Abstract
In some embodiments, a method is disclosed for manufacturing an undercut stator from a unitary cylindrical workpiece using broaching techniques. In other embodiments, methods are disclosed for manufacturing undercut and non-undercut stators using friction welding techniques to conjoin threaded end sections to stator sections having helical pathways formed therein.
Claims
1. A method for manufacturing one end of an undercut stator, the method comprising the steps of: (a) providing a cylindrical tube as a single workpiece, the tube having a tube length and a cylindrical internal surface; (b) designating a first end connection portion of the tube length at a first end of the tube, and designating a stator portion of the tube length wherein the stator portion immediately neighbors the first end connection portion; (c) forming a plurality of helical pathways on the internal surface of the stator portion, each helical pathway having a common major helical diameter and a common minor helical diameter, wherein step (c) includes the substep of: (c1) forming at least one of the helical pathways at least in part by broaching; and (d) forming threads on the internal surface of the first end connection portion such that the threads provide an internal minimum thread diameter, wherein the major helical diameter is selected to be greater than the internal minimum thread diameter.
2. The method of claim 1, further comprising, after step (c), the step of deploying a layer of elastomer on the helical pathways.
3. The method of claim 1, in which substep (c 1) further includes forming at least one of the helical pathways (1) initially by electrochemical machining (ECM), and then (2) by broaching to finish.
4. The method of claim 1, in which the broaching in substep (c 1) is controlled at least in part by computerized numeric control (CNC).
5. A method for manufacturing one end of an undercut stator, the method comprising the steps of: (a) providing an end tube with a cylindrical end internal surface and an end tube nominal diameter; (b) providing a stator tube with a cylindrical stator internal surface; (c) forming a plurality of helical pathways on the stator internal surface, each helical pathway having a common major helical diameter and a common minor helical diameter; (d) designating a connecting end of the end tube and a connecting end of the stator tube, wherein the connecting ends of the end tube and the stator tube are to be conjoined; (e) preparing the connecting ends of the end tube and the stator tube for friction welding together; (f) friction welding the connecting ends of the end tube and the stator tube together; and (g) forming threads on the end internal surface such that the threads provide an internal minimum thread diameter, wherein the major helical diameter is selected to be greater than the internal minimum thread diameter.
6. The method of claim 5, further comprising, after step (c), the step of deploying a layer of elastomer on the helical pathways.
7. The method of claim 5, in which step (e) includes machining cooperating flat faces onto the connecting ends of the end tube and the stator tube.
8. The method of claim 5, in which step (f) is accomplished at least in part by a process selected from the group consisting of: (1) inertia welding; and (2) direct drive welding.
9. The method of claim 5, in which step (c) is accomplished at least in part by a process selected from the group consisting of: (1) electrochemical machining (ECM); (2) roll forming; and (3) broaching.
10. The method of claim 5, in which step (I) also includes machining a stress-relieving geometry into a transition between the stator internal surface and the end internal surface, the transition formed when the end tube is friction welded to the stator tube.
11. The method of claim 5, in which the end tube is made from a material having a higher yield strength than the material from which the stator tube is made.
12. The method of claim 5, in which a welded connection is formed between the connecting ends of the end tube and the stator tube when the end tube is friction welded to the stator tube in step (f), and in which the welded connection is located at a position selected from the group consisting of: (1) minimum transverse cross-sectional area along the helical pathways formed in the stator tube; (2) maximum transverse cross-sectional area along the helical pathways formed in the stator tube; and (3) maximum transverse cross-sectional area of the end tube.
13. The method of claim 5, in which a welded connection is formed between the connecting ends of the end tube and the stator tube when the end tube is friction welded to the stator tube in step (f), and in which: (1) the welded connection is located at a position along the helical pathways formed in the stator tube; and (2) portions of the welded connection are removed after step (f) in order to provide a smooth transition between helical pathways and the end internal surface.
