For the manufacture of machining tools, four groups are mainly used tool materials(tool steels, hard alloys, superhard materials, cutting ceramics), each of which is divided into several subgroups (Fig. 1). None of these tool materials are universal and occupy their own niche in terms of toughness, strength, wear resistance and hardness.

Figure 1 - Classification of tool materials

The table shows data on the prevalence in Russia and in the world of instrumental materials:

High-speed steels - High-alloy, high-hardness tool steels with carbide hardening and a carbon content of over 0.6%. Improving the quality of high speed steels is achieved by using powder metallurgy (PM). The characteristic properties of high-speed steels made by the PM method are high bending strength, 1.5-2.5 times higher resistance compared to traditional grades.

Figure 2 - Characteristics of tool materials

Hard alloys are products of powder metallurgy, consisting of grains of carbides of refractory metals (WC, TiC, TaC) held together by a viscous metal binder. Most often, cobalt is used as a binder, which has a good ability to wet tungsten carbides. In hard alloys that do not contain tungsten carbides, nickel with molybdenum additives is used as a binder.

Tungsten, titanium and tantalum carbides have high hardness and refractoriness. The more carbides in the hard alloy, the higher its hardness and heat resistance, but the lower the mechanical strength. With an increase in the cobalt content, strength increases, but hardness and heat resistance decrease.

Modern hard alloys can be classified by composition into four main groups:

§ tungsten-cobalt (VC) hard alloys WC-Co;
§ titanium-tungsten-cobalt (TC) hard alloys WC-TiC-Co;
§ titanium-tantalum-tungsten-cobalt (TTK) hard alloys WC-TiC-TaC-Co;
§ tungsten-free (BVTS) hard alloys TiC (TiN)-Ni-Mo.

In foreign literature, all hard alloys containing tungsten are called tungsten, and not containing tungsten - titanium.

Tungsten or tungsten-cobalt (VC) hard alloys (single carbide) consist of tungsten carbide WC and cobalt (bond). Alloys of this group differ in cobalt content (from 3 to 15%), tungsten carbide grain sizes and manufacturing technology. With an increase in the cobalt content, the flexural strength of the hard alloy, impact strength and plastic deformation increase, however, at the same time, the hardness and modulus of elasticity decrease.

Tungsten-cobalt hard alloys are recommended mainly for processing materials that give fracture chips during cutting: cast iron, non-ferrous metals (bronze, silumin, duralumin), fiberglass. Fine-grained and extra-fine-grained alloys of this group (having the letters M and OM in the designation, respectively) are also recommended for processing heat-resistant and corrosion-resistant steels and alloys.

A significant influence on the physical, mechanical and operational properties of hard alloys, including those based on WC-Co, is exerted by the grain size of the solid phase. In normal grain alloys the average size WC grains is 2-3 microns. With the same cobalt content, a decrease in the average grain size leads to an increase in hardness and wear resistance with a slight decrease in strength.

Titanium-tungsten or titanium-tungsten-cobalt (TC) hard alloys WC-TiC-Co (two-carbide) are designed for machining steels and non-ferrous metals (brass) that produce drain chips during cutting. Compared to hard alloys VK based on WC-Co, they have greater resistance to oxidation, hardness and heat resistance, lower values of thermal and electrical conductivity, and modulus of elasticity.

Tungsten and titanium carbides, which form the basis of hard alloys, have a high natural heat resistance. The heat resistance of alloys of the TK group is: T5K10 - 1100ºC, T14K8 and T30K4 - 1150ºC. The number after the letter K indicates the percentage of cobalt, the number after the letter T - the content of TiC, the rest - WC. An increase in the content of tungsten and titanium carbides in a hard alloy with a corresponding decrease in the cobalt content leads to an increase in the heat resistance of hard alloys.

Alloys T30K4 and T15K6 are used for finishing and semi-finishing of steels with high cutting speeds and low tool loads, and alloys T5K10 and T5K12 are designed to work under severe conditions of shock loads with a reduced cutting speed.

Titanium-tantalum-tungsten or titanium-tantalum-tungsten-cobalt (TTK) hard alloys WC-TiC-TaC-Co (three-carbide) are characterized by increased strength and high hardness (including at temperatures of 600-800C). In the designations of alloys of this group, the numbers behind the letters TT mean the total content of titanium and tantalum carbides, the rest is WC.

Alloys of the TTK group are universal in terms of applicability and can be used both in the processing of steel and in the processing of cast iron. The main applications for tricarbide grades are cutting with very large shear sections in turning and planing conditions, as well as machining with heavy impacts. In these cases, the increased strength due to the presence of tantalum carbides compensates for their reduced heat resistance.

The above designations of grades of hard alloys manufactured in Russia reflect the chemical composition of these alloys. Foreign firms, as a rule, assign designations to their hard alloys that contain information about the areas of application of a particular grade.

Designations of tungsten hard alloys:

The International Organization for Standards ISO (ISO) has proposed a classification system for hard alloys, according to which all hard alloys are divided into applicability groups depending on the materials for which they are intended. This system distinguishes: a group of hard alloys P - for processing materials that give a drain chip; group of alloys K - for processing materials that give elemental chips and an intermediate group of alloys - M.

The larger the application subgroup index, the lower the wear resistance of the carbide and the allowable cutting speed, but the higher the strength (toughness), allowable feed and depth of cut. Thus, small indexes correspond to finishing operations, when high wear resistance and low strength are required from hard alloys, and large indexes correspond to roughing operations, when the hard alloy must have high strength.

Such a system, despite all its conventionality, played a positive role, since tool manufacturers, along with the brand of hard alloy, can conditionally indicate the area of its application, and consumers can choose the grade of hard alloy that most closely matches the working conditions.

In recent years, a promising direction is the creation and use of tungsten-free hard alloys (BVTS). Intensive research in this direction is carried out all over the world. The most developed production of tungsten-free hard alloys is in Japan (about 40% of the total output of hard alloys), in the USA, and in European countries.

Tungsten-free hard alloys, like tungsten-containing alloys, are products of powder metallurgy, however, titanium carbide and carbonitride, which have high hardness, wear and scale resistance, are used as a hard wear-resistant phase. Nickel is used as a cementing metal, and to improve the wetting of the carbide phase during sintering with a molten binder and, at the same time, to reduce the brittleness of BVTS, molybdenum and niobium are introduced into their composition.

