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CMT+P welding is less susceptible to hot cracking than the MAG welding process due to use of low heat input properties. Solidification cracking was found in all weld specimens that had greater 0.39KJ/mm heat inputs. Cracking occurs because of the contraction stresses generates during cooling. Hydrogen cracking is found in HAZ with low heat input parameters, this type of cracking occurred because of very rapid cooling and therefore not enough time to allow the hydrogen to dissipate from the specimen. To eliminate this type of cracking the experiment could be repeated by adding heating during welding to control and reduce the cooling rate. Due to high carbon content in the steel and very fast cooling the microstructure of the weld is martensitic in the base metal as well as the HAZ. Microstructure in the weld and base metal is martensitic due to high carbon con-tent and rapid cooling. At low heat inputs dilution is less and therefore lower carbon content in weld pool. Better weld appearance and weld quality is achieved with CMT+P welding process than the conventional GMA welding processes because of the new wire movement technology during welding

The feasibility of fully automatic GMAW processes may rely on the development of sophisticated equipment to emulate the manual welding torch oscillation pattern or on the development of high level methods of control to prevent the appearance of defects, especially the lack of sidewall fusion. An intermediate solution is to optimise the weaving parameters of a conventional pattern oscillator in such a way as to minimise the level of rejection. A prototype of a computerised system to work with Pulsed-GMAW equipment, in the vertical-up position, was proposed to produce a minimal level of rejection for welds in plates up to 25 mm thick. The system basically consists of optimised mode control algorithms, based on theoretical and experimental models of weld pool behaviour. Three tasks are performed by the system; the selection of parameters for an optimum working point, an off-line simulation of the operation and real-time error monitoring of the process. Statistical experimental modelling was applied in order to build most of the optimised models, because of the large number of variables to be treated and their complex inter-correlation. The welding variables were correlated with single responses. Partial and Correlation Analysis techniques were used to discover the relationship between the variables and the responses. Regression Analysis was then applied as a means of obtaining the 'weight' of the most significant variables. Finally, since some variables were found to be collinear, a corrective technique for biased variables was employed. Acceptance criteria for bead shapes were proposed and assessed. The effect of the oscillation parameters and other welding variables on the bead formation was analyzed and an operational 'envelope' for the parameters determined. A theoretical approach to predict the occurrence of poorly shaped beads, due to the lack of metal bridge between the joint walls, was successfully developed and applied in parallel with the statistical experimental methods. Equations for optimising the bead shape and for determining the operational envelope contours were subsequently generated and evaluated. An extension of the system to an actual adaptive control scheme was discussed and sensors and signals to be used were evaluated. Finally, a process instability phenomenon in long test plates was identified and investigated. This instability may prevent the use of GMA W in some conditions in the vertical-up position.

Argon TIG arc temperatures have been measured for a wide range of arc parameters using the 'Fowler-Milne' spectroscopic method. Prompted by widespread disagreement amongst temperatures published by previous groups, a detailed investigation has been carried out into those experimental and theoretical aspects of the measurement process that may have led to incorrect results. The tests have included the variation of experimental parameters, the choice of Abel inversion procedure, and the calculation of argon species number densities and partition functions. The existence of equilibrium within the TIG arc has been investigated by determining temperatures with a number of argon emission lines. Significant differences 'in derived values of the temperatures were observed within 1mm of the tungsten cathode tip, smaller variations were observed over the remainder of the arc. The results indicate that large scale departures from a Boltzmann distribution amongst argon atom excited states exists close to the tungsten tip, deviations decrease with increasing distance from the tip but do not disappear completely. lt is believed that the breakdown of equilibrium within the argon TIG arc may help to explain the disagreement in temperatures obtained by past groups that have used spectroscopic methods. Despite evidence for non-equilibrium within the arc. results from previous groups suggest that derived values of .the temperatures are substantially correct in the main body of the arc. The detailed temperature maps provide useful information on temperature changes with arc parameters for the purposes of modelling and understanding of the arc.

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, 2001. / Word processed copy. Summary in English. Includes bibliographical references (leaves 68-71). Also available online.

Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 106-108).

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, Cape Town, 2001 / Since the discovery of arc welding at the beginning ofthe century, metal transfer has been a topic ofresearch interest. Metal transfer can, in fact be related to weld quality, because it affects the arc stability. Furthermore, it determines the weld spatter, penetration, deposition rate and welding position. Gas Metal Arc Welding (also known as Metal Inert Gas- or MIG welding) is the most co=on method for arc welding steels and aluminurn alloys. Approximately 40% of the production welding in the country is accomplished by this process in which the thermal phenomena and melting ofthe solid electrode are coupled to the plasma arc and the weld pool. Thus the therrno- fluid behaviour of the electrode and detaching drops can have significant effects on the subsequent weld quality and production rate. The knowledge of how metal transfer affects this arc welding process is important for welding control and process automation, as well as in the development of improved welding consumables. Gas metal arc welding has a distinct feature, indicated by the results of Lesnewich [24], [23], that for most gases, there is a discrete metal droplet formation change between low and high current operations. Naturally the droplet size will have a significant influence on the properties ofthe welds. In globular transfer which occurs at low current, the welding electrode melts and produces large droplets (usually larger in diameter than the electrode wire diameter). This mode of transfer is associated with high spatter levels and thus undesirable in terms of welding economics. An increase in welding current will, for most welding! shielding gases, produce metal transfer with smaller droplets, which is termed spray transfer. This mode oftransfer is associated with high voltage and amperage settings, thus producing high deposition rates limited to the flaUhorizontal position.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 146-149).

Thesis (Ph.D.)--Tufts University, 2000. / Adviser: Charalabos Doumanidis. Submitted to the Dept. of Mechanical Engineering. Includes bibliographical references (leaves 118-124). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 133-139).