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

Investigation into coatings produced from nanoparticle blended feedstock for rotating equipment repair applications

Coating of carbon steel with conventional and nano particle blended feedstock material is considered in relation to repair applications of rotating equipment. Gas Metal Arc Welding (GMAW) and Wire Arc Spray (WAS) processes are used to produce the coatings on carbon steel workpieces. The wire arc sprayed workpieces are heat treated at temperature similar to the operating temperature of hot-path components of power gas turbines. The microstructure and metallurgy of the workpieces are examined using the Scanning Electron Microscope (SEM), Optical Microscope, Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD). The indentation tests are carried out to assess the microhardness variation across the coatings. In the case of coatings produced by GMAW, it is found that fine structures are formed in the coating due to the presence of nano particles and they resulted in increased microhardness of the coatings. In the case of the wire arc sprayed workpieces, the formation of dimples like structure at the surface increases the surface roughness of the coatings. In addition, the microhardness of the resulting coating is significantly higher than that of the base material. The heat treatment does not alter the microstructure and microhardness of the coatings significantly

Lithium-Ion Batteries

Lithium-ion batteries (LIBs), as a key part of the 2019 Nobel Prize in Chemistry, have become increasingly important in recent years, owing to their potential impact on building a more sustainable future. Compared with other batteries developed, LIBs offer high energy density, high discharge power, and a long service life. These characteristics have facilitated a remarkable advance of LIBs in many frontiers, including electric vehicles, portable and flexible electronics, and stationary applications. Since the field of LIBs is advancing rapidly and attracting an increasing number of researchers, it is necessary to often provide the community with the latest updates. Therefore, this book was designed to focus on updating the electrochemical community with the latest advances and prospects on various aspects of LIBs. The materials presented in this book cover advances in several fronts of the technology, ranging from detailed fundamental studies of the electrochemical cell to investigations to better improve parameters related to battery packs

JOINING SEQUENCE ANALYSIS AND OPTIMIZATION FOR IMPROVED GEOMETRICAL QUALITY

Disturbances in the manufacturing and assembly processes cause geometrical variation from the ideal geometry. This variation eventually results in functional and aesthetic problems in the final product. Being able to control the disturbances is the desire of the manufacturing industry. \ua0 Joining sequences impact the final geometrical outcome in an assembly considerably. To optimize the sequence for improved geometrical outcome is both experimentally and computationally expensive. In the simulation-based approaches, based on the finite element method, a large number of sequences need to be evaluated.\ua0 In this thesis, the simulation-based joining sequence optimization using non-rigid variation simulation is studied. Initially, the limitation of the applied algorithms in the literature has been addressed. A rule-based optimization approach based on meta-heuristic algorithms and heuristic search methods is introduced to increase the previously applied algorithms\u27 time-efficiency and accuracy. Based on the identified rules and heuristics, a reduced formulation of the sequence optimization is introduced by identifying the critical points for geometrical quality. A subset of the sequence problem is identified and solved in this formulation.\ua0 For real-time optimization of the joining sequence problem, time-efficiency needs to be further enhanced by parallel computations. By identifying the sequence-deformation behavior in the assemblies, black-box surrogate models are introduced, enabling parallel evaluations and accurate approximation of the geometrical quality. Based on this finding, a deterministic stepwise search algorithm for rapid identification of the optimal sequence is introduced.\ua0 Furthermore, a numerical approach to identify the number, location from a set of alternatives, and sequence of the critical joining points for geometrical quality is introduced. Finally, the cause of the various deformations achieved by joining sequences is identified. A time-efficient non-rigid variation simulation approach for evaluating the geometrical quality with respect to the sequences is proposed. \ua0 The results achieved from the studies presented indicate that the simulation-based real-time optimization of the joining sequences is achievable through a parallelized search algorithm and a rapid evaluation of the sequences. The critical joining points for geometrical quality are identified while the sequence is optimized. The results help control the assembly process with respect to the joining operation, improve the geometrical quality, and save significant computational time

CONTROL OF GAS METAL ARC WELDING USING PROCESS SENSING AND LASER ARC STABILIZATION FOR ADDITIVE MANUFACTURING

The goal of the present research was to bridge the gap between powder-based and wire-based additive manufacturing (AM) processes using gas metal arc welding (GMAW). Powder-based AM processes typically can produce components with high geometric resolution (small features), but at low deposition rates. Wire-based AM processes typically can produce components with low geometric resolution, but at high deposition rates. AM with GMAW is a wire-based AM process in the wire arc additive manufacturing (WAAM) category of AM. To bridge the gap between powder-based and wire-based AM processes, GMAW’s deposition rate has to be reduced, allowing small features to be built. The method proposed to build small features with GMAW was to develop a system, called GLADiS (GMAW laser assisted deposition integrated system), to perform an improved metal deposition strategy. The improved metal deposition strategy was composed of four components: single droplet deposition (SiDD), noncontact arc starting, electrode extension minimization, and laser arc stabilization. SiDD would allow single molten metal droplets to be deposited anywhere on a build plane rather than running continuous weld beads. SiDD would only be possible using an alternative, noncontact arc starting technique. Minimizing the electrode extension would allow the deposition rate to be reduced, while still maintaining sufficient current for droplet/substrate coalescence. Using a laser to stabilize the arc would ensure that individual droplets would be transferred to the correct location on the substrate. Results showed that GLADiS was capable of building extremely thin walls using SiDD. In addition, minimizing the electrode extension was found to improve droplet/substrate coalescence. The final system used a 532nm laser to assist in arc starting and to stabilize the arc. Linear wall specimens made of steel could be produced at a 0.1lb/hr deposition rate and with a wall thickness of 0.1in or less. Weld metal deposits produced by the SiDD process were found to have a microstructure composed of extremely small grains, indicating that it would have excellent strength and toughness. In addition, only a small number of voids were found in the deposits

Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact