SELECTION OF CUTTING MODE WHEN MILLING

§ 78. CONDITIONS DETERMINING THE CHOICE OF CUTTING MODE

The concept of the most advantageous cutting mode

The most advantageous cutting mode should be considered when working on a milling machine, in which the cutting speed, feed and depth of the cut layer are most successfully combined, providing under given specific conditions (i.e., taking into account the best use of the cutting properties of the tool, the speed and power capabilities of the machine) the highest labor productivity and the lowest cost of the operation while complying with the specified technical conditions regarding accuracy and cleanliness of processing.
The Labor Research Institute of the State Committee of the Council of Ministers of the USSR on Labor and Wages, with the participation of major domestic scientists, taking into account practical application in production conditions, cutting modes for milling with tools made of high-speed steel and hard alloys. They can serve as input data when assigning cutting speeds and minute feeds.
These standards are available in every plant and serve as guidelines for process development and operating charts such as those shown on pages 204-205. However, the cutting speeds and minute feeds given in them are not maximum and in some cases can be exceeded by milling operators if they use more productive tools or work on more powerful and rigid machines.
On the other hand, young, i.e., beginners and those without sufficient experience, milling operators cannot always work at extreme cutting conditions, therefore, less severe cutting conditions are provided for them in the “Young Milling Operator's Handbook”, starting from which it is necessary, as advanced training, move on to tougher ones.
In order to introduce new modes yourself, you need to know the order and sequence of establishing milling modes.

Milling cutter material

The decisive factor determining the level of cutting mode is the material of the cutting part of the cutter. As mentioned above, the use of cutters with carbide inserts allows you to work at high cutting speeds and high feeds compared to cutters made of high-speed steel; As we will see later, carbide cutters make it possible to increase productivity by two to three times compared to high-speed cutters. Therefore, it is advisable to use carbide cutters for almost all types of milling; an obstacle to their use may be insufficient power of the equipment or the specific properties of the material of the workpiece being processed.
However, in a number of cases, the use of carbon, alloy tool and high-speed steels for the cutting part of cutters is rational, especially when the cleanliness of the machined surface and the accuracy of the resulting surface of the part are more important than the speed of work.

Geometric parameters of the cutting part

An equally important factor influencing the choice of cutting modes are the geometric parameters of the cutting part of the cutter (cutting angles, dimensions and shape of the tooth), which is often called cutter geometry. Earlier, in § 7, the significance and influence of each of the elements of the cutter tooth geometry during the cutting process was considered; Here we will consider the recommended geometric parameters of the cutting part of milling cutters made of high-speed steel R18 and with carbide inserts.
In table 35 and 36 show the recommended values ​​of the geometric parameters of cylindrical, end, disk, cutting, end and shaped milling cutters made of high-speed steel.

Table 35

Geometric parameters of the cutting part of milling cutters made of high-speed steel P18

I. Front corners

II. Back corners

III. Lead and transition edge angles

Notes 1. For cylindrical cutters with a tooth inclination angle of more than 30°, the rake angle γ when processing steel σ b is less than 60 kg/mm 2 is taken equal to 15°.
2. For shaped cutters with a rake angle greater than 0°, contour correction is necessary when processing precise profiles.
3. When processing heat-resistant steels with end mills, take the upper values ​​of the rake angles, and with end and cylindrical mills, take the lower and middle values.
4. When sharpening, leave a circular sanding strip with a width of no more than 0.1 on the back surface of the cutters. mm. The teeth of slotted (slotted) and cutting (circular saw) cutters are sharpened without leaving a strip.

In table 37 - 40 show the recommended values ​​of the front and rear angles, the main, auxiliary and transition angles in the plan, the inclination angles of the cutting edge and helical grooves, the apex radius of face, cylindrical, end and disk milling cutters with carbide inserts.
The cutters used to process most workpieces are usually supplied by tool factories with geometric parameters corresponding to GOST, and it is almost impossible for the miller, unlike the turner and planer, to change the cutting angles of the cutters by sharpening. As a result, those given in table. 35 - 40 geometric parameters of the cutting part of the cutters will help the milling operator to correctly select the cutter appropriate for a given processing from the standard cutters available in the tool store of the training and production workshop. However, the main purpose of these tables is to provide recommendations in the event that the milling machine operator wants to order standard or special cutters from the tool department with optimal geometric parameters for a given processing.

Table 37

Geometric parameters of the cutting part of end mills with carbide inserts

Note: Small entering angles φ = 15 - 30° should be used when processing on rigid machines for roughing passes with small cutting depths or finishing passes with low requirements for cleanliness and accuracy of the machined surface.

Table 38

Geometric parameters of the cutting part of cylindrical milling cutters with screw inserts made of hard alloy

Note: On the back surface of the tooth along the cutting edge, a ribbon with a width of no more than 0.1 is allowed mm.

Table 39

Geometric parameters of the cutting part of end mills with carbide inserts when processing structural carbon and alloy steels

* With low rigidity of the machine - fixture - tool - workpiece system and with large chip sections ( IN more D; t more than 0.5 D), as well as when working at low cutting speeds with insufficient spindle speeds ( v less than 100 m/min) the front angle γ is assigned positive + from 0 to +8°.
** Larger values ​​for soft steels, smaller values ​​for hard steels.

Milling width and depth

Milling width specified in the part drawing. In the case of processing several workpieces clamped in parallel in one clamping device, the milling width is equal to the width of all workpieces. In the case of processing with sets of cutters, the milling width is equal to the total width of all mating surfaces.
Milling depth(cutting depth, thickness of the cut layer) is given as the distance between the machined and machined surfaces. To reduce processing time, it is recommended to perform milling in one pass. With increased requirements for accuracy and cleanliness of the machined surface, milling is carried out in two transitions - roughing and finishing. In some cases, when removing large allowances or when milling on machines with insufficient power, processing in two roughing passes is possible.

Table 40

Geometric parameters of the cutting part of disk cutters with carbide inserts

When milling steel forgings, steel and cast iron castings covered with scale, foundry crust or contaminated with foundry sand, the milling depth should be greater than the thickness of the contaminated layer so that the cutter teeth do not leave on the machined surface of the roughings, since sliding on the crust has a negative effect on the cutter, accelerating cutting edge wear.
For the most common milling cases, it is recommended to perform roughing on steel with a cutting depth of 3-5 mm, and for steel and cast iron castings - with a cutting depth of 5-7 mm. For finishing milling, take a cutting depth of 0.5-1.0 mm.

Cutter diameter

The diameter of the cutter is selected mainly depending on the width of the milling IN and cutting depths t. In table 41 shows data for choosing cylindrical cutters, table. 42 - end mills and in table. 43 - disk cutters.

* Use prefabricated composite cutters in accordance with GOST 1979-52.

Let's consider the influence of cutter diameter on milling performance.
The diameter of the cylindrical cutter affects the thickness of the cut: the larger the cutter diameter D the thinner the cut is; with the same feed s tooth and milling depth t.
In Fig. 327 shows the cut obtained at the same milling depth t and submission s tooth, but with different cutter diameters. The cut obtained with a larger cutter diameter (Fig. 327, a) has a smaller thickness than the cut with a smaller one; cutter diameter (Fig. 327, b).

Since the specific pressure increases with decreasing thickness of the cut layer A Naib (see Table 38), it is more profitable to work with thicker sections, i.e., all other things being equal, with a smaller cutter diameter.
The diameter of the cutter affects the distance that the cutter must travel for one pass.
In Fig. 328 shows the path that the cutter must travel when processing a part of length L; in Fig. 329 - the path that the face mill must travel when asymmetrically milling a workpiece of length L; in Fig. 330 - the path that a cake cutter must travel when symmetrically milling a workpiece of length L.

Infeed size l(plunge path):
when working with cylindrical, disk, cutting and shaped cutters depends on the diameter of the cutter D milling depths t and is expressed by the formula

when working with face and end mills for asymmetrical milling, depends on the diameter of the cutter D milling width IN and is expressed by the formula

when working with face mills for symmetrical milling, depends on the diameter of the cutter D milling width IN and is expressed by the formula

Overtravel value l 1 is selected depending on the cutter diameter within 2-5 mm.
Consequently, to reduce the cutting path and overtravel of the cutter, i.e., to reduce the idle speed of the machine, it is advisable to choose a smaller cutter diameter.
At the end of the book, in appendices 2 and 3, tables are given for the values ​​of the infeed and overtravel paths of cutters.
The diameter of the cutter affects the value torque: the smaller the diameter of the cutter, the less torque must be imparted to the machine spindle.
Thus, choosing a cutter with a smaller diameter would seem to be more appropriate. However, with a decrease in the diameter of the cutter, it is necessary to choose a thinner, i.e., less rigid milling mandrel, therefore it is necessary to reduce the load on the mandrel, i.e., reduce the cross-section of the cut layer.

Innings

Feed at roughing depends on the material being processed, the material of the cutting part of the cutter, the drive power of the machine, the rigidity of the machine - fixture - tool - part system, the processing dimensions and the sharpening angles of the cutter.
Feed at finishing depends on the class of surface cleanliness indicated on the drawing of the part.
The main initial value when choosing a feed for rough milling is the feed s tooth.
For face milling cutters, selectable feed s The tooth has a way of installing the cutter relative to the workpiece, which determines the angle of meeting of the cutter tooth with the workpiece and the thickness of the cut chips when the cutter tooth enters and exits contact with the workpiece. It has been established that for a carbide end mill, the most favorable conditions for cutting a tooth into a workpiece are achieved when the cutter is positioned relative to the workpiece, as in Fig. 324, in, i.e. when the cutter is displaced relative to the workpiece by an amount WITH = (0,03 - 0,05)D. This displacement of the cutter axis makes it possible to increase the feed per tooth against the feed during symmetrical milling (Fig. 324, a) of cast iron and steel by two times or more.
In table 44 shows the recommended feed rates for rough milling with carbide end mills for these two cases.

Notes 1. The given values ​​of roughing feeds are calculated for working with standard cutters. When working with non-standard cutters with an increased number of teeth, feed values ​​should be reduced by 15 - 25%.
2. During the initial period of operation of the cutter until wear equals 0.2-0.3 mm, the cleanliness of the machined surface during fine milling is reduced by approximately one class.

Note. Use larger feeds for smaller cutting depths and processing widths, smaller feeds for larger processing depths and widths.

Note. Feeds are given for the rigid system machine - fixture - tool - part.

