Grinding Wheel Bond

Grinding wheel

Porosity

Grain Bond fracture Microcracks Workpiece

Attritious wear

Wheel surface

Grain fracture

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

TABLE 9.1 Knoop hardness range for various materials and abrasives.

Common glass Flint, quartz Zirconium oxide Hardened steels Tungsten carbide Aluminum oxide

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350-500 800-1100 1000 700-1300 1800-2400 2000-3000

Titanium nitride Titanium carbide Silicon carbide Boron carbide Cubic boron nitride Diamond

2000 1800-3200 2100-3000 2800 4000-5000 7000-8000

Grinding Wheel Types Grinding face Grinding face (a) Type 1—straight

(b) Type 2— cylinder

Grinding face Grinding face (c) Type 6—straight cup

(d) Type 11—flaring cup

Grinding faces

Grinding faces

(f) Type 28—depressed center

(e) Type 27— depressed center

(g) Mounted

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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.

Superabrasive Wheels Type 1A1

2A2 1A1RSS

(a)

(b)

(c)

11A2 DW (d)

(e)

DWSE (f)

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.

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Grinding Wheel Marking System Example:

51 Prefix

Manufacturer!s symbol (indicating exact type of abrasive) (use optional)

A Aluminium oxide C Silicon carbide

–

A

–

Abrasive type

36 Abrasive grain size

–

L Grade

Coarse Medium Fine Very fine 8 220 70 30 10 80 240 36 12 90 280 46 14 100 320 54 16 120 400 60 20 150 500 24 180 600

Soft Medium Hard 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 Grade scale

–

5

–

Structure

Dense 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Open 15 16 etc. (Use optional)

V

–

Bond type

23

Manufacturer!s record Manufacturer!s private marking (to identify wheel) (use optional)

B BF E O R RF S V

Resinoid Resinoid reinforced Shellac Oxychloride Rubber Rubber reinforced Silicate Vitrified

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

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Diamond and cBN Marking System Example: M Prefix

Manufacturer!s symbol (to indicate type of diamond)

D

100

Abrasive type B Cubic boron nitride D Diamond

–

P

100

Grit size

Grade

Diamond concentration

20 24 30 36 46 54 60 80 90 100 120 150 180 220 240 280 320 400 500 600 800 1000

A (soft)

25 (low) 50 75 100 (high)

to Z (hard)

–

B Bond

1/8 Bond modification

B Resinoid M Metal V Vitrified

Diamond depth (in.)

1/16 1/8 1/4 Absence of depth symbol indicates solid diamond

A letter or numeral or combination (used here will indicate a variation from standard bond)

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

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Abrasive Grains A

Grain

Abrasive grain

Chip

V

Chip

Wear flat F

F v 10 Mm

Workpiece (a)

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.

Workpiece

(b)

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.

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Grinding Variables Chip length, external grinding V

Grinding wheel

D

l=

Grains

!

Dd 1 + (D/Dw)

t d v

l Workpiece

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.

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Chip length, internal grinding l=

!

Dd 1 − (D/Dw)

Chip length, surface grinding ! " 4v d t= VCr D

Grinding Parameters Ridges

Chip

ve o ro

G

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

Workpiece

Process Variable Wheel speed (m/min) Work speed (m/min) Feed (mm/pass)

Conventional Grinding 1500-3000 10-60 0.01-0.05

Creep-Feed Grinding 1500-3000 0.1-1 1-6

TABLE 9.2 Typical ranges of speeds and feeds for abrasive processes. Manufacturing Processes for Engineering Materials, 5th ed. Kalpakjian • Schmid © 2008, Pearson Education ISBN No. 0-13-227271-7

Buffing 1800-3600 -

Polishing 1500-2400 -

Specific Energy in Grinding Workpiece Material Aluminum Cast iron (class 40) Low-carbon steel (1020) Titanium alloy Tool steel (T15)

Hardness 150 HB 215 HB 110 HB 300 HB 67 HRC

Specific Energy W-s/mm3 hp-min/in3 7-27 2.5-10 12-60 4.5-22 14-68 5-25 16-55 6-20 18-82 6.5-30

TABLE 9.3 Approximate Specific-Energy Requirements for Surface Grinding.

