Material-Removal Processes: Cutting

Cutting Processes FIGURE 8.1 Examples of cutting processes.

Orthogonal Cutting FIGURE 8.2 Schematic illustration of a two-dimensional cutting process (also called orthogonal cutting).

Chip Formation FIGURE 8.3 (a) Schematic illustration of the basic mechanism of chip formation in cutting. (b) Velocity diagram in the cutting zone.

Chips Produced in Metal Cutting FIGURE 8.4 Basic types of chips produced in metal cutting and their micrographs: (a) continuous chip with narrow, straight primary shear zone; (b) secondary shear zone at the tool-chip interface; (c) continuous chip with built-up edge; (d) continuous chip with large primary shear zone; (e) segmented or nonhomogeneous chip; and (f) discontinuous chip. Source: After M. C. Shaw, P. K. Wright, and S. Kalpakjian.

Continuous Chip Formation FIGURE 8.5 Shiny (burnished) surface on the tool side of a continuous chip produced in turning.

Chips Produced In Turning FIGURE 8.8 Various chips produced in turning: (a) tightly curled chip; (b) chip hits workpiece and breaks; (c) continuous chip moving away from workpiece; and (d) chip hits tool shank and breaks off. Source: G. Boothroyd, Fundamentals of Metal Machining and Machine Tools.

Oblique Cutting FIGURE 8.9 (a) Schematic illustration of cutting with an oblique tool. (b) Top view, showing the inclination angle i. (c) Types of chips produced with different inclination angles.

Right-Hand Cutting Tool FIGURE 8.10 (a) Schematic illustration of a right-hand cutting tool. Although these tools have traditionally been produced from solid tool-steel bars, they have been largely replaced by carbide or other inserts of various shapes and sizes, as shown in (b).

Terminology in Lathe Turning FIGURE 8.19 Terminology used in a turning operation on a lathe, where f is the feed (in./rev or mm/rev) and d is the depth of cut. Note that feed in turning is equivalent to the depth of cut in orthogonal cutting (Fig. 8.2), and the depth of cut in turning is equivalent to the turning is equivalent to the width of cut in orthogonal cutting. See also Fig. 8.42.

Types of Cutting Tool Wear FIGURE 8.20 (a) Types of wear observed in cutting tools. The thermal cracks shown are usually observed in interrupted cutting operations, such as in milling. (b) Catastrophic failure of tools. (c) Features of tool wear in a turning operation. The VB indicates average flank wear. Source: (a) and (b) After V. C. Venkatesh. (c) International Organization for Standardization (ISO).

Crater and Flank Wear on a Tool FIGURE 8.21 (a) Crater wear and (b) flank wear on a carbide tool. Source: J. C, Keefe, Lehigh University.

Range of Surface Rough-nesses FIGURE 8.27 Range of surface roughnesses obtained in various machining processes. Note the wide range within each group. (See also Fig. 9.27).

Carbide Inserts FIGURE 8.32 (a) Typical carbide inserts with various shapes and chip-breaker features. Round inserts are also available. The holes in the inserts are standardized for interchangeability. Source: Courtesy of Kyocera Engineered Ceramics, Inc., and Manufacturing Engineering, Society of Manufacturing Engineers. (b) Methods of attaching inserts to a tool shank by clamping, (c) with wing lockpins, and (d) with a brazed insert on a shank.

Relative Edge Strength FIGURE 8.33 Relative edge strength and tendency for chipping and breaking of inserts with various shapes. Strength refers to that of the cutting edge shown by the included angles. Source: Kennametal, Inc. FIGURE 8.34 Edge preparation of inserts to improve edge strength. Source: Kennametal, Inc.

Properties of Tool Materials FIGURE 8.38 Ranges of properties for various groups of tool materials. (See also various tables in this chapter.)

Construction of Insert FIGURE 8.39 Construction of polycrystalline cubic-boron-nitride or diamond layer on a tungsten-carbide insert.

Machining Processes TABLE 8.7 General characteristics of machining processes.

Lathe Operations FIGURE 8.40 Various cutting operations that can be performed on a lathe.

Designations for a Right-Handed Cutting Tool FIGURE 8.41 (a) Designations and symbols for a right-hand cutting tool; solid high-speed-steel tools have a similar designation. The designation “right hand” means that the tool travels from right to left, as shown in Fig. 8.19 (b) Square insert in a right-hand toolholder for a turning operation. A wide variety of toolholder is available for holding inserts at various angles. Thus, the angles shown in (a) can be achieved easily by selecting an appropriate insert and toolholder. Source: Kennametal, Inc.

Turning Operation FIGURE 8.42 (a) Schematic illustration of a turning operation showing depth of cut, d, and feed, f. cutting speed is the surface speed of the workpiece at the tool tip. (b) Forces acting on a cutting tool in turning. Fc is the cutting force; Ft is the thrust or feed force (in the direction of feed); and Fr is the radial force that tends to push the tool away from the workpiece being machined. Compare this figure with Fig. 8.11 for a two-dimensional cutting operation.

Range of Cutting Speeds FIGURE 8.43 The range of applicable cutting speeds and fees for a variety of tool materials. Source: Valenite, Inc.

Cutting Speeds in Turning TABLE 8.8 Approximate range of recommended cutting speeds for turning operations.

Components of a Lathe FIGURE 8.44 Schematic illustration of the components of a lathe. Source: Courtesy of Heidenreich & Harbeck.

Machine Tool Parts Example FIGURE 8.46 Typical parts made on computer-numerical-control machine tools.

Chisel and Crankshaft-Point Drills FIGURE 8.48 (a) Standard chisel-point drill, with various features indicated. (b) Crankshaft-point drill.

Drills and Drilling Operations FIGURE 8.49 Various types of drills and drilling operations.

Speeds and Feeds in Drilling TABLE 8.10 General recommendations for speeds and feeds in drilling.

Reamer and Tap Terminology FIGURE 8.50 Terminology for a helical reamer. FIGURE 8.51 Terminology for a tap.

Milling Operations FIGURE 8.53 (a) Schematic illustration of conventional milling and climb milling. (b) Slab-milling operation, showing depth of cut, d; feed per tooth, f; chip depth of cut, tc; and workpiece speed, v. (c) Schematic illustration of cutter travel distance to reach full depth of cut.