RU2296035C2 - Method of turning cylindrical surfaces - Google Patents

Abstract

FIELD: mechanical engineering.

SUBSTANCE: method comprises rotating the blank around the axis that is in coincident with the centerline of the lathe, moving the tool longitudinally, and feeding the tool transversely. The tool is made of a cut provided with the straight main cutting edge that abuts against the straight auxiliary edge. Toe reduce roughness of the surface to be worked a cut is used whose auxiliary edge lies in the vertical plane parallel to the centerline of the machine tool and is inclined counterclockwise by an angle equal to the main angle of the plane of the standard cut stroke. The main edge of the cut abuts against the bottom end of the auxiliary edge and its extension intersects the centerline of the machine tool.

EFFECT: enhanced quality of turning.

1 cl, 4 dwg, 1 ex

Description

The invention relates to mechanical engineering and can be used in turning external cylindrical surfaces of machine parts, as it can significantly increase the roughness class according to GOST 2789-73 machine parts and significantly increase labor productivity during their processing due to the simultaneous execution of rough and finishing machining operations .

The method of turning cylindrical surfaces by rotating the workpiece around an axis, combined with the center line of the machine and periodic longitudinal and transverse feeds using a cutter as a tool, is widely known (B.F. Bobrov. Fundamentals of the theory of metal cutting. M .: Engineering. 1975. pg. 49-51).

This method is closest in technical essence and the achieved result to the proposed technical solution, therefore, adopted as a prototype. When processing surfaces according to the prototype method, namely during finishing, parts of a roughness class of 5-7 are obtained (Handbook of a metalworker, volume 3, M., 1977, p. 167, 1. Precision of processing on lathes).

To improve the quality of parts, it is necessary to switch after diamond cutting to diamond smoothing (see ibid. In the Metalworker's Guide) or grinding or some other processing method, which reduces labor productivity and increases the cost of processing machine parts and mechanisms.

It is especially difficult to achieve a higher class of surface roughness by the prototype method. This is explained by the fact that all modern lathe group machines have a cyclic kinematic error of the headstock spindle.

The spindle of the front headstock of the lathe, and with it the workpiece, rotate at an average constant speed, while periodically lagging behind the nominal position, and then catch up with the nominal position, therefore, during rotation make torsional vibrations. This is due to the fact that the headstock spindle drive, consisting mainly of gears, almost always has a kinematic error, since in accordance with GOST 1643-91 (Cylindrical gears. Tolerances, see paragraph 1 Degrees of accuracy and types of mating, note) cannot be made without kinematic errors. The sum of the kinematic errors of all the gears of the spindle drive is supplied to the gear wheel, rigidly fixed to the spindle of the front headstock of the machine.

This total kinematic error of the gear wheel rigidly mounted on the spindle is transmitted to the spindle and the workpiece, while during the operation of the machine it increases many times, since the active involute surfaces of the teeth of the gears of the spindle drive do not wear out uniformly. The peak and root of the teeth wear out the most, since the peak and the root of the teeth have a maximum amount of slipping, and wear is minimal on the pole line of the teeth, since the rolling is pure on the pole line. The sliding friction coefficient in gears is an order of magnitude greater than the rolling friction coefficient. f _ck = 0.07-0.1 = 0.85 - coefficient of sliding friction (A.I. Petrusevich. Gear and worm gears. In the book. Machine parts. GNTI, 1951, p. 187); f _kach = 0.008 cm is the coefficient of rolling friction (G.K. Trubin. Fatigue of materials for gears. Mashgiz, 1962, p. 55, tab. No. 5).

The ratio of the friction forces at the top (root) of the tooth and in the gearing pole of the last gear, the driven wheel of which is rigidly fixed to the spindle of the headstock, for example, 1A62 turning and screw-cutting machine (N.I. Shavlyuga. Kinematic chains of metal cutting machines. Mashgiz, 1950) ., pp. 24-26, Fig. 4, gear 24-25 z ₂₄ = 32, z ₂₅ = 64, m = 3.25 mm, α = 20, 45 °), is T _in : T _p = ( f _ck : f _qual ) · ρ _p = 12.9 times,

where T _in = f _SC · F is the friction force at the top (root) of the tooth;

T _p = t _Kach · F: ρ _p - rolling friction force in the gearing pole of the teeth;

ρ _p = 1.211 cm is the reduced radius of curvature at the gearing pole.

(1: ρ _p ) = (1: ρ ₁ ) + (1: ρ ₂ ); ρ ₁ = r ₁ · sinα = 52 · sin20.45 ° = 18.168 mm; similarly ρ ₂ = 36.337 mm; ρ _p = 12.11 mm.

