GRINDING MACHINE FOR BEARING RINGS

Abstract

A bearing ring grinding machine having a grinding unit arranged to machine the bearings with micron-size tolerances and reduce a grinding cycle period. The grinding unit includes a fixed plate which supports a horizontally movable loader and sliding carriage. A carriage stopper, in the loader, holds the ring against the plate and between two lateral channels. The fixed plate has an opening for passage of a rotatable spindle, equipped with a magnetizable bush, to support the ring during machining and support stops for automatically positioning the ring on the bush. Initially, the carriage releases a ring to be ground which then passes toward the bush. The ring is then secured, machined, carried by a magnetic carrier of an automatic discharge device.

Description

TECHNICAL FIELD

The present invention concerns a grinding machine for bearing rings comprising a support frame, an automatic feed device, a grinding unit, a device for the automatic discharge of ground bearing rings, a cabinet for electric equipment and a control console, the grinding unit comprising a rotary spindle equipped with a magnetizable bush for supporting a ring during its machining and two adjustable support stops for positioning the rotating ring automatically on the bush.

PRIOR ART

Machines for grinding bearing rings, whether for ball bearings or roller bearings, must operate fully automatically and for that reason are often dedicated exclusively to that function. Their tooling is matched to the dimensions of the bearings concerned and a given set of tools corresponds to each bearing gage. The definitive parameters for grinding bearing rings are the cycle time, the machining precision and the life of the grinding wheel between two successive dressing operations.

With known grinders of this type, the cycle time is often of the order of 7 to 9 seconds. The tolerance is of the order of 3.5 to 5 microns and the grinding wheel has to be dressed regularly after machining six to twelve rings, especially when grinding outer rings, for which the grinding wheel is necessarily small since it has to fit inside the ring during the process and its diameter must therefore be smaller than the inside diameter of the outer ring. Now, around 50 to 80% of the bearings used in the automotive industry and in electric appliances have diameters between 40 and 80 or 90 mm. Consequently, most grinding wheels for outer rings have diameters between 30 and 70 mm.

To boost the productivity of such grinding machines the only effective measure is to reduce the cycle time, obviously by influencing the effective machining time but also by reducing the time taken to load the rings and clear away the machined ones, and to increase the time interval between successive wheel dressing operations. These measures must be carried out while conserving the quality of the finished product, i.e. ensuring tolerances that comply with the requirements of the users.

It has been found that the known machines seem to have reached their limits. Cycle times still exceed 7.5 seconds and any reduction of those times affects the quality of the products, which then have to be subject to individual inspection to eliminate rejects, i.e. products outside the specified tolerances. Grinding wheels wear down rapidly and in some cases the attempt to reduce cycle times entails increasing the movement speed of components and this can lead to too violent a contact between the component being machined and the grinding wheel, which results in premature wear or even degradation of the wheel.

From the publication EP 0 131 366 a grinding machine is known, which is designed for grinding the inside diameter of an annular component such as a ball bearing race. In this machine, the component to be ground is held in position on a magnetic mandrel permanently fixed on a mobile component-carrying head. The wheel, besides, is fixed on a wheel carrier that can move relative to the component being machined. These are the only features in common between this machine and that according to the present invention.

The U.S. Pat. No. 5,148,638 also relates to a grinding machine for ball bearing races, which comprises a plurality of grinding stations and a loading device for moving the rings to those stations. The rings are positioned in cylindrical recesses of a mobile transporter bar which brings the positioned components up to the grinding tools.

Japanese abstract JP 05 004143 describes a device for the magnetic fixing of a component to be machined, and the subject of the publication database XP-002453046 is a loader for a grinding machine for bearing rings, in which the components are positioned on a magnetic support.

EXPLANATION OF THE INVENTION

The purpose of the present invention is to provide a grinding machine for bearing rings, whose performance is superior to that of machines known from the prior art, which is dedicated, has unequalled cycle time, gives a machining quality that ensures tolerances of the order of a micron, and which enables between sixty and a hundred rings to be ground between two successive dressing operations of the machining wheel.