In Russia, the most promising in terms of practical application tungsten-free alloys TN20, KNT16 and LCK20 proved themselves. An alloy of the TV4 brand based on titanium carbonitride contains 8-9% tungsten in the molybdenum-nickel bond to increase its strength and, in fact, is low-tungsten. A new group alloys TsTU and NTN30 has an increased operational reliability and an extended range of applications due to alloying with tungsten and titanium and niobium carbides, respectively.

These alloys are designed to replace tungsten-containing hard alloys of the TK group in the operations of turning and milling steels (applications P20-P30). However, in general, despite the savings in expensive tungsten, BVTS can serve as an equivalent substitute for tungsten hard alloys only under strictly defined processing conditions, and significant instability of properties and low cyclic strength make it impossible to recommend them as tool materials for automated production.

Cutting ceramics (RC) are characterized by high hardness and compressive strength, retain their properties at high temperatures, increased wear resistance and oxidation resistance, but significantly lower bending strength compared to hard alloys.

Cutting ceramic materials can be divided into four groups: 1) oxide (white ceramic) based on Al2O3,

2) oxycarbide (black ceramics) based on Al2O3-TiC composition,
3) oxide-nitride (cortinite) based on Al2O3-TiN,
4) nitride ceramics based on Si3N4.

Each of these groups has its own characteristics, both in manufacturing technology and in the field of application, primarily due to the composition and structure of the material. Reducing the grain size and porosity of mineral ceramics leads to an increase in wear resistance, strength and hardness of the material.

Domestic brands of oxide RK are TsM-332, VO-13, VO-18, VSh-75. Unlike high-speed steels and hard alloys, the RK marking does not reflect its composition. According to industrial practice oxide ceramics are preferred when turning workpieces from non-hardened structural steels and ferritic ductile irons (HB< 230) при скоростях резания свыше 250 м/мин.

The hardness of the RK of various grades is HRA 93-96, the strength is 400-950 MPa. Such a wide range of basic properties is determined by the different content of carbides and nitrides, as well as the grain size.

Comparative characteristics of the properties of carbides showed that the most promising of them is titanium carbide, which has high hardness, wear resistance, sufficient thermal conductivity and elastic properties, and is widely used as the basis of tool materials. In addition, it is not deficient and is easily obtained by reducing the oxide with soot.

Based on the above, titanium carbide was chosen as a hardening additive for alumina. The study of its effect on the properties of the oxide-carbide composition made it possible to select the composition and develop the technology of the VOK-71 alloy. The composition of VOK-71 consists of an Al2O3 base with the addition of 20% TiC. In terms of hardness, it is not inferior to the VOK-63 alloy, and surpasses it in strength. When cutting cast iron and steel of different hardness, mixed ceramics VOK-71 showed an advantage over other alloys.

In parallel with the improvement of oxide-carbide ceramic materials, new grades of cutting ceramics based on silicon nitride were developed. Ceramic material ONT-20 (cortinite) was developed on the basis of oxide ceramic material VSh-75.

Cortinite is an oxide-nitride RK, which includes finely dispersed titanium nitride. Adhesive interaction of cortinite with the processed material is less intense than that of oxide-carbide ceramic materials.

The positive properties of titanium nitride made it possible to create nitride cutting ceramics. In terms of its properties, the composition based on silicon nitride is somewhat inferior to oxide-carbide ceramics, however, such a ceramic material has a high bending strength and a low coefficient of thermal expansion, which distinguishes it favorably from the previously considered types of RC.

Nitride RK has a hardness of HRC 86-95, tensile strength of 600-950 MPa, toughness and thermal conductivity are higher than other types of ceramics. The advantage of nitride RK is the fact that at a temperature of 790-900ºC its hardness is higher than the hardness of oxide-carbide and oxide RK.

The preferred area of application of nitride RK is the processing of cast irons and high-temperature alloys. For the treatment of steels, this RC is not recommended due to the high rate of diffusion wear. Cutting speeds when machining cast iron with sialon reach 1500 m/min.

Work is underway to create compositions of nitride RK with carbides. For example, the addition of 20% TiC allows a 50% increase in toughness and hardness, which in turn makes it possible to use higher feed rates and cutting speeds (up to 1800 m/min). Such compositions are recommended primarily for the processing of nickel alloys.

The reasons hindering the widespread use of ceramics in metalworking are: low strength, high brittleness, significant sensitivity to local stresses and structural defects. Therefore, the main problem in the creation of new ceramic materials is the increase in strength.

In recent years great attention specialists in the field of RK is given to the development of reinforced ceramics. As a reinforcing element for RC, whiskers of silicon carbide SiC (having a strength of up to 4000 MPa) with a length of 20–30 μm and a diameter of up to 1 μm are most often used. It is noted that such reinforcement makes it possible to increase the viscosity of the oxide RC by 1.5 times without a significant decrease in hardness.

Sufficiently long crystals (2 or more times larger than the grain size of the matrix) serve as bridges between the grains, increasing their stability under load. In addition, the difference between the coefficients of thermal expansion of the SiC crystals and the base creates favorable compressive stresses during heating, which compensate for the tensile stresses that arise in the SMP during the cutting process.

Reinforced RK can be used for interrupted turning and milling. Because reinforced ceramic cutting tools are expensive, their use is only cost effective in certain applications, such as high temperature nickel alloys and hardened steels and cast irons.

Superhard tool materials (STMs) are tool materials having a Vickers hardness at room temperature in excess of 35 GPa. Superhard materials (SHM) used to equip metal cutting tools are divided into two main groups:

§ STM based on carbon - natural and artificial (polycrystalline) diamonds;
§ STM based on boron nitride (composites).

These two groups of STMs have different areas of application, which is due to the difference in their physical and mechanical properties and chemical composition.

Natural diamonds have a number of important properties required for tool materials. The hardness of natural diamonds is higher than the hardness of any natural or synthetic material. They have a low coefficient of friction, high thermal conductivity. When sharpening diamond tools, the radius of rounding of the cutting edge is provided within fractions of a micrometer, so it is possible to obtain an almost perfectly sharp and straight cutting edge, which is especially important for precision machining.

The disadvantages of natural diamonds are: anisotropy of properties, low strength, relatively low (700-750ºC) heat resistance and reactivity to iron-based alloys at elevated temperatures, as well as high cost.

These properties of natural diamonds determine the area of their effective use: precision machining details from non-ferrous metals and non-metallic materials. In particular, diamond tools with a cutting edge rounding radius of 5–6 µm are used in the processing of metal mirrors, memory disks, and optoelectronic parts with cutting depths of 12–20 µm.