Thus, the friction force at the tooth apex is 12.9 times greater than the friction force on the pole line. An order of magnitude, therefore, the involute tooth profiles do not wear out uniformly and acquire a significant magnitude of the cyclic kinematic error of the tooth frequency.

In 2004, TSNIITMASH investigated the stability of involute gears of the rolling mill 2000 of Severstal OJSC in Cherepovets. It was found that all involute gears (module 32-36 mm) have this pattern of wear on the active surfaces of the teeth.

The amplitude of torsional vibrations (cyclic kinematic error of the gear frequency of the driving and driven gear large-modular wheels, operated from one to three years, exceeds the permissible ones according to GOST 1643-91 from 24 to 84 times.

As a result, kinematic errors from manufacturing, from wear and other errors are summed up and transmitted to the workpiece. This error has a cyclical nature, its frequency is equal to the number of teeth of the gear wheel rigidly fixed to the spindle.

The amplitude of torsional vibrations of the workpiece during its turning is a circumferential feed to the tool (to the cutter) processing the part. In this regard, within each torsional vibration of the workpiece, the circumferential feed decreases when the part (spindle) is behind, and increases with accelerated rotation. As a result, the cutting force pulsates with a frequency equal to the frequency of the cyclic kinematic error of the part (spindle).

The radial component of the cutting force also pulsates, and when processed by the prototype method, relatively small waves are generated on the workpiece surface in the cross section of the workpiece due to the fact that the main and auxiliary edges are in the same horizontal plane containing the axis of rotation of the workpiece.

The height of these waves represents the maximum values of the roughness parameters that are regulated by GOST 2789-73 (surface roughness, parameters, characteristics). Due to the formation of irregularities on the machined surface, the processing of parts is divided into roughing and finishing, while finishing is performed at lower cutting conditions, which reduces labor productivity.

Consequently, the roughness class of parts processed on lathes depends significantly not only on the accuracy of manufacturing the tool, the machine itself, but also on the smoothness of the spindle of the machine headstock.

The aim of the invention is to improve the quality of cylindrical surfaces machined on a lathe, by reducing roughness and increasing processing productivity due to the simultaneous execution of roughing and finishing operations.

The goal is achieved by rotating the workpiece around an axis that coincides with the center line of the machine, the longitudinal movement of the tool and the transverse feed using a tool as a tool, the main edge of which is made with standard geometric parameters.

During the cutting process, the rectilinear auxiliary edge of the cutter covers the workpiece around its axis of rotation at an angle of more than one cyclic torsional vibration of the spindle of the headstock of the machine. The auxiliary edge of the cutter is placed in a vertical plane parallel to the center line of the machine, and the auxiliary edge is tilted counterclockwise by an angle numerically equal to the main corner of the standard through cutter in plan.

The auxiliary edge of the cutter is combined with the rectilinear generatrix of a single-cavity rotation hyperboloid, the imaginary axis of which is aligned with the center line of the machine, while the rectilinear generatrix of the hyperboloid makes the angle of intersection with its imaginary axis, equal to the angle in terms of the main edge of the standard passage cutter. The throat section of the named hyperboloid divides the auxiliary blade of the cutter into a shorter upper part located above the horizontal plane containing the line of machine centers, and a large active lower part, which is located below the named plane.

The total length of the auxiliary edge is determined by the dependence:

where L ₁ is the length of the lower part of the auxiliary edge of the cutter located below the line of the centers of the machine;

L ₂ = 2-3 mm - the length of the upper part of the auxiliary edge of the cutter located above the center line of the machine, theoretically not taking part in the cutting process, but necessary to compensate for the errors in the installation of the cutter in the tool holder relative to the workpiece;

t ₂ = 0.5 (Dd): 3 - side allowance for fine turning;

D is the diameter of the workpiece;

d is the diameter of the workpiece according to the drawing;

d _to (r _to ) - the diameter (radius) of the circumference of the workpiece, dividing the rough and finish parts of the machining allowance;

φ (β) is the angle of intersection between the rectilinear auxiliary edge of the cutter and the line of machine centers in a vertical plane parallel to the line of center of the machine (angle of intersection of the rectilinear generatrix of a single-cavity rotation hyperboloid with the imaginary axis of the hyperboloid).

The main edge of the cutter is placed below the center line of the machine with a standard angle in plan and is made rectilinear adjacent to the lower end of the auxiliary edge, while the straight line of the main edge of the cutter, when extended, intersects the center line of the machine.

