Metodología de detección de óxido residual en superficies de acero inoxidable mediante visión por computador

La presente tesis doctoral es una investigación que propone una alternativa basada en visión por computador a la detección, por parte de un operador humano, de un defecto superficial denominado óxido residual que puede producirse durante el procesamiento de bobinas de acero inoxidable en una línea de recocido y decapado de la industria siderúrgica. Se trata de un defecto cuya eliminación incompleta puede producir problemas operativos durante el procesamiento posterior que va a sufrir la bobina (laminación en frío, recocido final, revestimiento, tintado especial, etc.) afectando claramente a la calidad superficial del producto final. La tesis tiene dos objetivos fundamentales. Un primer objetivo que consiste en la elaboración de una metodología para la detección de óxido residual en superficies de acero inoxidable basada en visión por computador que cumple con una serie de requisitos: detecta el defecto sobre superficies en movimiento de manera fiable, robusta y eficiente, considera una amplia variedad de tipos de acero y acabados superficiales, cuantifica la cantidad de defecto existente sobre la superficie y lo clasifica dimensionalmente y, finalmente, es viable para su aplicación en un entorno industrial agresivo. Un segundo objetivo complementario donde se construye e implanta un sistema de inspección visual automatizado para la detección y clasificación de defectos de óxido residual basado en la metodología previamente elaborada y que permite la obtención de los datos necesarios para su validación. En la memoria de tesis se realiza un estudio del arte sobre detección y clasificación de defectos en la producción de acero y otro, más específico, sobre sistemas para la detección de óxido residual en superficies de acero. El proceso de adquisición de imágenes integra un nuevo sistema de iluminación difusa estroboscópica para inspección de superficies en movimiento que ilumina de forma homogénea la superficie de inspección y evita la formación de sombras provocadas por la topografía de la superficie del material. La estrategia de procesamiento de imágenes para la detección y clasificación dimensional de manchas de defecto integra una nueva técnica de segmentación basada en la umbralización automática del histograma a partir de conocimiento empírico. Para ello, se crea una base de conocimiento constituida por índices estadísticos descriptivos extraídos de una población de imágenes previamente caracterizadas por un experto. Sobre esta base de conocimiento, se construye un modelo matemático empírico basado en una red neuronal que permite establecer un rango de búsqueda del umbral de binarización final. La complejidad del sistema de inspección se reduce mediante una inspección automatizada basada en un muestreo aleatorio simple de la superficie de acero que agiliza la adquisición y el tratamiento de datos. El diseño de la arquitectura de adquisición y procesamiento de imagen, el accionamiento de los movimientos del sistema de inspección visual automatizado y la técnica de inspección basada en muestreo aleatorio han dado lugar a una patente internacional reconocida en varios países

A comparative study of image processing thresholding algorithms on residual oxide scale detection in stainless steel production lines

The present work is intended for residual oxide scale detection and classification through the application of image processing techniques. This is a defect that can remain in the surface of stainless steel coils after an incomplete pickling process in a production line. From a previous detailed study over reflectance of residual oxide defect, we present a comparative study of algorithms for image segmentation based on thresholding methods. In particular, two computational models based on multi-linear regression and neural networks will be proposed. A system based on conventional area camera with a special lighting was installed and fully integrated in an annealing and pickling line for model testing purposes. Finally, model approaches will be compared and evaluated their performance..Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The Upper Bound Theorem in forging processes: Model of Triangular Rigid Zones on parts with horizontal symmetry