14. The method of claim 5, in which step (c) is accomplished at least in part by broaching, wherein said broaching includes forming a relief bore in the stator, the relief bore having a relief bore diameter, and in which further: (1) a welded connection is formed between the connecting ends of the end tube and the stator tube when the end tube is friction welded to the stator tube in step (f); and (2) the welded connection is located in the relief bore.
15. The method of claim 14, in which step (e) includes forming a transition in the end internal surface at the connecting end of the end tube, wherein the transition enlarges the end tube nominal internal diameter to a diameter substantially equal to the relief bore diameter.
16. A method for manufacturing one end of a stator, the method comprising the steps of: (a) providing an end tube with a cylindrical end internal surface; (b) providing a stator tube with a cylindrical stator internal surface; (c) forming a plurality of helical pathways on the stator internal surface, each helical pathway having a common major helical diameter and a common minor helical diameter; (d) designating a connecting end of the end tube and a connecting end of the stator tube, wherein the connecting ends of the end tube and the stator tube are to be conjoined; (e) preparing the connecting ends of the end tube and the stator tube for friction welding together; and (f) friction welding the connecting ends of the end tube and the stator tube together.
17. The method of claim 16, further comprising, after step (c), the step of deploying a layer of elastomer on the helical pathways.
18. The method of claim 16, in which the end tube is made from a material having a higher yield strength than the material from which the stator tube is made.
19. The method of claim 16, in which a welded connection is formed between the connecting ends of the end tube and the stator tube when the end tube is friction welded to the stator tube in step (f), and in which the welded connection is located at a position selected from the group consisting of: (1) minimum transverse cross-sectional area along the helical pathways formed in the stator tube; (2) maximum transverse cross-sectional area along the helical pathways formed in the stator tube; and (3) maximum transverse cross-sectional area of the end tube.
20. The method of claim 16, in which a welded connection is formed between the connecting ends of the end tube and the stator tube when the end tube is friction welded to the stator tube in step (f), and in which: (1) the welded connection is located at a position along the helical pathways formed in the stator tube; and (2) portions of the welded connection are removed after step (f) in order to provide a smooth transition between helical pathways and the end internal surface.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] For a more complete understanding of the embodiments described in this disclosure, and their advantages, reference is made to the following detailed description taken in conjunction with the accompanying drawings, in which:
[0031] FIGS. 1A, 1B and 1C are flow charts describing exemplary stator manufacturing techniques consistent with this disclosure, in which FIG. 1A depicts manufacturing an integral (i.e., single-piece) stator tube/end connection assembly with broached undercut internal helical pathways, FIG. 1B depicts manufacturing a stator tube with internal helical pathways to which end connections are friction welded, and FIG. 1C depicts replacing damaged end connections on a stator tube via friction welding new end connections thereon;
[0032] FIGS. 2A and 2B illustrate stages in the exemplary manufacturing technique also described with reference to FIG. 1A;
[0033] FIGS. 3 through 7 illustrate different embodiments of stators with friction welded end connections consistent with manufacturing embodiments exemplified by FIGS. 1B and 1C, wherein each of FIGS. 3 through 7 depict locating the friction weld at varying locations with respect to helical pathways formed on the stator tube; and
[0034] FIG. 8 is an enlargement of details on FIG. 7, as shown on FIG. 7.
DETAILED DESCRIPTION
[0035] FIGS. 1A, 1B and 1C are flow charts depicting, in summary diagrammatic form, currently preferred embodiments of exemplary manufacturing techniques consistent with this disclosure. FIG. 1A should be viewed in conjunction with FIGS. 2A and 2B and associated text below. FIG. 1A describes an embodiment where an undercut stator is manufactured using broaching techniques in a unitary construction, i.e. where the helical pathways and end connections are formed integrally by broaching a single or unitary tubular workpiece. FIGS. 2A and 2B illustrate the same broached stator 200 of unitary construction that is being manufactured by embodiments exemplified by FIG. 1A, but at different stages of manufacture. FIG. 2A illustrates broached stator 200 after box 102 on FIG. 1A. FIG. 2B illustrates broached stator 200 after (or during) box 103 on FIG. 1A. Features and aspects of broached stator 200 that are illustrated on both FIGS. 2A and 2B have the same part number.
[0036] FIGS. 1B and 1C should be viewed in conjunction with FIGS. 3 through 8 and associated text below. FIG. 1B describes embodiments where a stator (undercut or non-undercut) is manufactured preferably using broaching techniques to form helical pathways inside a tube, and where the end connections are welded onto the ends of the stator tube using high strength welding techniques. FIG. 1C describes embodiments where an existing stator (undercut or non-undercut) with a damaged end connection may be repaired by removing the damaged end connection and welding a new end connection onto the stator using high strength welding techniques.
[0037] FIGS. 3 through 8 depict different embodiments of welded end connections formed by the methods illustrated in FIG. 1B or 1C. The welded end connections illustrated in FIGS. 2 through 8 are indifferent to whether formed according to FIG. 1A or FIG. 1B. A primary difference among FIGS. 3 through 7 is the location of the welded end connection with respect to other features of the stator. FIG. 8 is an enlargement of details of FIG. 7, as shown on FIG. 7.
[0038] It should be emphasized that embodiments exemplified by FIG. 1A (in conjunction with FIGS. 2A and 2B and associated text below) are confined to undercut stators of unitary one-piece construction made primarily by broaching techniques. By contrast, embodiments exemplified by FIGS. 1B and 1C (in conjunction with FIGS. 3 through 8 and associated text below) include stators with high strength welded end connections that are indifferent to whether the final stator product is undercut or non-undercut. Likewise, FIGS. 1B and 1C (in conjunction with FIGS. 3 through 8 and associated text below) include stators with high strength welded end connections that are indifferent to whether the final stator product's internal helical pathways are formed by broaching, or by some other manufacturing technique. Currently preferred embodiments exemplified by FIGS. 1B and 1C are undercut stators whose helical pathways are formed by broaching, in view of (1) the improved power density provided by undercut stators, and (2) the improved machinability provided by broaching, plus other advantages described elsewhere in this disclosure. However, it will be appreciated that embodiments exemplified by FIGS. 1B and 1C are not limited to undercut stators, and are not limited to stators whose internal helical pathways are formed by broaching. Both undercut and non-undercut stators, regardless of how their helical pathways are/were formed, will benefit from the disclosed advantages of selecting end connections made of material designed for specific end connection service, and then attaching same to a stator tube made of a different material via a high strength welded connection.
[0039] Referring first to FIG. 1A, method 100 begins, in preferred embodiments, with providing a blank stator tube with a precise hone (box 101). The precise hone aspect of the stator tube refers to a preference for a high-quality smooth internal surface of known internal diameter on the native tubular workpiece immediately prior to counter bore and broaching operations.
[0040] The tubular workpiece begins with a conventional wall thickness suitable for threading to form a desired end connection after broaching. The first phase of the method is to form a counter bore inside the workpiece (box 102 on FIG. 1A). The counter bore is formed at a large enough longitudinal distance inside the tube to allow the portion of the tube nearest the end to be long enough to be formed into the desired end connection. The counter bore may be formed in the tubular workpiece by machining, broaching or other suitable conventional techniques. The expandable/extensible broaching head and cutting tool assembly may then be inserted into the relief counter bore with sufficient room available to begin its broaching work. Refer also to FIG. 2A, in which broached stator 200 comprises counter bore 215 separating end connection portion 210 and helical pathway portion 205. Counter bore 215 has created relief bore diameter 217 that is larger than original tube bore diameter 212.
[0041] Refer now to box 103 on FIG. 1A. A specialized expandable/extensible broaching head and cutting tool assembly is then introduced into the counter bore. The counter bore allows the broaching tool head assembly sufficient space to be expanded to form the helical pathways with a major helical diameter that is greater than the minimum threaded end diameter. Helical pathway cutting is advantageously controlled by computerized numerical control (CNC).