The features that distinguish the proposed method from the prototype are not only new, but also significant. When processing the workpiece with the proposed method, the auxiliary edge of the cutter covers the workpiece around its axis of rotation. The angle of coverage is significantly greater than the wavelength of the cyclic kinematic error of the spindle (workpiece), therefore, the negative effect of torsional vibrations of the spindle on the roughness of the product is eliminated.

As a result, the part processed by the proposed method in the cross section will be free of waves, since the auxiliary edge is inclined relative to the axis of rotation of the part by the angle of the rectilinear generatrix of the single-cavity rotation hyperboloid. The length of the auxiliary edge of the cutter overlaps the wavelength of the cyclic kinematic error.

In this regard, in the cutting process, the humps and troughs of two adjacent waves of cyclic kinematic error emanating from the spindle are simultaneously processed.

The prototype does not have this property, since the auxiliary and the main edges of the cutter are in the same horizontal plane, which is very favorable for the formation of waves on the treated surface in the cross section of the part even with pulsation of a small amount of the horizontal (radial) component of the cutting force.

In this regard, using the prototype, it is impossible to simultaneously perform roughing and finishing operations when machining cylindrical surfaces with a cutter, since the roughness of the parts processed by the prototype method is not high enough.

The proposed method is illustrated by drawings:

figure 1 shows a diagram of the relative position of the workpiece and tool, top view;

figure 2 shows the location of the auxiliary edge of the cutter, right side view;

figure 3 shows the contours of a single-sheeted hyperboloid of revolution and a portion of its rectilinear generatrix, with which the auxiliary edge of the cutter is combined, front view;

figure 4 shows the geometric parameters of the cutter, with which the workpiece is processed according to the proposed method.

In the drawings, the following notation:

1 - cutter;

2 - the main edge of the cutter 1;

3 - workpiece;

4 - spindle of the front headstock of a lathe;

5-5 - contours of a single-cavity hyperboloid of revolution;

6-6 - throat section of a hyperboloid 5;

О-О - line of machine centers;

S _m - longitudinal feed;

t is the transverse feed;

L is the auxiliary edge of the cutter 1;

L ₁ is the active lower part of the auxiliary edge L;

L ₂ - the upper part of the auxiliary edge L;

φ is the angle in terms of the main edge of the cutter 1;

ν - cyclic kinematic error of the spindle 4 (workpiece 3) in the angular measurement;

β is the angle of intersection of the rectilinear generatrix of a single-cavity hyperboloid of revolution with its imaginary axis (the angle of inclination of the auxiliary edge L of cutter 1, numerically equal to the main angle of the standard through cutter in plan);

EE - the rectilinear generatrix of a hyperboloid of revolution 5-5;

Ψ is the angle of coverage by the auxiliary edge L of the workpiece 3 around its axis O-O during the cutting process.

The method of turning cylindrical surfaces is performed by rotating the workpiece around an axis that coincides with the line OO, Fig. 1, the centers of the machine, the longitudinal movement s _{m of the} tool and the lateral feed t using a tool 1 as the tool, the main edge 2 of which is made with standard geometrical parameters.

The proposed method is characterized in that in the process of cutting a straight auxiliary edge L, FIG. 2, the cutter 1 wraps around, FIG. 3, the workpiece 3 around its axis O-O at an angle Ψ, FIG. 2, which is greater than the angle ν of one cyclic torsional oscillations of the spindle 4, figure 1, the headstock of the machine.

For this, the auxiliary edge L, Fig. 3, cutter 1, Fig. 1, is placed in a vertical plane, Figs. 2, 4, parallel to the line OO of the centers and tilt the edge L counterclockwise, Fig. 3, by an angle β = φ, numerically equal to the main corner of the standard through-cutter in plan, while the edge L of the cutter 1 is aligned with the straight-line generatrix EE, Fig. 3, of a single-cavity hyperboloid of revolution 5-5, whose imaginary axis Z is aligned with the line OO of the machine centers.

The rectilinear generatrix EE of the hyperboloid 5-5 makes the angle β of crossing with its imaginary axis Z, equal to the angle φ, Fig. 1, in terms of a standard passage cutter, while the throat section 6-6, Fig. 3, of the named hyperboloid 5-5 divides the minor edge L of cutter 1 into a shorter upper part L ₂ located above the horizontal plane containing the line OO of the machine centers, and a large active lower part L ₁ which is located below the named plane.

