Lunes 09 Agosto 2010

The load and installation of a major oil and gas production platform (Carga e instalación de una plataforma de producción de petróleo y gas). John Bruskotter, American Welding Society, AWS, EE.UU

Resumen no disponible.

Friction based technology for joining and material processing (Tecnología basada en fricción para unión y procesamiento de materiales ) - Wayne Thomas, The Welding Institute, Inglaterra.

Friction welding is a process in which the heat for welding is produced by direct conversion of mechanical energy to thermal energy, at the interface between the workpieces. The thermal energy developed from the interaction of two surfaces, rubbed together under pressure and relative motion, can be harnessed to provide conditions suitable for welding and material processing. The friction welding process has, to a large extent, been restricted to round, square, or rectangular bars for the last five decades since its inception. More recently, however, TWI has been working on emergent techniques that now allow solid-phase friction welding as another option for the fabrication of a range of sheet and plate materials and the reprocessing of materials.

In friction welding and friction processing technology, the parts to be joined or processed are subjected to relative motion and pressure so that frictional heat is developed at the interface between the faying surfaces. Typically, the parts are subjected to dry friction during the initial contact, but quite rapidly, as a result of a microscopic local seizure and subsequent rupture by plastic deformation, a ‘third-body’ layer of finite thickness is formed. Once the processes of seizure and rupture occur, the accepted theory of basic friction no longer applies. The process is to some extent self regulating, essentially macroscopic melting is prevented because molten metal cannot transmit sufficient stress and it effectively behaves as a lubricant.

Keywords: Friction welding Solid-phase welding, Material processing.

Martes 10 Agosto 2010

Fusion welding of high Mo austenitic stainless steels (Soldadura por fusión de aceros inoxidables austeníticos de alto Mo). John DuPont, Lehigh University, EE.UU.

Resumen no disponible.

Hot cracking behavior of high manganese TWIP steels (Comportamiento a la fisuración en caliente de aceros TWIP de alto manganeso) - Manuela Zinke, University Magdeburg, Alemania.

This paper introduces investigations on the hot cracking behavior of four different high manganese TWIP-Steels. The TWIP-Steels were produced by the Max-Planck Institut für Eisenforschung GmbH (MPIE) Düsseldorf especially for this project and are characterized by different alloying concepts concerning the contents of carbon, manganese, silicon and aluminum. The investigations include the measurement of the thermo-physical properties (solidification temperature range, thermal expansion, thermal diffusivity, specific heat capacity) of the TWIP-Steels. Hot cracking tests are performed by PVR-test (deformation crack test), using TIG-welded externally loaded specimens to rank the hot cracking sensitivity with respect to other already assessed Cr-Ni-Steels and Ni-based alloys. Furthermore, a special self-restraint testing procedure for arc welding processes tailored to real weldment geometry was investigated and the results were compared to those of the PVR test. In order to gain further knowledge regarding formation and propagation of the hot cracks, optical microscopy, SEM-microscopy and EDX-analyses were performed.

Keywords: TWIP-steel, hot cracking, PVR, welding.

Factors determining failure strength properties of friction stir spot welds (Factores que determinan las propiedades de resistencia a la falla en soldaduras de punto por fricción batido). Thomas North, University of Toronto, Canadá.

Resumen no disponible.

A rapid manufacturing technique with metal cutting and welding (Una técnica rápida de manufactura con corte y soldadura de metal) - Alexandre Bracarense, Universidade Federal de Minas Gerais, Brasil.

