WO1997047432A1

WO1997047432A1 - Lapping apparatus

Info

Publication number: WO1997047432A1
Application number: PCT/AU1997/000372
Authority: WO
Inventors: Christopher Richard Mobbs; Valerie Joy Mobbs
Original assignee: Christopher Mobbs & Associates Pty. Ltd.
Priority date: 1996-06-13
Filing date: 1997-06-13
Publication date: 1997-12-18
Also published as: AUPO041896A0

Abstract

A lapping machine comprises two concentric and coplanar annular lapping plates (1, 9) disposed adjacent to one another to present a flat, planar lapping surface and mounted for rotation about the common central axis of the plates. A drive rotates the lapping plates (1, 9) in opposite directions about said common axis and at different angular velocities. Conditioning rings (5) are supported on the lapping surface and a ring plate (4) holds the conditioning rings against rotation about the common axis of the plates. As the lapping plates (1, 9) rotate, they move relatively to the conditioning rings (5) and each conditioning ring (5) rotates about its own central axis.

Description

LAPPING APPARATUS

Field of Invention

The invention relates to lapping apparatus used for cutting and/or polishing purposes to provide precision surface finishing. In particular, the invention is concerned with a lapping machine having a flat lapping plate which may be used to produce optically flat and polished surfaces. Flat lapping/polishing machines have a wide range of applications in industry and research for producing components having one or more faces lapped/polished to a high degree of flatness and surface finish.

Description of the Prior Art Known lapping machines of this type may comprise a rotatable flat lapping plate in the form of a wheel or disc. The lapping plate is rotatable about a substantially vertical axis with the upper lapping surface of the lapping plate disposed in a substantially horizontal plane The detailed design of lapping plates may be tailored to suit the components being lapped. Generally lapping plates are made from a variety of materials such as metals or ceramics. The lapping surface may be smooth or grooved in a variety of patterns. With the components to be lapped positioned on the lapping surface, an abrasive water based or oil based slurry is applied to the lapping surface as the lapping plate is rotated. A variety of abrasive particles may be used in the slurry and coarser abrasive particles are used for cutting purposes whereas finer particles or powders are used for polishing.

To produce the desired flatness in the components to be lapped, the lapping plates must be flat to the required tolerance and must in use retain this degree of flatness. To achieve the required plate flatness, cast iron conditioning rings are generally provided. These conditioning rings are supported on the upper surface of the lapping plate so that, in use, there is relative movement between the lapping surface and the conditioning rings. While the lapping plate rotates, each conditioning ring is free to rotate about its own axis but is held in a fixed position with respect to the vertical axis of the lapping plate by rollers carried by a yoke mounted on a stationary part of the lapping machine. The yoke is provided with means for lateral adjustment with respect to the lapping plate. A conditioning ring may be moved laterally with respect to the lapping plate by manually adjusting the position of its corresponding yoke.

The lapping plate must be constantly monitored at regular intervals and any deviation from the required degree of flatness necessitates stopping the machine and manually adjusting the position of the conditioning rings. For example, the position of the conditioning rings may be adjusted inwardly with respect to the lapping plate to correct a convex condition or outwardly to correct a concave condition. The amount of adjustment is determined by trial and error. This procedure can be time-consuming and may result in lost production and/or reject production.

For efficient lapping, each conditioning ring must rotate about its own axis with respect to the lapping plate. This generally occurs due to the greater surface speed on the outer extremities of the lapping plate causing drive at different speeds being applied to different parts of a conditioning ring as the lapping plate rotates. However, it has been found that rotation of the conditioning rings is not a consistent or predictable rotation. Sometimes there is a variation in the speed of rotation and sometimes the conditioning rings do not rotate at all, depending on the amount of grit/oil mixture applied to the lapping plate. This unpredictable rotation of the conditioning rings is particularly a problem when using composite lapping plate materials and diamond abrasive, as the lapping plate is run drier than when there is an abundance of oil/abrasive mixture on a cast iron lapping plate. This inconsistent and unpredictable rotation of the conditioning rings causes uneven wear of the lapping plate.

Description of the Invention

It is an object of the invention to improve the flatness control function of the conditioning rings. It is another object of the invention to facilitate rotation of the conditioning rings on the lapping plate.

It is a further object of the invention to retain automatically the flatness of a lapping plate.

In accordance with the invention, a lapping machine comprises two concentric and coplanar annular lapping plates disposed adjacent to one another to present a flat, planar lapping surface and mounted for rotation about the common central axis of the plates, drive means to rotate the lapping plates in opposite directions about said common axis, a plurality of conditioning rings supported on the lapping surface and means to hold the conditioning rings against rotation about the common axis of the plates such that, as the lapping plates rotate, the lapping plates move relatively to the conditioning rings and each conditioning ring rotates about its own central axis.

Preferably, the drive means is effective to rotate the lapping plates not only in opposite directions about said common axis but also at different angular velocities.

Brief Description of the Drawings The invention will be described in relation to the accompanying drawings which illustrate two embodiments. In one embodiment, the conditioning rings are concentrically mounted with respect to the common axis of the lapping plates. In the other embodiment, the conditioning rings are eccentrically mounted with respect to the common axis thereby imparting to the conditioning rings an additional lateral movement with respect to the lapping plates.

In the drawings -

Fig. 1 is a vertical sectional view of a lapping machine having two concentric and coplanar annular lapping plates according to one embodiment of the invention; Fig. 2 is a plan view of a lapping machine which incorporates a single flat lapping plate according to the known prior art;

Fig. 3 is a plan view of a lapping machine showing an eccentric version of the lapping machine illustrated in Fig. 1 ;

Fig. 4 is an exploded view of parts of the machine shown in Fig. 1 but including one component from both the concentric version and the eccentric version of the machine;

Fig. 5 is an enlarged perspective view of the component from the eccentric version of the machine;

Fig. 6 is an enlarged perspective view of the component from the concentric version of the machine;

Fig. 7 is an exploded view showing the conditioning rings and parts associated therewith; and

Fig. 8 is a perspective view showing parts illustrated in Fig. 7 in an assembled condition.

Description of the Embodiments Referring to the drawings, Fig. 2 is a plan view of a known type of lapping machine and illustrates a machine comprising a single, circular, flat lapping plate 19. In use, the upper lapping surface of lapping plate 19 is disposed in a substantially horizontal plane and lapping plate 19 is rotated in a counterclockwise direction about a vertical axis by known means (not shown). Supported on the lapping surface of lapping plate 19 are three conditioning rings 5. To retain the conditioning rings 5 in a fixed position with respect to the vertical axis of the lapping plate while lapping plate 19 rotates, a yoke 20, fitted with a pair of ring rollers 6, is associated with each conditioning ring 5. The yokes 20 are mounted on the body of the lapping machine and may be adjusted laterally with respect to lapping plate 19 in the manner described earlier. The workpieces to be lapped are retained in conditioning rings 5.

A lapping machine having flat lapping surfaces according to one embodiment of the invention is illustrated in Figs. 1. This lapping machine comprises two concentric and coplanar annular plates 1 and 9 disposed adjacent to one another to present a flat, planar, horizontal upper lapping surface. Plates 1 and 9 are mounted for rotation about the common central vertical axis of lapping plates 1 and 9 in opposite directions and at different angular velocities.

The inner lapping plate 1 is fixed to a vertically disposed main drive shaft 2 by a bolt 3 which has a threaded fastening section at its lower end fixed to main drive shaft 2 and an extended shaft at its upper end. An enlarged view of bolt 3 is shown in Fig. 6. The inner plate 1 and the extended bolt 3 rotate on rotation of drive shaft 2 and in the same direction. As illustrated in Figs.1 and 6, the extended shaft and the threaded fastening section of bolt 3 are concentric with drive shaft 2. When the extended shaft of bolt 3 rotates, it rides in bearings 8 mounted within a bush 7 which at its lower end is fixed to a ring plate 4, which is held against rotation about the common central axis of plates 1 and 9 (i.e. the longitudinal axis of drive shaft 2).

The ring plate 4 extends beyond the circumference of plate 9 and is suspended at the required height above the lapping surfaces from bush 7. Bush 7 has facility for vertical adjustment (by altering the position of the threaded bolt in the cylinder of the bush) which may be used to alter the height of ring plate 4 above the lapping surfaces and to compensate for wear of the lapping plates 1 and 9. Supported on the lapping surfaces are a plurality of (in this case three) conditioning rings 5 each of which is held in position within the confines of a circular aperture in ring plate 4. Preferably, the outer diameter of conditioning rings 5 equals or exceeds the radial distance from the outer circumference of plate 9 to the inner bore of plate 1 so that the conditioning rings cover the full radial extent of plates 1 and 9. The complete overlap of both plates 1 and 9 by the conditioning rings 5 assists evenness of wear over the entire lapping surfaces of plates 1 and 9. A plurality of rollers 6 mounted at spaced locations on ring plate 4 adjacent each aperture assist in holding the conditioning rings 5 in position and facilitate rotation of each conditioning ring 5 about its central axis within an aperture in ring plate 4. Detailed views of the ring plate assembly are shown in Figs. 7 and 8.