[0042] Refer also to FIG. 2B, depicting broached stator 200 after (or during) the broaching of helical pathways 220 into helical pathway portion 205. Helical pathways are formed with a major helical diameter 222 and a minor helical pathway 224. FIG. 2B illustrates undercut 230 formed by the difference between major helical diameter 222 and original tube bore diameter 212. It will be appreciated that a minimum thread diameter will be identified when eventually the desired thread form is cut into tube bore diameter 212 in end connection portion 210 (thread form not illustrated on FIGS. 2A and 2B, but referred to in box 105 on FIG. 1A). The desired thread form may be constant diameter or varying diameter, per user selection. However a minimum thread diameter will result, regardless of the shape of the thread form. At that point, undercut 230 on FIG. 2B will be the difference between major helical diameter 222 and the minimum thread diameter formed in tube bore diameter 212 in end connection portion 210.
[0043] Referring to box 103 on FIG. 1A in more detail, the height of the cutting tool assembly itself during broaching is controlled on a wedge support system built into the broaching tool head assembly. A wedge is pushed in or out to bring the cutter to a new cutting diameter upon each successive stroke. Consistent with conventional broaching techniques, the helical pathways are formed by making successive incremental cuts into the inside diameter of the tubular workpiece according to a programmed cut profile. The broaching head (and associated cutting tool) maintains its radial position by being stabilized on ribbons of workpiece material left uncut on the internal diameter of the workpiece. In currently preferred embodiments, a fixed cylindrical stabilizing pad, or centering chuck, on which the broaching cutter head assembly is mounted, is kept in sliding contact with the helical ribbons on the workpiece's internal diameter throughout the cutting process. In the final steps of shaping the helical profile, the helical ribbons may be rounded off by manufacturing techniques such as, for example, single point broaching, form tool broaching, shot blasting or shot peening.
[0044] Referring now to FIG. 2B, in some embodiments the relief bore diameter 217 on FIG. 2B may be the same as the intended final maximum helical diameter 222, and in other embodiments it may be slightly larger. Advantageously, counter bore 215 also provides a chamfer 216 into the work area of the broaching cutter, allowing the broaching cutter to load gradually upon entry into the workpiece material. In some embodiments, chamfer 216 may be 45 degrees.
[0045] Referring again to FIG. 1A, once broaching operations are complete, the stator product is completed by deploying the resilient elastomer liner on the broached helical pathways according to conventional techniques (box 104). The user-desired thread form is then cut into the end connection (box 105). Refer to the disclosure immediately above describing undercut 230 on FIG. 2B.
[0046] Further alternative embodiments of the disclosed broaching methods described above may use also techniques such as ECM to partially form the helical pathways in the tubular workpiece. The helical pathways may then be fully formed and finished using the broaching techniques described above.
[0047] FIGS. 1B and 1C depict alternative embodiments from the undercut stator manufacturing method described above with reference to FIG. 1A. In FIG. 1B, a stator (undercut or non-undercut) is manufactured by joining end connections to a stator tube in which helical pathways have previously been formed. The end connections are joined to the tube via high strength weld connections (advantageously, friction weld connections). The end connections may be made from a different material from the tube. FIG. 1C depicts a similar method to FIG. 1B, except that in FIG. 1C, a previously-used stator with damaged end connection(s) is repaired to provide new end connection(s) of selected material. As in FIG. 1B, the end connections in FIG. 1C are joined to the tube via high strength weld connections (and again, advantageously, friction weld connections).
[0048] Referring now to FIG. 1B, method 110 begins with forming helical pathways into a single (unitary) tubular workpiece by a suitable method (box 111). The scope of this disclosure is not limited to the methods by which helical pathways are formed on embodiments manufactured according to FIG. 1B. For example, ECM or roll-forming methods may be used to form the helical pathways. Alternatively, machining methods such as broaching may be used. Then, in box 112, the ends of the stator tube are prepared for friction welding onto end connections by machining a flat face onto the stator tube ends in a transverse plane that is normal to the longitudinal axis of the stator tube. In box 113, for each end of the stator tube, an end connection cylinder is prepared for friction welding on to the stator tube by machining a corresponding flat face onto the end connection cylinder in a normal transverse plane.
[0049] Box 114 on FIG. 1B depicts performing a high strength weld (advantageously, friction weld) between stator tube and end connection cylinder at the machined flat-faced ends. In currently preferred embodiments, friction welding is accomplished using inertia welding techniques, as described above in the Background section. Inertia welding is advantageous in stator applications in that one workpiece to be welded is rotated while the other is fixed. It will be appreciated that the end connection cylinder, as described on box 113 of FIG. 1B, may be more conveniently rotated because it is a short component as compared to the stator tube. Meanwhile, the stator tube, a comparatively long component, may be more conveniently fixed during inertia welding.
[0050] With further reference to box 114, it will be understood that various parameters may be programmed into the friction welding machine in order to achieve the desired weld. For inertial welding, the rotational speed of the workpiece and fly wheel will be optimized to provide the correct preheating and forging temperatures of the workpieces. Optimal rotational speeds will be in ranges determined by the flywheel size and the rotating workpiece size, as well as the amount of preheating that is applied to the workpiece from an extrinsic heat source (such as induction heaters or infrared heaters, refer discussion in Background section above). A further parameter governing the friction welding process is the thrust load urging the contact surfaces of the workpieces together. A light thrust load will be applied during the spinning and preheating stage of the welding process. After the workpieces are brought to the forging temperature, a higher thrust load is applied to the workpieces to create the wrought worked microstructure and to ultimately complete the weld. The magnitude and rate of increase of the thrust load will be optimized for the workpieces comprising the welded joint. The cooling rate of the weld and any subsequent post weld stress relief (via subsequent general heating of the finished welded joint) will also be optimized for the materials and geometry being joined.
[0051] Direct drive welding may be optimized in a similar manner to the inertial welding optimization described immediately above. With full friction welding machine programmability and control of rotational speed and thrust load, a wide variety of rotational speed and thrust load combinations can be anticipated to optimize the welded structure for strength and consistency.
[0052] Referring now to box 115 on FIG. 1B, now that the end connection cylinders have been joined to the stator tube, the end connection cylinders may be finished to desired specifications. The weld connection itself may be cleaned up, including the removal of flashing. Threads may be cut onto the interior of the end connection cylinder according to desired thread specifications. The interior transition from the end connection, over the weld, and into the stator tube helical pathways may also be machined according to desired transition specifications. For example, an upset configuration on the transition may be machined (e.g. via broaching) so as to create an undercut stator. Alternatively, or additionally, stress-relieving geometry may be machined into the transition to create a desired internal profile. This disclosure is not limited in this regard.
[0053] FIGS. 3 through 8 illustrate various exemplary embodiments of stator configurations that may be manufactured according to FIG. 1B (and FIG. 1C, as will be described further on in this disclosure). For the avoidance of doubt, FIG. 1B is not limited to the exemplary embodiments illustrated on FIGS. 3 through 8.
[0054] Referring first to FIG. 3, stator 300 comprises stator tube 315 joined to end connection 305 via friction weld 310. Stator tube 315 has helical pathways 317 formed therein via known techniques, such as ECM, machining, broaching or hot/cold rolling, or combinations thereof (refer box 111 on FIG. 1B and associated disclosure above). Stator tube end face 316 is machined onto stator tube 315, preferably in a transverse plane that is normal to longitudinal axis 318 (refer box 112 on FIG. 1B and associated disclosure above). End connection end face 306 is machined onto end connection 305, preferably also in a transverse plane that is normal to longitudinal axis 318 (refer box 113 on FIG. 1B and associated disclosure above). Friction weld 310 is performed joining end faces 306 and 316, and post-weld clean up, machining and thread cutting may be performed (refer boxes 114 and 115 on FIG. 1B and associated disclosure above).
