Lunes 16 Abril 2007

Desafíos mundiales de la soldadura y soluciones potenciales. Utrachi, Gerald – Presidente American Welding Society, USA

A shortage of welders may result in 40% fewer skilled welders available in the USA than will be needed.
Possible solutions to this dilemma are covered including:

1. A unique approach has been successful in a welding program at a technical college - training women as welders.
2. Increasing productivity is one way to reduce the need for skilled welders. This includes reducing waste and improving weld quality to reduce rework.
3. Simplified welding machine design to make learning easier an producing quality welds more failsafe is another method. This can be particularly useful in GMAW.

Recientes desarrollos en la soldadura robotizada en Brasil - La contribución del laboratorio de Robótica, Soldadura y Simulación en la Universidad de Minais Gerais. Bracarense, Alexandre Queiroz – Universidades Federal de la Minas de Gerais, Brazil

It is very well known that the use of robotics in the industry increases productivity and quality in many aspects. It is also very well known that some adjustments have to be made to guaranty feedback for the investment and to reach the expected results. Today in Brazil, the robotization shows itself as an alternative technique for production,
increasing qualitative and quantitative competence of its industries. One point that has been observed, however, is that inadequate procedure for robot application in welding process is reflecting in results not much satisfactory. These procedures are excessive time expending for implementation, lost of material, reworking and poor
weld quality.

The main problem detected is that the number of experts in welding “and” robotics is still reduced in Brazil and some industries are investing in robot without any planning or orientation, thinking that the robot will solve all theier problems. The results have been disastrous. In many cases even though the weld appearance is acceptable and
the welding time is significantly reduced, the weld quality is poor. The experts in robotics know very well what they are doing. However, many of them do not have experience in welding to understand that many features related to welding physics and metallurgy have to be considered when a welding procedure has to be implemented.
Because of this, some small and medium industries, with large potential for robotization, are holding investment and/or postponing it until its adaptation to implement the robot in their production line. It is believed however that very soon many small industries will have their own robot.

This paper addresses the concept o robotic welding and how it was interpreted to be applied in Brazil. It discuss about the participation of the Laboratory of Robotic, Welding and Simulation and how it has been working to apply robotic. Additionally, two major research topics and projects related to robotic welding developed in the Laboratory
are presented. The first discuss about robotic welding with covered electrodes.
The second is about the development of a robot for orbital pipeline welding.

Martes 17 Abril 2007

Manejo de las tensiones residuales a través de transformaciones de fase controladas para mejorar la resistencia a la fatiga de uniones soldadas. Liu, Stephen – Colorado School of Mines, USA.

Steel welding wires capable of inducing an overall compressive residual stress state, by means of controlled martensitic transformation at relatively low temperatures, was developed. Weld deposits produced using these designed wires transformed into martensite between 390 and 270°C with volumetric expansion. Nonload-carrying cruciform fillet welded joints were prepared for measurement of residual stresses and fatigue testing. Several designed wires reported high compressive residual stresses near the weld toe. Finite element analysis determined residual stresses with magnitudes inversely proportional to the transformation temperatures of the wires. Fatigue properties of these welds were superior to the reference welds prepared using commercial wires.

Keywords: Residual Stresses, Martensitic Transformation, Fatigue Properties, LTTW Electrodes, Cruciform Weld Specimens, Dilatometric Measurements.

Efectos de la capa de compuestos intermetálicos en la resistencia de unión de la interfase de capas de aleaciones de aluminio unidas por fricción a aceros. Ikeuchi, Kenji, Makoto Takahashi, Naotsugu Yamamoto, and Tomoya Morita - Osaka University Join

Joining Al alloy to steel has recently absorbed much attention to meet the requirement for the weight reduction of the transportation from an ecological point of view. As reviewed by
Wallach and Elliot in 1981, it has long been accepted that the intermetallic compound (IMC) layer forming at the interface brought about a serious impairment in the bond strength,
when its thickness exceeded a few ?m. In a previous paper, however, we reported that the IMC layer no more than 200 nm in thickness caused a premature fracture at the interface
on tensile test. In order to discuss the effects of even thinner IMC layer and alloying elements of the base metals on the bond strength, a further investigation based on TEM
observations has been carried out on a larger variety of Al alloys and steels. It turned out that the IMC layer of thickness down to 100 nm caused a brittle fracture of the joint at
stresses that could be extrapolated from a relation established for the IMC layer thicknesses of 200 – 1200 nm. Minor alloying elements in the Al alloy were found to
influence significantly the kind of IMCs formed at the interface.