The total length of the auxiliary edge L is determined by the dependence:

where L ₁ is the length of the lower active part of the auxiliary edge L of the cutter 1, located below the line OO of the centers of the machine, figure 3;

L ₂ = 2-3 mm - the length of the upper part of the auxiliary edge L of the cutter 1, located above the line OO of the centers of the machine, figure 3, theoretically not taking part in the cutting process, but necessary to compensate for errors in the installation of cutter 1 in the tool holder relative to the workpiece 3 ;

t ₂ = 0.5 (Dd): 3 - side allowance for fine turning;

D is the diameter of the workpiece;

d is the diameter of the workpiece according to the drawing;

d _to (r _to ) - the diameter (radius) of the circumference of the workpiece, dividing the rough and finish parts of the machining allowance, figure 2;

φ (β) is the angle of intersection between the rectilinear auxiliary edge L of cutter 1, Fig. 3, and the line OO of the centers of the machine in a vertical plane parallel to the line OO of the centers of the machine (the angle of intersection of the rectilinear generatrix EE of a single-cavity hyperboloid of rotation 5-5 with its imaginary Z axis).

The main edge 2, Fig. 1, of the cutter 1 is made rectilinear adjacent to the lower end of the auxiliary edge L, Fig. 4, while the straight line of the main edge 2, when extended, intersects the line O-O of the centers of the machine.

An example of a specific implementation of the proposed method. It is required to make a shaft with a diameter of 200 mm from a workpiece with a diameter of 209.5 mm in one pass on a screw-cutting lathe 1A62 (N.I. Shavlyuga. Kinematic chains of machine tools, Mashgiz, 1950, pp. 24-26). The total allowance on the side for roughing and finishing is: t = 9.5: 2 = 4.75 mm (Handbook of metalworker, t.3, M., 1977, Engineering, p.167, table.3). We accept roughing allowance on _Jun t = (2: 3) t = 3.166 mm and a finishing allowance _Num t = t 3 = 1.583 mm.

Determine the coordinates of the point To the circumference of the workpiece, dividing the rough and finish parts of the machining allowance, figure 2. According to the invention, the point K is on the circle d _to , figure 2; equation of this circle: x _k ² + y _k ² = r _k ² . The coordinates of the point K located on the circle d _k are: x _k = -r = -100 mm;

Determine the angle Ψ, figure 2, girth auxiliary blade L _{1 of the} machined shaft 3 around its axis O-O during the cutting process:

sinΨ = y _k : r _k = 17.865: 101.583 = 0.175866; Ψ = 10.129273 °

where r _k = r + (t: 3) = 100 + 1.583 = 101.583 mm;

r = 100 mm is the specified radius of the shaft.

Determine the wavelength of the cyclic kinematic error of the spindle (machined shaft) in the angular measurement:

ν = 360: z = 360: 64 = 5.625 °,

where z = 64 is the number of teeth of the wheel 7, figure 1, rigidly mounted on the spindle 4, since the frequency of the cyclic kinematic error (frequency of torsional vibrations) coming from the drive to the spindle is equal to the number of teeth of the gear 7.

We determine the coefficient of overlapping by the auxiliary edge L _{1 of the} cutter 1 of the wavelength ν of the cyclic kinematic error:

K = Ψ: ν = 10.129: 5.625 = 1.8.

We take the main angle φ in the plan according to well-known recommendations (Handbook of the metalworker, t.3, M .: Engineering, p. 190, table 19): φ = 70 ° and equate this angle φ = β to the angle of inclination of the auxiliary edge L, FIG. 3, cutter 1, figure 1.

где t₂=t_чист=0,5(D-d):3=1,583 мм.We determine the total length L of the auxiliary edge according to:

where t ₂ = t _net = 0.5 (Dd): 3 = 1.583 mm.

A cutter is made with the geometric parameters shown in FIG. 4, and using the calculations performed, the proposed method for turning cylindrical surfaces is performed.

The workpiece is mounted on the machine: one end of the workpiece is fixed in the headstock cartridge, and the other end is supported by the center of the tailstock of the machine. The cutter is fixed on the support of the machine in a position in which the rectilinear auxiliary edge L, Fig. 3, cutter 1 is aligned with the rectilinear generatrix of the single-cavity rotation hyperboloid, the imaginary axis Z of which is aligned with the line O-O of the centers of the machine.

This is achieved by sharpening the cutter, in which the auxiliary edge L is placed in a vertical plane, Fig. 4, parallel to the line OO of the centers of the machine and tilted relative to the line OO of the centers counterclockwise by an angle φ equal to the angle β of crossing the rectilinear generatrix EE of the single-cavity rotation hyperboloid 5-5 with its imaginary axis Z.

