MINISTRY OF EDUCATION AND SCIENCE

RUSSIAN FEDERATION

NOVOSIBIRSK STATE TECHNICAL UNIVERSITY

TEST

in engineering technology

Topic: " Tool materials »

Performed:

Student of the OTZ-873 group

Vasilyeva Olga Mikhailovna

Checked:

Martynov Eduard Zakharovich

Tatarsk 2010

Introduction…………………………………………………………………………………………...………3

1. Basic requirements for tool materials………………………………….…..4

2. Types of tool materials……………………………………………………….…..6

2.1. Carbon and Alloy Tool Steels……………………...................................6

2.2. High speed steels………………………………………………………….………....7

3. Hard alloys…………………………………………………………………………….……8

3.1.Mineral-ceramic materials………………………………………………………....10

3.2. Metal-ceramic materials………………………………………………………..11

3.3. Abrasive materials………………………………………………………………..…..12

4. Features of obtaining tool materials based on diamond and cubic boron nitride……………………………………………………………………………………………..14

5. Steels for the manufacture of element cases………………………………………….…..16 Conclusion………………………………………………………… ……………………………….…...17 List of references………………………………………………………………..….18

Introduction

The history of the development of metal processing shows that one of the effective ways increasing labor productivity in mechanical engineering is the use of new tool materials. For example, the use of high-speed steel instead of carbon tool steel made it possible to increase the cutting speed by 2...3 times. This required a significant improvement in the design of metal-cutting machines, primarily to increase their speed and power. A similar phenomenon has been observed

also when used as a tool material of hard alloys.

The tool material must have high hardness in order to shear chips for a long time. A significant excess of the hardness of the tool material compared to the hardness of the workpiece must be maintained even when the tool is heated during the cutting process. The ability of the tool material to maintain its hardness at high heating temperatures determines its red hardness (heat resistance). The cutting part of the tool must have a large

wear resistance under conditions of high pressures and temperatures.

An important requirement is also a sufficiently high strength of the tool material, since insufficient strength results in chipping of the cutting edges or breakage of the tool, especially with their small sizes.

Tool materials must have good processing properties, i.e. easy to process in the process of tool manufacturing and regrinding, and also be relatively cheap. At present, tool steels (carbon, alloy and high-speed), hard alloys, mineral-ceramic materials, diamonds and other superhard and abrasive materials are used for the manufacture of cutting elements of tools.

1. Basic requirements for tool materials.

The main requirements for tool materials are as follows:

1. Tooling material must have high hardness.

The hardness of the tool material must be at least 1.4 - 1.7 times higher than the hardness of the material being processed.

2. When cutting metals, a significant amount of heat is released and the cutting part of the tool heats up. Therefore, the instrumental material must have high heat resistance . The ability of a material to maintain high hardness at cutting temperatures is called heat resistance ... For high-speed steel - heat resistance is also called red hardness (i.e., the preservation of hardness when heated to the temperatures at which the steel begins to glow)

An increase in the level of heat resistance of the tool material allows it to work at high cutting speeds (Table 1).

Table 1 - Heat resistance and allowable cutting speed of tool materials.

3. An important requirement is enough high strength tool material. If the high hardness of the material of the working part of the tool is not provided with the necessary strength, then this leads to tool breakage and chipping of the cutting edges.

Thus, the tool material must have a sufficient level of toughness and resist the appearance of cracks (ie, have a high fracture toughness).

4. Tooling material must have high wear resistance at elevated temperature, i.e. have good abrasion resistance of the workpiece material, which is manifested in the resistance of the material to contact fatigue.

5. Necessary condition achieving high cutting properties of the tool is low physical and chemical activity of the tool material in relation to the processed . Therefore, the crystal-chemical properties of the tool material must differ significantly from the corresponding properties of the material being processed. The degree of such a difference strongly affects the intensity of physical and chemical processes (adhesion-fatigue, corrosion-oxidation and diffusion processes) and wear of the contact pads of the tool.

6. Tool material must have technological properties , providing optimal conditions for the manufacture of tools from it. For tool steels, these are good machinability by cutting and pressure; favorable features of heat treatment (low sensitivity to overheating and decarburization, good hardenability and hardenability, minimal deformation and cracking during hardening, etc.); good sandability after heat treatment.

2. TYPES OF TOOL MATERIALS

For cutting tools, high-speed steels are used, as well as, in small quantities, hypereutectoid carbon steels with a carbon content of 0.7-1.3% and a total content of alloying elements (silicon, manganese, chromium and tungsten) from 1.0 to 3.0 %.

2.1. Carbon and alloy tool steels.

Earlier, other materials for the manufacture of cutting tools began to be used carbon tool steels grades U7, U7A…U13, U13A. In addition to iron and carbon, these steels contain 0.2 ... 0.4% manganese. Tools from carbon steels have sufficient hardness at room temperature, but their heat resistance is low, since at relatively low temperatures (200 ... 250 ° C) their hardness decreases sharply.

alloyed tool steels, in their chemical composition, they differ from carbon ones in an increased content of silicon or manganese, or in the presence of one or more alloying elements: chromium, nickel, tungsten, vanadium, cobalt, molybdenum. For cutting tools, low-alloy steel grades 9HF, 11HF, 13X, V2F, XV4, KhVSG, KhVG, 9XS, etc. are used. These steels have higher technological properties - better hardenability and hardenability, less tendency to warp, but their heat resistance is 350 ... 400 °C and therefore they are used for the manufacture of hand tools (reamers) or tools intended for processing on machines with low cutting speeds (small drills, taps).

