1 - shaped; 2 - direct pass; 3- 5 - bent walkways; b - finishing; 7 - detachable drawn; 8 - threaded; 9 - undercut; 10 - boring

Figure 3 - Types of turning tools (A)

and multifaceted non-regrind plates (b)

The cutter head includes the front surface - the surface along which the chips come off, and the rear surfaces (main and auxiliary) facing the workpiece surface to be machined. When sharpening these three surfaces, cutting edges are formed. The intersection of the front and main rear surfaces forms the main cutting edge, which performs the main cutting work, and the intersection of the front and auxiliary rear surfaces forms the auxiliary cutting edge.

The top of the cutter - the point of conjugation of the main and auxiliary cutting edges - in the plan has a radius of curvature and can be straight (cutting cutters).

When turning a workpiece, the following surfaces and planes are distinguished (Fig. 5):

1- main rear surface; 2 - 1 - cutting plane; 2 – processed

main cutting edge; 3 - top; washable surface; 3 - over-

4 - front surface; 5 - body; cutting speed; 4 – processed

6 - head: 7 - auxiliary surface; 5 - base plane

cutting edge; 8 - auxiliary Figure 5 – surfaces

flank and planes when turning

Figure 4 - Main

cutter elements

The surface to be machined from which the chips are removed;

The machined surface from which the metal layer is cut;

Cutting surface - transitional surface between machined and machined surfaces, formed directly by the main cutting edge of the cutter;

The main plane is a plane parallel to the directions of the longitudinal and transverse feeds;

Cutting plane - the plane tangent to the surface
cutting and passing through the main cutting edge of the cutter;

Main cutting plane - a plane perpendicular to the projection of the main cutting edge onto the main plane;

Auxiliary cutting plane - a plane perpendicular to the projection of the auxiliary cutting edge on the main plane.

The angles of the cutter (Fig. 6) are divided into main, auxiliary and angles in plan. The main angles are measured in the main cutting plane: this is the main clearance angle α , front angle γ , taper angle β and cutting angle δ .

In the auxiliary cutting plane, the auxiliary rear angle is measured.

Plan angles- this is the main angle in the plan, the auxiliary angle in the plan and the corner at the top in the plan ε .

Main clearance α called the angle between the main back surface and the cutting plane; serves to reduce friction between the cutting surface and the main back surface of the cutter and is selected in the range from 6 to 12 °, while the larger value of the angle is taken for soft and viscous materials, the smaller one for hard and brittle ones.

front angle γ called the angle between the front surface of the cutter and the plane drawn through the main cutting edge perpendicular to the cutting plane; serves to facilitate chip flow, reduce the work of deformation and power consumption for cutting and is selected in the range from -10 to +30 °, while negative values ​​​​are assigned for carbide cutters when machining hardened steels, and positive ones - when machining soft and viscous materials.

taper angle β called the angle between the front and back surfaces of the incisor; it is determined by the formula

β = 90° - (α+γ).

cutting angle δ called the angle between the front surface and the cutting plane; it is equal to the sum of the angles α + β .

Leading angle φ the angle between the projection of the main cutting edge onto the main plane and the feed direction is called; is determined by the design features of the part, the rigidity of the system machine tool - fixture - tool - part (AIDS) and is selected in the range from 30 to 90 °. With decreasing angle φ the quality of the machined surface improves, the tool life increases, however, with insufficient rigidity of the AIDS system, a decrease in the angle φ causes

Figure 6 - Cutter angles

vibration of the workpiece and cutter, which leads to deterioration of the surface roughness. In this case, cutters with a main angle in the plan equal to 60, 75 or 90 ° are used.

Auxiliary lead angle- the angle between the projection of the secondary cutting edge and the feed direction - for cutters of various types is selected from 5 to 45 °.

Angle at the top of the cutter in the plan ε - the angle between the projections of the main and auxiliary cutting edges on the main plane - is determined by the formula

ε \u003d 180 - (φ + φ 1).

Angle of inclination of the main cutting edge λ - the angle between the main cutting edge and the plane drawn through the tool tip parallel to the main plane, determines the direction of chip flow and provides the necessary strength of the tool tip, can be positive (if the tool tip is the lowest point of the main cutting edge), negative (if the tool tip is the highest point of the main cutting edge) and equal to zero (if the main cutting edge is parallel to the main plane); when roughing is selected in the range from 4 to 20 °, when finishing - from 0 to -5 °.

Manual sharpening of cutters is performed on a grinding machine EZS-2 or on a grinding and grinding machine model 3B633, while for sharpening high-speed cutters it is recommended to install a grinding wheel made of white electrocorundum with a grain size of 16 - 25 and a hardness of CM1 - CM2, and for cutters equipped with plates of hard alloys, - a circle of green silicon carbide with a grit of 16 and a hardness of Μ or CM. High-quality sharpening of carbide cutters is performed with diamond wheels. When sharpening, do not press the cutter too hard against the grinding wheel. A bath of water is used to cool the cutter.

Parfenyeva I.E. TECHNOLOGY OF STRUCTURAL MATERIALS. M.: Study guide, 2009

4. Types of turning. The main types of turning tools. Elements and geometric parameters of the turning tool.

4.1. Types of turning

On lathes, and in particular on screw-cutting lathes, the following types of work can be performed: turning in centers, in a chuck and on a faceplate; boring; face turning; cutting and trimming; thread cutting; turning cones, shaped surfaces and other types of work using appropriate tools and fixtures.

Surface treatment is carried out either with longitudinal or transverse feed. The shaping of surfaces when machining with a longitudinal feed is carried out according to the trace method, when machining with a transverse feed, mainly according to the copying method.

Center turning

Bar parts (shafts, axles) with a ratio of length to diameter are usually subjected to longitudinal turning in the centers using through-cutting cutters. A part with drilled axial holes at the ends is clamped between the centers of the headstock and tailstock. The center of the headstock is installed in the spindle, and the back one is installed in the tailstock quills. At one end of the part, a clamp is fixed with a screw so that the finger enters the slot of the drive faceplate. The faceplate is screwed onto the front end of the spindle.

When processing long parts, guide devices - lunettes - are used to protect them from deflection. The lunette can be fixed (mounted on the bed rails) and movable (mounted on the caliper carriage and moves with it).

When processing heavy and long parts (from rolled products), one end is fixed in the chuck, and the other is supported by the center of the tailstock. This provides the necessary rigidity of the fastening of the part and reduces the wear of the centers.

Chuck turning

Processing parts with a ratio is carried out when fixing them in the chuck. Cartridges are three- and four-jaw.

A three-jaw self-centering chuck is usually used to secure symmetrical parts. In this chuck, the gripping jaws can simultaneously move radially towards or away from the center.

Four-jaw chucks have independent movement for each of the jaws. These cartridges are used to install and secure parts of complex and asymmetrical shape.

Faceplate turning

The faceplate screwed onto the spindle is used when machining non-symmetrical parts and parts of complex shape. The faceplate is a disk with radially cut grooves. The workpiece is fixed on the faceplate with bolts. Sometimes a square is first placed and the workpiece is attached to it. The fixed part is balanced by a counterweight.