This objective is achieved by a grinding machine according to the invention, and characterized in that the feed device comprises a magnetic surface for bringing in the bearing rings to be ground, arranged in the plane of the magnetizable bush, and a sliding carriage designed, at a first point in time, to free the passage of a bearing ring to be ground toward the magnetizable bush of the rotary spindle, at a second time to hold the ring in contact against two support stops while it is being machined, and at a third time to transfer the ground ring from its position in contact with the support stops toward the automatic discharging device.

Advantageously, the magnetic transporting surface for the bearing rings to be ground is a conveyor tape located in a magnetic field.

In other embodiments the conveyor tape can be a magnetic tape or a magnetizable tape.

In a preferred embodiment of the grinding machine according to the invention, the sliding carriage is fitted with a stop abutment designed to hold a bearing ring to be ground in a loading device while a previous bearing ring is undergoing grinding.

The stop abutment is advantageously designed to free the passage of a bearing ring waiting in the loading device toward the two support stops.

Preferably the two support stops, whose positions are adjustable, are fixed on the sliding carriage.

In a preferred manner, the sliding carriage has a base on which is fitted a support on which the two support stops are fixed, this support being mounted on two elastic arms which form two sides of an elastically deformable parallelogram.

The sliding carriage also comprises a hydropneumatic damper designed to co-operate with the support and its elastic arms, in order to damp the relative movement between a bearing ring to be ground and the grinding wheel.

The pneumatic damper can be mounted on the base of the sliding carriage by means of a support.

In the preferred design, the discharging device for ground bearing rings comprises a mobile carriage on which is fitted a cylindrical box in which there is a magnetic field generator, the box being closed by at least a first closing disk mounted on a sliding axial rod that passes through the cylindrical box, and a fixed stop designed to co-operate with the rod to discharge a ground bearing ring.

The magnetic field generator can comprise at least one permanent magnet positioned against the inside surface of the closing disk.

Advantageously, the sliding axial rod that passes through the cylindrical box is mounted axially in the cylindrical box so that it slides freely, and the closing disk is permanently attached to the end of the sliding axial rod and is designed to move away from the cylindrical box when the sliding axial rod encounters the fixed stop.

The closing disk can be made of a non-magnetic material.

The sliding carriage can carry a measuring probe in the form of a pneumatic nozzle to measure the outer diameter of a bearing ring to be ground.

When the grinding unit of the grinding machine according to the invention is designed to grind an outer bearing ring, it comprises a grinding wheel whose diameter is smaller than the inside diameter of the ring and the wheel is arranged so as to move at the same time as the ring to be ground, at least during part of the cycle of loading, machining and discharging the ring.

When the grinding unit of the grinding machine according to the invention is designed to grind an inner bearing ring, it comprises a grinding wheel whose diameter is larger than the outer diameter of the ring and the wheel is arranged so as to move at the same time as the ring to be ground, at least during part of the cycle of loading, machining and discharging the ring.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and its advantages will be better understood on reading the detailed description of a preferred embodiment of the grinding machine according to the invention, which refers to the attached drawings, presented for indicative but not limiting purposes and in which:

FIGS. 1A and 1B are perspective views illustrating a grinding machine for bearing rings according to the invention; FIG. 1B shows a detailed view of part of FIG. 1A;

FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G and 2H show the grinding unit of the grinding machine according to the invention, in successive phases of its operation;

FIGS. 3A, 3B and 3C show the discharging device in three successive stages of operation; and

FIG. 4 shows a perspective view of part of the sliding carriage of the grinding unit of the grinding machine according to the invention.

