Field of the invention

The present invention relates to grinding machines for grinding workpieces using grinding wheels carried on rotary tool spindles.

Background to the invention

Grinding machines, particularly but not exclusively of the type used to machine crankshafts are often built with two or more grinding spindles. Different grinding wheels are mounted on the spindles, with each of the wheels configured to perform a specific material removal task. This is advantageous as the time taken to grind a workpiece requiring general different grinding profiles can be significantly reduced if a multiplicity of features can be ground in a single part loading using differently shaped grinding wheels on the same machine to remove material from the workpiece.

For example, one spindle may carry a grinding wheel which is able to remove large quantities of material without suffering undue wear, whilst another wheel may be used to remove smaller amounts of material, but leave a high quality surface finish. Other wheel shapes may also be desirable, such as differing corner radii and formed edge profiles. Further driven machine axes may be added to accommodate additional wheel spindles. For example, in pending UK Patent Application No. 1513186.5 filed by the present applicant, a tool swivel assembly is provided which carries two or more wheel spindles. The swivel assembly may be used to carry several grinding wheels and bring them into grinding engagement with the workpiece in turn.

However, the addition of further wheel spindles and drive mechanisms increases the complexity of the machine as well as its footprint. The productivity of the machine is also reduced due to the time taken to withdraw one wheel spindle out of the work zone of the machine, and bring in another.

Summary of the invention The present invention provides a grinding machine comprising

two rotary tool spindles, each able to carry at least two grinding wheels; and a transfer mechanism operable to transfer a grinding wheel mounted on one of the tool spindles onto the other tool spindle.

This machine configuration enables the use of at least three grinding wheels using two tool spindles. Each tool spindle may carry the or each grinding wheel mounted thereon on a side of the tool spindle facing the other tool spindle. Each tool spindle may be operable to rotate the or each grinding wheel mounted thereon about a respective rotational axis and carry the or each grinding wheel mounted thereon on a respective mount which extends away from the body of the tool spindle in a direction axially towards the other tool spindle.

The machine may be configured such that a grinding wheel transferable from one tool spindle to the other may only be able to grind a workpiece when mounted on a specific one of the tool spindles.

In a preferred embodiment, the transfer mechanism is operable to transfer a grinding wheel mounted on one of the tool spindles onto the other tool spindle whilst both tool spindles are rotating. This reduces the time taken to switch from using one grinding wheel to another as it is not necessary to bring the tool spindles to a standstill.

The transfer mechanism may comprise a first wheel clamp on one of the tool spindles and a second wheel clamp on the other tool spindle. In this way, a transfer mechanism may be provided without requiring an additional substantial structure to be supported on the machine based separately from the tool spindles, which could increase the footprint of the machine significantly.

The grinding machine may further include a drive arrangement for moving at least one of the tool spindles relative to the other, wherein the drive arrangement is operable to move at least one of the tool spindles relative to the other to a location where the first and second wheel clamps are juxtaposed such that a grinding wheel supported on the first wheel clamp is releasable by the first wheel clamp and capturable by the second wheel clamp. Each wheel clamp may extend from the respective tool spindle in a direction towards the other tool spindle.

The drive arrangement may be configured to bring the wheel clamps into close proximity with each other or into contact during transfer of a grinding wheel from one tool spindle to the other. Each tool spindle may be arranged to rotate a respective tool about a reference axis which is coaxial with the reference axis of the other tool spindle as a grinding wheel is transferred between them.

Each tool spindle may be operable to grind a workpiece mounted in the grinding machine whilst the workpiece is held continuously by a mount of the machine, by moving at least one of the tool spindle and the workpiece/mount relative to the other.

In some examples, each tool spindle includes a wheel mount which is able to carry at least two grinding wheels simultaneously.

In a preferred embodiment, one of the tool spindles carries a first grinding wheel, the other tool spindle carries a second grinding wheel, and the machine includes a third grinding wheel which is transferable by the transfer mechanism from one tool spindle to another.