Turning is divided into rough and finish. When rough turning, an allowance of 2-5 mm is removed. Turning is carried out with through cutters (Fig. 1). The radius of curvature of the top of the rough cutters R = 0.5-1 mm, semi-finishing R = 1.5-2 mm, for fine turning R = 3-5 mm.

Fig.1. Turning patterns

1 - longitudinal turning with a straight through left cutter

2 - longitudinal turning with a straight through right cutter

3 - longitudinal turning with a bent right cutter

4 - longitudinal turning with a hard-through right cutter

Finishing allowances vary within 1-2 mm or less per side. Turning is carried out with cutters with a rounded cutting edge and wide cutters.

For turning end surfaces scoring cutters are used (Fig. 2). When processing the end surfaces, the workpieces are fixed in the same way as when processing the outer cylindrical surfaces. When fixing in the chuck, the overhang of the workpiece should be minimal. To trim the end of the workpiece when fixing it with a clamping back center, a special cut off reference fixed center is used.

Fig.2. Trimming the ends with cutters:

a) straight through

b) bent through

c) through-thrust

d) undercut

Boring of pre-drilled holes or holes obtained during blanking operations is performed by roughing and finishing (with a loaded cutting edge) cutters. Boring cutters for through holes have a main angle of entry less than 90 o, for boring cutters for blind holes, the angle is equal to or slightly greater than 90 o (Fig. 3).

Fig.3. Boring a through hole (a) and a blind hole (b) with a boring

peeling cutter

Cutting parts of workpieces and turning annular grooves are produced by cutting cutters and slotted (grooving) cutters (Fig. 4).

Fig.4. Grooving with a grooving tool or parting with a parting tool

For processing shaped surfaces, round and prismatic shaped cutters or copiers are used.

Tapering

The processing of conical surfaces can be carried out by the following methods:

1. By offsetting the tailstock housing

2. Turning the carriage of the upper caliper

3. With the help of a copy ruler

4. Turning with a wide cutter

Turning conical surfaces by transverse displacement of the tailstock body (Fig. 5)

Fig.5. Turning of cones by transverse displacement of the body of the tailstock

1-drive cartridge; 2- front center; 3- collar;

4- rear center; 5- tailstock quill; 6 - blank; 7 - cutter

With this method, the axis of centers is shifted by shifting the rear center in the transverse direction. The generatrix of the machined conical surface of the workpiece, installed in the centers of the headstock and tailstock, will be parallel to the line of the centers of the machine.

The value of the transverse displacement of the tailstock body is determined by the formula:

Where: d- diameter of the small base of the cone, mm; D is the diameter of the large base of the cone, mm; L– the length of the entire workpiece being processed, mm; l is the height of the conical surface, mm.

This method processes long outer conical surfaces with a small taper with an angle of not more than .

The disadvantages of the method: impossibility of processing internal conical surfaces; the possibility of obtaining only gentle cones; increased and uneven wear of centers and center holes due to misalignment of centers.

Processing of conical surfaces by turning the carriage of the upper support (Fig. 6).

Fig.6. Turning cones by turning the carriage of the upper support.

1- three-jaw chuck; 2 - blank; 3 - handle for manual movement of the upper caliper; 4 - upper support with a tool holder; 5 - cutter

In this way, short conical surfaces are turned (and bored) with any cone angle. To do this, the carriage of the upper caliper is rotated through an angle equal to half the angle at the top of the cone being machined. Processing is carried out with manual feed of the upper caliper at an angle to the line of machine centers. The angle value is determined from the expression:

The disadvantages of the method: the use of manual feed, which reduces labor productivity and increases the roughness of the machined surface; the impossibility of turning conical surfaces, the length of the generatrices of which exceeds the stroke length of the upper support carriage (100-150 mm).

Turning a conical surface with a wide turning tool (Fig. 7).

Fig.7. Turning cones with a wide turning tool

1 - three-jaw chuck; 2 - blank; 3 - rear center; 4 - cutter

In this way, short conical surfaces are turned with a generatrix length of not more than 25-30 mm with turning cutters, in which the main angle in the plan is equal to half the angle at the top of the turned conical surface. The length of the main cutting blade of the cutter should be 1-3 mm longer than the length of the generatrix of the conical surface. Processing is carried out with a transverse or longitudinal feed of the cutter. The method is widely used for chamfering machined cylindrical surfaces.

The disadvantages of the method: inability to process long tapered surfaces, as with an increase in the length of the part, vibrations occur that increase the roughness of the treated surface; low quality of the processed surface.

4. 2. Main types of turning tools

Turning cutters are classified according to a number of criteria.

1. By the type of work performed or by technological feature: through (1), undercut (2), boring (3), cut-off (4), threaded (5), etc.

2. According to the shape of the incisor head: straight (1), bent (2), curved (3), drawn (4).

3. In feed direction: left(1), right(2).

Right a cutter is called, in which the main cutting edge is located on the side of the thumb of the right hand, laid with the palm of the hand on the cutter so that the fingers are directed towards the top of the cutter. When turning with such cutters, the chips are cut off from the workpiece when the caliper is moved from right to left.

Left a cutter is called, in which the main cutting edge is located on the side of the thumb of the left hand, laid with the palm of the hand on the cutter so that the fingers are directed towards the top of the cutter. When turning with such cutters, the chips are cut off from the workpiece when the caliper is moved from left to right.

4. According to the material of the cutting part: high speed steel, hard alloy.

5. According to the design of the cutting part: solid and composite (with a soldered plate or with a mechanical fastening of the cutting plate).

4.3. Elements and geometric parameters of a turning tool

Any cutting tool consists of two parts: I - cutting part; II - fastening part (Fig. 8).

Fig.8. Elements of a turning tool

On the cutting part, the following elements are distinguished:

1 - the front surface along which the chips come off

2-main back surface adjacent to the main blade

3-main cutting blade

4-top cutter

5-auxiliary back surface adjacent to the auxiliary blade

6-auxiliary cutting blade

4. 4. Geometry of cutters in static

4.4.1. Coordinate planes

To carry out the cutting process, the cutter is sharpened along the front and back surfaces. To read the angles of the cutter, coordinate planes are used (Fig. 9, 10).

Main plane(OP) is a plane parallel to the directions of the longitudinal ( S pr) and transverse ( S p) innings. For turning cutters, the main plane usually coincides with the lower bearing surface of the cutter shaft.

Fig.9. Coordinate planes

cutting plane(PR) passes through the main cutting blade of the cutter, tangent to the cutting surface of the workpiece.

Principal cutting plane (NN) passes through an arbitrary point of the main cutting blade perpendicular to the projection of the main cutting blade onto the main plane.

Auxiliary cutting plane passes through an arbitrary point of the auxiliary cutting blade perpendicular to the projection of the auxiliary cutting blade onto the main plane.

Fig.10. Geometrical parameters of the cutting part of the direct turning

through cutter

4.4.2. Turning tool angles

The main sharpening angles of the cutter are measured in the main cutting plane.

front angle call the angle between the front surface and the plane perpendicular to the cutting plane, drawn through the main cutting blade.

back angle called the angle between the main back surface of the cutter and the cutting plane.

The angle between the front and main rear surfaces is called taper angle incisor.

The angle between the rake face and the cutting plane is called cutting angle .

Plan angles are defined in the base plane.

Leading angle- the angle between the projection of the main cutting blade on the main plane and the feed direction.

Auxiliary lead angle- the angle between the projection of the auxiliary cutting blade on the main plane and the direction opposite to the feed direction.

Corner at the top of the cutter- the angle between the projections of the main and auxiliary cutting blades on the main plane.

Angle of inclination of the main cutting blade measured in a plane passing through the main cutting blade perpendicular to the main plane, between the main cutting blade and a line drawn through the tip of the cutter parallel to the main plane.

The angle can be positive (the cutter tip is the lowest point of the main cutting blade), negative (the cutter tip is the highest point of the main cutting blade), or zero.

Auxiliary cutter angles considered in the auxiliary cutting plane.

Auxiliary rear corner- the angle between the secondary rear surface and the plane passing through the secondary cutting edge perpendicular to the main plane.

To main

section three

Fundamentals of the theory of metal cutting.
Choice of cutting data

Chapter VI

Fundamentals of the theory of metal cutting

The founders of the theory of cutting metals were the outstanding Russian scientists I. A. Time (1838-1920), K. A. Zvorykin (1861-1928), Ya. G. Usachev (1873-1941) and others. The works of these scientists, which received world recognition have not yet lost their value. However, in the conditions of backward tsarist Russia, all these works did not find practical application, since the industry was poorly developed.

The science of cutting metals gained wide scope only after the Great October Socialist Revolution, especially during the Soviet five-year plans, when science was placed at the service of socialist industry.

Soviet scientists V.D. Kuznetsov, V.A. Krivoukhov, I.M. metals, a distinctive feature of which is the close collaboration of science with production, scientists with production innovators.

An important role in the development of the science of cutting metals was played by the movement of innovators in production. In an effort to increase labor productivity, production leaders began to look for new ways to improve cutting conditions: they created a new cutting tool geometry, changed cutting conditions, mastered new cutting materials. Each workplace of the innovator turner has become, as it were, a small laboratory for the study of the cutting process.

A broad exchange of experience, possible only in the conditions of a socialist economy, and close cooperation between leading workers in production and science ensured the rapid development of the science of cutting metals.

1. Work of the cutter

Wedge and his work. The working part of any cutting tool is wedge(Fig. 44). Under the action of the applied force, the tip of the wedge cuts into the metal.

The sharper the wedge, that is, the smaller the angle formed by its sides, the less force is required to cut it into the metal. The angle formed by the sides of the wedge is called taper angle and is denoted by the Greek letter β ( beta). Therefore, the smaller the taper angle β, the easier the wedge penetrates into the metal, and, conversely, the larger the taper angle β, the greater the force that must be applied to cut the metal. When assigning the taper angle, it is necessary to take into account the mechanical properties of the metal being processed. If you cut hard metal with a cutter having a small sharpening angle β, then the thin blade will not withstand and will crumble or break. Therefore, depending on the hardness of the metal being processed, an appropriate wedge sharpening angle is assigned.

The layer of metal being processed, located directly in front of the cutter, is continuously compressed by its front surface. When the force of the cutter exceeds the forces of adhesion of metal particles, the compressed element is sheared and shifted by the front surface of the wedge upwards. The cutter, moving forward under the action of the applied force, will continue to compress, chip and shift the individual elements from which the chips are formed.

Basic movements in turning. When machining on lathes, the workpiece rotates, and the cutter receives movement in the longitudinal or transverse direction. The rotation of the workpiece is called main movement, and the movement of the cutter relative to the part - feed motion(Fig. 45).

2. The main parts and elements of the turning tool

The cutter consists of two main parts: the head and the body (rod) (Fig. 46). Head is the working (cutting) part of the cutter; body serves to secure the cutter in the tool holder.

The head consists of the following elements: front surface, along which the chips come off, and rear surfaces facing the workpiece. One of the rear surfaces facing the cutting surface is called main; the other, facing the treated surface, - auxiliary.

Cutting edges are obtained from the intersection of the front and back surfaces. Distinguish home And auxiliary cutting edge. Most of the cutting work is done by the main cutting edge.

The intersection of the main and secondary cutting edges is called incisor tip.

3. Surface treatment

Three types of surface are distinguished on the workpiece (Fig. 47): machined, machined and cutting surface.

processed surface is the surface of the workpiece from which chips are removed.

Surface treated called the surface of the part obtained after chip removal.

cutting surface called the surface formed on the workpiece by the main cutting edge of the cutter.

It is also necessary to distinguish between the cutting plane and the base plane.

cutting plane called the plane tangent to the cutting surface and passing through the cutting edge of the cutter.

Main plane called a plane parallel to the longitudinal and transverse feeds of the cutter. For lathes, it coincides with the horizontal support surface of the tool holder.

4. Cutter angles and their purpose

The angles of the working part of the cutter greatly affect the course of the cutting process.

By choosing the right angles of the cutter, you can significantly increase the duration of its continuous operation until blunting (durability) and process more parts per unit of time (per minute or hour).

The cutting force acting on the cutter, the required power, the quality of the machined surface, etc. also depend on the choice of the angles of the cutter. That is why every turner must study well the purpose of each of the sharpening angles of the cutter and be able to correctly select their most advantageous value.

The angles of the cutter (Fig. 48) can be divided into the main angles, the angles of the cutter in the plan and the angle of inclination of the main cutting edge.

The main angles include: back angle, front angle and taper angle; the angles of the cutter in the plan include the main and auxiliary.

The main angles of the cutter should be measured in the main cutting plane, which is perpendicular to the cutting plane and the main plane.

The working part of the cutter is a wedge (shaded in Fig. 48), the shape of which is characterized by the angle between the front and main rear surfaces of the cutter. This corner is called taper angle and is denoted by the Greek letter β (beta).

back angle α ( alpha) is the angle between the main flank and the cutting plane.

Clearance angle α serves to reduce friction between the back surface of the cutter and the workpiece. By reducing friction, we thereby reduce the heating of the cutter, which, due to this, wears out less. However, if the relief angle is greatly increased, the incisor is weakened and quickly destroyed.

front angle γ ( gamma) is the angle between the front surface of the cutter and the plane perpendicular to the cutting plane, drawn through the main cutting edge.

