Conventional graphic symbols for kinematic diagrams. Kinematic diagrams Symbols in kinematic diagrams of machines

GOST 2.770-68*. ESKD. Conditional graphic designations in schemes. Elements of kinematics. Kinematic diagrams symbols

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3 Kinematic diagrams of machines and symbols of their elements

Kinematic diagram of the machine - an image using symbols (Table 1.2) of the relationship of individual elements and mechanisms, machines involved in the transmission of movements to various organs.

Table 1.2 – Graphic symbols for kinematic diagrams GOST 2.770-68

Kinematic diagrams are drawn on an arbitrary scale. However, one should strive to fit the kinematic diagram into the contours of the main projection of the machine or its most important assembly units, ensuring that their relative position is preserved.

For machines that, in addition to mechanical transmissions, have hydraulic, pneumatic and electrical devices, hydraulic, pneumatic, electrical and other circuits are also drawn up.

4 Determination of gear ratios and movements in various types of gears

The ratio of the rotational speed (angular velocity) n2 of the driven shaft to the rotational speed n1 of the driving shaft is called the gear ratio:

Belting. Gear ratio without taking into account belt sliding (Figure 1.1, a)

i = n2/ n1 = d1 / d2,

where d1 and d2 are the diameters of the driving and driven pulleys, respectively.

Belt slip is taken into account by introducing a correction factor equal to 0.97-0.985.

Chain transmission. Gear ratio (Figure 1.1, b)

i = n2 / n1 = z1 / z2,

where z1 and z2 are the numbers of teeth of the driving and driven sprockets, respectively.

Gear transmission (Figure 1.1, c), carried out by cylindrical or bevel gears. Gear ratio

i = n2 / n1 = z1 / z2,

where z1 and z2 are the numbers of teeth of the driving and driven gears, respectively.

Worm-gear. Gear ratio (Figure 1.1, d)

i = n2 / n1 = z / zк,

where Z is the number of worm passes; zk is the number of teeth of the worm wheel.

Rack and pinion transmission. Length of linear movement of the rack per one revolution of the rack and pinion gear (Figure 1.1, d)

where p = m - rack tooth pitch, mm; z is the number of teeth of the rack and pinion gear; m - module of the rack and pinion gear teeth, mm.

Screw and nut. Moving the nut per revolution of the screw (Figure 1.1, e)

where Z is the number of screw passes; pv - propeller pitch, mm.

5 TRANSMISSION RATIO OF KINEMATIC CHAINS. CALCULATION OF ROTATION SPEED AND TORQUES

To determine the overall gear ratio of the kinematic chain (Figure 1.1, g), it is necessary to multiply the gear ratios of the individual gears included in this kinematic chain:

The rotation speed of the last driven shaft is equal to the rotation speed of the drive shaft multiplied by the total gear ratio of the kinematic chain:

n = 950 i total,

i.e. n = 950  59.4 min-1.

The torque on the Mshp spindle depends on the gear ratio of the kinematic chain from the electric motor to the spindle. If the electric motor develops torque Mdv, then

Мшп = Мдв/ i total

where i total is the gear ratio of the kinematic chain from the electric motor to the spindle;  - efficiency of the kinematic chain from the electric motor to the spindle.

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Conventional graphic symbols on kinematic diagrams

Conventional graphic symbols used on kinematic diagrams are established by GOST 2.770 - 68.

Conventional graphic designations of machine elements and mechanisms are given in Table 1.1, the nature of movement in Table 1.2.

Conventional graphic designations of machine and mechanism elements on kinematic diagrams

Conventional graphic designations of the nature of movement on kinematic diagrams

Name	Designation
Shaft, platen, axle, rod, connecting rod
Fixed link (stand). Note. To indicate the immobility of any link, part of its outline is covered with shading
Name	Designation
Connection of link parts:
motionless
fixed, adjustable
fixed connection of a part with a shaft, rod
Kinematic pair:
rotational
rotational multiple, for example, double
progressive
screw
cylindrical
spherical with finger
universal joint
spherical (ball)
planar
tubular (ball-cylinder)
point (ball-plane)
Sliding and rolling bearings on the shaft (without specifying the type):
radial
persistent
Plain bearings:
radial
Name			Designation
persistent one-sided
persistent double-sided
Rolling bearings:
radial
angular contact one-sided
angular contact double-sided
persistent one-sided
persistent double-sided
Clutch. General designation without specification of type
Non-disengaging clutch (uncontrolled)
deaf
elastic
compensating
Coupled coupling (controlled)
general designation
one-sided
bilateral
Coupled mechanical clutch
synchronous, for example, gear
asynchronous, for example, friction
Electric coupling
Coupling hydraulic or pneumatic
Automatic clutch (self-acting)
general designation
overtaking (freewheel)
centrifugal friction
safety with destructible element
Name			Designation
safety with non-destructible element
Brake. General designation without specification of type
Flat jaws:
longitudinal movement
rotating
rotating slotted
Drum cams:
cylindrical
conical
curvilinear
Pusher (driven link)
pointed
arc
roller
flat
Two-element linkage of lever mechanisms
crank, rocker arm, connecting rod
eccentric
slider
Name			Designation
backstage
Three-element linkage of lever mechanisms Notes: 1. Hatching may not be applied. 2. The designation of a multi-element link is similar to two- and three-element
Ratchet gears:
external gear single-sided
external gear double-sided
with internal gearing single-sided
rack and pinion
Maltese mechanisms with a radial arrangement of grooves at the Maltese cross:
external gear
internal gear
general designation
Name			Designation
Friction gears:
with cylindrical rollers
with tapered rollers
with tapered rollers adjustable
with curved generatrices of working bodies and tilting rollers, adjustable
end (frontal) adjustable
with spherical and conical (cylindrical) rollers, adjustable
Name			Designation
with cylindrical rollers, converting rotational motion into translational
with hyperboloid rollers that convert rotational motion into helical motion
with flexible rollers (wave)
Flywheel on shaft
Step pulley mounted on a shaft
Belt transmission:
without specifying the type of belt
flat belt
V-belt
round belt
toothed belt
Chain transmission:
general designation without specifying the type of chain
round link
Name			Designation
lamellar
gear
Gear transmissions (cylindrical):
external gearing (general designation without specifying the type of teeth)
the same, with straight, oblique and chevron teeth
internal gearing
with non-round wheels
Gear transmissions with flexible wheels (wave)
Gear transmissions with intersecting shafts and bevel gears:
Name			Designations
with straight, spiral and circular teeth
Gear transmissions with crossed shafts:
hypoid
worm with cylindrical worm
worm globoid
Rack and pinion transmissions:
general designation without specifying the type of teeth
Transmission by gear sector without specifying the type of teeth
Screw transmitting movement
Nut on the screw transmitting the movement:
one-piece
one-piece with balls
Name			Designation
detachable
Springs:
cylindrical compression
cylindrical tension
conical compression
cylindrical, torsional
spiral
leafy:
Single
Spring
disc-shaped
Shift lever
The end of the shaft for a removable handle
Lever
Handwheel
Mobile stops
Flexible shaft for transmitting torque

