DESCRIPTION OF PRIOR ART Often in CNC tool grinding machines, it is necessary to use several different grinding wheels to operate on a workpiece to produce a finished tool, such as a drill bit or the like, from the workpiece.

Conventional CNC tool grinding machines suffer from the inability to change one grinding wheel for another quickly during the grinding cycle. This results in down time when it is required to remove and replace wheels. In order to decrease the down time to change wheels several types of devices have been previously proposed.

It is, for example known to mount a wheel pack including a plurality of grinding wheels on a rotatable spindle. However, when wheels of significantly different diameters are mounted on a spindle, there is a danger that a large diameter wheel may exceed its maximum surface speed when a smaller wheel is grinding. There has also been proposed a double ended spindle having a respective grinding wheel or wheel packs on each end of the spindle. The spindle is rotatable about its own central longitudinal axis during a grinding cycle so that both wheels or wheel packs rotate, with only one of the wheels or wheel packs being used to grind the workpiece. At the end of part of a grinding cycle the spindle is rotated about an axis perpendicular to its central longitudinal axis and the second wheel or wheel pack on the other end of the spindle is used for the next part of the cycle. In order to change a wheel or

wheel pack, rotation of the spindle about its central axis must be stopped to enable wheel or wheel pack to be changed manually, which is time consuming.

Further, in order to change a wheel or wheel pack coolant pipes must be moved.

When the new wheel or wheel pack is mounted the coolant pipes must be manually manoeuvred to the correct position. This is a time consuming task.

In addition, a rotating, out of balance, wheel pack not in use would wear the spindle bearing. This is undesirable.

SUMMARY OF THE INVENTION It is therefore desirable to provide a wheel changing device for a CNC tool grinding machine in which various disadvantages and limitations of the prior art are alleviated.

It is also desirable to provide an improved means of changing grinding wheels or wheel packs in a CNC machine between different parts of grinding cycle.

It is further desirable to provide a method of and apparatus for changing wheels during a grinding cycle in a CNC machine tool grinder which results in reduced down time for the CNC machine when it is required to change grinding wheels.

According to a first aspect of the invention, there is provided a wheel changing device for a CNC tool grinding machine having a rotatable spindle for carrying at least one grinding wheel, said wheel changing device comprising: a wheel pack holder including holding means for holding at least two wheel packs; said wheel pack holder being movable between a first position for mounting a first one of the wheel packs on the spindle and a second position for mounting a second one of the wheel packs on the spindle; first coolant supply means for supplying coolant to the first wheel pack; and second coolant supply means for supplying coolant to the second wheel

pack.

Whilst a wheel pack will usually include a plurality of grinding wheels, it should be appreciated that a wheel pack may have a single wheel for mounting on a spindle.

Preferably, the first coolant supply means includes a first coolant pipe arrangement for the first wheel pack and the second coolant supply means includes a second coolant pipe arrangement for the second wheel pack.

In CNC tool grinding machines, different arrangements of coolant pipes or hoses are usually required for different grinding wheels or wheel packs. The set-up of a coolant pipe arrangement for an individual grinding wheel or wheel pack can be critical for effective cooling of the grinding wheel and workpiece during a grinding operation. By providing a wheel changing device with separate coolant supply means for each wheel or wheel pack, down time caused by moving and re-setting the coolant pipes during wheel changing is substantially eliminated.

The first coolant and second supply means may be provided by a common coolant supply block mounted on the wheel pack holder and having first and second coolant inlet ports, at least one first coolant outlet port for connection to a coolant pipe or hose for the first wheel pack and at least one second coolant outlet port for connection to a respective coolant pipe or hose for the second wheel pack.

Preferably, the spindle is rotatable about a first axis and the wheel pack holder is rotatable between said first and second positions about a second axis extending substantially parallel to the first axis, and the wheel pack holder includes holding means for holding a plurality of wheel packs at circumferentially spaced positions around the second axis.

