1. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Chapter 22 Cutting-Tool Materials and Cutting Fluids

2. Continuing the coverage of the fundamentals of machining in the preceding chapter, this chapter describes two essential elements in machining operations: cutting-tool materials and cutting fluids. The chapter opens with a discussion of the types and characteristics of cutting-tool materials. The properties and applications of high-speed steels, carbides, ceramics, cubic boron nitride, diamond, and coated tools are described in detail. The types of cutting fluids in common use are then described, including their functions and how they affect the machining operation. Trends in near-dry and dry machining are also discussed, and their importance with respect to environmentally friendly machining operations are explained. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

3. Cutting-Tool Materials and Cutting Fluids The cutting tool is subjected to (a) high temperatures, (b) high contact stresses, and (c) rubbing along the tool-chip interface and along the machined surface. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

4. Cutting-Tool Materials and Cutting Fluids Consequently, the cutting-tool material must possess the following characteristics: Hot hardness, so that the hardness, strength, and wear resistance of the tool are maintained at the temperatures encountered in machining operations Toughness and impact strength (or mechanical shock resistance), Thermal shock resistance, to withstand the rapid temperature cycling encountered in interrupted cutting Wear resistance, so that an acceptable tool life is obtained before replacement is necessary. Chemical stability and inertness with respect to the material being machined, to avoid or minimize any adverse reactions, adhesion, and tool-chip diffusion that would contribute to tool wear. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

5. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Hardness of Cutting Tool Materials as a Function of Temperature Figure 22.1 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.

6. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. General Properties of Tool Materials

7. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. General Characteristics of Cutting-Tool Materials

8. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Operating Characteristics of Cutting-Tool Materials

9. Tool Materials Tool materials generally are divided into the following categories 1.High-speed steels 2.Cast-cobalt alloys 3.Carbides 4.Coated tools 5.Alumina-based ceramics 6.Cubic boron nitride 7.Silicon-nitride-based ceramics 8.Diamond 9.Whisker-reinforced materials and nanomaterials Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

10. Tool Materials High-speed steel (HSS) tools are so named because they were developed to machine at higher speeds than was previously possible. High-speed steels are the most highly alloyed of the tool steels They can be hardened to various depths, have good wear resistance, and are relatively inexpensive Their most important limitation (due to their lower hot hardness) is that their cutting speeds are low compared with those of carbide tools There are two basic types of high-speed steels: molybdenum (M- series) and tungsten (T-series). High-speed steel tools are available in wrought (rolled or forged), cast, and powder-metallurgy (sintered) forms Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

11. Tool Materials Cast-cobalt alloys, commonly known as Stellite tools, have the following composition ranges: 38 to 53% Co, 30 to 33% Cr, and 10 to 20% W. Because of their high hardness (typically58 to 64 HRC), they have good wear resistance and can maintain their hardness at elevated temperatures. They are not as tough as high-speed steels and are sensitive to impact forces. Consequently, they are less suitable than high-speed steels for interrupted cutting operations They are now used only for special applications that involve deep, continuous roughing cuts at relatively high feeds and speeds-as much as twice the rates possible with high-speed steels Conversely, finishing cuts are performed at lower feeds and depths of cut, and the surface finish produced is a priority. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

12. Tool Materials Carbides, the two groups of tool materials just described possess the required toughness, impact strength, and thermal shock resistance, but they also have important limitations, particularly with respect to strength and hot hardness. Consequently, they cannot be used as effectively where high cutting speeds (hence high temperatures) are involved. To meet the challenge for increasingly higher cutting speeds, carbides (also known as cemented or sintered carbides) were introduced in the 1930s. Carbides are among the most important, versatile, and cost-effective tool and die materials for a wide range of applications. The two major groups of carbides used for machining are tungsten carbide and titanium carbide. In order to differentiate them from the coated tools, plain-carbide tools usually are referred to as uncoated carbides. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

13. Tool Materials Tungsten carbide (WC) typically consists of tungsten-carbide particles bonded together in a cobalt matrix. These tools are manufactured using powder-metallurgy techniques (hence the term sintered carbides or cemented carbides) Tungsten carbides frequently are compounded with titanium carbide and niobium carbide to impart special properties to the material. The amount of cobalt present, ranging typically from 6 to 16%, significantly affects the properties of tungsten-carbide tools. As the cobalt content increases, The strength, hardness, and wear resistance of WC decrease, while its toughness increases because of the higher toughness of cobalt. Tungsten-carbide tools generally are used for cutting steels, cast irons, and abrasive nonferrous materials and largely have replaced HSS tools because of their better performance. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