OPTIMUM METHOD FOR IMPLEMENTING THE INVENTION

Referring to FIGS. 1A and 1B, the grinding machine 10 shown comprises a support frame 11 with a lower portion 11a and an upper portion 11b, a cabinet 12 for electric equipment, a grinding unit 13 mounted on a bedplate in the upper portion 11b of the support frame 11 and associated with an automatic feed device 14 for bearing rings to be ground, an automatic discharging device 15 for ground rings, shown in FIGS. 3A to 3C, and a control console 16 fixed to a movable arm and provided with a display screen and a keyboard. The upper portion 11b of the support frame 11 preferably has glass windows and allows access to the grinding unit 13. The electric equipment cabinet 12 contains all the electric components required for supplying power to the machine and for controlling it. The space delimited by the lower portion 11a of the support frame accommodates the hydraulic elements and lubrication means needed during the machining of the workpieces. Depending on whether the rings to be ground are inner or outer bearing rings, the grinding unit 13 is different from one machine to another. Granted that the aim of the invention is to produce a dedicated machine, i.e. that is perfectly adapted for the product to be machined, for which it achieves the highest possible productivity, it is envisaged to differentiate, for bearings of a given type, between machines for grinding inner rings and machines for grinding outer rings. Nevertheless, to facilitate assembly and reduce the cost of these machines, both types use as many common elements as possible, in particular the support frame, the electric equipment cabinet, the hydraulic components and lubrication means, the ring-feeding machine and the device for discharging the ground rings. The grinding unit itself has as many identical components as possible, but certain components necessarily have to be different because they must correspond to specific functions related respectively to inner bearing rings and outer bearing rings.

The automatic feed device 14 comprises transfer means 14a for moving bearing rings from a storage unit (not shown) to the grinding unit 13. These transfer means 14a comprise mainly a magnetic transporting surface in the form of a conveyor tape 14b with a section that is substantially linear and a section incurved through an angle of about 90° arranged beyond the linear section. Downstream from the incurved section and extending beyond it is a loading device 14c that receives the bearing rings 100, which are outer bearing rings in the example described and illustrated. The loading device 14c comprises a baseplate and two lateral guides which hold the rings one above another, so that they slide down under their own weight as will be described later. The conveyor tape 14b is located in a magnetic field or is itself magnetic or magnetizable, so that the rings to be machined are held on its surface by magnetic attraction. The magnetic field is produced, for example, by one or more rows of permanent magnets positioned under the tape. There could also be electromagnets, which are energized so as to adapt the power of the magnetic field as a function of the nature and composition of the material from which the components to be treated are made. In this case the rings move down into the loading device under their own weight. In other designs their descent could be assisted by a finger or a small rod that help the rings to slide down onto the baseplate of the loading device made of a magnetizable metal.

The grinding unit 13, illustrated in more detail in FIG. 1B, comprises a fixed vertical plate 13a on which are mounted the loading device 14c and a sliding carriage 20 designed to move horizontally in the direction of the double arrow A. The sliding carriage 20 has an abutment stop 21 that moves with it and whose function is to keep the lowest ring 100 in the loading device 14c resting against the baseplate and between the two lateral guides of the loading device. The fixed plate 13a has an opening to allow the passage of a spindle 22 driven to rotate, which carries a magnetizable bush 23 on which a ring 100 is arranged during the grinding operation. This spindle is of the so-termed “center-less” type, i.e. without central retention of the ring, which is automatically centered during its machining by resting against two support stops 24 and 25 whose position can be adjusted as a function of the diameter of the rings to be ground. A ring 100 to be ground is placed in firm contact on the magnetizable bush 23 of the spindle 22 and moved along with it. When the ring 100 is an outer ring, as shown in the figures, so that the ball or rolling-cylinder race is on the inside thereof, a machining wheel 26 driven by a motor carried by a support 27 that can move in three dimensions, known per se, moves inside the ring and into contact with its internal surface. When the ring is an inner ring so that its ball or rolling-cylinder race is on the outside, the machining wheel is brought in contact with its outer surface. Clearly, in the first case the diameter of the wheel must necessarily be smaller than that of the ring, while in the second case the wheel diameter may well be larger than the diameter of the ring and for that reason, the wear of the grinding wheel will be less rapid in the latter case.

FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G and 2H show the various successive phases of grinding the bearing rings 100.

FIG. 2A shows a front view of the loading device 14c, containing for example three bearing rings 100, at a time when none of the rings is being machined and the machine can be regarded as in its start-up phase.

