RU2538519C2 - Dressing of abrasive wheel - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to machining and can be used for dressing of grinding wheel for relief of hobs at NC machines. Dressing tool composed of diamond needle or stick is positioned relative to grinding wheel and set at sand machine in the area of hob to be relieved. It is displaced relative to grinding wheel in preset curvilinear path in several passes. Dressing tool feed is performed in path identical to the edge of hob to be relieved. After every pass, dressing tool is fed by its turning around z axis of said hob through angle δ=0.1÷1.5° and relative to the grinding wheel surface by magnitude u parallel with axis z and magnitude w perpendicular to said axis z. Said magnitude u and w are taken equal to displacement of the hob relative to grinding wheel at hobbing, respectively, along hob axis z and perpendicular thereto during its turn around axis z through angle δ.

EFFECT: higher hobbing precision, enhanced hob performances.

5 cl, 6 dwg, 6 ex

Description

The invention relates to the field of processing by cutting - dressing an abrasive wheel for grinding worm mills on a CNC machine.

Editing a circle for backing worm mills designed for cutting various gear products (gears with different profiles, including involute, worm wheels, splined shafts, etc.), is a very complex and time-consuming part of the operation of grinding worm mills. The profile of the circle is always different from the profile of the back of the cutter; Calculation of the profile of the wheel is quite complicated and to date, when dressing the wheel, often laborious manual adjustment is often used (when after trial passes when grinding the mills, the profile of the circle is gradually adjusted to the required accuracy).

At the same time, high demands are made on the accuracy of the edges of the worm cutters; on the accuracy of the profile of the circle directly depends on the accuracy of the edges of the cutter and, accordingly, the accuracy of the profile of the cut teeth.

In the prior art, there are known methods for straightening a circle for grinding worm cutters, which consist in calculating the profile of the circle and then correcting it according to the calculated profile along the contour, using a pantograph or a shaped roller (Paley M.M., Technology and automation of tool production, Volgograd, 1995., 487 p., pp. 435-437).

There is a known method of straightening a circle for backing worm cutters, which consists in the fact that the ruling diamond in a device mounted on a backing machine instead of a backed up cutter performs a reciprocating movement in the axial plane of the cutter (for Archimedean worms), or in a plane tangent to the main cylinder (when grinding involute worms). When editing, the device moves along with the table and rotates relative to the axis of the centers with the speed set for the pitch of the main worm (Palei M.M., Dibner L.G., Flid M.D., Grinding and sharpening technology for cutting tools. M., Mechanical Engineering , 1988., 288 p., Pp. 158-159).

The disadvantage of this method is that the diamond moves in a plane, and its tip describes such a flat line, which, with the screw movement of the device, describes a ruled helical surface relative to the circle. Therefore, this editing method, under certain additional conditions (not indicated in the named source), can provide the shape of a circle profile, which, when grinding worm cutters, will give a straight-line flat profile of the backed surface of the cutter tooth in its axial section or in a section parallel to the axial plane.

Another disadvantage of this method is the need for a very slow rotation of the cutter (a small number of revolutions of the back of the cutter on the machine), and a quick reciprocating movement of the diamond. Otherwise, the dressing of the wheel will be inaccurate, since the diamond when dressing the wheel will describe not a ruled, but a complex indefinite surface, the shape of which depends on the ratio of the diamond motion speeds in the tool and the tool itself on the machine.

A known method of dressing the grinding wheel, in which the required shape and cutting ability is provided by turning the wheel with a diamond ruling tool (Tergan BC, Flat grinding, study guide for prof. And technical schools, 2nd edition, revised and ext. - M .: High school, 1974, p. 184-194).

The disadvantage of this method is that the dressing process of the grinding wheel is not controlled, the removed allowance is assigned according to reference materials that do not correspond to the real state of the surface of the wheel, which leads to a large consumption of abrasive material during the dressing process and wear of the ruling tool.