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GOST 2.770-68* - ESKD. Conditional graphic designations in schemes. Elements of kinematics.

Continuation of the table. 3.1

Continuation of the table. 3.1

End of table. 3.1

Among the transmissions of motion from the drive to the working parts of the machine, mechanical transmissions are most widespread (Fig. 3.1).

According to the method of transmitting motion from the driving element to the driven element, mechanical transmissions are divided as follows: gear transmissions with direct contact (gear - Fig. 3.1, a; worm - Fig. 3.1, b; ratchet; cam) or with a flexible connection (chain); friction transmissions with direct contact (friction) or with a flexible connection (belt - Fig. 3.1, c).

The main kinematic parameter characterizing all types of mechanical transmissions of rotational motion is the gear ratio - the ratio of the number of teeth of a larger wheel to the number of teeth of a smaller one in a gear drive, the number of teeth of a wheel to the number of worm runs in a worm gear, the number of teeth of a large sprocket to the number of teeth of a small one in a chain drive transmission, as well as the diameter of a large pulley or roller to the diameter of a smaller one in a belt or friction drive. The gear ratio characterizes the change in rotation speed in the transmission

where and is the rotation frequency of the driving I and driven II shafts, min -1 or s -1 (see Fig. 3.1, a, b and c).

So, for gears (see Fig. 3.1, A) and chain drives

where is the number of teeth of the larger gear or sprocket; - the number of teeth of the smaller gear or sprocket.

For worm gear (see Fig. 3.1, b)

where is the number of teeth of the worm wheel; - number of worm passes.

For belt drive (Fig. 3.1, c)

where is the diameter of the driven (larger) transmission pulley, mm; - diameter of the driving (smaller) transmission pulley, mm.

To convert rotational motion into translational motion or vice versa, a rack and pinion is used (Fig. 3.1, G) or helical (Fig. 3.1, e) gear. In the first case, the axis of rotational motion and the direction of translational motion are perpendicular, and in the second case they are parallel.

Gears that convert rotational motion into translational motion are characterized by the distance through which the moving element moves translationally during one revolution of the drive shaft.

In a rack and pinion transmission (see Fig. 3.1, d) the movement of the rack per revolution of the gear wheel (gear)

where is the number of wheel teeth; - engagement module.

Rice. 3.1. Gears in machines: a - gear: I - drive shaft; - number of gear teeth; - rotation speed of the drive shaft; II - driven shaft; - number of wheel teeth; - driven shaft rotation speed; b - worm: and - rotation speed and number of worm passes, respectively; and are the rotation speed and number of wheel teeth, respectively; c - belt: and - rotation speed of the drive roller and its diameter, respectively; and are the rotation speed of the driven roller and its diameter, respectively; g - screw: - screw pitch; - direction of movement of the nut; d - rack: - direction of movement of the rack; - rack tooth pitch; - number of wheel teeth; - direction of wheel rotation

The screw-nut pair is used in the feed mechanisms of almost all machine tools. When you turn the screw one turn, the nut moves to the right or left (depending on the direction of the thread) one step. There are designs in which the nut is stationary, and the screw rotates and moves, as well as designs with a rotating and moving nut. For screw-nut transmission, movement of a progressively moving element

where is the propeller pitch, mm; - number of propeller passes.

When several gears are arranged in series, their total gear ratio is equal to the product of the gear ratios of the individual gears

where is the total gear ratio of the kinematic chain; - gear ratios of all elements of the kinematic chain.

The rotation speed of the last driven shaft of the kinematic chain is equal to the rotation speed of the drive shaft divided by the total gear ratio,

Movement speed (mm/min) of the final element (node) of the kinematic chain

where is the rotation speed of the drive shaft of the initial element; - displacement of the progressively moving element per revolution of the drive shaft, mm.

The mathematical expression of the relationship between the movements of the leading and driven elements (initial and final links) of the kinematic chain of a machine tool is called the kinematic balance equation. It includes components that characterize all elements of the chain from the initial to the final link, including those that transform motion, for example, rotational into translational. In this case, the balance equation includes a unit of measurement of the parameter (lead screw pitch - when using a screw-nut transmission or module - when using a gear-rack transmission) that determines the conditions for this transformation, millimeter. This parameter also allows you to coordinate the motion characteristics of the initial and final links of the kinematic chain. When transmitting only rotational motion, the equation includes dimensionless components (gear ratios of mechanisms and individual gears), and therefore the units of measurement of the motion parameters of the final and initial links are the same.

For machines with main rotational motion, the limiting values ​​of spindle rotation speeds ensure processing of workpieces with a diameter of machined surfaces in the range from to .

The spindle speed control range characterizes the operational capabilities of the machine and is determined by the ratio of the highest machine spindle speed to the lowest:

The rotation speed values ​​from to form a series. In machine tool building, as a rule, a geometric series is used, in which adjacent values ​​differ by a factor of (- denominator of the series: ). The following denominator values ​​are accepted and normalized: 1.06; 1.12; 1.26; 1.41; 1.58; 1.78; 2.00. These values ​​form the basis for the table series of spindle speeds.

3.2. Typical machine parts and mechanisms

Beds and guides. The supporting system of the machine is formed by the totality of its elements, through which the forces arising between the tool and the workpiece during the cutting process are closed. The main elements of the machine's supporting system are the bed and body parts (crossbars, trunks, sliders, plates, tables, supports, etc.).

