Óscar Martín

Direct quality prediction in resistance spot welding process: Sensitivity, specificity and predictive accuracy comparative analysis

Abstract In this work, several of the most popular and state of the art classification methods are compared as pattern recognition tools for classification of resistance spot welding joints. Instead of using the result of a non-destructive testing technique as input variables, classifiers are trained directly with the relevant welding parameters, i.e. welding current, welding time and the type of electrode (electrode material and treatment). The algorithms are compared in terms of accuracy and area under the receiver operating characteristic curve metrics, using nested cross-validation. Results show that although there is not a dominant classifier for every specificity/sensitivity requirement, support vector machines using radial kernel, boosting and random forest techniques obtain the best performance overall.

Approach to the Study of Workpiece Damage in Drilling of Carbon Fiber Composites by Using Thermography IR

The present work shows the first results of the study methodology of the process parameters applied to drilling of composites reinforced with carbon fiber (CFRP) used in the aeronautical industry. The analysis uses both cutting forces and temperatures achieved in the cutting process, although it has focused on the application of IR thermography to the study of the hole. The study of the defects that can be found on the workpiece, associated with these processes (delamination), is approached by using both optical microscopy and SEM.

Independence of EPR and PAP tests performed on resistance spot welding joints

ABSTRACT In the present paper, the possible relationships among the variables of the potentiodynamic anodic polarisation (PAP) test and the electrochemical potentiokinetic reactivation (EPR) test, both performed on resistance spot welding joints of AISI 304 stainless steel, are investigated. Results show that PAP variables are statistically independent from those of EPR, which implies independence between the pitting corrosion behaviour and the degree of sensitisation of the material. Parameters from PAP test are dependent among them, but this association is found noisy since the current density along the passive zone is not exactly constant. The parameters from the EPR test are confirmed as very related, presenting a linear relationship and a high coefficient of determination.

Combined Effect of Resistance Spot Welding and Post-Welding Sensitization on the Pitting Corrosion Behavior of AISI 304 Stainless Steel

This work studies the combined effect of resistance spot welding and post-welding sensitization on the pitting corrosion behavior of AISI 304 (UNS S30400) by using cyclic potentiodynamic polarization tests. The combined effect of welding and post-welding sensitization give rise to worse pit nucleation resistances and better repassivation capacities than those of the state without prior welding. This behavior is caused by the weld metal zone, a cast dendritic microstructure with δ-ferrite in interdendritic regions, whose microstructural regeneration kinetics is faster than that of HAZ and that of the parent metal and where the chromium-rich phases are more homogeneously distributed than in the parent metal.

Dimensional Validation of a 3D Digitization System

A three-dimensional measurement system has been set up. The digital models have been obtained using a webcam and structured light. After this, a software for measuring the digital geometries has been applied. In order to validate the digital models, the workpiece has been measured in a Laboratory of Metrology by means of a Coordinate Measuring Machine. While digital models can be obtained from multiple scan system configurations, not all of them get the same degree of accuracy. After analyzing the results, it can be determined the best condition for obtaining the digital model so that discrepancies between measurements and corresponding digital model of the workpiece are minimized. Also, it has been estimated a value of measurement uncertainty for each of the models studied.

Thermography IR Applied to Analyse the Influence of the Deformation Speed in the Forming Process

This work presents the development of an experimental study which aims to establish arelationship of temperature variations, deformation speeds and the possible microstructural changes in the AISI 304 stainless steel. For this, an IR thermographic camera recorded serveral tensile test with different deformation speeds.