The limited reserves of natural diamonds, as well as their high cost, necessitated the development of synthetic diamond technology. The conditions for obtaining synthetic diamonds consist in exposing a diamond-forming material containing carbon (graphite, soot, charcoal). The impact occurs at a pressure of 60,000 atmospheres at a temperature of 2000-3000ºC, which ensures the mobility of carbon atoms and the possibility of rearranging the structure of graphite into the structure of diamond.

Synthetic diamonds for cutting tools usually have a polycrystalline structure. Examples of domestic polycrystalline diamonds (PCD) are ASPK (carbonado) and ASB (ballas). The microhardness of polycrystalline diamonds is on average the same as that of natural single crystals (56–102 GPa), but the range of its variation is wider for PCD. The density of synthetic ballas (ASB) and carbonado (ASPC) is higher than the density of natural diamond single crystals, which is explained by the presence of a certain amount of metallic inclusions.

Synthetic and natural diamonds cannot be opposed to each other, they complement each other and each of them has its own optimal areas of application. But both synthetic and natural diamonds are not recommended for processing materials and alloys containing iron, which is explained by the high physical and chemical affinity of ferrous metals and diamond.

Natural compounds of boron nitride (BN) do not exist. Obtained by artificial modification of boron nitride according to the type of crystal lattice are divided into graphite-like, wurtzite and cubic boron nitride (CBN). Dense modifications of BN differ in manufacturing technology, structure, and physical and mechanical properties.

Examples of domestic STMs based on boron nitride are composite 01 (elbor), composite 02 (belbor), SKIM-PK, Petbor, KP3. The most famous foreign materials of this group are cyborite, Wurbon, Borazon, Amborite, Sumiboron.

BN-based STMs are mainly used for machining hardened steels (HRC>45) and cast irons (HB>230) at higher cutting speeds, and cutting with BN is in many cases more efficient than grinding.

Figure 3 - STM classification

Thus, STMs are represented by two directions: based on carbon and based on boron nitride. The hardness of polycrystalline diamonds is higher than the hardness of composites, and the heat resistance is 1.5-3 times lower. Composites are practically inert to iron-based alloys, and diamonds exhibit significant activity towards them at high temperatures and contact pressures that occur in the cutting zone. Therefore, cutting tools made of composites are mainly used in the processing of steels and cast irons, while diamond tools are used in the processing of non-ferrous metals and alloys, as well as non-metallic materials.

The possibility of introducing superhard materials is currently constrained by the state of the equipment. Only about 50% of existing machines can provide the required level of cutting speeds, about 25% of machines need modernization and about 25% are unsuitable for using tools equipped with STM.

On the other hand, the possibility of implementing high cutting speeds that are optimal for STM on new equipment that has the necessary characteristics in terms of power, rigidity, and vibration resistance provides a significant increase in metalworking productivity.

Abrasive materials are grains of abrasive material with sharp edges that serve as cutting elements of grinding tools. They are divided into natural and artificial. Natural abrasive materials include minerals such as quartz, emery, corundum, etc. In industry, the most common are artificial abrasive materials: 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, which are the most promising, as they have maximum hardness (diamond) and heat resistance (CBN).

Innovative direction

Nanotechnology in the production of cutting tools is promising. According to expert forecasts, the share of nanotechnologies in the Russian market for monotools is now 63%, and for composite tools 6%.

Promising nanotechnologies in the production of machining tools.

The wear of a metal-cutting tool increases the dimensional error, affects the quality of the surface being machined, increases the cutting forces and leads to distortion of the surface layer of the part. The wear and technological period of tool life can be reduced through the use of advanced materials and prefabricated tools equipped with replaceable multi-faceted inserts.

The cutting process is accompanied by high pressure on the cutting tool, friction and heat generation. Such operating conditions put forward a number of requirements that must be met by materials intended for the manufacture of cutting tools.

Tool materials must have a high hardness, exceeding the hardness of the material being machined. The high hardness of the material of the cutting part can be provided by the physical and mechanical properties of the material (diamonds, silicon carbides, tungsten carbides, etc.) or

its heat treatment (quenching and tempering).

During the cutting process, the cut layer presses on the front surface of the tool, creating a normal stress within the contact area. When cutting structural materials with established cutting conditions, normal contact stresses can reach significant values. The cutting tool must withstand such pressures without brittle fracture and plastic deformation. Since the cutting tool can work under conditions of variable forces, for example, due to an unevenly removed layer of workpiece metal, it is important that the tool material combines high hardness with resistance to compression and bending, has a high endurance limit and impact strength. Thus, the tool material must be characterized by high mechanical strength.

When cutting from the side of the workpiece, a powerful heat flux acts on the tool, as a result of which a high temperature is established on the front surface of the tool. In this case, the cutting elements of the tool lose their hardness and wear out due to intense heating. Therefore, the most important requirement for the tool material is its high heat resistance - the ability to maintain the hardness required for the cutting process when heated.

The movement of chips along the front and rear cutting surfaces of the tool at high contact stresses and temperatures leads to wear of the working surfaces. Thus, high wear resistance is the most important requirement for the characteristics of the tool material. Wear resistance is the ability of a tool material to resist the removal of its particles from the contact surfaces of the tool during cutting. It depends on the hardness, strength and heat resistance of the tool material.

The tool material must have a high thermal conductivity. The higher it is, the less the risk of grinding burns and cracks.

In industry, a large number of tools are used, which requires an appropriate consumption of tool material. The tool material should be as cheap as possible, not contain scarce elements, which will not increase the cost of the tool and, accordingly, the cost of manufacturing parts.

In accordance with the chemical composition and physical and mechanical properties, tool materials are divided into:

carbon tool steels;

alloyed tool steels;

high-speed steels and alloys (high-alloyed);

hard alloys;

mineral ceramics;

abrasive materials;

diamond materials.

The most common carbon tool materials are grades: U9A, U10A, U12A, U13A.

The marking of carbon tool steels is deciphered as follows: the letter "U" means that the steel is carbon; the figure indicates the carbon content in it in tenths of a percent; the letter "A" indicates that the steel is high quality.

Due to the absence of alloying chemical elements, carbon steels are well ground and are a cheap tool material. At the same time, a tool made of carbon steel wears out relatively quickly and loses its hardness obtained during hardening.

These steels are used to make small-sized tools for working on soft materials at low cutting speeds. From steel grades U7A, U7, U8A, U8, U8GA, U9A and U9, various locksmith and blacksmith tools, tools for working wood, leather, etc. are produced. Holders and tool bodies equipped with hard alloy plates are made from the same steel grades.