The grinding machine may be switchable between a first configuration in which the first and second grinding wheels are able to grind a workpiece mounted in the machine (whilst the third is not), and a second configuration in which the first and third grinding wheels are able to grind the workpiece (whilst the second is not), by transferring the third grinding wheel from one tool spindle to the other.

The first grinding wheel may have a greater diameter than the third grinding wheel, and the third grinding wheel may have a greater diameter than the second grinding wheel. In some grinding machine configurations, when the third grinding wheel is carried by one of the tool spindles, the first grinding wheel surrounds the outer circumferential grinding surface of the third grinding wheel in a plane which extends transversely with respect to the rotational reference axis of the one tool spindle. The first grinding wheel may be used to grind a workpiece whilst the associated tool spindle carries the third grinding wheel, without the third grinding wheel impeding use of the first grinding wheel. The first and third grinding wheels may be shaped such that, when mounted on a common tool spindle, the third grinding wheel is substantially contained within a volume defined by the diameter and axial width of the first grinding wheel. This ensures that the third grinding wheel does not restrict the interaction between the first grinding wheel and the workpiece.

In some machine configurations, when the third grinding wheel is carried by the other of the tool spindles, the third grinding wheel surrounds the outer circumferential grinding surface of the second grinding wheel in a plane which extends transversely with respect to the rotational reference axis of the other tool spindle. The second and third grinding wheels may be shaped such that when they are mounted on a common tool spindle, the second grinding wheel is substantially contained within a volume defined by the diameter and axial width of the third grinding wheel. This ensures that the second grinding wheel does not restrict the interaction between the third grinding wheel and the workpiece.

The grinding surfaces of at least two of the grinding wheels may have different profiles in the axial direction. The machine may therefore make a set of different grinding wheel profiles available for use in a single part loading.

The grinding surfaces of at least two of the grinding wheels may have different abrasive properties. For example, one wheel may be designed to carry out rough grinding, whilst another is suitable for finish grinding.

The first and second wheel clamps may be operable to selectively engage with a radially inwardly facing surface that defines a central opening through a grinding wheel in order to fasten the grinding wheel to the respective tool spindle. This may enable the transferable wheel to be held on each mount more closely to another wheel on the mount, and so minimise the risk of one wheel interfering with the grinding operations carried out by another wheel on the same mount.

Each wheel clamp may be operable to increase the diameter of a distal end thereof to engage with the radially inwardly facing surface of the grinding wheel. In preferred configurations, the distal end of each wheel clamp defines a circumferentially and radially outwardly extending lip for engaging with a groove defined by the radially inwardly facing surface of the grinding wheel. The lip may include a frusto-conical surface which increases in diameter towards the outermost end of the wheel clamp.

The first and second wheel clamps may be configured such that they are able to clamp the same wheel simultaneously. During the process of transferring a wheel from one clamp to another, the wheel may be held by both clamps simultaneously (if only briefly) to ensure that the wheel is safely transferred from one clamp to the other.

Both clamps may engage with the same groove formed on a wheel at the same time in order to hold the wheel. Each clamp may be configured to only extend partway through a wheel mounted thereon, to enable a clamp extending into the wheel from the opposite side of the wheel to hold the wheel at the same time.

The present invention further provides a method of operating a grinding machine as described herein, wherein the method comprises a step of transferring a grinding wheel mounted on one of the tool spindles onto the other tool spindle using the transfer mechanism.

In some examples, the method comprises the steps of:

(a) providing the third grinding wheel on the one tool spindle;

(b) transferring the third grinding wheel to the other tool spindle;

(c) before step (b), grinding the workpiece with the second grinding wheel;

(d) after step (b), grinding the workpiece with the third grinding wheel; and

(e) before or after step (b), grinding the workpiece with the first grinding wheel. In further examples, the method comprises the steps of:

(a) providing the third grinding wheel on the other tool spindle;

(b) transferring the third grinding wheel to the one tool spindle;

(c) before step (b), grinding the workpiece with the third grinding wheel;

(d) after step (b), grinding the workpiece with the second grinding wheel; and

(e) before or after step (b), grinding the workpiece with the first grinding wheel.

These methods enable the grinding machine to use each of three grinding wheels using two tool spindles.

The present invention also provides a grinding wheel comprising:

a wheel body with a central axis about which the wheel is rotated in use, two opposing, transversely extending side surfaces, and a radially inwardly facing surface that defines a central opening which extends axially through the wheel,

wherein the radially inwardly facing surface defines a circumferentially extending groove for engagement by a clamping mechanism extending into the opening from either side of the wheel.

Such a wheel is suitable for use in a grinding machine as described herein. The groove may be for engagement by a clamping mechanism of a grinding machine. The clamping mechanism may extend into the opening from either side of the wheel. The clamping mechanism may fasten the grinding wheel to a tool spindle of the grinding machine.

The area of the wheel surface prepared for grinding may substantially be located only around the peripheral region of the wheel body. The wheel body may have a radially outwardly facing peripheral grinding surface. The area of the wheel surface prepared for grinding may be substantially localised at the peripheral grinding surface. As the wheel may be engaged by a clamping mechanism on either side of the wheel, it is transferable from a tool spindle on one side to another tool spindle located on the other side of the wheel.

The groove may extend around the majority of or substantially entirely or entirely around the radially inwardly facing surface of the grinding wheel in the circumferential direction. The surface provided by the groove for engagement with a clamping mechanism may therefore be substantially the same irrespective of the rotational orientation of the wheel, thereby simplifying the engagement procedure.

The groove defined by the radially inwardly facing surface of the wheel may be symmetrical about a plane which is transverse with respect to the central axis of the wheel. In this way, the wheel can be engaged in a similar manner from either side. Preferably, the whole of the radially inwardly facing surface of the wheel is symmetrical about that plane.

Preferably, the groove comprises two sidewall surfaces, which converge towards each other in the radially outward direction. This tapered groove configuration enables a clamping mechanism to engage the wheel securely and accurately by expanding outwardly into the groove. This groove configuration may also allow the wheel to be temporarily engaged with clamping mechanisms which extend into its central opening from opposite sides simultaneously. This may ensure that the wheel can be transferred safely and reliably from one clamping mechanism to another. Each clamping mechanism may engage with a respective one of the two sidewall surfaces of the groove.

Brief description of the drawings

Embodiments of the invention will now be described by way of example and with reference to the accompanying schematic drawings, wherein: Figures 1 to 3 show perspective views of part of a grinding machine which includes two tool spindles according to an embodiment of the invention, during successive stages in operation of the machine;

Figures 4a to 4c are cross- sectional perspective views of part of the tool spindles and grinding wheels shown in Figures 1 to 3 during successive stages of operation of the machine;

Figure 5 shows an example of a workpiece formed using three different grinding wheel profiles; and

Figures 6 to 8 are perspective views showing grinding of the workpiece of Figure 5 by a grinding machine embodying the present invention during successive stages of the grinding operation.

Detailed description of the drawings

Figures 1 to 3 show perspective views of part of a grinding machine according to an embodiment of the invention. A bed or base 2 of the grinding machine supports two wheel spindles 4 and 6. Each wheel spindle is carried by a base member 8, 10, respectively, which is linearly slideably mounted on the bed 2. Each wheel spindle is linearly slideable relative to the respective base members 8 and 10.

