CHAPTER 9 Material-Removal Processes: Abrasive, Chemical, Electrical, and High-energy Beams

Knoop Hardness for Various Materials TABLE 9.1 Knoop hardness range for various materials and abrasives.

Physical Model of a Grinding Wheel FIGURE 9.1 Schematic illustration of a physical model of a grinding wheel, showing its structure and wear and fracture patterns.

Common Types of Grinding Wheels FIGURE 9.2 Some common types of grinding wheels made with conventional abrasives. Note that each wheel has a specific grinding face. Grinding on other surfaces is improper and unsafe.

Superabrasive-Wheel Configurations FIGURE 9.3 Examples of superabrasive-wheel configurations. The annular regions (rim) are superabrasive grinding surfaces, and the wheel itself (core) is generally made of metal or composites. Note that the basic numbering of wheel type is the same as 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.

Standard Marking System For Aluminum-Oxide Abrasives FIGURE 9.4a Standard marking system for aluminum-oxide and silicon-carbide bonded abrasives.

Standard Marking System for Diamond Abrasives FIGURE 9.4b Standard marking system for diamond and cubic-boron-nitride bonded abrasives.

Grinding and Chip Production FIGURE 9.5 The grinding surface of an abrasive wheel (A46-J8V), showing grains, porosity, wear flats on grains (see also Fig. 9.8), and metal chips from the workpiece adhering to the grains. Note the random distribution and shape of the abrasive grains. Magnification: 50X FIGURE 9.6 Grinding chip being produced by a single abrasive grain: (A) chip, (B) workpiece, (C) abrasive grain. Note the large negative rake angle of the grain. The inscribed circle is 0.065 mm (0.0025 in.) in diameter. Source: M. E. Merchant.

Variables in Surface Grinding TABLE 9.2 Typical ranges of speeds and feeds for abrasive processes. FIGURE 9.7 Variables in surface grinding. In actual grinding, 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.

Chip Formation FIGURE 9.8 Chip formation and plowing of the workpiece surface by an abrasive grain. FIGURE 9.9 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.

Energy in Abrasive Machining TABLE 9.3 Approximate specific energy requirements for surface grinding.

Residual Stresses on Workpiece Surface FIGURE 9.10 Residual stresses developed on the workpiece surface in grinding of tungsten: (a) effect of wheel speed and (b) effect of grinding fluid. Tensile residual stresses on a surface controlled to minimize residual stresses. This process is known as low-stress grinding. Source: After N. Zlatin et al., 1963.

Wheel Dressing FIGURE 9.11 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 surface at point of contact. Source: Okuma Machinery Works Ltd.

Surface-Grinding Operations FIGURE 9.12 Schematic illustration 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).

Horizontal-Spindle Surface Grinder FIGURE 9.13 Schematic illustration of a horizontal-spindle surface grinder. The majority of grinding operations are done on such machines.

Traverse and Plunge Grinding of Threads FIGURE 9.14 Thread grinding by (a) traverse and (b) plunge grinding.

Internal-Grinding Operations FIGURE 9.15 Schematic illustrations of internal-grinding operations.

Centerless-Grinding Operations FIGURE 9.16 Schematic illustration of centerless-grinding operations.

Characteristics of Abrasive Machining TABLE 9.4 General characteristics of abrasive machining operations.

Characteristics of Abrasive Machining (cont.)

Ultrasonic-Machining Process FIGURE 9.19 (a) Schematic illustration of the ultrasonic-machining process by which material is process by which material is removed through microchipping and erosion. (b) and (c) typical examples of holes produced by ultrasonic machining. Note the dimensions of cut and the types of workpiece materials.

Honing Tool FIGURE 9.21 Schematic illustration of a honing tool to improve the surface finish of bored or ground holes.

Superfinishing of a Cylindrical Part FIGURE 9.22 Schematic illustration of the superfinishing process for a cylindrical part: (a) cylindrical microhoning; (b) centerless microhoning.

Lapping Process FIGURE 9.23 (a) Schematic illustration of the lapping process. (b) Production lapping on flat surfaces. (c) Production lapping on cylindrical surfaces.

Magnetic Fields Used to Polish Balls and Rollers FIGURE 9.24 Schematic illustration of the use of magnetic fields to polish balls and rollers: (a) magnetic float polishing of ceramic balls; (b)magnetic-field-assisted polishing of rollers . Source: R. Komanduri, M. Doc, and M. Fox.

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. FIGURE 9.30 Typical parts made by electrochemical machining. (a) Turbine blade made of a nickel alloy, 360 HB. Source: Metal Handbook, 9th ed., Vol. 3, Materials Park, OH: ASM International, 1980, p. 849. (b) Thin slots on a 4340-steel roller-bearing cage. (c) Integral airfoils on a compressor disk.

Laser-Beam-Machining Process FIGURE 9.36 (a) Schematic illustration of the laser-beam-machining process. (b) and (c) Examples of holes produced in nonmetallic parts by LBM.

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

Water-Jet-Machining FIGURE 9.38 (a) Schematic illustration of water-jet machining. (b) Examples of various nonmetallic parts cut by a water-jet machine. Source: Courtesy of Possis Corporation.

Abrasive-Jet-Machining Process FIGURE 9.39 Schematic illustration of the abrasive-jet-machining process.