Eurico Assuncao

Characterisation of residual stress state in laser welded low carbon mild steel plates produced in keyhole and conduction mode

Abstract Characterisation of residual stress state was performed in 4 mm low carbon steel plates laser welded in keyhole and conduction mode. Residual stress characterisation was carried out at the ENGIN-X strain scanner at ISIS (Oxford, UK). It was shown that although the maximum magnitude of tensile residual stress is similar in welded specimens manufactured under different welding modes, the distribution profile is quite distinguished. The conduction welding mode resulted in a larger tensile stress domain as compared to the keyhole mode in the longitudinal direction. This also resulted in a different magnitude of balancing compressive residual stress field. Understanding of such different stress profiles is important for application of such advanced welding processes in joining of design efficient structural material.

Effect of material properties on the laser welding mode limits

Aluminum, mild steel, and stainless steel have very dissimilar thermal properties. This study focuses on the effect of power density on the laser welding conduction mode limit in these three materials. The objective is to evaluate how these different materials will behave in conduction mode and in keyhole mode and also to understand how the thermal properties of the materials will influence the transition between the different welding modes. A comparison between the penetration depth and the melted area for the different materials under the same conditions was also made. The experimental results show that thermal properties conductivity, melting temperature, vaporization temperature, and thermal diffusivity have an important role in the transition between the welding modes. An analytical model was developed in order to study the effect of thermal properties on the power density value necessary to achieve melting and vaporization in these materials. Also all three materials showed a transition mode between...

Numerical sensitivity analysis of single pulse laser welding with a C-shaped beam

Even though Gaussian and top-hat beam profiles are suitable for most laser welding applications, for certain cases other beam distributions can be favored in terms of weld quality or performance. One promising method to generate a tailored beam shape is diffractive optical elements. A numerical model on the temperature field generated by specific beam shapes is therefore under development to iteratively identify desired beam shapes for specific applications. The present study is based on two thin steel sheets that are conduction welded in a lap joint mode by a C-shaped single laser pulse. The main aim is to ensure a specified weld width along the C-weld shape at the overlap interface between the two sheets in a robust manner. The sensitivity of main criteria like the interface weld width and phase changes at the workpiece top and bottom is studied and discussed in a systematic manner by applying a numerical heat transfer model for various parameters and conditions.

Conduction laser welding

Abstract: Laser welding has two different operational regimes: conduction and keyhole welding. The key difference between these two modes is the power density applied to the welding area. Conduction takes place when the intensity is not sufficient to cause boiling. In keyhole mode, the intensity used is high enough to cause vaporisation and create a keyhole in the melt pool. The current definition of conduction laser welding mode based on power density is discussed. Some studies focused on conduction laser welding are also discussed, emphasising the effect of beam diameter in this mode. Finally, an overview of some of the most relevant applications of conduction laser welding in industry is presented. This chapter not only emphasises how good and diverse the applications of this welding mode are, when compared to keyhole laser welding, but also helps in understanding the flexibility of this welding process.

European harmonised system for training and qualification of adhesive bonding personnel

The rapid developments in materials technology has resulted in unprecedented innovations in products and processes using adhesive bonding. A basic knowledge of the materials, technologies and their relationship is necessary in order to fully utilize this potential and optimize manufacturing operations. Employee training is therefore a key activity, and especially so in high-tech fields.EWF - The European Federation for Welding, Joining and Cutting, was created in 1992 by all the welding institutes of the European Union with the aim of updating and harmonizing training, education, qualification and certification in the field of joining technology.Since then EWF has operated a harmonized training and qualification system offering courses and qualifications for Welding Engineers, Inspectors, Welders and others. These qualifications form the basis of the widely accepted International diplomas and are referred in ISO and EN standards.The EWF System comprises guidelines defining training syllabuses and examinations and rules for implementing the Quality Assurance system that ensures the control and monitoring of the system in all the 43 countries that presently use it.In terms of training of Adhesive bonding personnel EWF has developed harmonized guidelines for the European Adhesive Engineer, the European Adhesive Specialist and the European Adhesive Bonder.The present paper aims at explaining the structure of the EWF harmonized system and detailing the contents of the guidelines in adhesive bonding and quality assurance methodology.

Interaction time effects on the transition between conduction and keyhole laser welding

Welding with a laser in keyhole mode provides deep penetration and/or high process speeds. On the other hand welding in the conduction provides much higher quality with no defects or spatter. When welding in conduction mode it is essentially to avoid keyhole effect in order to maintain this quality. We have studied the transition between conduction and keyhole modes by varying the laser intensity and the interaction time, which is defined as the laser beam diameter divided by the travel speed. The results show that there is not one unique intensity value where the transition between keyhole and conduction mode occurs. Rather there is a range of values dependant on the interaction time. In practice this means that for a given laser spot size there are combinations of laser power and travel speed that can be indentified where keyhole effects can be avoided. The transition study was also extended to pulsed laser, where interaction time is defined as the pulse duration.Welding with a laser in keyhole mode provides deep penetration and/or high process speeds. On the other hand welding in the conduction provides much higher quality with no defects or spatter. When welding in conduction mode it is essentially to avoid keyhole effect in order to maintain this quality. We have studied the transition between conduction and keyhole modes by varying the laser intensity and the interaction time, which is defined as the laser beam diameter divided by the travel speed. The results show that there is not one unique intensity value where the transition between keyhole and conduction mode occurs. Rather there is a range of values dependant on the interaction time. In practice this means that for a given laser spot size there are combinations of laser power and travel speed that can be indentified where keyhole effects can be avoided. The transition study was also extended to pulsed laser, where interaction time is defined as the pulse duration.