Each wheel spindle has a wheel mount 12, 14, respectively. Each mount is supported by the respective wheel spindle for rotation about respective axes 16 and 18. Axes 16 and 18 are at the same height above the machine bed 2. Each wheel spindle includes a drive for rotating the respective mount about its rotational axis. Each wheel spindle is moveable relative to the machine base 2 in a direction parallel to its rotational axis 16, 18 by a respective drive (not shown) which is able to move the associated base member 8, 10 relative to the bed 2. Also, each wheel spindle is moveable relative to the machine base 2 in a direction perpendicular to its rotational axis by drives (not shown) which move the spindles relative to their base members in an infeed direction. In the initial configuration shown in Figure 1, mount 12 carries two grinding wheels 20 and 22. Mount 14 of the other wheel spindle carries a single wheel 24. In this configuration, grinding of a workpiece can be carried out by either of wheels 20 and 24, without interference from wheel 22. Wheel 22 is mounted coaxially with wheel 20. Wheels 20 and 22 are dimensioned such that wheel 22 is mounted within the outermost dimensions of wheel 20 so that it does not protrude to any significant extent in the axial direction beyond wheel 20 and is radially located inwardly from the outer cylindrical surface of wheel 20.

Once the grinding tasks associated with wheel 24 for a given workpiece are complete, the grinding machine interrupts the machining process briefly in order to transfer wheel 22 from mount 12 to mount 14. As shown in Figure 2, this is achieved by bringing the wheel spindles 4 and 6 together so that a wheel clamp mechanism retaining wheel 22 can interact with a wheel clamp mechanism carried by mount 14. The clamp mechanisms allow wheel 22 to simultaneously be released from a hub of mount 12 and captured by a hub of mount 14. The transfer process is arranged to occur only when the mounts 12 and 14 are joined so that there is no danger that wheel 22 could become detached from both mounts.

Once the wheel clamp mechanism of mount 14 has securely engaged wheel 22, the wheel spindles 4 and 6 can move apart as shown in Figure 3. Grinding can now be carried out by wheels 20 and 22, with no interference from wheel 24.

A process for transferring wheel 22 from one mount to another is illustrated in more detail by the partial cross-sectional perspective views shown in Figures 4a to 4c. These views correspond to the stages shown in Figures 1 to 3 respectively.

As can be seen in Figure 4a, initially, grinding wheels 20 and 22 are carried by the mount 12. Wheel 20 is held on mount 12 against an annular, transversely extending surface 30 by a clamping mechanism which is not shown in the drawings. This mechanism is releasable to allow wheel 20 to be removed and replaced as necessary (when wheel 22 is not present on mount 12). A clamping mechanism of the form described in UK patent application no. 1611715.2 (filed by the present applicants, and the contents of which are incorporated herein by reference) may be employed for example. Alternatively, a ring-shaped version of the clamping system disclosed in GB-A-2285846 may be used. Wheel 20 has a centrally located circular opening 32 which closely fits around a cylindrical hub portion 34 of mount 12.

Wheel 22 is securely fastened to mount 12 by a wheel clamp mechanism 40. This mechanism is operable to selectively release the wheel 22. Wheel 22 has a central opening 50, which has a smaller diameter than the opening 32 of wheel 20. The radially inwardly facing surface of wheel 22 which defines the opening 50 includes a circumferentially extending groove 52 for engagement by clamp mechanism 40. Groove 52 comprises two opposing sidewall faces 54 and 56. These faces converge towards each other in the radially outward direction.

Clamp mechanism 40 comprises an expandable collar which defines a raised lip or ridge 57 at its distal end. The lip extends circumferentially around the collar and projects radially outwardly from the collar. It includes a frusto-conical surface 59 which increases in diameter towards the outermost end of the clamp mechanism. This surface facilitates reliable and secure engagement of the collar with the groove 52 of the wheel 22. The surface 59 may define the same angle with the central axis of the clamp mechanism as the angle defined by the sidewall face 54 of the wheel with the central axis of the wheel.

Wheel 20 defines a recess 58 in one of its transversely extending sides, which receives wheel 22 when it is mounted on mount 12 along with wheel 20. In this configuration, wheel 22 does not extend axially away from the mount 12 any further than wheel 20 so that it does not interfere with grinding operations carried out by wheel 20.