[0055] In the embodiment illustrated on FIG. 3, arrow 320 denotes that stator 300 is designed such that friction weld 310 is placed at the point of minimum cross section. This allows for convenient initial formation of the helical pathways 317 (without any requirement, for example, for a pre-form such as a relief counter bore). The placement of friction weld 310 at the point of minimum cross section also facilitates subsequent repair or replacement of end connection 305 should it become damaged in service.
[0056] FIG. 4 illustrates an embodiment similar to FIG. 3, only in FIG. 4, stator 400 comprises stator tube 415 joined to end connection 405 via friction weld 410. Arrow 420 denotes that stator 400 is designed such that friction weld 410 is placed at the maximum cross section of helical pathways 417. In some embodiments, friction weld 410 may be placed from 1 to 6 further into stator 400 from undercut bore 403. Comparable to the embodiment illustrated in FIG. 3, the placement of friction weld 410 on FIG. 4 again allows for convenient initial formation of the helical pathways 417 (without any requirement, for example, for a pre-form such as a relief counter bore). At the same time, FIG. 4's placement of friction weld 410 allows for maximum strength in undercut 403's cross section in this type of welded-connection stator design, since undercut 403 on FIG. 4 is formed in end connection 405, which will typically be made from higher yield strength material.
[0057] FIG. 5 illustrates an embodiment similar to FIGS. 3 and 4, only in FIG. 5, stator 500 comprises stator tube 515 joined to end connection 505 via friction weld 510. Arrow 520 denotes that stator 500 is designed such that friction weld 510 is placed at the maximum cross section of end connection 505, so that undercut 503 is formed entirely in stator tube 515. The embodiment of FIG. 5 recognizes that typically (although not in every case), end connection 505 will be made from higher yield strength (and costlier) material than stator tube 515. Since undercut 503 is formed entirely in stator tube 515 on FIG. 5, formation of undercut 503 may be easier in lower yield strength material used in stator tube 515. At the same time, the amount of higher yield strength (and thus costlier) material used in end connection 505 is minimised in FIG. 5. It will be appreciated that the embodiment of FIG. 5 is ideal for the method described further below with reference FIG. 1C, in which a used stator's end connections may be replaced using high strength friction weld connections to new end connections.
[0058] FIG. 6 illustrates an embodiment similar to FIG. 3, only in FIG. 6, stator 600 comprises stator tube 615 joined to end connection 605 via friction weld 610. In particular, the embodiment of FIG. 6 is similar to the embodiment of FIG. 3, inasmuch that arrow 620 denotes that stator 600 is designed such that friction weld 610 is placed such that friction weld 610 is placed at the point of minimum cross section of undercut 603. As with the embodiment of FIG. 3, this placement allows for convenient initial formation of the helical pathways 617 in stator tube 615 (without any requirement, for example, for a pre-form such as a relief counter bore). Further, as with the embodiment of FIG. 3, the placement of friction weld 610 at the point of minimum cross section facilitates subsequent repair or replacement of end connection 605 should it become damaged in service. Different from the embodiment of FIG. 3, however, the embodiment of FIG. 6 places friction weld 610 immediately next to transition 602 in end connection 605. This placement on FIG. 6 facilitates straightforward machining of both end connection 605 and stator tube 615 to achieve undercut 603 when end connection 605 and stator tube 615 are conjoined. Cleanup of weld 610 is also facilitated in the embodiment of FIG. 6.
[0059] FIGS. 7 and 8 should be viewed together. FIG. 8 is an enlargement of details of FIG. 7, as shown on FIG. 7. FIGS. 7 and 8 illustrate an embodiment in which stator 700 comprises stator tube 715 joined to end connection 705 via friction weld 710. Features and aspects of stator 700 that are illustrated on both FIGS. 7 and 8 have the same part number.