FIG. 2B shows the next phase, during which the sliding carriage 20 has moved to the right in the figure as far as it can go, as indicated by the arrow B, taking the abutment stop 21 with it. The movement of the stop 21 frees the next bearing ring 100 to be ground, which is the one at the bottom of the loading device 14c and which slides down under its own weight onto the sliding carriage 20. Immediately after the fall of the ring, the sliding carriage 20 moves to the left in the direction of the arrow C (FIG. 2C), so that the two support stops 24 and 25 come into contact with the bearing ring 100 to be ground (FIG. 2D). Note that the two stops are angularly spaced apart by an angle larger than 90° so that the resultant of the driving forces applied on the inside surface of the ring during its machining holds the ring firmly in contact against the stops. The sliding carriage continues moving in the direction of the arrow C until the ring 100 is positioned on the magnetizable bush 23 when the carriage 20 has reached the end of its path (FIG. 2E).

It is then that the grinding of the ring 100 begins. The grinding wheel, which has entered the inside space of the ring 100, comes in contact with its inside wall. At the same time a measuring probe 30 such as a pneumatic nozzle, which is represented only schematically, measures the external size of the ring. The position of the sliding carriage 20 remains unchanged throughout the machining phase. Only the grinding wheel support moves relative to the ring during the machining phase.

During the next phase, represented in FIG. 2F, the sliding carriage 20 again moves in the direction of the arrow B, drawing with it the abutment stop 21 to the right in the figure and enabling advancement of the next bearing ring 100 to be ground. At the same time, the bearing ring 100 whose grinding has just been completed is automatically transferred in the direction of the automatic discharging device. When the carriage 20 arrives at its stop (FIG. 2G) the ground bearing ring 100 is taken up by the automatic discharging device. When the ring has been discharged (FIG. 2H), the sliding carriage 20 can start off again in the direction of the arrow C so that the support stops 24 and 25 can receive a fresh bearing ring 100 and position it on the magnetizable bush 23, ready to be machined.

The complete cycle, from the beginning of loading to the completion of discharge, lasts around 4.5 seconds, which is only possible because the wheel starts moving into the inside of the ring even before the ring has been finally positioned. In other words, the wheel moves together with the ring both before machining begins and after the machining operation during the transfer to the discharging device. Furthermore, the fact that the wheel's movement is controlled so that it accompanies the ring enables the contact between the wheel and the components to be machined, in this case the bearing rings 100, to take place gently and not violently so that damage to the grinding wheel is avoided, and ensuring that its wear is slow and regular, thereby extending the intervals between two successive dressing operations. Various additional measures for the same purpose have been adopted. They are explained in detail below.

The discharging device 15, shown in part in FIGS. 3A, 3B and 3C, comprises a mobile carriage 40 on which is mounted a cylindrical body 41 in which is accommodated a magnetic field generator preferably consisting of permanent magnets. The front end of this body can be closed by a first closing disk 42a, made for example of a ferromagnetic material which is magnetized under the action of the magnetic field produced by the permanent magnets, or of a non-magnetic material, and by a second disk 42b made of a non-magnetic material, for example a synthetic material, which is mounted on a sliding axial rod 43 that passes through the cylindrical body 41. In the example shown the permanent magnets are magnetic pellets 42c stuck to the inside surface of the first closing disk 42a, which generate a magnetic field intense enough to hold a ground bearing ring 100 against the front face of the second disk 42b. In addition, the discharging device comprises a fixed stop 44 designed to co-operate with the rod 43 to discharge a ground bearing ring 100.

In the initial phase of discharging, the mobile carriage 40 is in the forward position shown in FIG. 3A. The second disk 42b is adjacent to the first disk 42a so that the ground ring 100 remains fixed by magnetic attraction against the surface of that disk. During the next phase, shown in FIG. 3B, the mobile carriage 40 moves back in the direction of the arrow M taking with it the body 41 until the end of the rod 43 comes in contact with the fixed stop 44. During the following phase, shown in FIG. 3C, the mobile carriage 40 continues moving back in the direction of the arrow M, taking the body 41 with it. However, since the rod 43 is blocked by the fixed stop 44, this has the effect of pushing the disk 42b apart from the disk 42a. As it moves away from the disk 42a, the disk 42b creates an expanding gap between the ground ring 100 carried by the disk 42b and the magnetic field source formed by the disk 42a, until the magnetic attraction becomes too weak to hold the ring any longer. At that moment the ring falls onto a receiving element such as a clearing ramp or a conveyor tape 45, as shown in FIGS. 3A, 3B and 3C. Once the ring has been moved away, the mobile carriage 40 returns to its starting position shown in FIG. 3A.