When face milling with carbide cutters, the feed rate is also affected by the leading angle φ. Feeds given in table. 44, designed for cutters with φ = 60 - 45°. Reducing the leading angle φ to 30° allows you to increase the feed by 1.5 times, and increasing the angle φ to 90° requires a reduction in feed by 30%.
Feed rates for finishing with carbide cutters, given in table. 44, are given for one revolution of the cutter, since the feeds per tooth are too small. Feeds are given depending on the cleanliness class of the treated surface according to GOST 2789-59.
In table 45 shows the recommended feeds per cutter tooth for rough milling of planes with cylindrical, face and disk three-sided cutters made of P18 high-speed steel.
In table 46 shows the feed rates for finishing milling of planes with cylindrical cutters made of high-speed steel P18, and in table. 47 - for finishing milling of planes with face and disk three-sided cutters made of P18 high-speed steel. Due to the low feed rates per cutter tooth obtained during finishing milling, in Table. 46 and 47 show the feeds per revolution of the cutter.
It should be borne in mind that working with the feeds indicated in table. 44-47, makes it an indispensable condition for the presence of minimal runout of the cutter teeth (see Table 50).

Note. Feeds are given for a rigid system machine - fixture - tool - workpiece when machining with cutters with an auxiliary entering angle φ 1 = 2°; for cutters with φ 1 = 0, feeds can be increased by 50 - 80%.

TO category:

Milling work

Selection of rational milling modes

Choosing a rational milling mode on a given machine means that for the given processing conditions (material and grade of the workpiece, its profile and dimensions, processing allowance), it is necessary to select the optimal type and size of the cutter, grade of material and geometric parameters of the cutting part of the cutter, lubricating and cooling liquid and assign optimal values ​​for the following cutting mode parameters: B, t, sz. v, p, Ne, Tm.

From formula (32) it follows that the parameters B, t, sz and v have the same influence on the volumetric milling productivity, since each of them is included in the formula to the first degree. This means that if any of them is increased, for example, by a factor of two (with other parameters remaining unchanged), the volumetric productivity will also double. However, these parameters have far from the same influence on tool life (see § 58). Therefore, taking into account the tool life, it is more profitable, first of all, to choose the maximum permissible values ​​of those parameters that have a lesser effect on the tool life, i.e. in the following sequence: depth of cut, feed per tooth and cutting speed. Therefore, the selection of these cutting mode parameters when milling on this machine should begin in the same sequence, namely:

1. The cutting depth is assigned depending on the processing allowance, the requirements for surface roughness and machine power. It is advisable to remove the processing allowance in one pass, taking into account the power of the machine. Typically, the cutting depth during rough milling does not exceed 4-5 mm. When rough milling with carbide end mills (heads) on powerful milling machines, it can reach 20-25 mm or more. When finishing milling, the cutting depth does not exceed 1-2 mm.

2. The maximum feed allowed under processing conditions is assigned. When establishing the maximum permissible feeds, feeds per tooth that are close to “breaking” should be used.

The last formula expresses the dependence of feed per tooth on the depth of milling and the diameter of the cutter. The value of the maximum cut thickness, i.e. the value of the constant coefficient I c in formula (21), depends on the physical and mechanical properties of the material being processed \ (for a given type and design of the cutter). The values ​​of the maximum permissible feeds are limited by various factors:

a) during roughing - the rigidity and vibration resistance of the tool (with sufficient rigidity and vibration resistance of the machine), the rigidity of the workpiece and the strength of the cutting part of the tool, for example, a cutter tooth, insufficient volume of chip flutes, for example, for disk cutters, etc. So , the feed per tooth when rough milling steel with cylindrical cutters with insert knives and large teeth is selected in the range of 0.1-0.4 mm/tooth, and when processing cast iron up to 0.5 mm/tooth;

b) during finishing processing - surface roughness, dimensional accuracy, condition of the surface layer, etc. When finishing milling steel and cast iron, a relatively small feed per cutter tooth is assigned (0.05-0.12 mm/tooth).

3. The cutting speed is determined; Since it has the greatest influence on the durability of the tool, it is selected based on the standard of durability accepted for a given tool. The cutting speed is determined by formula (42) or from tables of cutting mode standards depending on the depth and width of milling, feed per tooth, cutter diameter, number of teeth, cooling conditions, etc.

4. The effective cutting power Ne for the selected mode is determined using the tables of standards or formula (39a) and compared with the power of the machine.

5. Based on the set cutting speed (u, or i^), the nearest level of machine spindle rotation speed from among those available on this machine is determined using formula (2) or according to the schedule (Fig. 174). A horizontal line is drawn from the point corresponding to the accepted cutting speed (for example, 42 m/min), and a vertical line is drawn from the point with the mark of the selected cutter diameter (for example, 110 mm). At the point of intersection of these lines, the nearest level of spindle speed is determined. So, in the example shown in Fig. 172, when milling with a cutter with a diameter of D = 110 mm with a cutting speed of 42 m/min, the spindle rotation speed will be equal to 125 rpm.

Fig. 174 Nomogram of cutter rotation speed

6. The minute feed is determined using formula (4) or according to the schedule (Fig. 175). Thus, when milling with a cutter D = 110 mm, z = 10 at sz = 0.2 mm/tooth and n = 125 rpm, the minute feed according to the schedule is determined as follows. From the point corresponding to the feed per tooth sg = 0.2 mm/tooth, draw a vertical line until it intersects with an inclined line corresponding to the number of cutter teeth r = 10. From this point we draw a horizontal line until it intersects with an inclined line corresponding to the accepted spindle speed l = 125 rpm. Next, draw a vertical line from the resulting point. The point of intersection of this line with the lower scale of minute feeds available on a given machine determines the nearest step of minute feeds.

7. Machine time is determined.

Machine time. The time during which the chip removal process occurs without the direct participation of the worker is called machine time (for example, for milling the workpiece plane from the moment the mechanical longitudinal feed is turned on until it is turned off).

Rice. 1. Nomogram of minute feed

Increasing productivity when processing on metal-cutting machines is limited by two main factors: the production capabilities of the machine and the cutting properties of the tool. If the production capabilities of the machine are small and do not allow full use of the cutting properties of the tool, then the productivity of such a machine will be only a small part of the possible productivity with maximum use of the tool. In the case when the production capabilities of the machine significantly exceed the cutting properties of the tool, the maximum possible productivity with a given tool can be achieved on the machine, but the capabilities of the machine will not be fully used, i.e. the power of the machine, the maximum permissible cutting forces, etc. d. Optimal from the point of view of productivity and economical use of the machine and tool will be those cases when the production capacity of the machine and the cutting properties of the tool coincide or are close to each other.

This condition is the basis for the so-called production characteristics of machines, which were proposed and developed by prof. A.I. Kashirin. The production characteristic of a machine is a graph of the capabilities of the machine and the tool. Production characteristics make it easier and simpler to determine optimal cutting conditions when processing on a given machine.

The cutting properties of a particular tool are characterized by the cutting modes that are allowed during the processing process. The cutting speed under given processing conditions can be determined by formula (42, a). In practice, it is found from the table of cutting modes, which are given in the reference books of a standardizer or technologist. However, it should be noted that standards for cutting modes both for milling and for other types of processing are developed based on the cutting properties of the tool for various processing cases (type and size of the tool, type and grade of material of the cutting part, material being processed, etc.), and are not associated with the machines on which the processing will be carried out. Since the production capabilities of different machines are different, the practically feasible optimal processing mode on different machines will be different for the same processing conditions. The production capabilities of machine tools depend primarily on the effective power of the machine, rotation speed, feeds, etc.

Rice. 2. Plunge and overtravel

The production characteristics of milling cutters for the case of cutting milling cutters were developed by Prof. A. I. Kashirin and the author.

The principle of constructing the production characteristics of milling machines (nomograms) for working with end mills is based on a joint graphical solution of two equations that characterize the dependence of the cutting speed vT according to formula (42) with -Bz' = const, on the one hand, and the cutting speed and permissible power machine, on the other. The cutting speed vN can be determined by the formula

Rice. 3. Production characteristics of the 6P13 cantilever milling machine

Let us determine the cutting modes for rough milling of a flat surface on a milling machine in the following sequence:

1.4.1. Depth of cutt , mm, determined depending on the type

the cutter used, the configuration of the machined

surface and the type of equipment.

1.4.2. Assign submissionS , mm/rev

When milling, the feed per tooth is distinguished S z , mm/tooth, feed per cutter revolution S and a minute feed S m, mm/min, which are in the following ratio:

, (9.28)

Where n– cutter rotation speed, min -1;

z– number of cutter teeth.

The initial feed rate for rough milling is the feed rate per tooth S z, the value of which for various cutters and cutting conditions is given in Table 9.13 and Table 9.14 of Appendix E.

Select the model of the milling machine on which milling will be performed, taking into account the specified power of the machine.

, (9.29)

Where D– cutter diameter, mm;

S z– feed, mm/tooth;

t– processing depth, mm;

IN– processing width, mm;

z– number of cutter teeth;

WITH v , q,m, – coefficients whose values ​​are determined

x,at, u,p according to table 9.15 of Appendix D;

T– tool life period, min, is determined

according to table 9.16 of Appendix D;

TO v– correction factor for speed,

taking into account actual cutting conditions,

determined by the formula:

, (9.30)

Where K mv– coefficient taking into account quality

processed material is determined by

Table 9.3 of Appendix D;

K nv– coefficient taking into account the state of the surface

blanks:

For steel workpiece K nv = 0,9;

For cast iron workpiece K nv =0,8;

For copper billet K nv =0,9;

K And v– coefficient taking into account the influence of the material

tool, determined according to table 9.5

applications D.

1.4.4. Determine and adjust the cutter speedn , min -1, according to the recommendations of paragraph 1.2.4.

1.4.6. Determine the value of the minute feedS m , mm/min:

, (9.31)

and adjust the value of the received feed S m according to the passport data of the selected machine. Taking into account the adjusted value S m adjust feed value S z, mm/tooth:

, (9.32)

Where n– cutter rotation speed available on the machine, min -1;

z– number of cutter teeth.

1.4.7. Determine the main component of the cutting force during milling - circumferential forceR z , N, according to the formula:

, (9.33)

Where D– cutter diameter, mm;

S z– feed, mm/tooth;

t– processing depth, mm;

IN– processing width, mm;

z– number of cutter teeth;

n– cutter rotation speed available on the machine, min -1.

WITH p , q,m, – coefficients whose values ​​are determined

x,at, And,w according to table 9.17 of Appendix D;

K m p – correction factor, which

determined according to Table 9.7 of Appendix D;

, (9.34)

Where D– cutter diameter, mm;

R z– the main component of the cutting force during milling, N

1.4.9. Determine cutting powerNp, kW, according to the formula:

,(9.35)

Where Pz– main component of the cutting force, N;

V– actual cutting speed, m/min.

Obtained cutting power value N p compare with the power of the electric motor of the selected machine according to the recommendations set out in paragraph 1.2.7.

