Modelo de conocimiento para la planificación automática de la inspección en máquinas de medir por coordenadas

384 p.En esta tesis se presenta un modelo de conocimiento que sirve de base para la planificación automática de la inspección con Máquinas de Medir por Coordenadas (MMC) en el ciclo de desarrollo de productos. El modelo es flexible y está abierto a cualquier sistema de inspección o incluso a sistemas híbridos que incluyan la tecnología por contacto para geometrías sencillas típicas en piezas mecánicas basadas en primitivas o sus composiciones, y sistemas sin contacto para inspección de superficies complejas. Para el desarrollo del modelo se han aplicado técnicas de elicitación del conocimiento y metodologías de identificación y representación de éste, como son metodologías SADT, mapas conceptuales, diagramas de flujo, diagramas entidad-relación, etc. Para cada una de las actividades involucradas en el proceso de planificación, el conocimiento que se representa procede tanto de la sistematización de reglas ya conocidas pero no representadas formalmente y de reglas definidas exprofeso en esta tesis, al haberse constatado que no había base de conocimiento práctica donde apoyarse en algunos aspectos. Además, se ha estructurado y almacenado el conocimiento a través de la definición de una ontología, a la que se ha denominado ONTO-Process, válida para ser utilizada en la planificación de cualquier otro proceso del ciclo de vida de una pieza. Las reglas así definidas y representadas se han validado a través de su aplicación a dos piezas test. Estas dos piezas se han definido de tal manera que permiten jugar con los diferentes conceptos de conocimiento tratados en los modelos desarrollados

Influence of 17-4 PH stainless steel powder recycling on properties of SLM additive manufactured parts

[EN] Metal Additive Manufacturing (AM) processes are developing quickly. These processes have several attractive qualities, however, the quality of manufactured parts still remains a major issue that needs to be addressed if it is to become a prevalent technology in the industry. In some powder bed fusion techniques, such as Selective Laser Melting (SLM), there is a portion of initial powder that does not melt and it can be recycled to ensure the economic and environmental viability of the process. In previous research, we demonstrated the morphological, chemical and microstructural change suffered by 17-4 PH stainless steel powder after reusing it in a SLM manufacturing process. In this work, the properties of 17-4 PH stainless steel parts, printed from powder in different recycling states (virgin powder (P0) and 20 times reused powder (P20)), were evaluated, in order to establish good recycling procedures and optimise the SLM process performance. Analyses of the properties revealed a slight decrease in roughness and pore size with powder recycling. The external porosity of the samples is similar in both powder states; however, internal porosity decreases by increasing the number of reuse cycles. Regarding the microstructural analysis, a slight increase in the γ-phase is observed with the powder recycling, which leads to a slight increase in ductility and decrease in hardness of the samples. Therefore, it is concluded that the 17-4 PH powder recycling process in SLM manufacturing is adequate and recommended to ensure the economic and environmental viability of the process without adversely affecting the properties of the parts.S

New procedure for qualification of structured light 3D scanners using an optical feature-based gauge

[EN] This work evaluates the performance and operative limits to the dimensional accuracy of 3D optical scanning based on blue-light fringe projection technology. This technology, also known as structured light 3D scanning, is widely used in many reverse engineering applications. It allows the user to quickly capture and create point-clouds, by using images taken at different orientations of white-or blue-light fringe projected patterns on the part. For the survey, a large and feature-based gauge has been used with specific optical properties. The gauge is endowed with canonical geometrical features made of matt white ceramic material. The gauge was calibrated using a coordinate measuring machine (CMM) by contact. Therefore, it is possible to compare the measurements obtained by the structured blue-light sensor with those obtained by the CMM, which are used as reference. In the experimentation, the influence of the scanner software in the measurement results was also analysed. Besides, different tests were carried out for the different fields of view (FOV) of the sensor. The survey offers some practical values and limits to the accuracy obtained in each configuration.SIMinisterio de Economía y Competitividad de EspañaJunta de Castilla y Leó

Evaluation of the influence of post-processing on the optical inspection accuracy of additively manufactured parts

[EN] Optical measurement systems are important techniques for rapid inspecting additively manufactured parts by techniques such as selective laser melting (SLM). Depending on their application, SLM parts require post-processes such as sandblasting or heat treatment, commonly applied in order to improve their surface finish or mechanical properties, respectively. These post-processes modify the parts surface characteristics, and therefore the suitability for optical inspection. This work evaluates the influence of these SLM post-processes on optical inspection. For this, a test part, manufactured in 17-4PH stainless steel using a 3DSystems ProX100 machine, was optically measured using a structured light scanner and compared to the values obtained from contact measurements (reference values). Both optical and contact measurements were performed under three conditions: as-built, post sandblasting, and post sandblasting and subsequent heat treatment. The analysis results show that applying the sandblasting postprocessing provides a surface finish to the SLM parts suitable for optical inspection. This postprocess allows precise inspection of this type of parts, reaching values close to those obtained by contact. Likewise, it is concluded that the used structured blue-light scanner is suitable for inspecting SLM parts.SIMinisterio de Ciencia, Innovación y UniversidadesInstituto Universitario de Tecnología Industrial (SV-18-1-GIJON-1-06 and SV-19-GIJON-1-14

Proposal of design rules for improving the accuracy of selective laser melting (SLM) manufacturing using benchmarks parts

[EN] Purpose: Among the different methodologies used for performance control in precision manufacturing, the measurement of metrological test artefacts becomes very important for the characterization, optimization and performance evaluation of additive manufacturing (AM) systems. The purpose of this study is to design and manufacture several benchmark artefacts to evaluate the accuracy of the selective laser melting (SLM) manufacturing process. Design/methodology/approach: Artefacts consist of different primitive features (planes, cylinders and hemispheres) on sloped planes (0°, 15°, 30°, 45°) and stair-shaped and sloped planes (from 0° to 90°, at 5° intervals), manufactured in 17-4PH stainless steel. The artefacts were measured optically by a structured light scanner to verify the geometric dimensioning and tolerancing of SLM manufacturing. Findings: The results provide design recommendations for precision SLM manufacturing of 17-4PH parts. Regarding geometrical accuracy, it is recommended to avoid surfaces with 45° negative slopes or higher. On the other hand, the material shrinkage effect can be compensated by resizing features according to X and Y direction. Originality/value: No previous work has been found that evaluates accuracy when printing inwards (pockets) and outwards (pads) geometries at different manufacturing angles using SLM. The proposed artefacts can be used to determine the manufacturing accuracy of different AM systems by resizing to fit the build envelope of the system to evaluate. Analysis of manufactured benchmark artefacts allows to determine rules for the most suitable design of the desired parts.SIThe authors gratefully acknowledge the financial support provided by the Junta de Castilla y León and FEDER (project ref. LE027P17)

Influence of the scanning strategy parameters upon the quality of the SLM parts

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Impact of the laser scanning strategy on the quality of 17-4PH stainless steel parts manufactured by selective laser melting

[EN] A significant correlation between scanning strategies and the quality of parts manufactured additively with Selective Laser Melting (SLM) technology is shown. Therefore, a in deep study of the influence of scanning strategy is of great value for the manufacturing process in order to promote SLM technology in applications with high service requirements. In particular, this research is carried out on 17-4PH stainless steel parts, which is an alloy widely used in sectors such as aerospace or automotive for its excellent mechanical properties. This research proposes to evaluate the properties of 17-4PH parts manufactured using three usual scanning strategies (normal, concentric and hexagonal) in order to optimize the SLM process depending on the final part application. According to the obtained results, the following general conclusions have been drawn. Hexagonal strategy can be considered the most appropriate in terms of porosity. Both hexagonal and normal strategy have good mechanical properties, as well as geometrical and dimensional quality. Regarding surface finish of top face (where the used scanning pattern is visible), normal strategy is the most appropriate. In general, concentric strategy presents different results from the others: larger and irregular pores, ductile tensile behaviour, low roughness on lateral faces, and high geometrical errors in samples with large scanning vectors. As a future work, it is proposed to manufacture SLM parts combining these strategies in order to improve their properties. In addition, it is proposed to evaluate the influence of different post-process operations on the quality of parts printed by SLM using different strategies.S

Aplicación de la metodología CTMTC para evaluación formativa del trabajo grupal en ingeniería de fabricación

Se presenta una propuesta de aplicación de la metodología CTMTC para evaluar de forma más objetiva el trabajo en equipo que se desarrolla en una asignatura en el ámbito de la ingeniería de fabricación. La aplicación de esta metodología permite evaluar no sólo el resultado del trabajo final sino también las aportaciones y grado de compromiso de cada miembro del grupo. Además, se define un esquema de seguimiento del trabajo a lo largo del cuatrimestre, con hitos y entregables claves para realizar una verdadera evaluación formativa y garantizando la adquisición de competencias. La evaluación final se compone de una nota referente al trabajo grupal que es corregida por la nota del rendimiento individual de cada estudiante

Analysis of Modern Optical Inspection Systems for Parts Manufactured by Selective Laser Melting

[EN] Metal additive manufacturing (AM) allows obtaining functional parts with the possibility of optimizing them topologically without affecting system performance. This is of great interest for sectors such as aerospace, automotive, and medical–surgical. However, from a metrological point of view, the high requirements applied in these sectors constitute a challenge for inspecting these types of parts. Non-contact inspection has gained great relevance due to the rapid verification of AM parts. Optical measurement systems (OMSs) are being increasingly adopted for geometric dimensioning and tolerancing (GD&T) verification within the context of Industry 4.0. In this paper, the suitability (advantages and limitations) of five different OMSs (based on laser triangulation, conoscopic holography, and structured light techniques) for GD&T verification of parts manufactured by selective laser melting (SLM) is analyzed. For this purpose, a specific testing part was designed and SLM-manufactured in 17-4PH stainless steel. Once the part was measured by contact (obtaining the reference GD&T values), it was optically measured. The scanning results allow comparing the OMSs in terms of their inspection speed as well as dimensional and geometrical accuracy. As a result, two portable systems (handheld laser triangulation and structured blue-light scanners) were identified as the most accurate optical techniques for scanning SLM parts.S

Laser Defocusing Effect on the Microstructure and Defects of 17-4PH Parts Additively Manufactured by SLM at a Low Energy Input

[EN] In this paper, the microstructure, defects, hardness, and tensile strength of the 17-4PH specimens manufactured additively using the selective laser melting (SLM) technique were studied. The analyzed parts (10 mm size cubic specimens and tensile specimens) were manufactured with different defocus parameter values (−1, 0, +1 mm) in order to evaluate this effect with a low power laser (38 W). The study was carried out on three different sections of each cubic specimen, one perpendicular to the laser beam or SLM manufacturing direction (transversal section), and another two parallel to the laser beam direction (longitudinal sections). The specimens microstructures were analyzed with an X-ray diffraction technique, as well as optical, scanning electron, and transmission electron microscopes. Image J software was used to characterize the defects and phase ratio. In addition, hardness and tensile tests were performed according to the corresponding standards. The results show that the amount of austenitic phase and the average grain size varied with defocusing. The percentage of defective area was less than 0.25%. The analyzed defocus distance did not affect the number and average size of the defects. Adjusting the defocusing SLM parameter is important for manufacturing parts with good mechanical properties.S