This thesis describes advancements in the modelling, optimisation, process control and mechanical performance of novel high deposition rate gas metal arc welding processes for large scale additive manufacturing applications. One of the main objectives of this study was to develop fundamental understanding of the mechanisms involved during processing with particular focus on single layer welds made of carbon steel using both pulsed-current gas metal arc welding and cold metal transfer processes. The effects of interactions between critical welding process variables and weld bead and plate fusion characteristics are studied for single and multi-layers. It was shown that several bead and plate fusion characteristics are strongly affected by the contact tip to work distance, TRIM, wire feed speed, wire feed speed to travel speed ratio, and wire diameter in pulsed-current gas metal arc welding. The arc-length control, dynamic correction and the contact tip to work distance are shown to strongly influence the weld bead geometry in the cold metal transfer process. This fundamental knowledge was essential to ensure the successful development of predictive interaction models capable of determining the weld bead geometry from the welding process parameters. The models were developed using the least-squares analysis and multiple linear regression method. The gas tungsten constricted arc welding process was utilised for the first time for out-of-chamber fabrication of a large scale and high-quality Ti-6Al-4V component. The main focus was, however, in the use of the cold metal transfer process for improving out-of-chamber deposition of Ti-6Al-4V at much higher deposition rates. The effect of the cold metal transfer process on the grain refinement features in the fusion zone of single layer welds under different torch gas shielding conditions was investigated. It was shown that significant grain refinement occurs with increasing helium content. The morphological features and static mechanical performance of the resulting multi-layered Ti-6Al-4V walls were also examined and compared with those in gas tungsten constricted arc welding. The results show that a considerable improvement in static tensile properties is obtained in both testing directions with cold metal transfer over gas tungsten constricted arc welding. It was suggested that this improvement in the mechanical behaviour could be due to the formation of more fine-grained structures,which are therefore more isotropic. The average ultimate tensile strength and yield strength of the as-deposited Ti-6Al-4V material processed via cold metal transfer meet the minima specification values recommended for most Ti-6Al-4V products. Neutron diffraction technique was used to establish the effect of repeated thermo-mechanical cycling on the generation, evolution and distribution of residual stresses during wire and arc additive manufacturing. The results show a significant redistribution of longitudinal residual stresses along both the substrate and multi-bead with repeated deposition. However, a nearly complete relaxation occurs along the built, once the base plate constraint is removed.

This work deals with the description and analysis of suitable methods for measurement of non-periodical high-level current pulses. For pulsed current source design and development a suitable measurement system is required. In this work shunt resistor, Rogowski sensor and magneto-optic sensor are presented. The analysis of their properties is performed in order to design a suitable sensor for test current pulse measurement. A design of Rogowski coil sensor has been made. An experimental measurement of current pulses with short time relations has been performed. The suitability of the coil sensor for non-harmonic waveforms measurement has been evaluated on the basis of measurement results. In case of the magneto-optic sensor a concept utilizing an optical fiber has been proposed. The design of the sensor has been performed also. Individual parts of the sensor were verified. Experimental magneto-optic sensors have been built and their properties have been studied.

The theoretical part of the thesis deals with the explanation of the actions that occur during the stimulation of tissues with the electric current. A significant analogy with electrical circuits is used to describe the phenomena at the molecular and cellular level. The models of membrane and cell are necessary for understanding the behaviour of more complex structures, such as tissues and organs. A considerable attention is paid to the conditions of electrical stimulation which bring about response in the stimulated area. Next, the cumulative effect of the subthreshold stimulation is analysed. The mechanisms of common treatment effects of the electrotherapeutic methods are outlined. The research results in the practical part of the thesis – the design for a microstimulator. Properties of the microstimulator and compliance with standard requirements are verified by testing the electromagnetic compatibility and electrical safety, conducted by the Institute for testing and certification, JSC. The effects of microstimulation on living organisms are experimentally investigated on horses, in collaboration with the Veterinary and Pharmaceutical University. For the first time, thermodynamic sensors are used for the objective assessment of the microstimulation therapeutic effect. These miniature sensors are placed on the horse´s front legs and monitor the changes in thermal activity while only one limb is really stimulated and the other is just considered as a reference. Comparison and statistical evaluation of the measured signals could provide a more detailed view of the thermal changes within the stimulated area, which is significantly related to blood circulation in limbs, and with the support of the reduction of edema. The course of the experiment which deals with the effect of microstimulation on edema of the horse´s legs caused by minor injuries (tendinitis, sprains, etc.), is documented in photographs or videos that are significant for possible evaluation of the effectiveness of the stimulation in this application.