The closest technical solution for the totality of the essential features is the method of dressing the grinding wheel, in which dressing is carried out in several passes, with a message to the grinding wheel rotation, and the ruling tool longitudinal movement along the generatrix of the circle, after each longitudinal movement the tool reports a transverse movement, the value of which is selected in depending on the nature of the wear of the working surface, while before dressing on the ends of the circle are applied conductive layers, and on the draft m stage, the moment of contact of the electrically conductive layer with the ruling tool at the end face of the circle having the smallest wear of the diameter is fixed and the draft stage is stopped, while when the moment of contact of the electrically conductive layer is fixed at the end of the circle with the largest diameter wear, the stage of roughing is terminated (RU 2400346 C2 27.09 .2010, B24B 53/00).

The disadvantages of this method include the need for special refinement of the grinding wheel for applying an electrically conductive layer and embedding sensors and a control unit on the ruling tool, which limits the versatility of the method, as well as the lack of reliable control of the depth of the abrasive layer to be removed during dressing.

The technical result, the achievement of which the claimed invention is directed, is to increase the accuracy of the profile shape of the abrasive wheel for grinding worm mills on a CNC machine.

The specified technical result is achieved by the fact that in the method of dressing the abrasive wheel for grinding the worm cutters on a CNC machine, including positioning the cutting tool in the form of a diamond needle or pencil relative to the grinding wheel for grinding the worm cutters, installing the cutting tool on the said machine in the area of the back of the cutter and its movement relative to the said rotating abrasive wheel along a predetermined curved path in several passes, the movement of the governing body In each passage, the path is identical in shape to the edge of the back of the cutter, and after each pass, the ruling tool is fed by turning it around the longitudinal axis z of the back of the cutter by an angle δ = 0.1 ÷ 1.5 ° with its subsequent movement relative to the surface of the aforementioned abrasive wheel at the same time and parallel to the z axis and w perpendicular to the z axis, while the values u and w of the displacements of the ruling tool are taken equal to the displacement of the cutter relative to the aforementioned abrasive wheel in the process of backing, respectively along the longitudinal axis z of the cutter and perpendicular to it during its rotation around the z axis by angle δ, in the particular case of implementing the method, the aforementioned values u and w of the displacements of the ruling tool for worm milling cutters hardened along an Archimedean spiral determine accordingly, according to the formulas:

u = p · δ and w = a · δ, where

p = P _x z _zs / 360;

a = (k · z _s / 360) · [(P _z + _{z Zech · P x) / P z]} ;

P _x is the axial pitch of the turns of the cutter;

z _zh - the number of cutters;

k is the amount of backing;

z _z - the number of teeth of the cutter;

P _z - pitch helical front surface,

in addition, the ruling tool in the form of a diamond needle is made with rounding of the tip with a radius of 2-5 mm, while the ruling tool in the form of a diamond needle is informed of additional rotation around the tip of the needle, and the ruling tool with a radius of curvature is informed of additional rotation around the center of curvature, provided that the axis of the ruling tool is located approximately normal to the profile of the abrasive wheel.

The number of passes of the ruling tool is preferably from 4-10 passes.

The essence of the claimed invention is illustrated by graphic materials, where:

- in FIG. 1 presents a general scheme for editing a circle;

- in FIG. 2 - scheme of editing a circle in 4 passes;

- in FIG. 3 is a straightening diagram of a disk circle with a convex profile for backing off worm mills cutting involute and worm wheels;

- in FIG. 4 is a diagram of the motion of a diamond needle around an axis when straightening a circle;

- in FIG. 5 is a diagram of the backing of a worm cutter (right-handed) with an abrasive wheel;

- in FIG. 6 is a profile of the base worm of the worm cutter.

The proposed method of editing an abrasive wheel for grinding worm mills is as follows.

When dressing with a diamond needle 1 of circle 2, the same movements ω, D _x , D _z are used as when backing up a worm cutter, but discrete (intermittent), and the movement of the ruling diamond along the paths of 3 edits is also used. In FIG. 1 is a diagram of editing the circle: 1 - diamond needle; 2 - abrasive wheel; 3 - trajectories of the tip of the diamond needle; ω, D _x , D _z - the movement of the diamond needle. Diamond dressing is performed in several (N) passes along trajectories 3, each of which coincides in shape with the edge of the back of the cutter. In FIG. Figure 2 shows the correction for 4 passes (N = 4), with each diamond, respectively, describes the paths 3 ₁ , 3 ₂ , 3 ₃ , 3 ₄ .

The circle is set on the machine in the same position at which the worm cutter is backed up (the beginning of the backing of the tooth). Diamond 1 describes the path 3 ₁ in the form of a spatial line coinciding in shape with the edge of the cutter (Fig. 2). After completing one or more dressing moves, in which the diamond in the reciprocating motion describes the same spatial path 3 ₁ (Fig. 2), the dressing stops, and the movements ω, D _x , D _{z are} reported to the diamond (Fig. 1) .

After the motions ω, D _x , D _{z of the} diamond are completed, they are informed of the movement along the path coinciding with the edge of the cutter. That is, they make the next edit pass along the path 3 ₂ (Fig. 2). Upon completion of the correction along the path 3 _{2, the} diamond is again informed of the movements ω, D _x , D _z (Fig. 1). At the end of the movements ω, D _x , D _{z the} diamond is informed of the movement along the path 3 ₃ (Fig. 2). That is, they carry out the next (third) edit pass. After its completion, the diamond is informed of the same movements ω, D _x , D _z , (Fig. 1), after which they make the 4th pass of dressing along the path 3 ₄ (Fig. 2). If the total number N of passes is N = 4, then the edit is completed.

If a larger number N is accepted, then dressing cycles, each of which includes a dressing pass and moving before the subsequent diamond cutting in the movements ω, D _x , D _z , continue until the completion of the last, Nth pass. For mills with a profile height of H = 5-40 mm, the number N of passes is assigned in the range from 4 to 8-10; large values of N - for large H and in the presence of a positive rake angle γ of the cutter. At each pass, the top of the diamond describes the same trajectory, in shape coinciding with the edge of the cutter. Before each subsequent passage, the diamond is informed of the movements ω, D _x , D _z . In motion with diamond is rotated around the z axis of the cutter by an angle δ, which is counted from the moment of the start of movement ω before each subsequent pass (Fig. 1).

The value of δ for a disk-shaped circle is δ = 0.2-1.5 °. For a cup circle, δ = 0.1-1 °, for a finger circle, δ = 0.1-0.5 °. For milling cutters with a tooth profile height H of 5-40 mm, smaller values of δ are taken for a lower height H. Diamond movements D _z (parallel to the z axis) and D _x (parallel to the x axis, i.e. perpendicular to the z axis) are linear translational, with moving, respectively, by the value of u and by the value of w (Fig. 1).

The value u is equal to the displacement relative to the circle of the cutter during its backing, in the direction parallel to the z axis, during the rotation ω of the cutter around its z axis by the angle δ.

The value of w is equal to the displacement relative to the mill circle in the process of its backing, in the direction perpendicular to the z axis, during the rotation of the mill around its z axis by the same angle δ. The numerical value of u and w depends on the angle δ and the backing method. In any method, the quantities u and w are set functionally on the value of δ. If the backing method is known, then the dependence of u and w on δ is necessarily known. The displacements u and w are counted relative to the position of the circle before the next pass. In FIG. Figure 1 shows the movements of ω, D _x , D _{z of} diamond 1 relative to a fixed circle 2. Editing of a circle is made for backing the right-hand milling cutter. (The rotation of the circle 2 around its own axis O _to -O _to provides cutting speed, but does not affect the formation of the rear surfaces and therefore is not taken into account). The motions D _x and D _z can be defined in a circle, then they have a direction opposite to that shown in FIG. 1. In this case, the z axis, around which the motion ω occurs, remains stationary, and the relative motion of the circle and diamond shown in FIG. 1, does not change. To edit the circle when backing up the worm cutters in an Archimedean spiral, the values of u and w are taken equal to: u = p · δ; w = a · δ; where: p = P _x z _zach / 360; a = (k · z _s / 360) · [(P _z + _{z Zech · P x) / P z]} , P x - axial pitch of cutter (or parent worm); z _zh - the number of cutters; k is the amount of backing; z _z - the number of teeth of the cutter; P _z - pitch helical front surface. To edit the circle when backing along an Archimedean spiral, milling cutters with straight grooves (parallel to the milling axis) take a equal to a = (k · z _s / 360).