The rake angle γ plays an important role in the chip formation process. With an increase in the rake angle, it is easier to cut the cutter into the metal, the deformation of the cut layer is reduced, the chip flow is improved, the cutting force and power consumption are reduced, and the quality of the machined surface is improved. On the other hand, an excessive increase in the rake angle leads to a weakening of the cutting edge and a decrease in its strength, to an increase in cutter wear due to chipping of the cutting edge, and to a deterioration in heat removal. Therefore, when processing hard and brittle metals, to increase the strength of the tool, as well as its durability, cutters with a smaller rake angle should be used; when machining soft and ductile metals, cutters with a large rake angle should be used to facilitate chip removal. In practice, the choice of the rake angle depends, in addition to the mechanical properties of the material being machined, on the material of the cutter and the shape of the rake surface. Recommended rake angles for carbide cutters are given in Table. 1.

Plan angles. Leading angle φ ( fi) is the angle between the main cutting edge and the feed direction.

The angle φ is usually chosen in the range of 30-90° depending on the type of processing, the type of cutter, the rigidity of the workpiece and the cutter and the method of their attachment. When processing the majority of metals with pass-through peeling cutters, it is possible to take the angle φ = 45°; when processing thin long parts in the centers, it is necessary to use cutters with an approach angle of 60, 75 or even 90 ° so that the parts do not bend or tremble.

Auxiliary angle in planφ 1 is the angle between the secondary cutting edge and the feed direction.

Angle λ ( lambda) inclination of the main cutting edge(Fig. 49) is the angle between the main cutting edge and the line drawn through the top of the cutter parallel to the main plane.

Table 1

Recommended rake and clearance angles for carbide tools
Note. The mechanical properties of metals are determined on special machines and instruments, and each property is given its own designation. The designation σ b given in this and subsequent tables expresses the tensile strength of the metal; the value of this limit is measured in kg/mm ​​2 . The letters HB denote the hardness of the metal, which is determined on the Brinell device by pressing a hardened steel ball into the surface of the metal. The value of hardness is measured in kg / mm 2.

Cutters whose apex is the lowest point of the cutting edge, i.e. angle λ positive(Fig. 49, c), are more durable and resistant; with such cutters it is good to process hard metals, as well as intermittent surfaces that create an impact load. When processing such surfaces with carbide cutters, the angle of inclination of the main cutting edge is adjusted to 20-30°. Cutters whose apex is the highest point of the cutting edge, i.e. angle λ negative(Fig. 49, a), it is recommended to use for processing parts made of soft metals.

5. Materials used for the manufacture of incisors

When working on the cutting edges of the cutter, high pressure occurs, as well as high temperature (600-800 ° and above). The friction of the rear surface of the cutter on the cutting surface and chips on the front surface of the cutter causes more or less rapid wear of its working surfaces. Due to wear, the shape of the cutting part changes and the cutter after some time becomes unusable for further work; such a cutter must be removed from the machine and resharpened. To increase the tool life without regrinding, it is necessary that its material resists wear at high temperatures well. In addition, the material of the cutter must be strong enough to withstand the high pressures generated during cutting without breaking. Therefore, the following basic requirements are imposed on the material of the cutters - hardness at high temperature, good wear resistance and strength.

Currently, there are many tool steels and alloys that meet these requirements. These include: carbon tool steels, high speed steels, hard alloys and ceramic materials.

Carbon tool steel. For the manufacture of cutting tools, steel with a carbon content of 0.9 to 1.4% is used. After quenching and tempering, the cutting tool made of this steel acquires high hardness. However, if during the cutting process the temperature of the cutting edge reaches 200-250 °, the hardness of the steel drops sharply.

For this reason, carbon tool steel is currently of limited use: cutting tools are made from it, operating at a relatively low cutting speed, when the temperature in the cutting zone reaches a small value. Such tools include: dies, reamers, taps, files, scrapers, etc. Cutters are not currently manufactured from carbon tool steel.

High speed steels. High-speed steels contain a large number of special, so-called alloying elements - tungsten, chromium, vanadium and cobalt, which give the steel high cutting properties - the ability to maintain hardness and wear resistance when heated during cutting to 600-700 °. HSS cutters allow 2-3 times higher cutting speeds than carbon cutters.

At present, the following grades of high-speed steel (GOST 9373-60) are produced in the USSR: R18, R9, R9F5, R14F14, R18F2, R9K5, R9KYU, R10K5F5 and R18K5F2.

Cutters made entirely of high-speed steel are expensive, therefore, in order to save high-speed steel, cutters with welded plates are mainly used.

Hard alloys . Carbide alloys are characterized by very high hardness and good wear resistance.

Hard alloys are made in the form of plates from tungsten and titanium powders combined with carbon. The combination of carbon and tungsten is called tungsten carbide, and with titanium, titanium carbide. Cobalt is added as a binder. This powdery mixture is pressed under high pressure to obtain small plates, which are then sintered at a temperature of about 1500°. The finished plates do not require any heat treatment. The plate is soldered with copper to the holder of a carbon steel cutter or attached to it with the help of adjustments and screws (mechanical fastening of the plates).

The main advantage of hard alloys lies in the fact that they resist abrasion by falling chips and the workpiece well and do not lose their cutting properties even when heated to 900-1000 °. Due to these properties, cutters equipped with hard alloy inserts are suitable for processing the hardest metals (hard steels, including hardened ones) and non-metallic materials (glass, porcelain, plastics) at cutting speeds that are 4-6 times or more than the cutting speed. allowed by high-speed cutters.

The disadvantage of hard alloys is increased brittleness.

At present, two groups of hard alloys are produced in the USSR. The main ones are - tungsten(VK2, VKZ, VK4, VK6M, VK6, VK8 and VK8M) and titanium-tungsten(T30K4, T15K6, T14K8, T5K10). Each of these groups has a specific scope (Table 2).

All tungsten alloys are intended for processing cast iron, non-ferrous metals and their alloys, hardened steels, stainless steels and non-metallic materials (ebonite, porcelain, glass, etc.). For the processing of steels, hard alloys of the titanium-tungsten group are used.

Ceramic materials. Recently, Soviet metallurgists have created cheap materials with high cutting properties, which in many cases replace hard alloys. These are ceramic materials thermocorundum), produced in the form of white plates, reminiscent of marble, which, like hard alloys, are either soldered to the tool holders or mechanically attached to them. These inserts do not contain such expensive and scarce elements as tungsten, titanium, etc. At the same time, ceramic inserts are characterized by higher hardness than hard alloys and retain their hardness when heated up to 1200°, which makes it possible to cut metals with high cutting speeds.

The disadvantage of ceramic plates is their insufficient viscosity. Cutters equipped with ceramic inserts can be used for finishing or semi-finishing of cast iron, bronze, aluminum alloys and mild steels.