It should be noted that over the past 15-20 years there have been no significant changes in these grades, however, there is a steady downward trend in their share in the total volume of tool materials used.

2.2. High speed steels.

Currently, high speed steels are the main material for the manufacture of cutting tools, despite the fact that tools made of carbide, ceramic and STM provide higher machining performance.

The widespread use of high-speed steels for the manufacture of complex-shaped tools is determined by a combination of high hardness values ​​(up to [email protected]) and heat resistance (600-650°C) with a high level of brittle strength and toughness, significantly exceeding the corresponding values ​​for hard alloys. In addition, high-speed steels have a fairly high manufacturability, as they are well processed by pressure and cutting in the annealed state.

In the designation of high-speed steel, the letter P means that the steel is high-speed, and the number following the letter indicates the content of the average mass fraction of tungsten in%. The following letters denote: M - molybdenum, F - vanadium, K - cobalt, A - nitrogen. The numbers following the letters indicate their average mass fraction in%. The content of mass fraction of nitrogen is 0.05-0.1%.

Modern high-speed steels can be divided into three groups: normal, high and high heat resistance.

To the steels normal heat resistance include tungsten R18 and tungsten-molybdenum R6M5 steel (Table 2.2). These steels have hardness in the hardened state of 63…64 HRC, flexural strength of 2900…3400 MPa, impact strength of 2.7…4.8 J/m2 and heat resistance of 600…620°C. These steel grades are most widely used in the manufacture of cutting tools. The volume of production of R6M5 steel reaches 80% of the total output of high-speed steel. It is used in the processing of structural steels, cast irons, non-ferrous metals, plastics.

Steels of increased heat resistance characterized by a high content of carbon, vanadium and cobalt.

Among vanadium steels the most widely used brand R6M5F3.

Along with high wear resistance, vanadium steels

have poor grindability due to the presence of vanadium carbides (VC), since the hardness of the latter is not inferior to the hardness of the grains of the electrocorundum grinding wheel (Al2 O3). Machinability during grinding - "grindability" - is the most important technological property, which determines not only the features in the manufacture of tools, but also during its operation (regrinding).

Table 2. Chemical composition of high speed steels

3.3. Abrasives Great place in modern production machine parts are occupied by grinding processes in which various abrasive tools are used. The cutting elements of these tools are hard and heat-resistant grains of abrasive material with sharp edges. Abrasive materials are divided into natural and artificial. Natural abrasive materials include minerals such as quartz, emery, corundum, etc. Natural abrasive materials are highly heterogeneous and contain foreign impurities. Therefore, in terms of the quality of abrasive properties, they do not meet the growing needs of the industry. Currently, processing with artificial abrasive materials occupies a leading place in mechanical engineering. The most common artificial abrasive materials are electrocorundum, silicon and boron carbides. Artificial abrasive materials also include polishing and finishing powders - oxides of chromium and iron. A special group of artificial abrasive materials are synthetic diamonds and cubic boron nitride. Electrocorundum is obtained by electric melting of materials rich in aluminum oxide, for example, from bauxite or alumina, mixed with a reducing agent (anthracite or coke). Electrocorundum is produced in the following varieties: normal, white, chromium, titanium, zirconium, monocorundum and spherocorundum. Normal electrocorundum contains 92-95% aluminum oxide and is divided into several grades: 12A, 13A, 14A, 15A, 16A. Grains of normal electrocorundum, along with high hardness and mechanical strength, have a significant viscosity, which is necessary when performing work with variable loads at high pressures. Therefore, normal electrocorundum is used for processing various materials of increased strength: carbon and alloy steels, malleable and high-strength cast iron, nickel and aluminum alloys. White electrocorundum grades 22A, 23A, 24A, 25A are distinguished by a high content of aluminum oxide (98-99%). Compared to normal electrocorundum, it is harder, has increased abrasive ability and brittleness. White electrocorundum can be used for processing the same materials as normal electrocorundum. However, due to its higher cost, it is used in more demanding jobs for final and profile grinding, thread grinding, and sharpening of cutting tools. Chromium electrocorundum grades 32A, ZZA, 34A, along with aluminum oxide A12O3, contains up to 2% chromium oxide Cr2O3. The addition of chromium oxide changes its microstructure and structure. In terms of strength, chromium electrocorundum approaches normal electrocorundum, and in terms of cutting properties - to white electrocorundum. It is recommended to use chromium electrocorundum for circular grinding of products made of structural and carbon steels under intensive conditions, where it provides a 20-30% increase in productivity compared to white electrocorundum. Titanium electrocorundum grade 37A along with aluminum oxide contains TiO2 titanium oxide. It differs from normal electrocorundum in greater constancy of properties and increased viscosity. This allows it to be used in conditions of heavy and uneven loads. Titanium electrocorundum is used in preliminary grinding operations with increased metal removal. Electrocorundum zirconium grade ZZA along with aluminum oxide contains zirconium oxide. It has high strength and is mainly used for peeling operations with high specific cutting pressures. Monocorundum grades 43A, 44A, 45A is obtained in the form of a grain with increased strength, sharp edges and peaks with a more pronounced self-sharpening property compared to electrocorundum. This provides him with increased cutting properties. Monocorundum is preferred for grinding hard-to-cut steels and alloys, for precision grinding of complex profiles and for dry grinding of cutting tools, Spherocorundum contains more than 99% A1203 and is obtained in the form of hollow spheres. In the process of grinding, the spheres are destroyed with the formation of sharp edges. Spherocorundum is advisable to use when processing such materials as rubber, plastics, non-ferrous metals. Silicon carbide is obtained by reacting silica and carbon in electric furnaces and then crushing into grains. It consists of silicon carbide and a small amount of impurities. Silicon carbide has a high hardness, exceeding the hardness of electrocorundum, high mechanical strength and cutting ability. Black silicon carbide grades 53C, 54C, 55C are used for processing hard, brittle and very viscous materials; hard alloys, cast iron, glass, non-ferrous metals, plastics. Silicon carbide green grades 63C, 64C is used for sharpening carbide tools, grinding ceramics. Boron carbide B4C has high hardness, high wear resistance and abrasive ability. At the same time, boron carbide is very brittle, which determines its use in industry in the form of powders and pastes for finishing hard-alloy cutting tools. Abrasive materials are characterized by such basic properties as the shape of abrasive grains, granularity, hardness, mechanical strength, abrasive ability of grains. The hardness of abrasive materials is characterized by the resistance of grains to surface grinding, local impact of applied forces. It must be higher than the hardness of the material being processed. The hardness of abrasive materials is determined by scratching the tip of one body on the surface of another or by pressing a diamond pyramid under a small load into the abrasive grain. Mechanical strength is characterized by the crushability of grains under the influence of external forces. Strength is assessed by crushing a sample of abrasive grains in a steel mold under a press using a certain static load. Roughing conditions with high metal removal require strong abrasives, while fine grinding and machining of difficult-to-cut materials prefer abrasives with greater brittleness and the ability to self-sharpen.