1.4.10. Determine main timeT 0 , min.

MINISTRY OF AGRICULTURE AND FOOD OF THE RUSSIAN FEDERATION

DEPARTMENT OF PERSONNEL POLICY AND EDUCATION

Moscow State Agricultural Engineering University

named after V.P. Goryachkina

Bagramov L.G. Kolokatov A.M.

CALCULATION OF CUTTING MODES

Part I - Face Milling

MOSCOW 2000

Calculation of cutting conditions for face milling.

Compiled by: L.G. Bagramov, A.M. Kolokatov - MSAU, 2000. - XX p.

Part I of the guidelines provides general theoretical information about milling and outlines the sequence of operations for calculating the cutting mode for face milling based on reference data. The methodological instructions can be used when doing homework, in coursework and diploma design by students of the faculties of TS in AIC, PRIMA and Engineering Pedagogical, as well as when carrying out practical and research work.

Fig.9, table XX, list of libraries. - XX titles.

Reviewer: Bocharov N.I. (MSAU)

Ó Moscow State Agricultural Engineering

University named after V.P. Goryachkina. 2000.

1. GENERAL INFORMATION 1.1. Elements of cutting theory

Milling is one of the most common and highly productive methods of machining by cutting. Processing is carried out with a multi-bladed tool - a milling cutter.

When milling, the main cutting movement D r is the rotation of the tool, the feed movement D S is the movement of the workpiece (Fig. 1), on rotary milling and drum milling machines the feed movement can be carried out by rotating the workpiece around the axis of a rotating drum or table, in some cases the movement feeds can be carried out by moving the tool (copy milling).

Horizontal, vertical, inclined planes, shaped surfaces, ledges and grooves of various profiles are processed by milling. A feature of the cutting process during milling is that the teeth of the cutter are not in contact with the machined surface all the time. Each cutter blade sequentially enters the cutting process, changing the thickness of the cut layer from the largest to the smallest, or vice versa. Several cutting edges can be present during the cutting process at the same time. This causes shock loads, uneven process flow, vibrations and increased tool wear, increased loads on the machine.

When processing with cylindrical cutters (cutting edges are located on a cylindrical surface), two processing methods are considered (Fig. 2.) depending on the direction of movement of the workpiece feed:

Up-milling, when the direction of movement of the cutting edge of the cutter during the cutting process is opposite to the direction of feed movement;

Climb milling, when the direction of movement of the cutting edge of the cutter during the cutting process coincides with the direction of feed movement.

During up milling, the load on the tooth increases from zero to maximum, the forces acting on the workpiece tend to tear it away from the table and raise the table. This increases the gaps in the AIDS system (machine - fixture - tool - part), causes vibrations, and deteriorates the quality of the machined surface. This method is well applicable for processing workpieces with a crust, cutting from under the crust, tearing it off, thereby greatly facilitating cutting. The disadvantage of this method is the large sliding of the blade along the pre-treated and riveted surface. If there is some rounding of the cutting edge, it does not immediately enter the cutting process, but initially slips, causing high friction and wear of the tool along the rear surface. The smaller the thickness of the cut layer, the greater the relative amount of slipping, the greater the cutting power is spent on harmful friction.

With down milling, this is not a drawback, but the tooth starts working from the greatest thickness of the cut layer, which causes large impact loads, but eliminates the initial slipping of the tooth, reduces cutter wear and surface roughness. The forces acting on the workpiece press it against the table, and the table against the bed guides, which reduces vibrations and increases processing accuracy.

1.2. Design of cutters.

Milling tools are cutters (from the French la frais - strawberry), which are a multi-edge tool, the blades of which are arranged sequentially in the direction of the main cutting movement, designed for processing with a rotary main cutting movement without changing the radius of the trajectory of this movement and with at least one feed movement , the direction of which does not coincide with the axis of rotation.

There are cutters:

in shape - disk, cylindrical, conical;

by design - solid, composite, prefabricated and mounted, tail;

according to the cutting edge material used - high-speed and carbide;

according to the location of the blades - peripheral, end and peripheral-end;

in the direction of rotation - right-handed and left-handed;

according to the shape of the cutting edge - profile (shaped and rolling), straight, helical, with a screw tooth;

according to the shape of the back surface of the tooth - backed and non-backed,

by purpose - end, corner, slotted, keyed, shaped, threaded, modular, etc.

Let's consider the elements and geometry of the cutter using the example of a cylindrical cutter with helical teeth (Fig. 3.).

The cutter is distinguished by the front surface of the blade A γ, the main cutting edge K, the auxiliary cutting edge K", the main rear surface of the blade A α, the auxiliary rear surface of the blade A" α, the top of the blade, the cutter body, the cutter tooth, the back of the tooth, and the chamfer.

In the coordinate planes of the static coordinate system (Fig. 4.), the geometric parameters of the cutter are considered, among which γ, α are the front and back angles in the main secant plane, γ H is the front angle in the normal secant plane, ω is the angle of inclination of the tooth.

The rake angle γ facilitates the formation and flow of chips, the main relief angle α helps to reduce the friction of the flank surface on the machined surface of the workpiece. For non-backed teeth, the rake angle is within the range γ = 10 o...30 o, the rear angle α = 10 o...15 o depending on the material being processed.

For a backed tooth, the back surface follows an Archimedes spiral, which ensures a constant cross-section profile for all tool sharpenings. The backed tooth is ground only along the front surface and, due to its complexity, is performed only with a profile tool (shaped and running), i.e. the shape of the cutting edge is determined by the shape of the machined surface. The front angle of the backed teeth is, as a rule, equal to zero, the rear angle has the values ​​α = 8 o...12 o.

The angle of inclination of the teeth ω ensures a smoother entry of the blade into the cutting process compared to straight teeth and gives a certain direction to the flow of chips.

An end mill tooth has a cutting blade with a more complex shape. The cutting edge consists (Fig. 5.) of the main, transition and auxiliary, having a main plan angle φ, a plan angle of the transition cutting edge φ p and an auxiliary plan angle φ 1. The geometric parameters of the cutter are considered in a static coordinate system. Plane angles are angles in the main plane P vc. The main angle in the plan φ is the angle between the working plane P Sc and the cutting plane P nc The value of the main angle in the plan is determined based on the cutting conditions as for a turning tool, at φ=0˚ the cutting edge becomes only an end edge, and at φ=90˚ it becomes peripheral. The auxiliary planing angle φ 1 is the angle between the working plane P Sc and the auxiliary cutting plane P" nc, it is 5°...10°, and the planing angle of the transition cutting edge is half of the main planing angle. Transitional cutting blade increases tooth strength.

The wear of cutters is determined, just as during turning, by the amount of wear on the flank surface. For a high-speed cutter, the permissible width of a worn strip along the rear surface is 0.4...0.6 mm for roughing steels, 0.5...0.8 mm for cast irons, and 0.15...0 for semi-finishing steels. .25 mm, cast iron - 0.2...0.3 mm. For a carbide cutter, the permissible wear on the flank surface is 0.5...0.8 mm. The durability of a cylindrical high-speed cutter is T = 30...320 min, depending on the processing conditions, in some cases it reaches 600 minutes, the durability of a carbide cutter is T = 90...500 min.

There are three types of milling - peripheral, face and peripheral - face. The main planes and surfaces processed on cantilever milling machines (Fig. 6.) include:

horizontal planes; vertical planes; inclined planes and bevels; combined surfaces; ledges and rectangular grooves; shaped and corner grooves; dovetail grooves; closed and open keyways; grooves for segment keys; shaped surfaces; cylindrical gears using the copying method.

Horizontal planes are processed with cylindrical (Fig. 6. a) on horizontal milling machines and end mills (Fig. 6. b) on vertical milling machines. Since an end mill has a larger number of teeth involved in cutting at the same time, processing with them is more preferable. Cylindrical cutters usually process planes up to 120 mm wide.

Vertical planes are processed with end mills on horizontal machines and end mills on vertical machines (Fig. 6. c, d).

Inclined planes are processed with face and end mills on vertical machines with rotation of the spindle axis (Fig. 6. e, f), and on horizontal machines with corner cutters (Fig. 6. g).

Combined surfaces are processed with a set of cutters on horizontal machines (Fig. 6. h).

Shoulders and rectangular grooves are processed with disk (on horizontal) and end (on vertical) cutters (Fig. 6. i, j), while end cutters allow high cutting speeds, since a larger number of teeth are simultaneously involved in the work. When machining grooves, disc cutters are preferable.

Shaped and corner grooves are processed on horizontal machines with shaped, single- and double-angled cutters (Fig. 6. l, m).

Dovetail and T-slots are machined on vertical milling machines, usually in two passes, first using an end mill (or on a horizontal milling machine with a disk cutter) to machine a rectangular groove across the width of the top. After this, the groove is finally processed with a single-angle end cutter and a special T-shaped (Fig. 6. n, o) cutter.

Closed keyways are machined with end mills, and open ones with keyways on vertical machines (Fig. 6. p, p).

The grooves for segment keys are machined on horizontal milling machines using disk cutters (Fig. 6. c).

Shaped surfaces of an open contour with a curved generatrix and a straight guide are processed on horizontal and vertical machines with shaped cutters (Fig. 6.t).

Face milling is the most common and productive method of processing flat surfaces of parts in serial and mass production.

2. FACE MILLING. 2.1. Basic types and geometry of end mills.

In most cases, for processing open and recessed planes, end mills with peripheral blades are used (Fig. 7.), i.e. working on the peripheral-end principle. The designs of end mills are standardized, the main types of which are given in Table 1 /GOST ____-__, ____-__, ____-__, ____-__, ____-__, ____-__ /.

When processing planes with these cutters, the main work of removing allowance is performed by the cutting edges located on the conical and cylindrical surface. The cutting edges located at the end act as if they clean the surface, so the roughness of the machined surface is less than when milling with cylindrical cutters.

In Fig. 7. The geometric parameters of the end mill are shown /GOST 25762-83/. An end mill tooth has two cutting edges: a main edge and a secondary one.

In the main plane P v the plan angles considered are: the main plan angle j, the auxiliary plan angle j 1 and the vertex angle ε. The main angle j is the angle between the cutting plane P n and the working plane P S . With a decrease in the leading angle at a constant feed per tooth and a constant depth of cut, the thickness of the cut decreases and the width increases, as a result of which the durability of the cutter increases. However, the operation of a cutter with a small cutting angle (j £ 20 0) causes an increase in the radial and axial components of the cutting forces, which, if the AIDS system is not rigid enough, leads to vibrations of the workpiece and the machine. Therefore, for carbide end mills with a rigid system and with a depth of cut t = 3...4 mm, the angle j = 10...30 0 is taken. With normal system rigidity - j = 45...60 0; usually take j = 60 0 . The auxiliary angle j 1 for end mills is taken equal to 2...10 0. The smaller this angle, the lower the roughness of the machined surface.

In the main cutting plane P τ the front angle g and the main back angle a are considered. The rake angle g is the angle between the main plane P v and the front surface A γ, the main relief angle a is the angle between the cutting plane P n and the main rear surface A α.

Rake angle g for carbide end mills g = (+10 0)...(-20 0).

Main relief angle a for carbide end mills a = 10...25 0.

In the cutting plane, the inclination angle of the main cutting edge l is considered. This is the angle between the cutting edge and the main plane P v . It affects the tooth strength and the durability of the cutter. For carbide end mills, the angle l is recommended to range from +5 0 to +15 0 when processing steel and from -5 0 to +15 0 when processing cast iron.

The inclination angle of the helical teeth w ensures more uniform milling and reduces the instantaneous cutting width when plunging. This angle is selected within 10...30 0.

2.2. Selecting an end mill 2.2.1. Choosing a cutter design.

When choosing a cutter design (type), it is preferable to use prefabricated cutter designs with non-grindable carbide inserts. Mechanical fastening of the inserts makes it possible to rotate them in order to update the cutting edge and allows the use of cutters without regrinding. After the plate is completely worn out, it is replaced with a new one. The manufacturer supplies each cutter with 8...10 sets of spare plates. The entire set of plates can be replaced directly on the machine, while the time required to replace 10...12 knives does not exceed 5...6 minutes.

2.2.2. Selection of cutting part material.

Milling cutters for working at low cutting speeds and low feeds are made from high-speed and alloy steels R18, KhG, KhV9, 9KhS, KhVG, KhV5. Milling cutters for processing heat-resistant and stainless alloys and steels are made from high-speed steels R9K5, R9K10, R18F2, R18K5F2, and when milling with impacts - from steel grade R10K5F5.

Brands of hard alloys are selected depending on the material being processed and the nature of the processing (Table 5). For finishing processing, a hard alloy with a lower cobalt content and a higher content of carbides is used (VK2, VK3 T15K6, etc.), and for roughing - with a high cobalt content, which imparts a certain ductility to the material and promotes better performance under uneven and impact loads (VK8, VK10, T5K10, etc.).

2.2.3. Selecting the type and diameter of the cutter.

Standard cutter diameters (GOST 9304-69, GOST 9473-80, GOST 16222 - 81, GOST 16223 - 81, GOST 22085 - 76, GOST 22086 - 76, GOST 22087 - 76, GOST 22088 - 76, GOST 26595 - 85), are given in tables 1...4, their designations (for right-handed end mills) are in tables 2, 3 and 4. Left-handed cutters are manufactured to special order of the consumer.

Types of end mills are selected according to the processing conditions from Table 1. The dimensions of the cutter are determined by the dimensions of the surface being processed and the thickness of the layer being cut. The diameter of the cutter, in order to reduce the main technological time and the consumption of tool material, is selected taking into account the rigidity of the technological system, the cutting pattern, the shape and size of the workpiece being processed.

When face milling, in order to achieve cutting conditions that provide the greatest productivity, the cutter diameter D must be greater than the milling width B: D = (1.25...1.5) B

2.2.4. Selection of geometric parameters

2.3. Selecting a milling pattern

The milling pattern is determined by the location of the axis of the workpiece end mill relative to the center line of the machined surface (Fig. 8.). There are symmetrical and asymmetrical face milling /5/.

Symmetrical milling is called milling in which the axis of the end mill passes through the center line of the machined surface (Fig. 8.a).

Asymmetrical milling is called milling in which the axis of the end mill is shifted relative to the center line of the machined surface (Fig. 8.b, 8.c).

Symmetrical face milling is divided into complete, when the diameter of the cutter D is equal to the width of the machined surface B, and incomplete, when D is greater than B (Fig. 8.a).

Asymmetrical face milling can be up or down milling. The classification of milling into these varieties is done by analogy with milling a plane with a cylindrical cutter.

With asymmetrical counter face milling (Fig. 8.b), the thickness of the cut layer a changes from a certain small value (depending on the displacement value) to the largest a max =S z, and then decreases slightly. The displacement of the cutter tooth beyond the machined surface from the side of the tooth starting cutting is usually taken within the range C 1 = (0.03...0.05) D

With asymmetrical down-milling (Fig. 8.c), the cutter tooth begins to work with a cut thickness close to the maximum. The displacement of the cutter tooth beyond the machined surface from the side of the tooth finishing cutting is assumed to be insignificant, close to zero) C 2 ≈ 0.

When processing cast iron workpieces, in many cases, the diameter of the cutter is less than the width of the surface being machined, since cast iron workpieces, due to the fragility of cast iron, especially in the manufacture of body parts, are made of large dimensions.

Face milling of cast iron workpieces at B< D ф рекомендуется проводить при симметричном расположении фрезы.

When face milling steel workpieces, their asymmetrical arrangement relative to the cutter is mandatory, in this case:

For workpieces made of structural carbon and alloy steels and workpieces with a crust (rough milling), the workpieces are shifted in the direction of the cutter tooth cutting in (Fig. 8.b), which ensures the start of cutting at a small thickness of the cut layer;

For workpieces made of heat-resistant and corrosion-resistant steels and during finishing milling, the workpiece shifts towards the cutter tooth exiting cutting (Fig. 8.c), which ensures that the tooth exits cutting with the minimum possible thickness of the cut layer.

Failure to comply with these rules leads to a significant reduction in the durability of the cutter /5/.

2.4. Assignment of cutting mode

The elements of the cutting mode during milling include (Fig. 9.):

Depth of cut;

Cutting speed;

Milling width.

Depth of cut t is defined as the distance between the points of the machined and machined surfaces located in the cutting plane and measured in the direction perpendicular to the direction of feed movement. In some cases, this value can be measured as the difference in the distances between the points of the machined and machined surfaces to the machine table or to some other constant base parallel to the direction of feed movement.

The depth of cut is selected depending on the processing allowance, power and rigidity of the machine. We must strive to carry out rough and semi-finish milling in one pass, if the power of the machine allows it. Typically the cutting depth is 2...6 mm. On powerful milling machines, when working with face mills, the cutting depth can reach 25 mm. When the machining allowance is more than 6 mm and with increased requirements for the surface roughness, milling is carried out in two transitions: roughing and finishing.

During the finishing transition, the cutting depth is taken within the range of 0.75...2 mm. Regardless of the height of microroughnesses, the cutting depth cannot be less. The cutting edge has a certain radius of rounding, which increases as the tool wears out; at a small depth of cut, the material of the surface layer is crushed and undergoes plastic deformation. In this case, no cutting occurs. As a rule, with small processing allowances and the need for finishing processing (roughness value R a = 2...0.4 µm), the cutting depth is taken within 1 mm.

For small cutting depths, it is advisable to use cutters with round plates (GOST 22086-76, GOST 22088-76). For cutting depths greater than 3...4 mm, cutters with six-, five- and tetrahedral inserts are used (Table 2).

When choosing the number of transitions, it is necessary to take into account the requirements for the roughness of the machined surface:

Rough milling - R a = 12.5...6.3 µm (3...4 class);

Finish milling - R a = 3.2...1.6 µm (5...6 class);

Fine milling - R a = 0.8...0.4 µm (grade 7...8).

To ensure finishing processing, it is necessary to carry out roughing and finishing transitions; the number of working strokes during roughing is determined by the size of the allowance and the power of the machine. The number of working strokes during finishing is determined by the requirement of surface roughness.

In production conditions, when roughing and finishing are required, they are divided into two separate operations. This is due to the following considerations.

Roughing and finishing machining are carried out using different materials for the cutting part of the cutter and at different cutting speeds, which would cause an unreasonably large amount of time to readjust the machine if these transitions are performed in one operation.

Roughing leads to high vibrations and uneven and alternating loads, this, in turn, leads to rapid wear of the machine and loss of processing accuracy.

Roughing leads to the formation of large amounts of chips and abrasive dust, which requires special measures for waste removal. As a rule, machines for roughing are located separately from machines performing final processing - finishing and thinning.

Feed during milling is the ratio of the distance traveled by the workpiece point in question in the direction of feed movement to the number of revolutions of the cutter or to the part of the revolution of the cutter corresponding to the angular pitch of the teeth.

Thus, when milling, we consider the feed per revolution S o (mm/rev) - the movement of the considered point of the workpiece in the time corresponding to one revolution of the cutter, and the feed per tooth S z (mm/tooth) - the movement of the considered point of the workpiece in the time corresponding to the rotation cutters for one angular tooth pitch.

In addition, the feed speed v s is also considered (previously defined as the minute feed, and in old literature and on some machines this term is still used), measured in mm/min. The feed motion speed is the distance traveled by the workpiece point in question along the path of that point in the feed motion per minute. This value is used on machines to adjust to the required mode, since on milling machines the feed movement and the main cutting movement are not kinematically related to each other.

Using the ratio of feed and cutting speeds helps to correctly determine the values ​​of S o and S z . Using the dependencies: S o = S z · z, v s = S o · n where z is the number of cutter teeth, n is the number of cutter revolutions (rpm), we determine v s = S o · n = S z · z · n.

The initial value for rough milling is the feed per tooth S z, since it determines the rigidity of the cutter tooth. The feed rate during roughing is chosen to be as high as possible. Its value may be limited by the strength of the machine feed mechanism, the strength of the cutter tooth, the rigidity of the AIDS system, the strength and rigidity of the mandrel, and other considerations. When finishing milling, the decisive factor is the feed per revolution of the cutter S o , which affects the roughness of the machined surface.

Milling width B (mm) - the size of the machined surface, measured in the direction parallel to the cutter axis - for peripheral milling, and perpendicular to the direction of feed movement - for face milling. The milling width is determined by the smaller of two values: the width of the workpiece being processed and the length or diameter of the cutter.

The permissible (calculated) cutting speed is determined by the empirical formula

where Cv is a coefficient characterizing the material of the workpiece and cutter;

T - cutter life (min);

t - cutting depth (mm);

S z - feed per tooth (mm/tooth);

B - milling width (mm);

Z - number of cutter teeth;

q, m, x, y, u, p - exponents;

k v - general correction factor for changed processing conditions.

The values ​​of C v q, m, x, y, u, p are given in Table 11.

The average values ​​of the service life of end mills for the diameter of the cutter are as follows:

Table 2.2.4. - 1

Cutter diameter (mm)	40...50	65...125	160...200	250...315	400...650
Durability (min)	120	180	240	300	800

General correction factor K v . Any empirical formula is determined subject to the constancy of certain factors. In this case, these factors are the physical and mechanical properties of the workpiece and the material of the cutting part of the tool, the geometric parameters of the tool, etc. In each specific case, these parameters change. To take these changes into account, a general correction factor K v is introduced, which is the product of individual correction factors, each of which reflects a change, relative to the original, individual parameters /5/:

K v = K m v K pv K иv K j v ,

K m v - coefficient taking into account the physical and mechanical properties of the material being processed, tables 12, 13;

K pv - coefficient taking into account the state of the surface layer of the workpiece, table 14;

K иv - coefficient taking into account instrumental material, table 15;

K j v - coefficient taking into account the value of j - the main angle in the plan,

Table 2.2.4. - 2

j
	1,6	1,25	1,1	1,0	0,93	0,87

Knowing the permissible (design) cutting speed v, determine the design speed of the cutter

where n is the number of revolutions of the cutter, min -1; D - cutter diameter, mm.