Bed 1 (Fig. 3.2) is used for mounting parts and assemblies of the machine; moving parts and assemblies are oriented and moved relative to it. The bed, like other elements of the supporting system, must have stable properties and ensure, during the service life of the machine, the ability to process workpieces with specified modes and accuracy. This is achieved by the correct choice of bed material and its manufacturing technology, and the wear resistance of the guides.

Rice. 3.2. Machine beds: a - screw-cutting lathe; b - turning with program control; c - surface grinding; 1 - bed, 2 - guides.

For the manufacture of beds, the following basic materials are used: for cast beds - cast iron; for welded ones - steel, for the beds of heavy machine tools - reinforced concrete (sometimes), for high-precision machine tools - synthetic synthetic material, made on the basis of crumbs of mineral materials and resin and characterized by minor temperature deformations.

Guides 2 provide the required relative position and the possibility of relative movement of units carrying the tool and the workpiece. The design of the guides for moving the unit allows only one degree of freedom of movement.

Depending on the purpose and design, there is the following classification of guides:

By type of movement - main movement and feed movement; guides for rearranging associated and auxiliary units that are stationary during processing;

Along the trajectory of movement - rectilinear and circular movement;

In the direction of the trajectory of movement of the node in space - horizontal, vertical and inclined;

By geometric shape - prismatic, flat, cylindrical, conical (only for circular motion) and their combinations.

Rice. 3.3. Examples of sliding guides: a - flat; 6 - prismatic; c - in the form of a “dovetail”

The most widely used are sliding guides and rolling guides (the latter use balls or rollers as intermediate rolling elements).

For the manufacture of sliding guides (Fig. 3.3) (when the guides are made as one piece with the frame) gray cast iron is used. The wear resistance of the guides is increased by surface hardening, hardness HRC 42...56.

Steel guides are overhead, usually hardened, with a hardness of HRC 58…63. Most often, steel 40X is used with hardening with HDTV 1, steel 15X and 20X - followed by carburization and hardening.

Reliable operation of the guides depends on protective devices that protect the working surfaces from dust, chips, and dirt (Fig. 3.4). Protective devices are made from various materials, including polymers.

Spindles and their supports. A spindle is a type of shaft that serves to secure and rotate a cutting tool or device that carries a workpiece.

To maintain processing accuracy during the specified service life of the machine, the spindle ensures the stability of the axis position during rotation and translational motion, and the wear resistance of the supporting, seating and basing surfaces.

Spindles, as a rule, are made of steel (40Kh, 20Kh, 18KhGT, 40KhFA, etc.) and are subjected to heat treatment (cementation, nitriding, volumetric or surface hardening, tempering).

To secure a tool or fixture, the front ends of the spindles are standardized. The main types of machine spindle ends are shown in table. 3.2.

Rice. 3.4. The main types of protective devices for guides: a - shields; b - telescopic shields; c, d and d - tape; e - harmonica-shaped bellows

Sliding and rolling bearings are used as spindle supports. The design diagram of adjustable sliding bearings, made in the form of bronze bushings, one of the surfaces of which has a conical shape, is shown in Fig. 3.5.

The sliding bearings of spindles use lubricant in the form of a liquid (in hydrostatic and hydrodynamic bearings) or gas (in aerodynamic and aerostatic bearings).

There are single and multi-wedge hydrodynamic bearings. Single wedge ones are the simplest in design (bushing), but do not provide a stable position of the spindle at high sliding speeds and low loads. This disadvantage is absent in multi-wedge bearings, which have several load-bearing oil layers covering the spindle neck evenly on all sides (Fig. 3.6).

Table 3.2

Main types of machine spindle ends

Rice. 3.5. Adjustable plain bearings: a - with a cylindrical spindle neck: 1 - spindle neck; 2 - split bushing; 3 - body; b - with a conical spindle neck: 1 - spindle; 2 - solid bushing

Rice. 3.6. Grinding wheel spindle support with hydrodynamic five-liner bearing: 1 - self-aligning inserts; 2 - spindle; 3 - clip; 4 - screw; 5 - rolling bearings; 6 - screws with a spherical support end; 7 - cuffs

Hydrostatic bearings - sliding bearings in which an oil layer between the rubbing surfaces is created by supplying oil under pressure from a pump - ensure high accuracy of the position of the spindle axis during rotation, have greater rigidity and provide fluid friction at low sliding speeds (Fig. 3.7 ).

Gas-lubricated bearings (aerodynamic and aerostatic) are similar in design to hydraulic bearings, but provide lower friction losses, which allows them to be used in supports of high-speed spindles.

Rolling bearings are widely used as spindle supports in machine tools of various types. There are increased demands on the rotational accuracy of spindles; therefore, bearings of high accuracy classes are used in their supports, installed with preload, which eliminates the harmful effects of clearances. The interference in angular contact ball and tapered roller bearings is created when they are installed in pairs as a result of the axial displacement of the inner rings relative to the outer ones.

This displacement is carried out using special structural elements of the spindle assembly: spacer rings of a certain size; springs ensuring constant preload force; threaded connections. In roller bearings with cylindrical rollers, the preload is created by deforming the inner ring 6 (Fig. 3.8) when tightening it onto the conical neck of the spindle 8 using a bushing 5 moved by nuts 1. The spindle bearings are reliably protected from contamination and leakage of lubricant by lip and labyrinth seals 7 .

Rolling bearings 4 are widely used as thrust bearings, fixing the position of the spindle in the axial direction and absorbing loads arising in this direction. The preload of the ball thrust bearings 4 is created by springs 3. The springs are adjusted using nuts 2.

Rice. 3.7. Hydrostatic bearing: 1 - bearing shell; 2 - spindle neck; 3 - pocket creating the bearing surface (arrows indicate the direction of supply of lubricant under pressure and its removal)

Rice. 3.8. Front support of the lathe spindle on rolling bearings: 1 - nuts; 2 - adjusting nuts; 3 - springs; 4 - thrust rolling bearings; 5 - bushings; 6 - inner ring of the roller bearing; 7 - seals; 8 - spindle

An example of the use of angular contact ball bearings to absorb axial loads is shown in Fig. 3.6. Preload is created by adjusting the position of the outer
bearing rings 5 ​​using nut 4.