4. Features of Obtaining Tool Materials Based on Diamond and Cubic Boron Nitride

Diamond as a tool material has been widely used in mechanical engineering in recent years. Currently released a large number of a variety of tools using diamonds: grinding wheels, tools for dressing grinding wheels made of electrocorundum and silicon carbide, pastes and powders for finishing and lapping operations. Diamond crystals of considerable size are used for the manufacture of diamond cutters, milling cutters, drills and other cutting tools. The scope of the diamond tool is expanding every year. Diamond is one of the modifications of carbon crystal structure. Diamond is the hardest mineral known in nature. The high hardness of diamond is explained by the peculiarity of its crystal structure, the strength of the bonds of carbon atoms in the crystal lattice, located at equal and very small distances from each other. The thermal conductivity coefficient of diamond is two or more times higher than that of the VK8 alloy, so heat is removed from the cutting zone relatively quickly. The increased demand for diamond tools cannot be fully met by natural diamonds. Currently mastered industrial production synthetic diamonds from graphite at high pressures and high temperatures. Synthetic diamonds can be of various grades, which differ in strength, brittleness, specific surface area and grain shape. In order of increasing strength, decreasing brittleness and specific surface, grades of grinding powders made of synthetic diamonds are arranged as follows: AC2, AC4, AC6, AC15, AC32. Among the new types of tool materials are superhard polycrystals based on diamond and cubic boron nitride.

Cubic boron nitride (CBN) is a superhard material that has no natural analogue. For the first time, cubic boron nitride was synthesized in 1956 (by the General Electric Company) at high pressures (over 4.0 GPa) and high temperatures (over 1473 K) from hexagonal boron nitride in the presence of alkaline and alkaline earth metals(lead, antimony, tin, etc.). Cubic boron nitride manufactured by General Electric was named Borazon.

The diameter of blanks made of superhard polycrystals is in the range of 4-8mm, and the height is 3-4mm. Such dimensions of workpieces, as well as a combination of physical and mechanical properties, make it possible to successfully use the considered materials as a material for the manufacture of the cutting part of such tools as cutters, end mills, etc. Superhard diamond-based polycrystals are especially effective in cutting materials such as fiberglass, non-ferrous metals and their alloys, titanium alloys. The significant distribution of the considered composites is explained by a number of unique properties inherent in them - hardness approaching the hardness of diamond, high thermal conductivity, and chemical inertness to iron. However, they have increased brittleness, which makes it impossible to use them under shock loads. Composite 09 and 10 tools are more resistant to impact. They are effective in heavy duty and impact machining of hardened steels and cast irons. The use of superhard synthetic materials has a significant impact on mechanical engineering technology, opening up the prospect of replacing grinding, turning and milling in many cases. perspective view tool material are two-layer plates of round, square, trihedral or hexagonal shapes. The upper layer of the plates consists of polycrystalline diamond, and the lower one is made of a hard alloy or a metal substrate. Therefore, inserts can be used for mechanically held tools in the holder. Silinit-R alloy based on silicon nitride with additions of aluminum oxide and titanium occupies an intermediate position between hard alloys based on carbide and superhard materials based on diamond and boron nitride. Studies have shown that it can be used for fine turning of steels, cast iron, aluminum and titanium alloys. The advantage of this alloy is that silicon nitride will never become scarce. 5. Steels for the manufacture of element cases For prefabricated tools, the bodies and fastening elements are made of structural steel grades: 45, 50, 60, 40X, 45X, U7, U8, 9XS, etc. Steel 45 is most widely used, from which cutter holders, drill shanks, countersinks, reamers, taps, prefabricated cutter bodies, boring bars. 40X steel is used for the manufacture of tool cases operating in difficult conditions. After quenching in oil and tempering, it maintains the accuracy of the grooves into which the knives are inserted. In the case when individual parts of the tool body work for wear, the choice of steel grade is determined by considerations of obtaining high hardness in friction points. Such tools include, for example, carbide drills, countersinks, in which the guide strips come into contact with the surface of the machined hole during operation and wear out quickly. For the body of such tools, carbon tool steel is used, as well as alloy tool steel 9XC. Conclusion

Development new technology dictates the requirements for the development of new materials, which include superhard materials. Traditionally, they are used in metalworking, tool making, stone and glass processing, building materials, ceramics, ferrites, semiconductor and other materials. In recent years, intensive work has been carried out on the use of diamonds in electronics, laser technology, medicine, and other fields of science and technology. In the industrialized countries of the world, much attention is paid to the production of superhard materials and products from them. Russian Federation in recent years has made significant progress in creating a domestic diamond production. A large contribution to solving this problem is made by the state scientific and technical program "Diamonds", thanks in large part to the support of which over 25% of the republic's needs for diamond products are now met by own production.

A more complete solution to the problem of import substitution requires further work to improve existing and develop new materials and technologies for producing superhard materials and products based on them, expanding their areas of application. Today, work in the field of superhard materials in Russia is carried out in a wide range of problems, including: the synthesis of powders of diamond and cubic boron nitride, the growth of large single crystals of diamond, the growth of single crystals of precious stones, the production of polycrystals of diamond, cubic boron nitride and compositions based on them, in including the use of nanopowders, the development of new composite diamond-containing materials and technologies for obtaining tools from them, the development of technology and equipment for applying diamond films and coatings, the certification of diamond products, as well as the development of facilities for the production of diamond products.

1. New tool materials and areas of their application. Textbook allowance / V.V. Kolomiets, - K .: UMK VO, 1990. - 64 p.

2. Vasin S.A., Vereshchaka A.S., Kushnir V.S. Cutting metals: Thermomechanical approach to the system of relationships in cutting: Uchebn. for tech. universities. - M .: Publishing house of MSTU im. N.E. Bauman, 2001. - 448 p.

3. Metalworking carbide tool: V.S. Samoilov, E.F. Eichmans, V.A. Falkovsky and others. - M .: Mashinostroenie, 1988. - 368 p.

4. Tools from superhard materials / Ed. N.V. Novikova. - Kyiv: ISM NASU, 2001. - 528 p.

High performance characteristics cutting tools are largely dependent on the quality of the material from which these tools are made. Materials intended for cutting tools should, in a number of indicators, significantly exceed the materials used in mechanical engineering for the manufacture of various parts.

The main requirements for tool materials are as follows:

1. The tool material must have high hardness - not less than 63 ... 66 HRC according to Rockwell (scale C).

2. When cutting metals, a significant amount of heat is released and the cutting part of the tool heats up. The temperature of the working surfaces and cutting edges of the tool can reach several hundred degrees. It is necessary that at significant cutting temperatures the hardness of the tool surfaces does not decrease significantly.

The ability of a material to maintain high hardness at elevated temperatures and its original hardness after cooling is called heat resistance.

The tool material must have high heat resistance.

3. Along with heat resistance, instrumental material must have high wear resistance at elevated temperatures, i.e., have good abrasion resistance of the material being processed.

4. An important requirement is high strength tool material. If the high hardness of the material of the working part of the tool is accompanied by significant brittleness, this leads to tool breakage and chipping of the cutting edges.

5. The tool material must have technological properties that provide optimal conditions for the manufacture of tools from it.

For tool steels they are:

The cutting wedge, when interacting with the material of the workpiece, carrying out continuous deformation and separation of the material, is subjected to force and heat, as well as abrasion. These operating conditions allow us to formulate the basic requirements for the material of the cutting part of the tool. The suitability of such materials is determined by their hardness, heat resistance, mechanical strength, wear resistance, manufacturability and cost.

1. Hardness. The introduction of one material (wedge) into another (workpiece) is possible only with the prevailing hardness of the wedge material, therefore, the hardness of tool materials, as a rule, is higher than the hardness of the materials being machined. However, as the temperature of the tool material increases, its hardness decreases and may not be sufficient to effect deformation and separation of the material. The property of materials to maintain the required hardness at high temperatures is called heat resistance.

2. Heat resistance. It is determined by the critical temperature at which the change in hardness occurs. If the temperature is above critical, the tool will not work. In general, heat resistance determines the new cutting speed.

3. Mechanical strength. The importance of mechanical strength for a tool material is explained by its operating conditions, which are characterized by bending, compressive and impact loads, and therefore the material's bending strength, compression and impact strength are the main indicators of the strength of the tool material.

4. Wear resistance. The ability of the material to resist wear determines the life of the tool material. Wear resistance is characterized by the work of the friction force related to the value of the worn mass of the material. The importance of this characteristic is that it determines the conservation initial geometry tool in time, because in the process of work, there is a constant abrasion of the tool (surface of the wedge).