The wheel pack holder preferably includes a body rotatable about said second axis and wheel pack clamping means in the form of clamping jaws disposed at circumferentially spaced positions around said axis for engagement with the respective wheel packs.

In a particularly preferred embodiment, the wheel pack holder is movable relative to the spindle assembly in the direction of the second axis between a first retracted position for mounting one of the wheel packs on the rotatable spindle and a second advanced position in which the wheel pack holder can be rotated to change the positions of the wheel packs. Preferably, the clamping jaws of the clamping means for the wheel pack mounted on the spindle are automatically released as the wheel pack holder moves into the retracted position to allow the spindle to rotate during a subsequent grinding operation.

According to another aspect of the invention, there is provided a wheel changing device for a CNC tool grinding machine having a spindle for carrying at least one grinding wheel, said spindle being rotatable about its central longitudinal axis, the wheel changing device comprising: a wheel pack holder including means for holding a plurality of wheel packs at circumferentially spaced positions around a second axis extending substantially parallel to the axis of rotation of the rotatable spindle; said wheel pack holder including a body rotatable about said second axis for changing the wheel pack to be carried by the spindle; said wheel pack holder having wheel pack clamping means for each of the wheel packs; said wheel pack holder body being movable relative to the spindle in the direction of the second axis between a first position for mounting one of the wheel packs on the rotatable spindle and a second position in which the wheel pack holder can be rotated to change the positions of the wheel packs; wherein movement of the wheel pack holder body into said first position automatically causes the clamping means for the wheel pack on the spindle to be released to allow the spindle to rotate during a subsequent grinding operation.

Preferably, the or each grinding wheel of each wheel pack is mounted on a cylindrical wheel arbor which is adapted to be mounted on the rotatable spindle. Each wheel pack clamping means preferably includes clamping jaws

engageable within an annular groove in the wheel arbor of a respective wheel pack. The clamping jaws are preferably spring-loaded and are normally urged into engagement with the wheel arbor of a respective wheel pack. The clamping jaws are preferably pivotally mounted on the wheel pack holder body, the clamping jaws having portions engageable in the first, retracted position of the wheel pack holder with forwardly projecting prongs on the spindle assembly which urge the jaws apart in the first retracted position. Preferably, releasable locking means, such as locking pins, may be provided for locking the clamping jaws on the wheel arbors.

According to a further aspect of the invention, there is provided a CNC tool grinding machine incorporating a wheel changing device in accordance with the first or second aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view of a wheel changing assembly in accordance with the invention; Figure 2 is a front end view of a wheel pack holder of the assembly of Figure 1; and Figure 3 is a front perspective part view of the wheel changing assembly of Figure 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The wheel changing assembly shown in the drawings comprises a wheel changing device 10 mounted to a spindle assembly 20 of a CNC tool grinding machine including a rotatable spindle 22 adapted to carry one or more grinding wheels for operating upon a workpiece mounted in another part of the CNC machine (not shown). The spindle 22 of the spindle assembly 20 is journalled for rotation about a first axis A.

The wheel changing device 10 comprises a wheel pack holder in the form of a generally rectangular body 12 having wheel pack holding means 14,16 at each end 13,15 of the body 12. The body 12 of the wheel pack holder is mounted on a rotatable shaft 24 which is journalled for rotation about a second axis B relative to a mounting block 26. The mounting block 26 is movable relative to the spindle assembly 20 in the direction of the second axis B which extends substantially parallel to the first axis A.

