Metalcutting Tools

Metalcutting Tools

 

production tools for changing the shape and dimensions of metal blanks by removing part of the material in the form of metal chips with the aim of producing finished or semifinished parts. A distinction is made between machine and hand tools.

The principal parts of a metalcutting tool are the working part, which may consist of cutting and gauging parts, and the mounting part. The cutting part of a metalcutting tool is the part that directly penetrates the metal of the blank and cuts away part of it. The cutting part consists of a number of structural elements: one or more blades; channels for guiding the removal of the chips; chip breakers; chip formers; elements that serve as reference elements in the manufacture, testing, and sharpening of the tool; and channels for the supply of liquid coolants and lubricants. The purpose of the gauging part is the restoration of the cutting part during sharpening, final shaping of the surface being machined, and guidance of the metalcutting tool during its operation.

The mounting part of a metalcutting tool is used to set the tool in the machine in a precisely determined position or for manual holding of the tool. It must counteract the forces arising during the process of cutting. The mounting part may be designed in the form of brackets or shanks (bit-type cutting tools), or it may have an opening for mounting in on mandrels (attachment-type metal-cutting tools).

A distinction is made among cutting tools, milling cutters, broaches, gear-cutting tools, thread-cutting tools, tools for machining of openings, and abrasive and diamond tools, depending on purpose.

Cutting tools are used in turning lathes, turret lathes, vertical turning lathes, and boring, planing, and slotting machines (with the exception of thread-cutting and gear-cutting tools) for turning, boring openings, shaping flat and profiled surfaces, and cutting channels. Milling cutters are multiblade rotary tools that are used in turning lathes for machining flat and profiled surfaces, as well as for cutting blanks apart. Broaches are multiblade tools for machining smooth and shaped internal and external surfaces. Openings are bored and machined by means of drills, countersinks, counterbores, reamers, boring bars, and combination tools, which are used in boring, turning, turret, drilling, and jig-boring lathes. Gear-cutting tools are designed for cutting and milling of the teeth on gears, gear racks, and worm gears.

Thread-cutting tools are used for cutting and milling interior and exterior threads. This category also includes thread tools and cutters, taps, and dies. Among the abrasive tools are grinding wheels and bricks, honing heads, and emery cloths, which are used for grinding, polishing, and lapping parts, as well as for sharpening tools. The diamond tools include disks, cutters, and milling cutters with diamond blades.

Among the hand tools are chisels, files, broach files, hacksaws, and scrapers, which are used without metalcutting machinery. Portable tools with electric, hydraulic, or pneumatic drive that use hand tools as the working members have come into widespread use.

The properties of the material being milled, the lubricating and cooling fluid, and the rigidity of the system formed by the lathe, attachment, tool, and part are taken into account in selecting the shape and leap angle of metalcutting tools, which determine their durability, productivity, and economy and the quality of milling. The cutting capacity of a tool is determined by the properties of the material from which the cutting part is made. The most important indicator is the red hardness of the material. The following main groups of materials are used: tool steels (carbon, high-speed, and alloy steels), hard alloys, and superhard powdered ceramic materials. Tools made from carbon steels (red hardness, 200°-250°C) are used for milling common materials at moderate cutting speeds. High-speed steels alloyed with tungsten make possible an increase in the cutting rate by a factor of 2–4. Blanks made from heat-resistant alloys and steels of increased hardness are milled with tools made from steel with increased content of vanadium, cobalt and molybdenum and with decreased tungsten content. The red hardness of these materials may be as high as 600°-620°C, but their brittleness also increases. Hard alloys, the most modern and widespread materials for metalcutting tools, are replacing the tool steels (except in cases where intermittent turning and profile milling of great depth are required). They have a red hardness of 750°-900°C and have great wear resistance. Hard alloys for metalcutting tools are produced in the form of plates of various shapes and dimensions. Small one-piece hard-alloy metalcutting tools are also produced. Metal-cutting tools with cutting parts reinforced by powdered ceramic plates produced from an aluminum oxide base with added molybdenum and chromium have even higher red hardness (1100°-1200°C) and wear resistance. However, the use of powdered ceramics is limited by their low plasticity and high brittleness. The use of superhard materials, such as natural and synthetic diamonds and cubic boron nitride, for grinding and sharpening of cutting tools is highly promising.

The performance parameters of metalcutting tools depend on the depth of cutting, the feed rate, and the cutting speed. The width of the worn area on the relief surface of the tool, taking into account the type of tool, the required precision of milling, and the degree of surface roughness, is an accepted criterion for wear of the cutting portion of a metalcutting tool. The wearresistance of metalcutting tools is determined by the duration of actual cutting (in minutes) between sharpenings. The principal requirement for a metalcutting tool—high output for a given degree of surface roughness and milling precision—is satisfied by fulfilling the conditions with respect to manufacturing tolerances, deviations from the geometric parameters, hardness of the cutting elements, and external appearance. The design of metalr cutting tools must provide for repeated sharpening, as well as reliable and rapid mounting. Special elements for mounting metalcutting tools, such as bit holders, conical openings, and mandrels, are taken into account in the design of metalcutting equipment.

In the design of new types of metalcutting tools, the tendency is toward improvement of their geometric parameters and structural elements, as well as the use of materials with better cutting properties (including new materials). The solution of these problems leads to metalcutting tools of increased stability, including dimensional stability, as well as to improved breaking of chips, particularly for automatic lines and lathes with programmed control. Studies of the physical principles of tool wear and the geometric parameters of the tool, as well as the invention of new lubricating and cooling fluids, are of great importance. The development of new types of lathes and the adoption of modern electrochemical and electrophysical methods for the processing of hard-alloy tools are closely related to problems of metalcutting tool production.

REFERENCES

Granovskii, G. I. Metallorezhushchii instrument, 2nd ed. Moscow, 1954.
Chetverikov, S. S. Metallorezhushchie instrument)?, 5th ed. Moscow, 1965.
Zhigalko, N. I., and V. V. Kiselev. Proektirovanie i proizvodstvo rezhushchikh instrumentov. Minsk, 1969.
Spravochnik tekhnologa-mashinostroitelia, 3rd ed., vols. 1–2. Moscow, 1972.
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