No description available.

No description available.

The aim of this research was to develop an adaptive quality control strategy for robotic gas metal arc welding of thin steel sheets. Statistical methods were used to monitor and control the quality of welds produced. The quality of welds cannot be directly measured during welding. It can however be estimated by correlating weld quality parameters to relevant process variables. It was found sufficient to do this using welding current and voltage transient signals only. The strategy developed was problem solving oriented with emphasis on quality assurance, defect detection and prevention. It was based on simple algorithms developed using multiple regression models, fuzzy regression models and subjective rules derived from experimental trials. The resulting algorithms were used to control weld bead geometry; prevent inadequate penetration; detect and control metal transfer; assess welding arc stability; optimise welding procedure; prevent undercut; detect joint geometry variations. Modelling was an integral part of this work, and as a feasibility study, some of the models developed for process control were remodelled using 'Backpropagation' Artificial Neural Networks. The neural network models were found to offer no significant improvement over regression models when used for estimating weld quality from welding parameters and predicting optimum welding parameter. As a result of the work a multilevel quality control strategy involving preweld parameter optimisation, on line control and post weld analysis was developed and demonstrated in a production environment. The main emphasis of the work carried out was on developing control models and means of monitoring the process on-line; the implementation of robotic control was outside the scope of this work. The control strategy proposed was however validated by using post weld analysis and simulation in software.

The last decade has seen a considerable growth in the exploitation of deep sea mineral reserves. Accompanying these developments has come the need for suitable underwater repair and uainten-nce techniques. one such technique involves the use of fusion welding processes in localised dry high pressure environments created around weldments. Pressure chambers at Cranfield have been employed to simulate this sitiu. ation. These have been used to investigate the influence of ambient pressure (1 to 45 bars) on gas-tungsten arcs. The study has been of a basic nature with emphasis on arc characteristics and arc structure. Special attention is given to the argon TIG arc although helium TIG arcs and constricted argon-tungsten arcs have also been examined. Arc characteristics are reported in terms of arc appearance and modes, electrical characteristics and weld bead studies. The investigation of arc structure is concerned with gaining an understanding of observed characteristics. This has involved experimental and theoretical developments. Experimental techniques used include, electrostatic probes, calorimetry and the measurement of total power radiated from an arc. Models developed here have successfully explained many of the experimental findings and special emphasis has been directed at understanding gas flow in the column and arc stability. Much of the work included in this thesis has implications for the development of underwater welding procedures. Results presented should also contribute to gaining a better understanding of arcs operating under normal ambient conditions. However, these aspects are not discussed in any detail as the main emphasis has been placed on documenting and explaining the influence of pressure on gas-tungsten arcs.

No description available.

No description available.

Forging provides an elegant solution to the problem of producing complicated shapes from heated metal. This study attempts to relate some of the important parameters involved when considering, simple upsetting, closed die forging and extrusion forging. A literature survey showed some of the empirical graphical and statistical methods of load prediction together with analytical methods of estimating load and energy. Investigations of the effects of high strain rate and temperature on the stress-strain properties of materials are also evident. In the present study special equipment including an experimental drop hammer and various die-sets have been designed and manufactured. Instrumentation to measure load/time and displacement/time behaviour, of the deformed metal, has been incorporated and calibrated. A high speed camera was used to record the behaviour mode of test pieces used in the simple upsetting tests. Dynamic and quasi-static material properties for the test materials, lead and aluminium alloy, were measured using the drop hammer and a compression-test machine. Analytically two separate mathematical solutions have been developed: A numerical technique using a lumped-mass model for the analysis of simple upsetting and closed-die forging and, for extrusion forging, an analysis which equates the shear and compression energy requirements to the work done by the forging load. Cylindrical test pieces were used for all the experiments and both dry and lubricated test conditions were investigated. The static and dynamic tests provide data on Load, Energy and the Profile of the deformed billet. In addition for the Extrusion Forging, both single ended and double ended tests were conducted. Material dependency was also examined by a further series of tests on aluminium and copper. Comparison of the experimental and theoretical results was made which shows clearly the effects of friction and high strain rate on load and energy requirements and the deformation mode of the billet. For the axisymmetric shapes considered, it was found that the load, energy requirement and profile could be predicted with reasonable accuracy.

No description available.

No description available.

No description available.