Alloy tool steels are obtained by adding to carbon steels a large number alloying elements: chromium (X), tungsten (B), vanadium (F), silicon (C), manganese (G). The greatest application in the manufacture of tools found steel grades HV5, HVG, 9XC.

Steel ХВ5 after heat treatment acquires a very high hardness ( HRC 67 ... 67), is poorly calcined, but is not inferior in strength to U12A steel, but due to its high hardness it has a high resistance to small plastic deformations. The tools made from it are characterized by high dimensional stability of the blades. This steel is used for the manufacture of tools operating at low cutting speeds.

CVG steel after quenching and tempering acquires hardness HRC 63 ... 65 and a sufficiently high viscosity, it is characterized by small volumetric changes during hardening, it is well annealed, but has a reduced resistance to small plastic deformations. The tool made of this steel is little deformed and lends itself well to editing.

Steel 9XC after heat treatment acquires hardness HRC 63…64. It has good hardenability. The tool from this steel is slightly deformed. Steel is also insensitive to overheating. Steel 9XC is particularly suitable for the manufacture of tools with thin cutting elements.

High-alloy tool (high-speed) steels and alloys are obtained by adding a large number of alloying elements to carbon steel: tungsten, vanadium, molybdenum, chromium. By introducing tungsten, vanadium, molybdenum and chromium into steel in significant quantities, complex carbides are obtained that bind almost all of the carbon, which ensures an increase in the heat resistance of high-speed steel.

Unlike carbon and alloyed tool steels, high-speed steels have higher hardness, strength, heat and wear resistance, resistance to small plastic deformations, and good hardenability. Due to the high heat resistance of high-speed steels, tools made from these steels operate at cutting speeds 2.5 ... 3 times higher than those that, with equal resistance, allow carbon tools. According to the level of heat resistance, high-speed steels are divided into:

steels of normal heat resistance (R18, R9, R12, R6M3 and R6M5);

steels of increased heat resistance alloyed with vanadium (vanadium steels R18F2, R14F4, R9F5) and cobalt (cobalt steels R9K5, R9K10);

high-alloy steels and alloys of high heat resistance (high-speed steels of increased strength) - carbon-free alloys (R18M3K25, R18M7K25 and R10M5K25), differing in the content of tungsten and molybdenum.

In addition to traditional high speed steels obtained by smelting, in Lately the production of powder high-speed steels with higher cutting properties due to a special fine-grained structure has been mastered. Such steels make it possible to obtain blades with a very small initial radius of rounding of the cutting edge.

The widespread use of high-speed steel in the manufacture of a variety of tools is due to its good cutting and technological properties. High-speed steels are used to manufacture various cutting tools, including milling cutters for processing wood and composite materials. Due to the high cost of high-speed steels, they are mainly used in the manufacture of prefabricated tools in the form of cutting plates.

hard alloys. In addition to prefabricated tools, with inserts made of high-speed steels, designs of cutters equipped with hard alloys are widely used. Unlike carbon, alloy and high-speed steels produced by smelting in electric furnaces followed by rolling, hard alloys are produced by the cermet method of powder metallurgy (sintering). The starting materials for the manufacture of hard alloys are powders of carbides of refractory metals: tungsten, titanium, tantalum and cobalt that does not form carbides. Powders are mixed in certain proportions, pressed in molds and sintered at a temperature of 1500 ... 2000 0 C. During sintering, hard alloys acquire high hardness and do not need additional heat treatment.

Tungsten, titanium and tantalum carbides have high refractoriness and hardness. They form the cutting base of the alloy, and cobalt, in comparison with tungsten, titanium and tantalum carbides, is much softer and stronger, and therefore in the alloy it is a binder that cements the cutting base. An increase in the amount of tungsten, titanium, tantalum carbides leads to an increase in the hardness and heat resistance of the alloy and reduces its mechanical strength. With an increase in the cobalt content, the hardness and heat resistance of the alloy decrease, but its strength increases.

The industry produces four groups of hard alloys:

tungsten single carbide (VC), sintered from tungsten carbide and cobalt: VK2, VK3M, VK4, VK4V, VK6M, VK6, VK6V, VK8, VK8V;

tungsten two-carbide (titanium-tungsten TC), sintered from tungsten carbide, titanium carbide and cobalt: T30K4, T5K6, T14K8, T5K10, T5K12V;

tungsten three-carbide (titanotantalum-tungsten TTK), sintered from titanium carbide, tantalum carbide and tungsten carbide and cobalt: TT7K12;

tungsten-free (TNT - CNT), sintered from titanium carbide (TNT), titanium nitride (CNT), nickel and molybdenum.

Various physico-mechanical and cutting properties of tools are determined by the chemical composition of grades of hard alloys. The main properties of hard alloys are presented in table. 1. 2 .

Alloys of the VK group are used for processing brittle materials.

Table 1.2

Basic properties of hard alloys

Properties	VC	TC	TTC	TNT - KNT
Density, kg / m 3	12900… 15300	10100… 13600	12000… 13800	5500… 9500
σ bend, MPa	1180…2450	1170…1770	12500…17000	400…1750
Microhardness, MPa	8,8…16,2	11,3…21,6	13,9…14,4	~ 18
Operating temperature, 0 С	~ 500	~ 900	~ 1000	~ 800

The alloys of the TK group have high wear and heat resistance, but are more brittle than the alloys of the VK group. The main properties and chemical composition of some alloys of the VK group are presented in Table. 1. 3 .

Alloys of the TTK group are universal in terms of applicability and are suitable for processing many structural materials. The alloys are characterized by lower brittleness, higher retention strength of the carbide phase, better resistance to high-temperature fluidity, and higher tensile strength under cyclic loading than TK and VK alloys. Therefore, tools equipped with TTC inserts are especially effective in interrupted cutting processes. In these cases, the increased strength of TTK alloys compensates for their reduced heat resistance. The main properties and chemical composition of some alloys of the TK and TTK groups are presented in Table. 1. 4 .

Table 1.3

Basic properties and chemical composition of some alloys of the VK group

Alloy grade	WC, %	TiC, %	TaC, %	Co, %	σ bend, MPa	HRA		σ cj, MPa	HB	Properties
VK2					1100		15,2	416		High wear.
VK3					1100		16,2
VK3M
VK6					1450		14,8	460		Higher than VK2, VK3M
VK6M					1500		14,8			The grains are large, wear. below
VK8
VK10					1700		14,8		366
VK25					2000	83,5	13,0		370

The most important rules when choosing a carbide grade within each group are:

under severe working conditions of the tool in terms of force, the hard alloy must contain a sufficiently large percentage of cobalt;

the easier the power mode of operation, the more titanium and tungsten carbides should be contained in the alloys.