Typical mechanisms for carrying out translational motion. Translational motion in the machines under consideration is provided by the following mechanisms and devices:

Mechanisms that convert rotational motion into translational motion: a gear wheel or a worm with a rack, a lead screw - nut and other mechanisms;

Hydraulic devices with a cylinder-piston pair;

Electromagnetic devices such as solenoids, used mainly in drives of control systems. Let us give examples of some of these mechanisms (for symbols, see Table 3.1).

The gear-rack pair has a high efficiency, which makes it suitable for use in a wide range of rack speeds, including in main motion drives that transmit significant power, and in auxiliary motion drives.

A worm-and-rack gear differs from a gear-rack pair in its increased smoothness of movement. However, this transmission is more difficult to manufacture and has lower efficiency.

The lead screw - nut mechanism is widely used in drives for feeds, auxiliary and installation movements and provides: a small distance over which the moving element moves per one revolution of the drive; high smoothness and accuracy of movement, determined mainly by the accuracy of manufacturing of the pair elements; self-braking (in pairs of screw-sliding nut).

In the machine tool industry, six accuracy classes are established for lead screws and sliding nuts: 0 - the most accurate; 1, 2, 3, 4 and 5 classes, with the help of which the permissible deviations in pitch, profile, diameters and surface roughness parameters are regulated. The design of the nuts depends on the purpose
mechanism.

Pairs of lead screw - sliding nut are replaced with rolling screw pairs due to low efficiency (Fig. 3.9). These pairs eliminate wear, reduce friction losses, and can eliminate clearances by creating preload.

The disadvantages inherent in pairs of screw-sliding nut and screw-rolling nut, due to the peculiarities of their operation and manufacture, are eliminated in the hydrostatic screw-nut transmission. This pair operates under conditions of friction with a lubricant; Transmission efficiency reaches 0.99; the oil is supplied to pockets made on the sides of the nut threads.

Typical mechanisms for performing periodic movements. During operation, some machines require periodic movement (change of position) of individual components or elements. Periodic movements can be carried out by ratchet and maltese mechanisms, cam mechanisms and with overrunning clutches, electric, pneumatic and hydraulic mechanisms.

Ratchet mechanisms (Fig. 3.10) are most often used in the feed mechanisms of machine tools, in which periodic movement of the workpiece, cutting (cutter, grinding wheel) or auxiliary (diamond for dressing the grinding wheel) tool is carried out during the overrun or reverse (auxiliary) stroke (in grinding and other machines).

In most cases, ratchet mechanisms are used for linear movement of the corresponding unit (table, caliper, quill). With the help of a ratchet transmission, circular periodic movements are also carried out.

Couplings are used to connect two coaxial shafts. Depending on the purpose, there are non-disengaging, interlocking and safety couplings.

Non-disengaging couplings (Fig. 3.11, a, b, c) are used for rigid (blind) connection of shafts, for example, connection using a sleeve, through elastic elements or through an intermediate element that has two mutually perpendicular protrusions on the end planes and makes it possible to compensate for the misalignment of the shafts being connected .

Rice. 3.9. Pair of screw-friction nut: 1, 2 - nut, consisting of two parts; 3 - screw; 4 - balls (or rollers)

Rice. 3.10. Ratchet mechanism diagram: 1 - ratchet; 2 - dog; 3 - shield; 4 - traction

Interlocking couplings (Fig. 3.11, d, e, f) are used for periodic connection of shafts. The machines use interlocking cam couplings in the form of disks with end teeth-cams and gear couplings. The disadvantage of such meshed couplings is the difficulty of engaging them when there is a large difference in the angular velocities of the driving and driven elements. Friction clutches do not have the disadvantages inherent in cam clutches and allow them to be engaged at any rotation speed of the driving and driven elements. Friction clutches come in cone and disk types. In main motion and feed drives, multi-disc clutches are widely used, transmitting significant torques with relatively small overall dimensions. The compression of the driving disks with the driven ones is carried out using mechanical, electromagnetic and hydraulic drives.

Rice. 3.11. Couplings for connecting shafts: a - rigid sleeve type; b - with elastic elements; c - cross-movable; g - cam; d - multi-disc with mechanical drive: 1 - washer; 2 - pressure disk; 3 - balls; 4 - fixed bushing; 5 - bushing; 6 - nut; 7 - springs; e - electromagnetic: 1 - splined bushing; 2 - electromagnetic coil; 3 and 4 - magnetically conductive disks; 5 - anchor; 6 - bushing

Safety couplings (Fig. 3.12) connect two shafts under normal operating conditions and break the kinematic chain when the load increases. Chain rupture can occur when a special element is destroyed, as well as as a result of slippage of mating and rubbing parts (for example, disks) or disengagement of the cams of two mating parts of the coupling.

A pin is usually used as a destructible element, the cross-sectional area of ​​which is calculated to transmit a given torque. Disengagement of the mating elements of the coupling occurs provided that the axial force arising on the teeth, cams 1 or balls 5 , when overloaded, exceeds the force created by the springs 3 and adjusted by the nut 4. When displaced, the movable element 2 of the clutch acts on the limit switch, which breaks the electrical power supply circuit of the motor
drive.

Overrunning clutches (Fig. 3.13) are designed to transmit torque when the links of a kinematic chain rotate in a given direction and to disconnect the links when rotating in the opposite direction, as well as to transmit to the shaft different rotation frequencies (for example, slow - working rotation and fast - auxiliary ). The overrunning clutch allows you to transmit additional (fast) rotation without turning off the main chain. The most widely used in machine tools are roller type couplings, which can transmit torque in two directions.

Ratchet mechanisms are also used as overtaking clutches.

Rice. 3.12. Schemes of safety couplings: a - ball; b - cam; 1 - cams; 2 - movable element of the coupling; 3 - springs; 4 - nut; 5 - balls

Rice. 3.13. Overrunning roller clutch: 1 - clip; 2 - hub; 3 - rollers; 4 - drive fork; 5 - springs

3.3. Main and feed drives

A set of mechanisms with a source of motion, which serves to activate the executive body of a machine tool with specified characteristics of speed and accuracy, is called a drive.

Metal-cutting machines are equipped with an individual drive; On many machines, the main movement, feed movement, and auxiliary movements are carried out from separate sources - electric motors and hydraulic devices. The speed change can be stepless or stepwise.

Electric motors of direct and alternating current, hydraulic motors and pneumatic motors are used as drives for metal-cutting machines. Electric motors are the most widely used drives for machine tools. Where stepless control of the shaft speed is not required, asynchronous AC motors are used (as they are the cheapest and simplest). For stepless speed control, especially in feed mechanisms, DC electric motors with thyristor control are increasingly used.

The advantages of using an electric motor as a drive include: high rotation speed, the possibility of automatic and remote control, and the fact that their operation does not depend on the ambient temperature.

Among the transmissions of motion from the engine to the working parts of the machine, mechanical transmissions are most widespread. According to the method of transmitting motion from the driving element to the driven element, mechanical transmissions are divided as follows:

Friction transmissions with direct contact (friction) or with a flexible connection (belt);

Gear transmissions with direct contact (gear, worm, ratchet, cam) or with a flexible connection (chain).

Friction transmissions with a flexible connection include belt transmissions (Fig. 3.14). In these transmissions, the pulleys of the drive and driven shafts are covered by a belt with a certain tension force, which provides the friction force between the belt and the pulleys necessary to transmit force. The tension, limited by the strength of the belt, is adjusted by moving the shafts apart or using a special tensioning device.

Belts are made of leather, rubberized fabric, plastic, and they have different cross-sectional shapes. Belts with a flat section (Fig. 3.14, b) are used when transmitting high speeds (50 m/s and above) with relatively little effort. Large powers are transmitted by several V-belts (Fig. 3.14, c) or a poly-V-belt (Fig. 3.14, d). Transmissions with round belts (Fig. 3.14, e) are used for low relative forces and in transmissions between cross shafts. Belts with a poly-V-section are widely used (see Fig. 3.14, d) to increase the friction force (at the same tension as for flat belts).

In friction and belt drives, slipping always occurs between the rubbing surfaces, so the actual gear ratio for them is:

where is the theoretical gear ratio; - slip coefficient.

To prevent slipping, toothed belts are used (Fig. 3.14, e).

Rice. 3.14. Diagram of a belt drive (a) and transmission with a flat belt (b), V-belt (c), poly V-belt ( G), round belt (d), timing belt ( e): 1 - pulling metal cable of the toothed belt; 2 - toothed belt base made of plastic or rubber; 3 - pulley; - leading roller; and are the center of rotation and the diameter of the drive roller, respectively; - driven roller; and are the center of rotation and the diameter of the driven roller, respectively; - belt tension force; - distance between the centers of rotation of the driving and driven rollers

Chain transmissions (Fig. 3.15) (for lubrication and cooling systems), like transmission by toothed belts, more stably transmit rotation speed to the driven shaft and can transmit greater power.

Rice. 3.15. Chain drive: - drive sprocket; - driven sprocket

Gear transmission (Fig. 3.16) is the most common transmission, as it provides high stability of rotation speeds, is capable of transmitting high powers and has relatively small overall dimensions. Gears are used to transmit rotation between shafts (parallel, intersecting, intersecting), as well as to convert rotational motion into translational motion (or vice versa). Movement from one shaft to another is transmitted as a result of the mutual engagement of gears forming a kinematic pair. The teeth of these wheels have a special shape. The most common gearing is one in which the profile of the teeth is outlined along a curve called the involute of a circle or simply the involute, and the gearing itself is called involute.

The drive with gearboxes is the most common drive for the main movement and feed movement in metal-cutting machines and is called a gearbox and a feedbox, respectively.

Speed ​​boxes (Fig. 3.17) are distinguished by their layout and method of switching speeds. The layout of the gearbox is determined by the purpose of the machine and its standard size.

Gearboxes with replaceable wheels are used in machine tools with relatively rare drive settings. The box is characterized by simplicity of design and small overall dimensions.

Speed ​​boxes with movable wheels (Fig. 3.17, a) are widely used mainly in universal manually operated machines.

Rice. 3.16. Types of gears for rotational movements: a and b - straight-cut cylindrical gear of external and internal gearing, respectively; c - helical cylindrical gear of external gearing; g - spur bevel gear; d - chevron wheel; e - worm gear

Rice. 3.17. Kinematic diagrams of gearboxes: a - with mobile wheels: - gears; b - with cam clutches: 0, I, II, III, IV - gearbox shafts; - gears; - electric motor; Mf1, Mf2, MfZ, Mf4 - friction clutches; - claw coupling

The disadvantages of these boxes are: the need to turn off the drive before changing gears; the possibility of an accident if the lock is broken and two gears of the same group are simultaneously engaged between adjacent shafts; relatively large dimensions in the axial direction.

Speedboxes with cam clutches (Fig. 3.17, b) are characterized by small axial movements of the clutches during switching, the possibility of using helical and chevron wheels, and low switching forces. The disadvantages include the need to turn off and slow down the drive when changing gears.

Gearboxes with friction clutches, unlike gearboxes with cam clutches, provide smooth gear changes on the go. In addition to the disadvantages inherent in boxes with claw couplings, they are also characterized by limited transmitted torque, large overall dimensions, reduced efficiency, etc. Despite this, boxes are used in machines of turning, drilling and milling groups.

Gearboxes with electromagnetic and other clutches that allow the use of remote control are used in various automatic and semi-automatic machines, including CNC machines. To unify the drive of the main movement of such machines, the domestic machine tool industry produces unified automatic gearboxes (AKS) in seven overall sizes, designed for a power of 1.5...55 kW; number of speed steps - 4... 18.

Depending on the type of gear mechanisms used to adjust the feeds, the following feed boxes are distinguished:

With replaceable wheels at a constant distance between the shaft axes;

With movable wheel blocks;

With built-in stepped wheel cones (sets) and draw keys;

Norton (with ring gear);

With guitars of interchangeable wheels.

To obtain feed boxes with specified characteristics, they are often designed using several of the listed mechanisms simultaneously.

