FRICTION WELDING

Abstract

A method for friction welding of inter alia coarse grain superalloy components, involving conditioning a shear zone of components to be welded by; a) pre-determining temperature profile for which the material of the shear zone of the components approaches viscoplasticity but does not undergo undesirable phase transformations, b) introducing friction at one or both surfaces of the components to be welded to provide a pre-defined quantum of energy sufficient to generate a peak temperature of the temperature profile at that surface whilst simultaneously applying pressure to the surfaces which is below a pressure which will cause upset at the surface, c) withdrawing the friction and/or pressure allowing the heat to disperse by conduction through the shear zone; d) after the temperature at the surface falls below peak temperature, repeating steps b) and c); and repeating step d) as necessary until the pre-determined temperature gradient is achieved throughout the shear zone.

Claims

1. A method for conditioning a shear zone of components to be welded in a friction welding process comprising; introducing friction between the surfaces of the components to be welded, simultaneously applying a pressure to the surfaces which is below a pressure which will cause upset at the surface, withdrawing the friction and/or pressure allowing the heat to disperse by conduction through the shear zone; after the temperature at the surface has fallen, repeating the cycle of applying friction and pressure and withdrawing the friction and/or pressure as necessary until the shear zone is conditioned for upset.

2. A method as claimed in claim 1 comprising; a) pre-determining a temperature profile for which the material of the shear zone of the components approaches viscoplasticity but does not undergo undesirable phase transformations, b) introducing the friction at one or both surfaces of the components to be welded to provide a pre-defined quantum of energy sufficient to generate a peak temperature of the temperature profile at that surface whilst simultaneously applying the pressure to the surfaces which is below a pressure which will cause upset at the surface, c) withdrawing the friction and/or pressure allowing the heat to disperse by conduction through the shear zone; d) after the temperature at the surface has fallen below the peak temperature, repeating steps b) and c); and repeating step d) as necessary until the pre-determined temperature gradient is achieved throughout the shear zone.

3. A method as claimed in claim 2 further comprising; e) after the peak temperature has been reached, applying an upsetting force to the surfaces to be welded resulting in concomitant generation of burn-off at the surface; f) maintaining the upsetting force as the surfaces come to rest and commence cooling to consolidate the weld; and g) removing the upsetting force.

4. A method as claimed in claim 1 wherein the steps of applying and withdrawing the friction and/or pressure involve dynamically adjusting a relative rubbing speed at the surfaces to be welded to follow a predetermined rubbing speed profile.

5. A method as claimed in claim 1 wherein the steps of applying and withdrawing the friction and/or pressure involve dynamically adjusting a forge force at the surfaces to be welded to follow a predetermined forge force profile.

6. A method as claimed in claim 1 wherein the steps of applying and withdrawing the friction and/or pressure involve monitoring of the temperature at or near the surfaces to be welded and adaptively controlling the amount of frictional heat applied in response to changes in the monitored temperature.

7. A method as claimed in claim 1 wherein applying friction involves rotating one of the surfaces relative to the other using conventional rotary friction welding apparatus.

8. A method as claimed in claim 2 wherein step a) involves monitoring changes in temperature at various positions along the component whilst a known amount of energy is introduced at the surfaces to be welded and/or investigating the presence of undesirable phase changes in the shear zone after the energy has been introduced.

9. A method as claimed in claim 2 involving providing a machine controller to control operation of a machine to introduce energy to the surfaces to be welded at a predetermined rate to create the pre-determined temperature profile in the shear zone.

10. A method as claimed in claim 9 wherein the machine controller incorporates a feedback loop whereby it continually monitors parameters of the machine for consistency with a stored temperature profile model and adjusts them when they deviate from the model.

11. A method as claimed in claim 9 wherein the machine controller controls the spin rate of a flywheel of a rotary welding machine.

12. A method as claimed in claim 9 wherein the machine controller further controls the application of an upsetting force by the machine.

13. A method as claimed in claim 9 wherein the machine controller is further operable to control the subsequent steps e), f) and g) of claim 2 in sequence immediately upon completion of steps a) to d) of claim 1.

14. A method as claimed in claim 3 further comprising the step of removing “upset” material displaced at the weld interface, inspecting weld and surface finishing.

15. A method as claimed in claim 1 wherein the components comprise parts just one of which comprises a coarse grain superalloy.

16. A welded component for a gas turbine engine welded in accordance with the method of claim 1.

17. A component as claimed in claim 16 which is selected from; a blade integrated disc (blisk); a high pressure (HP), intermediate pressure (IP) or low pressure (LP) turbine disc; a drum; a shaft, the component comprising titanium, steel and/or superalloys.

