RU2647724C2 - Method of grinding on machines with a round magnetic holding plate of ends of the details in the form of a ring - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to the field of abrasive processing and can be used for grinding the ends of details of the type of rings with small axial rigidity. Ring is placed on the magnetic holding plate of the machine by the indicator during its rotation and grinding the first and second ring ends by the periphery of the circle by the method of penetration with the elimination of non-flatness. Grinding of the first ring end is carried out in the standard modes when the ring is fixed by means of the magnetic field of the magnetic holding plate with a preset value of the specific attractive force, which is within the specified values of the minimum and maximum specific attractive force. Grinding of the second ring end is carried out in the standard modes when the ring is fixed by means of the magnetic field of the magnetic holding plate with specific attractive force without the restriction of its maximum value. When grinding the first end, the maximum value of the specific attractive force is determined with allowance for ensuring the flatness of the end face of the ring from the reduced mathematical expression.

EFFECT: as a result, the time required to prepare the production is reduced and the accuracy of the final processed rings is increased.

1 cl, 5 dwg, 3 ex, 1 tbl

Description

The proposed solution relates to the field of machining machine parts by grinding and can be used at enterprises manufacturing rolling bearings, as well as other engineering enterprises when machining the ends of parts of the ring class with low axial rigidity by grinding on machines with a round magnetic table, for example, when machining large-sized rings and oversized rolling bearings.

Known methods for processing the ends of flat or ring-shaped parts by grinding on machines with rectangular or round tables with fastening them with a magnetic field, in which stops are used in the form of metal strips or special prismatic stops (Tergan BC, Flat grinding, M., Higher School, 1974, p. 209, Fig. 130, RF patent No. 2030280, IPC B24B 5/32, BI No. 7, 1995).

The disadvantages of these methods include the fact that the initial deviations from flatness and the curvature of the ends of the ring as a result of heat treatment or previous machining operations are saved after grinding. This is due to the fact that the presence of initial deviations from the flatness of the ends of the ring causes the appearance of axial elastic deformations of the ring under the action of the force of attraction of the magnetic field of the machine table and the cutting force. After grinding and removing the magnetic field, axial elastic deformations return a certain amount of deviation from flatness to the treated end face.

To eliminate the non-flatness of the ends of the parts of the class of rings by grinding, they resort to various technological methods, leading to an increase in the complexity of processing.

There is a method of eliminating the curvature of the ends of parts of a class of rings with low axial rigidity by grinding, carried out on machines with a round magnetic table, according to which compensators are introduced into the gaps formed by the curvature between the end of the ring and the surface of the magnetic table, the ring is fixed with a magnetic field and the first end is processed on modes in which the vertical component _y of R is less effort needed for the deformation of the ring in the axial direction (RF Patent №2107604 IPC B24B 7/04, BI №9, 1998); this embodiment of the method allows you to almost completely eliminate the residual internal stresses in the ring from exposure to the magnetic field of the table; in this case, the installation of rings with an asymmetric cross-section on the magnetic table is performed by the end face with the smallest area.

However, the internal stresses in the ring from the influence of the magnetic field of the table on it are not completely excluded, and additional finishing operations are required to ensure the required accuracy of the ends, which reduces the processing efficiency of the rings. In addition, the costs of manufacturing expansion joints increase. The shape of the surface of the compensator, mating with the end surface of the ring, does not provide complete conjugation of the surfaces in the gaps, which causes additional distortion of the shape of the grinding end surface of the ring.

The closest is a method of eliminating the curvature of the ends of parts of a class of rings with low axial rigidity by grinding carried out on machines with a round magnetic table, according to which the grinding of the first end of the ring is carried out without fixing the ring with a magnetic field at two vertical feeds. First, grinding is carried out at the lowest possible feeds until the waviness is completely ground and the stock is stabilized, and then at optimal feeds with a vertical force less than the maximum allowable. The axial stiffness and dimensions of the ring, the shape of its cross section, the number of bending waves and limit the maximum deflection are taken into account (RF Patent No. 2271918 IPC B24B 1/00, V24V 7/04, V24V 7/16, BI No. 8, 2006). The specified method for eliminating the curvature of the ends adopted by the authors as a prototype.