Norton boxes are used in feed drives of screw-cutting machines due to the possibility of accurately implementing specified gear ratios. The advantages of boxes of this type are a small number of gears (the number of wheels is two more than the number of gears), the disadvantages are low rigidity and accuracy of mating of the engaged wheels, the possibility of clogging of gears if there are cutout in the box body.

Feed boxes with replacement wheels (Fig. 3.18) make it possible to adjust the feed with any degree of accuracy. The features of guitars with interchangeable wheels make them convenient for use in various types of machines, especially in machines for serial and mass production. Such machines are equipped with appropriate sets of replacement wheels.

Rice. 3.18. Kinematic diagram (a) and design (b and c) of the guitar of replaceable gears: 1 - rocker; 2 - nut; 3 - screw; K, L, M, N - gears

3.4. General information about the technological process
machining

The process of creating material wealth is called production.

The part of the production process that contains targeted actions to change and (or) determine the state of the object of labor is called the technological process. The technological process can be related to the product, its component, or to methods of processing, shaping and assembly. Objects of labor include blanks and products. Depending on the execution method, the following elements of technological processes are distinguished:

Shaping (casting, molding, electroforming);

Processing (cutting, pressure, thermal, electrophysical, electrochemical, coating);

Assembly (welding, soldering, gluing, sub-assembly and general assembly);

Technical control.

The completed part of the technological process, performed at one workplace, is called a technological operation. The definition of these terms is given in GOST 3.1109-82.

In production, a worker most often has to deal with the following types of descriptions of technological processes in terms of their level of detail:

A route description of a technological process is an abbreviated description of all technological operations in the route map in the sequence of their execution, without indicating transitions and technological modes;

Operational description of the technological process, a complete description of all technological operations in the sequence of their execution, indicating transitions and technological modes;

An abbreviated description of technological operations in a route map in the sequence of their execution, with a full description of individual operations in other technological documents, is called a route-operational description of the process.

The description of manufacturing operations in their technological sequence is given in compliance with the rules for recording these operations and their coding. For example, cutting operations performed on metal-cutting machines are divided into groups. Each group is assigned specific numbers: 08 - program (operations on computer-controlled machines); 12 - drilling; 14 - turning; 16 - grinding, etc.

When recording the content of operations, the established names of technological transitions and their conventional codes are used, for example: 05 - bring; 08 - sharpen; 18 - polish; 19 - grind; 30 - sharpen; 33 - grind; 36 - milling; 81 - secure; 82 - configure; 83 - reinstall; 90 - remove; 91 - install.

The part of the technological operation carried out with constant fixation of the workpieces being processed is called at camp The fixed position occupied by a workpiece permanently fixed in a fixture relative to a tool or a stationary piece of equipment for performing a certain part of the operation is called position.

The main elements of a technological operation include transitions. A technological transition is a completed part of a technological operation, performed by the same means of technological equipment under constant technological conditions and installation. An auxiliary transition is a completed part of a technological operation, consisting of human and (or) equipment actions that are not accompanied by a change in the properties of the object of labor, but are necessary to complete the technological transition.

When registering technological processes, a set of technological documentation is created - a set of sets of technological process documents and individual documents necessary and sufficient to carry out technological processes in the manufacture of a product or its components.

The Unified System of Technological Documentation (UTDS) provides the following documents: route map, sketch map, operational map, equipment list, materials list, etc. Description of the content of technological operations, i.e. a description of the route technological process is given in a route map - the main technological document in the conditions of single and pilot production, with the help of which the technological process is brought to the workplace. In the route map, in accordance with the established forms, data on equipment, accessories, material and labor costs are indicated. The operational technological process is presented in operational cards compiled together with sketch cards.

A technological document can be graphic or text. It separately or in combination with other documents defines the technological process or operation of manufacturing a product. A graphic document, which, by its purpose and content, replaces a working drawing of a part in a given operation, is called an operational sketch. The main projection on the operational sketch depicts the view of the workpiece from the side of the workplace at the machine after the operation has been completed. The machined surfaces of the workpiece in the operational sketch are shown as a solid line, the thickness of which is two to three times greater than the thickness of the main lines in the sketch. The operational sketch indicates the dimensions of the surfaces processed in this operation and their position relative to the bases. You can also provide reference data indicating “dimensions for reference”. The operational sketch indicates the maximum deviations in the form of numbers or symbols of tolerance and fit fields in accordance with the standards, as well as the roughness of the processed surfaces that must be ensured by this operation.

The rules for recording operations and transitions, encoding them and filling out cards with data are determined by the standards and methodological materials of the parent organization for the development of the UST.

Control questions

1. Give formulas for determining the cutting speed during the main rotational motion.

2. How are the gear ratios of kinematic pairs of machine tools found?

3. What is the regulation range?

4. What are the requirements for machine beds and guides?

5. Tell us about the purpose and designs of spindle units and bearings.

6. What couplings are used in machine tools?

7. Define a drive and tell us about the drives used in machine tools.

8. What basic elements of machine tool drives do you know?

9. Tell us about the types and designs of gearboxes.

10.What designs of feed boxes are used in machine tools?

11.What is called a technological process? Name the components of technological processes.

In accordance with GOST 2.703 - 68, the kinematic diagram must depict the entire set of kinematic elements and their connections, all kinematic connections between pairs, chains, etc., as well as connections with sources of motion.

The kinematic diagram of the product should be drawn, as a rule, in the form of a development. It is allowed to depict diagrams in axonometric projections and, without disturbing the clarity of the diagram, move elements up or down from their true position, as well as rotate them to positions that are most convenient for depiction. In these cases, the conjugate links of the pair, drawn separately, should be connected by a dashed line.

All elements of the diagram must be depicted with conventional graphic symbols in accordance with GOST 2.770 - 68 (Fig. 10.1) or simplified external outlines.

The elements of the diagram should be depicted:

shafts, axes, rods, etc. - with solid main lines of thickness S;

elements depicted in simplified external outlines (gears, worms, pulleys, sprockets, etc.) - with solid thin lines of thickness S/2;

the outline of the product in which the diagram is inscribed - with solid thin lines of thickness S/3;

kinematic connections between the conjugate links of the pair, drawn separately, by dashed lines of thickness S/2;

the extreme positions of the element that changes its position during operation of the product - thin dash-dotted lines with two dots;

shafts or axes covered by other elements (invisible) - dashed lines.

