Towards the understanding of the transient behaviour and sources of variability on the process outcomes in inertia friction welding

Raimondi, Luca (2021) Towards the understanding of the transient behaviour and sources of variability on the process outcomes in inertia friction welding. PhD thesis, University of Nottingham.

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The difficulty in creating high-quality joints in high-strength/high-temperature materials for aerospace applications fostered the interest in solid-state friction-based joining techniques. Among these, inertia friction welding (IFW) found numerous industrial applications to join axisymmetric components since highly repeatable and fully automated, does not require filler material, shielding gas or vacuum, produces a small heat-affected zone and is not affected by bulk melting. Two workpieces, one rotating and the other stationary, are pressed together and the frictional heat generated at the weld interface causes a localised plastic deformation and their junction.

IFW found large interest among researchers and several studies focused on the modelling of the thermo-mechanical evolution of the joint to predict the welding response to changes in process parameters. To cope with the complexity of the phenomena occurring during welding, these models usually rely on simplifications in term of weld geometry, alignment and interaction between the workpieces, machine behaviour, process loads and clamping conditions. In addition, despite many studies showed that dynamic effects can deeply affect the process evolution and the quality of the outcomes in manufacturing processes that share similarities with IFW, no study presented a satisfactory dynamic analysis of IFW.

To fill these research gaps, three main objectives were addressed: (i) development of a novel monitoring system for the in-process characterisation of the IFW machine that can act as a diagnostic tool; (ii) investigate the machine response to the process conditions and assess the validity of the axisymmetric assumption conventionally adopted to study IFW; (iii) modelling the effect of the imperfect contact between the workpieces on the pressure distribution at the weld interface and the dynamic behaviour of the system.

The monitoring system developed is a significant step forward from the existing systems. In fact, the simultaneous measurement of complementary parameters related to the weld evolution provided a holistic view of the process that proved fundamental in giving physical meaning to the phenomena observed. From data extracted with a set of rundown tests and steel welds, a non-negligible relative runout between the headstock and tailstock was measured. The imperfect contact between the workpieces caused by the runout was correlated to a pressure variation in the circumferential direction at the weld interface and radial non-axisymmetric loads particularly evident in the initial stages of the process. These findings are important because not only differ from the idealised conditions conventionally assumed but also, when combined with the compliance of the machine, can foster a larger misalignment.

This research allowed to shed light on the actual interaction between the workpieces and point out that when local phenomena at the weld interface need to be evaluated, the traditional axisymmetric assumption can fail in providing realistic results. In addition, the versatility of the monitoring system makes it ideal as a research platform for further studies and tool to assess the equivalency of different machines.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Bennett, Christopher
Axinte, Dragos
Gameros, Andres
Keywords: Inertia friction welding, Solid-state joining, Monitoring system, Rotordynamics, Rotor-bearing system, Finite element method
Subjects: T Technology > TJ Mechanical engineering and machinery
T Technology > TL Motor vehicles. Aeronautics. Astronautics
Faculties/Schools: UK Campuses > Faculty of Engineering
UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Item ID: 64321
Depositing User: Raimondi, Luca
Date Deposited: 11 Dec 2023 10:27
Last Modified: 11 Dec 2023 10:27

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