The Laminated Object Design (LOD) is a rapid prototyping / manufacturing technique developed at the Federal University of Minas Gerais, Brazil, in the Welding and Robotics Lab (LRSS) to solve several problems related to the construction of special welding robots. The LOD is based on product design techniques, like the “Design for Manufacture and Assembly (DFMA)”, the rapid prototyping method of “Laminated Object Modeling (LOM)”, and good practices involved in LASER cutting of steel and welding, incorporating all that philosophy in the product design early on. The LOD starts with the optimization of the concept to minimize the part count (DFA) followed by the breaking down of every part in two dimensional shapes to be cut in metal plates of a single thickness (DFM taken to a extreme), making possible the construction of the concept from a single LASER cut metal sheet. Since every part shape concept was broken down into several small sub components, they must be welded together to make the desired part, and this is achieved by autogenous TIG welding. The precision and structural compliance is achieved through small male – female insert at every side of the sub component, making the assembly self aligning and holding the components in place prior to welding, without the need of jigs, vises or any kind of toll to ensure proper positioning. This technique has been used since 2004 for the construction of several prototypes in the laboratory, including welding robots, CNC mil and plasma table, welding jigs and production machines. The economy achieved when building small welding robots for field welding was over 80% compared to a conventional prototyping with CNC milling. The technique allows the manufacture of all the components in one step, allowing that hundreds of different parts to be build in a couple of hours, from one metal sheet and only LASER cutting with one G Code. This provides a simplified logistics and an excellent turn over for the development of industrial equipment.

Keywords: Welding, Metal cutting, LASER, LOM, DFMA, LOD

Miércoles 11 Agosto 2010

In situ electronic-elastic-magnetic wave analytical metallography laboratory (Laboratorio de metalografía analítica in-situ con onda electro-elástico-magnética). David Olson, Colorado School of Mines, EE.UU.

Resumen no disponible.

Characterization of explosive dissimilar metal joints: fine microstructures and thermal excursion along bond interface. Stephen Liu, Vilem Petr, and John Banker. Colorado School of Mines, EE.UU.

In this work, ammonium nitrate with fuel oil (ANFO) was used to study several explosive parameters. Pure copper and A516 G-70 steel were selected as model materials for investigation of the bonding process. Tracers were inserted between the copper and steel plates in some of the explosive experiments. The wavy nature of the explosive bond interface, e.g. amplitude, frequency, and the leading and trailing angle of the waves, was examined using standard metallographic techniques and image analysis software. Stainless steel-to-mild steel bonds were also examined in detail for microstructural characterization.

Several techniques were tested to measure velocity of detonation (VOD). VOD values determined were then used to examine the effect of fuel oil, perlite, and ANFO density. The microstructures of the explosive bonds were examined in detail. The amount of pearlite colonies, observed in the form of banding in the base steel plate, was found to decrease when approaching the bond interface. In the immediate adjacency of the interface, no pearlite was evident in the light micrographs. One of the bonds showed hardness readings comparable to martensite hardness but most others showed hardness values below martensite hardness for the steel carbon concentration. Examination of the bond interface using scanning and transmission electron microscopy (SEM and TEM) revealed extremely large deformation leading to the fragmentation of cementite particles to dimensions beyond resolution of light microscopy. Recrystallization was clearly observed in the adjacency of the bond interface. Steel grain morphology indicates that the local temperature reached well above 1000oC. Fine tungsten tracers introduced between the copper and steel plate showed clear evidence of dendritic solidification, which is an indication of localized melting of the tungsten particulates. A model was developed to explain the jet formation, spalling, melting and solidification phenomena observed in the experiments.

Fundamental studies conducted in this work characterized the effects of explosives and joint conditions on bond formation in dissimilar metals. The knowledge acquired through the Cu-steel system can be applied to other material systems.

Keywords: Explosive bonding, Interfacial microstructure, Interfacial Temperature, Wavy Interface, Velocity of detonation, Jet formation, Spalling, Localized melting, and Dendritic solidification

3-D surface engineering of forming tools (Ingeniería de superficies en 3-D de herramientas de conformado) - Wolfgang Tillmann, Technische Universitat Dortmund, Alemania.

Within this study, two different coating processes have been investigated to produce near-net-shape coatings for the wear protection of complex-shaped forming tools. The focus was on achieving coatings with a dense and homogenous morphology and a smooth surface, adapted to the demands of the forming operation. The first approach combines a conventional twin arc-spray (TWAS) or atmospheric plasma spray process (APS) with an in-situ post-treatment by roller-burnishing in order to optimize the coating characteristics. For the second approach a novel high velocity oxy-fuel flame spraying process (HVOF), utilizing fine powders, was employed to manufacture thin coatings with enhanced properties to avoid post-treatments.

Keywords: Thermal spraying, APS, TWAS, HVOF, surface engineering, near net shape, fine powders.