Each wheel pack holding means 14,16 comprises a pair of clamping jaw members 51,52 for clamping a respective wheel pack assembly 30,40. Each wheel pack assembly 30,40 has a number of grinding wheels 31,32,33; 41, 42,43 mounted on a cylindrical wheel arbor 34,44 having a central bore 36, 46 for receiving the rotatable spindle 22 of the spindle assembly 20. As shown in Figure 1, there are three grinding wheels 31,32,33; 41,42,43 in each wheel pack assembly 30,40 but it will be appreciated that the number of grinding wheels in a wheel pack assembly may vary for different applications. For instance, a wheel pack assembly may have only a single grinding wheel. In a particularly preferred embodiment, each wheel pack assembly can have up to four grinding wheels enabling a total of eight wheels to be used to manufacture a tool from a workpiece, if necessary. For example, one of the wheel packs may have four taper-grinding wheels on its arbor, with the other wheel pack having four face-grinding wheels. Mounting wheels with similar surface speeds on the same wheel pack reduces the risk of a large diameter wheel exceeding its surface speed while a smaller diameter wheel is grinding.

Each of the clamping jaw members 51,52 has a rear portion 53 received in a slot 18 in a respective side wall 17 of the wheel changer body 12 and a forward portion in the shape of a claw 54. Clamping jaw members 51,52 are connected to the wheel pack holder body 12 by pivotal mountings 55 at intermediate locations between the forward and rear ends of the jaw members 51,52.

The ends 13,15 of the body 12 of the wheel pack holder are formed with

arcuate recesses 19 and the claws 54 of the clamping jaw members 51,52 have generally arcuate inner surfaces 56, which are adapted to engage in closed positions in an annular groove 39,49 in the wheel arbor 34,44 of a respective wheel pack assembly 30,40. The pivotally mounted clamping jaw members 51, 52 are preferably spring-loaded so that the claws 54 are normally urged into engagement with the grooves 39,49. Movable locking pins 59 may also be provided for locking the clamping jaw members 51,52 in their closed positions.

The side walls 17 of the wheel pack holder body 12 have generally rectangular recesses 57 in the region of the rear portions 53 of the clamping jaw members 51,52. As previously mentioned, the mounting block 26 of the wheel changing device 11 is movable relative to the spindle assembly 20 in the direction of the second axis B. The mounting block 26 is movable between an advanced position in which the wheel pack assemblies 30,40 are held at forward positions in front of the spindle 22 and a retracted position in which the wheel arbor 34 of the lower wheel pack assembly 30 is mounted on the spindle 22 of the spindle assembly 20. In the retracted position, forwardly projecting prongs 58 which are fixedly mounted on the front of the spindle assembly 20 engage with the lower locking pins 59 and extend into the recesses 57 to engage with the rear portions 53 of the clamping jaw members 51,52 of the lower wheel pack holding means 14. This causes the lower locking pins 59 to release and the prongs 58 overcome the spring loading of the jaw members 51,52 causing the claws 54 of the lower wheel pack holding means 14 to move away from each other out of engagement with the groove 39 so that the spindle 22 and lower wheel pack assembly 30 is free to rotate about the first axis A. The mounting block 26 may be moved between its advanced and retracted positions by any convenient means, for instance by means of a pedal-operated pneumatic or hydraulic actuating mechanism.

The wheel changing device 10 also includes a coolant supply block 60 mounted on the front face of the wheel pack holder 12. The coolant supply

block 60 is of elongate rectangular form extending substantially perpendicularly to the major axis of the rectangular wheel pack holder body 12. The front face of the coolant supply block 60 has a first, lower row of coolant outlet ports 61, a second, upper row of coolant outlet ports 62, and the rear face of the supply block 60 has first and second coolant inlet ports 63,64 provided at opposite ends of the coolant supply block 60.

The first coolant inlet port 63 is adapted to communicate with the first row of coolant outlet ports 61 by a longitudinally extending passage within the coolant supply block 60 and the second coolant inlet port 64 is adapted to communicate with the second row of coolant outlet ports 62 by another longitudinally extending passage within the coolant supply block 60. The coolant inlet ports 63,64 are connected to a source of coolant and, as shown in Figures 1 and 3, a plurality of coolant pipes or hoses 65,66 are connected to at least some of the coolant outlet ports 61,62. The coolant hoses 65 are arranged to direct coolant onto the grinding wheels 31,32,33 of the wheel pack assembly 30 when it is in operation and the coolant hoses 66 are arranged to direct coolant onto the grinding wheels 41,42 and 43 of the wheel pack assembly 40 when it is in operation. As shown in Figures 2 and 3, the coolant supply block 60 has six coolant outlet ports 61,62 in each row which allows for the connection of up to six coolant hoses 65,66 for each wheel pack assembly 30,40. However, when all of the outlet ports 65,66 are not in use, those ports not in use may be closed by plugs 67.

