GB2105228A

GB2105228A - A machine for simultaneous internal and external grinding of a workpiece to be machined

Info

Publication number: GB2105228A
Application number: GB08224739A
Authority: GB
Inventors: Paul Favrot
Original assignee: CLICHY CONST SA; CONSTRUCTIONS DE CLICHY
Current assignee: CLICHY CONST SA; CONSTRUCTIONS DE CLICHY
Priority date: 1981-09-10
Filing date: 1982-08-27
Publication date: 1983-03-23
Also published as: IT8223190A0; IT1152824B; FR2512373A1; DE3233328A1; JPS5930651A

Abstract

The grinding machine is of the of plunge-grinding motion of the external wheel and of the internal wheel are substantially perpendicular. The grinding wheels are dressed by profiled dressing wheels. <IMAGE>

Description

SPECIFICATION A machine for simultaneous internal and external grinding of a workpiece to be machined This invention relates to the field of machine-tools and is primarily directed to a machine for simultaneous internal and external grinding of a workpiece of revolution to be machined.

Grinding machines are already known in which it is possible to perform simultaneous grinding of the interior and of the exterior of a workpiece without removing the workpiece from the chuck. These machines are equipped with an external grinding wheel and an internal grinding wheel each supported on a feed carriage. The carriages cause the spindles of the grinding wheels to travel in the same plane which is usually substantially horizontal. In machines of this type, the workpiece is held in position and driven in rotation by means of a mechanical chuck.

Grinding machines are also known in which the workpiece is driven by a magnetic chuck and is positioned by said chuck and by two fixed supports or "shoes" against which the workpiece is applied.

Gripping of the workpiece between magnetic chuck and shoes clearly offers considerable advantages over gripping of the workpiece within a chuck of the mechanical clamping type. Up to the present time, however, it has proved impossible to carry out internal and external grinding with this type of machine, even in a more or less simultaneous manner.

The system consisting of two grinding wheels (namely an internal grinding wheel and an external grinding wheel) having spindles which undergo a simultaneous displacement along the same axis is known and well-suitedto use in the above-mentioned machines which are equipped with mechanical chucks. But the transposition of this system to machines of the type comprising magnetic chucks and shoes in fact results in unstable rotation of the workpiece on its shoes. Even by carefully choosing the position of the shoes, it is impossible to achieve sufficient stability of the workpiece during simultaneous grinding (or more or less simultaneous grinding) to obtain satisfactory machining.

This instability appears to arise mainly from the fact that, although the grinding reactions of one of the wheels on the workpiece are well absorbed by the two shoes, the grinding reactions of the other wheel are not well balanced by the same shoes and con versely. Furthermore, this does not take into account other reactions such as, for example, those produced by friction of the workpiece on its magnetic chuck or resulting from the weight of the workpiece.

The aim ofthe present invention is to overcome the aforesaid disadvantage arising from instability of the workpiece and to permit simultaneous internal and external grinding on a machine in which the partto be machined is held between shoes and a magnetic chuck.

The invention relates to a grinding machine which comprises a magnetic chuck for driving the work piece in rotation, two shoes for supporting said work piece, a first external grinding wheel which is capable of undergoing displacement towards the workpiece surface to be ground, and a second internal grinding wheel which is capable of undergoing displacement towards the workpiece surface to be ground. The distinctive feature of the machine lies in the fact that, in order to carry out a grinding operation on the workpiece, the movement of the internal grinding wheel and the movement of the external grinding wheel take place along two substantially perpendicular axes.

Preferably, the plunge-feed grinding movement of the external grinding wheel takes place in a substantially horizontal forward direction whilst the plungefeed grinding movement of the internal grinding wheel takes place in a substantially vertical downward direction.

Advantageously, the angle between the two plunge-feed movements of the two grinding wheels is approximately 900 but can be of smaller value and reduced to approximately 50 , for example.

By virtue of this arrangement, which is very different from the known arrangement adopted in mechani & l-chuck machines in which the two movements of the two grinding wheels are parallel (angle = 0 ), it is possible to obtain perfect stabilization of the rotating workpiece between its magnetic chuck and its two supports during a simultaneous grinding operation.

The invention is also directed to a machine as defined in the foregoing and in which truing of the internal grinding wheel is carried out by means of an internal diamond wheel provided with helical grooves and placed within the magnetic chuck, said diamond wheel being obviously formed of nonmagnetic materials.

A further object of the invention is to provide a machine as hereinabove defined in which truing of the external grinding wheel is performed by means of an external diamond wheel which always remains positioned in such a manner as to ensure that the grinding wheel is tangent to said diamond wheel when the workpiece reaches the end of the grinding operation or in other words the required dimensional value.