According to the machine’s passport, select a speed level at which the number of revolutions of the cutter will be equal to or less than the calculated one, i.e. n f £ n, where n f is the actual number of revolutions of the cutter that should be installed on the machine. It is allowed to use a speed level at which the increase in the actual number of revolutions relative to the calculated one will be no more than 5%. Based on the selected number of revolutions of the machine spindle, the actual cutting speed is determined.

and determine the feed rate (minute feed):

v S (S m) = S z z n f = S o n f (mm/min.)

Then, according to the machine’s passport, the most suitable value is selected - the closest value less than or equal to the calculated value.

2.5. Checking the selected cutting mode

The selected cutting mode is checked by the use of power on the machine spindle and the force required to implement the feed movement.

The power spent on cutting must be less than or equal to the power on the spindle:

where N r - effective cutting power, kW;

N sp - permissible power on the spindle, determined by the drive power, kW.

The machine drive is a set of mechanisms from the source of motion to the working element. The drive of the main cutting movement is a set of mechanisms from the electric motor to the machine spindle, and its power is determined based on the power of the electric motor and losses in the mechanisms.

The power on the spindle is determined by the formula

N sh = N e h,

where N e is the power of the electric motor driving the main cutting movement, kW, h is the efficiency of the machine drive mechanisms, h = 0.7 ... 0.8.

The torque on the machine spindle is determined by the formula:

where P z is the main component (tangential) of the cutting force, N; D - cutter diameter, mm.

when milling is determined by the formula

where C p is a coefficient characterizing the material being processed and other conditions;

K p - general correction factor, which is the product of coefficients reflecting the state of individual parameters that affect the amount of cutting force,

K р = K m р K vр K g р K j v ,

K m r - coefficient taking into account the properties of the material of the workpiece being processed (Table 17);

K vр - coefficient taking into account the cutting speed (Table 18);

K g r - coefficient taking into account the value of the front angle g (Table 19);

K j r - coefficient taking into account the magnitude of the angle in plan j (Table 19).

The values ​​of the coefficient C p and the exponents x, y, u, q, w are given in Table 16.

The magnitude of the radial component of the cutting force Р y can be determined by the relation Р y ≈ 0.4 Р z.

If the condition N r £ N sh is not met, then it is necessary to reduce the cutting speed or change other cutting parameters.

When milling, the representation of the cutting force by the vertical P in and horizontal P g components is of great importance. The horizontal component of the cutting force P r represents the force that must be applied to ensure the feed movement; it must be less than (or equal to) the greatest force allowed by the longitudinal feed mechanism of the machine:

P g £ P add, N.

where P additional is the maximum force allowed by the longitudinal feed mechanism of the machine (N), taken from the machine’s passport data (Table 20).

The horizontal component of the cutting force is determined from the relationships below and depends on the type of face milling /5/:

For symmetrical milling - P g = (0.3...0.4) P z;

With an asymmetrical counter - P g = (0.6...0.8) P z;

With an asymmetrical tailwind - P g = (0.2...0.3) P z;

If the condition P g £ P add is not met, it is necessary to reduce the cutting force P z by reducing the feed per tooth S z and, accordingly, the feed speed v S (minute feed S m).

2.6. Calculation of operation time and equipment use

Piece time T piece - the time spent on performing an operation is defined as a time interval equal to the ratio of the cycle of a technological operation to the number of simultaneously manufactured products and is calculated as the sum of the components

T pcs = T o + T vsp + T obs + T dept, (min)

where T o is the main time, this is the part of the piece time spent on changing and subsequently determining the state of the subject of labor, i.e. time of direct impact of the tool on the workpiece;

T vsp - auxiliary time, this is part of the piece time spent on performing the techniques necessary to ensure a direct impact on the workpiece.

T obs - workplace maintenance time, this is part of the piece time spent by the contractor on maintaining technological equipment in working condition and caring for them and the workplace. Workplace maintenance time consists of organizational maintenance time (inspection and testing of the machine, laying out and cleaning of tools, lubrication and cleaning of the machine) and maintenance time (adjustment and adjustment of the machine, change and adjustment of cutting tools, dressing of grinding wheels, etc.) ;

T department - time for personal needs, this is part of the piece time spent by a person on personal needs and, in case of tedious work, on additional rest;

2.6.1. Main time

The main time during milling is equal to the ratio of the length of the path traveled by the cutter during the number of working strokes to the feed speed, and is determined by the formula

- with symmetrical incomplete (for the case in Fig. 2a):

With an asymmetrical counter (for the case in Fig. 2b):

- with an asymmetrical tailwind (for the case in Fig. 2c):

where D is the cutter diameter, mm; B - workpiece width, mm; C 1 - the amount of displacement of the cutter relative to the end of the workpiece (Fig. 2b).

2.6.2 Auxiliary time.

This time includes the time spent on installation, securing, and removal of the workpiece (Table 21), time spent on controlling the machine when preparing the working stroke (Table 22), and taking measurements during processing (Table 23).

2.6.3. Operational time.

The sum of main and auxiliary time is called operational time:

T op = T o + T aux.

Operational time is the main component of piece time.

2.6.4. Time for workplace maintenance and time for personal needs

Time for workplace maintenance and time for personal needs are often taken as a percentage of operational time:

T obs = (3...8%) T op; T dep = (4...9%) T op; T obs + T dep ≈ 10% T op.

2.6.5. Piece - calculation time

To determine the standard time - the time for performing a certain amount of work in specific production conditions by one or more workers, it is necessary to determine the piece - calculation time T shk, which includes, in addition to the piece time, also the time for preparing workers and means of production to perform a technological operation and bringing them to their original state after its completion - preparatory - final time T pz. This time is necessary to receive the task, devices, equipment, tools, install them, set up the machine to perform the operation, remove all equipment and hand it over (Table 24). In the piece-calculation time, preparatory-final time is included as its share per workpiece. The greater the number of workpieces n is processed from one machine setup (from one installation, in one operation), the smaller the part of the preparatory - final time is included in the piece-costing time.

The estimated number of machines (Z) to perform a certain operation is calculated using the formula

where T pcs - piece time, min; P - program for completing parts per shift, pcs.;

T cm - operating time of the machine per shift, hours. In calculations, the operating time of the machine per shift is T cm = 8 hours; in real conditions at each enterprise, this time may be taken differently.

2.6.7. Technical and economic efficiency.

The assessment of the technical and economic efficiency of a technological operation is carried out according to a number of coefficients, including: the main time coefficient and the machine power utilization coefficient /7, 8, 9/.

The main time coefficient K o determines its share in the total time spent on performing the operation

where Ko is the main time coefficient /9/.

The higher K o, the better the technological process is constructed, since the longer the time allocated for the operation, the machine is working and not idle, i.e. in this case, the share of auxiliary time decreases.

The approximate value of the coefficient K o for different machines is within the following limits

Broaching machines - K o = 0.35...0.945;

Continuous milling - K o = 0.85...0.90;

The rest - K o = 0.35...0.90.

If the main time coefficient Ko is lower than these values, then it is necessary to develop measures to reduce auxiliary time (use of high-speed devices, automation of part measurements, combining main and auxiliary time, etc.).

The machine power utilization coefficient K N is defined as

de K N - machine power utilization factor /9/; N Р - cutting power, kW (in the calculation, we take that part of the technological operation that occurs with the greatest expenditure of cutting power); N st - power of the main drive of the machine, kW; h - machine efficiency.

The closer K N is to 1, the more fully the machine’s power is used.

When the machine is not fully loaded, the energy consumption indicator deteriorates. The total electrical power consumed from the network, S, is distributed into active P and reactive Q. Their ratios are defined as

When the electric motor is fully loaded, the cosφ value will not be equal to 1, i.e. At the same time, reactive energy is also consumed from the network. Taking into account the electric motors used, the approximate values ​​of cosφ will be as follows: at 100% load cosφ = 0.85, at 50% load - 0.7, at 20% load - 0.5, and at idle - 0.2 of this value.

Let's consider an example of the correct use of a number of milling machines (models 6Р13, 6Н13, 6Р12, 6Н12, 6Р11), if the power required for cutting is N cut = 3.2 kW.

	Indicators		Models of milling machines
			6Р13	6N13	6Р12	6N12	6Р11
	Electric power engine		11,0	10,0	7,5	7,0	5,5
	Idle power		2,200	2,500	2,250	1,750	1,100
	Cutting power		3,200	3,200	3,200	3,200	3,200
	Active power	P=N xx +N res	5,400	5,700	5,450	4,950	4,300
	Usage rate		0,491	0,570	0,727	0,707	0,782
	electric motor power
	Cosine phi	cosφ	0,585	0,635	0,718	0,708	0,740
	Total power consumption	S	9,231	8,976	7,591	6,992	5,811
	Efficiency coefficient of consumed electricity. power		0,585	0,635	0,718	0,708	0,740
	Overused power from the mains		3,831	3,276	2,141	2,042	1,511
	Unjustified expenses electrical power		2,320	1,766	0,630	0,531	0,000

From the above example it is clear that the wrong choice of machine leads to such excessive energy consumption that can be compared with the cutting power.

In order to repay excessively used reactive power, for which enterprises pay significant fines, it is necessary to create special devices to repay it with capacitive power.

3. EXAMPLE OF CALCULATION OF CUTTING MODE 3.1. Conditions of the problem. 3.1.1 Initial data.

The initial data for calculating the cutting mode are:

workpiece material - forging from steel 20X;

tensile strength of the workpiece material - s in = 800 MPa (80 kg/mm ​​2);

width of the workpiece surface to be processed, B - 100 mm;

length of the workpiece surface to be processed, L - 800 mm;

required roughness of the treated surface, R a - 0.8 µm (7th roughness class);

total processing allowance, h - 6 mm;

average daily production program for this operation, P - 200 pcs.

3.1.2. Purpose of calculations.

As a result of the calculations, it is necessary:

select a cutter based on elements and geometric parameters;

check the selected cutting mode based on drive power and the strength of the machine feed mechanism;

calculate the time required to complete the operation;

calculate the required number of machines;

check the effectiveness of the selected cutting mode and selection of equipment.

3.2. Calculation procedure. 3.2.1. Selection of cutting tools and equipment.

Based on the general machining allowance h = 6 mm and the requirements for surface roughness, milling is carried out in two transitions: roughing and finishing. Using Table 1, we determine the type of cutter - select a face mill with multifaceted carbide inserts in accordance with GOST 26595-85. The diameter of the cutter is selected from the ratio:

D = (1.25...1.5) B = 1.4 100 = 140 mm

We specify the choice of cutter according to tables 1, 2, 3, 4 - GOST 26595-85, diameter D = 125 mm, number of teeth z = 12, pentagonal plates, symbol - 2214-0535.

We select the material of the cutting part of the cutter according to Table 5 for rough milling of carbon and alloy non-hardened steel - T5K10, for finishing milling - T15K6.

We select the geometric parameters of the cutter according to Tables 6 and 7 for cutters with carbide inserts (Table 6) when processing structural carbon steel with σв ≤ 800 MPa and feed for rough milling > 0.25 mm/tooth: g = -5 0 ; a = 8 0 ; j = 45 0 ; j o = 22.5 0; j 1 = 5 0 ; l = 14 0 ; for finishing milling with feed< 0,25 мм/зуб: g = -5 0 ; a = 15 0 ; j = 60 0 ; j о = 30 0 ; j 1 = 5 0 ; l = 14 0 .

We carry out rough milling according to the scheme - asymmetrical uphill (Fig. 8.b), finishing milling - asymmetrical downhill (Fig. 8.c).

We preliminarily accept work on a 6P13 vertical milling machine, passport data in table 20.

3.2.2. Calculation of cutting mode elements. 3.2.2.1. Setting the cutting depth.

When setting the cutting depth, first of all, from the total allowance, the part that remains for finishing is selected - t 2 = 1 mm. Finish milling is carried out in 1 working stroke i 2 = 1. Hence, the allowance h 1 for rough milling will be:

h 1 = 6 - 1 = 5 mm.

To remove this allowance, one working stroke is enough, so we take the number of working strokes during rough milling i 1 = 1. Then the cutting depth t 1 during rough milling will be

t 1 = h 1 / i 1 = 5 / 1 = 5 mm.

3.2.2.2. Submission purpose.

The feed rate for rough milling is selected from tables 8 and 9. For face mills with carbide inserts (Table 8) with a machine power > 10 kW with asymmetrical counter milling for the T5K10 plate, the feed per tooth is within the range S z1 = 0.32... 0.40 mm/tooth We accept a smaller value to guarantee the conditions for power on the spindle S z1 = 0.32 mm/tooth, the feed per revolution will be. S o1 = S z1 z =0.32 12 = 3.84 mm/rev.

The feed rate for finishing milling is selected according to Table 10. For face mills with carbide inserts (part B) with a material having σ ≥ 700 MPa with a machined surface roughness R a = 0.8 μm with an angle j 1 = 5 0 feed per The rotation of the cutter is within the range of S o2 = 0.30...0.20 mm/rev. We accept a larger value to increase the productivity of the process S o2 = 0.30 mm/rev. In this case, the feed will not be a tooth

S z2 = S o2 / z = 0.30 / 12 = 0.025 mm/tooth.

3.2.2.3. Determination of cutting speed.

The cutting speed is determined by the formula:

The values ​​of the coefficient C v and exponents are determined from Table 11. For roughing and finishing milling of structural carbon steel with σ ≥ 750 MPa using carbide inserts:

C v = 332, q = 0.2; m = 0.2; x = 0.1; y = 0.4; u = 0.2; p = 0.

We accept T = 180 min, clause 2.4 table 1.

General correction factor

Kv = K m v K pv K иv K j v

Kmv is found from table 12 for steel processing. Calculation formula K m v = K g (750/s in) nv. According to Table 13, we find for processing carbon steel with σ in > 550 MPa for a tool material made of hard alloy K g = 1, n v = 1. Then K m v 1.2 = 1 (750/800) 1.0 = 0.938.

K j v is found from table 2.2.4. - 2 for rough milling at j = 45 o K j v1 = 1.1; for finishing milling at j = 60 o K j v2 = 1.0.

K pv is found from Table 14 for processing during rough milling - forgings K pv1 = 0.8, for finishing milling - without crust K pv2 = 1.

We find Kiv from Table 15 for processing steel with a structural milling cutter with plates made of T5K10 hard alloy during rough milling K and v1 = 0.65, with plates made of T15K6 hard alloy during finishing milling K and v2 = 1.

K v1 = 0.938 1.1 0.8 0.65 = 0.535.

The general correction factor for rough milling is

K v2 = 0.938 1.0 1.0 1.0 = 0.938.

The cutting speed during rough milling is

The cutting speed during finishing milling is:
The estimated number of revolutions of the cutter is determined for roughing and finishing milling by the expression

3.2.2.4. Clarification of cutting conditions

Using the passport of the 6P13 machine, we clarify the possible setting of the cutter speed and find the actual values ​​for roughing n f1 = 200 min -1, for finishing n f2 = 1050 min -1, i.e. We select the nearest smallest values ​​from the calculated ones. As a result of this, the actual cutting speed will also change, which will be during roughing

v f1 = πDn/1000 = 3.14 125 200/1000 = 78.50 m/min,

and during finishing

v f2 = πDn/1000 = 3.14 125 1050/1000 = 412.12 m/min.

To clarify the feed values, it is necessary to calculate the feed speed v S based on the feed per tooth and per revolution

v S = S o n = S z z n;

v S1 = 0.32 12 200 = 768 mm/min; v S2 = 0.3 1050 = 315 mm/min.

Using the machine's passport, we find a possible setting for the feed speed, choosing the nearest lowest values, v S1 = 800 mm/min, since this value is only 4.17% higher than the calculated one and v S2 = 315 mm/min. Based on the accepted values, we clarify the values ​​of feeds per tooth and per revolution

Sof1 = 800 / 200 = 4 mm/rev; S zф1 = 4 / 12 = 0.333 mm/tooth;

Sof2 = 315 / 1050 = 0.3 mm/rev; S zф2 = 0.3 / 12 = 0.025 mm/tooth;

3.2.3. Checking the selected cutting mode

We check the selected cutting mode according to the characteristics of the machine: the power on the machine spindle and the maximum permissible force applied to the feed mechanism. Since the load on the machine during roughing is much higher than during finishing, we check the selected cutting mode for rough milling.

The power spent on cutting must be less than or equal to the power on the spindle: N р £ N sp.

Spindle power

N sp = N e h = 11 0.8 = 8.8 kW.

The main component of the cutting force is determined by the formula
The value of the coefficient Ср and the exponents x, y, u, q, w are found from Table 16: Ср = 825; x = 1.0; y = 0.75; u = 1.1; q = 1.3; w = 0.2. When the cutter is dulled to an acceptable value, the cutting force on steel increases from σв > 600 MPa by 1.3...1.4 times. We accept an increase of 1.3 times.

General correction factor K р = K m р K vр K g р K j р.

K m p is determined according to Table 17 for processing structural carbon and alloy steels K m p = (s in /750) np, exponent n p = 0.3, then K m p = (800/750)0.3 = 1, 02.

K vр is determined according to Table 18 for roughing at cutting speeds up to 100 m/min with negative values ​​of the rake angle K vр1 = 1, for finishing at cutting speeds up to 600 m/min K vр2 = 0.71.

K g р and K j р are determined according to Table 19. At g = -5 о Kgр = 1.20 and at j = 45 о K j р1 = 1.06, at j = 60 о K j р2 = 1.0.

The value of the general correction factor will be

K p1 = 1.02 1 1.20 1.06 = 1.297; K p2 = 1.02 0.71 1.20 1.0 = 0.869

The cutting power during rough milling is determined as
The condition for the correct selection of the cutting mode based on the drive power N p £ N sh is not met, since 48.51 > 8.8, this means that the selected cutting mode cannot be implemented on this machine.

The most effective way to reduce cutting power is by reducing the cutting speed, as well as reducing the feed per tooth. The cutting power must be reduced by 5.5 times, for this we will reduce the cutting speed by reducing the number of revolutions of the cutter from 200 to 40 rpm from 78.5 m/min to 14.26 m/min. In this case, the feed speed will decrease from 768 mm/min to v S1 = 0.32 12 40 = 153.6 mm/min. Since changing the cutting depth will lead to the need for a second working stroke, we will change the feed speed to 125 mm/min (Table 20), while the feed per cutter tooth will be S z1 = 125/12 40 = 0.26 mm/tooth.

Substituting the new value of feed per tooth into the formula for calculating the main component of the cutting force, we obtain P z1 = 31405.6 N, the torque becomes equal to M cr1 = 1960.3 Nm, cutting power N p1 = 8.04 kW, which meets the requirements for drive power .

The second condition is that the horizontal component of the cutting force (feed force) must be less than (or equal to) the greatest force allowed by the longitudinal feed mechanism of the machine: P g £ P add.

For machine 6Р13 Р additional = 15000 N.

Horizontal component of the cutting force Pr under the condition of asymmetrical counter rough milling

P g = 0.6 P z1 = 0.6 31364.3 = 18818.58 N.

Since the condition P g £ P add is not met (18818.58 > 15000), the selected cutting mode does not satisfy the strength condition of the longitudinal feed mechanism of the machine. To reduce the horizontal component of the cutting force, it is necessary to reduce the feed per cutter tooth. Let us present the formula for calculating the main component of the cutting force in the form

Using the newly selected value of S z1, we determine v s1 = 0.192 12 40 = 92.16 mm/min, the nearest smaller value on the machine is v s1 = 80 mm/min. The actual feed per revolution of the cutter will be S оф = 2 mm/rev, the actual feed per cutter tooth will be S zф = 0.167 mm/tooth.

Due to the multiple excess of the first calculation parameters over the permissible ones, it is necessary to check the correctness of the choice of cutting mode during the finishing transition.

The main component of the cutting force during finishing is significantly lower than the permissible values, and therefore there is no need to adjust the calculation.

The final calculation data are summarized in the table

The name of indicators	Units	To go
		rough	finishing
Depth of cut t	mm	5	1
	mm/tooth	0,323	0,025
Calculated feed per revolution of the cutter S o	mm/rev	3,84	0,3
Design cutting speed v	m/min	88,24	503,25
Design cutter speed n	rpm	224,82	1282,16
	rpm	200	1050
	m/min	78,50	412,12
	mm/min	768	315
	mm/min	800	315
Actual feed per revolution of the cutter S of	mm/rev	4	0,3
Actual feed per cutter tooth S zф	mm/tooth	0,333	0,025
Main component of cutting force P z	N	37826,7	521
Torque Mcr	Nm	2364,17
Cutting power N	kW	48,51
First adjustment of cutting mode
Actual number of revolutions of the cutter n f	rpm	40
Actual cutting speed v f	m/min	15,7
Design feed speed v S	mm/min	159,84
Actual feed speed v S f	mm/min	160
Main component of cutting force P z	N	31364,3
Torque Mcr	Nm	1960,3
Cutting power N	kW	8,08
Horizontal composition cutting force P g	N	18818,58
Second cutting mode adjustment
Calculated feed per cutter tooth S z	mm/tooth	0,192
Design feed speed v S	mm/min	92,16
Actual feed speed v S f	mm/min	80
Actual feed per revolution S of	mm/rev	2
Actual feed per tooth S zф	mm/tooth	0,167

Thus, the machine is adjusted according to the following values:

Rough transition n f1 = 40 min -1, v S1 = 80 mm/min;

Finishing transition n f2 = 1050 min -1, v S2 = 315 mm/min.

