Device and method for whirling an internal thread

Abstract

A device for whirling an internal thread (3) comprises a whirling mandrel (4), located on which there is a machining tool (5) intended for producing the internal thread (3), and also comprises an elongated guiding part (7), which supports the whirling mandrel (4) and at the end of which there is formed a guiding portion (8) which, as a portion of increased diameter in relation to the adjoining region of the guiding part (7), is intended for contacting an inner circumferential surface (10) of a workpiece, wherein the whirling mandrel (4) is arranged eccentrically in relation to the guiding portion (8). The whirling mandrel (4) is arranged opposite the guiding part (7), wherein means (11, 12) for aligning the whirling mandrel (4) in relation to the guiding part (7) are formed on the end faces of the whirling mandrel (4) and of the guiding portion (8).

Description

[0001] Device and method for whirling an internal thread

[0002] The invention relates to a device for whirling an internal thread, designed according to the preamble of claim 1. Furthermore, the invention relates to a method for producing an internal thread by whirling.

[0003] A method for producing an internal thread by whirling is known, for example, from EP 1 820 592 A2. EP 1 820 592 A2 deals with the production of multi-start thread-like profiles, wherein it is proposed to synchronize the speeds and angles of rotation of a workpiece and a cutting tool such that the production of at least some of the threads of the profile takes place continuously. A whirling mandrel used for cutting in the machine described in EP 1 820 592 A2 is guided in a so-called support head, which is a tubular part. At its end, the support head has a cylindrical guide section as a section of enlarged diameter, which is guided in a sliding manner on an inner surface of the workpiece. The whirling mandrel projects beyond the support head including the guide section and carries a cutting tool in the area projecting beyond the guide section.In the case of the machine according to EP 1 820 592 A2, the cutting tool comprises a tool body fitted with a carbide cutting insert.

[0004] Thread whirling is generally a circular thread milling process. A whirling tool rotates at high speed while the workpiece rotates comparatively slowly. The tool and workpiece can rotate either synchronously or in opposite directions. In either case, relative movements between the tool and the workpiece in the axial direction must be coordinated with the profile to be created and with the rotational movement of the workpiece. Since both the tool and the workpiece are rotationally driven, machine tools with two opposing spindles are particularly suitable for thread whirling. DE 19922 891 C2 discloses a tool holder with a rotatably driven tool spindle for whirling internal threads, wherein the rotational axis of the tool runs obliquely to the axis of the threaded hole in the workpiece. A drive spindle is connected to a tool spindle by a double-joint cardan shaft.This is intended to provide adjustment options that allow the tool holder to be used to produce different thread pitches.

[0005] DE 1 280638 A relates to a device for whirling steep-pitch and / or long internal threads. According to DE 1 280 638 A, the reciprocating motion of a whirling mandrel is derived from an inclined disc, on which the whirling mandrel is supported in an articulated manner via a sliding shoe.

[0006] A whirling device described in DE 102011 110 131 B4 comprises a tool mounted on a spindle that can be driven in a rotational or linearly displaceable manner. It is possible to achieve either only a rotational movement or only a linear movement of the spindle, or to achieve simultaneous rotational and linear movement.

[0007] The invention is based on the object of achieving progress compared to the aforementioned prior art in the whirling of internal threads, whereby a particularly favorable relationship between manufacturing effort and precision is sought even for threads with a large length / diameter ratio.

[0008] This object is achieved according to the invention by a device configured for whirling an internal thread having the features of claim 1. The object is likewise achieved by a method for whirling an internal thread according to claim 8. The embodiments and advantages of the invention explained below in connection with the manufacturing method, i.e., the machining method in the form of whirling, also apply mutatis mutandis to the machining device provided for whirling internal threads. The machining device according to the application comprises, in a basic concept known per se, a whirling mandrel on which a machining tool provided for producing the internal thread is located. Furthermore, the machining device comprises an elongated guide part supporting the whirling mandrel.At the end of the guide part, a guide section is formed which has an enlarged diameter in relation to the adjacent area, i.e. shaft, of the guide part and is intended for contacting an inner circumferential surface of a workpiece.

[0009] The shank of the guide part, like the guide section also provided by the guide part, does not necessarily have a circular cross-section. By designing the cross-section of the guide section in which contact is established between the inner surface of the workpiece and the surface of the guide section only at defined surface sections that are small compared to the total surface of the guide section, the risk of the tool jamming in the workpiece bore can be effectively counteracted. In particular, the outer contour of the guide part can be left free where no supporting force is required. For example, contact with the workpiece bore is only provided on two separate surfaces, which are arranged opposite the force introduction by the machining process.During machining, i.e. the machining of the internal thread by whirling, the whirling mandrel is always arranged eccentrically to the guide section.

[0010] In the device according to the application, the vortex dome is arranged opposite the guide part, wherein means for aligning the vortex dome in relation to the guide part are formed on the opposite end faces of the vortex dome and the guide section.

[0011] If the workpiece, which already has a hollow shape with a continuous cylindrical inner circumferential surface (i.e., a through-bore) prior to whirling, is located in the machining fixture, the accessibility of the bore from both sides can be utilized to provide highly effective mechanical support to the whirling mandrel during machining and to machine the workpiece both at high machining speed and with precision. The machining fixture can be used for the production of single-start threads as well as for the production of multi-start threads or other structured internal surfaces, with particular suitability for small diameters and large bore depths relative to the bore diameter.

[0012] Regarding the type of cutting tool, various design options exist. For example, the cutting tool can be a cutting head that is an integral part of the swirl dome. Instead of a cutting head formed integrally with the swirl dome, a replaceable cutting head attached to a shaft of the swirl dome can also be provided. Likewise, designs are possible in which the cutting tool is in the form of at least one replaceable cutting plate attached to the swirl dome. In all cases, the cutting tool can have either a single cutting edge or a plurality of cutting edges, for example, three cutting edges.

[0013] The aforementioned means for aligning the swirl dome relative to the guide part allow for relative rotation between the swirl dome and the guide part and are formed, for example, by a pin and a corresponding bore, with the pin located on one of the two parts, the swirl dome and the guide part, and the bore located on the front side of the other part. A purely segmental design of contours for aligning the swirl dome relative to the guide part during machining is also possible.

[0014] In a pin-bore combination, the pin, for example, is located on the turret in a section that protrudes beyond the cutting tool, while the guide section is provided with a corresponding bore. Conversely, the guide section can also be provided with a pin-shaped extension that engages a bore on the front side of the turret. With the same functionality, interaction between the turret and the guide part can also be provided via a separate bearing.

[0015] The process for producing an internal thread by whirling generally includes the following steps:

[0016] - Provision of a tubular workpiece, i.e. one with a through hole, to be provided with the internal thread,

[0017] - Clamping the workpiece using a center drive spindle of a machine tool so that the through hole is accessible from both sides,

[0018] - Provision of a vertebral dome and an elongated guide part, wherein alignment contours are formed on the end faces of the vertebral dome and the guide part, which enable a defined relative positioning of the longitudinal axes of the vertebral dome and the guide part with simultaneous relative rotation between the vertebral dome and the guide part,

[0019] - feeding the swirl dome to the workpiece from the first side of the through-hole and feeding the guide part from the opposite side, wherein the workpiece, the swirl dome and the guide part are initially arranged at least approximately concentrically to one another,

[0020] - Moving the vortex dome in the radial direction and merging the alignment contours of the vortex dome and the guide part, whereby a guide section of the guide part is guided in the through hole, i.e. supported in the radial direction,

[0021] - Machining of the internal thread by advancing the assembly of whirling mandrel and guide member through the through-hole. No axial displacement occurs between the whirling mandrel and guide member, the guide member does not rotate, the whirling mandrel rotates at a defined, high speed, and simultaneously the workpiece rotates at a comparatively low speed. During whirling, i.e., the machining process, the whirling mandrel and the workpiece can rotate either in the same direction, for example, both clockwise, or in opposite directions. The functionality of a center-drive spindle can also be performed by a finishing machine in which the workpiece is firmly clamped, while the tool's rotational axis and the alignment contour of the guide member are moved in a consistent circular motion.