5. Manufacturability. Manufacturability of the material - its ability to meet the requirements of heat treatment technology, pressure treatment, machining, etc., is a property that determines the possibility of manufacturing a tool of a given design.

6. Cost. The material of cutting tools should not be of high cost, because. this ultimately determines the breadth of its use.

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Groups of tool materials,
used to make cutting tools

1. Tool steels

U7, U7A, U13, U13A

Carbon steels are used for the manufacture of tools that operate at low cutting speeds of 15-18 m / min, as well as at temperatures not lower than 200-230 ° C. This is a bench tool (chisel, files, taps, dies, etc.). The hardness of carbon steels after heat treatment reaches HRC 62-64.

2. Alloy steel

To improve the technical or other properties of carbon steels, alloying elements are introduced into them. So, for example:

(Ni) Nickel (H) - increases ductility and toughness, increases hardenability

(Mn) Manganese (G) - increases strength, hardenability, wear resistance

(Cr) Chromium (X) - hardens steel

(W) Tungsten (B) - increases hardness, wear resistance, heat resistance

· (V) Vanadium (F) limits the change in properties when heated, improves surface quality and weldability, but worsens grindability.

(Mo) Molybdenum (M) increases hardenability, strength, ductility, toughness

· (Si) Silicon (C) increases hardenability.

The heat resistance of alloyed steel is not more than 300-350 ° C. Low-alloy steels (X) with chromium are used for the manufacture of metalwork tools. High alloy steels KhVG, HSVG for shaped cutters, small diameter drills, broaches, reamers and other tools operating at cutting speeds up to 25 m/min.

3. High speed steels

A special group of tool steels are high-speed steels with a tungsten content of 6-18% with high heat resistance (up to 650 ° C). They are suitable for making tools operating at cutting speeds up to 60 m/min.

Drills, taps, cutters, countersinks, reamers, dies, etc. are made from high-speed steel of normal productivity R9, R18, and tools for processing high-strength and difficult-to-machine materials are made from high-performance steels R18F2, R18F5, R10K5F5 or R9F5, since these types of steel have increased wear resistance and allow you to work at speeds up to 100 m/min.

In view of the scarcity of tungsten, as a rule, only the cutting part is made of the tool material (plates welded to the holders), and the body part is made of ordinary structural steel. After heat treatment, the hardness of high speed steel reaches HRC 64 or more.

4. Metal-ceramic hard alloys

These materials are alloys of refractory metal carbides with pure metallic cobalt acting as a binder (TiC, TaC, WC).

Hard alloys are obtained by pressing followed by sintering the molded material. They are used in the form of plates obtained by sintering at 1500 o -1900 o. This material has a heat resistance of 800 o -1000 o, which allows processing at a speed of 800 m/min. In industry, multifaceted plates are used (3, 4, 6). The disadvantage is that the material does not withstand impact loads well due to brittleness (the more cobalt in the composition, the higher the ductility).

All metal-ceramic alloys are divided into three groups:

Single carbide. Tungsten-cobalt hard alloys VK2, VK6, VK8, where the numbers after the letters indicate the percentage of cobalt. Increasing the percentage of cobalt increases the toughness. Alloys of this group are the most durable. They are used for processing cast iron, non-ferrous metals and their alloys, non-metallic materials. Heat resistance 250-1000 o C.

· Two-carbide. In these alloys, in addition to the components of alloys of the VK groups, it includes titanium carbide T5K10, T15K6, where 6% cobalt, 15% titanium carbide, and the rest is tungsten carbide. It is used in the processing of carbon and alloy steels. Limit heat resistance 1050 o C.

· Three-carbide. Additionally introduced tantalum carbide in addition to those listed above. TT17K6, TT17K12, where 17 is the total content of titanium and tantalum carbides, 12 is the content of cobalt, i.e. 71-tungsten carbide. These alloys have high strength, are used in the processing of heat-resistant steels and titanium alloys.

Group R- (blue)

Group P alloys are needed for processing materials that give drain chips (steel)

Group M - (yellow)

When machining stainless, heat-resistant steels and titanium alloys

M40-TT7K12, VK10-OM

M - small, OM - very small

Group K - (red)

Group K alloys are used for processing low-plastic materials, non-ferrous alloys, plastics, wood, cast iron

5. Mineral ceramics tool alloys

These alloys are prepared on the basis of aluminum oxide Al 2 O 3 with small additions of magnesium oxide, and are sintered at 1700 o. For example, TsM332 is used for semi-finishing and finishing of steel and cast iron blanks, has high wear resistance, good cutting properties, is cheaper than hard alloys, but brittle. The material has heat resistance up to 1200 o.

6. Superhard tool materials.

These are materials based on cubic boron nitride (CBN) with high hardness and heat resistance. An example is elbor-R, which is used in the finishing of cast iron and hardened steels. This achieves the roughness characteristic of grinding. The cutting part of the tool is made of single crystals with a diameter of 4 mm and a length of 6 mm.