The disadvantages of the use of the prototype include the fact that it does not provide reliable fastening of the ring in all modes and for all possible ring sizes, and the allowable deflection indicated in the prototype does not provide the required accuracy of eliminating the non-flatness of the finished end according to the technical conditions, because it is determined by the values not associated with the tolerance of flatness of the finished end face.

The objective of the invention is to develop a reliable method of fixing the rings on the magnetic table of the machine when grinding the ring.

The technical result of the invention is to reduce the time required to prepare the production and increase the accuracy of the finished rings.

The specified technical result is achieved in the method of grinding the ends of the part in the form of a ring on machines with a round magnetic table, including exposing the ring on the magnetic table according to the indicator by rotating with the magnetic table relative to its axis and grinding the first and second ends of the ring with the periphery of the circle by the cutting method with eliminating non-flatness, in this case, grinding of the first end of the ring is carried out at standard conditions when fixing the ring by means of the magnetic field of the table with a predetermined specific attractive forces p, defined by the condition:

where [p] ₁ is the minimum specific gravity; [p] ₂ - the maximum value of the specific gravity, and grinding the second end of the ring is carried out at standard conditions, when fixing the ring by means of the magnetic field of the table with the specific gravity p without limiting its maximum value, the maximum value of the specific gravity when [p] ₂ grinding the first end face is determined taking into account the tolerance of flatness of the end surface of the ring according to the formula:

,

,

where i is the number of supporting contacts of the base end surface of the ring with the surface of the machine table, selected from a row at i = 3,4,5,6; Δ is the tolerance of flatness of the end surface on the grinding operation; Δ _m - flatness tolerance when grinding a hard workpiece; y _i is the level of macroscopic deviations of the profile of the base end surface of the ring corresponding to the i-th contact contact with the surface of the machine table; r is the radius of the central axis of the ring passing through the center of gravity of the cross section; I _yc is the axial moment of inertia of the cross section of the ring relative to the central axis y _c , perpendicular to the plane of the ring; I _z , I _y - the main central moments of inertia of the cross section of the ring; I _to - moment of inertia of the cross section of the ring during torsion; E, G - moduli of longitudinal elasticity and shear of the material of the ring; P _y is the radial component of the cutting force; b is the width of the base end of the ring; m is the mass of the ring; g is the acceleration of gravity.

The method is illustrated by drawings, where in FIG. 1 is a diagram of grinding parts of a class of rings by the periphery of a circle by the plunge method on machines with a round magnetic table; in FIG. 2 presents design schemes for determining the maximum axial elastic deformation of the ring w _max at three and six supporting contact of the end surface of the ring blank with the surface of the machine table; in FIG. 3 shows the geometric parameters of the cross section of the rings; in FIG. 4 shows the deviation from the flatness of the end face for the ring 1077756.01; in FIG. 5 shows the distribution of the vertices of the macro-deviations of the end surfaces along the profile height for the ring 1077756.01.

The non-flatness of the ends of the blanks of the rings 1 is eliminated on the magnetic table 2 by means of the grinding wheel 3 under the action of the radial component P _y and the tangential component P _{z of} the cutting force.

To do this, the blank of the ring 1 to be processed is installed on the magnetic table 2, expose it according to the indicator by rotation with the magnetic table 2 relative to its axis, fix the magnetic field of the table 2 of the machine, for which the value of the specific gravity p is pre-set, and grind the first end face regulatory regimes. In this case, the specific gravity p is set within [p] ₁ ≤p≤ [p] ₂ , where [p] ₁ is the minimum specific gravity, [p] ₂ is the maximum specific gravity. Grinding of the second end face is carried out at standard conditions with the workpiece of the ring 1 being fixed by the magnetic field of table 2 without limiting the maximum value of the specific gravity. The grinding of the ends of the workpiece of the ring 1 is carried out by the periphery of the circle 3 by the plunge method.

The workpiece of the ring 1 is loaded with a concentrated force P _v (from the action of the grinding wheel 3) and a uniformly distributed load of intensity q = q _c + q _m (from the force of attraction of the magnetic field of the table 2 of the machine - q _c and the mass of the ring - q _m ), perpendicular to the plane blanks of ring 1 (see Fig. 2). The initial moment of loading is characterized by a three-contact contact of the workpiece of the ring 1 with the surface of the magnetic table 2. As the load increases, the number of support contacts of the workpiece of the ring 1 with the surface of the table 2 increases to six.