For the manufacture of cutting tools, hard alloys are supplied in the form of plates of a certain shape and size.

Hard alloys in the form of plates are connected to the fastener by soldering or using special high-temperature adhesives. Multifaceted carbide plates are fixed with tacks, screws, wedges, etc.

Table 1.4

Basic properties and chemical composition of some alloys of the TK and TTK groups

Alloy grade	WC, %	TiC, %	TaC, %	Co, %	σ bend, MPa	HRA		σ cj, MPa	Properties
T30K4					900		9,7		High wear. resistance impact loads
T15K6					1159		11,3	3900	High wear.
Т5К10					1385		13,0	4000	Resist. higher than T14K8
TT7K12					1600		13,0		Zoom V R 2 times (compared to BRS
TT10K8B					1400		13,6		Moderate wear., high ekspl. strength

Small-sized carbide tools are made in the form of carbide rods and crowns soldered to the shanks or entirely from carbide.

In addition to tungsten hard alloys, there are also alloys that do not contain tungsten carbide and are called tungsten-free hard alloys.

The reason for the complete or partial replacement of tungsten carbide with other hard materials was the shortage of tungsten as a raw material for the production of cermet hard alloys.

Complete replacement of tungsten carbide can be carried out in three ways:

The use of other hard materials, such as nitrides, borides, silicides, oxides or carbides of non-metals (boron and silicon carbides);

Replacement of tungsten carbide with other refractory metal carbides (carbides of niobium, zirconium, hafnium, vanadium, etc.) or their binary or ternary hard alloys;

Simple exclusion of tungsten carbide from the carbide composition.

Tungsten-free hard alloys, compared to tungsten, have lower bending strength, but have higher hardness and low adhesion to steels. Tools made of these alloys work on steels with virtually no build-up formation, which determines the scope of their application (finishing and semi-finishing turning and milling of low-alloy, carbon steels, cast iron and non-ferrous alloys). Wear resistance is 1.2 - 1.5 times higher than that of alloys of the TK group. The main physical and mechanical properties of tungsten-free hard alloys are presented in Table. 1. 7 .

Table 1.5

Physical and mechanical properties of tungsten-free hard alloys

Carbide grade	Density, g / cm 3	σ bend, MPa	σ cj, MPa	Hardness, HRA	Modulus of elasticity 10 3 MPa	Grain size, microns
TM3	5,9	1150	3600		410
TN-20	5,5	1000	3500	89,5	400	1-2
TP-50	6,2	1250		86,5
KST-16	5,8	1150	3900		440	1,2-1,8
MNT-A2	5,5	1000

The disadvantage is that tungsten-free hard alloys are difficult to solder and sharpen due to unsatisfactory thermal properties and therefore are used mainly in the form of non-regrindable plates.

The material for the manufacture of tools can also serve as mineral ceramics, which is a crystalline aluminum oxide ( Al 2O3 ). Mineral ceramics brand TsM-332 is widely used.

As a result of sintering, mineral ceramics becomes a polycrystalline body, which consists of the smallest corundum crystals and an intercrystalline layer in the form of an amorphous vitreous mass. Mineral ceramics is a cheap and accessible tool material, since it does not contain scarce and expensive elements that are the basis of tool steels and hard alloys.

In addition, mineral ceramics have high hardness and exceptionally high heat resistance. In terms of heat resistance, mineral ceramics surpasses all common tool materials, which allows mineral ceramic tools to work at cutting speeds that are much higher than those of carbide tools, and which is the main advantage of mineral ceramics.

Together with the indicated advantages of mineral ceramics, it has disadvantages that limit its use: reduced bending strength, low impact strength, and extremely low resistance to cyclic changes in thermal load. As a result, during interrupted cutting, temperature fatigue cracks appear on the contact surfaces of the tool, which are the cause of premature failure of the tool.

The low bending strength and high brittleness of mineral ceramics make it possible to use it only in tools for processing structural materials in finishing operations with continuous turning and with small sections of the cut layer in the absence of shocks and impacts.

The cutting tool is equipped with mineral-ceramic plates of certain shapes and sizes. The plates are attached to the body of the instruments by soldering, gluing and mechanically.

Increasingly, diamond and superhard materials are used in woodworking, which can be divided into three varieties:

natural and synthetic diamonds in the form of mono- and polycrystals;

cubic boron nitride, in the form of mono- and polycrystals;

synthetic polycrystalline composite materials (composites) obtained by synthesis or sintering.

Natural diamonds are a special group of materials for equipping cutting tools.

The varieties of diamond are: ballas, carbonado, board. Useful property diamonds is, first of all, their exceptionally high hardness. High thermal conductivity, much higher than thermal conductivity

The consistency of all known tool materials and the low coefficient of linear expansion of diamond make it possible to carry out precise dimensional processing with a diamond tool. The low coefficient of friction on the material being processed and the low tendency to adhesion provide low surface roughness when cutting with diamond tools.

In industry, both natural (grade A) and synthetic diamonds (grades ASO, ACP, DIA, etc.) are used. Synthetic diamonds are obtained from graphite and carbonaceous substances. Varieties of natural diamond: board and carbonado are used only in industry.

Cubic boron nitride (CBN) is a synthetic superhard material for the same purpose as diamond. It is formed as a result of the chemical combination of boron and nitrogen. The hardness of elbor is lower than that of diamond, however, cubic boron nitride surpasses diamond in heat resistance, but approximately 3 times lower in thermal conductivity. The production of large polycrystalline formations of cubic boron nitride with a diameter of 3…4 and a length of 5…6 mm, which have high strength, makes it possible to equip cutting tools with them.

Carbon and alloy tool steels. The range of tool materials is diverse. 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 made of 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.

Alloy tool steels in my own way chemical composition 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 9HF, 11HF, 13X, V2F, KhV4, KhVSG, KhVG, 9HS, 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 ° C and therefore they are used for the manufacture of hand tools (reamers) or tools intended for processing on machines with low speeds cutting (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, R6MZ, R8MZ (Table 6.1). These steels have hardness in the quenched state of 63...66 HRC e, flexural strength of 2900...3400 MPa, impact strength of 2.7...4.8 J/m 2 and heat resistance of 600...650 °C. . These steel grades are most widely used in the manufacture of cutting tools. 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 high carbon content - 10P8MZ, 10P6M5; vanadium - R12FZ, R2MZF8, R9F5; cobalt - R18F2K5, R6M5K5, R9K5, R9K10, R9M4K8F, 10R6M5F2K8, etc.