[0060] Referring first to FIG. 7, end connection 705 is a cylindrical or tubular shape with minimum thread diameter 733. Stator tube 715 has helical pathways 717 formed therein, and helical pathways have major helical diameter 731 and minor helical diameter 732. It will be appreciated from viewing FIG. 7 that in the illustrated embodiment, end connection 705 requires no machining or other work to provide an upset or transitional profile such as illustrated on comparative end connections on FIG. 3, 4 or 6. Likewise, in the embodiment illustrated on FIG. 7, stator tube 715 requires no counter bore or relief bore diameter in order to create an undercut geometry, such as illustrated on the comparative stator tube 515 on FIG. 5. Instead, the outside diameter and wall thickness of end connection 705 on FIG. 7 is selected such that minimum thread diameter 733 is less than major helical diameter 731, thus providing an undercut 725 on FIG. 7.
[0061] The embodiment of FIG. 7 thus provides an undercut stator design calling for minimum machining or other work of end connection 705. End connection 705 may begin as a cylinder, have end connection end face 706 formed thereon prior to friction welding Threads may be cut on the inside of end connection 705 after friction welding and helical pathway transition (as further described below). Likewise, the embodiment of FIG. 7 provides a design calling for minimum machining or other work of stator tube 715. Helical pathways 717 may be formed in stator tube 715, onto which stator tube end face 716 may be formed directly prior to friction welding.
[0062] Friction weld 710 on FIG. 7 is made so that on the stator tube 715 side, the welded joint is formed all the way across the lobes of helical pathways 715 to include minor diameter 732. This aspect for friction weld 710 to include minor helical diameter 732 is emphasized and enlarged on FIG. 8. With further reference to FIG. 8, dotted line 730 illustrates the horizon of the fluted helical pathway hidden behind. Distance 720 on FIG. 7 and distance 735 on FIG. 8 indicate the material that must be removed from friction weld 710 all around the circumference of stator 700 in order to provide a smooth transitional curvature from end connection 705 into helical pathways 717 after welding. This transition work may be performed at the same time that friction weld 710 is cleaned up to remove weld flash and other surplus after welding. In currently preferred embodiments, a further small undercut or relief may then be formed on the transitions to secure the termination edge of the elastomer lining deployed later on the helical pathways 717 (small undercut/relief not illustrated). Such weld clean up and helical pathway transition work may be performed with a ball nose end mill, a ball grinder or a rotary saw style mill head, for example.
[0063] It will be appreciated that although end connection 705 on FIGS. 7 and 8 is illustrated as a cylinder, the scope of this disclosure is not limited in this regard. Other non-illustrated embodiments may provide end connections with upset geometries, in which machining or other work may be required before or after welding.
[0064] It will be further appreciated that although the embodiments illustrated on FIGS. 3 through 8 all illustrate (1) undercut stators and (2) cylindrical thread profiles on end connections, the scope of this disclosure is again not limited in either of these regards. Other non-illustrated embodiments, consistent with the specific disclosure associated with each of FIGS. 3 through 8, may provide non-undercut stator geometries and/or tapered thread profiles on end connections.
[0065] FIG. 1C depicts a similar method to FIG. 1B, except that in FIG. 1C, a previously-used stator with damaged end connection(s) is repaired to provide new end connection(s) of selected material. As in FIG. 1B, the end connections in FIG. 1C are joined to the tube via high strength weld connections (and again, advantageously, friction weld connections). Any of the embodiments depicted in FIGS. 3 through 8 may be used with the repair method illustrated on FIG. 1C, although as noted above with reference to FIG. 5, the embodiment illustrated on FIG. 5 is particularly suitable for repairs in accordance with FIG. 1C.