Temperature rise:

! "1/2 1/4 3/4 V Temperature rise ∝ D d v

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Tension

Residual Stresses

0.10

0.15

4000 ft/min (20 m/s) 400

20

3000 (15)

0

0

2000 (10)

220 240

2200 0

0.002 0.004 0.006 Depth below surface (in.) (a)

MPa

200

0

0.15

Soluble oil (1:20) 200 20 Highly sulfurized oil 0

0

220 240

5% KNO2 solution

2200

MPa

60

0.05

2400

260 Compression

0

Residual stress (psi x 103)

Tension

80

40 Compression

Residual stress (psi x 103)

mm

40

mm 0.05 0.10

280

2600

2100 0

2800 0.002 0.004 0.006 Depth below surface (in.) (b)

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.

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Dressing Single-point dressing diamond for dressing forms up to 608 on both sides of the grinding wheel

60°

Fixed-angle swivelling dresser to dress forms up to 908 on both sides of the grinding wheel

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

Grinding wheel

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

Formed diamond roll dressing for high-volume production

Dressing tool

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

(a) Diamond dressing tool Grinding face

Grinding wheel

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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.

Surface Grinding Wheel

Wheel

Workpieces Wheel Work table

Workpiece

Workpiece

Horizontal-spindle surface grinder: Traverse grinding

Rotary table

Horizontal-spindle surface grinder: Plunge grinding

(a)

(b)

(c)

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). Wheel guard Worktable Workpiece

Wheel head Column

Saddle Feed Bed

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

Thread and Internal Grinding Grinding wheel

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

(b)

Workpiece

Workpiece

Workpiece Wheel

Wheel Wheel

(a) Traverse grinding

(b) Plunge grinding

(c) Profile grinding

FIGURE 9.15 Schematic illustrations of internal-grinding operations.

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Centerless Grinding Through-feed grinding

Plunge grinding Grinding wheel

Feed Grinding wheel

!

End stop

Workpiece

Work-rest blade Regulating wheel

Regulating wheel (a)

(b)

Internal centerless grinding Pressure roll

Regulating wheel

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

Grinder shaft Workpiece (revolves clockwise) Support roll (c)

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(d)

Creep-Feed Grinding

d = 1–6 mm

Low work speed, v

(a)

(b)

(c)

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.

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Finishing Operations Abrasive grains Size coat Make coat Backing

Spindle

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.

Stone

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

Oscillation (traverse if necessary)

Motor Stone

Holder

Rotation

Stone Workpiece

Workpiece (a)

Rolls (b)

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

Lapping Lap position and pressure control Upper lap Lap

Abrasive

Workpiece

Workpiece

Before Workholding plate After

Guide rail

(a)

Workpieces

Machine pan

(b)

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

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(c)

Lower lap

Chemical-Mechanical Polishing Abrasive slurry

Workpiece

Workpiece carrier

Workpiece carrier

Workpiece (disk)

Polishing pad

Polishing table Polishing table (a) Side view

(a) Top view

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.

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Polishing Using Magnetic Fields

Drive shaft

S-pole

Workpiece

N-pole

Guide ring Magnetic fluid and abrasive grains Ceramic balls (workpiece) Float NSNSNSNSNSNS Magnetic fluid

Permanent magnets (a)

(b)

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.

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Ultrasonic Machining Power supply

Transducer

Glass-graphite epoxy composite

Workpiece

1.2 mm (0.048 in.) 50 mm (2 in.) diameter

Abrasive slurry

Tool

Glass

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

Holes 0.4 mm (0.016 in.) diameter

(b)

(c)

(a)

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.