The hardness of steels in the hardened state reaches 66...70 HRC e, they have a higher heat resistance (up to 620...670 °C). This makes it possible to use their 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.

Tab. 3. The content of alloying elements in high-speed steels,%

Steels of high heat resistance characterized by a low carbon content, but a very large number of alloying elements - Bl1M7K23, V14M7K25, ZV20K20Kh4F. They have a hardness of 69...70 HRC Oe, and a heat resistance of 700....720 °C. 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 (by 3...8 times).

Due to the acute shortage of tungsten in the USSR and abroad, tungsten-free tool materials are being developed, in including high speed steels.

Such steels include low-tungsten R2M5, RZMZF4K5. R2MZF8, A11RZMZF2 and tungsten-free 11M5F (see Table 6.1). The operational properties of these steels are close to the properties of traditional high-speed steels of the corresponding groups.

A promising direction in improving the quality of high-speed steels is their production by powder metallurgy. Steels R6M5K5-P (P - powder), R9M4K8-P, R12MZFZK10-P and others have a very uniform fine-grained structure, are well ground, deform less during heat treatment, and are distinguished by the stability of operational properties. The service life of cutting tools made of such steels increases up to 1.5 times. Along with powder high-speed steels, the so-called carbide steels, containing up to 20% TiC, which, according to service characteristics, occupy an intermediate position between high-speed steels and hard alloys.

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 (Tables 6.2, 6.3).

Hard alloys have high hardness -88...92 HRA (72...76 HRC Oe) and heat resistance up to 850...1000 °C. This allows you to work with cutting speeds 3...4 times higher than with tools made of high-speed steels.

Currently used hard alloys are divided into:

1) for tungsten alloys VK groups: VKZ, VKZ-M, VK4, VK6, VK6-M, VK6-OM, VK8, etc. In the symbol, the number shows 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;

2) on titanium tungsten alloys TC groups:

T5K10, T15K6, T14K8, TZOK4, 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;

Tab. 4. Grades, chemical composition and properties of tungsten-containing hard alloys

Tab. 5. Grades, chemical composition and properties of tungsten-free hard alloys

3) on 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;

4) on tungsten-free hard alloys TM-1, TM-3, TN-20, KNT-16, TS20XN, the composition of which is given in Table. 6.3. The designations of this group of hard alloys 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).

The right choice carbide grade ensures efficient operation of cutting tools. For a particular case of processing, the alloy is selected based on the optimal combination of its heat resistance and strength. For example, alloys of the TK group have higher heat resistance than VK alloys. Tools made from these alloys can be used at high cutting speeds, so they are widely used in steel machining.

Such alloys 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. In addition, 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. Therefore, three- and four-carbide hard alloys are used to equip tools that work with impacts and contaminated skin. However, the heat resistance temperature of these alloys is lower than that of two-carbide alloys. Of the hard alloys with a significantly improved structure, it should be noted that they are especially fine-grained, used for processing materials with a high abrasion ability. OM alloys have a dense, especially fine-grained structure, and also have a small (up to 0.5 μm) grain size of tungsten carbides. The latter circumstance makes it possible to sharpen and finish a tool made from them with the smallest cutting edge radii. Tools from alloys of this group are used for finishing and semi-finishing of parts made of high-strength tough steels with an increased tendency to work hardening.

A slight addition of tantalum and cobalt carbide to the alloys of the OM group contributes to an increase in their heat resistance, which makes it possible to use these alloys in the manufacture of tools intended for roughing parts from various steels. Very effective replacement for tantalum carbides chromium carbides . This ensures the production of alloys with a fine-grained uniform structure and high wear resistance. A representative of such materials is an alloy VK10-XOM.

Alloys with a low percentage of cobalt (TZOK4, VKZ, VK4) have a lower viscosity and are used for the manufacture of tools that cut thin chips in finishing operations. On the contrary, alloys with a high content of cobalt (VK8, T14K8, T5K10) are more viscous and are used when removing large-section chips in roughing operations.

The performance of hard alloys increases significantly when wear-resistant coatings are applied to them.

Mineral ceramics. Of modern tool materials, mineral ceramics deserves attention, which does not contain expensive and scarce elements. It is based on aluminum oxides AO3 with a small addition (0.5 ... 1%) of magnesium oxide MgO. The high hardness of mineral ceramics, heat resistance up to 1200°C, chemical inertness to metals, oxidation resistance in many respects exceed the same parameters of hard alloys. However, mineral ceramics is inferior to these alloys in terms of thermal conductivity and has a lower bending strength.

Modern mineral ceramics, created in the USSR and abroad, is close in strength to the most wear-resistant hard alloys. Mineral ceramics based on aluminum oxide can be divided into three groups:

1) pure oxide ceramics (white), the basis of which is aluminum oxide with minor impurities (AlOz - up to 99.7%);

2) ceramics, which is aluminum oxide with the addition of metals (titanium, niobium, etc.);

3) oxide-carbide (black) ceramics - aluminum oxide with the addition of carbides of refractory metals (titanium, tungsten, molybdenum) to increase its strength properties and hardness.

Domestic industry currently produces oxide ceramics TsM-332, VO-13 and oxide-carbide VZ, VOK-60, VOK-63, which includes up to 40% titanium, tungsten and molybdenum carbides. Along with materials based on aluminum oxide, a material based on silicon nitride is produced - silinit-R and cortinite ONT-20 (with additions of aluminum oxides and some other substances). Physical and mechanical properties of cutting mineral ceramics are given in table. 6.4.

High cutting properties of mineral-ceramic tools 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 parts processing up to 2 times while increasing the tool life periods up to 5 times compared with machining with hard alloy tools.

Mineral ceramics is produced in the form of non-regrindable plates, which greatly facilitates the conditions for its operation.

Tab. 6. Physical and mechanical properties of cutting mineral ceramics

The main requirements for tool materials are as follows:

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

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

4. 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.

5. 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 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 plates, during grinding and tool sharpening.

TYPES OF TOOL MATERIALS AND THEIR FIELDS OF 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 ° C) 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 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 ° 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, reamers).

