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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.

Capacitor discharge welding (CDW) is a rapid solidification joining process under the influence of one-dimensional thermal gradients. Although CDW is useful for joining small parts and dissimilar metals, CD welded joints have a large variability in weld strength. CDW is not widely accepted because of a lack of automated process control. Studying the sources of variability in the CDW process can guide the automation of CDW. Therefore, the objectives of this study were to investigate sources of variability that affect weld strength and to generate a model to predict the weld strength variability in CDW. The source of variability was investigated by using screening experiments. Four different materials, stainless steel, Nitronic 50 Steel, copper, and low oxygen copper (C101), were selected to represent various levels of thermal conductivity and absorbed gas content. Thermal conductivity, percentage of gas content absorbed, diameter, and welding time were treated as the independent variables while the dependent variables were the standard deviation of CD weld strength as a percentage of base material strength and the mean of CD weld strength as a percentage of base material strength. A screening experiment and a statistical analysis of the data were used to develop a predictive model of the weld strength variability in CDW. Electron photomicrographs of weld fracture surfaces and dynamic current and resistance curves for each welding cycle were used to support conclusions from the statistical analysis. Conclusions of this study are that thermal conductivity and absorbed gas content do have a significant influence on weld strength variability in CDW. / Graduation date: 1999

Automation of Capacitor Discharge Welding (CDW) has not been investigated in industry due to the limited understanding of the process. The US Department of Energy's Albany Research Center (ALRC) has done an extensive study of the process and reported applications of welds in the manufacture of electro-mechanical products such as relays and circuit-breakers. The main purpose of this work was to investigate automation of the load/unload cycle of CDW. An automatic CDW machine was built with real-time quality monitoring capabilities. Tooling and fixtures were fabricated for joining silver to brass components used in a circuit breaker assembly. A machine controller was used to automatically sequence the process and the actuators. Computer-based instrumentation was developed for on-line data acquisition and quality monitoring of the weld. This demonstrational setup shows that the equipment can be compact and the process can be easily automated for high production rates. The automation architecture developed can be used as a general model for automating CDW operations in other environments. The automated CDW system was tested by welding silver contacts to brass brackets at different parameter settings. Metallographic examination of the resultant capacitor discharge (CD) welds (made by the automated CDW system) revealed the formation of continuous metallurgical bonds between silver and brass. A comparison of CD welds made by the manual and the automated system was performed to determine the effect of CDW automation on weld quality. The welds were also found to be superior to resistance welds. / Graduation date: 1997

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A survey of robotized seam-tracking techniques was conducted in preparation for a project consisting of using an infrared camera on a robot for on one side collect continuous weld images for NDT inspection and on the other one track the weld joint. The tracking system can be used to discover the position of the weld bead without previous information. The robust system is outlined, along with its merits and disadvantages.

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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The conceptual design of a fixtureless reconfigurable automated spot welding system for manufacturing subassemblies for residential circuit breakers was investigated. This research was aimed at developing a possible low cost automation alternative to a South African industrial manufacturer, which is presently heavily dependent on personnel for manual assembly of their core products. System reconfiguration allows for the assembly of a range of subassemblies with geometric component variation on a given system configuration, as well as the potential for the system to be reconfigured to assemble other ranges of circuit breaker subassemblies. The subassembly selected as focus consists of six different components, which vary geometrically from one product variant to another. A fixtureless approach was selected, to minimise reconfiguration down time and the need for reconfigurable fixtures since reconfigurable fixtures have not found significant acceptance in industry. This varies from a fixture-based approach, which was considered in related research. The conceptual assembly system presented here consists of the following modules: a flexible vision based part feeder, twin 6 DOF robotic manipulators each with a multipurpose gripper, and a stationary spot welding station. Critical conceptual design elements were further investigated to refine their selection and confirm feasibility with respect to the target industry application. This process ended with a preliminary cost estimate which served as a basis for comparison between the fixtureless, fixture-based and present manual assembly process. The fixtureless concept was overall more expensive than the fixture-based concept, primarily because of the limits to production throughput. The fixtureless concept was however cheaper than the present manual assembly approach but had a far longer payback period than desired by the industry. The complexity and possible uncertainties of the concept combined with the long payback period indicated that the fixtureless concept is not suitable for the target application. / AFRIKAANSE OPSOMMING: Die konsepsionele ontwerp van 'n setmaatlose herkonfigureerbare outomatiese puntsweisstelsel vir die vervaardiging van subsamestellings van huishoudelike stroombrekers is ondersoek. Hierdie navorsing is gemik op die ontwikkeling van 'n moontlike lae koste outomatiese alternatief vir 'n Suid Afrikaanse industriële vervaardiger, wat tans sterk afhanklik is van werkers wat die montering van hul kern produkte met die handsamestelling doen. Stelsel herkonfigurasie laat die samestelling van 'n reeks subsamestellings, met geometriese komponentvariasies, op 'n gegewe stelsel toe, asook die potensiaal om die stelsel te herkonfigureer om ander reekse van stroombreker-subsamestellings te monteer. Die subsamestelling wat as fokus gekies is, bestaan uit ses verskillende komponente met geometriese verskille van tussen produkvariante. 'n Setmaatlose benadering is gekies ten einde aftyd vir herkonfigurasie en die noodsaaklikheid van herkonfigureerbare setmate te minimeer, omdat laasgenoemde nie noemenswaardig deur die industrie aanvaar word nie. Hierdie benadering verskil van 'n setmaat-gebaseerde benadering wat in verwante navorsing ondersoek is. Die konsepsionele monteringstelsel wat hier aangebied word, bestaan uit die volgende modules: 'n plooibare, visiegebaseerde voerapparaat; dubbele sesvryheidsgraad robotiese manipuleerders, elk met 'n veeldoelige gryper; en 'n statiese puntsweisstasie. Kritiese elemente van die konseptuele ontwerp is verder ondersoek om hul keuses te verfyn en uitvoerbaarheid in die teiken industriële toepassing te bevestig. Hierdie proses is afgesluit deur 'n voorlopige kosteraming wat gedien het as 'n basis vir die vergelyking van setmaatlose, setmaat-gebaseerde en die huidige handsamestellingstelsels. Die setmaatlose konsep was oorhoofs duurder as die setmaat-gebaseerde konsep, hoofsaaklik as gevolg van beperkings op die produksie-deurset. Die setmaatlose konsep was egter goedkoper as die huidige handmonteringsproses, maar het 'n veel langer terugbetalingstydperk as wat deur die industrie verlang word. Die kompleksiteit en moontlike onsekerhede van die konsep, gepaard met die lang terugbetalingstydperk, dui daarop dat die setmaatlose konsep nie vir die teiken toepassing geskik is nie.