A two-piece stator disc and method of manufacture

Abstract

A method of manufacturing a two piece stator disc and a stator disc manufactured by the method. The method comprising: mounting a disc with a central aperture on a rotatable mounting means of a machin

Description

FIELD OF THE INVENTION The field of the invention relates to the manufacture of two piece stator discs and the discs manufactured by the method. BACKGROUND Stator discs such as those for a turbomolecular pump may be manufactured on a mill-turn machine, which is a machine that can perform both milling and turning operations on a workpiece. Milling involves rotating a cutting tool into the workpiece to remove material, while turning involves rotating the workpiece into a stationary cutting tool. Mill-turn machines can rotate both the cutting tool and the workpiece to shape the part. Owing to the rotational nature of this manufacturing method, it would be efficient to manufacture the stator disc as a single part, however, to mount it around a rotor it needs to be in two pieces. SUMMARY One aspect provides a method of manufacturing a two piece stator disc comprising: mounting a disc with a central aperture on a rotatable mounting means of a machine; using a cutting tool of the machine to form flow channels between an inner and outer ring of the disc: making at least one indent in one of the inner or outer ring with an angled cutting tool, the inner or outer ring being maintained intact; cutting through the stator disc with a cutting tool of the machine along a line such that the stator disc except at least a portion of the inner or outer ring receiving the at least one indent is divided into two pieces; wherein the at least one indent and cutting line are radially aligned; removing the disc from the machine; aligning the at least one indent with a cutter device; and cutting through the ring comprising the at least one indent with the cutter device to form the two piece stator disc. Forming a stator disc by rotatably mounting the disc on a machine with a cutting tool, allows the flow channels to be cut into the disc in an efficient manner. However, where a two piece stator disc is required then the cutting of the stator disc into two halves using the cutting tool of the machine may be more problematic. A solution to this has been provided by using an angled cutting tool of the machine to form at least one indent in one of the inner or outer rings and using a cutting tool of the machine to cut through the other of the inner or outer rings and much of the flow channels between the rings along a line that is radially aligned with the indent(s). In this way the ring receiving the indent(s) remains intact and substantially the rest of the stator disc is divided into two pieces. In this way the integrity of one of the rings is maintained, allowing it to be stably mounted on the machine, while a cutting tool of the machine is used to mark with an indent where that ring should be cut, when the processes of forming the channels and dividing the stator disc up to that ring have been completed. Radial alignment of the cut and the indent(s) are thus, simply and accurately provided by the machine and when the disc has been taken from the machine, the indent(s) can be used to align the disc with a separate cutting device, allowing the intact ring to be cut and thus, the stator disc as a whole to be divided in two. It should be noted that the steps performed on the machine of forming the flow channels, making the indent(s) and cutting through much of the stator disc may be performed in any order. The rotatable mounting means may comprise a clamping means for clamping one of the inner or outer circumference of the stator disc, the at least one indent being formed in the ring adjacent to the clamping means. The disc may be clamped in position on the machine via one of the rings, and provided that this ring remains intact that is in one piece the disc may be securely held. - 3- Although, a single indent in the inner ring may be sufficient to align the cutter device, in some embodiments there may be two indents in diametrically opposed sides of the inner or outer ring. This may allow easier alignment of the disc and more accurate cutting. In some embodiments, the step of making the at least one indent in the one of the inner or outer ring comprises making an indent with an angled cutting tool on both faces of the one of the inner or outer ring. Having indents on both faces and on both sides of the ring allows the cutting by the separate cutter device to be performed more simply and also makes for smoother edge surfaces of the cuts, these being formed by a cutting tool of the machine, and thereby inhibits the formation of burrs. In some embodiments, the rotatable mounting means comprises a clamp for clamping the outer circumference of the disc, the at least one indent being formed in the outer ring, and the cut being made through the inner ring and up to the outer ring. In some cases the cut may be made beyond the inner diameter of the outer ring, such that an inner portion of the outer ring is cut. The outer ring should remain intact that is in one piece such that it can be maintained stably mounted on the machine. In some embodiments, the rotatable mounting means comprises a spindle and the inner ring of the disc is mounted on the spindle, the at least one indent being formed in the inner ring, and the cut being made through the outer ring and though the flow channels towards the inner ring. In some cases the cut stops at the inner ring and in some cases it stops before the inner ring, the inner ring and a portion of a flow channel wall remaining intact. The portion of the flow channel may be less than 10% of its length. Although the stator disc may be mounted on and held securely by either the inner or the outer ring, where it is the inner ring that is used, the rotatable mounting means may be a spindle and the final step of cutting through the inner ring may be a simple step done by a cutter device with a blade of a length equal to or slightly greater than the length of the outer diameter of the inner ring. The disc may be mounted on the rotatable mounting means via the central aperture, the inner ring surrounding the central aperture. In some embodiments, the machine comprises a main spindle and a counter spindle, the step of making the indent on one face of the stator disc being performed when the disc is mounted on the main spindle and the step of making the indent on the other face being performed when the disc is mounted on the counter spindle. In some embodiments, the step of making the flow channels is performed when the disc is mounted on the main spindle and the step of cutting through the outer ring towards the inner ring being performed when the disk is mounted on the counter spindle. The machine may have a main spindle and a counter spindle and much of the cutting of the flow channels may be done while it is mounted on the main spindle and the indent may be cut into the inner ring at this time too. The finishing and the separating of the outer ring into two parts may then be done when the disc is transferred to the counter spindle. The inner ring is left intact during this process such that the stator disc can be securely held during the whole procedure. In some embodiments, the angled cutting tool comprises an engraver, an angled blade of the cutting comprising an angle of between 30 and 90 degrees, preferably between 55 and 65 degrees. ln some embodiments, the cutting tool for cutting through the stator disc along the line radially aligned with the at least one indent comprises a rotatable saw. In some embodiments, the cutter device comprises a press comprising a wedge-shaped cutter tool. A press may be used to cut through the ring that is maintained intact while the stator disc is on the machine and the cutter tool or blade may be aligned with the indent on the other ring. The indent is made using the machine and thus is correctly aligned with the cut through the rest of the stator disc. Where the ring remaining intact is the inner ring, the cutting device may have a blade with a length substantially equal to the outer diameter of the inner ring, that is within 10% of the length. In some embodiments, the machine comprises a lathe. In some embodiments, the machine comprises a mill-turn machine. Although, the stator disc may be for different types of pumps, in some embodiments the stator disc comprises a turbomolecular pump stator disc. A further aspect provides a two piece stator disc formed by a method according to one aspect. The stator disc formed by a method of one aspect will provide a stator disc where the contacting surfaces of the inner and outer rings of the two portions of the stator disc are surfaces where at least a central portion of one of the rings has been cut by a manual press cutting device and has not been milled and as such this portion of the surfaces is rougher than the contacting surfaces of the other ring that has been cut on a machine such as a lathe or mill-turn machine which provides smoother surfaces. Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims. Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which: Figure 1 shows one face of a stator disc mounted on a main spindle of a mill-turn machine; Figure 2 shows the opposing face of the stator disc mounted on a counter spindle of the mill-turn machine; Figure 3 shows a cutting device; Figure 4 shows the cut surfaces of the inner ring of a two piece stator disc according to an embodiment; and Figure 5 schematically shows a flow chart illustrating steps in a method according to an embodiment. DESCRIPTION OF THE EMBODIMENTS Before discussing the embodiments in any more detail, first an overview will be provided. When manufacturing a stator disc, it is advantageous to produce the two halves from an initially complete, circular disc. In particular, the flow channels can be produced efficiently on mill-turn machines. In particular, the flow channels can be produced using a disc milling cutting tool, which has advantages in terms of stability and manufacturing time. Once the complete disc has been pre-turned and the flow channels have been milled, the disc must be separated into two equally sized half discs in a final work step. This cannot be done with the conventional clamping devices on the same machine on which the previous production steps were carried out. In an earlier process, the disc had to be reclamped and aligned on a second machine. Embodiments allow this step to be omitted by only cutting through one of the inner or outer rings of the stator disc on the first machine and making a small mark or indentation on the other ring where the final separation is to take place. By retaining one of the inner or outer rings intact, the disc can remain mounted on the mill-turn machine. The final separation is then carried out on an external press in a quick work process, where the indent is used to align the inner ring in the press and a small, wedge-shaped tool then cuts through the intact ring. The indent may be formed with an engraving tool, with a break edge of between 30° and 90° preferably between 55° and 65° and may have a depth of between 1 and 1.5 mm. This may be less than 10% of the thickness of the stator disc. Figure 1 shows a stator disc mounted on a main spindle of a mill-turn machine. Stator disc 10 has had flow channels 15 cut into the disc by the mill-turn machine between an outer ring 12 and an inner ring 16 of the stator disc. As the stator disc 10 is mounted on a spindle it is the inner ring that should remain intact while it is on the machine and a cutting tool with an angled blade is used to make indents 17 and 18 on the inner ring. The indents are at diametrically opposed sides of the inner ring and are indicative of where a cut should be made to separate the stator disc into two halves once it has been removed from the machine. Figure 2 shows the opposite face of the stator disc 10 where the stator disc has been moved from the main spindle onto a counter spindle 27 where it is held by chucks 29. A rotating saw 25 of the mill-turn machine is used to cut through the outer ring 12 and the flow channel walls along a line radially aligned with the indents from the outer diameter of the stator disc towards the inner ring, such that the stator disc except for the inner ring and in some cases a portion of a flow channel wall are separated into two halves. A cutting tool with an angled blade is used to make further indents on diametrically opposed sides of the inner ring on this face of the stator disc, which indents are aligned with the indents on the other face. The stator disc 10 is then removed from the counter spindle of the mill-turn machine and is mounted on a press shown in Figure 3. The indents are aligned with the blades of the wedge-shaped cutter device 33 of the press and this is used to cut through the inner ring of the stator disc and through any portion of the flow channel walls extending from the inner ring that were not cut through on the machine. The cutter blade 33 has a width similar in size to the length of the outer diameter of the inner ring 16 of the stator disc 10. The stator disc 10 is thus divided into two halves. Figure 4 shows the surfaces 19 of the inner ring at the divide of the two halves of the stator disc. As can be seen portions that are cut by the cutter device of the press, that is those towards the centre of the stator disc are relatively rough. The surfaces of the outer rings (not shown) that are cut by the mill-turn machine will be smoother than this. Furthermore, in this case the outer surfaces of the inner ring divide that were formed as indents on the mill-turn machine are substantially smoother than the portions towards the centre that are cut by the cutter device. The cut through the flow channel walls made on the mill-turn machine and providing smooth surfaces can be seen to extend almost to the inner ring, with a small rougher portion 13 adjacent to the inner ring, which portion was not cut by the mill-turn machine but was cut by the press cutter. Thus, a stator disc that has been manufactured in this way may be identified by the difference in texture between the surfaces at the junction between the two halves of the stator disc, smooth surfaces being provided where the cut is made on the mill-turn machine and rougher surfaces being provided where the cut is made by the press. Figure 5 shows steps in a method for manufacturing a stator disc according to an embodiment. At step S10 a disc with a central aperture is mounted on a spindle of a mill-turn machine. At S20 a cutting tool of the mill-turn machine is used to form flow channels through the disc, the flow channels extending between an inner and outer ring of the disc. At step S30 an indent is made in the inner ring with the cutting tool. This may be one indent on one side of the inner ring or it may be two indents on diametrically opposing sides of the inner ring. At step S40 the disc is mounted on a counter spindle of the mill-turn machine such that the other face of the stator disc faces the cutting tools. At step S50 a cutting tool of the mill-turn machine cuts through the outer ring and flow channels along a line that is radially aligned with the indent or the indents to divide a portion of the stator disc up to or close to the inner ring into two pieces. In some cases further indents may be made in the inner ring of the disc, such that there are indents on both faces of the stator disc. It should be noted that the steps S20 to S50 of forming the flow channels, making the indents and cutting through a portion of the stator disc can be performed in any order. At step S60 the disc is removed from the machine and at step S70 it is placed within a press and a cutter device is used to cut through the inner ring at the point marked by the indents to form a two-piece stator disc. Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents. REFERENCE SIGNS Stator disc outer ring rough surface of flow channel wall flow channel inner ring 18 indents cut surface of inner ring main spindle rotatable saw counter spindle chuck cutter device 15