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…3400MPa, impact strength of 2.7…4.8 J/m 2 and heat resistance of 600…650°C. 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 a higher heat resistance (up to 620...670°C). 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°C. 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 have high hardness – 88…92 HRA (72…76 HRC) 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:

1) for tungsten alloys VK groups: VK3, VK3-M, VK4, VK6, VK6-M, VK6-OM, VK8, etc. In the symbol, the number shows 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;

2) 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;

3) 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;

4) 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. There are also tools working part which are 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.

Tools made of hard alloys 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°C, 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 in 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.

PURPOSE OF TOOL GEOMETRY AND OPTIMUM CUTTING CONDITIONS IN TURNING, DRILLING, MILLING.

Relief corner selection a. It is known that when processing steels, a larger optimal angle a corresponds to a smaller thickness of the cut layer: sin a opt \u003d 0.13 / a 0.3.

For practical purposes, when machining steels, the following clearance angles are recommended: for rough cutters with S>0.3mm/rev - a=8°; for finishing cutters with S<0,3 мм/об - a=12°; для торцовых и цилиндрических фрез - a=12…15°.

The value of the clearance angles when machining cast irons is somewhat less than when machining steels.

Choice of rake angle g. The rake angle should be the greater, the lower the hardness and strength of the material being processed and the greater its plasticity. For high-speed steel tools when machining soft steels, the angle is g=20…30°, medium-hard steels - g=12…15°, cast iron - g=5…15° and aluminum - g=30…40°. In a carbide tool, the rake angle is made smaller, and sometimes even negative, due to the fact that this tool material is less durable than high speed steel. However, a decrease in g leads to an increase in cutting forces. To reduce cutting forces in this case, a negative chamfer is sharpened on the front surface of both carbide and high-speed tools.

Choice of main angle in plan j. When processing non-rigid parts, in order to reduce the radial component P y, the main angle in the plan should be increased to j=90°. In some cases, the angle j is assigned for design reasons. The entering angle also affects the roughness of the machined surface, so when finishing it is recommended to use smaller values of j.

Choice of auxiliary angle in plan j 1. For certain types of instruments, j 1 ranges from 0 to 2…3°. For example, for drills and taps j 1 =2…3¢, and for a cutting tool j 1 =1…3°.

Selecting the angle of inclination of the main cutting edge l. Recommended angles for finishing and roughing cutters made of high-speed steel, respectively, l=0…(-4)° and l=5…+10°, for carbide cutters when working without impacts and with impacts, respectively, l=5…+10° and l =5…+20°.

Assignment of optimal cutting conditions:

1. First of all, choose instrumental material, tool design and geometrical parameters of its cutting part. The material of the cutting part is selected depending on the properties of the material being processed, the state of the surface of the workpiece, and also on the conditions of the cutting being carried out. The geometric parameters of the tool are assigned depending on the properties of the material being processed, the rigidity of the technological system, the type of processing (roughing, finishing or finishing) and other cutting conditions.

2. Appoint cutting depth subject to processing allowance. When roughing, it is desirable to assign a depth of cut that provides cutting of the allowance in one pass. The number of passes over one during roughing should be allowed in exceptional cases when removing increased allowances. Semi-finishing is often done in two passes. The first, rough, is carried out with a depth of cut t=(0.6...0.75)h, and the second, final with t=(0.3...0.25)h. Machining in two passes in this case is due to the fact that when removing a layer with a thickness of more than 2 mm in one pass, the quality of the machined surface is low, and the accuracy of its dimensions is insufficient. When finishing, depending on the accuracy and roughness of the machined surface, the cutting depth is assigned within 0.5 ... 2.0 mm per diameter, and when processing with a roughness less than Ra 1.25 - within 0.1 ... 0.4 mm.

3. Select the feed (when turning and drilling - S 0, mm / rev; when milling S z, mm / tooth). When roughing, it is set taking into account the rigidity of the technological machine system, the strength of the part, the method of its fastening (in the chuck, in centers, etc.), the strength and rigidity of the working part of the cutting tool, the strength of the machine feed mechanism, as well as the set depth of cut. When finishing, the purpose of the feed must be coordinated with the specified roughness of the machined surface and the quality of accuracy, while taking into account the possible deflection of the part under the action of cutting forces and the error in the geometric shape of the machined surface. After selecting the normative feed, check calculations are made according to the formulas: Р x = , or .

4. Determine the cutting speed. The cutting speed allowed by a cutting tool with a certain period of its resistance depends on the depth of cut and feed, the material of the cutting part of the tool and its geometric parameters, on the material being processed, the type of processing, cooling, and other and other factors.

Given the depth of cut, feed and tool life, the cutting speed can be calculated: when turning: ; when drilling: ; when milling: .

5. When roughing the selected cutting mode is checked according to the power of the machine. In this case, the ratio must be observed: N res £1.3hN st. If it turns out that the power of the electric motor of the machine on which the processing is performed is not enough, a more powerful machine must be selected. If this is not possible, the chosen values of u or S must be reduced.

6. Determine main time of each pass(formulas for its calculation for various types of processing are given in the reference literature.

GRINDING PROCESS

grinding- the process of cutting metals, carried out by grains of abrasive material. Grinding can practically process any materials, since the hardness of abrasive grains (2200 ... 3100HB) and diamond (7000HB) is very high. For comparison, we note that the hardness of hard alloy is 1300HB, cementite is 2000HB, hardened steel is 600…700HB. Abrasive grains are bound together in tools of various shapes or applied to fabric (abrasive skins). Grinding is used most often as a finishing operation and makes it possible to obtain parts of the 7th ... 9th and even 6th grades with a roughness of Ra = 0.63 ... 0.16 μm or less. In some cases, grinding is used for grinding castings and forgings, for cleaning welds, i.e. as a preparatory or roughing operation. Currently, deep-feed grinding is used to remove large allowances.

The characteristic features of the grinding process are as follows:

1) multi-pass, which contributes to the effective correction of errors in the shape and size of parts obtained after previous processing;

2) cutting is carried out by a large number of randomly arranged abrasive grains with high microhardness (22000 ... 31000 MPa). These grains, forming an intermittent cutting contour, cut through the smallest depressions, and the volume of metal cut off per unit time is much less in this case than when cutting with a metal tool. One abrasive grain cuts about 400,000 times less metal per unit time than one cutter tooth;

3) the process of cutting chips with a separate abrasive grain is carried out at high cutting speeds (30 ... 70 m / s) and in a very short period of time (within thousandths and hundred-thousandths of a second);

abrasive grains are located randomly in the body of the circle. They are polyhedrons of irregular shape and have vertices rounded with radius r (P. 301).