Each kinematic element should be assigned a serial number, starting from the source of motion. The shafts are numbered with Roman numerals, the remaining elements are numbered with Arabic numerals. Elements of purchased or borrowed mechanisms (for example, gearboxes) are not numbered; a serial number is assigned to the entire mechanism.

The serial number is placed on the leader line shelf. Under the shelf it is necessary to indicate the main characteristics and parameters of the kinematic element:

power of the electric motor, W and speed of its shaft, min -1 (angular speed, rad/s) or power and speed of rotation of the input shaft of the unit;

torque, N·m, and rotational speed, min -1 of the output shaft;

the number and angle of inclination of the teeth and the module of gears and worm wheels, and for a worm - the number of starts, the module and diameter coefficient;

diameters of belt pulleys; number of sprocket teeth and chain pitch, etc.

If the diagram is overloaded with images of connections and kinematic links, the characteristics of the diagram elements can be indicated in the field of the drawing - diagram in the form of a table. It provides a complete list of constituent elements.

Let us explain some aspects of the process of reading and executing kinematic diagrams, and, first of all, with the accepted conventions when creating kinematic diagrams.

1. The kinematic diagram is usually depicted in the form of a sweep. What does this word mean in relation to the kinematic diagram?

The fact is that the spatial arrangement of the kinematic links in the mechanism is for the most part such that it makes it difficult to depict them on the diagram, since the individual links obscure each other.

This in turn leads to misunderstanding or misconception about the circuit. To avoid this, the circuits use the conditional method of so-called expanded images.

In Fig. 10.1, a shows an image of two pairs of gears. Since gear wheels are usually depicted in kinematic diagrams as rectangles, it is easy to imagine that for a given spatial arrangement of gear wheels their images will overlap in pairs.

To prevent such overlaps, regardless of the spatial location of the kinematic links in the mechanism, they are usually depicted in expanded form, that is, the rotation axes of all mating gears must lie in the same plane, parallel to the image plane (see Fig. 10.1, b).

An example of the development of kinematic links in a diagram.

2. The transition from a constructive scheme to a kinematic one facilitates the figurative perception of the latter (Fig. 10.2). From this diagram it can be seen that crank 1 has a rigid support, which is marked by a thick basic line with shading; piston 2, shown in the kinematic diagram as a rectangle, has a gap with the cylinder walls, which, as stationary elements, also have one-sided hatching. The gap indicates possible reciprocating movement of the piston.

Structural and kinematic diagrams of an internal combustion engine

3. In all diagrams, shafts and axles are depicted with the same thick main line (Fig. 10.3). The difference between them is as follows:

a) shaft supports are depicted by two dashes with a gap along both shaft stops; Since the shafts rotate together with gear wheels (pulleys) mounted and keyed to them, the supports are either plain or rolling bearings. In cases where it is necessary to clarify the type of shaft supports, the standard provides special designations based on the given dashes;

b) the axis is a stationary product, therefore its ends are embedded in stationary supports, marked on the diagram by straight segments with one-sided hatching. The gear wheel mounted on the axle rotates freely when the driven wheel rotates on the shaft.

Shafts and axles on kinematic diagrams

4. Some rules for reading kinematic diagrams:

a) for the most part, the driving gear (pulley) is the smaller of the mating pair, and the larger is the driven one (Fig. 10.4). The letters n 1 and n 2 indicated in the diagram are the designation of the gear ratio or the ratio of the rotation speed n of the driving and driven wheels: n 1 / n 2 ;

Drive shaft and driven shaft on kinematic diagrams

b) in Fig. Figure 10.5 shows a reduction gear, since n 1 > n 2. In a gear drive, the mating gears are made from the same module, so the larger wheel has more teeth. Gear ratio:

where Z 1 and Z 2 are the number of teeth of the gear wheels;

Reducing gear transmission

c) in Fig. 10.6 shows an overdrive, since n 1< n 2 ;

d) in Fig. Figure 10.7 shows transmissions at three speeds: a step-pulley transmission with a flat belt and a gearbox with a movable block of gears.

In a belt drive, for the use of one belt at all stages, the following condition is provided: d 1 + d 2 = d 3 + d 4 = d 5 + d 6, where d 1, d 2, d 3, d 4, d 5, d 6 - pulley diameters in mm.

Rotation is transmitted from shaft I to shaft II (n I and n II).

Rotation frequency:

n II =n I d 1 /d 2 ; n II =n I d 3 /d 4 ; n II =n I d 5 /d 6 .

Overdrive gearing

Three speed gears

In Fig. 10.7, b shows a gearbox for three rotation speeds with a movable block of gears Z 1 - Z 3 - Z 5, which can move along the shaft key I; on shaft II, the wheels are rigidly connected to the shaft with keys.

Shaft speed II:

n II = n I · Z 1 / Z 2 ; n II = n I · Z 3 / Z 4 ; n II = n I · Z 5 / Z 6 .

where Z 1, Z 2, Z 3, ..., Z 6 - the number of wheel teeth.

Since the gears are of one module, then

Z 1 +Z 2 =Z 3 +Z 4 = Z 5 +Z 6.

5. It should be noted that “scale-free” schemes are a relative feature. Thus, for basic kinematic diagrams, the ratio of the sizes of the conventional graphic symbols of interacting elements on the diagram should approximately correspond to the actual ratio of the sizes of these elements.

This can be seen from the consideration of the basic kinematic diagrams of the bevel differential of a gear hobbing machine, shown in orthogonal and axonometric projections (see Fig. 10.8). In these diagrams, the geometric dimensions of bevel gears 3...6 are the same.

Kinematic schematic diagram of a bevel differential:

a – orthogonal projection; axonometric projection.

In Fig. 10.9 shows an example of a basic kinematic diagram, which consists of conventional graphic symbols of elements, connections between them and alphanumeric positional designations of elements, as well as constituent elements of the diagram, made in the form of a table. From the image you can imagine the sequence of motion transmission from the engine to the actuator. The table shows the designations of the constituent elements, their explanations and parameters.