14. Tool Materials Titanium carbide (TiC) consists of a nickel-molybdenum matrix. It has higher wear resistance than tungsten carbide but is not as tough. Titanium carbide is suitable for machining hard materials (mainly steels and cast irons) and for cutting at speeds higher than those appropriate for tungsten carbide. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

15. Tool Materials Inserts; High-speed steel tools are shaped in one piece and ground to various geometric features; such tools include drill bits and milling and gear cutters. After the cutting edge wears, the tool has to be removed from its holder and reground. Although a supply of sharp or resharpened tools usually is maintained, toolchanging operations are time consuming and inefficient. The need for a more effective method has led to the development of inserts, which are individual cutting tools with several cutting points A square insert has eight cutting points, and a triangular insert has six. Inserts usually are clamped on the tool/colder with various locking mechanisms. Clamping is the preferred method of securing an insert because each insert has a number of cutting points and, after one edge is worn, it is indexed (rotated in its holder) to make another cutting point available. Carbide inserts are available in a variety of shapes, such as square, triangle, diamond, and round. The strength of the cutting edge of an insert depends on its shape. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

16. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Inserts and Toolholders Figure 22.2 Typical carbide inserts with various shapes and chip-breaker features: Round inserts are also available, as can be seen in Figs. 22.3c and 22.4. The holes in the inserts are standardized for interchangeability in toolholders. Source: Courtesy of Kyocera Engineered Ceramics, Inc. Figure 22.3 Methods of mounting inserts on toolholders: (a) clamping and (b) wing lockpins. (c) Examples of inserts mounted with threadless lockpins, which are secured with side screws. Source: Courtesy of Valenite.

17. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Insert Edge Properties Figure 22.4 Relative edge strength and tendency for chipping of inserts with various shapes. Strength refers to the cutting edge indicated by the included angles. Source: Courtesy of Kennametal, Inc. Figure 22.5 Edge preparation for inserts to improve edge strength. Source: Courtesy of Kennametal, Inc.

18. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. ISO Classification of Carbide Cutting Tools

19. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Classification of Tungsten Carbides According to Machining Applications

20. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Relative Time Required to Machine with Various Cutting-Tool Materials Figure 22.6 Relative time required to machine with various cutting-tool materials, indicating the year the tool materials were first introduced. Note that machining time has been reduced by two orders of magnitude with a hundred years. Source: Courtesy of Sandvik.

21. Coated Tools Coatings have unique properties, such as Lower friction Higher adhesion Higher resistance to wear and cracking Acting as a diffusion barrier Higher hot hardness and impact resistance. Coated tools can have lives 10 times longer than those of uncoated tools, allowing for high cutting speeds and thus reducing both the time required for machining operations and production costs. Coated tools now are used in 40 to 80% of all machining operations, particularly turning, milling, and drilling. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

22. Coated Tools Coating Materials and Coating Methods Commonly used coating materials are titanium nitride (TiN), titanium carbide (TiC), titanium carbonitride (TiCN), and aluminum oxide (Al2O3). These coatings, generally in the thickness range from 2 to 15  m, are applied on cutting tools and inserts by two techniques, –Chemical-vapor deposition (CVD), including plasma-assisted chemical- vapor deposition. –Physical-vapor deposition (PVD). Coatings for cutting tools and dies should have the following general characteristics –High hardness at elevated temperatures, to resist wear. –Chemical stability and inertness to the workpiece material, to reduce wear. –Low thermal conductivity, to prevent temperature rise in the substrate. –Compatibility and good bonding to the substrate, to prevent flaking or spalling. –Little or no porosity in the coating, to maintain its integrity and strength. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

23. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Typical Wear Patterns on High-Speed-Steel Uncoated and Titanium-Nitride Coated Tools Figure 22.7 Schematic illustration of typical wear patterns of high-speed-steel uncoated and titanium-nitride coated tools. Note that flank wear is significantly lower for the coated tool.

24. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Multiphase Coatings on a Tungsten-Carbide Substrate Figure 22.8 Multiphase coatings on a tungsten-carbide substrate. Three alternating layers of aluminum oxide are separated by very thin layers of 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.

25. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Ranges of Mechanical Properties for Groups of Tool Materials Figure 22.9 Ranges of mechanical properties for various groups of tool materials. See also Tables 22.1 through 22.5.

26. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Cubic Boron Nitride Inserts Next to diamond, cubic boron nitride (CBN) is the hardest material available. Introduced in 1962 under the trade name Borazon, cubic boron nitride is made by bonding a 0.5 -to-1-mm layer of polycrystalline cubic boron nitride to a carbide substrate by sintering under high pressure and high temperature. Figure 22.10 An insert of polycrystalline cubic boron nitride or a diamond layer on tungsten carbide. Figure 22.11 Inserts with polycrystalline cubic boron nitride tips (top row), and solid-polycrystalline cBN inserts (bottom row). Source: Courtesy of Valenite.

27. Whisker-reinforced Materials and Nanomaterials In order to further improve the performance and wear resistance of cutting tools (particularly in machining new materials and composites), continued progress is being made in developing new tool materials with enhanced properties such as the following: High fracture toughness Resistance to thermal shock Cutting-edge strength Creep resistance Hot hardness. Advances include the use of whiskers as reinforcing fibers in composite cutting tool materials. Examples of whisker-reinforced cutting tools include (a) silicon-nitride based tools reinforced with silicon-carbide whiskers and (b) aluminum-oxide-based tools reinforced with 25 to 40% silicon-carbide whiskers, sometimes with the addition of zirconium oxide (ZrO2). However, the high reactivity of silicon carbide with ferrous metals makes SiC-reinforced tools unsuitable for machining irons and steels. Nanomaterials are also becoming important in advanced cutting-tool materials. Suitable nanomaterials are carbides and ceramics. Often, nanomaterials are applied as a thin coating, usually in an attempt to obtain a reasonable tool life without the use of a coolant or to machine at high speeds Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

28. Tool Costs and Reconditioning of Tools Tool costs vary widely, depending on the tool material, size, shape, chip- breaker features, and quality. The cost for a typical 12.5-mm insert is approximately (a) $5 to $10 for uncoated carbides, (b) $6 to $10 for coated carbides, (c) $8 to $15 for ceramics, (d) $50 to $60 for diamond-coated carbides, (e) $60 to $100 for cubic boron nitride, and (f) $90 to $125 for a diamond-tipped insert. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

29. Cutting fluids Cutting fluids have been used extensively in machining operations to achieve the following results: Reduce friction and wear, thus improving tool life and the surface finish of the workpiece. Cool the cutting zone, thus improving tool life and reducing the temperature and thermal distortion of the workpiece. Reduce forces and energy consumption. Flush away the chips from the cutting zone, thus preventing the chips from interfering with the cutting process, particularly in operations such as drilling and tapping. Protect the machined surface from environmental corrosion. Depending on the type of machining operation, the cutting fluid needed may be a coolant, a lubricant, or both. The effectiveness of cutting fluids depends on a number of factors, such as the type of machining operation, tool and workpiece materials, cutting speed, and the method of application. Water is an excellent coolant and can effectively reduce the high temperatures developed in the cutting zone. However, water is not an effective lubricant; hence, it does not reduce friction. Furthermore, it can cause oxidation (rusting) of workpieces and machine-tool components. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

30. Types of Cutting Fluids Four general types of cutting fluids are commonly used in machining operations: Oils (also called straight oils), including mineral, animal, vegetable, compounded, and synthetic oils, typically are used for low-speed operations where temperature rise is not significant. Emulsions (also called soluble oils), a mixture of oil and water and additives, generally are used for high-speed operations because the temperature rise is significant. The presence of water makes emulsions highly effective coolants. The presence of oil reduces or eliminates the tendency of water to cause oxidation. Semisynthetics are chemical emulsions containing little mineral oil, diluted in water, and with additives that reduce the size of oil particles, making them more effective. Synthetics are chemicals with additives, diluted in water, and containing no oil. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

31. Methods of Cutting-fluid Application There are four basic methods of cuttingfluid applications in machining: Flooding. This is the most common method. Flow rates typically range from 10 L/min for single-point tools to 225 L/min per cutter for multiple-tooth cutters, as in milling. Mist. This type of cooling supplies fluid to inaccessible areas, in a manner similar to using an aerosol can, and provides better visibility of the workpiece being machined High-pressure systems. With the increasing speed and power of modern computer-controlled machine tools, heat generation in machining has become a significant factor. Particularly effective is the use of high-pressure refrigerated coolant systems to increase the rate of heat removal from the cutting zone. Through the cutting tool system. Narrow passages can be produced in cutting tools, as well as in toolholders, through which cutting fluids can be applied under high pressure. Two applications of this method are (a) gun drilling, with a long, small hole through the body of the drill itself, and (b) boring bars, Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

32. Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid. ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved. Proper Methods of Applying Cutting Fluids Figure 22.12 Schematic illustration of the proper methods of applying cutting fluids (flooding) in various machining operations: (a) turning, (b) milling, (c) thread grinding, and (d) drilling.