The analysis to determine the necessary forces with which to achieve a plastic deformation in metallic materials, in particular, in forging processes and under conditions of plain strain, has been raised over the years through a double approach; on the one hand, by analytical methods that involve a great complexity in their developments but that allow a direct understanding of the parameters that direct these processes. On the other hand, numerical methods, in which, thanks to the enormous development of computer technology, they provide solutions with a high approximation but, in most cases, do not allow to interpret independently the effect of each one of the parameters that come into play. The development of computers relegated analytical methods to the background. An alternative of great interest to apply these methods comes from the study of the Upper Bound Theorem by means of the Triangular Rigid Zones (TRZ) Model. One of the main limitations in the application of this model come from the fact that it is necessary to define a kinematically admissible velocity field and for complex geometric configurations of parts, this field becomes increasingly complicated. A new approach has delimited, from a theoretical perspective, a modular configuration based on a General Module formed by three TRZ that adapts to any geometry of flat surfaces of the part. Another limitation of the Upper Bound Method is the consideration of the plain strain represented by a flat section with double symmetry. Obviously, this imposition only allows to study a limited number of part configurations, which restricts its application in forging processes since the great majority of forged parts do not present geometrically this double symmetry. The present work releases one of these boundary conditions allowing to expand the possibilities of application of this method.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Guide for the implementation of operational control procedures in underwater cutting and welding activities.

Professional diving is an occupation that includes a wide spectrum of different activities, but with the same common denominator: its performance underwater. It is carried out in both fresh and salt waters and encompasses such disparate tasks that professional diving is currently present in numerous productive sectors: hydrocarbon extraction, offshore platforms, port maintenance, public works, civil engineering, infrastructure hydraulic, power plants (hydroelectric, thermal and nuclear), shipbuilding, underwater construction, aquaculture, ship and boat salvage, NDT filming and reporting, teaching and training, and scientific research (geological, biological, archaeological, etc.). It is also characterized by being one of the most dangerous professions and presenting very specific risks, derived from the workplace in a hyperbaric environment, combined with to other hazards of the work activity similar to those of the ground workers. The objective of this study is to analyze procedural models based on the UNE_EN_ISO 45001:2018 Standard, applied to the execution of thermal cutting and underwater welding works. In order to carry out this work safely and in the most effective way, it must be systematically analyzed, generating procedures and work instructions based on the tasks considered critical, and essential knowledge for all personnel who perform them. Such procedures and instructions should be based on a systematic analysis of the steps taken to perform each task, including the risks involved and the safety measures to be taken to control, reduce or, where appropriate, eliminate them.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Thermal Measurements based on Image Processing for In-Situ Monitoring of 3D Fused Filament Fabrication (FFF).

Nowadays new applications based on the 3D printing technique demand increasingly strict product quality requirements. The in-situ monitoring of variables associated with the manufacturing process through the application of different techniques could help to evaluate the process and ultimately to ensure product quality. In this regard, the acquisition and evaluation of variables and indexes derived from thermographic analysis during the process are key for an early defect detection and can contribute to quality estimation. In this work, a new methodology is proposed for the monitoring and analysis of the additive manufacturing process based on the processing of thermographic images from an LWIR (Long Wave Infrared) camera. The methodology and the suitability of the variables and indexes extracted during the monitoring of the manufacturing process are discussed for the case of a 3D fused filament fabrication of polymers.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Laser profilometry application in welding geometrical characterization.

Welding processes are commonly used in the industry for the manufacture of large parts or due to their complex geometry that does not allow the part to be manufactured as a whole. Nevertheless, the union can show worst mechanical properties than the rest of the piece, affecting negatively its service behavior, so it is necessary evaluate weald seam to ensure the correct process application. Electrical welding operations are commonly used due to the reduced equipment size or their possibilities application in numerous metallic materials. Notwithstanding, different variables have to be taken into account during the metal deposition, as intensity or speed deposition, among others. Weald seam geometrical evaluation is usually utilized to validate the union surface conditions. Despite this, surface irregularities caused during the process make its difficult to measure correctly with conventional equipment. However, laser profilometry is a non-contact technique that can be used to generate 3D profile of weald seam, facilitating its measurement with high accuracy. Therefore, in this work an initial analysis of the influence of material deposition speed and arc welding intensity on the weald seam geometry will be carried out using a laser profilometry equipment. In addition, to ensure a correct information acquisition, the laser profilometer requires a constant speed movement in relation with the weald seam analyzed, so new equipment has been manufactured, using additive manufacturing techniques, to support the profilometer throughout the information acquisition process.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech