CHAPTER 21. Cutting-Tool Materials and Cutting Fluids. Kalpakjian Schmid Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-1

Transcription

1 CHAPTER 21 Cutting-Tool Materials and Cutting Fluids Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-1

2 Cutting Tool Material Hardnesses Figure 21.1 The hardness of various cutting-tool materials as a function of temperature (hot hardness). The wide range in each group of materials is due to the variety of tool compositions and treatments available for that group. See also Table 21.1 for melting or decomposition temperatures of these materials. Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-2

3 Typical Properties of Tool Materials Table 21.1 Carbides Property High-speed steels Cast alloys WC TiC Ceramics Cubic boron nitride Single-crystal diamond * Hardness HRA HRA HRA HRA HRA HK HK HRC HK HK HK Compressive strength MPa psi x Transverse rupture strength MPa psi x Impact strength J in.- lb Modulus of elasticity GPa 200 psi x Density kg/m < 0.1 < ,000 15, lb/in Volume of hard phase, % Melting or decomposition temperature C F < 0.5 < < 0.2 < Thermal conductivity, W/ m K Coefficient of thermal expansion, x10 6 C * The values for polycrystalline diamond are generally lower, except impact strength, which is higher Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-3

4 General Characteristics of Cutting-Tool Materials TABLE 21.2 General Characteristics of Cutting- Tool Materials. These Tool Materials Have a Wide Range of Compositions and Properties; Thus Overlapping Characteristics Exist in Many Categories of Tool Materials. Hot hardness Toughness Impact strength Wear resistance Chipping resistance Cutting speed Thermal-shock resistance Tool material cost Depth of cut Carbon and low- to medium- alloy steels Light to medium High speed steels Light to heavy Wrought, cast, HIP * sintering Cast- cobalt alloys Light to heavy Cast and HIP sintering Uncoated carbides Light to heavy Cold pressing and sintering Coated carbides Light to heavy Ceramics Light to heavy Polycrystalline cubic boron nitride Light to heavy Diamond Very light for single crystal diamond Finish obtainable Rough Rough Rough Good Good Very good Very good Excellent Method of Wrought CVD or processing PVD Fabrication Machining and grinding Machining and grinding Cold pressing and sintering or HIP sintering High-pressure, high-temperature sintering Grinding Grinding Grinding Grinding and polishing Source : R. Komanduri, Kirk- Othmer Encyclopedia of Chemical Technology, (3d ed.). New York: Wiley, * Hot- isostatic pressing. Chemical- vapor deposition, physical- vapor deposition. High-pressure, high-temperature sintering Grinding and polishing Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-4

5 Operating Characteristics of Cutting-Tool Materials TABLE 21.3 Tool materials High-speed steels Uncoated carbides Coated carbides Ceramics Polycrystalline cubic boron nitride (cbn) Polycrystalline diamond General characteristics High toughness, resistance to fracture, wide range of roughing and finishing cuts, good for interrupted cuts High hardness over a wide range of temperatures, toughness, wear resistance, versatile and wide range of applications Improved wear resistance over uncoated carbides, better frictional and thermal properties High hardness at elevated temperatures, high abrasive wear resistance High hot hardness, toughness, cutting-edge strength Hardness and toughness, abrasive wear resistance Source: After R. Komanduri and other sources. Modes of tool wear or failure Flank wear, crater wear Flank wear, crater wear Flank wear, crater wear Depth-of-cut line notching, microchipping, gross fracture Depth-of-cut line notching, chipping, oxidation, graphitization Chipping, oxidation, graphitization Limitations Low hot hardness, limited hardenability, and limited wear resistance Cannot use at low speed because of cold welding of chips and microchipping Cannot use at low speed because of cold welding of chips and microchipping Low strength, low thermomechanical fatigue strength Low strength, low chemical stability at higher temperature Low strength, low chemical stability at higher temperature Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-5

6 Carbide Inserts Figure 21.2 Typical carbide inserts with various shapes and chip-breaker features; round inserts are also available (Fig. 21.4). The holes in the inserts are standardized for interchangeability. Source: Courtesy of Kyocera Engineered Ceramics, Inc., and Manufacturing Engineering Magazine, Society of Manufacturing Engineers. Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-6

7 Insert Attachment (a) (b) (c) (d) Figure 21.3 Methods of attaching inserts to toolholders: (a) Clamping, and (b) Wing lockpins. (c) Examples of inserts attached to toolholders with threadless lockpins, which are secured with side screws. Source: Courtesy of Valenite. (d) Insert brazed on a tool shank (see Section 30.2). Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-7

8 Edge Strength Figure 21.4 Relative edge strength and tendency for chipping and breaking of insets with various shapes. Strength refers to the cutting edge shown by the included angles. Source: Kennametal, Inc. Figure 21.5 Edge preparation of inserts to improve edge strength. See also Section Source: Kennametal, Inc. Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-8

9 Classification of Tungsten Carbides Table 21.4 Classification of Tungsten Carbide According to Machining Applications. See also Chapters 22 and 23 for Cutting Tool Recommendations ISO Standard ANSI Classification Number Materials to be machined Machining Operation Type of carbide Characteristics of Cut Carbide K30-K40 C-1 Cast iron, Roughing K20 C-2 nonferrous metals General purpose K10 C-3 and nonmetallic Light finishing K01 C-4 materials requiring Precision abrasion resistance machining Wear-resistant grades; generally straight WC-Co with varying grain sizes Cutting speed hardness and wear resistance P30-P50 C-5 Steels and steel Roughing P20 C-6 alloys requiring General purpose P10 C-7 crater and Light purpose P01 C-8 deformation resistance Precision finishing Note: The ISO and ANSI comparisons are approximate. Crater-resistant grades; various WC-Co compositions with TiC and/or TaC alloys Feed rate Cutting speed Feed rate strength and binder content hardness and wear resistance strength and binder content Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-9

10 ISO Classification of Carbide Cutting Tools According to Use TABLE 21.5 Designation in increasing order of wear resistance and decreasing order of toughness in Symbol Workpiece material Color code each category, in increments of 5 P Ferrous metals with long chips Blue P01, P05 through P50 M Ferrous metals with long or short Yellow M10 through M40 chips; nonferrous metals K Ferrous metals with short chips; nonferrous metals; nonmetallic materials Red K01, K10 through K40 Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-10

11 Effect of Coating Materials Figure 21.6 Relative time required to machine with various cutting-tool materials, indicating the year the tool materials were introduced. Source: Sandvik Coromant. Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-11

12 Multiphase Coatings Figure 21.7 Multiphase coatings on a tungsten-carbide substrate. Three alternating layers of aluminum oxide are separated by very thin layers ot titanium nitride. Inserts with as many as thirteen layers of coatings have been made. Coating thicknesses are typically in the range of 2 to 10 µm. Source: Courtesy of Kennametal, Inc., and Manufacturing Engineering Magazine, Society of Manufacturing Engineers. Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-12

13 Properties for Groups of Tool Materials Figure 21.8 Ranges of properties for various groups of tool materials. See also Tables 21.1 through Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-13

14 Cubic Boron Nitride Figure 21.9 Construction of a polycrystalline cubic boron nitride or a diamond layer on a tungsten-carbide insert. Figure Inserts with polycrystalline cubic boron nitride tips (top row) and solid polycrystalline cbn inserts (bottom row). Source: Courtesy of Valenite. Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-14

15 Approximate Cost of Selected Cutting Tools TABLE 21.6 Tool Size (in.) Cost ($) High-speed steel tool bits 1/4 sq.x 2 1/2 long 1 2 1/2 sq. x Carbide-tipped (brazed) tools for turning 1/4 sq. 2 3/4 sq. 4 Carbide inserts, square 3/16"thick Plain 1/2 inscribed circle 5 9 Coated 6 10 Ceramic inserts, square 1/2 inscribed circle 8 12 Cubic boron nitride inserts, square 1/2 inscribed circle Diamond-coated inserts 1/2 inscribed circle Diamond-tipped inserts (polycrystalline) 1/2 inscribed circle Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-15

16 Application of Cutting Fluids Figure Schematic illustration of proper methods of applying cutting fluids in various machining operations: (a) turning, (b) milling, (c) thread grinding, and (d) drilling. Manufacturing Engineering and Technology 2001 Prentice-Hall Page 21-16