Browsing by Author "Norrish, J."
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Item Open Access Automated off-line programming for Rapid Prototyping using Gas Metal Arc Welding(Cranfield University, 1995-06) Ribeiro, A. F. M.; Norrish, J.; McMaster, R.Rapid Prototyping is a recent CAD/CAM based manufacturing technique which produces prototypes of components in a fraction of the time normally required. This technique normally involves drawing the part as a 3 Dimensional solid model using a CAD program and then 'printing' it in 3 Dimensions. The raw material can be a photopolymer or thermoplastic which solidifies when in contact with light. Other materials are available although producing the final parts a 100% metal is not very usual. Some disadvantages of these techniques are: a) 100% metal prototypes cannot normally be made directly. b) only prototypes can be produced instead of the final component. c) machine size limits the size of the final component. d) very thin layers are deposited. This makes the build up more time consuming and mostly suitable to small components. The main objective of this work was to overcome these disadvantages by creating a new Rapid Prototyping technique using Robot Fusion Welding. In the pre-production phase, it is important to make a prototype not only for visualisation but also to test and assess it in its real function. Therefore, prototyping in resin a component which is going to be made in metal has no use for assessing purposes. This technique, besides making the prototype in metal can also be used as a production technique to make the real usable final component. It even allows the use of different metals along its structure in the welding filler wire is changed. This makes it possible to have different structural characteristics in the same component a required. None of the slicing algorithms developed for other Rapid Prototyping processes were applicable to this new technique and therefore a new slicing concept (and routine) was created specifically. I addition, an interface for off-line programming and quality documentation was evolved. The technique developed has been tested by fabricating several 'test' components and both the dimensional accuracy and component integrity have been evaluated and proved to be successful.Item Open Access The coupling mechanisms in the CO2 laser welding of copper(1994) Gouveia, H. N.; Norrish, J.The CO2 laser is a potentially powerful tool for welding, allowing high integrity joints to be produced with minimal thermal damage and high joint completion rates. Its use in the joining of reflective, high conductivity materials, such as copper is, however, limited. The current work examined the high power CO2 laser welding of oxygen free high conductivity copper and in particular the coupling mechanisms which appear to control the consistency of the process. The role of the plasma control jet was found to have a fundamental influence on the coupling behaviour. Due to the practical problems of direct observation of the jet gas flow during welding, the process was modelled using a flow simulation package. The results of the simulation enabled a satisfactory theory for the coupling mechanism to be developed. Plasma plume formation and maintenance during the welding process appeared to be responsible for coupling and to occur by a non-conventional mechanism. The theory explains the anomalies in previous work and indicates how the process consistency may be improved.Item Open Access Objective on line assessment of the performance of flux cored wires by real time computer based monitoring(1993-04) Chawla, Kawalprit Singh; Norrish, J.The aim of this research was to devise an innovative technique to obtain an objective assessment of the quality performance of tubular cored wires by sensing and measuring the signals available during welding. The work comprised: Identification of the parameters to assess. A study of the different monitoring techniques. Design of specific quality evaluation methods. The production of a system which allowed a quality index of welding performance to be obtained. Initially, the arc voltage, arc current, wire feed rate, arc light and arc sound signals were identified as possible sources of useful information. After a useful technique was accepted, the non-useful techniques were abandoned and a quality measuring instrument was built. The work involved development of statistical analysis techniques, Fast Fourier Transforms and mathematical modelling. A new approach to process modelling was devised which provided an objective and very flexible method of assessing, comparing and developing welding consumables. The final system was evaluated against conventional subjective assessment techniques and very good correlation was obtained.Item Open Access Objective on line assessment of the performance of flux cored wires by real time computer based monitoring(1993-04) Chawla, Kawalprit Singh; Norrish, J.The aim of this research was to devise an innovative technique to obtain an objective assessment of the quality performance of tubular cored wires by sensing and measuring the signals available during welding. The work comprised: Identification of the parameters to assess. A study of the different monitoring techniques. Design of specific quality evaluation methods. The production of a system which allowed a quality index of welding performance to be obtained. Initially, the arc voltage, arc current, wire feed rate, arc light and arc sound signals were identified as possible sources of useful information. After a useful technique was accepted, the non-useful techniques were abandoned and a quality measuring instrument was built. The work involved development of statistical analysis techniques, Fast Fourier Transforms and mathematical modelling. A new approach to process modelling was devised which provided an objective and very flexible method of assessing, comparing and developing welding consumables. The final system was evaluated against conventional subjective assessment techniques and very good correlation was obtained.Item Open Access The prediction of risk of welding defects at the procedure stage using computer knowledge based systems.(Cranfield University, 1992-08) Da Costa, S. C.; Norrish, J.The purpose of this research was to develop a methodology to evaluate the likelihood of defective welds as a procedure proposal is entered into a computerised database system. The approach developed was assessed for hydrogen induced cold cracking (HICC) since this defect is a major problem in welding technology. An expert system was used to implement the methodology. The information for the expert system knowledge base was partly gathered from previous work in this area. The technique necessary to analyze and incorporate knowledge was organized in a structured form including the major area to be attacked. The final system was implemented using an expert system shell. The global task of analyzing a welding procedure was broken-down into three different stages. A welding procedure specification comprised the first stage. In the second stage, an interface between the expert system software and a database was implemented. Having proved the feasibility and advantages of integrating the expert system shell with a relational database the remainder of the work was devoted to the development of a strategy for operating the expert system and in particular dealing with uncertainty. Detailed validation of the knowledge base and the system as a whole were confined to a single defect type in the belief that the modularity of the system would allow extension to other defect types and the strategies developed in the present work should it be applicable. Results have shown that the system performs well in the specified area. Validation trials using simulated welding conditions generated by the expert system have shown a very good correlation with practical results for different classes of steels. The integration between approved welding procedure records and procedure qualification records could be the basis for a complete welding database management. Practical application of this system could be extended for educational purpose and training facilities.Item Open Access 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.Item Open Access Process monitoring and adaptive quality control for robotic gas metal arc welding(Cranfield University, 1995-06) Ogunbiyi, T. E. B.; Norrish, J.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.