Example of a kinematic circuit diagram

In order to schematically depict the main components of a machine tool or other mechanism, kinematic diagrams are used.

In such diagrams, components, details, and interactions between individual elements of the mechanism are depicted conventionally. Each standard element has its own designation.

How to read kinematic diagrams of machine tools

In order to learn to read kinematic diagrams, you need to know the designations of individual elements and learn to understand the interaction of individual components. First of all, we will study the most common designations of the most common elements; symbols on kinematic diagrams are presented in GOST 3462-52.

Shaft designation

The shaft on the kinematic diagram is indicated by a thick straight line. The spindle diagram shows the tip.

Designation of bearings in diagrams

The bearing designation depends on its type.

Sleeve bearing depicted in the form of ordinary bracket supports. If a thrust bearing is used, the supports are shown at an angle.

Ball bearings on the kinematic diagrams of the machines are depicted as follows.

The balls in bearings are conventionally depicted as a circle.

In conditional images roller bearings the rollers are shown as rectangles.

Schematic designation of parts connections

Kinematic diagrams depict various types of shaft and part connections.

The designation of the coupling depends on its type, the most common of which are:

• cam
• friction

The designations of one-way couplings on the kinematic diagrams of machine tools are shown in the figure.

The designation of a double-sided coupling can be obtained by mirroring the horizontal diagram of a single-sided coupling.

Designation of gears on machine diagrams

Gears are one of the most common elements of machine tools. The symbol allows you to understand what type of transmission is used - spur, helical, chevron, bevel, worm. In addition, using the diagram you can find out which wheel is larger and which is smaller.

Name	Designation	Name	Designation
Shaft		Gears:
Connection of two shafts:	cylindrical wheels
deaf
deaf with overload protection		conical wheels
elastic
articulated		screw wheels
telescopic
floating clutch		worm
gear coupling
Connecting the part to the shaft:
free to rotate		rack and pinion
movable without rotation
using a draw key		Transmission by lead screw with nut:
deaf		one-piece
Plain bearings:	detachable
radial		Couplings:
		cam one-sided
		cam double-sided
Rolling bearings:	conical one-sided
radial
angular contact one-sided		disk one-sided
angular contact double-sided		disk double-sided
Belt drives:	electromagnetic one-way
flat belt
electromagnetic two-way
one-way overtaking
V-belt
double-sided overtaking
Brakes:
conical
Chain transmission
block
disk

with wheel z 6 it is necessary that the block passes freely past the wheel z 8 without catching it with the wheel z 9 . This is possible if z 7 – z 9 > 5. Otherwise, it is necessary to use the transmission scheme shown in Fig. 2.15, b. In Fig. 2.15, V brute force transmission is shown. Shaft I can receive rotation from the wheel z 5 when the wheel clutch is engaged z 1 And z 4. With the clutch disengaged and the wheel engaged z 4 With z 3 rotation is transmitted to shaft I through gears z 1 /z 2, shaft II and wheels z 3 /z 4 .

Rice. 2.15. Gearbox mechanisms: A─ with two

mobile units; b─ with a three-crown block;

V─ with overkill; G─ with friction double-sided clutch

Transmissions with moving blocks and claw couplings are simple in design, reliable in operation and easy to control, but do not allow switching during rotation and are large in the axial direction. In Fig. 2.15, G a transmission is presented that is devoid of these shortcomings. Wheels z 2 And z 4 freely mounted on shaft II and constantly engaged with the wheels z 1 And z 3, rigidly fixed to shaft I. The transmission of motion to shaft II from shaft I occurs when a friction double-sided clutch is engaged, which rigidly connects the wheels to shaft II z 2 And z 4. In this case, the rotation speed can be changed on the fly.

Modern metal-cutting machines with automatic gearboxes use single- and double-sided friction electromagnetic clutches.

In Fig. 2.16, A shows the miander mechanism with a cap wheel z 0, allowing the gear ratio to be doubled when an adjacent pair of gears is engaged. If we take shaft I as the driving one, and shaft II as the driven one, and z = z 2 = z 3 = z 6= 56, a z 1 = z 4 = z 5 = z 7= 28, then we get the gear ratios of the mechanism:

Rice. 2.16. Mechanisms of feed boxes:

a ─ with a cap wheel; b ─ with a movable wheel

The miander mechanism is also called the “multiplying mechanism.” The mechanism with a ring wheel has the disadvantage that it does not provide a constant center distance between the ring wheel z 0 And z 2, since the rotary lever 2 is fixed with a non-rigid movable cylindrical clamp 1.

In Fig. 2.16, b a more advanced design of the miander mechanism is shown, from which the ring wheel with a rotary lever is excluded.

The blocks are connected to the wheels by a movable wheel z, which ensures constant axle distances.

The Norton mechanism (Fig. 2. 17) is a cone made up of gears, with a ring wheel mounted on a rotary lever with a cylindrical lock. Union wheel z 0 can alternately engage with all the wheels of the cone ( z 1 – z 6) and transmit movement from shaft I to shaft II. In this way, six different gear ratios can be obtained. The choice of the number of teeth of the cone wheels is not related to the constancy of the center distance between the drive and driven shafts. The advantage of this mechanism is its compactness, the disadvantage is low rigidity. The main purpose of this mechanism is to create an arithmetic series of gear ratios. Mainly used in universal screw-cutting lathes.

Shown in Fig. 2.15, A The six-speed gearbox circuit is a conventional multiplying structure, consisting of one kinematic chain with a series connection of movable units (gear groups), and provides a geometric series of circular rotation frequencies of the output shaft. This structure makes it possible to successfully create rational drives of the main movement. However, in a number of cases, for example, in universal screw-cutting lathes, when the speed control range increases, it is impossible to create a simple drive that meets the requirements based on such a structure. Therefore, so-called folded structures are used in machine tool construction. Folded is the structure of a multi-speed step drive, consisting of two, less often three, kinematic chains, each of which is a conventional multiplying structure. One of these chains (short) is intended for high drive speeds, the other (longer) for low speeds. As an example in Fig. Figure 2.18 shows a diagram of a gear box for 12 values ​​of spindle (output shaft) rotation speed, which has a folded