6. Sharpening and finishing of cutters

In factories, the sharpening of cutters is usually carried out centrally on sharpening machines by special workers. But the turner himself must be able to sharpen and finish the cutters.

table 2

Properties and purpose of some grades of hard alloy

Sharpening and finishing of high-speed cutters is carried out in compliance with the following rules:
1. The grinding wheel should not hit, its surface should be even; if the working surface of the circle has developed, it should be corrected.
2. During sharpening, you need to use a handpiece, and not hold the cutter on weight. The handpiece should be installed as close as possible to the grinding wheel, at the required angle and give reliable support to the cutter (Fig. 50, a-d).
3. The cutter to be sharpened must be moved along the working surface of the circle, otherwise it will wear unevenly.
4. In order not to overheat the cutter and thereby avoid the appearance of cracks in it, do not strongly press the cutter to the circle.
5. Sharpening must be carried out with continuous and abundant cooling of the cutter with water. Drip cooling, as well as periodic immersion of a highly heated cutter in water, is not allowed. If continuous cooling is not possible, it is better to switch to dry sharpening.
6. Sharpening of cutters made of high-speed steel should be done using electrocorundum wheels of medium hardness and grain size 25-16.
The order of sharpening cutters is set as follows. First, the main back surface is sharpened (Fig. 50, a). Then the auxiliary back surface (Fig. 50, b), then the front surface (Fig. 50, c) and, finally, the radius of the top (Fig. 50, d).
7. It is strictly forbidden to sharpen cutters on machines with the protective cover removed.
8. Be sure to wear safety goggles when sharpening.

After sharpening the cutter, small notches, burrs and risks remain on its cutting edges. They are eliminated by finishing on special finishing machines. Finishing is also carried out manually using a fine-grained whetstone moistened with mineral oil. First, with light movements of the touchstone, the rear surfaces are adjusted, and then the front and the radius of the top.

Sharpening and finishing of cutters equipped with carbide inserts. Sharpening of cutters with plates of hard alloys is carried out on grinding machines with circles of green silicon carbide. Sharpening is carried out both manually (Fig. 50, a-d), and with the fixing of the incisors in the tool holders. The order of sharpening these cutters is the same as for cutters made of high-speed steel, i.e., first the cutter is sharpened along the main back (Fig. 50, a), then along the auxiliary back surfaces (Fig. 50, b), then along the front surface (Fig. 50, c) and, finally, round off the top of the incisor (Fig. 50, d).

Preliminary sharpening is carried out with green silicon carbide wheels with a grit of 50-40, and final sharpening with a grit of 25-16.

The cutter should not be strongly pressed against the working surface of the circle in order to avoid overheating and cracking of the hard alloy plate. In addition, it must be constantly moved relative to the circle; this is necessary for uniform wear of the circle.

Sharpening can be carried out both dry and with abundant cooling of the cutter with water.

After sharpening a carbide cutter, it is imperative to finish its surface. Finishing is done manually or on a finishing machine. Manual finishing is carried out using a cast-iron or copper lap, the working surface of which is rubbed with a special paste or boron carbide powder mixed with machine oil or kerosene is applied to the surface in an even layer. Finishing is carried out to a width of 2-4 mm from the cutting edge.

More productive finishing on a special finishing machine using a cast-iron disk with a diameter of 250-300 mm, rotating at a speed of 1.5-2 m / s; a paste or powder of boron carbide mixed with machine oil or kerosene is applied to the surface of this disc.

7. Chip formation

Types of shavings. The detached chip under the action of the pressure of the cutter greatly changes its shape or, as they say, is deformed: it shortens in length and increases in thickness. This phenomenon was first discovered by Prof. I. A. Time and named chip shrinkage.

The appearance of the chip depends on the mechanical properties of the metal and the conditions under which cutting occurs. If viscous metals are processed (lead, tin, copper, mild steel, aluminum, etc.), then the individual elements of the chips, tightly adhering to each other, form a continuous chip that curls into a tape (Fig. 51, a). Such a strand is called drain. When processing less viscous metals, such as hard steel, chips are formed from individual elements (Fig. 51, b), weakly connected to each other. Such a strand is called chipping chips.

If the metal being machined is brittle, such as cast iron or bronze, then the individual elements of the chips break and separate from the workpiece and from each other (Fig. 51, c). Such a chip, consisting of individual irregularly shaped flakes, is called broken chips.

The considered types of chips do not remain constant, they can change with changing cutting conditions. The softer the metal being processed and the smaller the chip thickness and cutting angle, the more the chip shape approaches the drain. The same will be observed when cutting speed is increased and cooling is applied. With a decrease in cutting speed, instead of a drain chip, chipping chips are obtained.

Outgrowth. If you examine the front surface of the cutter that was used for cutting, then at the cutting edge you can sometimes find a small lump of metal welded to the cutter under high temperature and pressure. This is the so-called outgrowth(Fig. 52). It appears under certain cutting conditions of ductile metals, but is not observed when processing brittle metals. The hardness of the build-up is 2.5-3 times higher than the hardness of the metal being processed; thanks to this, the growth itself has the ability to cut the metal from which it was formed.

The positive role of the build-up is that it covers the cutting blade, protecting it from wear by descending chips and heat, and this somewhat increases the durability of the cutter. The presence of a build-up is useful when peeling, since the cutting blade heats up less and its wear is reduced. However, with the formation of build-up, the accuracy and cleanliness of the machined surface deteriorate, since the build-up distorts the shape of the blade. Therefore, the formation of build-up is unfavorable for finishing work.

8. The concept of the elements of the cutting mode

In order to perform processing more efficiently in each individual case, the turner must know the basic elements of the cutting mode; these elements are depth of cut, feed and cutting speed.

Depth of cut called the distance between the machined and machined surfaces, measured perpendicular to the latter. The depth of cut is indicated by the letter t and is measured in millimeters (Fig. 53).

When turning a workpiece on a lathe, the machining allowance is cut off in one or more passes.

To determine the depth of cut t, it is necessary to measure the diameter of the workpiece before and after the cutter passes, half the difference in diameters will give the depth of cut, in other words,

where D is the diameter of the part in mm before the cutter passes; d is the diameter of the part in mm after the cutter has passed. The movement of the cutter in one revolution of the workpiece (Fig. 53) is called filing. The feed is denoted by the letter s and is measured in millimeters per revolution of the part; for brevity, it is customary to write mm / rev. Depending on the direction in which the cutter moves relative to the frame guides, there are:
A) longitudinal feed- along the bed guides;
b) cross feed- perpendicular to the bed guides;
V) oblique feed- at an angle to the guides of the bed (for example, when turning a conical surface).

Sectional area of ​​cut denoted by the letter f (eff) and is defined as the product of the depth of cut by the feed (see Fig. 53):

In addition to the depth of cut and feed, they also distinguish the width and thickness of the cut layer (Fig. 53).

Cutting layer width, or chip width, - the distance between the machined and machined surfaces, measured along the cutting surface. It is measured in millimeters and is denoted by the letter b (be).

Cut thickness, or chip thickness, is the distance between two successive positions of the cutting edge in one revolution of the part, measured perpendicular to the chip width. Chip thickness is measured in millimeters and is denoted by the letter a.

With the same feed and depth of cut, as the main angle φ decreases, the chip thickness decreases, and its width increases. This improves heat dissipation from the cutting edge and increases the tool life, which in turn allows you to significantly increase the cutting speed and process more parts per unit time. However, a decrease in the main angle in the plan φ leads to an increase in the radial (repulsive) force, which, when processing insufficiently rigid parts, can cause them to bend, loss of accuracy, and also strong vibrations. The appearance of vibrations, in turn, leads to a deterioration in the purity of the machined surface and often causes chipping of the cutting edge of the cutter.