3.2.4. Calculation of operation execution time. 3.2.4.1. Calculation of main time.
l 1 = 0.5 125 - √0.04 125 (125 - 0.04 125) = 62.25 - 24.25 = 38 mm.

The overtravel of the cutter l 2 for roughing and finishing milling is assumed to be the same l 2 = 5 mm.

The number of working strokes i for finishing and rough milling is 1.

Total cutter length for rough and finish milling

L = 800 + 38 + 5 = 843 mm.

The main time during face milling of a workpiece during roughing and finishing transitions will be:

3.2.4.2. Determination of piece time.

The unit time spent on this operation is defined as

T pcs = T o + T vsp + T obs + T dep

The auxiliary time T vsp spent on installing and removing the part is determined from Table 21. We accept the method of installing the part with a length of 800 mm - on a table with an alignment of average complexity; with a part weight of up to 10 kg, the time for installing and removing the workpiece is 1.8 minutes. The auxiliary time for the working stroke (Table 22) is taken for processing planes with one test chip - 0.7 minutes and for subsequent passes - 0.1 minutes, in total - 0.8 minutes. The time for measuring the workpiece using a caliper (Table 23) for the width and thickness of the workpiece (height from the table) - dimensions up to 100 mm with an accuracy of 0.1 mm, is taken equal to 0.13 min.

Tfsp = 1.8 + 0.8 + 0.13 = 2.73 min.

Then operational time

T op1 = T o + T vsp = 10.54 + 2.73 = 13.27 min.

T o2 = 2.68 + 2.73 = 5.41 min

Time for servicing a workplace and time for rest are taken as a percentage of operational time:

T dep1 + T obs1 = 10% T op = 0.1 13.27 = 1.32 min;

T dep2 + T obs2 = 10% T op = 0.1 5.41 = 0.54 min;

The unit time spent on this operation is

T pc1 = T o1 + T vsp1 + T obs1 + T dep1 = T o1 0.1 T o1 = 13.27 + 1.32 = 14.59 min.

T pcs2 = T o2 + T vsp2 + T obs2 + T dep2 = T o2 0.1 T o2 = 5.41 + 0.54 = 5.95 min.

3.2.4.3. Determination of piece-calculation time
3.2.5.1. Determining the required number of machines

We accept the number of machines required to perform roughing - Z 1f = 6 pcs., and for finishing machining Z 2f = 3 pcs. Six machines for a roughing operation are not enough for the entire operating batch, but if we take 7 machines, we will get a large underload of machines in terms of operating time. It is preferable to accept the loading of six machines with the addition of one whole shift for a certain period of time. For the finishing operation, 3 machines will not be fully loaded during the shift and in order not to be readjusted to perform another operation, it is necessary to adjust the size of the shift task - the operating batch. One shift for a certain period can be freed up to perform other work or perform equipment maintenance. In this case, the operating batches will be

P 1f = Z 1f T cm 60 / T wk1 = 6 8 60 / 14.71 = 196 pcs.

P 2f = Z 2f T cm 60 / T wk2 = 3 8 60 / 6.07 = 237 pcs.

During roughing, the equipment shortage will be

(P 1 - P 1f) / P 1 = (200 - 196) / 200 = 1 / 50,

those. After 50 shifts, you need to add one more to complete the entire task.

When finishing machining, the excess equipment time will be

(P 2f - P 2) / P 2 = (237-200) / 200 = 10 / 54,

those. approximately every 6 shifts, one shift may be freed up to perform other work.

3.2.5.2. Main time coefficient

In calculated operations, the main time as part of the piece time will have the following share

K o1 = T o1 / T w1 = 10.54 / 14.59 = 0.72

K o2 = T o2 / T w2 = 2.68 / 5.95 = 0.45

The data suggests that when performing finishing processing, relatively much time is allocated for auxiliary actions, therefore organizational or technological measures should be taken to mechanize processes, reduce auxiliary time, combine main and auxiliary time, etc. When performing rough processing, the share of the main time is quite high and does not require any priority activities.

3.2.5.3. Machine power utilization factor

During the roughing operation, the cutting power is 8.04 kW with a machine spindle power of 8.8 kW, and the power utilization factor is

K N = N p / N st h = 8.04 / 11 0.8 = 0.92

The power utilization factor of the machine K N is quite high; if necessary, it can be slightly increased by increasing the feed per tooth.

LIST OF SOURCES USED

1. Kolokatov A.M. Guidelines for calculating (assigning) cutting modes during face milling. - M., MIISP, 1989. - 27 p.

2. Nekrasov S.S. Processing of materials by cutting. - M.: Agropromizdat, 1988. - 336 p.

3. Cutting of structural materials, cutting tools and machines / Krivoukhov V.A., Petrukha P.P. and others - M.: Mashinostroenie, 1967. - 654 p.

4. A short reference book for metalworkers./ Ed. A.N. Malova and others - 2nd edition - M.: Mashinostroenie, 1971. - 767 p.

5. Handbook of technologist - mechanical engineer. In 2 volumes /Ed. A.G. Kosilova and R.K. Meshcheryakov. - 4th ed., revised. and additional - M.: Mashinostroenie, 1985.

6. Dolmatovsky G.A. Technologist's guide to metal cutting. - 3rd ed., revised. - M.: GNTI, 1962. - 1236 p.

7. Nekrasov S.S., Baikalova V.N. Methodological recommendations for completing homework for the course “Processing of structural materials by cutting” (for students of the faculties of agricultural mechanization and engineering-pedagogical). - M.: MIISP, 1988. - 38 p.

8. Nekrasov S.S., Baikalova V.N., Kolokatov A.M. Determination of the technical standard for the time of machine operations: Methodological recommendations. - M.: MGAU, 1995. - 20 p.

9. Nekrasov S.S., Kolokatov A.M., Bagramov L.G. Particular criteria for assessing the technical and economic efficiency of technological processes: Methodological recommendations. - M.: MGAU, 1997. - 7 p.

APPLICATIONS

Table 1

Standard face mills

GOST	Types of Face Mills	Cutter diameter, (mm) / number of cutter knives, (pcs).
26595-85	End mills with mechanical fastening of multifaceted inserts. Types and main sizes.	50/5, 63/6, 80/8, (80/10), 100/8, 100/10, 125/8, 125/12, 160/10, 160/14, (160/16), 200/12, 200/16, (200/20), 250/14, 250/24, 315/18, 315/30, 400/20, 400/40, 500/26, 500/50
24359-80	End mills are mounted with insert knives equipped with carbide plates. Design and dimensions.	100/8, 125/8, 160/10, 200/12, 250/14, 315/18, 400/20, 500/26, 630/30
22085-76	End mills with mechanical fastening of pentagonal carbide inserts
22087-76	Face end mills with mechanical fastening of pentagonal carbide inserts	63/5, 80/6
22086-76	End mills with mechanical fastening of round carbide inserts	100/10, 125/12, 160/14, 200/16
22088-76	Face end mills with mechanical fastening of round carbide inserts	50/5, 63/6, 80/8
9473-80	Fine-tooth mounted end mills with insert knives equipped with carbide plates. Design and dimensions.	100/10, 125/12, 160/16, 200/20, 250/24, 315/30, 400/36, 500/44, 630/52
9304-69	End mills are mounted. Types and main sizes.	40/10, 50/12, 63/14, 80/16, 100/18, 63/8, 80/10,100/12,
16222-81	End mills for machining light alloys	50, 63, 80 at z = 4
16223-81	End mills with insert knives and carbide inserts for processing light alloys. Design and dimensions.	100/4, 125/6, 160/6, 200/8, 250/10, 315/12

Note: Milling cutters of a different design are indicated in brackets

table 2

Face milling cutters with mechanical fastening of polyhedral inserts

(GOST 26595-85)

Note: An example of a symbol for a face mill with a diameter of 80 mm, right-hand cutting, with mechanical fastening of triangular inserts made of hard alloy, with the number of teeth 8: Mill 2214-0368 GOST 26595-85.

The same for plates made of tungsten-free carbide:

Mill 2214-0368 B GOST 26595-85.

Table 3

End mills with insert knives equipped with

hard alloy plates (GOST 24359-80)

Designation	D, mm	Z	Designation	D, mm	Z

Notes: 1. The main plan angle j can be 45 0, 60 0, 75 0, 90 0

An example of a symbol for a right-handed end mill

with knives equipped with hard alloy plates

T5K10 with a diameter of 200 mm and an angle j = 60 0:

Mill 2214-0007 T5K10 60 0 GOST 24359-80

Table 4

End and attachment end mills with mechanical fastening

round carbide inserts

GOST	Designation	D, mm	Z
22088-76
22086-76

Note: An example of a symbol for a cutter with a diameter of 80 mm:

Mill 2214-0323 GOST 22088-76

Table 5

Carbide grades for face mills

	Grade of carbide for face milling cutters during processing
Type of milling	carbon and alloy unhardened	difficult to process washable	cast iron
	become		HB 240	HB 400...700
rough	T5K10, T5K12B			-
semi-finish				VK6M
finishing				VK3M

Note: In the VK6M alloy, the letter M means fine-grained structure.

Letters OM - particularly fine-grained structure

Table 6

Geometric parameters of the cutting part of end mills

with carbide inserts

Including only one design dimension or one allowance, it forms a technological dimensional chain. The values ​​of the minimum allowances Zi-jmin for forming operations are taken from the calculation of operational dimensions-coordinates using the normative method and entered in the table. 7.2. Having determined Zi-jmin, we compose the initial equations of dimensional chains regarding Zi-jmin: where Xr min is the smallest...

		Rear angle for		Approach angle			Corner
Processable material		work with feed			transition edge
	g	< 0,25	> 0,25	j			l
structural carbon: s at £800 MPa s in > 800 MPa					j/2
Gray cast iron					j/2
Malleable cast iron

Surface processing of workpieces by milling can be carried out only after the development of a technological map, which indicates the main processing modes. Such work is usually carried out by a specialist who has undergone special training. Cutting conditions during milling can depend on a variety of indicators, for example, the type of material and the tool used. The main indicators on the milling machine can be set manually, and the indicators are also indicated on the numerical control unit. Thread milling deserves special attention, since the resulting products are characterized by a fairly large number of different parameters. Let us consider the features of choosing cutting modes during milling in detail.