The minimum specific gravity [p] ₁ is determined from the conditions of the absence of shear, rotation, and overturning of the billet of the ring according to known relations (Handbook of a machine-building engineer. 2 vols. T. 2 / Ed. By AM Dalsky and others. 5th ed. ., Rev. M .: Mashinostroenie-1, 2003. 944 s, pp. 127-137., Machine tools: Handbook in 2 volumes / Edited by B.N. Vardashkin, V.V.Danilevsky. M .: Mechanical engineering, 1984. T. 1. 592 p., P. 495-513.).

To determine the magnitude of the maximum specific gravity [p] ₂ from the condition of ensuring the tolerance of flatness of the end surface of the ring, mathematical models of the maximum axial deformations of the ring are obtained.

When developing mathematical models of axial deformation of the ring under the action of the magnetic field of the machine table, the mass of the ring and the radial component of the grinding force, the shape of the end surfaces of the outer rings of a tapered single row roller bearing is analyzed. The geometric parameters of the test bearing ring are given in the table, where D, D ₁ , C are the outer, inner diameters and width of the ring, respectively; β is the angle of taper; r = D _0/2 - respectively, the radius and diameter of the central axis of the ring passing through the center of gravity of the cross section; I _zc and I _yc are the axial moments of inertia relative to the central axes z _c , y _c ; I _z and I _y are the main central moments of inertia of the cross section of the ring; and ₁ and a ₂ are the coefficients for assessing the applicability of the theory of rods of small curvature (see Fig. 3).

Heat treatment of the rings is made in dies. Research conducted on a three-coordinate measuring machine Millenium. The end surface of the ring was examined along the circumference of an average diameter in microprocessor mode. Deviation from flatness has six pronounced waves (see Fig. 4).

The maximum axial deformation when fixing the ring blank with the magnetic field of the table will be equal to:

w _q = w _m + w _qmax + w _qк ,

where w _m , w _qmax is the maximum axial elastic deformation of the ring during bending, respectively, under the action of the mass of the workpiece and the force of attraction of the magnetic field of the table; w _qк - contact deformation of the end surface of the ring with the plane of the table.

When grinding the end face, the axial maximum axial elastic deformation of the ring during bending w _pmax under the action of the radial component of the cutting force applied at the center of the span between the supports and the contact deformation of the end surface of the ring with the table plane w _rk are added to axial deformation:

w _p = w _pmax + w _pk.

The contact deformation of the smooth table surface and the rough wavy end surface of the ring blank was determined by the NB method. Demkina. The assessment of the magnitude of contact deformations allows us to conclude that its value for the rings under study at maximum loads does not exceed three percent of the flatness tolerance. In this regard, in further calculations, the effect of contact deformations is not taken into account. Experimental studies of axial deformations of rings under the action of an attractive force of the magnetic field of the table confirm this assumption.

From the table it follows that for the rings in question α ₁ = 2πr / C> 10, α ₂ = 0.5 (DD ₁ ) / r <0.2. The fulfillment of this condition allows us to use the theory of rods of small curvature to determine the maximum axial elastic strains during bending of the ring w _pmax and w _qmax .

The maximum axial elastic deformation of the ring during bending w _pmax and w _qmax is determined by the Mohr method. The static indeterminacy of the ring is revealed by the method of forces.

In the General case, the main Central axis of the cross section of the ring z and y can be tilted with respect to the plane of the ring (see Fig. 3). To simplify further calculations, it is advisable to introduce auxiliary coefficients of the cross-sectional shape of the ring: η _y = I _yc / I _zc ; η _zy = I _yczc / I _zc ; η _k = EI _y I _z / (CI _zc I _k ); where I _to - the moment of inertia of the cross section of the ring during torsion; I _yc , I _zc , I _y , I _z , I _yczc - axial and centrifugal moments of inertia; E, G are the moduli of longitudinal elasticity and shear of the material of the ring.