Claims

1. A method of manufacturing a two piece stator disc comprising: mounting a disc with a central aperture on a rotatable mounting means of a machine;using a cutting tool of the machine to form flow channels between an inner and outer ring of the disc:making at least one indent in one of the inner or outer ring with an angled cutting tool, the inner or outer ring being maintained intact;cutting through the stator disc with a cutting tool of the machine along a line such that much of the stator disc, except for at least a portion of the inner or outer ring receiving the at least one indent, is divided into two pieces;wherein the at least one indent and cutting line are radially aligned;removing the disc from the machine;aligning the at least one indent with a cutter device; andcutting through the ring comprising the at least one indent with the cutter device to form the two piece stator disc.

2. A method according to claim 1, wherein the rotatable mounting means comprises a clamping means for clamping one of the inner or outer circumference of the stator disc, the at least one indent being formed in the ring adjacent to the clamping means.

3. A method according to any preceding claim, wherein the step of making the at least one indent in the one of the inner or outer ring comprises making two radially aligned indents on diametrically opposing sides of the ring.

4. A method according to any preceding claim, wherein the step of making the at least one indent in the one of the inner or outer ring comprises making an indent with an angled cutting tool on both faces of the one of the inner or outer ring.

5. A method according to any preceding claim, wherein the rotatable mounting means comprises a clamp for clamping the outer circumference of the disc, the at least one indent being formed in the outer ring, and the cut being made through the inner ring and up to the outer ring.

6. A method according to any one of claims 1 to 4, wherein the rotatable mounting means comprises a spindle and the inner ring of the disc is mounted on the spindle, the at least one indent being formed in the inner ring, and the cut being made through the outer ring and though the flow channels towards the inner ring.

7. A method according to claim 6 when dependent on claim 4, wherein the machine comprises a main spindle and a counter spindle, the step of making the indent on one face of the stator disc being performed when the disc is mounted on the main spindle and the step of making the indent on the other face being performed when the disc is mounted on the counter spindle.

8. A method according to any preceding claim, wherein the angled cutting tool, comprises an engraver, an angled blade of the cutting tool comprising an angle of between 30 and 90 degrees, preferably between 55 and 65 degrees.

9. A method according to any preceding claim, wherein the cutting tool for cutting through the stator disc along the line radially aligned with the at least one indent comprises a rotatable saw.

10. A method according to any preceding claim, wherein the cutter device comprises a press comprising a wedge-shaped cutter tool.

11. A method according to any preceding claim, wherein the machine comprises a lathe.

12. A method according to any preceding claim, wherein the machine comprises a mill-turn machine.

13. A method according to any preceding claim, wherein the stator disc5 comprises a turbomolecular pump stator disc.

14. A two-piece stator disc formed by a method according to any preceding claim.io

Images