REAL-TIME MODEL PREDICTIVE CONTROL OF QUASI-KEYHOLE PIPE WELDING

Quasi-keyhole, including plasma keyhole and double-sided welding, is a novel approach proposed to operate the keyhole arc welding process. It can result in a high quality weld, but also raise higher demand of the operator. A computer control system to detect the keyhole and control the arc current can improve the performance of the welding process. To this effect, developing automatic pipe welding, instead of manual welding, is a hot research topic in the welding field. The objective of this research is to design an automatic quasi-keyhole pipe welding system that can monitor the keyhole and control its establishment time to track the reference trajectory as the dynamic behavior of welding processes changes. For this reason, an automatic plasma welding system is proposed, in which an additional electrode is added on the back side of the workpiece to detect the keyhole, as well as to provide the double-side arc in the double-sided arc welding mode. In the automatic pipe welding system the arc current can be controlled by the computer controller. Based on the designed automatic plasma pipe welding system, two kinds of model predictive controller − linear and bilinear − are developed, and an optimal algorithm is designed to optimize the keyhole weld process. The result of the proposed approach has been verified by using both linear and bilinear model structures in the quasi-keyhole plasma welding (QKPW) process experiments, both in normal plasma keyhole and double-sided arc welding modes

Advances in Plasma Arc Welding: A Review

The nature of welding in the aeronautical industry is characterized by low unit production, high unit cost, extreme reliability and severe service conditions. These characteristics point towards more expensive and more concentrated heat sources such as plasma arc, laser beam and electron beam welding as the processes of choice for welding of critical components. Among various precision welding processes, Plasma Arc welding has gained importance in small and medium scale industries manufacturing bellows , diaphragms etc because of less expensive and easy to operate. This paper reviews the works on Plasma Arc welding and associated phenomena such as Micro Plasma Arc Welding, Variable Polarity Plasma Arc welding and Keyhole Plasma Arc Welding. The review covers works carried out by various researchers on various metals using different modes of plasma arc

ROBUST GENERIC MODEL CONTROL FOR PARAMETER INTERVAL SYSTEMS

A multivariable control technique is proposed for a type of nonlinear system with parameter intervals. The control is based upon the feedback linearization scheme called Generic Model Control, and alters the control calculation by utilizing parameter intervals, employing an adaptive step, averaging control predictions, and applying an interval problem solution. The proposed approach is applied in controlling both a linear and a nonlinear arc welding system as well in other simulations of scalar and multivariable systems

NONLINEAR SYSTEM MODELING UTILIZING NEURAL NETWORKS: AN APPLICATION TO THE DOUBLE SIDED ARC WELDING PROCESS

The need and desire to create robust and accurate joining of materials has been one of up most importance throughout the course of history. Many forms have often been employed, but none exhibit the strength or durability as the weld. This study endeavors to explore some of the aspects of welding, more specifically relating to the Double Sided Arc Welding process and how best to model the dynamic non-linear response of such a system. Concepts of the Volterra series, NARMAX approximation and neural networks are explored. Fundamental methods of the neural network, including radial basis functions, and Back-propagation are investigated

CONTROL OF METAL TRANSFER AT GIVEN ARC VARIABLES

Gas Metal Arc Welding (GMAW) is one of the most important welding processes in industrial application. To control metal transfer at given variables is a focus in the field of research and development in welding community. In this dissertation, laser enhanced GMAW is proposed and developed by adding a lower power laser onto the droplet to generate an auxiliary detaching force. The electromagnetic force needed to detach droplets, thus the current that determines this force, is reduced. Wire feed speed, arc voltage, and laser intensity were identified as three major parameters that affect the laser enhanced metal transfer process and a systematic series of experiments were designed and conducted to test these parameters. The behaviors of the laser enhanced metal transfer process observed from high speed images were analyzed using the established physics of metal transfer. In all experiments, the laser was found to affect the metal transfer process as an additional detaching force that tended to change a short-circuiting transfer to drop globular or drop spray, reduce the diameter of the droplet detached in drop globular transfer, or decrease the diameter of the droplet such that the transfer changed from drop globular to drop spray. The enhancement of the laser was found to increase as the laser intensity increased. The larger laser intensity tended to help reduce the size of the droplet detached. The arc voltage affected the metal transfer process through changing the current and changing the gap and possible time interval of the droplet development. A larger arc voltage helped reduce the size of the droplet detached through an increased electromagnetic force. Desired heat input and current/arc pressure waveforms may thus be both delivered and controlled by GMAW through laser enhancement. Laser recoil pressure force was estimated based on the difference of gravitational force with and without laser pulse, and the result was with an acceptable accuracy. Good formation of welds and full penetration of thin plate could be obtained using laser enhanced GMAW. A nonlinear model was established to simulate the dynamic metal transfer in laser enhanced GMAW, and the results agree with the experimental one

Welding Processes

Despite the wide availability of literature on welding processes, a need exists to regularly update the engineering community on advancements in joining techniques of similar and dissimilar materials, in their numerical modeling, as well as in their sensing and control. In response to InTech's request to provide undergraduate and graduate students, welding engineers, and researchers with updates on recent achievements in welding, a group of 34 authors and co-authors from 14 countries representing five continents have joined to co-author this book on welding processes, free of charge to the reader. This book is divided into four sections: Laser Welding; Numerical Modeling of Welding Processes; Sensing of Welding Processes; and General Topics in Welding