When static uncertainty is revealed by the force method, we position the section of the ring in the plane of symmetry, at point A (see Fig. 2), which allows you to use the symmetry properties and it is enough to determine one unknown bending moment. Under the action of the indicated load, the maximum axial deformation of the ring (deflection) w occurs at point A (see Fig. 2). Using the Mohr method, in the polar coordinate system we get:

,

,

,

- моменты от действия единичной силы; М_zc, М_к - моменты в эквивалентной системе.Where

,

- moments from the action of a single force; M _zc , M _to - moments in the equivalent system.

The final expressions for the maximum axial elastic deformation of the ring with three-, four-, five- and six-bearing contact of the end surface of the ring with the table surface:

.Where

.

Given the change in the number of supports when fixing the ring with the magnetic field of the machine table, the axial elastic deformation will be equal to:

where y _i is the level corresponding to the i-th number of supports (y ₃ taken equal to zero) (see Fig. 5); w _qi - axial deformation at i supports, 3≤i≤6.

The determination of the number of contact contacts during ring loading and the value of the maximum axial elastic deformation of the ring under the action of the magnetic field attractive force of the table and the mass of the ring in accordance with formula (9) is carried out in the following order:

if w _q3 ≤y ₄ , the axial elastic deformation in the formula (4) w _q = w _q3 ,

if w _q3 > y ₄ , we find w _q4 . For w _q4 ≤y ₅ -y ₄ , w _q = y ₄ + w _q4 ;

if w _q4 > y ₅ -y ₄ , we find w _q5 . When w _q5 ≤y ₅ -y _6, w _q = y ₅ + w _q5;

if w _q5 > y ₆ -y ₅ , w _q ≈y ₆ .

The maximum axial elastic deformation when fixing the ring with the magnetic field of the machine table and the action of the radial component of the cutting force, taking into account the change in the number of supporting contacts, will be equal to:

When determining the number of support contacts and the value of the maximum axial elastic deformation of the ring in this case, the deformation w _pi is added.

The intensity of the uniformly distributed load q _c from the action of the force of attraction of the magnetic field of the table on the ring will be equal to q _c = pb, where p is the specific gravity of the magnetic field of the table of the machine; b = (DD ₁ ) / 2 is the width of the base end face of the ring blank (see Fig. 3).

The maximum specific gravity of the magnetic field [p] _{2 of the} table is determined from the condition for ensuring the tolerance of flatness of the finally machined end surface of the ring according to the technical conditions:

where [Δ] = λΔ-Δ _m is the permissible axial elastic deformation of the ring, λ = 0.75 is the accuracy margin; Δ is the tolerance of flatness of the end surface on the grinding operation; Δ _m - flatness tolerance when grinding a hard workpiece, determined from the reference literature.

The maximum axial elastic deformation when the ring is fixed with the magnetic field of the machine table and the action of the radial component of the cutting force, taking into account the change in the number of support contacts w _max, is determined by formulas (1) - (10).

The power approximation of the ductility coefficients of the ring allows us to express the maximum deformations and conditions for ensuring the tolerance of flatness of the finally machined end surface of the ring according to the technical conditions in the form:

.

.

Then [p] ₂ is the maximum specific gravity, determined from the condition for ensuring the flatness tolerance of the finally machined end surface of the ring, is selected as the largest value from the series for i = 3, 4, 5, 6:

where i is the number of support contacts of the base end surface of the ring with the surface of the machine table;

b = (DD ₁ ) / 2 - the width of the base end of the ring;

D, D ₁ - respectively, the outer and inner diameters of the ring;

p _m = mg / (2⋅π⋅r⋅b) - specific force from the action of the mass of the ring; m is the mass of the ring; g is the acceleration of gravity.

By substituting the calculated values, we obtain the expression:

,

,

Limiting the magnitude of the specific gravity of the magnetic field of the machine table p within [p] ₁ ≤p≤ [p] ₂ when grinding the first end of the ring billet under standard conditions allows the flatness of the final machined end surface to be admitted according to the technical conditions without finishing operations.