Wheel 24 is securely fastened to mount 14. It engages an annular transversely extending surface 60 defined by a shoulder 62 of the mount 14. Wheel 24 is held on mount 14 by a clamping mechanism which is not shown in the drawings. This mechanism is releasable to allow wheel 24 to be removed and replaced as necessary (when wheel 22 is not present on mount 14). Mount 14 also includes a wheel clamp mechanism 64 similar for wheel 22 to clamp mechanism 40 of mount 12. Each of wheels 20, 22 and 24 may provide grinding surfaces having different profiles for use as required during grinding of the same workpiece. In the example illustrated in the drawings, wheel 20 has a cylindrical grinding surface 66, wheel 22 has a tapered grinding surface 68, and wheel 24 has a rounded grinding surface 70.

A subsequent stage in the transfer of wheel 22 from mount 12 to mount 14 is shown in Figure 4b. Mount 14 includes a clamp mechanism 64 which is identical to clamp mechanism 40 and extends towards it. It can be seen that wheel clamp mechanisms 40 and 64 have been brought into engagement with each other in Figure 4b and both are temporarily in engagement with the groove 52 of wheel 22. Wheel clamp mechanism 64 has moved from the radially contracted configuration shown in Figure 4a to a radially expanded configuration shown in Figure 4b in order to engage with sidewall face 56 of groove 52.

Wheel 22 is then released by the clamp mechanism 40, by moving it to the contracted configuration shown in Figure 4c. The wheel 22 is now fastened solely to the wheel clamp mechanism 64 of mount 14. The wheel spindles 4 and 6 can be moved axially apart as shown in Figure 4c, with wheel 22 now fastened to wheel mount 14.

Wheel 22 defines a recess 80 in its transversely extending surface which faces wheel 24. Wheels 22 and 24 are dimensioned such that when wheel 22 is fastened to mount 14, wheel 24 is received by the recess 80. Wheel 24 is radially inwardly spaced from the grinding surface 68 of wheel 22 and does not extend axially toward mount 14 beyond wheel 22 so that it does not interfere with grinding operations carried out by wheel 22.

The clamp mechanisms 40 and 64 of the example shown in Figure 4 comprise expanding collars which selectively engage with the groove 52 around the central opening 50 of wheel 22. Other configurations of these clamp mechanisms and/or wheel 22 may be used in other embodiments of this invention. For example, an arrangement of the form disclosed in GB-A-2208276 (the contents of which are incorporated herein by reference) may be employed. In this approach, a wheel is transferable from one spindle to another whilst both of the spindles are rotating. The wheel has anchoring portions which extend from opposite sides of the wheel that can be releasably clamped by the spindles. Alternatively, wheel clamping mechanisms of the form disclosed in UK patent application no. 161 1715.2 may be operated to engage with a central opening of a wheel or a portion projecting from a side of a wheel.

By way of illustration, Figure 5 shows a workpiece which could be machined using the three wheel profiles provided by the three grinding wheels shown in Figures 1 to 4 by way of example.

Workpiece 90 has four plain diameters (that is axially extending portions 92) having cylindrical surfaces, a circumferentially extending groove 94 and a tapered portion 96.

In Figures 6 to 8, workpiece 90 is continuously mounted on the machine bed 2 for rotation about a central longitudinal axis 98 by means of a headstock 100 and a footstock 102.

Initially the grinding wheels may be configured as shown in Figure 1. Wheel 20 may then be used to grind the cylindrical portions 92 as shown in Figure 6. In this configuration, wheel 24 may also be employed to grind the grooved portion 94 as shown in Figure 7.

Following the transfer of wheel 22 from mount 12 to mount 14 as described herein, the tapered portion 96 may then be ground by wheel 22 as shown in Figure 8. Wheel 20 is also available in this configuration to be used to carry out further grinding of cylindrical surfaces 92 if appropriate.