FIG. 4 shows part of the sliding carriage 20 in more detail, the part comprising a base 50 fixed on the guide of the sliding carriage 20 and carrying a support 51 to which are attached the two fixed stops 24 and 25 that serve to support a bearing ring 100 during the grinding operation, as well as position adjustment elements 24a and 25a respectively associated with those stops. The support 51 is mounted on two elastic arms 52 and 53 which form two sides of an elastically deformable parallelogram for damping any shocks due to rapid movements of the components. In addition, for the same purpose of damping any shocks, the base 50 carries an essentially vertical support 54 on which a pneumatic damper 55 is mounted horizontally. A second fixed support 56 permanently attached to the guide of the carriage 20 carries an adjustable prestressing stop 57 which acts upon the elastic arm 52. The advantage of having these elastic arms enables the grinding wheel to be brought rapidly into contact with the component to be machined, this contact accompanied by deformation of the elastic arms 52 and 53 the result of which is to damp the shock of coming into contact. The thickness of the material to be removed by grinding is of the order of 0.10 to 0.15 mm. The wheel removes this material until the moment when the elastic arms 52 and 53 return to their initial positions. Consequently, the pressure of the wheel on the workpiece during machining is substantially constant and machining ends at the instant when the stress due to the spring effect of the elastic arms disappears.

The support 51 carries the pneumatic measuring probe that enables no-contact measurement of the outer diameter of the bearing ring 100 during and on completion of the grinding, comparing the effective diameter of the ring 100 with that of a standard component. This measuring probe also enables the wear of the grinding wheel to be measured during the machining cycle, making it possible to compensate for the wear if needs by, with a view to the next dressing of the wheel. It has the advantage of making those measurements without contact and therefore with no risk of shock, with great precision and reliability.

The objectives are achieved by the machine according to the invention. The shorter grinding cycle results from the kinematics of the machining wheel and the component being machined, the kinematics being made possible by virtue of the design of the machine. On the other hand, the grinding precision is obtained by virtue of the constant checking and measurement of the rings during machining, and of the grinding wheel during and at the end of each cycle. A major contribution toward reducing the cycle time is made by the automatic loading device for components to be machined and the automatic discharging device for ground components. The simplicity of the design and operation makes it possible to produce a machine that is compact, easy to control, and reliable.

Claims

1-18. (canceled)

19. A grinding machine (10) for bearing rings (100), the grinding machine comprising: a support frame (11),an automatic feed device (14),a grinding unit (13),an automatic discharging device (15) for ground bearing rings,an electric equipment cabinet (12), anda control console (16),the grinding unit (13) comprising a rotary spindle (22) fitted with a magnetizable bush (23) which supports a bearing ring, during a machining process, and two adjustable support stops (24, 25) which automatically position the rotating ring on the magnetizable bush (23), the feed device (14) comprises a magnetic transport surface for the bearing rings to be ground, arranged in a plane of the magnetizable bush (23), and a sliding carriage (20) designed, at a first point in time, to free passage of the bearing ring (100) to be ground toward the magnetizable bush (23) of the rotary spindle (22) so as to, at a second point in time, hold the ring (100) in contact against the two support stops (24, 25) while the ring (100) is being machined and, at a third point in time, to transfer the ground ring (100) from the position of contact against the support stops (24, 25) toward the automatic discharging device (15).

20. The grinding machine according to claim 19, wherein the magnetic transport surface for the bearing rings to be machined is a conveyor (14b) located in a magnetic field.

21. The grinding machine according to claim 20, wherein the conveyor (14b) is a magnetic tape.

22. The grinding machine according to claim 20, wherein the conveyor (14b) is a magnetizable tape.

23. The grinding machine according to claim 19, wherein the sliding carriage (20) carries an abutment stop (21) which retains a bearing ring (100) to be subsequently ground in a loading device (14c) during grinding of a previous bearing ring (100).

24. The grinding machine according to claim 23, wherein the stop (21) frees the bearing ring (100) to be subsequently ground to pass from the loading device (14c) toward the two support stops (24, 25).

25. The grinding machine according to claim 24, wherein the two support stops (24, 25) are permanently fixed on the sliding carriage (20) at positions which are adjustable.

26. The grinding machine according to claim 19, wherein the sliding carriage (20) has a base (50) on which a support (51) is mounted to which the two support stops (24, 25) are fixed, the support (51) is mounted on two elastic arms (52, 53) which form two sides of an elastically deformable parallelogram.

27. The grinding machine according to claim 26, wherein the sliding carriage (20) comprises a hydropneumatic damper (55) which co-operates with the support (51) and the elastic arms (52, 53) to dampen relative movement between the bearing ring (100) to be ground and a grinding wheel (26).

28. The grinding machine according to claim 27, wherein the hydropneumatic damper is mounted on the base (50) of the sliding carriage (20) via a further support (54).

29. The grinding machine according to claim 19, wherein the discharging device (15), for ground bearing rings (100), comprises a mobile carriage (40) on which a cylindrical body (41) is mounted in which is accommodated a magnetic field generator, the body is closed by at least a first closing disk (42a, 42b) which is mounted on a sliding axial rod (43) that passes through the cylindrical body (41), and a fixed stop (44) which co-operates with the rod (43) to discharge the ground bearing ring (100).

30. The grinding machine according to claim 29, wherein the magnetic field generator comprises at least one permanent magnet located against an inside surface of the first closing disk (42a).

31. The grinding machine according to claim 29, wherein the sliding axial rod (43), passing through the cylindrical body (41), is mounted axially in the cylindrical body so as to slide freely.

32. The grinding machine according to claim 29, wherein the first closing disk (42a, 42b) is permanently attached to an end of the sliding axial rod (43) and is arranged to move clear of the cylindrical body (41) when the sliding axial rod (43) contacts the fixed stop (44).

33. The grinding machine according to claim 29, wherein the closing disk (42a, 42b) is made of a non-magnetic material.

34. The grinding machine according to claim 19, wherein the sliding carriage (20) supports a pneumatic measuring probe (30) which measures an outside diameter of the bearing ring (100) to be ground.

35. The grinding machine according to claim 19, wherein the grinding unit (13) grinds an outer bearing ring (100), and comprises a grinding wheel (26) having a diameter smaller than an inside diameter of the outer bearing ring (100), the grinding wheel moves at the same time as outer bearing ring (100) to be ground, at least during a portion of a loading cycle, for machining and discharging the outer bearing ring (100).

36. The grinding machine according to claim 19, wherein the grinding unit (13) grinds an inner bearing ring (100), and comprises a grinding wheel having a diameter larger than an outside diameter of the inner bearing ring (100), the grinding wheel moves at the same time as the inner bearing ring (100) to be ground, at least during a portion of a loading cycle, for machining and discharging the inner bearing ring (100).

37. A machine (10) for grinding bearing rings (100), the machine comprising: a support frame (11),an automatic feed device (14),a grinding unit (13),an automatic discharging device (15),an electric equipment cabinet (12), anda control console (16),the feed device (14) has a magnetic transport surface which conveys the bearing rings (100) from a supply of bearing rings (100) to the grinding unit (13), the feed device (14) aligning the bearing rings (100) with a magnetizable bush (23) of the grinding unit (13); the magnetizable bush (23) of the grinding unit (13) being supported by a rotatable spindle (22), the magnetizable bush (23) securing one of the bearing rings (100) to the rotatable spindle (22) such that the bearing ring (100) rotates during a grinding process,the grinding unit (13) supporting two adjustable stops (24, 25) which communicate with and automatically position the bearing ring (100) on the magnetizable bush (23); anda sliding carriage (20) is biased from a first position to facilitate passage of the bearing ring (100) from the feed device (14) to the magnetizable bush (23) of the rotatable spindle (22), the bearing ring (100) is supported by the two adjustable stops, when the sliding carriage (20) is in a second position, to facilitate grinding of the bearing ring (100), in a third position of the sliding carriage (20), the bearing ring (100) is magnetically coupled to the automatic discharging device (15) and removed from the sliding carriage (20).