Contact time: 5r ! co "1/5 to ! co v Manufacturing Processes for Engineering Materials, 5th ed. Kalpakjian • Schmid © 2008, Pearson Education ISBN No. 0-13-227271-7

Contact force: 2mv Fave = to

Process

Characteristics

Chemical machining (CM)

Shallow removal (up to 12 mm) on large flat or curved surfaces; blanking of thin sheets; low tooling and equipment cost; suitable for low production runs. Complex shapes with deep cavities; highest rate of material removal; expensive tooling and equipment; high power consumption; medium to high production quantity. Cutting off and sharpening hard materials, such as tungsten-carbide tools; also used as a honing process; higher material removal rate than grinding. Shaping and cutting complex parts made of hard materials; some surface damage may result; also used for grinding and cutting; versatile; expensive tooling and equipment. Contour cutting of flat or curved surfaces; expensive equipment. Cutting and hole making on thin materials; heataffected zone; does not require a vacuum; expensive equipment; consumes much energy; extreme caution required in use. Cutting and hole making on thin materials; very small holes and slots; heat-affected zone; requires a vacuum; expensive equipment. Cutting all types of nonmetallic materials to 25 mm (1 in.) and greater in thickness; suitable for contour cutting of flexible materials; no thermal damage; environmentally safe process. Single or multilayer cutting of metallic and nonmetallic materials. Cutting, slotting, deburring, flash removal, etching, and cleaning of metallic and nonmetallic materials; tends to round off sharp edges; some hazard because of airborne particulates.

Electrochemical machining (ECM) Electrochemical grinding (ECG) Electrical-discharge machining (EDM) Wire EDM Laser-beam machining (LBM) Electron-beam machining (EBM) Water-jet machining (WJM) Abrasive water-jet machining (AWJM) Abrasive-jet machining (AJM)

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Process Parameters and Typical Material Removal Rate or Cutting Speed 0.025-0.1 mm/min

V: 5-25 dc; A: 2.5-12 mm/min, depending on current density. A: 1-3 A/mm2 ; typically 1500 mm3 /min per 1000 A.

Advanced Machining Processes

V: 50-380; A: 0.1-500; typically 300 mm3 /min. Varies with workpiece material and its thickness. 0.50-7.5 m/min.

1-2 mm3 /min Varies considerably with workpiece material. Up to 7.5 m/min. Varies considerably with workpiece material.

TABLE 9.4 General characteristics of advanced machining processes.

Chemical Milling

4 mm (before machining) 2 mm (after machining)

Chemically machined area

Section

(a)

(b)

FIGURE 9.25 (a) Missile skin-panel section contoured by chemical milling to improve the stiffness-toweight ratio of the part. (b) Weight reduction of space launch vehicles by chemical milling of aluminumalloy 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.

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Chemical Machining Agitator 3rd Tank

Maskant

Steps 2nd 1st

Edge of maskant Material removed

Undercut

Workpiece Heating

Chemical reagent

Cooling coils (a)

Depth Workpiece (b)

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.

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Roughness and Tolerance Capabilities µin. 2000 500 125 32 8 1000 250 63 16

2 4

0.5 1

100 50

MECHANICAL Abrasive-flow machining Low-stress grinding Ultrasonic machining

±0.001 in. 20 10 5 2 1

0.5 0.2 0.1 0.05

ELECTRICAL Electrochemical deburring Electrochemical grinding Electrochemical milling (frontal) Electrochemical milling (side wall) Electrochemical polishing Shaped tube electrolytic machining

(b) (c) (b) (d) (a) (b)

THERMAL Electron-beam machining Electrical-discharge grinding Electrical-discharge machining (finishing) Electrical-discharge machining (roughing) Laser-beam machining Plasma-beam machining (a) (a) (b)

CHEMICAL Chemical machining Photochemical machining Electropolishing CONVENTIONAL MACHINING Turning Surface grinding

25 50

6.3 1.60 0.4 0.1 0.025 12.5 3.12 0.8 0.2 0.05 0.012 Surface Roughness, Ra (µm)

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.

