OSCILLATING MECHANISM

Abstract: A mechanism suitable for friction welding aerofoil blades to the periphery of a disc. The mechanism comprises a first member (flywheel 12) which has an eccentric crank pin. Two pivotally interconnected links 18 and 20 are connected between the crank pin and a second member 19 which is pivotally mounted. A blade to be friction welded (by rubbing it in an arcuate path on the disc) is mounted at the point of pivotal connection 32 between the second link 20 and the member 19. An actuator lever 24 is pivotally mounted on a pivot 22 which is located in the vicinity of the locus of movement of the pivotal interconnection 30 between the two links 18, 20. The actuator has a third link 28 which is of the same length as the link 20. The third link is connected by a pivot 26 to the lever 24 at a radius equal to the length of the second and third links 20 and 28. Movement of the lever 24 about its pivot 22 when the pivots 30 and 22 coincide, to bring the pivot 26 into line with the pivot 32 freezes the oscillation of the pivot 32 to enable the blade to be welded to the disc at a precise location along the arcuate path.

Description: This invention relates to a mechanism for oscillating an object along an arcuate path and for stopping the object precisely at a predetermined point along the arcuate path. In gas turbine engines there is a need to weld preformed aerofoil shaped blades to the periphery of a disc to produce what is known as a blisk. One method of welding such blades to the periphery of the disc is friction welding. In friction welding, the inner end of the aerofoil blade is held in contact with the periphery of the disc and oscillated in the axial direction to heat the inner end of the aerofoil and a localised region of the periphery of the disc until they become plastic. As soon as they become plastic the oscillation of the blade is stopped and the blade is pushed radially inwards to effect the weld. Although friction welding is a simple and effective method of welding there is a fundamental problem that has eluded many previous attempts to achieve a successful technique. Basically the problem resides in devising a device for oscillating the blade at say 3000 oscillations per minute with loads (normal and parallel to the surfaces) of about 5 to 15 tons with an amplitude of a few millimetres (eg 4mm), and stopping the oscillation of the blade instantly at exactly the same axial position so that all the blades lie between the same axial planes. A further complication resides in the fact that it is preferable to oscillate the blade along an arcuate path because the shape of the inner end of the aerofoil blade is predominantly curved. An object of this invention is to provide a mechanism which is capable of oscillating a blade along an arcuate path and stopping it precisely along the path. The invention as claimed enables the oscillation of the object to be stopped precisely by moving the actuator lever to bring the pivot between the third link and the actuator lever in line with the pivot between the second link and the second member. Two embodiments of the present invention will now be described, by way of examples with reference to the accompanying drawings, in which:- Figure 1 illustrates schematically a method of friction welding blades to a disc, and Figures 2 and 3 show two mechanisms constructed in accordance with the present invention. Referring to Figure 1, there is shown a metal disc 2 to the periphery of which it is desired to weld a plurality of equispaced aerofoil shaped blades. Each blade is held in contact with the periphery of the disc 2 by means of a clamp 6 operated by the mechanism shown in figure 2 or figure 3. The blade is oscillated along an arcuate path 8 which is approximately of the same radius as the radius of curvature of the blade to be welded. The clamp is moved with a force X of between 5 and 15 tons and a force Y of 5 to 15 tons is applied radially inwards to cause frictional heating. As soon as the surfaces are plastic the blade and the disc are urged together radially a predetermined amount to form an upset and effect the welding. It is imperative that all the leading edges of the blades are accurately located relative to each other so that the blades lie parallel to each other between common axial planes. Referring to Figure 2, there is shown a base 10 on which is rotatably mounted a first member (flywheel 12) having an eccentrically mounted crank pin 14. Pivotally mounted on the crank pin 14 is a first link 18. The base 10 is also provided with a pivotally mounted second member 19 which is approximately the same length as the radius of curvature of the blade to be welded. Pivotally connected to the end of the link 18 remote from the crank pin 14 is a second link 20. The other end of the link 20 is pivotally connected to the free end of the second member 19. Pivotally mounted on base 10 (on pivot 22) is an actuator lever 24. The actuator lever 24 has a pivot 26 which is at a radius equal to the length of the link 20. Pivotally mounted on the pivot 26 is a third link 28 of equal length to the link 20. The other end of the link 28 is pivotally connected to the links 18 and 20 at their pivotal interconnection 30. The pivot 22 is located relative to the length of link 18 and the radius of the crank pin 14 so that the locus of the pivot 30 passes over it as the flywheel 12 rotates. The blade to be oscillated during the friction welding is mounted in the clamp 6 which is mounted on the pivot 32 at the end of the member 19. Rotation of the flywheel 12 causes the pivot 32 to be oscillated in an arcuate path when the actuator lever 24 is in the position shown in figure 2. Rotation of the lever 24 about its pivotal axis 22 is used to freeze the arcuate motion of the pivot 32. Movement of the actuator level 24 may be synchronised with the rotation of the flywheel 12 (but need not be )so that the oscillation of the pivot 32 can be stopped precisely by decreasing the amplitude without stopping the rotation of the flywheel 12. When the pivot 26 is co-axially aligned with the pivot 32 the pivot 32 stops oscillating at a point along the path of oscillation (ie over the same zone of frictional heating). Thereafter, the pivot 30 follows an arcuate path about the pivot 26. We prefer to strobe, or time, the movement of the lever 24 relative to the rotational speed of the flywheel 12 so as to initiate movement of the lever 24, to bring the pivot 26 in line with the pivot 32 the instant that the pivot 30 coincides with pivot 22. Referring to Figure 3 there is shown a second embodiment of the invention. The same reference number have been used for the same parts shown in figure 2. As will be seen, the second member 19 is mounted to pivot about an axis 33 intermediate its ends. The blade carrier 6 is provided at one end of the second member 19 (not as the pivot 32) at a radius from the pivot 33 equal to the radius of curvature of the blade to be welded. Rotation of the flywheel 12 drives the carrier long an arcuate path and movement of the lever 24 (to bring the pivot 26 into alignment with the pivot 32) freezes the motion of the carrier 6. The exact position P along the total arc of movement is proportional to the ratio of length of the first link 18 to the length of the second link 20, and would be mid-way along the arc for links of equal length. The actual location of the axis 33 relative to the axis of rotation of the first member 12 is not critical. The axis 33 could be located so that at a mid-point in the travel of the mechanism the second link 20 is normal to the second member 19. If desired, a brake could be applied to the flywheel 12 when moving the lever 24 thereby to decrease the frequency of oscillation of the pivot 32 whilst at the same time decreasing the amplitude of the oscillation. In this way the frequency can be accurately controlled.

Claims: 1. A mechanism (10) for oscillating an object along an arcuate path and for stopping the object at a predetermined point along the path, characterised in that the mechanism (10) comprises: a first member (12) mounted for rotation about a first axis, the first member (12) having a crank pin (14) eccentrically mounted thereon; a second member (19) mounted for pivotal movement about a second axis and having means (16) for carrying the object along an arcuate path relative to the second axis; a first link (18) rotatably connected to the crank pin (14); a second link (20) pivotally connected at one end to the second member (19) by a pivot (32) and pivotally connected at the other end to the first link (18) by a pivot (30); an actuator lever (24) mounted for pivotal movement about a third axis; a third link (28) which is the same length as the second link (20) and which is pivotally mounted on the actuator lever (24) by means of a pivot (26) and pivotally connected at the other end at the pivotal interconnection (30) between the first and second links (18, 20); said actuator lever being movable to a position where the pivot (26) between the third link (28) and the actuator lever (24) is aligned with the pivot (32) between the second member (19) and the second link (20) thereby to stop the pivot (32) between the second member (19) and the second link (20) and hence the object moving along the arcuate length. 2. A mechanism according to claim 1 wherein the pivot (30) between the first (18) and second links (20) follows a path which intersects the third axis, there being provided a timing means for timing the movement of the actuator lever (24) so as to cause the pivot (26) between the third link (28) and the actuator lever (24) to be aligned with the pivot (32) between the second member (10) and the second link (20) when the pivot (30) between the first and second links (18, 20) coincides with the third axis. 3. A mechanism according to claim 1 or claim 2 wherein the first axis and the second axis are the same axis. 4. A friction welding apparatus incorporating the mechanism (10) claimed in claim 1 or claim 2.

Inventors: GODDARD, JOHN
Applicants: ROLLS-ROYCE PLC
Application year: 1988
Main classification: B23K20
IPC codes: F01D5, B23K20