.

Abrasive-jet machining(AJM)

Cutting, slotting, deburring, flash removal, etch-ing, and cleaning of metallic and nonmetallic ma-terials; tends to round off sharp edges; some haz-ard because of airborne particulates.

Varies considerably with work-piece material.

TABLE 9.4 General characteristics of advanced machining processes.


Chemical Milling

FIGURE 9.25 (a) Missile skin-panel section contoured by chemical milling to improve the stiffness-to-weight ratio of the part. (b) Weight reduction of space launch vehicles by chemical milling of aluminum-alloy plates. These panels are chemically milled after the plates have first been formed into shape, such as by roll forming or stretch forming. Source: ASM International.

(a)

Chemically machined area

4 mm (before machining)

2 mm (after machining)

Section

(b)


Chemical Machining

FIGURE 9.26 (a) Schematic illustration of the chemical machining process. Note that no forces are involved in this process. (b) Stages in producing a profiled cavity by chemical machining.

3rd

Undercut

Workpiece

(b) (a)

2nd 1st

Steps

Depth

Material removed

Edge of maskant

Heating

Agitator

Cooling coils

Maskant Tank

Chemical reagent

Workpiece


Roughness and Tolerance Capabilities

FIGURE 9.27 Surface roughness and dimensional tolerance capabilities of various machining processes. Note the wide range within each process. (See also Fig. 8.26.) Source: Machining Data Handbook, 3rd ed., 1980. Used by permission of Metcut Research Associates, Inc.

2000 1000

500 250

125 63

32 16

8 2 4 1

0.5

(b)

(b)

(b)

(b)

(c)

(d)

(a)

(a)

(a)

25 6.3 50 12.5 3.12

1.60 0.8

0.4 0.2

0.1 0.025 0.05 0.012

2500 1250 500 250 125 50 25 12.5 5 2.5 1.25

Tolerance, mm x 10-3

100 50 20 10 5 2 1 0.5 0.2 0.1 0.05

0.001 in.

ELECTRICAL

MECHANICAL

THERMAL

CHEMICAL

CONVENTIONAL MACHINING

Surface Roughness, Ra (m)

in.

Surface grinding

Turning

Electropolishing

Photochemical machining

Chemical machining

Plasma-beam machining

Laser-beam machining

Electrical-discharge machining (roughing)

Electrical-discharge machining (finishing)

Electrical-discharge grinding

Electron-beam machining

Shaped tube electrolytic machining

Electrochemical polishing

Electrochemical milling (side wall)

Electrochemical milling (frontal)

Electrochemical grinding

Electrochemical deburring

Ultrasonic machining

Low-stress grinding

Abrasive-flow machining

Note: (a) Depends on state of starting surface.

(b) Titanium alloys are generally rougher than nickel alloys.

(c) High current density areas.

(d) Low current density areas.

Average application (normally anticipated values)

Less frequent application (unusual or precision conditions)

Rare (special operating conditions)


Chemical Blanking

FIGURE 9.28 Typical parts made by chemical blanking; note the fine detail. Source: Courtesy of Buckabee-Mears St. Paul.


Electrochemical Machining

FIGURE 9.29 Schematic illustration of the electrochemical-machining process. This process is the reverse of electroplating, described in Section 4.5.1.

DC

power supply

Insulating coating

Pump for circulating electrolyte

Tool

Tank

Workpiece

(-)

(+)

Electrolyte

FIGURE 9.30 Typical parts made by electrochemical machining. (a) Turbine blade made of a nickel alloy, 360 HB; the part on the right is the shaped electrode. Source: ASM International. (b) Thin slots on a 4340-steel roller-bearing cage. (c) Integral airfoils on a compressor disk.

(a)

Copper electrode Electrode carrier

Ram

Electrolyte Forging

Machined workpiece

Feed

Insulating layer

Telescoping cover 75 mm

65 mm

140 mm

(b)

14 holes

112 mm

86 mm

(c)


Electrochemical Grinding

FIGURE 9.31 (a) Schematic illustration of the electrochemical grinding process. (b) Thin slot produced on a round nickel-alloy tube by this process.

(a) (b)

Inconel1 in (3.1 mm)

164

in. (0.4 mm)

0.020 in.(0.5 mm)

Insulatingabrasiveparticles

Electrolyte from pump

Electrical connection

Electrode (grinding wheel)

Spindle

Insulatingbushing

DC

powersupply

Worktable (1)

(2)Workpiece

8


Electrical Discharge Machining

FIGURE 9.32 Schematic illustration of the electrical-discharge-machining process.

(+)(-)

RectifierCurrentcontrol

Power supply

Servocontrol

Movableelectrode

Dielectric fluid

Workpiece

Tank

Spark

Meltedworkpiece

Worn electrode


EDM Examples

FIGURE 9.33 (a) Examples of shapes produced by the electrical-discharge machining process, using shaped electrodes. The two round parts in the rear are a set of dies for extruding the aluminum piece shown in front; see also Section 6.4. Source: Courtesy of AGIE USA Ltd. (b) A spiral cavity produced using a shaped rotating electrode. Source: American Machinist. (c) Holes in a fuel-injection nozzle produced by electrical-discharge machining.

