METHOD AND APPARATUS FOR FRICTION WELDING

Abstract

A method and apparatus for friction welding of workpieces (2, 3), which are softened and welded in a friction phase (R) with frictional contact and under frictional pressure (p) in a relative rotational movement about a process axis (8) through the effect of frictional heat. The frictional pressure (p) applied during axial advancement of one of the workpieces (3) is preferably ramped and increased during the friction phase (R).

Claims

1. A method for the friction welding of workpieces, the method comprising: plasticizing and welding together the workpieces by frictional heat during a friction phase in frictional contact and with a frictional pressure during a relative motion about a process axis; changing and increasing the frictional pressure during the duration of the friction phase in a range of about 4 N/mm.sup.2, initially, to 100 N/mm.sup.2.

2. (canceled)

3. A method in accordance with claim 1, wherein the frictional pressure is changed and increased during the friction phase steadily according to a linear ramp.

4. A method in accordance with claim 1, wherein the frictional pressure is changed and increased continuously during most of the friction phase or during the entire friction phase.

5. A method in accordance with claim 1, wherein the frictional pressure is increased from an initial value of 5 N/mm.sup.2 to 80 N/mm.sup.2 during the friction phase.

6. A method in accordance with claim 1, wherein the frictional pressure is applied along the process axis.

7. A method in accordance with claim 1, wherein workpieces are pressed axially against one another during an upset phase following the friction phase.

8. A method in accordance with claim 1, wherein workpieces with a frictionally active diameter of 200 mm or larger, preferably 500 mm to 650 mm, are friction-welded.

9. (canceled)

10. A method in accordance with claim 1, wherein the workpieces are rotated relative to one another during the friction phase at a speed of about 500 rpm.

11. A method in accordance with claim 1, wherein the workpieces are rotated relative to one another at a circumferential velocity of 5 m/sec or higher at a contact point during the friction phase.

12. A friction welding device for the friction welding of workpieces, which are plasticized and welded together in a friction phase by frictional heat in frictional contact and under the action of a pressing force during a relative rotation about a process axis, the friction welding device comprising: workpiece mounts; a rotating device producing relative motion a pressing device for pressing the workpieces; a control configured to control the pressing device such that the frictional pressure is changed and increased during the duration of a friction phase in a range of about 4 N/mm.sup.2, initially, to 100 N/mm.sup.2.

13. A friction welding device in accordance with claim 12, wherein the pressing device is controlled such that the frictional pressure is increased during the duration of the friction phase from an initial value of 5 N/mm.sup.2 to 80 N/mm.sup.2.

14. A friction welding device in accordance with claim 12, wherein the frictional pressure is increased during the friction phase steadily according to a linear ramp.

15. A friction welding device in accordance with claim 12, wherein the pressing device is controlled such that the frictional pressure is changed and increased continuously during most of the friction phase or during the entire friction phase.

16. A friction welding device in accordance with claim 12, wherein the rotating device and the pressing device are arranged and act along the central process axis.

17. A friction welding device in accordance with claim 12, wherein the pressing device is controlled such that the workpieces are pressed axially against one another following the friction phase during an upsetting phase with an increased upset force.

18. A friction welding device in accordance with claim 12, wherein the friction welding device is configured for workpieces with a frictionally active diameter of 200 mm or.

19. A friction welding device in accordance with claim 12, wherein the friction welding device is configured for workpieces comprised of steel with a higher carbon content.

20. A friction welding device in accordance with claim 12, wherein the rotating device is controlled such that the workpieces are rotated relative to one another at a speed (n) of about 500 rpm during the friction phase.

21. A friction welding device in accordance with claim 12, wherein the rotating device is controlled such that the workpieces are rotated relative to one another at a circumferential velocity of 5 m/sec or higher during the friction phase at a contact point.

22. A friction welding device in accordance with claim 12, wherein the friction welding device is configured for workpieces that are configured as pipes or have at least one tubular section in an area of the friction-welded connection.

23. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the drawings:

[0020] FIG. 1 is a schematic view showing a friction welding device;

[0021] FIG. 2 is a diagram for the curve of the speed and the frictional pressure over time according to the present invention; and

[0022] FIG. 3 is a diagram for the curve of the speed according to the state of the art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Referring to the drawings, the present invention pertains to a method and to a device (1) for the friction welding of workpieces (2, 3).

[0024] The workpieces (2, 3) may be of any type and size and may consist of any material suitable for friction welding. The workpieces are preferably configured as pipes or have at least one tubular section in the area of the friction-welded connection.

[0025] The workpieces (2, 3) preferably consist of metal. In the following exemplary embodiments, they consist of steel with a higher carbon content, which tends to undergo a hardness increase at a higher rate of cooling. The workpieces (2, 3) may consist, in principle, of the same material or of different materials. There may be differences especially in terms of the melting point and the thermal conductivity. For example, material pairs of steel with cast materials, especially cast metal with graphite inclusions, iron and nonferrous metals and the like can be friction-welded. In addition, nonmetallic friction-welding partners are possible.

[0026] In the exemplary embodiments shown, the workpieces (2, 3) have very large frictionally active diameters at the contact and connection point (4). This diameter is 200 mm or larger. The diameter is preferably larger than 350 mm, especially preferably in the range of 500 mm to 650 mm.

[0027] For the friction welding, the workpieces (2, 3) to be connected to one another are moved and pressed along a central process axis (8) axially against one another and rotated relative to one another and in a circulating manner. The workpieces (2, 3) are pressed axially against one another with a defined frictional pressure (p) at the contact and connection point (4) during the relative rotation. Heat is introduced into the contact and connection point (4) due to the frictional resistance, and this heat leads to heating and partial melting of the workpieces (2, 3) in this area. The workpieces (2, 3) are subsequently pressed together with an upset stroke, and the relative rotation is ended beforehand or at the same time.

[0028] At the beginning of the friction welding process, the workpieces (2, 3) are spaced axially apart, and the rotary motion of one workpiece (2) is started. The workpieces (2, 3) are then brought axially closer to one another during the feed and brought into physical contact, and a frictional pressure (p) is applied on the circulating contact and connection area (4) by the axial pressing force (F). The feed into the already rotating workpiece (2) takes place on the fly in this variant. The beginning of the pressure increase on contact between the workpieces signals the actual position of the front edges of the workpieces to be welded together and is stored in the analysis unit as a so-called zero position. The zero position is significant for the control or regulation of the feed paths and of the desired end position of the welded part as well as of the workpiece shortenings.

[0029] In another variant, the workpieces (2, 3) may be brought into physical contact first without relative rotation in order to detect said zero position and the actual position based on the increase in pressure. They are then spaced again apart from one another somewhat, while the relative rotation starts and the axial feed takes place at the same time. The desired speed (n) is reached on physical contact in both variants.

[0030] Beginning from the physical contact with rotation, the friction phase (R) starts, in which the workpiece edges are plasticized by the heat under the frictional pressure on the contact and connection area (4) and a friction bead is possibly formed radially at the point (4) and the workpieces (2, 3) correspondingly continue to be brought axially closer to one another. At the end of the friction phase, the relative rotation or the rotating workpiece (2, 3) can be decelerated, and the axial pressing force is markedly increased during a so-called upset stroke at the time or shortly thereafter to provide the upsetting phase (S).

[0031] FIG. 3 shows for this a diagram for the curve of the frictional pressure (p) and of the speed (n) according to the state of the art in case of an application for large frictionally active diameters and usual circumferential velocities of about 3 m/sec with a correspondingly dimensioned friction welding device. The frictional pressure (p) is already very high right at the beginning of the friction phase (R) and remains constant during the friction phase. A conventional pressure value is, e.g., about 80 N/mm.sup.2. The desired or nominal rotational speed (n) is likewise constant after a start phase and is about 100 rpm. Such a friction welding method with the conventional welding parameters (p, n) requires a very powerful rotating drive and an oversized machine design.

[0032] The diagram in FIG. 2 shows the friction welding method according to the present invention. The exemplary embodiment shown pertains here to workpieces (2, 3) consisting of steel, in which at least one workpiece (2, 3) has an increased carbon content and is prone to hardness increase. The frictionally active diameter of the workpieces (2, 3) is 560 mm.

[0033] The frictional pressure (p) is markedly lower at the beginning of the friction phase (R) than in the state of the art. It is, e.g., approx. 5 N/mm.sup.2. It initially remains at this low level for some time to subsequently rise accordingly to a ramp and linearly up to a frictional pressure of, e.g., 80 N/mm.sup.2 at the end of the friction phase (R).

[0034] The offset or the time delay until the beginning of the pressure increase may correlate with the start phase until the desired or nominal speed (n) is reached. As soon as the desired speed is reached, the frictional pressure (p) rises as well. The frictional pressure at the end of the friction phase (R) is approximately equal to that seen in the state of the art according to FIG. 3.

[0035] According to FIG. 2, the nominal speed (n) of the rotating drive (6) is also higher in the friction welding method according to the present invention than in the state of the art according to FIG. 3. It equals approx. 500 rpm. After the end of the start phase, it likewise remains constant until the end of the friction phase (R) and is then preferably abruptly reduced.

[0036] A circumferential velocity of about 14.4 m/sec is obtained at the desired or nominal speed (n) at the contact or connection area (4) in this exemplary embodiment. It is substantially higher than in the state of the art, where it is approx. 1 m/sec to 5 m/sec.

[0037] Different parameters may be obtained for other exemplary embodiments and friction welding pairs. The frictional pressure (p) is increased in a range of approx. 4 N/mm.sup.2 to 100 N/mm.sup.2 during the friction phase. At the end of the friction phase, the frictional pressure is always higher than at the beginning Unlike in the exemplary embodiment shown, the frictional pressure (p) may optionally also rise in one or more steps and optionally also in step-like increments or with a stepped ramp function. The frictional pressure (p) is preferably changed steadily or continuously during the friction phase (R). The pressure increase may also take place according to a nonlinear curve function.

[0038] Corresponding to the variable frictionally active diameter, the circumferential velocities may vary at the contact and connection area (4). They are preferably higher than 5 m/sec. A range between 12 m/sec and 17 m/sec is preferred. The predefined speed (n) maybe varied correspondingly.

[0039] The above-mentioned exemplary embodiment and the variants pertain to friction welding with a continuous motor drive for the relative motion and active deceleration of the motor drive. They may be correspondingly different for flywheel welding with moment of inertia and with the rotating drive switched off.

[0040] In the preferred embodiment shown, the friction welding device (1) may have a frame (5), on which a machine head with (6) and with a coupled workpiece mount (10) for the one workpiece (2) is arranged stationarily or axially movably. Further, a pressing device (7) with a workpiece mount (11) for the other workpiece (3) is arranged on the frame (5). It may be arranged, e.g., according to FIG. 1, axially opposite the machine head.

[0041] Two workpieces (2, 3) are friction-welded in the exemplary embodiment shown. In other variants, not shown, so-called double-head friction welding machines are possible, in which three or more workpieces are friction-welded to one another in one process.

[0042] In the exemplary embodiment shown, the rotating device (6) has a drive motor, which rotates the workpiece mount (10) arranged on a spindle about the process axis (8). This may be a direct drive or a drive with an interconnected transmission. The rotating device (6) may further have a braking device.

[0043] In another embodiment, not shown, the rotating drive may be configured as a flywheel drive, in which the drive motor sets a flywheel mass into rotation about the process axis (8), and this flywheel mass will then introduce the necessary kinetic energy during the friction welding process.

[0044] The drive motor is preferably configured as a controllable and optionally regulatable electric motor in the different embodiments. It may be configured as a d.c. motor or a.c. motor, especially as a three-phase motor.