The throat section 6-6 of the named hyperboloid 5-5 should divide the auxiliary edge L into two parts: a lower upper length L ₂ and a lower lower L ₁ , located respectively above and below the horizontal plane containing the line OO of the machine centers. After installing the workpiece and the cutter, the machine support is removed to the right with the cutter fixed to the support, the machine’s electric engine is turned on and grinding is performed on the workpiece. Measure the diameter of the workpiece at the point of sharpening. The caliper is moved to the right again, the cutting depth is determined by the nonius due to the transverse feed, and the workpiece is processed cleanly in one pass.

If the workpiece was previously subjected to roughing, then exactly the same finishing operation is performed in one pass. In this case, the design of the cutter is simplified, since the main edge performing the roughing operation is no longer required, the cutting process becomes open, and the role of the main edge passes to the auxiliary edge L, without any adjustments to the proposed method.

The processed cylindrical surface using the proposed method has a significantly higher roughness class according to GOST 2789-73 than the cylindrical surface processed by the prototype method. This is explained by the fact that the part of the metal, which is an allowance for finishing, is cut off by the auxiliary edge L ₁ covering the part, while the edge L ₁ overlaps the wavelength with an overlap factor of 1.8, so the hump and trough of the cyclic kinematic error are processed simultaneously, unlike processing parts according to the prototype method.

When processing by the method of the prototype, the main and auxiliary edges are in the same horizontal plane containing the axis of rotation of the workpiece, so cutting occurs without overlapping the edges of the cutter with the wavelength of the kinematic error (torsional vibration) of the spindle (part) of the headstock of the machine. When processing by the prototype method, within each torsional vibration of the workpiece (spindle), the peripheral feed decreases when the part lags behind the nominal position, and increases with accelerated rotation. Therefore, the cutting force pulsates, the radial component of the cutting force also pulsates, and when processing the part according to the prototype method, small waves inevitably form small waves in the cross section of the machined part.

The height of these waves relative to the troughs of the waves is according to GOST 2789-73 the maximum value of R _z roughness of the machined surface of the part. When processing parts according to the proposed method, the cause of the formation of roughnesses R _z formed due to torsional vibrations of the machine spindle was eliminated.

The proposed method allows not only to significantly improve the quality of the processed surface by reducing its roughness, but also is more productive, as it allows you to simultaneously perform, in a single pass, roughing and finishing operations when machining cylindrical surfaces of machine parts and mechanisms. In this regard, the economic effect of using the proposed method consists of the effect of increasing the durability of the workpieces by improving the quality of the parts and of the effect of reducing the cost of processing due to increased labor productivity.

Claims (2)

1. The method of turning cylindrical surfaces, including the rotation of the workpiece around an axis that coincides with the center line of the machine, the longitudinal movement of the tool and its transverse feed using as a tool a cutter having a straight main cutting edge with standard geometric parameters adjacent to a straight auxiliary line, characterized in that they use a cutter, the auxiliary edge of which is located in a vertical plane parallel to the line of the centers of the machine and it is counterclockwise by an angle numerically equal to the main angle in terms of a standard through-cutter, while the throat section of a single-sheeted hyperboloid of revolution, the forming of which is the auxiliary edge, and the imaginary axis is aligned with the center line of the machine, divides the auxiliary edge of the tool into a shorter upper part located above the horizontal plane containing the line of centers of the machine, and a large active lower part located below the specified horizontal plane, and the auxiliary edge covers the workpiece around its axis of rotation at an angle of more than one cyclic torsional vibration of the spindle of the headstock of the machine, while the main edge of the cutter is adjacent to the lower end of the auxiliary edge and when it extends crosses the line of the centers of the machine. 2. The method according to claim 1, characterized in that the total length of the auxiliary edge is determined by the dependence

, where L ₁ is the length of the lower part of the auxiliary edge of the cutter, located below the line of the centers of the machine; L ₂ = 2-3 mm - the length of the upper part of the auxiliary edge of the cutter, located above the center line of the machine, theoretically not taking part in the cutting process, but necessary to compensate for errors in the installation of the cutter in the tool holder relative to the workpiece; t ₂ = 0.5 (Dd): 3 - allowance on the side equal to the depth of cut for finish turning; D is the diameter of the workpiece; d is the diameter of the workpiece according to the drawing; d _to (r _to ) - the diameter (radius) of the circumference of the workpiece, dividing the rough and finish parts of the machining allowance; φ (β) is the angle of intersection between the rectilinear auxiliary edge of the cutter and the center line of the machine in a vertical plane parallel to the line of center of the machine, equal to the angle of intersection of the rectilinear generatrix of the single-cavity hyperboloid of revolution with the imaginary axis of the hyperboloid.

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