Structure and Properties of Aluminium Alloys

The demand for aluminum alloys is increasing because of their lightness, high specific strength and other attractive properties, which can exploited in improved products for a greener environment. This book gives a correlation between the processing, microstructure and properties of several aluminium alloys. Some of them are well established and used in an enormous number of applications, while others are still under development. The processing spans from casting, rapid solidification, additive manufacturing, forming, heat-treatment and welding, which can produce interesting microstructures and a useful combination of properties

Computational and experimental investigations of laser drilling and welding for microelectronic packaging

Recent advances in microelectronics and packaging industry are characterized by a progressive miniaturization in response to a general trend toward higher integration and package density. Corresponding to this are the challenges to traditional manufacturing processes. Some of these challenges can be satisfied by laser micromachining, because of its inherent advantages. In laser micromachining, there is no tool wear, the heat affected zone can be localized into a very small area, and the laser micromachining systems can be operated at a very wide range of speeds. Some applications of laser micromachining include pulsed Nd:YAG laser spot welding for the photonic devices and laser microdrilling in the computer printed circuit board market. Although laser micromachining has become widely used in microelectronics and packaging industry, it still produces results having a variability in properties and quality due to very complex phenomena involved in the process, including, but not limited to, heat transfer, fluid flow, plasma effects, and metallurgical problems. Therefore, in order to utilize the advantages of laser micromachining and to achieve anticipated results, it is necessary to develop a thorough understanding of the involved physical processes, especially those relating to microelectronics and packaging applications. The objective of this Dissertation was to study laser micromachining processes, especially laser drilling and welding of metals or their alloys, for the microscale applications. The investigations performed in this Dissertation were based on analytical, computational, and experimental solutions (ACES) methodology. More specifically, the studies were focused on development of a consistent set of equations representing interaction of the laser beam with materials of interest in this Dissertation, solution of these equations by finite difference method (FDM) and finite element method (FEM), experimental demonstration of laser micromachining, and correlation of the results. The contributions of this Dissertation include: 1)development of a finite difference method (FDM) program with color graphic interface, which has the capability of adjusting the laser power distributions, coefficient of energy absorption, and nonlinear material properties of the workpiece as functions of temperature, and can be extended to calculate the fluid dynamic phenomena and the profiles of laser micromachined workpieces, 2)detailed investigations of the effect of laser operating parameters on the results of the profiles and dimensions of the laser microdrilled or microwelded workpiece, which provide the guideline and advance currently existing laser micromachining processes, 3)use, for the first time, of a novel optoelectronic holography (OEH) system, which provides non-contact full-field deformation measurements with sub-micrometer accuracy, for quantitative characterization of thermal deformations of the laser micromachined parts, 4)experimental evaluations of strength of laser microwelds as the function of laser power levels and number of microwelds, which showed the lower values than the strength of the base material due to the increase of hardness at the heat affected zone (HAZ) of the microwelds, 5)measurements of temperature profiles during laser microwelding, which showed good correlations with computational results, 6)detailed considerations of absorption of laser beam energy, effect of thermal and aerodynamic conditions due to shielding gas, and the formation of plasma and its effect on laser micromachining processes. The investigations presented in this Dissertation show viability of the laser micromachining processes, account for the considerations required for a better understanding of laser micromachining processes, and provide guideline which can help explaining and advancing the currently existing laser micromachining processes. Results of this Dissertation will facilitate improvements and optimizations of the state-of-the-art laser micromachining techniques and enable the emerging technologies related to the multi-disciplinary field of microelectronics and packaging for the future

DIRECT METAL LASER SINTERING OF TI-6AL-4V ALLOY: PROCESS-PROPERTY-GEOMETRY EMPIRICAL MODELING AND OPTIMIZATION

DIRECT METAL LASER SINTERING OF TI-6AL-4V ALLOY: PROCESS-PROPERTY-GEOMETRY EMPIRICAL MODELING AND OPTIMIZATIO

Thermomechanical and metallurgical modelling of laser hardening and laser cladding processes

[Abstract] The development of high stresses and distortions is one of the main concerns in laser surface heat treatments. The objective of the present thesis is to contribute to the better understanding of the thermomechanical behavior during laser transformation hardening and laser metal deposition techniques, including as well the development of a exible tool with customizable models for the numerical calculation of the thermomechanical variables, and the microstructural evolution through phase transformation models. Such a tool will be useful for the prediction of the residual strains and stresses after the processes as well as the phase changes, helping with its optimization and understanding, thus reducing the number of test trials necessary to achieve the desired results. Something that has paramount importance when unique or expensive workpieces should be treated. The model was validated using several experimental techniques to assess its predictions and ne tune some of its parameters.[Resumo] A xeración de altas tensións e deformacións é unha das maiores preocupacións dos tratamentos térmicos super ciais por láser. O obxectivo da presente tesis é o de contribuir ao mellor entendemento do comportamento termomecánico durante o endurecemento super cial por láser e as técnicas de deposición de metal por láser, incluindo tamén o desenvolvemento dunha ferramenta exible con modelos adaptables para o cálculo numérico das variables termomecánicas, así como da evolución microestrutural mediante modelos de transformación de fase. Tal ferramenta será de utilidade na predicción dos esforzos e deformacións residuais despois do tratamento, axudando coa sua optimización e mellorando o seu entendemento, e por tanto diminuindo o número de ensaios necesarios para obter os resultados desexados. Algo de meirande importancia cando pezas únicas ou de gran custo deben ser tratadas. O modelo foi validado mediante o uso de varias técnicas experimentais para comparar o grao de axeitamento das súas prediccións e axustar algúns dos seus parámetros