A more complete understanding of the invention will be gained from the following detailed description, reference being made to the accompanying drawings, wherein Figure 1 is a diagrammatic sectional view taken along a radial vertical plane and showing the essential elements of the machine; Figure 2 is a diagrammatic sectional view taken along the diametral vertical plane Il-Il of Figure 1 and illustrating in particular the mode of displacement of the internal grinding wheel; Figure 3 is a plan view of the machine.

The machine essentially comprises a magnetic chuck 2 which is driven in rotation by a workpiecehead 4 about an axis 03 and which drives the work piece 6 to be ground in the direction of the arrow 5, said workpiece being retained magnetically on the chuck.

The workpiece 6 is supported during the grinding operation by two shoes 8-10 which are stationarily mounted on the bed 12 of the machine (shown in Figure 1) substantially in the plane A-A' (shown in Figure 2).

The machine is equipped with a first external grinding wheel 14, the profile 15 of which corresponds to the external profile of the workpiece 6.

The external grinding wheel 14 is driven in rotation in the direction ofthe arrow 16 by a shaft 18 having an axis O1 which is capable of displacement along the axis X-X', said axis being preferably substantially horizontal.

This displacement of the center of the grinding wheel permits plunge-feed motion of the wheel on the workpiece 6 for the grinding operation, withdrawal of the grinding wheel on completion of grinding and also compensation for wear of the grinding wheel.

By way of example, the shaft 18 is supported by a carriage 20 which is capable of sliding under the action of known driving means (not shown in the drawings) within a stationary guide 22 carried by the bed 12 of the machine.

The machine is also equipped with a second grinding wheel 24 which is used for internal grinding and the external profile 26 of which corresponds to the internal profile of the workpiece 6. The point of action of said second wheel on the internal surface of the workpiece 6 is located within the angle formed between the shoes 8 and 10. The internal grinding wheel 24 is carried by an extension 28 to which it is fixed by means of a nut 30 and is driven in rotation about an axis 02 in the direction of the arrow 32 (shown in Figure 1) by means of a conventional grinding spindle 34.

The internal grinding spindle 34 can have two movements apart from its movement of rotation.

Thus the first movement takes place along a radially oriented axis Z-Z' and permits plunge-feed grinding towards the interior of the workpiece 6, withdrawal after grinding as well ascompensationforwearofthe grinding wheel. The second movement is longitudinal and takes place along the axis Y-Y' ( as shown in Figure 2) in order to engage the grinding wheel within the workpiece, to disengage the grinding wheel from the workpiece for removal and replacement by the following workpiece. Said second movement also has a wheel-truing function which will be considered at greater length hereinafter.

In accordance with the invention, the radial piunge-feed motion of the internal grinding wheel 24 takes place along an axis Z-Z' which is substantially perpendicular to the axis X-X' of plunge-feed motion of the external grinding wheel 14. In other words, in the preferred case in which the axis X-X' of displacement of the external grinding wheel is substantially horizontal as mentioned earlier, the plunge-feed motion of the internal wheel takes place in a downward direction along a substantially vertical axis Z-Z' for the plunge grinding operation.

This angular arrangement of the axes of displacement X-X' and Z-Z' ofthetwo grinding wheels 1 4 and 24 which are located substantially at 90 results in perfect stability of the workpiece on its supports during simultaneous grinding of its external and internal faces, the two shoes 8 and 10 being located within the lower half-sector beneath the workpiece. This stability is achieved when the grinding wheels and work piece rotate in the direction indicated earlier (that is, more generally, when the grinding wheels tend to drive the workpiece in its direction of rotation and do not tend to produce a braking action on this latter).

There are shown in Figure 1 the forces R1 and R2 applied on the workpiece 6 by the grinding wheels, by the magnetic chuck and by its weight. By virtue of the fact that the points of contact of the external grinding wheel with the workpiece and ofthe internal grinding wheel with said workpieces are at approximately 90 with respect to the center of the workpiece, the reactions R1-R2 both pass between the shoes 8 and 10, thus ensuring the desirable stability of the workpiece during external and internal grinding.

In more general terms, it is only necessary to ensure that the resultant of the aforementioned forces passes between the shoes, which means that the angle a between the direction of displacement of the two grinding wheels could be smaller than 90 and could be within the range of only 50 to 60% for example. It is preferable, however, to balance the reactions on both shoes in order to obtain optimum stability.