Here, under the Archimedean helix, here and in the literature we mean the method of backloging, in which the ratio of the velocities of motion ω and D _{x is} constant.

The profile of the disk circle for backing cutters with a straight profile (with a zero rake angle γ of the cutter) is also close to a straight shape, and has a slight bulge s (Fig. 3). A disk circle with a convex profile for the backing of worm mills, cutting involute and worm wheels: 1 - the ruling diamond pencil; 2 - circle; R _to - the outer radius of the circle.

Depending on the height H of the profile, the dimensions of the cutter and the circle, as well as on its installation on the machine, the value of s can be from several microns to several tens of microns. The value of s, as a rule, exceeds the tolerance on the profile of the cutters or is a significant part of it. Therefore, replacing the convex profile of a circle with a straight line is permissible only in limited cases.

When using the proposed method, dressing a circle with a convex profile shape, with small convexity values s (up to 100-200 μm), is carried out with a diamond pencil (Fig. 3). Milling of milling cutters with a small profile height H (up to 5-10 mm) can be carried out simultaneously on the left and right lateral sides of the tooth (in the cavity, i.e. along the lateral surfaces of two adjacent profile teeth. Editing a circle for simultaneously grinding two sides of the milling profile along the proposed method is carried out with a diamond needle, with an additional rotational movement of ω ₁ around the axis AA passing through the top of the needle (through the top of the axis of the pencil) (Fig. 4).

The rotation of ω _{1 is} carried out continuously or discretely at each ruling passage of the diamond, so that the axis of the needle (pencil) is approximately normal to the profile of the grinding wheel.

As a material for the straightening tool can be used diamond or other highly hard material.

The top of the ruling tool to increase its durability can be performed with a constant rounding radius of up to 2-5 mm. In this case, the axis AA rotation ω ₁ passes through the center of this circle, and the trajectory of the center of the circle when editing the circle is equidistant to the edge line of the cutter.

The equations of the edge of the worm cutters are given in the work: Yulikov MI, Gorbunov BI, Kolesov NV. Design and production of cutting tools. M. Engineering, 1987, pp. 122-124.

The method can be implemented either on a CNC machine on which the milling is performed, or on a special CNC device, that is, outside the backing machine. In the latter case, the circle is corrected on the device and then installed on the machine for cutting the milling cutter.

It is also possible to edit the circle with a roller either on the back of the machine, or on a special device: in this case, the profile of the roller is polished by a circle, the editing of which is carried out as described above.

Grinding of helical conical and cylindrical surfaces (conical and cylindrical chip grooves of axial tools and their sharpening, grinding of conical and cylindrical worms and threads) according to the kinematics of the movements of the wheel relative to the surface being grinded is a special case of worm milling.

Therefore, the method described above can also be used to straighten a circle grinding helical conical and cylindrical surfaces. In the latter case, there is no movement D _x and movement w = 0. At the same time, during the editing process, the top of the ruling tool in the shape of a needle describes, at each ruling pass, the path coinciding with the profile of the surface being ground; and in the form of a hemisphere, the path along the equidistant curve to the profile of the surface to be grinded.

Example 1

Editing of a disk-shaped circle is performed for backing using a special method (different from backing over with an Archimedean spiral) of a right-handed worm milling cutter with an outer diameter of 180 mm (for cutting involute cylindrical wheels with a 12 mm module). Cutter dimensions: P _x = 37.286; P _z = 5602; z _zh = 1; z _s = 9; γ = 0. The height H of the cutter profile as the difference of two radii r of the extreme design points of the side edge of the cutter: r _a = 87, r _f = 63, H = 24. (The method of backing this milling cutter is set and based on the fact that the rear vertex angle at a radius r _a is 11 ° and does not change when grinding the milling cutter). The movement of the cutter relative to the circle is set (Fig. 5). The milling cutter is designed on the basis of the main involute worm, the coordinates (r, z _o ) of the profile of which at any point M are known (Fig. 6).

