遼字石油化工大學⊙ Toughness and impact strength( or mechanical shock resistance ): so that impact forces on the tool that are encountered repeatedly in interrupted cutting operations or forces due to vibration and chatter during machining do not chip or fracture the tool 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
Toughness and impact strength ( or mechanical shock resistance) : so that impact forces on the tool that are encountered repeatedly in interrupted cutting operations or forces due to vibration and chatter during machining do not chip or fracture the tool. 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
遼字石油化工大學⊙ It must be recognized, however, that the tool materials may not have all of the desired properties for a particular machining operation. For example, (a high-speed steels are tough, but they have limited hot hardness (b)ceramics have high resistance to temperature and wrar, but they are brittle and can chip Note also that the cost of tools increases as we move from HSS to diamond(which is the most expensive
It must be recognized, however, that the tool materials may not have all of the desired properties for a particular machining operation. For example, (a) high-speed steels are tough, but they have limited hot hardness, (b) ceramics have high resistance to temperature and wrar, but they are brittle and can chip. Note also that the cost of tools increases as we move from HSS to diamond (which is the most expensive)
遼字石油化工大學⊙ Table 2.2 shows the operating characteristics of tool materials in machining General Operating Characteristics of Cutting-tool Materials Tool materials Modes of tool characteristics wear or failure Limitations High-speed steels High toughness, resistance Flank wear, crater wear Low hot hardness, limited to fracture, wide range of hardenability, and limited wear roughing and finishing cuts, resistance good for interrupted cuts Uncoated carbides High hardness over a wide Flank wear, crater wear Cannot use at low speeds range of temperatures. because of cold welding of chips toughness, wear resistance, and microchipping versatile, wide range of applications Coated carbides Improved wear resistance Flank wear, crater wear Cannot use at low speeds over uncoated carbides. because of cold welding of chips better frictional and thermal and microchipping properties Ceramics High hardness at elevated Depth-of-cut line notching, Low strength and low temperatures, high abrasive mIcrochipping, gross thermomechanical fatigue wear resistance fracture strengt Polycrystalline High hot hardness, toughness, Depth-of-cut line notching, Low strength, and low chemical cubic boron cutting-edge strength chipping, oxication, stability at higher temperature itride(cBN) graphitization Low strength, and low chemical Diamond High hardness and toughness, Chipping, oxidation, abrasive wear resistance graphitization stability at higher temperatures
Table 2.2 shows the operating characteristics of tool materials in machining
遼字石油化工大學⊙ ool materials generally are divided into the following categories, listed in the order in which they were developed and implemented in industry( note that many of these materials also are used for dies and molds in casting, forming, and shaping metallic and nonmetallic materials) 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
Tool materials generally are divided into the following categories, listed in the order in which they were developed and implemented in industry ( note that many of these materials also are used for dies and molds in casting, forming, and shaping metallic and nonmetallic materials): 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
遼字石油化工大學⊙ 1. High-speed Steels High-speed steel(Hss)tools are so named because they were developed to machine at higher speeds than was previously possible. First produced in the early 1900s, HHS are the most highly alloyed of the tool steels. They can be hardened to various depths have good wear resistance, and are relatively inexpensive. Because of their toughness, high speed steels are suitable especially for (a).high positive rake-angle tools (b). interrupted cuts (c)machine tools with low stiffness that are subject to vibration and chatter (d).complexandsingle-piecetools
1. High-speed Steels High-speed steel(HSS) tools are so named because they were developed to machine at higher speeds than was previously possible. First produced in the early 1900s, HHS are the most highly alloyed of the tool steels. They can be hardened to various depths, have good wear resistance, and are relatively inexpensive. Because of their toughness, highspeed steels are suitable especially for: (a).high positive rake-angle tools, (b).interrupted cuts, (c).machine tools with low stiffness that are subject to vibration and chatter, (d).complex and single-piece tools