Design and Integration of Ultrasonic Vibration Systems in Wire Arc Additive Manufacturing

This thesis investigates the influence of ultrasonic vibrations on the as-built microstructure of Ti-6Al-4V components manufactured using the Wire Arc Additive Manufacturing process with Cold Metal Transfer welding technique. A test setup was developed to introduce vibrations into the weld pool using ultrasonic transducers. These vibrations were intended to induce cavitation within the weld pool, with the implosion of cavitation bubbles aimed at refining and isotropizing the columnar microstructure of multi-layer arc welding. An experimental series also included modifications to the test setup, resulting in five distinct configurations, to address potential factors such as transducer alignment, temperature effects, and electrical insulation. The final configuration consists of an ultrasonic transducer with piezoelectric elements that generate the vibrations from an electrical signal. This sinusoidal electrical signal is produced by a frequency generator and is magnified by a signal amplifier before being transmitted to the transducer. The resulting vibrations are propagated via an electrically insulating coupling element to a base plate, which carries the welding substrate and is mechanically decoupled from the welding table. In addition to the design of the test setup, a simplified finite element analysis was conducted to simulate wave propagation. The simulation applied a periodic pressure on a surface equivalent to the contact area of the transducer. Subsequent vibrometer tests, which measured displacements at 13 points on the physical test setup, revealed that the finite element analysis did not accurately replicate the real world scenario, due to simplifications made to the model. Welding experiments on 13 single wall structures, conducted under the influence of ultrasonic vibrations, showed little differences in micrographs or hardness tests compared to reference samples produced without ultrasonic vibrations. Therefore, further approaches and experiments are suggested.