Cranfield University at Silsoe (1975-2008)

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Browsing Cranfield University at Silsoe (1975-2008) by Supervisor "Apps, R. L."

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    Process modelling to establish control algorithms for automated GMAW
    (Cranfield University, 1991-09) Scotti, A.; Norrish, J.; Apps, R. L.
    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.
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    ItemOpen Access
    Welding C-Mn steels using the pulsed current MIG welding process
    (Cranfield University, 1986-03) Foote, W. J.; Apps, R. L.
    The welding of C-Mn steels using the pulsed current MIG welding process was investigated. Following initial work on the basic fusion characteristics, the process was applied to the production of closed butt joint linepipe welding and narrow gap welding (in the flat and H-V positions). The initial stage of the work covered the determination of pulse parameters for controlled metal transfer with a variety of wires and shielding gases. Basic bead-on-plate fusion characteristics were investigated 1n all welding positions and quantified in terms of the major welding variables of current and travel speed. Welding position was shown to have no effect on fusion behaviour. Successful full penetration closed butt root welds were produced in all welding positions. Heat input was shown to be the factor controlling bead dimensions. Close control over welding parameters are needed to maintain consistent bead sizes. Complete joint simulations were also made. The vertical-up technique was shown to give superior fusion characteristics with the process producing excellent quality results in all positions. Narrow gap MIG welding was shown to be feasible without wire manipulation at gap widths below 12 mm in the flat position. A wire manipulation technique gave excellent fusion characteristics with gap widths greater than 12 mm. A computer program was devised as a guide to the selection of process parameters and possible fusion behaviour. Modelling considerations showed that H-V position narrow gap welding would be feasible only with gap widths less than 10 ... A short experimental programme validated the predictions of fusion behaviour by the model and indicated the direction for future development work.