We take the number of passes N = 6 (trajectories 3 ₁ , 3 ₂ , ... 3 ₆ ; Fig. 2); δ = 0.8 °.

Since the method of milling the milling cutter is specified, the displacements u and w of the milling cutter are known.

The movement u of the cutter in the movement D _z parallel to the axis z of the cutter, for each (first and subsequent) rotation ω of the cutter by an angle δ = 0.8 °, is: u = p · δ, where p = P _x / 360 = 0, 105073 (mm / degree).

The displacements w perpendicular to the z axis at each rotation ω of the cutter by an angle δ = 0.8 °, counting from the initial moment of backing, are:

0.23580 (mm) - at the first turn; 0.23516 - in the second; 0.23453 - with the third; 0.23389 - with the fourth; 0.23336 - during the fifth rotation of the cutter by an angle δ.

That is, if the mill, in the process of its backing, rotates through an angle of 0.8 ° · 5 = 4 °, then it will move during the same time relative to the circle perpendicular to the z axis by (0.23580 + 0.23516 + 0.23453 + 0.23389 + 0.23336) mm.

In accordance with the proposed dressing method, diamond, after each successive dressing and turning passage in the movement ω, the angle δ = 0.8 ° is moved along the z axis by 0.105073 (mm), and perpendicular to the z axis - by values: 0, 23580 (mm) - after the first pass of editing; 0.23516 - after the second; 0.23453 - after the third; 0.23389 - after the fourth; 0.23336 - after the fifth pass, that is, before the last, 6th pass.

For the same cutter, in the presence of a rake angle of γ = 5 °, the number of N passes should be increased (approximately to 8).

Example 2

Editing of a disk-shaped circle is performed for backing along an Archimedean spiral of a worm-shaped starting mill with an outer diameter of 180 mm (for cutting involute cylindrical wheels with a module of 12 mm). Cutter dimensions: P _x = 37.286; P _z = 5602; z _zh = 1; z _s = 9; k = 12; γ = 0.

The height H of the cutter profile as the difference of two radii r of the extreme design points of the side edge of the cutter: r _a = 87 r _f = 63, H = 24.

We take the number of passes N = 6 (trajectories 3 ₁ , 3 ₂ , ... 3 ₆ ; Fig. 2); δ = 0.8 °.

We calculate: p = P _x / 360 = 0.105073; a = (k · z / 360) · [(P _z + z _o · P _x ) / P _z ] = 0.302026.

The movement of the diamond in the movements ω, D _z , D _x , (Fig. 1) after each pass of straightening the circle: δ = 0.8 °; u = p · δ = 0.08406 (mm); w = a · δ = 0.241621 (mm).

Example 3

Editing a circle is performed for backing (along an Archimedean spiral) of a mill with dimensions as in Example 2, but the mill is made with straight chip grooves, the front surface of the teeth is flat, parallel to the z axis of the mill. The values of p and u - do not change (the same as in example 2). The value of a = (k · z / 360) = 0,300 (mm); w = a · δ = 0.240 (mm).

Example 4

The dressing circle is made for grinding the worm cutter with the dimensions given in example 1. For dressing use a diamond in the frame with a working surface in the form of a hemisphere with a radius of 2 mm

All straightening movements are the same as in example 1, but for each of the 6 governing passes, the center of the spherical surface of the diamond describes a spatial path along the equidistant to the edge of the cutter, that is, along a line, each point of which is distant from the edge of the cutter, equal to the radius of the diamond, that is, to a distance of 2 mm.

Example 5

The dressing circle is made to back the worm cutter with the dimensions given in example 1. The dressing tool can be in the form of a diamond needle, in the form of a pencil or in the form of a diamond with a hemisphere.

All editing movements are the same as in example 1, if the diamond is made in the form of a pencil or needle; and the same as in example 4, if the diamond is made in the form of a hemisphere.

After editing the circle, it is used to grind the ruling roller. The latter is made, for example, of hardened steel with a profile previously cut through it. The diameter of the roller in this example should be at least 80-90 mm (given the height of the profile H = 24 mm).

The roller is subsequently used to straighten the circle as it is worn by the copy method, since the profiles of the roller and the circle are identical.