(b)(a)

Electrode

(c)

1.5 mm dia.

8 holes,0.17 mm

Workpiece

FIGURE 9.34 Stepped cavities produced with a square electrode by EDM. In this operation, the workpiece moves in the two principal horizontal directions, and its motion is synchronized with the downward movement of the electrode to produce these cavities. Also shown is a round electrode capable of producing round or elliptical cavities. Source: Courtesy of AGIE USA Ltd.


Wire EDM

FIGURE 9.35 Schematic illustration of the wire EDM process. As much as 50 hours of machining can be performed with one reel of wire, which is then recycled.

Workpiece

Wireguides

Dielectricsupply

Wire

Reel

Spark gap

Slot (kerf)

Wire

diameter


Laser Machining

FIGURE 9.36 (a) Schematic illustration of the laser-beam machining process. (b) Cutting sheet metal with a laser beam. Source: (b) Courtesy of Rofin-Sinat, Inc.

(b)

Powersupply

Flash lamp

Lens

Workpiece

Partiallyreflective end

Laser crystal

Reflective end

(a)

Application Laser TypeCutting

Metals PCO2; CWCO2; Nd:YAG; rubyPlastics CWCO2Ceramics PCO2

DrillingMetals PCO2; Nd:YAG; Nd:glass; rubyPlastics Excimer

MarkingMetals PCO2; Nd:YAGPlastics ExcimerCeramics Excimer

Surface treatment (metals) CWCO2Welding (metals) PCO2; CWCO2; Nd:YAG; Nd:glass; rubyNote: P=pulsed; CW=continuous wave.

TABLE 9.5 General applications of lasers in manufacturing.


Electron-Beam Machining

FIGURE 9.37 Schematic illustration of the electron-beam machining process. Unlike LBM, this process requires a vacuum, and hence workpiece size is limited by the chamber size.

High voltage cable (30 kV, DC)

Electron stream

Anode

Valve

Workpiece

Work table

Vacuum chamber

Cathode grid

Magnetic lens

Deflection coils

Highvacuumpump

Opticalviewingsystem

Viewingport


Water-Jet Machining

FIGURE 9.38 (a) Schematic illustration of water-jet machining. (b) A computer-controlled water-jet cutting machine. (c) Examples of various nonmetallic parts machined by the water-jet cutting process. Source: Courtesy of OMAX Corporation.

(a)

(c)(b)

Control panel y-axiscontrol

x-axiscontrol

Abrasive-jethead

Collectiontank

Mixer and filter

Sapphire nozzle

Fluid supply

HydraulicunitIntensifier

Pump

Accumulator Controls

Valve

Workpiece

Jet

Drain


Abrasive-Jet Machining

FIGURE 9.39 (a) Schematic illustration of the abrasive-jet machining process. (b) Examples of parts produced by abrasive-jet machining; the parts are 50 mm (2 in.) thick and are made of 304 stainless steel. Source: Courtesy of OMAX Corporation.

(b)(a)

Gassupply

Pressureregulator

Vibrator

FiltersPowdersupplyand mixer

Foot controlvalve

Handholder

Workpiece

Nozzle

Hood

Exhaust


Design Considerations

FIGURE 9.40 Design guidelines for internal features, especially as applied to holes. (a) Guidelines for grinding the internal surfaces of holes. These guidelines generally hold for honing as well. (b) The use of a backing plate for producing high-quality through-holes by ultrasonic machining. Source: After J. Bralla.

(b)

Undercut 3 mm

(1/8 in) wide

or greater

Through

hole

(a)

Sharp corner

Poor

Radius 0.25 mm

(0.010 in)

or greater

Good

Best

Breakaway

chipping

Backup plate

Coolant hole


Economic Considerations

2000 16326312525050010000

100

200

300

4000.50 10 5 0.4

m

Ma

ch

inin

g c

ost

(%)

Surfacefinish, Ra (in.)

As-c

ast,

sa

we

d,

etc

.

Se

mifin

ish

turn

Fin

ish

tu

rnRough turn

Grin

d

Ho

ne

1

FIGURE 9.41 Increase in the cost of machining and finishing operations as a function of the surface finish required. Note the rapid increase associated with finishing operations.


Case Study: Stent Manufacture

Guide wire0.356 mm(0.014 in.) max

Proximal and distal markersindicate position of stent on radiograph

Variable Thickness Strut (VTSTM)3-3-3 Pattern

Catheter and balloonused for stent expansion

2.5 mm4.0 mm(0.0100.16 in.)

8 mm38 mm

(0.3151.50 in.)

FIGURE 9.42 The Guidant MULTI-LINK TETRATM coronary stent system.

a

b

Notes:

a. 0.12 mm (0.0049 in.)

section thickness to provide

radiopacity

b. 0.091 mm (0.0036 in.)

thickness for flexibility

(a) (b) (c)

FIGURE 9.43 Detail of the 3-3-3 MULTI-LINK TETRATM pattern.

FIGURE 9.44 Evolution of the stent surface. (a) MULTI-LINK TETRATM after lasing. Note that a metal slug is still attached. (b) After removal of slug. (c) After electropolishing.

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