[0045] The pressing device (7) ensures the axial approach of the workpieces (2, 3) over the path (s) and the pressing force or frictional force (F) acting in the process. The pressing device (7) may have any desired and suitable configuration and arrangement for this. It may generate axial pulling forces or forces of pressure.

[0046] In the preferred embodiment shown, it is configured as a feeding device (14). It has a feed drive (15) for feeding the workpiece mount (11) along the process axis (8). The feed drive is configured, e.g., as a hydraulic cylinder. As an alternative, it may also be configured as another linear drive, especially as an electrical spindle drive or the like. The feed drive (15) is controllable and also regulatable in conjunction with a suitable force- and/or displacement-detecting sensor system.

[0047] The feed drive (15), which is arranged and supported, e.g., stationarily on the frame (5), acts on a holder (16) mounted axially movably on the frame (5) by means of a rod-shaped feed element in the exemplary embodiment shown. The workpiece (11) is permanently or detachably fastened to the holder (16).

[0048] The workpiece mounts (10, 11) may have any desired and suitable configuration. In the exemplary embodiments shown, they are equipped with a clamping device (12), which clamps the workpiece (2, 3) radially from the outside or the inside. The clamping device (12) may have, e.g., a chuck with two or more radially adjustable clamping jaws.

[0049] To support the clamping forces, a support device (13), which is located opposite and acts against the clamping device (12), while supporting the clamping forces and the workpiece (2, 3), may be arranged at a workpiece (2, 3) to support the clamping forces. The support device (13) is arranged, e.g., in the rotating workpiece (2), but it may also be located at both or all workpieces (2, 3). It may be connected to the respective workpiece mount (10, 11) and held through the cavity of the workpiece (2, 3).

[0050] The friction welding device (1) has a preferably memory-programmable control (9), which is connected to the different components of the machine, especially to the rotating drive (6) and the feed drive (15) as well as to a sensor system, which detects the paths traveled by the friction welding partners and the acting forces. The control (9) controls the friction welding device (1) and the components thereof in a manner corresponding to the manner in which the aforementioned friction welding device is carried out. It may contain one or more stored friction welding programs. It may also have a technology data bank with ready-to-use friction welding parameters or friction welding parameters to be calculated as well as a suitable computer along with input and output interfaces.

[0051] Any desired variation of the above-described exemplary embodiments and of the variants is possible. In particular, the features of the different exemplary embodiments and variants may be combined and optionally also transposed with one another.

[0052] In particular, a different kinematics of the relative motion between the workpieces (2, 3) and a correspondingly different design configuration of the friction welding device (1) are possible.

[0053] Multiple rotating drives (6) and a different design configuration of the pressing device (7) are possible in other friction welding devices, especially double-head friction welding devices. In particular, a holder (16) fed by the pressing device (7) may have a rotating drive (6), wherein one or more additional workpieces and preferably workpieces held nonrotatably in relation to one another are arranged between the rotating workpieces. The pressing device (7) may also be connected to machine heads movable axially in both directions and move these axially in relation to one another as well as in relation to a central holder for a third workpiece or for additional workpieces.

[0054] In a variant of FIG. 1, a pressing device (7) may also be supported in a single-head friction welding machine on the side on a stationary holder (16), and said machine head is moved during the axial feed relative to the workpiece (3) located at a stationary holder (16). In one embodiment, a feed device (14) may be formed by cylinders, wherein the housing is connected to this axially movable machine head or headstock.

[0055] The friction welding device (1) may also be configured as a double single-head friction welding machine, which has a common central and stationary support device or holder (16) with workpiece mounts (11) on both sides and a mirror-symmetrical arrangement of machine heads with respective rotating drives (6) of their own along with pressing device (7). A pressing device (7) may be arranged in this embodiment as well as in other embodiments at the stationary or axially movable machine head shown in FIG. 1 with rotating drive (6) and exert pulling forces.

[0056] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.