Operation of the wheel changing device will now be described for a complete grinding cycle of the CNC machine. First, with the wheel pack holder 12 and mounting block 26 in the advanced position, the first and second wheel pack assemblies 30,40 are mounted to the wheel pack holder 10 by moving the claws 51,52 of the wheel pack holding means 14,15 into engagement with the grooves 39,49 of the respective wheel pack assemblies 30,40. For instance, the first wheel pack assembly 30 may include taper-grinding wheels for initial flute- grinding work on a workpiece and the wheel pack assembly 40 may include

face-grinding wheels for finishing work on the workpiece. Then, an arrangement of coolant hoses 65,66 is set up for the respective wheel pack assemblies 30,40.

The wheel pack holder 12 and mounting block 26 are then moved relative to the spindle assembly 20 into the retracted position as shown in Figure 2 to mount the first wheel pack assembly 30 on the spindle 22. This also causes the prongs 58 to engage with and release the locking pins 59 and to engage with the rear portions 53 of the clamping jaws 51,52 of the wheel pack holding means 14 for the first wheel pack assembly 30. This moves the claws 54 of the clamping jaws 51,52 out of engagement with the groove 39, allowing the spindle 22 and grinding wheels 31,32,33 of the first wheel pack assembly 30 to rotate to perform grinding operations on the workpiece during a first part of the grinding cycle.

After the first grinding cycle is completed, with the spindle and lower wheel pack assembly stationary, the wheel pack holder 10 and mounting block 26 are moved forwardly into the advanced position to disengage the first wheel pack assembly 30 from the spindle 22. Simultaneously, prongs 58 are disengaged from the rear portions 53 of the clamping jaws 51,52 and the spring-loaded claws 54 of the clamping jaws 51,52 of the wheel pack holding means 14 are moved into engagement with the groove 39 to clamp the first wheel pack assembly 30. The prongs 58 are also disengaged from the locking pins 59 which move back into their locking positions.

The wheel pack holder 10 is then rotated through 180° about the second axis B so that the second wheel pack assembly 40 becomes the lower assembly.

The wheel pack holder 10 and mounting block 26 are then moved rearwardly into the retracted position to mount the second wheel pack assembly 40 on the spindle 22. This also causes the prongs 58 to open the clamping jaws 51,52 of the wheel pack holding means 15 allowing the spindle 22 and grinding wheels 41,42 43 of the second wheel pack assembly to rotate to perform grinding operations e. g. finishing operations, on the workpiece during a second

part of the grinding cycle.

The wheel pack changing device described above provides several advantages over conventional arrangements for changing grinding wheels in CNC tool grinding machines including: (a) the ability to change one wheel pack for another rapidly between different parts of a complete grinding cycle; (b) the need to move and re-set the arrangement of coolant hoses when changing wheels in conventional machines is eliminated by the use of separate sets of coolant hoses and coolant supply means, one for each wheel pack; (c) only one wheel pack is rotating during a grinding operation, resulting in reduced wear and improved safety compared with a double-ended spindle; and (d) when two wheel packs are sufficient to complete a grinding operation, only one grinding cycle is required.

It will be appreciated that various modifications may be made to the specific embodiment of the wheel changing device described above without departing from the scope and spirit of the present invention. For instance, it is conceived that a rotary wheel pack holder having more than two wheel pack holding means for more than two wheel pack assemblies located at circumferentially spaced positions may be provided.

In this specification, the term"comprising"and its grammatical equivalents, is to be taken as meaning"including".