The second end face of the ring blank is polished at standard conditions when the table is secured with a magnetic field with a specific gravity p≥ [p] ₁ without limiting the maximum value, since the processed first end face with the required flatness tolerance in this case will be basic, and the maximum elastic axial deformation will not will exceed the flatness tolerance.

Example 1

The outer ring of a tapered single row roller bearing 1077756.01 with the original dimensions shown in table 1, made of hardened steel ШХ15, with a hardness of HRC _e = 60 ... 62 after quenching in the dies had a six-wave non-flatness (Fig. 4). In FIG. 5 shows the distribution of the vertices of the macro-deviations of the end surfaces of the ring along the height of the profile. Abrasive tool - circle 25AF46.K6V, coolant - Avazole. By the method of planning the experiment, the optimal grinding conditions for the ends were established at the maximum process performance and providing a roughness parameter R a = 2.5 μm and the absence of grinding burns:

optimal grinding depth t _opt = 0.02 mm / stroke; the optimal value of the feed rate of the workpiece - v _sopt = 13 m / min; at maximum productivity Q _max = 260 mm ² / min. For these parameters, the value reduced to the width of the end face of the radial p _y and tangent p _{z of the} components of the cutting force are equal to:

p _y = 16.2 N / mm;

p _z = 6 N / mm.

For the studied ring, λ = 0.75; Δ = 25 μm, Δ _m = 9 μm.

Permissible axial elastic deformation of the ring:

[Δ] = λΔ-Δ _m = 0.75⋅25-9 = 9.75 mm.

The minimum specific gravity [p] _{1 is} determined from the conditions of the absence of shear, rotation, and overturning of the ring blank (Handbook of a machine-building engineer. 2 vols. T. 2 / Ed. By AM Dalsky et al. 5th ed., Rev. M.: Mashinostroenie-1, 2003. 944 p., Pp. 127-137., Machine tools: Handbook in 2 volumes / Edited by B.N. Vardashkin, V.V.Danilevsky. M .: Engineering, 1984. T. 1. 592 p., P. 495-513):

where k = 0.1515 is the coefficient of sliding friction;

P _y = p _y b ₁ = 16.2⋅15.5 = 251 N is the radial component of the cutting force;

b ₁ = 15.5 mm - the width of the base of the end of the ring;

m = 15 kg is the mass of the ring;

g = 9.81 m / s ² - acceleration of gravity;

P _z = p _z ⋅b = 6⋅29.5 = 177 N is the tangent component of the cutting force;

b = 29.5 mm - the width of the base end of the ring;

Q = [p ₁ ] ⋅b⋅2⋅π⋅r = [p ₁ ] ⋅29.5⋅2⋅3.14⋅218.4 = 40460⋅ [p ₁ ] - the force of attraction of the magnetic field of the table;

r = 218.4 mm is the radius of the central axis of the ring.

From condition (13) we obtain:

[p ₁ ] = (P _z / kP _y -mg) / 40460 = 0.02 MPa.

The value of the maximum specific gravity [p] _{2 is} determined from the condition for ensuring the flatness tolerance (11) using the above algorithm and mathematical models of maximum axial deformations of the ring (1) - (10). The axial compliance parameter of the ring is: A = 8.07,010 ^-7 mm / N. Macro deviation levels: y ₄ = 0.0036 mm; y ₅ = 0.0067 mm; y ₆ = 0.0097 mm (see Fig. 5).

By the formula (12) for i = 3, 4, 5, 6 we get the following series:

i = 3: p ₂ = 0.04 MPa;

i = 4: p ₂ = 0.16 MPa;

i = 5: p ₂ = 0.211 MPa;

i = 6: p ₂ = -0.266 MPa.

Choose the largest value for the maximum specific gravity of the magnetic field of the machine table:

[p ₁ ] ₂ = 0.211 MPa.

In this case, the ring drops under the action of the load to five support contacts.

The first end face of the ring with initial maximum flatness deviations of 35 μm after grinding at the established conditions when fixing the ring blank with the magnetic field of the table with a specific gravity p = 0.2 MPa had the required deviation from flatness of 24 μm without finishing operations.

The second end face was machined under the same established grinding conditions when the ring billet was fixed with the table magnetic field with a specific gravity p = 0.25 MPa (without limiting the maximum value). The required flatness tolerance of 25 μm was ensured after grinding without finishing operations and for the second highlander.