2500 1250 500 250 125 50 25 12.5 Tolerance, ±mm x 10-3

5 2.5 1.25

Average application (normally anticipated values) Less frequent application (unusual or precision conditions) Rare (special operating conditions)

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

Chemical Blanking

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

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Electrochemical Machining 75 mm

DC

power supply Insulating coating

(-)

Pump for circulating electrolyte

Telescoping cover

140 mm

Ram

Insulating layer Feed

65 mm

Electrolyte Forging Machined workpiece

Tool

Copper electrode

Electrode carrier

(a)

(+) Tank 14 holes

Workpiece

86 mm

Electrolyte 112 mm

(b)

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

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(c)

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 rollerbearing cage. (c) Integral airfoils on a compressor disk.

Electrochemical Grinding Electrolyte from pump Electrode (grinding wheel) Spindle Electrical connection 1 in (3.1 mm) 8

Insulating abrasive particles

0.020 in. (0.5 mm)

DC

Insulating bushing

Workpiece Work table

Inconel

(2)

power supply

1 in. (0.4 mm) 64

(1)

(a)

(b)

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

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Electrical Discharge Machining Current Rectifier control

Servo control

Movable electrode Worn electrode

(+)

(-)

Power supply

Spark Tank Workpiece

Melted workpiece

Dielectric fluid

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

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EDM Examples 1.5 mm dia.

Workpiece

8 holes, 0.17 mm

Electrode (a)

(b)

(c)

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.

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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 Wire Dielectric supply

Wire diameter Spark gap

Workpiece Slot (kerf) Wire guides

Reel

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.

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Laser Machining Flash lamp Reflective end Laser crystal

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.

Partially reflective end Lens

Power supply

Workpiece

(a)

(b)

TABLE 9.5 General applications of lasers in manufacturing.

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

Application Laser Type Cutting Metals PCO2 ; CWCO2 ; Nd:YAG; ruby Plastics CWCO2 Ceramics PCO2 Drilling Metals PCO2 ; Nd:YAG; Nd:glass; ruby Plastics Excimer Marking Metals PCO2 ; Nd:YAG Plastics Excimer Ceramics Excimer Surface treatment (metals) CWCO2 Welding (metals) PCO2 ; CWCO2 ; Nd:YAG; Nd:glass; ruby Note: P=pulsed; CW=continuous wave.

Electron-Beam Machining High voltage cable (30 kV, DC)

Cathode grid Anode Optical viewing system

Valve

Electron stream Magnetic lens Deflection coils

Viewing port Vacuum chamber

Workpiece Work table

High vacuum pump

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.

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Water-Jet Machining Accumulator

Controls Valve

Fluid supply Mixer and filter Sapphire nozzle

Pump

Hydraulic unit

Intensifier

Jet Workpiece Drain

(a)

Control panel

x-axis control

y-axis control

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.

Abrasive-jet head Collection tank

(b)

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(c)

Abrasive-Jet Machining Filters

Powder supply and mixer Exhaust Hood

Pressure regulator

Gas supply

Hand holder

Nozzle Workpiece

Vibrator

Foot control valve (a)

(b)

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.

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Design Considerations Poor Sharp corner

Good Breakaway chipping

Radius 0.25 mm (0.010 in) or greater

Undercut 3 mm (1/8 in) wide or greater

Backup plate Coolant hole

Best

Through hole (a)

(b)

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

Economic Considerations µm 10

5

0.4

1

300

200

63

32

16 Hone

Rough turn

Semifinish turn

As-cast, sawed, etc.

Surface 0 finish, Ra (µin.) 2000 1000 500 250 125

Grind

100

Finish turn

Machining cost (%)

0.50 400

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

Case Study: Stent Manufacture Proximal and distal markers indicate position of stent on radiograph

38 m 8 mm –

Guide wire 0.356 mm (0.014 in.) max

m (0.315 – 1.50 in.)

2.5 mm–4.0 mm (0.010–0.16 in.) Catheter and balloon used for stent expansion

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

b

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

Notes: a. 0.12 mm (0.0049 in.) section thickness to provide radiopacity b. 0.091 mm (0.0036 in.) thickness for flexibility

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

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(b)

(c)

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.