Cutting speed. When machining on a lathe, point A, located on a circle of diameter D (Fig. 54), in one revolution of the part travels a path equal to the length of this circle.

The length of any circle is approximately 3.14 times its diameter, therefore it is equal to 3.14 D.
The number 3.14, showing how many times the length of a circle is greater than its diameter, is usually denoted by the Greek letter π (pi).

Point A in one revolution will make a path equal to πD. The diameter D of the part, as well as its circumference πD, is measured in millimeters.

Assume that the workpiece will make several revolutions per minute. Let us denote their number by the letter n revolutions per minute, or abbreviated as rpm. The path that point A will take in this case will be equal to the product of the circumference and the number of revolutions per minute, i.e. πDn millimeters per minute or abbreviated mm / min, and is called circumferential speed.

The path traveled by the point of the workpiece surface during turning relative to the cutting edge of the cutter in one minute is called cutting speed.

Since the part diameter is usually expressed in millimeters, to find the cutting speed in meters per minute, divide πDn by 1000. This can be written as the following formula:

where v is the cutting speed in m/min;
D is the diameter of the workpiece in mm;
n is the number of revolutions per minute.

Example 3 Processed roller diameter D = 100 = 150 rpm. Determine the cutting speed.
Solution: Spindle speed count. When turning a part of a known diameter, it may be necessary for a turner to adjust the machine to such a number of spindle revolutions in order to obtain the required cutting speed. For this, the following formula is used: where D is the diameter of the workpiece in mm;

Example 4 What number of revolutions per minute should a roller with a diameter of D \u003d 50 mm have at a cutting speed of v \u003d 25 m / min?
Solution:

9. Basic information about the forces acting on the cutter and cutting power

Forces acting on the cutter. When removing chips from the workpiece, the cutter must overcome the force of adhesion of metal particles to each other. When the cutting edge of the cutter cuts into the material being processed and the chip is separated, the cutter experiences pressure from the metal being separated (Fig. 55).

From top to bottom, the force P z presses on the cutter, which tends to press the cutter down and bend the part up. This force is called cutting force.

In the horizontal plane in the direction opposite to the feed movement, the cutter is pressed by the force P x, called axial force, or feed force. This force during longitudinal turning tends to press the cutter towards the tailstock.

In the horizontal plane, perpendicular to the feed direction, the cutter is pressed by the force P y, which is called the radial force. This force tends to push the cutter away from the workpiece and bend it in a horizontal direction.

All listed forces are measured in kilograms.

The largest of the three forces is the vertical cutting force: it is about 4 times the feed force and 2.5 times the radial force. The cutting force loads the parts of the headstock mechanism; it also loads the cutter, the part, often causing large stresses in them.

Experiments have established that the cutting force depends on the properties of the material being processed, the size and shape of the section of the chip being removed, the shape of the cutter, cutting speed and cooling.

To characterize the resistance of various materials to cutting, the concept of cutting coefficient has been established. The cutting factor K is the cutting pressure in kilograms per square millimeter of the cut section, measured under certain cutting conditions:

Depth of cut t......................5 mm
Feed s......................1 mm/rev
Rake angle γ......................15°
Leading angle φ.......45°
The cutting edge of the cutter - rectilinear, horizontal
The tip of the cutter is rounded with a radius r = 1 mm
Work is done without cooling

In table. 3 shows the average values ​​of the cutting factor for some metals.

Table 3

Average values ​​of the cutting factor K when turning

If the cutting factor K is known, then by multiplying it by the cross-sectional area of ​​​​the cut f in mm 2, you can find the approximate value of the cutting force using the formula

P z \u003d Kf kg. (8)

Example 5 A shaft made of machine-made steel with σ b = 60 kg / mm 2 is turned on a lathe. Determine the cutting force if the depth of cut t = 5 mm and the feed s = 0.5 mm/rev.
Solution. According to formula (8), cutting force P z \u003d Kf kg. (8) We determine the value of f: f \u003d ts \u003d 5x0.5 \u003d 2.5 mm 2. According to the table 3 we find the value of K for machine-made steel with σ b \u003d 60 kg / mm 2: K \u003d 160 kg / mm 2. Therefore, z = Kf = 160x2.5 = 400 kg. cutting power. Knowing the cutting force and cutting speed, you can find out how much power is required to cut chips of a given section.
Cutting power is determined by the formula (9) where N res - cutting power in hp;
P z - cutting force in kg;
v - cutting speed in m/min.

The power of the electric motor of the machine tool must be slightly greater than the cutting power, since part of the power of the electric motor is spent on overcoming friction in the mechanisms that transmit movement from the electric motor to the machine spindle.

Example 6 Determine the cutting power for turning the shaft, considered in the previous example, if the processing is carried out at a cutting speed, υ = 60 m/min. Solution . According to formula (9), cutting power

Cutting power is usually expressed not in horsepower, but in kilowatts (kW). A kilowatt is 1.36 times horsepower, so in order to express power in kilowatts, you need to divide horsepower by 1.36:

and vice versa,

10. Heat of cut and tool life

With an increase in the cutting force, the friction force increases, as a result of which the amount of heat released during the cutting process increases. The heat of cutting increases even more as the cutting speed increases, as this speeds up the entire process of chip formation.

The generated heat of cutting with insufficient removal of it softens the cutter, as a result of which the wear of its cutting part occurs more intensively. This makes it necessary to change the cutter or sharpen it and reinstall it.

The time of continuous work of the cutter before blunting is called the tool life (measured in minutes). Frequent change of the cutter (short tool life) causes additional costs for sharpening and installing the cutter, as well as for replenishing worn cutters.

Therefore, tool life is an important factor when choosing cutting data, especially when choosing cutting speed.

The durability of the cutter depends primarily on the qualities of the material from which it is made. The most resistant will be the cutter, which is made of a material that allows the highest heating temperature without significant loss of hardness. The cutters equipped with hard alloy plates, mineral-ceramic plates have the greatest resistance; significantly less resistance - cutters made of high-speed steel, the smallest - cutters made of carbon tool steel.

The resistance of the cutter also depends on the properties of the material being processed, the cut section, the sharpening angles of the cutter, and the cutting speed. Increasing the hardness of the material being machined reduces the tool life.

By changing the sharpening angles and the shape of the front surface, it is possible to achieve a significant increase in the durability of the cutters and their performance.

Cutting speed has a particularly strong effect on tool life. Sometimes even the slightest increase in speed leads to rapid blunting of the cutter. For example, if, when processing steel with a high-speed cutter, the cutting speed is increased by only 10%, i.e., 1.1 times, the cutter will become dull twice as fast and vice versa.

With an increase in the cross-sectional area of ​​the cut, the tool life decreases, but not as much as with the same increase in cutting speed.

The tool life also depends on the size of the tool, the shape of the cut section and cooling. The more massive the cutter, the better it removes heat from the cutting edge and, therefore, the greater its durability.

