Friction bonding

Abstract: Apparatus and a method for attaching individual blades (2) to a disc rotor (4) of a BLISK is described. Blade blanks or preforms are gripped between adjustable jaws (6,8) of a rigid frame member (18) of a linear friction bonding machine, and are attached in a non-rotational friction bonding operation. Blade preforms may be finished to final airfoil shape in a further operation after attachment. The technique is suitable for repair work or original manufacture.

Description: The invention relates to apparatus for performing friction bonding operations. In particular, it concerns apparatus for performing a non-rotational frictional bonding operation. Prior art in the field of friction bonding is to be found in US-A-3,584,777 (Loyd) and EP-A1-0,290,134 (Rolls-Royce plc). US-A-3,584,777 discloses a tailstock for feeding a workpiece in a rotary friction welding application. The work is firmly held in blocks which are biased together by hydraulic and/or spring means. The block pressure is temporarily relaxed when fresh work is fed into the rear of the tailstock from a hopper and delivery means. EP-A1-0,290,134 concerns the friction welding of a blade to a disk by rubbing the blade in an oscillatory manner in an arcuate path on the disk, and relates in particular to a linkage of pivots and levers whereby the oscillatory movement of the blade may be brought to a sudden stop at a precise location on the disk by bringing one pivot into alignment with another. US-A-3,584,777 and EP-A1-0,290,134 do not address the problem of linear friction bonding, which is that of holding a workpiece securely as the frictional forces are suddenly reversed. In the rotary friction welding of US 3,584,777 these sudden reversals do not occur. An embodiment of the invention is described in detail hereinafter is particularly concerned with the manufacture or repair of a bladed disc, sometimes known as a BLISK. A bladed disc comprises a disc or wheel on the periphery of which there is attached or carried a multiplicity of blades. In a conventional rotor assembly the blades are attached to a disc or wheel by interlocking root fixtures. In bladed discs the blades are either formed integrally with the disc or are non-dismountably attached thereto. The present invention finds application for the manufacture or repair of assemblies in which the inter-blade spacing is very close and the blades may also be small. Such an example may be in the repair of a high pressure compressor bladed disc rotor. Small blades are also relatively fragile and may be easily damaged during a friction bonding operation which involves very large forces to produce the required frictional heating effects. Therefore, it is preferred to work with a blade blank or preform and to finish the blade to its final shape after bonding. According to the invention in its broadest aspect a blade or blade preform is attached to the rim of a bladed disc in a non-rotational friction bonding operation. According to one aspect of the present invention apparatus for linear friction bonding a first component, defining a longitudinal direction to a second component, includes a generally C-shaped frame member having a pair of longitudinally extending limb members arranged either side of the first component and jaw pieces adapted to positively engage opposite sides of the first component, and is characterised in that each limb member is provided with a channel extending longitudinally from its distal end and facing the corresponding channel of the other limb member, each channel being shaped to have a tapering cross-section as it extends longitudinally from its respective distal end, and each jaw piece is adapted to slide longitudinally within and to cooperate with a respective channel so that when the jaw pieces move in the channels away from the distal ends of the limb members the jaw pieces tend to grip the first component more positively. The invention and how it may be carried into practice will now be described in greater detail with reference by way of example to the accompanying drawings, in which: Figure 1 shows a schematic diagram of a blade replacement operation viewed in a radial direction, Figure 2 shows a view in the direction of arrows AA in figure 1. Referring now to the drawings, in which like parts have been given like references, the example illustrated involves the repair of a bladed disc, or BLISK, using a linear friction bonding operation. A blade preform or blank 2 is bonded to the periphery of disc 4, a fragment of which is shown in the drawing, at a predetermined location. Figure 1 shows such a blade preform 2 clamped between jaw pieces 6,8 at the start of a bonding operation. The preform 2 consists of solid block of metal of appropriate shape and size. At the leading and trailing edge regions 10,12 a considerable amount of sacrificial metal is left by which the jaw pieces 6,8 grip the preform 2. The edges are formed with angled faces for engagement by the jaw pieces 6,8. In figure 1 the radially outer ends of preforms 2 are shown hatched for easier reference. After finishing of the blade airfoil shape these end faces form the blade tip faces. The jaw pieces 6,8 are moveably located in channels 24,26 in the inner faces of limbs 14,16 respectively of a C-shaped frame 18. The jaw pieces 6,8 have angled grip faces, V-shaped in plan to grip the complementary angled faces on the leading and trailing edges of the preform 2. At the apex of the angled faces relatively deep grooves 20,22 are cut into the jaw pieces to provide the angled faces with a degree of resilience in gripping the preform. The jaw pieces 6,8 are located, as mentioned above, in channels 24,26 formed in the inner faces of the frame limbs 14,16. The jaw pieces are slideable longitudinally in the channels 24,26 in the direction of arrows 28,30.. Towards the distal end of each limb 14,16 the base of the channel and the abutting face of the respective jaw piece 6,8 are angled obliquely with respect to the longitudinal direction of movement 28,30. These angled surfaces converge towards the upper or closed part of the clamping frame so that by drawing the jaw pieces 6,8 upwardly in figure 2, in the direction of arrows 28,30, their grip on the blade preform 2 is tightened. The jaw pieces 6,8 may extend longitudinally in the directions of arrows 28,30 as shown in the drawings or may be attached to tensile members. The remote ends of the jaw piece extensions or the tensile members are connected to hydraulic tensioning means (not shown) which is energised to draw the jaw pieces upwardly to grip the preform. Clearly the clamping means may be released from the preform after a bonding operation by relaxing the tensioning force in the jaw pieces. The moveable clamping frame 18 also carries a ram 32 which bears against the tip face of blade preform 2 and applies the required upset force to effect bonding at the end of the frictional heating phase of the operation. It is preferred to replace a blade belonging to a BLISK rotor using this method as follows. First, the old or damaged blade is removed just above the peripheral surface 34 of the disc rim leaving a stub portion 36. The upper surface 38 of this stub is made flat and the foot of the replacement blade preform is bonded to it. The preform 2 is at least longer than the stub 36 due to the presence of the sacrificial gripping regions 10 and 12. It may be slightly wider also. The lower margin of the preform is therefore preferably chamfered so that lower surface 40 matches upper surface 38 of stub 36. The surface 40 may be made shaped for better control of the frictional heating phase. During the frictional heating phase of a bonding operation the clamping means containing the preform 2 is moved back and forth. Several directions of movement are available in the plane of the joint. The amplitude of this movement is small, generally only a few millimetres is required and is at a low frequency. For maximum rigidity the jaws of the clamping means are wider than the inter-blade spacing. Because of the resulting overlap the distance between the jaws must provide sufficient clearance for the chosen motion. The extra distance is easily provided for in the edge regions 10,12 on the preform 2. Thus, during the whole of a bonding operation clearance is maintained between the clamping means and adjacent blade tips. For maximum lateral rigidity the jaw pieces 6,8 are preferably flush with the face of the clamping means. Where the blades are closely spaced the clearance distance must be maintained to avoid blade damage. It follows, therefore, that the edge regions 10,12 of a blade preform which are intended to be engaged by the clamping means must be removed after bonding and before another blade may be bonded at an adjacent location. Alternatively, a number of blade preforms may be bonded sequentially at locations sufficiently far apart. In the illustrated case the minimum spacing is alternate locations. A whole BLISK could be manufactured, if desired, in this way by bonding blades at, say, alternate locations in a first operation, subsequently removing surplus metal and then bonding the remaining blades in a further operation. Finally, after the bonding operation, or operations if more than one blade preform is attached, the preform or preforms are finished to final blade airfoil shape by a further manufacturing operation. Surplus metal including that upset during bonding is removed at this stage, for example, by electro-chemical machining.