As illustrated in Figs 3, 4 and 5, the extended shaft of bolt 3 (and thus bush 7) may be eccentric to the threaded fastening section thereof and to drive shaft 2. In this case, as main drive shaft 2 rotates, a lateral movement is imparted to ring plate 4 and conditioning rings 5. A member 21 mounted on a stationary part of the lapping machine has a fixed pin adapted to ride in a slot in the edge of ring plate 4 to prevent rotation of ring plate 4 while allowing lateral movement of ring plate 4 caused by the eccentric disposition of bush 7. A similar adjunct is provided in the concentric version of the machine. In this case the pin may be fixed both to member 21 and ring plate 4. In the eccentric version of the machine, the outer diameter of the conditioning rings exceeds the radial distance from the outer circumference of plate 9 to the inner bore of plate 1 so that the conditioning rings 5 always extend over the full radial extent of plates 1 and 9 in all positions of ring plate 4.

The outer lapping plate 9 is fixedly mounted on a spoked wheel 10 which rotates freely around main drive shaft 2 by means of tapered bearings 1 1 mounted in hub 12 of spoked wheel 10. The coplanar relationship of the lapping surfaces of plates 1 and 9 is achieved by means of bush 13 which is fixed to the main drive shaft 2. Hub assembly 12 is fastened against bush 13 by means of locknut 14.

Rotation of a vertical secondary drive shaft 15 in the opposite direction to main drive shaft 2 is achieved by means of two intermeshing gears 16, each of which is fixed to one of drive shafts 2 and 15, respectively. Sprockets 17 are fixed to secondary drive shaft 15 and spoked wheel 10 and a chain sprocket drive transmits rotation of secondary drive 15 to spoke wheel 10. Rotation of secondary drive shaft 15 and spoked wheel 10 is in the same direction but in the opposite direction to that of main shaft 2. Varying relative angular velocities of lapping plates 1 and 9 can be achieved by varying the sprocket ratios.

In use, the angular velocities of lapping plates 1 and 9 are adjusted so that they transmit drive to the inner and outer parts of a conditioning ring 5 at approximately the same velocity and in the direction of rotation of each conditioning ring 5 about its central axis. This ensures that conditioning rings 5 rotate continuously in use. Because lapping plates 1 and 9 move in opposite directions and each imparts a similar drive to conditioning rings 5, there is a more effective rotation of conditioning rings 5 and they are not likely to stall. More efficient cutting is obtained as portions of conditioning rings 5 move from one lapping plate to the other and the direction of cutting in that area reverses.

A waste tray 18, disposed underneath lapping plates 1 and 9, extends beyond the outer circumference of plate 9 to catch the waste products of the lapping process(i.e. spent oil (water)/ grit mixture). The waste is transferred to a tank via a tube eliminating any possibility of contamination of any of the working parts of the machine.

In presently known lapping/polishing machines, it is necessary to stop the machine and to move the conditioning rings manually in or out laterally to control lapping plate flatness. In the present invention, it is possible to leave the conditioning^' rings in a fixed position (other than the lateral oscillation in the eccentric version) and vary the speed ratio of the inner and outer lapping plates to hold optimum flatness. This eliminates any requirement for the operator to monitor plate flatness and make trial and error adjustments. Any deviation in flatness in either or both lapping plates 1 and 9 will be corrected automatically by one plate counteracting the other. Further, the lapping plates will hold their flatness longer. The efficiency of the lapping/polishing process is markedly increased by the frequent change in cutting directions. In a modification, means may be provided to adjust the position of conditioning rings 5 within the confines of the apertures in ring plate 4. This would enhance the flatness holding capability of the machine.

Claims

1. A lapping machine comprising two concentric and coplanar annular lapping plates disposed adjacent to one another to present a flat, planar lapping surface and mounted for rotation about the common central axis of the plates, drive means to rotate the lapping plates in opposite directions about said common axis, a plurality of conditioning rings supported on the lapping surface and means to hold the conditioning rings against rotation about the common axis of the plates such that, as the lapping plates rotate, the lapping plates move relatively to the conditioning rings and each conditioning ring rotates about its own central axis.

2. A lapping machine as claimed in Claim 1, wherein the drive means is effective to rotate the lapping plates not only in opposite directions about said common axis but also at different angular velocities.

3. A lapping machine as claimed in Claim 2, wherein the means to hold the conditioning rings against rotation about the common axis of the plates comprises a ring plate suspended above the lapping surface and held against rotation about said common axis, a plurality of apertures in said ring plate, each conditioning ring positioned within the confines of an aperture.

4. A lapping machine as claimed in Claim 3, wherein a plurality of rollers are mounted at spaced locations on said ring plate adjacent each aperture to assist in holding the conditioning rings in position and to facilitate rotation of each conditioning ring about its central axis.

5. A lapping machine as claimed in Claim 3, wherein means are provided to adjust the height of the ring plate above the lapping surface.

6. A lapping machine as claimed in Claim 3, wherein said ring plate is mounted concentrically with respect to said common axis and is fixed to a stationary part of the machine.

7. A lapping machine as claimed in Claim 3, wherein said ring plate is mounted eccentrically with respect to said common axis and is associated with a stationary part of the machine so that, on rotation of the lapping plates, the ring plate and the conditioning rings move laterally with respect to the lapping surface.