Experiments show that with the same section of cut, a large depth of cut and a smaller feed provide greater tool life than a smaller depth of cut with a correspondingly larger feed. This is explained by the fact that with a greater depth of cut, the chips come into contact with a greater length of the cutting edge, so cutting heat is better removed. That is why, with the same cut section, it is more profitable to work with a greater depth than with a greater feed.

The durability of the cutter increases significantly when it is cooled.

Coolant must be supplied plentifully (emulsion 10-12 l/min, oil and sulfofresol 3-4 l/min); a small amount of liquid not only does not benefit, but even spoils the cutter, causing small cracks to appear on its surface, leading to chipping.

11. Choice of cutting speed

The productivity of labor depends on the choice of cutting speed: the higher the cutting speed, the less time spent on processing. However, with an increase in cutting speed, the tool life decreases, therefore, the choice of cutting speed is influenced by the tool life and all factors that affect the tool life. Of these, the most important are the properties of the material being machined, the quality of the material of the cutter, the depth of cut, the feed, the dimensions of the cutter and sharpening angles, and cooling.

1. The longer the tool life should be, the lower the cutting speed should be selected and vice versa.

2. The harder the material being machined, the less tool life, therefore, to ensure the necessary resistance when machining hard materials, the cutting speed has to be reduced. When machining cast and forged workpieces, on the surface of which there is a hard crust, shells or scale, it is necessary to reduce the cutting speed against that which is possible when machining materials without crust.

3. The material properties of the cutter determine its durability, therefore, the choice of cutting speed also depends on these properties. Other things being equal, high speed steel cutters allow a significantly higher cutting speed than carbon steel cutters; even higher cutting speeds allow cutters equipped with hard alloys.

4. In order to increase the resistance of the cutter when processing viscous metals, it is advantageous to use cooling of the cutters. In this case, with the same tool life, it is possible to increase the cutting speed by 15-25% compared to machining without cooling.

5. The dimensions of the cutter and the angles of its sharpening also affect the allowable cutting speed: the more massive the cutter, especially its head, the better it removes the heat generated during cutting. Incorrectly selected cutter angles that do not correspond to the material being processed increase the cutting force and contribute to faster wear of the cutter.

6. With an increase in the cut section, the tool life decreases, therefore, with a larger section, it is necessary to choose a cutting speed that is lower than with a smaller section.

Since small chips are removed during finishing, the cutting speed during finishing can be much higher than during roughing.

Since an increase in the cut section has less effect on tool life than an increase in cutting speed, it is advantageous to increase the cut section by slightly reducing the cutting speed. The processing method of the innovator turner of the Kuibyshev Machine Tool Plant V. Kolesov is based on this principle. Working at a cutting speed of 150 m/min, T. Kolesov finishes steel parts with a feed rate of up to 3 mm/rev instead of 0.3 mm/rev, and this leads to a reduction in machine time by 8-10 times.

The question arises: why do advanced turners often increase labor productivity by increasing cutting speed? Doesn't this contradict the basic laws of cutting? No, it doesn't contradict. They increase the cutting speed only in cases where the opportunities to increase the section of the cut are fully used.

When semi-finishing or finishing is performed, where the depth of cut is limited by a small allowance for machining, and the feed is limited by the requirements of high purity of machining, an increase in the cutting mode is possible by increasing the cutting speed. This is what advanced turners do, working on semi-finishing and finishing. If it is possible to work with large sections of the cut (with large allowances), then first of all it is necessary to choose the greatest possible depth of cut, then the greatest possible technologically permissible feed and, finally, the corresponding cutting speed.

In cases where the machining allowance is small and there are no special requirements for surface finish, the cutting mode should be increased by using the largest possible feed.

12. Cleanliness of the machined surface

When machining with a cutter, irregularities in the form of depressions and scallops always remain on the machined surface of the part, even with the most careful finishing. The height of the roughness depends on the processing method.

Practice has established that the cleaner the surface of the part is treated, the less it is subject to wear and corrosion, and the part is stronger.

Careful surface finishing when machining a part is always more expensive than a rough surface finish. Therefore, the cleanliness of the machined surface should be assigned depending on the operating conditions of the part.

Designation of surface cleanliness in drawings. According to GOST 2789-59, 14 classes of surface cleanliness are provided. To designate all purity classes, one sign is established - an equilateral triangle, next to which the class number is indicated (for example, 7; 8; 14). The cleanest surfaces are graded 14 and the roughest grade 1.

The surface roughness according to GOST 2789-59 is determined by one of two parameters: a) the arithmetic mean deviation of the profile R a and b) the height of the irregularities R z .

To measure the roughness and assign the treated surface to a particular class, special measuring instruments are used, based on the method of feeling the surface profile with a thin diamond needle. Such devices are called profilometers and profilographs.

To determine the roughness and classify the treated surface to one or another class of cleanliness in shop conditions, tested samples of various classes of cleanliness are used - the so-called standards of cleanliness, with which the machined surface of the part is compared.

Factors Affecting Surface Finish. It has been established by practice that the cleanliness of the machined surface depends on a number of reasons: the material being machined, the material of the cutter, the sharpening angles and the condition of the cutting edges of the cutter, the feed and cutting speed, the lubricating and cooling properties of the liquid, the rigidity of the system machine - cutter - part, etc.

Of particular importance for obtaining a high quality surface when turning is the cutting speed, feed, lead angles and radius of curvature of the tool tip. The smaller the feed and entering angle and the larger the corner radius, the cleaner the machined surface. Cutting speed greatly affects surface finish. When turning steel at a cutting speed of more than 100 m/min, the machined surface is cleaner than at a speed of 25-30 m/min.

To obtain a cleaner machined surface, attention should be paid to careful sharpening and finishing of the cutting edges.

Control questions 1. What shape is the chip formed when machining viscous metals? When processing brittle metals?
2. Name the main elements of the incisor head.
3. Show the front and back surfaces on the incisor; front and rear corners; sharpening angle.
4. What is the purpose of the front and rear corners of the incisor?
5. Show lead angles and lead angle.
6. What materials are cutters made of?
7. What grades of hard alloys are used in steel processing? When processing cast iron?
8. List the cutting mode elements.
9. What forces act on the cutter?
10. What factors and how do they affect the magnitude of the cutting force?
11. What determines the durability of the cutter?
12. What factors influence the choice of cutting speed?

Turning parts involves the use of different types of cutters: through, boring, threaded, shaped. They carry out roughing and finishing of the surfaces of the part, internal sampling, threading. has many features. They are structurally formed by the following main parts: holder, working head (for some types of cutters it can be replaceable).

Proper sharpening is understood as giving a certain geometric shape to the head of the cutter - ensuring the required values ​​of the angular parameters.

The correct orientation of the cutting edge is determined by three planes. They have the names established by the standards: front, rear and additional (auxiliary).

Along the first is the movement of the formed chips. It is called the main back surface. The second is directed along the back surface of the incisor. It is called the auxiliary back surface. Both surfaces of the cutter are called edges. They face the workpiece. During sharpening, attention is paid to the characteristics of the meeting of both edges. Incorrect operation reduces the quality of processing. Leads to mechanical damage to the cutter.

