Chapter 22 Cutting-Tool Materials and Cutting Fluids

CUTTING TOOLS MATERIALS High speed steel Carbides Ceramics Diamond

Cutting tools are subjected to: 1. High temperatures 2 Cutting tools are subjected to: 1. High temperatures 2. High contact stresses 3. Rubbing along the tool-chip surface interface 4. Rubbing along the machined surface

Cutting tool material must possess the following properties: 1 Cutting tool material must possess the following properties: 1. Hot hardness 2. Toughness and impact strength 3. Thermal chock resistance 4. Wear resistance 5. Chemical stability and inertness to work piece material

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.

TABLE 22.1 Wear Resistance of Cutting–tool Materials

TABLE 22.1 (continued) Wear Resistance of Cutting–tool Materials

TABLE 22.2 General Characteristics of Cutting-tool Materials (These Materials Have a Wide Range of Compositions and Properties; Overlapping Characteristics Exist in Many Categories of Tool Materials)

TABLE 22.3 General Operating Characteristics of Cutting-tool Materials

CARBIDES 1. Have a high hardness over a wide range of temperatures 2 CARBIDES 1. Have a high hardness over a wide range of temperatures 2. Have high elastic modulus 3. Have a high thermal conductivity 4. have low thermal expansion 5. Moderate cost 6. The two major groups are Tungsten Carbide and Titanium Carbide

HIGH SPEED STEELS 1. Most highly alloyed among alloyed steels 2 HIGH SPEED STEELS 1. Most highly alloyed among alloyed steels 2. Can be hardened to various depths 3. Have good wear resistance 4. Are relatively inexpensive 6. Very tough 7. Have high resistance to fracture 8. Due to their lower hot hardness, the cutting speeds are low compared with those of carbide tools

INSERTS Individual cutting tools with several cutting edges Clamped to the tool holder When one edge is worn the insert is indexed (rotated) on the tool holder and another cutting edge is available Available in a variety of shapes: square, triangle, ..

FIGURE 22.2 Typical cutting-tool inserts with various shapes and chip-breaker features; round inserts also are 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 Kennametal 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.

FIGURE 22.9 Ranges of mechanical properties for various groups of tool materials. HIP = hot isostatically pressed. (See also Tables 22.1–22.5.)

CUTTING FLUIDS Reduce friction and wear Improve tool life Improve surface finish of work piece Cool cutting zone Reduce the temperature Reduce distortion of the work piece Reduce forces and energy consumption Flush away the chips from the cutting zone Protect the machined surface from environmental corrosion

FACTORS AFFECTING EFFECTIVENESS OF CUTTING FLUIDS 1 FACTORS AFFECTING EFFECTIVENESS OF CUTTING FLUIDS 1.Type of machining operation 2. Tool material 3. Work piece material 4. Cutting speed 5. Method of application Why is water not used as a cutting fluid? (it does not reduce friction and it can cause corrosion) Why is grease not used as a cutting fluid? action of cutting fluid is through seeping from the sides of the chip so must have small molecular size which grease does not have

TYPES OF CUTTING FLUIDS 1 TYPES OF CUTTING FLUIDS 1. oils: used for low speed operations where temperature rise is not significant 2. Emulsions: mixture of oil and water and additives used for high speed operations where temperature rise is significant 3. Semi-synthetics: chemical emulsions containing little mineral oil diluted in water with some additives to reduce the size of the particles 4. Synthetics: chemicals with additives diluted in water and containing no oil

METHODS OF APPLICATION OF CUTTING FLUIDS 1. Flooding 2 METHODS OF APPLICATION OF CUTTING FLUIDS 1. Flooding 2. Mist (like aerosol): it has limited cooling capacity and requires venting to prevent inhalation by machine operator 3. High-pressure refrigerated coolant system to increase the rate of heat removal 4. Through the cutting tool system through narrow passages in cutting tools or toolholders

FIGURE 22.12 Schematic illustration of the methods of applying cutting fluids (by flooding) in various machining operations: (a) turning, (b) milling, (c) thread grinding, and (d) drilling.

Near dry and dry machining To decrease the impact of using cutting fluids Improving air quality Reducing health hazards Reducing the cost of machining operations (including cost of recycling and disposal of cutting fluids)