For the manufacture of the cutting part of the tool, natural diamonds (A) and synthetic (AC) diamonds weighing from 2 to 0.85 carats * are used. Natural diamonds are used for fine turning of non-ferrous metals and alloys of plastics and other non-metallic materials. Synthetic diamonds are used in the processing of high-silicon materials, fiberglass and plastics. Diamonds have high hardness, low coefficient of friction and slight ability to stick together with chips, high wear resistance. The disadvantage is its low heat resistance and high cost.

Comparative characteristics
tool materials

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Turning tool geometry

When processing materials by cutting distinguish the following surfaces:

1- processed

2 - processed

3 - cutting surface

A common tool for processing external and internal surfaces is turning tool, it consists of a working part - I and a body - II. Working part is supplied with tool material, the body is made of structural steels. The latter is needed to mount the tool in the holder.

The working part of the cutter is formed by a number of surfaces, which, intersecting, form the cutting edge and the top of the cutter-6. 1 - the surface on which the chips come off. Back surfaces 2 and 3 face the workpiece. Intersecting with the front surface 1, they form cutting edges: main - 4 and auxiliary - 5. Accordingly, the rear surface 2 (it faces the cutting surface) is the main one, and 3 is the auxiliary one (directed towards the machined surface). The tip of the cutter is the point of intersection of the cutting edges.

An important role in the physical processes occurring in the cutting processes is played by cutter angles(cutting angles)

a - Clearance angle reduces friction between the back surface of the tool and working surface, an increase in the angle leads to a decrease in strength

a 1 - the presence of this angle reduces friction

g - the rake angle can be both positive and negative or zero, with a decrease in the angle, the deformation of the cut layer decreases, since the tool cuts into the material more easily, cutting forces decrease, chip flow conditions improve, and with a strong increase in the angle, thermal conductivity decreases, chipping increases

b - taper angle - the angle between the front and main rear surfaces of the cutter

d - cutting angle - the angle between the front surface of the cutter and the cutting plane

j - the main angle in the plan determines the surface roughness, by this decrease the surface quality improves, but at the same time the thickness decreases and the width of the cut material layer increases, with a decrease in this angle, vibration may occur

j 1 - auxiliary angle in the plan, with a decrease in the angle, strength increases

e - angle at the top of the cutter angle between the projections of the cutting edges on the main plane = 180°- (j+j1)

l - the angle of inclination of the cutting edge is positive when the top of the cutter is the highest point, and negative when the top of the cutter is the lowest point, affects the direction of chip flow

The angle values ​​change due to the error of the cutter.

The rational area of ​​application of a particular tool material is determined by the totality of its operational and technological properties (which, in turn, depend on the physical, mechanical and chemical properties), as well as economic factors.

Tool materials work in difficult conditions– at high loads and temperatures. Therefore, all properties of tool materials can be divided into mechanical and thermal.

The most important operational properties of tool materials include: hardness, strength, wear resistance, heat resistance, thermal conductivity.

HardnessH and contact surfaces of the tool must be higher than the hardness H m of processed material. This is one of the main requirements for the tool material. But with increasing hardness of the tool material, as a rule, its resistance to brittle fracture decreases. Therefore, for each pair of processed and tool materials, there is an optimal value of the ratio H and / H m, at which the wear rate of the tool material will be minimal.

From point of view strength tool, it is important that the tool material combines high hardness at elevated temperatures of the cutting zone with good resistance to compression and bending, and also has high values ​​of endurance limit and impact strength.

wear resistance is measured by the ratio of the work expended on the removal of a certain mass of material to the value of this mass. Wear observed in cutting as a total loss of tool material mass is caused by various mechanisms: adhesion-fatigue, abrasive, chemical-abrasive, diffusion, etc. The wear resistance of the tool material during adhesive wear depends on the microstrength of the surface layers and the intensity of adhesion with the material being processed. With brittle adhesive wear, the wear resistance of the tool material is correlated with its endurance limit and strength, with plastic wear, with the yield strength and hardness. As a measure of wear resistance of a tool material during abrasive wear, its hardness is approximately taken. Diffusion wear of the cutting tool occurs due to the mutual dissolution of the components of the cutting and processed materials, followed by the destruction of the surface layers of the cutting material, softened due to diffusion processes. A characteristic of resistance to diffusion wear is the degree of inertness of tool materials in relation to the processed ones.

The hardness of the contact surfaces of the tool in the cold state, i.e. measured at room temperature does not fully characterize its cutting ability. To characterize the cutting properties of tool materials at elevated temperatures, such concepts as "hot" hardness, red hardness and heat resistance are used.

Under red hardness is understood as the temperature that causes a decrease in the hardness of the tool material not below the specified value. According to GOST 19265-73, the red hardness of high-speed steel of normal productivity should be 620°C, and of high-performance steel - 640°C. Red hardness is determined by measuring the hardness of samples at room temperature after heating to temperatures of 620°-640°C with exposure for 4 hours and subsequent cooling. For the control rate of softening of steel after the specified heating, the hardness HRC 58 was taken.

Under heat resistance tool material is understood as the ability of the material to maintain, when heated, hardness sufficient for the cutting process. Heat resistance is characterized by the so-called critical temperature. The critical temperature is the temperature established during the cutting process at which the tool material does not yet lose its cutting properties, and the tool from which it is made is able to cut.