The machine in accordance with the invention is preferably provided in addition with a system fortruing the two grinding wheels by means of a cutting wheel. It is a well-known practice to true or dress a grinding wheel by means of a diamond wheel on which the diamonds are placed at the external periphery accordingtothe desired profile to be given to the grinding wheel. In known truing-wheel sys tems, the truing operation always takes place outside the workpiece-finishing period, for example during a change of workpiece or sometimes between initial grinding and finishing.

The truing system adapted to a machine in accordance with the invention is such that operations which involve truing of both grinding wheels are carried out while grinding of one workpiece is in progress, that is, during a single grinding cycle.

The system for truing the external grinding wheel 14 will first be described. This grinding wheel is dressed by a diamond wheel 36 which rotates about an axis 04 and the external profile of which isthe same as the external profile of the workpiece 6 to be ground.

The shaft 38 of the diamond wheel 36 is supported by a carriage 40 which is capable of displacement on fixed slideways (not shown) along an inclined axis T-T' (shown in Figure 1) which is parallel to the line EF of the points of contact of the external grinding wheel 1 4 with the diamond wheel 36 and with the workpiece 6. The movement of displacement of the diamond wheel 36 along the axis T-T' takes place as a function of the diameter of the grinding wheel or in other words as a function of the degree of wear of said wheel and in such a manner as to ensure that the external grinding wheel 14 is tangent to the diamond wheel 36 (as shown in Figure 1) when theworkpiece 6 has attained the required dimensional value.

In accordance with this arrangement, when the external grinding wheel 14completes its plunge-feed movement of displacement along the axis X-X', said wheel finishes the external surface oftheworkpiece 6 while being trued against the diamond wheel 36 at the end of travel.

The system adopted fortruing the internal grinding wheel 24 will now be described.

There is placed within the magnetic chuck 2 a hollow diamond wheel 42, the internal dimensions of which are equal to the internal dimensions of the workpiece 6 to be ground. Said hollow diamond wheel is made of non-magnetic materials and is provided with a series of helical grooves 44 having the function of facilitating removal of cutting particles and coolant fluid. These grooves produce a pump effect by reason of the fact that the hollow diamond wheel 42 is driven in rotation with the chuck 2.

Atube 46 extending through the workpiece head 4 forthe supply of coolant fluid serves both to carry out sprinkling during the grinding operation and sprinkling at the time of truing of the grinding wheel.

A deflector 48 which also serves to lock the diamond wheel 42 in position on the chuck 2 as well as the head of the nut 30 which is given a suitable shape serve to guide the streams of coolant fluid.

As described earlier, the internal grinding spindle 34 which carries the internal grinding wheel 24 is capable of displacement in two perpendicular directions, namely along a radial axis Z-Z' (in a vertical or substantially vertical direction) and along a longitudinal axis Y-Y' (horizontal direction) as shown in Figure 2, the grinding spindle being mounted in a conventional manner on a set of slides (not shown in Figure 2).

The horizontal displacement along the axis Y-Y' has the function of bringing the center B of the internal grinding wheel 24 either to the point C in order to permit truing of said grinding wheel by the diamond wheel 42 or to the point Din orderto permit removal ofthe ground part, positioning ofthefollowing workpiece and changing of the grinding wheel.

There will now be given one example of an operating cycle of the machine starting from the moment when a workpiece 6 to be machined is positioned on the magnetic chuck 2 and the shoes 8-10; - forward displacement of the internal grinding wheel 24 from point D to point B; -simultaneous plunge-feed motion of the external grinding wheel 14 along the axis X-X' and of the internal grinding wheel 24 along the axis Z-Z'; - before the final dimensions of the workpiece are attained and at a distance of 0.05 mm from said dimensions, for example, the internal grinding wheel moves upwards along the axis Z-Z' to a mean position B, then moves from point B to point C along the axis Y-Y'; - the external grinding wheel finishes the external surface of the workpiece and is then trued by the diamond wheel 36 atthe end ofthe plunge-feed travel of said grinding wheel.At the same time, the internal grinding wheel 24 travels in plunge-feed motion along the axis Z-Z' from the point B in order to be trued against the diamond wheel 42, then moves upwards along the axis Z-Z' to point C and returns along the axis Y-Y' to point B; - the internal grinding wheel 24 again undergoes a plunge-feed movement from point B along the axis Z-Z' so as to finish the internal surface of the work piece, then returns upwards to point B and finally undergoes a displacement along the axis Y-Y' to point Din order to permit removal of the ground part and positioning of the following workpiece.

As can readily be understood, a cycle of this type can be programmed and controlled automatically at the machine, said machine being normally completed by an automatic feed and discharge system of known type.