Of particular interest is the point of intersection of the planes, called the vertex. She bears the greatest burden.

The angles that define the characteristics of the cutter are divided into the following categories:

• main (in the amount of two);
• auxiliary (the same number);
• angles in plan or projection (three angles are considered).

The values ​​of the listed indicators depend on the following characteristics:

• the shape of the selected workpiece;
• purpose and design of incisors;
• specified quality of processing;
• material of the cutting head (if it is removable);
• physical and mechanical characteristics of the metal of the product;
• allowable allowance;
• spindle speed.

Structurally, cutters have four types:

• straight (they have a holder and a head located in two versions, along one axis or on two parallel axes);
• curved (has a curved holder);
• bent (deflected to the side from the direction of the translational movement of the workpiece);
• drawn (the width of the head is smaller in size than the holder). Of great importance for the shape of the tip is the quality of the required operation. They are divided into the following categories:
• roughing (called peeling);
• semi-finishing;
• finishing;
• precision (high precision).

When setting angles, pay attention to the feed side. The process can take place on the left or on the right.

The main plane is called, oriented along the movement of the cutter. It is located perpendicular to the previous one - it is called the cutting plane.

The third is the auxiliary plane. Its trace determines the angles of the incisor. To obtain a quality product, attention is paid to the cutting angle and sharpening.

Principal angles

One received the name - the main front corner. The second is respectively called - the main rear.

Each affects the result of processing:

• The first directly determines the quality of the surface to be removed (the resulting chips). If it increases, there is an increased deformation in the upper layer. A small value makes it much easier for the tool to remove excess metal. Does not cause increased compression of this layer. Significantly facilitates the process of removal and removal of excess metal.
• An increase in the numerical value of the second weakens the reliability of mounting the tool on the tool holder. Promotes an increase in the frequency and amplitude of oscillations. Changing the characteristics increases the wear rate of the cutter. Decreasing the value increases the contact area of ​​the cutting edge with the machined surface. It leads to an increase in the temperature of the cutter.

Auxiliary corners

Located on the auxiliary plane. The first is formed by its angular difference with the direction oriented by the continuation of the cutting edge.

The second is the parameter formed by a straight line segment passing through the vertex and the edge location surface.

Plan angles

For they have the following names of angles in the plan:

• main corner;
• auxiliary;
• corner at the top.

The first one is formed between the plane of the projection of the edge with the main plane of the tool.

The second is determined between the continuation of the projection of the cutting edge with a plane directed along the movement of the workpiece.

The third one is between the first listed plane with the main plane.

The numerical values ​​of the parameter located at the top can take positive and negative values. It is positive when the top of the sharpening point is at the bottom point of the workpiece. Minus sign - the top reaches the highest point.

Measurement of cutter angles

Each sample undergoes a procedure for measuring the listed characteristics. They are carried out using special measuring instruments. Use a desktop protractor, or mechanical, equipped with a vernier. The results obtained must be recorded in the journal.

The first type of meter allows you to determine the parameters of the angles located on the main plane. Structurally, it consists of the following parts:

• massive base;
• racks with a moving template (to set the direction of the planes);
• measuring sector (equipped with a degree ruler);
• locking screw (for fixing the received direction).

The sequence of measurements is carried out as follows. The selected pattern is placed on the base. The edge surface is aligned with one rack plane. The second is directed parallel to the studied edge. The obtained values ​​on the degree ruler are the value of the measured indicator. A prerequisite for carrying out measurements is to ensure a snug fit of the template to the corresponding surface of the cutter.

Measurement of such specific parameters as angles in the plan is carried out by a mechanical goniometer equipped with a vernier. Its design includes the following main elements:

• two special sectors, each of which has its own angular scale;
• two independent measuring guides;
• special movable vernier.

The sequence of measurements is somewhat different from the sequence of operations of a desktop goniometer.

To obtain the exact value of the parameter, it is necessary to precisely align one bar with the side surface of the case. The cutting edge should be directed parallel to the second bar. Numerical values ​​are read using the built-in vernier. The obtained values ​​are recorded in the documentation.

The rake angle has a great influence on the vibration resistance of the cutter, which decreases sharply with a decrease in its value (from zero and below). Therefore, in order to avoid the appearance of vibrations, it is necessary to take a front angle of 15-25 °, and usually it is made equal to the angle of insertion of the plate. In order to ensure chip curling and favorable removal of it, it is recommended to make the front surface of the cutter either curved or with a hole. To harden the main cutting edge, it is advisable to provide a ribbon 0.2-0.3 mm wide with a negative rake angle of -3 - 5°. However, we should not forget that such a ribbon is permissible only if there are sufficiently severe working conditions for the cutter. If the stiffness conditions do not allow the use of a reinforcing tape with a negative angle, it is recommended to make it with a positive angle of 5° for hard and 10° for soft and viscous materials. The reinforcing ribbon, with its small width, does not affect the value of cutting resistance, since the center of pressure of the chip goes beyond the border of the ribbon into the zone of the curved front surface, equipped with a large rake angle.

Figure 66 - Cut-off tool angles

In practice, there are cutting cutters, in which the front surface is formed in the form of a dihedral angle (Fig. 66, b). Its planes are inclined to the reference plane at an angle μ = 10÷15°. The line of intersection of these planes is parallel to the reference plane. This design contributes to better penetration of the cutter into the workpiece.

Rear corner

The rear angle of the main cutting edge is taken equal to 8º on the plate and 12° on the holder.

cutting edge

The main cutting edge of the cutter can be designed in several ways. For cutting off large workpieces, a cutter with two cutting edges can be recommended (Fig. 66, c)². They ensure the separation of the chips into two parts, which makes it easier to remove them from the cutting zone. This design is more suitable for high speed steel cutters, while it is less suitable for carbide cutters due to the difficulty of sharpening and the low strength of the cutting edge.

Noteworthy is the design of the main cutting edge at two angles φ (Fig. 66, d). This shape facilitates the cutting of the cutter into the workpiece and lengthens its edge. Plan angles φ are accepted within 60-80° (ς = 30 ÷10º).

In the event that the main cutting edge is made at an angle φ = 90°, it is recommended to chamfer f = 1 ÷ 1.5 mm on it at an angle of 45° on both sides or make small roundings (Fig. 66, e).

In practice, there are cases when, during cutting, it is undesirable to leave the cylindrical process at the core of the workpiece uncut (for example, when processing on automatic machines). To cut such a rod, the cutting edge is formed at an angle φ = 75 ÷ 80°.

Increased vibration resistance

Sometimes blanks are cut with a cutter, in which the main cutting edge has a concave shape, obtained by grinding a hole on the main back surface (Fig. 66, g). The purpose of this form is to increase the vibration resistance of the cutter and the possibility of increasing the feed rate.

Severe working conditions of cut-off cutters force, as a rule, to use them in the form of a monolithic structure, while prefabricated structures are rarely found in practice.