Cutting Tool


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cutting tool

[′kəd·iŋ ‚tül]
(mechanical engineering)
The part of a machine tool which comes into contact with and removes material from the workpiece by the use of a cutting medium. Also known as cutter.

Cutting Tool

 

(cutter), a cutting device used in machining workpieces on regular, turret, and vertical lathes, boring and slotting machines, planers, gear-shaping machines, and special machine tools. It consists of a shank comprising a head with the cutting element and a holder that secures the cutter to the machine tool.

Figure 1. Top-surface shapes for cutting tools
Form numberNameFormUse
IFlat without bevelCutting ToolCutting tools of all types for working pig iron and copper alloys
IIFlat with bevelCutting ToolCutting tools of all types for working steel: t = 0.2-0.3 mm for finishing, t = 0.8-1.0 mm for roughing; γ = 0° for cutting tools made from high speed steel, γ = -5° to -10° for cutting tools made from hard alloys
IIIRadiused with bevelCutting ToolCutting tools of all types for working steel: R = 3-18 mm for high-speed steel, R = 2-6 mm for hard alloys; t and γɸ as for form II
IVFlat with negative rakeCutting ToolCutting tools with hard alloy blades for rough sharpening of steel having a yield point σu1 > 1,000 meganewtons/m2; blades are steel castings with a skin for sharpening using percussion techniques
VFlat with bevel and reduced noseCutting ToolRough sharpening of steel with large chips and feed > 1.5 mm/revolution; γɸ = -10° to -15°

Cutting tools are classified according to the shape of the head as straight, bent, cranked, and round-nosed cutters and according to the cross section of the holder as rectangular, square, and round. Cutting-tool designs may feature a head or cutting blade that is welded on, a blade that is soldered on, a head that is guided by a slide or produced in the form of an insert, or a blade that is mechanically fixed. Various types of cutting tools are distinguished according to the intended purpose, including straightway, facing, cut-off and grooving, boring, thread-cutting, radiusing, and shaping cutters. Depending on the machining process, cutting tools may also be classified as roughing, finishing, fine turning, and smoothing. A distinction is made between right-hand and left-hand cutters according to the feed direction. Among the materials used for the cutting element are tool steel, including high-speed steel, hard alloys, mineral and ceramic materials, synthetic diamonds, and Elbor (a synthetic corundumlike material).

The shape chosen for the top surface (seeGEOMETRY OF A CUTTING TOOL) depends on the material used for the cutting element, the material being worked, the method used to produce the billet, and the type of machining (see Figure 1). The geometric parameters of the cutting element affect the primary factors of the cutting process, including the friction between the cutter and the billet material, the shape of the chip and the direction in which it is removed, deformation of the surface layer, the strength of the cutter, cutting forces, the rate and degree of cutter wear, and the roughness of the surface being worked.

Figure 2. Cutting tool with finishing edge: (1) side-cutting edge, (2) transitional cutting edge, (3) finishing edge

Optimum parameters for the geometry of the cutting element have been established experimentally. They depend on the actual machining conditions, such as the material being worked; the cutting mode; the type of cutter; the rigidity of the system comprising the lathe, attachment, tool, and workpiece; the type of machining; and the method used to produce the workpiece billet. The optimum parameters (see Figures 2, 3) are γ = - 10° to 25°, α = 6° to 12°, ɸ = 10° to 90°, ɸ1, = 0° to 20°, and λ = -4° to 15°.

When workpieces are machined using a cutting tool with an enlarged nose radius r, the surface roughness is reduced, but the forces pressing the cutter away from the workpiece are increased; the cutting tool exhibits increased deflections, and there is more vibration. Therefore, the value of r is maintained

Figure 3. Cutting tool with mechanically secured blade, designed at the Central Scientific Research Institute of Heavy-duty Machine Building: (1) holder, (2) backing, (3) blade, (4) bolt, (5) washer, (6) clamp, (7) movable support

at 1 mm. In order to simplify the sharpening of hard-alloy cutters, a cutter with a transitional cutting edge 1-2 mm long with ɸ0 = ɸ/2 is used instead of one with a rounded nose. For cutters with mineral and ceramic blades, the following values are recommended: γ = –5° to - 10°, α = 8° to 10° and ɸ = 75° to 90° for soft workpieces and ɸ = 10° to 30° for hard workpieces.

Machining is the most labor-consuming process in production, and its efficiency depends significantly on the properties of the tool material, the design of the cutter, and the geometry of the cutting elements. The problem of efficiency is of fundamental concern in the working of new materials that are difficult to machine and it is a prime factor in the growing demands for precision in manufacture and surface quality, for provision of size-presetting capabilities, and for rapid tool-replacement capabilities without the need for further adjustment. The All-Union Scientific Research Insititute of Hard Alloys (VNIITS) has developed the following alloys for cutting tools: the especially fine-grained hard alloys VK6-OM, VK10-OM, and VK15-OM for machining stainless and heat-resistant steels and alloys; the hard alloy TT8K16 for the high-speed finishing and semifinishing of alloy, inoculated, and malleable cast iron; and the hard alloy TT20K9 for intermittent work using percussion techniques. Multifaceted, throwaway, hard-alloy blades are now being used that feature a wear-resistant titanium carbide coating; the coating is applied in a thin layer up to 5 microns thick by precipitation from the gaseous phase. The All-Union Scientific Research Tool Institute (VNII) has developed a series of cutter designs using multifaceted cutter inserts and chip breakers. Cutters with mechanically secured blades and those with inserts made of composite materials and polycrystalline diamonds are also widely used. (SeeMETALCUTTING MACHINE TOOL and WOODCUTTING TOOL.)

REFERENCES

Granovskii, G. I. Metallorezhushchii instrument: Konstruktsiia i ekspluatatsiia, 2nd ed. Moscow, 1954.
Semenchenko, I. I., V. M. Matiushin, and G. N. Sakharov. Proektirovanie metallorezhushchikh instrumentov. Moscow, 1963.
Rezhushchii instrument: Reztsy. Moscow, 1965.
Rezanie konstruktsionnykh materialov, rezhushchie instrumenty i stanki. Edited by V. A. Krivoukhov. Moscow, 1967.
Arshinov, V. A., and G. A. Alekseev. Rezanie metallov i rezhushchii instrument, 2nd ed. Moscow, 1967.
Puti sovershenstvovaniia metallorezhushchego instrumenta: Obzor. Moscow, 1972.
Bobrov, V. F., and D. E. Ierusalimskii. Rezanie metallov samovrashchaiushchimisia reztsami. Moscow, 1972.
Gladilin, A. N., and N. P. Malevskii. Spravochnik molodogo instrumental’shchikapo rezhushchemu instrumentu, 3rd ed. Moscow, 1973.
Rezanie konstruktsionnykh materialov, rezhushchie instrumenty i stanki, 2nd ed. Moscow, 1974.

D. L. IUDIN

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Key words: cutting tool, wear, CAD/CAM, tool geometry