Claims: An apparatus for linear friction bonding a first component (2), defining a longitudinal direction (28,30) to a second component (4), the apparatus including a generally C-shaped frame member (18) having a pair of longitudinally extending limb members (14,16) arranged either side of the first component (2) and jaw pieces (6,8) adapted to positively engage opposite sides of the first component (2), characterised in that each limb member (14,16) is provided with a channel (24,26) extending longitudinally from its distal end and facing the corresponding channel (24,26) of the other limb member (14,16), each channel (24,26) being shaped to have a tapering cross-section as it extends longitudinally from its respective distal end, and each jaw piece (6,8) is adapted to slide longitudinally within and to cooperate with a respective channel (24,26) so that when the jaw pieces (6,8) move in the channels (24,26) away from the distal ends of the limb members (14,16) the jaw pieces (6,8) tend to grip the first component (2) more positively. An apparatus as claimed in claim 1 characterised in that each jaw piece (6,8) is provided with an angled grip face, V-shaped in plan, to grip a respective complementary angled face of the component (2). An apparatus as claimed in claim 2 characterised in that a groove (20,22) is provided in each jaw piece (6,8) at the apex of its respective angled grip face, so as to provide the angled grip face with a degree of resilience in gripping the first component (2) when the jaw piece (6,8) moves in, and cooperates with, the taper of its respective channel (24,26). An apparatus as claimed in any preceding claim characterised in that the C-shaped frame member (18) is provided with ram means (32) adapted to bear longitudinally against the first component (2) and to apply a required force to effect bonding between the first component (2) an the second component (4).

Inventors: DAINES JOHN WALKER, DAINES, JOHN WALKER
Applicants: ROLLS ROYCE PLC, ROLLS-ROYCE PLC
Application year: 1991
Main classification: B23K20
IPC codes: F01D5, B23K20