[0022] The method according to the application can, for example, be used to create an internal thread for a screw drive nut. In the simplest case, the screw drive is a simple linear motion thread. Otherwise, the screw drive can be designed, in particular, as a rolling screw drive. This means that whirling creates raceways for rolling elements, in particular balls of a ball screw drive.

[0023] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings:

[0024] Fig. 1 shows a detail of a device for whirling an internal thread,

[0025] Fig. 2 Components of the device according to Fig. 1 in a position before the start of the machining process, i.e. thread whirling.

[0026] A manufacturing machine, designated overall by the reference numeral 1, is constructed as a center-drive machine tool. This means that a tubular workpiece 2 can be machined from both sides. The manufacturing machine 1 is used as a device for whirling an internal thread 3. Regarding the manufacturing technology of thread whirling in general, reference is made to the prior art cited at the beginning. A whirling mandrel 4 of the device 1 comprises a cutting head 5 and a shaft 6. The cutting head 5 is generally referred to as a cutting tool. In the present case, the cutting head 5 is integrally connected to the shaft 6. Alternatively, the cutting tool 5 could be in the form of cutting plates, for example, which are attached directly or indirectly to the shaft 6. The center axis of the whirling mandrel 4 including the cutting head 5 is designated MA4.

[0027] Furthermore, the device 1, i.e. the production machine for internal thread whirling, includes a rod-shaped guide part 7. At the end of the guide part 7 there is a cylindrical guide section 8 with a diameter that is larger than the rest of the guide part 7. The diameter of the guide section 8 approximately corresponds to the inner diameter of the workpiece 2. The shaft of the guide part 7 is designated 9. When the guide part 7 is inserted into the workpiece 2, as is the case in the configuration according to Fig. 1, an annular gap is formed between the outer peripheral surface of the shaft 9 and the inner peripheral surface of the workpiece 2, designated 10. The workpiece 2 is supported by the guide section 8 resting against the inner peripheral surface 10. The central axis of the guide part 7, designated MA7, coincides with the central axis of the workpiece 2 in this state.

[0028] The machining process carried out with the production machine 1 for producing the internal thread 3 is particularly characterized in that the whirling mandrel 4 and the guide part 7 are inserted into the workpiece 2 from opposite sides, as can be seen from both Fig. 1 and Fig. 2. In the configuration shown in Fig. 2, which shows a preparatory step for thread whirling, the whirling mandrel 4 is located centrally in the workpiece 2. A slightly eccentric arrangement of the whirling mandrel 4 would also be possible in this phase, as long as the cutting head 5 does not touch the inner circumferential surface 10. The whirling mandrel 4 is displaced from right to left with reference to the arrangement according to Fig. 2. Axial displacements of the whirling mandrel 4 are generally designated AV4.The whirl mandrel 4 has a pin 11 projecting beyond the cutting head 5, which, in conjunction with a recess 12 designed as a blind hole on the front side of the guide section 8, provides a means for aligning the whirl mandrel 4 in relation to the guide part 7. The recess 12 is located eccentrically in the guide section 8. In order to insert the pin 11 into the recess 12, the originally existing radial offset between the pin 11 and the recess 12 must be eliminated. This is achieved by a radial displacement of the whirl mandrel 4, designated RV4.

[0029] The internal thread 3 can be produced by machining either from right to left or from left to right, based on the arrangements shown in Figs. 1 and 2. During the machining process, the axial displacement of the guide part 7, designated AV7, corresponds to the axial displacement AV4 of the whirling mandrel 4. This means that the axial distance between the guide section 8 and the cutting head 5 does not change during whirling. Likewise, the guide part 7, including the guide section 8, remains in an unchanged angular position during thread whirling. During whirling, the whirling mandrel 4, including the cutting head 5, performs a rapid rotation RS. At the same time, a relatively slow rotation RW of the workpiece 2 occurs, which is coordinated with the axial displacements AV4 and AV7.