18. A gas turbine engine comprising one or more components in accordance with claim 16.

19. An apparatus including a computer programmed to control a welding machine to perform the method of claim 2.

20. An apparatus including a computer programmed to control a welding machine to perform the method of claim 3.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0044] An embodiment of the method is now further described with reference to the accompanying Figure in which;

[0045] FIG. 1 shows graphically the temperature gradient introduced to a shear zone of a component welded in accordance with an embodiment of the invention;

[0046] FIG. 2 shows a logic chart setting out process steps and a decision tree for controlling a temperature gradient introduced into the shear zone in accordance with an embodiment of the invention;

[0047] FIG. 3 shows a cyclic schematic for the weld shear zone represented in FIG. 1.

DETAILED DESCRIPTION OF FIGURES AND EMBODIMENT

[0048] The following summarises a practical embodiment of the method of the invention using a conventional rotary friction welding machine programmed with an inertia friction weld (IFW) auto-cycle. [0049] 1. With weld components aligned, run up the spindle (with/without flywheel) [0050] 2. Make one or more contacts between the faying surfaces until the required preheat is met; methods to determine this include but are not limited to: [0051] a. use of thermal measurement (e.g. thermocouples, pyrometry) to monitor temperature and control feedback loop AND/OR [0052] b. modelling to calculate energy input (work done, thermal conductivity, deceleration of flywheels etc.) AND/OR [0053] c. pre-determined cycle/method based on prior knowledge.

[0054] NOTE: The flywheel speed must not drop to below a speed where any time taken to re-spin exceeds a limit required to maintain the desired temperature profile in the part. [0055] 3. Decouple or reduce pressure (if required) [0056] 4. Adjust spindle speed AND/OR inertia to predetermined settings for welding (if required) [0057] 5. Conduct weld cycle

[0058] Methodology for step 2 is further detailed in FIG. 1.

[0059] A machine controller is configured to use the torque and/or effective friction and/or temperature and/or energy and/or time based model to measure the temperature gradient at the weld interface. As an alternative, power, torque energy or effective friction might be measured or derived from flywheel deceleration in the case of an inertia weld. A feedback loop in the controller operates then to modulate the pressure applied by the machine in order to maintain a bounding effective friction co-efficient (or corresponding torque or power as a proxy therefor) at the weld interface. The pressure applied in this pre-conditioning step is significantly low compared to the pressure required to upset the weld. This avoids excessive undesirable microstructural change on a macro level during the pre-conditioning step. Typically the energy in the pre-conditioning phase will be additional to the energy available at the required conventional welding speeds of available inertia at conventional weld pressures. For example in a conventional superalloy weld requiring 120% of available energy at maximum inertia and preferred rotational speeds requires the extra 20% of energy to be delivered during the pre-conditioning phase using a lower pressure and higher rotational speed. If the higher rotational speed for pre-conditioning is beyond the limits of the flywheel or machine capability then a stepped re-spin can be used (refer to steps 3 and 4 above).

[0060] FIG. 2 illustrates an example of the logic applied by a controller in performing a method in accordance with the invention. In the shown embodiment, the controller controls the speed and axial movement of a flywheel in a rotary friction welding process. In the Figure, E represents energy input and A represents unit area. By following the steps in the logic chart, the controller can generate a plurality of temperature gradients across the shear zone. These temperature gradients are represented in FIG. 1 as a number of curves. The process enables the controller incrementally to move towards a profile which achieves the required peak temperature of step a) without exceeding that temperature within the shear zone. Once that temperature profile is achieved, then the component can be welded from the pre-conditioned workpieces.

[0061] Relative to the energy/power/inertia limits of existing friction welding machines, the modulation and feedback/control of pressure during a pre-conditioning phase in accordance with the method of the invention provides the following benefits: [0062] 1. Extends the capability of existing friction welding machines. [0063] 2. Reduces the peripheral contact speed at the point of the upsetting phase in order to weld within a preferred welding speed range. [0064] 3. Reduces the energy required during the upsetting phase of the IFW cycle (e.g. for large high gamma prime vol. fraction Ni parts). [0065] 4. A successful weld with limited inertia capability (linked to 1). [0066] 5. The ability to weld larger faying surface areas. [0067] 6. In a direct drive system, reducing the required torque for a given system. [0068] 7. Influences the cooling phase as a result of creating a desired temperature profile for managing residual stress or microstructural transformations (e.g. martensite formation in steel). [0069] 8. The method can be used to produce a desired cooling rate for a given size of HAZ.

[0070] FIG. 3 shows the cyclical variations over time of rotational speed, axial thrust and upset occurring during the weld process represented in FIG. 1 when the weld process is performed using inertia weld equipment. As can be seen rotational speed and thrust are cycled together with a maximum thrust applied at peak speeds resulting in a gradual conditioning of the shear zone represented by the gradual increase in upset. When the desired temperature gradient has been achieved across the shear zone, full upset and welding can be achieved.

[0071] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the scope of the invention as defined by the appended claims. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.