Example 6

The grinding wheel is used to grind a worm with an outer diameter, axial pitch and axial profile — the same dimensions as the worm cutter in example 2.

Grinding the profile of such worms - with dimensions identical to the dimensions of the cutter, but without backing - is actually carried out for prefabricated cutters with turning rails and with straight chip grooves; the worm’s profile in its axial section is slightly different in height and profile angle from the profile of the cutter.

Editing a circle is carried out in the same way as in example 2, but in the absence of movement D _x , that is, they take w = 0. The ruling tool in the form of a needle in this case describes the trajectory in the form of a profile of the grinding worm, and the ruling tool in the form of a hemisphere - in the form of an equidistant to the profile of the worm. By the trajectory of the ruling tool is meant the trajectory of the needle tip or the trajectory of the hemisphere center.

Editing a circle according to the described method when milling milling cutters with a height H of a profile of 24 mm ensured a milling profile error of not more than 2-3 microns, which is much less than the tolerance on the profile of precision milling cutters (class AA according to GOST 9324-80).

The method allows to solve one of the most difficult tasks of shaping in the manufacture of worm mills, improves the accuracy of dressing circle and greatly simplifies the manufacture of mills with rational geometry.

The analysis of the claimed technical solution for compliance with the conditions of patentability showed that the characteristics indicated in the independent claim are interrelated with each other with the formation of a stable set of necessary attributes unknown at the priority date from the prior art sufficient to obtain the required synergistic (over-total) technical result.

Thus, the above information indicates the fulfillment of the following set of conditions when using the claimed technical solution:

- a method embodying the claimed technical solution, when implemented, is intended for dressing abrasive wheels for grinding worm mills on CNC machines;

- for the claimed method in the form described in the independent clause of the formula below, the possibility of its implementation using the methods described above or known from the prior art on the priority date of the funds is confirmed;

- the method embodying the claimed technical solution, when implemented, is able to achieve the achievement of the technical result perceived by the applicant.

Therefore, the claimed method meets the requirements of the patentability conditions of "novelty", "inventive step" and "industrial applicability" under applicable law.

Claims (5)

1. The method of dressing the abrasive wheel for grinding the worm cutters on a CNC machine, including positioning the cutting tool in the form of a diamond needle or pencil relative to the grinding wheel for grinding the worm cutters, installing the cutting tool on the said machine in the area of the back of the cutter and moving it relative to the said rotating abrasive circle along a given curved path in several passes, and the movement of the ruling tool in each pass is carried out along a path identical to the shape of the edge of the back of the milling cutter, and after each pass, the ruling tool is fed by turning it around the longitudinal axis z of the back of the milling cutter by an angle δ = 0.1 ÷ 1.5 ° with its subsequent movement relative to the surface of the mentioned abrasive wheel at the same time by the value of u parallel to the axis z and by the value of w perpendicular to the z axis, while the values of u and w of the movements of the ruling tool are taken equal to the values of the movement of the back of the cutter relative to the mentioned abrasive wheel in the process of backing, respectively enno, along the longitudinal axis z and perpendicular to the cutter during its rotation around z axis by an angle δ. 2. The method according to claim 1, characterized in that the aforementioned values u and w of the displacements of the ruling tool for worm cutters, backed by an Archimedean spiral, are determined, respectively, by the formulas:
u = p · δ and w = a · δ, where
p = P _x z _zax / 360;
a = (k · z _3/360) · [(P _z + _{z zax · P x) / P z]} ,
P _x is the axial pitch of the turns of the cutter;
z _zax - the number of cutters;
k is the amount of backing;
z _z - the number of teeth of the cutter;
P _z - pitch helical front surface. 3. The method according to claim 1, characterized in that the ruling tool in the form of a diamond needle is made with a rounded tip with a radius of 2-5 mm.  4. The method according to claim 1, characterized in that the ruling tool in the form of a diamond needle is informed of additional rotation around the tip of the needle. 5. The method according to claim 3, characterized in that the ruling tool with a radius of curvature inform additional rotation around the center of the curve, provided that the axis of the ruling tool is located approximately normal to the profile of the abrasive wheel.

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