Cutting speed

The most important mode during milling can be called cutting speed. It determines over what period of time a certain layer of material will be removed from the surface. Most machines have a constant cutting speed. When choosing a suitable indicator, the type of workpiece material is taken into account:

1. When working with stainless steel, the cutting speed is 45-95 m/min. Due to the addition of various chemical elements to the composition, hardness and other indicators change, and the degree of workability decreases.
2. Bronze is considered a softer composition, so this milling mode can be selected in the range from 90-150 m/min. It is used in the manufacture of a wide variety of products.
3. Brass has become quite widespread. It is used in the manufacture of locking elements and various valves. The softness of the alloy allows you to increase the cutting speed to 130-320 m/min. Brasses tend to increase in ductility when exposed to high heat.
4. Aluminum alloys are very common today. In this case, there are several design options that have different performance characteristics. That is why the milling mode varies from 200 to 420 m/min. It is worth considering that aluminum is an alloy with a low melting point. That is why, at high processing speeds, there is a possibility of a significant increase in the plasticity index.

There are quite a large number of tables that are used to determine the main operating modes. The formula for determining cutting speed revolutions is as follows: n=1000 V/D, which takes into account the recommended cutting speed and the diameter of the cutter used. A similar formula allows you to determine the number of revolutions for all types of processed materials.

The milling mode in question is measured in meters per minute cutting parts. It is worth considering that experts do not recommend driving the spindle at maximum speed, as wear increases significantly and there is a possibility of damage to the tool. Therefore, the result obtained is reduced by approximately 10-15%. Taking this parameter into account, the most suitable tool is selected.

The rotation speed of the tool determines the following:

1. The quality of the resulting surface. For the final technological operation, the largest parameter is selected. Due to axial rotation with a large number of revolutions, the chips are too small. For roughing operations, on the contrary, low values ​​are selected, the cutter rotates at a lower speed, and the chip size increases. Due to fast rotation, a low surface roughness is achieved. Modern installations and equipment make it possible to obtain a mirror-type surface.
2. Labor productivity. When setting up production, attention is also paid to the performance of the equipment used. An example is the workshop of a machine-building plant, where mass production is being established. A significant decrease in processing modes causes a decrease in productivity. The most optimal indicator significantly increases labor efficiency.
3. The degree of wear of the installed tool. Do not forget that when the cutting edge rubs against the surface being processed, severe wear occurs. With severe wear, the accuracy of the product changes and labor efficiency decreases. As a rule, wear is associated with strong surface heating. That is why high-throughput production lines use equipment that can supply coolant to the material removal zone.

In this case, this parameter is selected taking into account other indicators, for example, feed depth. Therefore, the technological map is drawn up with the simultaneous selection of all parameters.

Depth of cut

The other most important parameter is the milling depth. It is characterized by the following features:

1. The cutting depth is selected depending on the material of the workpiece.
2. When choosing, attention is paid to whether roughing or finishing is carried out. When roughing, a larger plunge depth is selected, since a lower speed is set. During finishing, a small layer of metal is removed by setting the tool to a high rotation speed.
3. The indicator is also limited by the design features of the tool. This is due to the fact that the cutting part can have different sizes.

The depth of cut largely determines the performance of the equipment. In addition, such an indicator in some cases is selected depending on what kind of surface needs to be obtained.

The power of the cutting force during milling depends on the type of cutter used and the type of equipment. In addition, rough milling of a flat surface is carried out in several passes when it is necessary to remove a large layer of material.

A special technological process can be called the work of obtaining grooves. This is due to the fact that their depth can be quite large, and the formation of such technological recesses is carried out exclusively after finishing the surface. Milling T-slots is carried out using a special tool.

Innings

The concept of feed is similar to plunge depth. Feed during milling, as with any other operation for machining metal workpieces, is considered the most important parameter. The durability of the tool used largely depends on the feed. The features of this characteristic include the following points:

1. How thick is the material removed in one pass?
2. Productivity of the equipment used.
3. Possibility of roughing or finishing processing.

A fairly common concept can be called feed per tooth. This indicator is indicated by the tool manufacturer and depends on the cutting depth and design features of the product.

As previously noted, many indicators are related to the cutting mode. An example is cutting speed and feed:

1. As the feed value increases, the cutting speed decreases. This is due to the fact that when removing a large amount of metal in one pass, the axial load increases significantly. If you choose high speed and feed, the tool will quickly wear out or simply break.
2. By reducing the feed rate, the permissible processing speed also increases. By quickly rotating the cutter, it is possible to significantly improve the quality of the surface. At the time of finishing milling, the minimum feed value and maximum speed are selected; when using certain equipment, an almost mirror-like surface can be obtained.

A fairly common feed value is 0.1-0.25. It is quite sufficient for processing the most common materials in various industries.

Milling width

Another parameter that is taken into account when machining workpieces is the milling width. It can vary over a fairly large range. The width is selected when milling on a Have machine or other equipment. Among the features we note the following points:

1. The milling width depends on the diameter of the cutter. Such parameters, which depend on the geometric features of the cutting part and cannot be adjusted, are taken into account when directly selecting a tool.
2. The milling width also influences the selection of other parameters. This is because as the value increases, the amount of material removed in one pass also increases.

In some cases, the milling width allows you to obtain the required surface in one pass. An example is the case of obtaining shallow grooves. If cutting a flat surface of large width is carried out, the number of passes may differ slightly; it is calculated depending on the width of the milling.

How to choose a mode in practice?

As previously noted, in most cases, technological maps are developed by a specialist and the master can only select the appropriate tool and set the specified parameters. In addition, the master must take into account the condition of the equipment, since limit values ​​can lead to breakdowns. In the absence of a technological map, you have to select milling modes yourself. Calculation of cutting conditions during milling is carried out taking into account the following points:

1. Type of equipment used. An example is the case of cutting when milling on CNC machines, when higher processing parameters can be selected due to the high technological capabilities of the device. On older machines that were put into operation several decades ago, lower parameters are selected. At the time of determining suitable parameters, attention is also paid to the technical condition of the equipment.
2. The next selection criterion is the type of tool used. Various materials can be used in the manufacture of cutters. For example, a version made of high-quality high-speed steel is suitable for processing metal at high cutting speeds; a milling cutter with refractory tips is preferably selected when it is necessary to mill a hard alloy with a high feed rate during milling. The sharpening angle of the cutting edge, as well as the diametrical size, also matters. For example, as the diameter of the cutting tool increases, the feed rate and cutting speed decrease.
3. The type of material being processed can be called one of the most important criteria by which the cutting mode is selected. All alloys are characterized by a certain hardness and degree of machinability. For example, when working with soft non-ferrous alloys, higher speed and feed rates can be selected; in the case of hardened steel or titanium, all parameters are reduced. An important point is that the cutter is selected not only taking into account cutting conditions, but also the type of material from which the workpiece is made.
4. The cutting mode is selected depending on the task at hand. An example is rough cutting and finishing cutting. Black is characterized by a high feed rate and a low processing speed; for finishing, the opposite is true. To obtain grooves and other technological holes, the indicators are selected individually.

As practice shows, the depth of cut in most cases is divided into several passes during roughing, while during finishing there is only one. For various products, a table of modes can be used, which significantly simplifies the task. There are also special calculators that calculate the required values ​​automatically based on the entered data.

Selecting a mode depending on the type of cutter

To obtain the same product, a variety of types of cutters can be used. The choice of basic milling modes is carried out depending on the design and other features of the product. Cutting modes when milling with disk cutters or other design options are selected depending on the following points:

1. The rigidity of the system used. An example is the features of the machine and various equipment. The new equipment is characterized by increased rigidity, which makes it possible to use higher processing parameters. On older machines, the rigidity of the system used is reduced.
2. Attention is also paid to the cooling process. Quite a large amount of equipment provides for the supply of coolant to the processing zone. Due to this substance, the temperature of the cutting edge is significantly reduced. Coolant must be supplied to the material removal zone continuously. At the same time, the resulting chips are also removed, which significantly improves cutting quality.
3. Processing strategy also matters. An example is that the production of the same surface can be carried out by alternating various technological operations.
4. The height of the layer that can be removed in one pass of the tool. The limitation may depend on the tool size and many other geometric features.
5. Size of processed workpieces. Large workpieces require a tool with wear-resistant properties that will not heat up under certain cutting conditions.

Taking into account all these parameters allows you to select the most suitable milling parameters. This takes into account the distribution of allowance when milling with spherical cutters, as well as the features of processing with an end mill.

The classification of the instrument in question is carried out according to a fairly large number of characteristics. The main thing is the type of material used in the manufacture of the cutting edge. For example, the VK8 cutter is designed to work with workpieces made of hard alloys and hardened steel. It is recommended to use this design option at low cutting speeds and sufficient feed. At the same time, high-speed cutters can be used for processing with a high cutting rate.

As a rule, the choice is made taking into account common tables. The main properties are:

1. Cutting speed.
2. Type of material being processed.
3. Type of cutter.
4. Speed.
5. Innings.
6. Type of work performed.
7. Recommended feed per tooth depending on the cutter diameter.

The use of regulatory documentation allows you to select the most suitable modes. As previously noted, only a specialist should develop the technological process. Mistakes made can lead to tool breakage, a decrease in the quality of the workpiece surface and errors in the tools, and in some cases, equipment breakdown. That is why you need to pay a lot of attention to choosing the most suitable cutting mode.

Selecting a mode depending on the material

All materials are characterized by certain performance characteristics, which must also be taken into account. An example is bronze milling, which is carried out at cutting speeds from 90 to 150 m/min. Depending on this value, the feed amount is selected. PSh15 steel and stainless steel products are processed using other parameters.

When considering the type of material being processed, attention is also paid to the following points:

1. Hardness. The most important characteristic of materials is hardness. It can vary over a wide range. Too much hardness makes the part strong and wear-resistant, but at the same time the processing process becomes more complicated.
2. Degrees of machinability. All materials are characterized by a certain degree of workability, which also depends on ductility and other indicators.
3. Application of technology to improve properties.

A fairly common example is hardening. This technology involves heating the material followed by cooling, after which the hardness index increases significantly. Forging, tempering and other procedures for changing the chemical composition of the surface layer are also often carried out.

In conclusion, we note that today you can find simply a huge number of different technological maps, which you just need to download and use to obtain the required parts. When considering them, attention is paid to the type of workpiece material, type of tool, and recommended equipment. It is quite difficult to independently develop cutting modes; in this case, you need to do a preliminary check of the selected parameters. Otherwise, both the tool and the equipment used may be damaged.