[0030] List of reference symbols

[0031] 1 production machine

[0032] 2 Workpiece

[0033] 3 internal threads

[0034] 4 vertebral dome

[0035] 5 Cutting head, cutting tool

[0036] 6 Shaft of the vertebral spine

[0037] 7 Guide part

[0038] 8 Guide section

[0039] 9 Shaft of the guide part

[0040] 10 inner peripheral surface

[0041] 11 cones

[0042] 12 Recess, blind hole

[0043] AV4 axial displacement of the vertebral dome

[0044] AV7 Axial displacement of the guide part

[0045] MA4 Central axis of the vertebral dome

[0046] MA7 Center axis of the guide part

[0047] RS Rotation of the cutting head

[0048] RV4 radial displacement of the vertebral spine

[0049] RW Rotation of the workpiece

Claims

Patent claims 1. A device for whirling an internal thread (3), comprising a whirling mandrel (4) on which a cutting tool (5) provided for producing the internal thread (3) is located, and comprising an elongated guide part (7) supporting the whirling mandrel (4), at the end of which guide part a guide section (8) is formed, which is provided as a section with an enlarged diameter in relation to the adjacent region of the guide part (7) for contacting an inner circumferential surface (10) of a workpiece, wherein the whirling mandrel (4) is arranged eccentrically to the guide section (8), characterized in that the whirling mandrel (4) is arranged opposite the guide part (7), wherein means (11, 12) for aligning the whirling mandrel (4) in relation to the guide part (7) are formed on the end faces of the whirling mandrel (4) and of the guide section (8).

2. Device according to claim 1, characterized in that the cutting tool (5) is designed in the form of a cutting head as an integral part of the vortex dome (4).

3. Device according to claim 1, characterized in that the cutting tool (5) is in the form of at least one replaceable cutting plate fastened to the whirling mandrel (4).

4. Device according to claim 1, characterized in that the cutting tool (5) as a cutting head is detachably connected to a shaft (6) of the whirling mandrel (4).

5. Device according to one of claims 1 to 4, characterized in that the means (11, 12) for aligning the vortex dome (4) in relation to the guide part (7) are present as a pin (11) of one of the two parts, vortex dome (4) and guide part (7), which engages in a front-side bore (12) of the other part (7, 4).

6. Device according to claim 5, characterized in that the pin (11) is located on the vortex dome (4).

7. Device according to claim 5, characterized in that the pin (11) is formed by the guide part (7).

8. Method for whirling an internal thread (3), comprising the following steps: - provision of a tubular workpiece (2), i.e. one having a through-bore, - clamping the workpiece (2) by means of a center drive spindle of a machine tool so that the through hole is accessible from both sides, - Providing a swirl dome (4) and an elongated guide part (7), wherein alignment contours (11, 12) are formed on the end faces of the swirl dome (4) and the guide part (7), which enable a defined relative positioning of the longitudinal axes (MA4, MA7) of the swirl dome (4) and the guide part (7) with simultaneous relative rotation between said parts (4, 7), - feeding the swirl dome (4) to the workpiece (2) from the first side of the through-bore and feeding the guide part (7) from the opposite side, wherein the workpiece (2), the swirl dome (4) and the guide part (7) are initially arranged concentrically to one another, - moving the vortex dome (4) in the radial direction and merging the alignment contours (11, 12) of the vortex dome (4) and the guide part (7), wherein a guide section (8) of the guide part (7) is guided in the through-bore, i.e. supported in the radial direction, - machining of the internal thread (3) by advancing the arrangement of the swirl dome (4) and guide part (7) through the through-bore, wherein the guide part (7) does not rotate, the swirl dome (4) rotates at a defined, high speed and the workpiece (2) rotates at a comparatively low speed.

9. Method according to claim 8, characterized in that the vortex dome (4) and the workpiece (2) rotate in opposite directions.

10. Method according to claim 8 or 9, characterized in that an internal thread (3) of a nut of a screw drive is produced thereby.

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