The performance of processing the ends of the ring increased by 25%, because the grinding of both ends of the ring is carried out immediately in optimal conditions without preliminary processing at minimum feeds and the installation operation of the adjustment ring is eliminated.

Example 2

We give an example of calculation for a bearing ring that differs from the considered ring 1077756.01 only in the radius of the central axis of the ring, ceteris paribus. For r = 250 mm, according to formula (12) for i = 3, 4, 5, 6, we obtain the following series:

i = 3: p ₂ = 0MPa;

i = 4: p ₂ = 0.054 MPa;

i = 5: p ₂ = 0.063 MPa;

i = 6: p ₂ = - 0.237 MPa.

Choose a large value for the maximum specific gravity of the magnetic field of the machine table:

[p] ₂ = 0.063 MPa.

In this case, the ring drops under the action of the load to five support contacts.

The first end face of the ring must be grinded in the established modes when fixing the ring blank with the magnetic field of the table with control of the specific gravity within:

0.02≤p≤0.063 MPa,

to ensure the required flatness tolerance without finishing operations. The second end face is polished without limiting the maximum value of the specific gravity of the magnetic field of the table.

Example 3

We give an example of calculation for a bearing ring that differs from the considered ring 1077756.01 only in the radius of the central axis of the ring, ceteris paribus. With r = 270 mm, according to formula (12) with i = 3, 4, 5, 6, we obtain the following series:

i = 3: p ₂ = - 0.013 MPa;

i = 4: p ₂ = 0.020 MPa;

i = 5: p ₂ = 0.014 MPa;

i = 6: p ₂ = - 0.221 MPa.

Choose a large value for the maximum specific gravity of the magnetic field of the machine table:

[p] ₂ = 0.020 MPa.

In this case, the ring is lowered to four support contacts under load.

The first end face of the ring must be grinded in the established modes when fixing the ring blank with the magnetic field of the table with control of the specific gravity within:

0.02≤p≤0.02 MPa,

to ensure the required flatness tolerance without finishing operations. The second end face is polished without limiting the maximum value of the specific gravity of the magnetic field of the table.

Thus, the claimed method allows to eliminate the initial non-flatness of the ends of the rings and to increase the accuracy of their processing, to optimize the grinding process according to the regimes, to reduce the time required to prepare the production and, accordingly, to increase the productivity of processing the ends of the rings by approximately 25%.

Claims (19)

The method of grinding on the machines with a round magnetic table the ends of the part in the form of a ring, including exposing the ring on the magnetic table according to the indicator by rotation with the magnetic table relative to its axis and grinding the first and second ends of the ring with the periphery of the circle by the cutting method with eliminating non-flatness, characterized in that grinding the first end of the ring are in standard conditions when fixing the ring by means of the magnetic field of the table with a pre-set value of the specific gravity p, determined from conditions:

where [p] ₁ is the minimum specific gravity; [p] ₂ - the maximum value of the specific gravity, and grinding the second end of the ring is carried out at standard conditions when fixing the ring by means of a magnetic field with a specific gravity p without limiting its maximum value, while the maximum specific gravity [p] ₂ when grinding the first end is determined taking into account the tolerance of flatness of the end surface rings according to the formula:

where i is the number of support contacts of the base end surface of the ring with the surface of the machine table, selected from a row at i = 3, 4, 5, 6; Δ is the tolerance of flatness of the end surface on the grinding operation; Δ _m - flatness tolerance when grinding a hard workpiece; y _i is the level of macroscopic deviations of the profile of the base end surface of the ring corresponding to the i-th contact contact with the surface of the machine table; r is the radius of the central axis of the ring passing through the center of gravity of the cross section; I _wh - the axial moment of inertia of the cross section of the ring relative to the central axis of y _s , perpendicular to the plane of the ring; I _z , I _y - the main central moments of inertia of the cross section of the ring; I _to - moment of inertia of the cross section of the ring during torsion; E, G - moduli of longitudinal elasticity and shear of the material of the ring; R _y is the radial component of the cutting force; b is the width of the base end of the ring; m is the mass of the ring; g is the acceleration of gravity.

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