This rounding is small (usually r=8...20 µm), but it must always be taken into account, since in microcutting the thickness of the layers removed by individual grains is commensurate with r;

5) high cutting speeds and unfavorable geometry of the cutting grains contribute to the development of high temperatures in the cutting zone (1000 ... 1500 ° C);

6) the grinding process can be controlled only by changing the cutting conditions, since changing the geometry of the abrasive grain, which acts as a cutter or cutter tooth, is practically difficult to implement. Diamond wheels using a special manufacturing technology can have a preferential (required) orientation of diamond grains in the body of the circle, which provides more favorable cutting conditions;

7) the abrasive tool can self-sharpen during operation. This occurs when the cutting edges of the grains become blunt, which causes an increase in cutting forces and, consequently, the forces acting on the grain. As a result, blunt grains fall out, break out of the bundle or split, and new sharp grains come into play;

8) the ground surface is formed as a result of the simultaneous action of both geometric factors characteristic of the cutting process and plastic deformations accompanying this process.

With regard to the geometric scheme for the formation of a ground surface, the following must be borne in mind:

to better match the actual process of chip formation, one should consider the cutting of grains into a rough surface, and the grains themselves should be considered randomly located throughout the entire volume of the circle (P. 302).

Grinding should be considered as a spatial phenomenon, not a planar one. In the cutting zone, the elementary surface being processed during its contact with the grinding wheel comes into contact not with one row of grains, but with several;

2) the smaller the irregularities of the abrasive cutting tool, the closer it comes to a solid cutting blade and the less rough the machined surface is. The same cutting contour can be created by reducing the grit number or increasing the time of abrasive exposure, for example, by lowering the speed of rotation of the part or reducing the longitudinal feed per one revolution of the product;

3) an ordered cutting relief is achieved by diamond dressing. In the process of grinding, as individual grains are destroyed and fall out, the ordered cutting relief is disturbed;

4) abrasive grains in the cutting process can be divided into cutting (for example, grains 3, 7), scraping, if they cut to such a shallow depth that only plastic extrusion of the metal occurs without chip removal, pressing 5 and non-cutting 4. In the actual grinding process Approximately 85…90% of all grains do not cut, but in one way or another plastically deform the thinnest surface layer, i.e. stabs him.

5) the roughness is affected not only by the granularity, but also by the bond of the abrasive tool, which has a polishing effect, which is more pronounced at lower wheel rotation speeds.

CHARACTERISTICS OF ABRASIVE TOOLS AND PURPOSE OF GRINDING MODES

All abrasive materials are divided into two groups: natural and artificial. Natural materials include corundum and emery, consisting of Al 2 O 3 and impurities. Of the artificial abrasive materials, the most widely used are: electrocorundum, silicon carbide, boron carbide, synthetic diamond, cubic boron nitride (CBN), Belbor.

Under the granularity of abrasive materials understand the size of their grains. According to their size (fineness), they are divided by numbers:

1) 200, 160, 125, 100, 80, 63, 50, 40, 32, 25, 20, 16 - grinding;

2) 12, 10, 8, 6, 5, 4, 3 - grinding powders;

3) M63, M50, M40, M28, M20, M14 - micropowders;

4) M10, M7, M5 - fine micropowders.

The granularity of micropowders is determined by the grain size of the main fraction in microns. According to GOST 3647-80, the following grain fractions are distinguished: B (60 ... 55%), P (55 ... 45%), H (45 ... 40%), D (43 ... 39% of the grains of the main fraction).

The hardness of the wheels is understood as the ability of the bond to keep abrasive grains from being pulled out from the surface of the wheel under the action of external forces, or the degree of resistance of the bond to tearing out the grains of the circle from the material of the bond.

In terms of hardness, wheels on ceramic and bakelite bonds, according to GOST 18118-79, are divided into seven classes: M - soft (M1, M2, M3), M2 is harder than M1; SM - medium soft (SM1, SM2); C - medium (C1, C2); CT - medium hard (CT1, CT2, CT3); T - solid (T1, T2); VT - very hard (VT); HT - extremely hard (HT).

Wheels on a volcanic bond differ in hardness: medium soft (CM), medium (C), medium hard (ST) and hard (T).

GOST 2424-83 provides for the manufacture of grinding wheels of three accuracy classes: AA, A and B. Depending on the accuracy class of the wheels, grinding materials with the following indices should be used: C and P - for accuracy class AA; V, P and N - for accuracy class A; C, P, N and D - for accuracy class B.

The structure of the grinding wheel is understood as its internal structure, i.e., the percentage and relative arrangement of grains, bonds and pores per unit volume of the wheel: V c + V c + V p = 100%.

The basis of the system of structures is the content of abrasive grains per unit volume of the tool:

Structure number

Grain content, %

Structures 1 to 4 are closed or dense; from 5 to 8 - medium; from 9 to 12 - open.

GOST 2424-83 regulates the production of 14 profiles of grinding wheels with a diameter of 3 ... 1600 mm, a thickness of 6 ... 250 mm.

The optimal cutting mode during grinding should be considered the mode that provides high productivity, lowest cost and obtaining the required quality of the ground surface.

To define the grinding mode:

1) the characteristic of the grinding wheel is selected and its circumferential speed u k is set;

2) a transverse feed is assigned (cutting depth t) and the number of passes is determined to ensure the removal of the entire allowance. The feed varies within 0.005 ... 0.09 mm per double stroke;

3) a longitudinal feed is assigned in fractions of the circle width S pr \u003d KV, where K \u003d 0.4 ... 0.6 for rough grinding, K \u003d 0.3 ... 0.4 - for fine grinding;

4) the circumferential speed of rotation of the part u d is selected. For rough grinding, one should proceed from the established period of wheel life (T = 25 ... 60 min), for finishing - from ensuring the specified surface roughness. Usually the speed of rotation of the part is in the range of 40 ... 80m / min;

5) coolant is selected;

6) the cutting forces and power necessary to ensure the grinding process are determined. The power (kW) required to rotate the circle, N k ³P z u to /10 3 h, and to rotate the part N d ³P z u d /(60 × 10 3 h);

7) the selected grinding modes are adjusted according to the machine's passport. With a lack of power, u d or S decrease, because. they affect the cutting power N to and machine time t m;

8) the conditions of burn-free grinding are checked in terms of specific power per 1 mm of the circle width: N beats \u003d N to /B. It must be less than the allowable specific power given in the reference literature;

9) the machine time is calculated.

Similar information.

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

Tool materials work under 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 important is their 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 instrumental 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.

Marking of tool materials. Cutting tool materials

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