Do dia 14/05/2020 Ã 22/05/2020 via SIGA, abertas as inscriÃ§Ãµes para a disciplina TÃ“PICOS ESPECIAIS EM ENGENHARIA E CIÃŠNCIA DOS MATERIAIS II – Advanced Aspects of the Welding Process Technology
Esta disciplina serÃ¡ doÂ perÃodo de 25/05/2020 a 19/08/2020Â via Skype ou Teams
Numero de vagas: 15
Professor ministrante: AmÃ©rico Scotti
1) Introduction to welding Processes;
2) Fusion welding: heat source and metal melting;
3) Physics of Arc 1: the plasma arc as a heat source
4) Physics of Arc 2: the welding arc;
5) Fusion of the electrode;
6) Arc Jet, Magnetic Blow and Power Sources;
7) Arc Welding Protection (slag and gas);
8) Metal Transfer;
9) Weld bead formation;
10) Residual Stresses and Distortions;
11) Waveform controlled and High production processes;
12) Special topics on arc welding: performance of MAG-CO2, metal transfer regularity index;
13) Parameter setting: Prediction of arc length, current and voltage;
14) Laboratory activities
In-class course content (block of 4 hours lectures):
1) Introduction to welding Processes: advantages on replacing riveting and bolting, history, application and trends; A special process, according to ISO 9000: demands and consequences; The importance of learning based on fundamentals; An overview on welding processes: definition of welding and process evolution (timeline); Fusion welding: heat transfer from de heat source to the base metal (concept of heat conduction and thermal diffusibility); Heat x temperature of a heat source; Power x energy; Heat efficiency: definition, heat losses from different welding processes, determination of Melting efficiency: definition, effect of power density.
2) The arc as a heat source: producing plasma (ionization concept); Enthalpy (ionization potential, dissociation, latent and sensible heat); Arc shape and temperature distribution; Temperature x heat; electrical power conversion (the role of voltage and current on heat generation); Arc starting (contact resistance heating and high voltage-high frequency excitation; ignition voltage and transitory period); Maintenance of a welding arc: lasma properties and heat transfer during arcing, elÃ©ctron shocks into molecules (voltage and current), deionization and reionization; Effect of the gas in the voltage drop; Thermionic and field emissions: mechanisms, materials, cathode spots; Cathodic cleaning of aluminium.
3) Regions of a welding arc (cathode, anode and arc column; spacing and voltage drop); Generation and losses of heat in an arc (arc energy, heat input and arc efficiency); lectrode melting rate: physical phenomenon, melting rate generic equation, representation of current (mean and effective) in the generic melting rate equation; Static characteristic of arcs: definition, attainment, influence of arc length, gas, lectrode material and size; The differences and reasons for between static characteristics of consumable and non-consumable electrodes.
4) Arc Jet: formation and action onto pool: static and dynamic forces acting on the pool; Influence of the arc jet on the shape of the arc-plate coupling; Magnetic Blow: formation and impact on the welding arc, causes for magnetic blow formation, means of mitigation; Power sources for arc welding: basics; static characteristics of power sources and working point; Arc length maintenance: constant voltage and constant current power sources operational modes.
5) Arc Welding Protection: slag and gas (an overview on the available types of consumables, characteristics, protection mechanisms, performance and limitations); Physical-chemical properties of the shielding gases and relationship with the metal pool.
6) Metal transfer: mechanisms and types; natural and controlled metal transfer (applications).
7) Consume x Production: types of losses; Weld bead formation: phenomena inherent to the weld bead formation (mechanical and thermal effects); average or effective values of current; Operational welding imperfections: discontinuities and defects; discontinuity identification and acceptance; types and cause of imperfections.
8) Fundamentals of thermal stress: primary concept (dilatation and contraction); Residual stress, distortion and collapse; Thermal stress generation (3-bar and 5 bar models); Second concept (phase transformation); Temperature x Stress Thermal diagram; The main thermal stress components and distribution (longitudinal, transverse and normal); Governing parameters on residual stress generation: heated volume related parameters and phase transformation related parameters, LTT filler metal; Stress relief methods (PWHT and vibration); Techniques to mitigate and correct distortions.
9) Waveform controlled processes: GTAW and GMAW (pulsed, double pulse, controlled shortcircuiting): fundamentals, performance advantages, applications and limitations; High production processes: multi-wires (SAW and GMAW); cold and hot wires: fundamentals, performance, advantages, applications and limitations; DCEN GMAW; infocus TIG.
10) Influence of CO2 content and arc length setting on performance of MAG-CO2; metal transfer regularity index: concept and application to obtain no spattering and higher melting efficiency in parametrizations; Parameter setting: prediction of arc length, current and voltage in response to parameter setting or adjustment In-Laboratory activities content (block of an estimated 5-hour-lecture): Note: the approach (media-assisted welding lab) is to demonstrate through actual arc welding some fundamentals given in the classroom lectures, such as the effect of shielding gas on metal transfer, effect of arc energy on bead geometry, rather than teaching students to weld or operate a machine. A script of all experiments will be given to the students in advance. A report based on the acquired data followed by a critical analysis of the results are individually expected from the students after some days.