The dependence of the tool performance on the temperature conditions of its operation is also expressed by such a characteristic of the tool material as thermal shock resistance. This characteristic determines the maximum temperature difference at which the material retains its integrity and reflects the possibility of brittle fracture of the tool as a result of thermal stresses. Knowledge of thermal shock resistance is especially important when using relatively brittle tool materials in interrupted cut conditions. The magnitude of thermal stresses depends on thermal conductivity, coefficient of linear expansion, modulus of elasticity, Poisson's ratio and other properties of the tool material.

Thermal conductivity- one of the most important physical properties of tool materials. The lower the thermal conductivity, the higher the temperature of the contact surfaces of the tool and, consequently, the lower the permissible cutting speeds.

Among the technological properties of tool materials, the most importance has them machinability in hot (forging, casting, stamping, welding, etc.) and cold (cutting, grinding) states. For tool materials subjected to heat treatment, the conditions of their heat treatment are of no less importance: the range of hardening temperatures, the amount of residual austenite, the ability of residual austenite to transform, deformation during heat treatment, sensitivity to overheating and decarburization, etc. Machinability of tool materials by cutting depends on many factors, the main of which are: chemical composition, hardness, mechanical properties (strength, toughness, plasticity), microstructure and grain size, thermal conductivity. Machinability should not be considered in terms of the possibility of using high cutting speeds in tool making, but also in terms of the quality of the resulting surfaces. Tool material, during the processing of which scuffs, high roughness, burns and other defects are obtained, is difficult to use for the manufacture of cutting tools.

Price tool material, refers to economic factors. Tool material should be as cheap as possible. But this requirement is conditional, since more expensive material can provide cheaper processing. In addition, the ratio between the cost of individual materials is constantly changing. It is important that instrumental material is not in short supply.

It is impossible to create an ideal tool material that is equally suitable for the whole variety of machining conditions. Therefore, a large range of tool materials is used in industry, united in the following main groups: carbon and alloy steels; high speed steels; hard alloys; cutting ceramics; superhard materials; coated tool.

The main requirements for tool materials are as follows:

The tool material must have a high hardness in the state of delivery or achieved as a result of its heat treatment - not less than 63 ... 66 HRC according to Rockwell.

It is necessary that at significant cutting temperatures the hardness of the tool surfaces does not decrease significantly. The ability of a material to maintain high hardness at elevated temperatures and its original hardness after cooling is called heat resistance. The tool material must have high heat resistance.

Along with heat resistance, the tool material must have high wear resistance at elevated temperatures, i.e. have good resistance to abrasion of the processed material.

An important requirement is a sufficiently high strength of the tool material. If the high hardness of the material of the working part of the tool is accompanied by significant brittleness, this leads to tool breakage and chipping of the cutting edges.

The tool material must have technological properties that provide optimal conditions for the manufacture of tools from it. For tool steels, this is good machinability by cutting and pressure; favorable features of heat treatment; good sandability after heat treatment. For hard alloys, good grindability is of particular importance, as well as the absence of cracks and other defects that occur in the hard alloy after soldering the plates, during grinding and tool sharpening.

16 Types of tool materials and areas of their application.

Previously, all materials began to be used carbon tool steels grades U7, U7A ... U13, U 13A. In addition to iron, they contain 0.2 ... 0.4% manganese, have sufficient hardness at room temperature, but their heat resistance is low, since at relatively low temperatures (200 ... 250С) their hardness decreases sharply.

Alloy tool steels in their chemical composition, they differ from carbon ones by an increased content of silicon or manganese, or by the presence of one or more alloying elements: chromium (increases the hardness, strength, corrosion resistance of the material, reduces its ductility); nickel (increases strength, ductility, impact strength, hardenability of the material); tungsten (increases the hardness and heat resistance of the material); vanadium (increases the hardness and strength of the material, promotes the formation of a fine-grained structure); cobalt (increases the impact strength and heat resistance of the material); molybdenum (increases the elasticity, strength, heat resistance of the material). For cutting tools, low-alloy steel grades 9ХФ, 11ХФ, 13Х, V2F, KhV4, KhVSG, KhVG, 9ХС, etc. are used. These steels have higher technological properties - better hardenability and hardenability, less tendency to warp, but their heat resistance is almost equal to that of carbon steels 350 ... 400С and therefore they are used for the manufacture of hand tools (reamers) or tools intended for processing on machines with low cutting speeds (small drills, reamers).

High-speed tool steels. From the group of high-alloy steels for the manufacture of cutting tools, high-speed steels with a high content of tungsten, molybdenum, cobalt, and vanadium are used. Modern high-speed steels can be divided into three groups.

To steels of normal heat resistance include tungsten R18, R12, R9 and tungsten-molybdenum R6M5, R6M3, R8M3. These steels have hardness in the hardened state of 63…66HRC, flexural strength of 2900…3400 MPa, impact strength of 2.7…4.8 J/m 2 and heat resistance of 600…650С. They are used in the processing of structural steels, cast irons, non-ferrous metals, plastics. Sometimes high-speed steels are used, additionally alloyed with nitrogen (P6AM5, P18A, etc.), which are modifications of conventional high-speed steels. Alloying with nitrogen increases the cutting properties of the tool by 20...30%, hardness - by 1 - 2 HRC units.

Steels of increased heat resistance characterized by an increased carbon content - 10P8M3, 10P6M5; vanadium - R12F3, R2M3F8; R9F5; cobalt - R18F2K5, R6M5K5, R9K5, R9K10, R9M4K8F, 10R6M5F2K8, etc.

The hardness of steels in the hardened state reaches 66…70HRC, they have higher heat resistance (up to 620…670С). This makes it possible to use them for processing heat-resistant and stainless steels and alloys, as well as structural steels of increased strength and hardened. The service life of tools made of such steels is 3–5 times higher than that of steels R18, R6M5.

Steels of high heat resistance characterized by a low carbon content, but a very large number of alloying elements - V11M7K23, V14M7K25, 3V20K20Kh4F. They have a hardness of 69…70HRC, and a heat resistance of 700…720С. The most rational area of ​​their use is the cutting of hard-to-cut materials and titanium alloys. In the latter case, the tool life is 30–80 times higher than that of R18 steel, and 8–15 times higher than that of VK8 hard alloy. When cutting structural steels and cast irons, the tool life increases less significantly (3-8 times).

hard alloys. These alloys are obtained by powder metallurgy methods in the form of plates or crowns. The main components of such alloys are tungsten carbides WC, titanium TiC, tantalum TaC and niobium NbC, the smallest particles of which are connected by relatively soft and less refractory cobalt or nickel mixed with molybdenum.

Hard alloys have high hardness – 88…92 HRA(72…76HRC) and heat resistance up to 850…1000С. This allows you to work with cutting speeds 3-4 times higher than with high-speed steel tools.

Currently used hard alloys are divided into:

for tungsten alloys VK groups: VK3, VK3-M, VK4, VK6, VK6-M, VK6-OM, VK8, etc. symbol the figure indicates the percentage of cobalt. For example, the designation VK8 shows that it contains 8% cobalt and 92% tungsten carbides. The letters M and OM denote the fine-grained and especially fine-grained structure;

for titanium-tungsten alloys TK groups: T5K10, T15K6, T14K8, T30K4, T60K6, etc. In the symbol, the number after the letter T indicates the percentage of titanium carbides, after the letter K - cobalt, the rest - tungsten carbides;

for titanium-tantalum-tungsten alloys TTK groups: TT7K12, TT8K6, TT20K9, etc. In the symbol, the numbers after the letter T indicate the percentage of titanium and tantalum carbides, after the letter K - cobalt, the rest - tungsten carbides;

for non-tungsten hard alloys TM-1, TM-3, TN-20, KNT-16, TS20HN. Designations are conditional.

Carbide grades are available as standardized inserts that are brazed, glued or mechanically attached to structural steel toolholders. Tools are also produced, the working part of which is entirely made of hard alloy (monolithic).

Alloys of the TK group have higher heat resistance than VK alloys. They can be used at high cutting speeds, so they are widely used in steel machining.

Hard alloy tools of the VK group are used in the processing of parts made of structural steels in conditions of low rigidity of the AIDS system, with interrupted cutting, when working with impacts, as well as in the processing of brittle materials such as cast iron, which is due to the increased strength of this group of hard alloys and not high temperatures. in the cutting area. They are also used in the processing of parts made of high-strength, heat-resistant and stainless steels, titanium alloys. This is explained by the fact that the presence of titanium in most of these materials causes increased adhesion with alloys of the TK group, which also contain titanium. Alloys of the TK group have significantly worse thermal conductivity and lower strength than VK alloys.

The introduction of tantalum carbides or tantalum and niobium carbides (TT10K8-B) into the hard alloy increases its strength. However, the heat resistance temperature of these alloys is lower than that of the two carbide alloys.

Particularly fine-grained hard alloys are used for processing materials with high abrasion ability. They are used for finishing and semi-finishing of parts made of high-strength tough steels with an increased tendency to hardening.

Alloys with a low cobalt content (T30K4, VK3, VK4) are used in finishing operations, with a high cobalt content (VK8, T14K8, T5K10) are used in roughing operations.

Mineral ceramics. It is based on aluminum oxides Al 2 O 3 with a small addition (0.5 ... 1%) of magnesium oxide MgO. High hardness, heat resistance up to 1200С, chemical inertness to metals, oxidation resistance in many respects surpass the same parameters of hard alloys, but are inferior in thermal conductivity and have a lower bending strength.

High cutting properties of mineral-ceramics are manifested during high-speed machining of steels and high-strength cast irons, and fine and semi-finish turning and milling increase the productivity of machining parts up to 2 times while increasing the tool life periods up to 5 times compared to machining with hard alloy tools. Mineral ceramics is produced in the form of non-regrindable plates, which greatly facilitates the conditions for its operation.

Superhard tool materials (STM)– the most promising are synthetic superhard materials based on diamond or boron nitride.

Diamonds are characterized by high hardness and wear resistance. In terms of absolute hardness, diamond is 4-5 times harder than hard alloys and tens and hundreds of times higher than the wear resistance of other tool materials in the processing of non-ferrous alloys and plastics. Due to their high thermal conductivity, diamonds better remove heat from the cutting zone, however, due to their brittleness, their area of ​​application is very limited. A significant drawback of diamond is that at elevated temperatures it enters into a chemical reaction with iron and loses its efficiency.

Therefore, new superhard materials were created that are chemically inert to diamond. The technology for obtaining them is close to the technology for obtaining diamonds, but not graphite, but boron nitride was used as the starting material.