It is therefore clearly apparent from the foregoing that the machine in accordance with the invention permits simultaneous internal and external grinding of parts in conjunction with truing of both grinding wheels during the grinding cycle.

Figure 3 is a plan view of a machine in accordance with the invention and shows the workpiece head 4 together with its magneticchuck2 and its drive motor 50 as well as the internal grinding spindle 34 and the extension 28 which carries the internal grinding spindle.

The spindle 34 is supported by a first carriage 52 which is capable of displacement along the axis Z-Z' within a first vertical slide 54, said slide being in turn supported by a second carriage 56 which is capable of displacement along the axis Y-Y' within a horizontal slide 58, said slide being in turn supported by the bed 12 of the machine.

Figure 3 also showsthe grinding-wheel support 60, the motor 62 of which is adapted to drive the external grinding wheel 14. The carriage 20 of the grinding wheelsupportiscapableofdisplacementwithin horizontal guides 22 in orderto cause the displacement of the external grinding wheel along the axis X-X'. The figure also shows the diamond truing device 64which carries the diamond wheel 36 for truing the external grinding wheel and the carriage 40 of which is capable of displacement in a sliding motion along an oblique guide track in order to produce a displacement of the diamond wheel 36 along the axis T-T' as well as on horizontal guides 66 in orderto position the diamond wheel as a function of the different diameters of grinding wheels employed. The machine can be completed by a known assembly 68 for automatic feed and discharge of parts.

As will readily be understood, the invention is not limited in any sense to the embodiment described in the foregoing with reference to the accompanying drawings. Depending on the applications which are contemplated, many alternative forms of construction within the capacity of those versed in the art may accordingly be considered without thereby departing either from the scope or the spirit of the invention.

Claims

1. A machine for simultaneous internal and external grinding of a workpiece to be machined, comprising a magnetic chuck for driving the workpiece in rotation, two stationary shoes for supporting the said workpiece, a first external grinding wheel which is capable of displacement towards the external workpiece surface to be ground, and a second internal grinding wheel which is capable of displacement towards the internal workpiece surface to be ground, characterized in that the movement of the internal grinding wheel and the movement of the external grinding wheel take place along two sub stantially perpendicular axes in order to carry out a grinding operation on the said workpiece.

2. A machine in accordance with claim 1, characterized in that the plunge-feed grinding movement of the external grinding wheel takes place in a substantially horizontal forward direction whilst the plungefeed grinding movement of the internal grinding wheel takes place in a substantially vertical downward direction.

3. A machine in accordance with claim 2, characterized in that the angle a between the axes of displacement of the two grinding wheels is within the range of 50 to 90 approximately.

4. A machine in accordance with any one of claims 1, 2 or 3, characterized in that the internal grinding wheel is also capable of displacement along a longitudinal axis which coincides with the axis of rotation of the said grinding wheel.

5. A machine in accordance with any one of the preceding claims, characterized in that the direction of rotation in which the workpiece is driven by the magnetic chuck and the direction of rotation of the internal grinding wheel are identical whilst rotation of the external grinding wheel takes place in the opposite direction.

6. A machine in accordance with any one of the preceding claims, characterized in that it comprises an external diamond wheel for truing the external grinding wheel, the said diamond wheel being positioned so asto be tangent to the external grinding wheel at the end of the plunge-grinding travel of the said external wheel, and that the diamond wheel is supported by a carriage which is capable of displacement along an oblique axis substantially parallel to a straight line passing through the points of tangential contact ofthe external grinding wheel with the diamond wheel and with the external surface of the workpiece for the purpose of grinding the said workpiece.

7. A machine in accordance with any one of the preceding claims, characterized in that the said machine comprises a hollow diamond wheel fortruing the internal grinding wheel and that the said diamond wheel carries out the truing operation with its internal diamond surface.

8. A machine in accordance with claim 7, characterized in that the internal diamond wheel is housed within the magnetic chuck behind the workpiece and is driven in rotation in rigidly fixed relation to the said chuck.

9. A machine in accordance with claim 7 or claim 8, characterized in that the internal grinding wheel is capable of displacement along the longitudinal axis from its work position on the workpiece to its truing position against the internal diamond wheel and in the opposite direction up to a position of discharge and positioning of the workpiece.

10. A machine in accordance with any one of claims 7 to 9, characterized in that helical grooves are cut in the internal diamond wheel and that provision is made within and at the centre of the chuck for an axial admission of coolant fluid.

11. A machine in accordance with claim 10, characterized in that the said machine is provided with coolant fluid deflectors.

12. A machine for simultaneous internal and external grinding of a workpiece to be machined, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.