[0066] Referring now to FIG. 1C, method 120 begins by removing the damaged end connection from the stator tube, and, depending on the configuration and geometry of the existing stator tube, preparing the undercut or helical ends thereof and machining a flat end face thereon (box 121). The flat end face will form a contact surface for friction welding. It will be appreciated that the point at which the cut is made to remove the damaged end connection will determine the point at which the flat end face is formed in the stator tube. The cut point therefore dictates to a large extent (1) the overall final configuration and geometry of the repaired stator and (2) the overall methodology by which the repaired stator will be specifically made. Again, refer to FIGS. 3 through 8 and associated disclosure above for examples.
[0067] In box 122 on FIG. 1C, the new end connection cylinder(s) is/are prepared, advantageously made from a material selected to be of the same or higher yield strength than the stator tube material. A flat end face is machined on the end connection to form a contact surface for friction welding.
[0068] Boxes 123 and 124 on FIG. 1C refer to substantially the same processes and related disclosure as described above with respect to boxes 114 and 115 on FIG. 1B. In summary, the end connection is friction welded to the stator tube, and any necessary post-weld machining, grinding, milling or other treatment is applied so that the repaired stator conforms to the desired geometry, configuration and/or specification (for example, one of the embodiments illustrated on FIGS. 3 through 8).
[0069] Earlier in this disclosure, the advantage was described wherein embodiments manufactured according to FIG. 1B or 1C (examples of which are illustrated on FIGS. 3 through 8) allow for selection of different materials to be used in end connections and stator tubes. For example, end connections subjected to high bending stresses in service may optimally be made of higher yield strength material than the stator tube, in which a lower yield strength material may be used to facilitate formation of internal helical pathways. Table 1 below sets forth examples of end connection and stator tube materials that may be combined in friction-welded stators in accordance with the present disclosure.
TABLE-US-00001 TABLE 1 End Connection material Stator Tube material (Yield Strength) (Yield Strength) 4140 - 110 ksi 4140 - 110 ksi 4142 - 110 ksi 4142 - 110 ksi 4145 - 110 ksi 4145 - 110 ksi 4130Mod - 130 ksi 4130Mod - 130 ksi 4340 - 125 - 140 ksi 4340 - 125-140 ksi 4145H - 120 ksi 1525 - 85 ksi 300M - 180 - 210 ksi 1040 - 80 ksi EN25 - 140 ksi 1026 - 75 ksi EN26 - 140 ksi 1018 - 65 ksi
[0070] Table 1 identifies exemplary steel types and grades for end connections and stator tubes, along with approximate yield strengths for each type and grade in units of kilopounds per square inch (ksi). It will be understood that materials identified in Table 1 are exemplary only, and that the scope of this disclosure is not limited to any particular combination of materials for end connections and stator tubes, whether called out as an example on Table 1 or not. The selection of materials will depend on a number of factors specific to the desired application and manufacturing method, including type of service, actual yield strength, toughness, workability, cost, availability and other factors. However, in currently preferred embodiments, end connections are made from steel with a similar or greater yield strength than the steel from which the stator tube is made. See Table 1 for examples. Preferably, end connections are made from a steel with a yield strength greater than 110 ksi, and more preferably greater than 120 ksi, and yet more preferably greater than 140 ksi. Likewise, in currently preferred embodiments, stator tubes are made from a steel with a yield strength greater than 65 ksi, and more preferably greater than 100 ksi, and yet more preferably greater than 120 ksi.
[0071] It will be appreciated that many of the exemplary material combinations suggested by Table 1 combine steels with comparable yield strengths that fall within the preferable criteria set out in the previous paragraph. However, additional consideration should be made when friction welding materials that have a wide difference in yield strength. Welded connections including particularly high yield strength steels may require additional preheat and/or post weld heat treatment, for example. Unless for a very specific application, in which the friction weld technique may have to be specially engineered, the end connection yield strength is preferably no more than 80 ksi greater than the stator tube yield strength, and more preferably no more than 40 ksi greater.
[0072] Although the inventive material in this disclosure has been described in detail along with some of its technical advantages, it will be understood that various changes, substitutions and alternations may be made to the detailed embodiments without departing from the broader spirit and scope of such inventive material as set forth in the following claims.