Materiales para sistemas de escape de automóbiles: Propiedades e influencia de los aleantes en la soldabilidad. Merino Concepción, José Luis Sastre de Miguel - Universidad Complutense de Madrid, España

Se presenta un estudio sobre las propiedades de los materiales base y de aportación utilizados en sistemas de escape. Se describen las condiciones de servicio junto con los requerimientos aplicables en los aspectos medioambientales, de durabilidad, menor peso y temperaturas de trabajo de estos componentes, para seguir después con la selección de los materiales correspondientes. Se comparan propiedades entre las diferentes clases de aceros inoxidables que permiten justificar su aplicación en las distintas zonas del sistema de escape, profundizando en la influencia de los elementos de aleación, así como en la selección de los consumibles más adecuados a cada caso. Se presentan también los ensayos que se realizan tanto a los materiales base como a las uniones soldadas.

Palabras clave: Sistemas de escape, Materiales, Aceros inoxidables, Elementos de aleación, Consumibles de soldadura.

Tecnologías robustas de unión y de integración para sistemas aeroespaciales: Desafíos técnicos y oportunidades. Singh, M – Nasa Glenn Research Center , USA.

Resumen no disponible.

Miércoles 18 Abril 2007

Capas nanoestructuradas depositadas por PVD y por técnicas de rociado térmico. Tillmann, Wolfgang, I. Baumann, E. Vogli - Lehrstuhl für Werkstofftechnologie, Universität Dortmund, Alemania.

Nanostructured materials are of key interest in many applications owing to their specific property profile. A novel way to exploit those properties is by utilizing surface technologies such Physical Vapour Deposition and Thermal Spraying. Corresponding nanostructured layers exhibit superior wear resistance, better adhesion or a smoother surface finish. Whereas PVD-processes offer the opportunity to generate layers of thicknesses in the nanometre range thermal spray processes have to employ extremely fine powders in order to come up with a nanostructured surface. Powder feeding and a corresponding process adjustment are central questions related to the deposition of nanostructured thermal sprayed layers. High energy processes such as detonation flame spraying that provide high particle velocities at comparatively low particle temperatures are a promising approach. Process requirements will be discussed with particular emphasis on metallurgical and technological properties. Interesting applications can be found in the forming industry. The potential of nanostructured coatings in this context will be analysed and first results are going to be presented.

Keywords: nanostructured layers, superlattice, physical vapor deposition, thermal spraying, hardening.

Evaluación de uniones soldadas mediante medidas de potencial termoeléctrico. Olson, David L., A.N. Lasseigne-Jackson, J.E. Jackson, B. Mishra, T. Koenig, Colorado School of Mines, USA.

Thermoelectric power (TEP) coefficient measurement techniques have been devel-oped for numerous welding applications to guarantee material integrity by providing a non-destructive electronic property correlation to weld metal microstructure, phase stability, specific solute additions, and lattice strain. The electron concentration and effective mass, and the dominating scattering mechanisms associated with TEP are described. Because thermoelectric power is dependent upon numerous variables, additional non-destructive techniques are useful to further characterize or classify weldments or material. The concept of an electronic metallography laboratory is developed using additional collaborative NDE technologies.
Thermoelectric power (TEP) has been utilized for assessment of interstitials such as hydrogen, carbon, oxygen, and nitrogen in steel and various hydrogen storage alloys, including development of activity diagrams and characterization of interstitial nitrogen contents. Thermoelectric power has also been utilized for residual stress measure-ments in a nickel-aluminum-bronze specimen with increasing strain. Residual stress measurements for stainless steel welds correlate well with the difference in the TEP coefficient caused by a change in welding speed for GTA welds. An increase in weld travel speed results in a decrease in the area of the weld bead, hence changing the amount of residual stress, which results in an increase in the TEP coefficient for welding processes.

Keywords: Thermoelectric Power; Weld Assessment; Non-destructive Testing.

Sistemas EWF integrados para la certificación de compañías manufactureras en calidad, Ambiente, salud y Seguridad. German Hernandez Riesco - President European Welding Federation (EWF).

Este documento presenta el sistema armonizado de la Federación Europea de Soldadura, EWF, y del Instituto Internacional de Soldadura, IIW, para la implantación de las Normas ISO-EN relativas al soldeo en el campo de la calidad, el medioambiente, la salubridad y la seguridad.
También describe la forma de evaluación de las Entidades Nacionales Autorizadas que certifican los sistemas de calidad, medioambiente, salubridad y seguridad de las empresas en nombre de la EWF y del IIW.

Palabras clave: Certificación, calidad, medioambiente, salubridad, seguridad.