Contact characterization between a cam and a crowned roller follower

In the higher pairs of a mechanism, like the one existing between a cam and roller follower, it is common to localize the maximum deformations, the maximum contact pressures and that appears the surface fatigue failure due to the relative motion between the cam and the roller. The formulations that characterized the contact are based in Hertz elastic contact theory. In this paper the contact between a cam and a crowned roller is studied applying the formulation for elliptical point contact proposed by Johnson. The contact ellipse obtained experimentally is presented to validate the elliptical point contact. The comparison of the width of the axes of the contact ellipse obtained experimentally and by the formulation presents the same level of errors than more sophisticated experimental methods.Postprint (published version

Assessment of the potential economic impact of the use of AM technologies in the cost levels of manufacturing and stocking of spare part products

Additive manufacturing (AM) technologies are appropriate manufacturing technologies to produce low rotation products of high added value. Products in the spare parts business usually have discontinuous demand levels of reduced numbers of parts. Indeed, spare parts inventories handle myriad of products that require big immobilized investments while having an intrinsic risk of no-use (for example due to obsolescence or spoilage). Based on these issues, the present work analyses the fundamental cost factors in a real case study of a company dedicated to the supply of spare parts for fluid conduction systems. Real inventory data is assessed to determine the product taxonomy and its associated costs. A representative product of the stock is analyzed in detail on original manufacturing costs, in AM costs and then redesigned with topological optimization to reduce the AM cost levels (via design for additive manufacturing). A general equation for cost assessment is formulated. Given the specific data collected from the company, the parameters in this general equation are calculated. Finally, the general equation and the product cost reduction achieved are used to explore the potential economic impact of the use of AM technologies in the cost levels of manufacturing and stocking of spare part products.Postprint (published version

Quantitative analysis of the effects of incorporating laser powder bed fusion manufactured conformal cooling inserts in steel moulds over four types of defects of a commercially produced injected part

The introduction of additively manufactured conformal cooling inserts in steel moulds for plastic injection is becoming a recommended standard. Fine adjustment of the temperatures in the mould has demonstrated potential to reduce cycle times and to increase production volumes. Within this context, the present article explores the historical production data of a commercially produced part, before and after the incorporation of an LPBF conformal cooling insert, to analyse what is the quantitative real effect on the efficiency of the production runs. The article analyses the change in the global rejection rates, and its effect over four different product defect types, i.e.: optical (surface), part integrity (bubbles, transparency, geometry), incomplete fill-in (interior), and breakages during extraction. The results demonstrate a specific decrease on the average appearance (from 20.53% to 13.48%; reduction of 7.05%) and variability (standard deviation from 14.16% to 6.81%; reduction of a 7.35%), of the global scrap rates, and a significant decrease in the scrap rates generated by optical defects and extraction part breakages. The article also characterises the former and the new processes by adjusting two distribution functions (Pareto Type-I and Weibull) and compares different estimates for the global expected scrap rates in past and future production runs.Peer ReviewedPostprint (published version

Análisis de las variables geométricas del frontal del vehículo en la protección del peatón

El objetivo principal de este proyecto de investigación es determinar la influencia de las variables geométricas del frontal del vehículo en las potenciales lesiones que pueden producirse a un peatón como consecuencia de un accidente. Este objetivo se consigue mediante el desarrollo de algoritmos específicos a partir de las medidas geométricas del frontal como variables de entrada y obteniendo la aceleración, el momento flector y el esfuerzo cortante como resultados. Este algoritmo puede aportar resultados iniciales sin necesidad de preparar un modelo de simulación específico o realizar ensayos de choque en laboratorio. Los principales resultados conseguidos en este proyecto de investigación son: La aceleración mínima y media del impacto desciende cuando la distancia longitudinal entre la traviesa de deformación y la traviesa de peatones aumenta. Asimismo, se detecta un decremento del esfuerzo cortante al aumentar esta distancia, por la influencia en la cinemática y dinámica que implica en el impactor. La distancia vertical entre la traviesa de deformación y la traviesa de peatones se considera como no significativa después de analizar los resultados del algoritmo. Por otro lado, la aceleración, minima y media, aumenta cuando se incrementa la altura del vehículo, resultado de la menor rotación del impactor en el impacto. El comportamiento del momento flector es análogo a la aceleración. El esfuerzo cortante varia en función de los puntos de contacto con el frontal, detectándose los valores máximos cuando los puntos de impacto con la rodilla están cercanos a la altura de la traviesa de deformación. Como resultado global, la cinemática y la dinámica del impactor indican que cuando se incrementa la distancia longitudinal entre traviesas, se obtiene un frontal con mayor capacidad de energía, y una rotación diferente del impactor durante el choque. Este trabajo de investigación proporciona un nuevo modelo de simulación aplicado a la protección de peatones. Este modelo es capaz de predecir los resultados de lesiones en un impacto con la extremidad inferior, en términos de aceleración, esfuerzo cortante y momento flector del impactor, únicamente teniendo un primer modelo del frontal del vehículo. Por tanto, este modelo matemático es de aplicación general en la industria del automóvil en los próximos años.Postprint (published version

Metodologia del modelo de asignación en el estudio de trafico de vigo

El modelo de transporte privado desarrollado para la ciudad de Vigo persigue una mejora de las condiciones de circulación. El estudio desarrolla diversos tipos e alternativas. Un primer grupo de alternativas aborda reordenaciones viales donde se evalúan diversas reconversiones de vías de doble sentido a vías de sentido único, así como la redistribución más conveniente de los espacios de aparcamiento para incrementar la capacidad vial. Un segundo grupo de alternativas evalúa el impacto de la construcción de la primera fase del trazado de un cinturón de circunvalación urbano. El estudio efectuado combina las etapas metodológicas clásicas, con la innovación en el procedimiento de construcción de los modelos derivada de las herramientas empleadas. La construcción semiautomática de modelos de grafos de transporte se ha realizado con el editor gráfico de redes TEDI del entorno de simulación de tráfico GETRAM que permite, a partir de una cartografía digitalizada, la definición ágil de las características de las distintas secciones de la red modelizada en un ámbito de estudio ( carriles, anchura, velocidad, longitud, capacidad ).Peer ReviewedPostprint (author’s final draft

Modelado del transporte de distribución mediante programación lineal entera

En este artículo se presenta un modelo de transporte de distribución usando programación lineal. El proceso global de distribución se considera dividido en sucesivos niveles entre la empresa y sus clientes. En cada nivel se distinguen unidades de origen-destino, entre un origen y varios destinos, con transporte directo y con ventanas en las fechas de entrega de los pedidos a transportar. La programación de la distribución se realiza en cada unidad, mediante programación lineal entera, considerando en la formulación flota limitada de vehículos y flota ilimitada. La programación global se obtiene como superposición de las programaciones de todas las unidades origen-destino. Para validar el modelo se han utilizado los datos proporcionados por una empresa del sector textil que cumple las características requeridas. Se concluye que el modelo presentado, resulta ser adecuado para modelar las empresas caracterizadas y ha permitido diseñar e implementar un procedimiento exacto para la programación de la distribución del producto de la empresa.Peer Reviewe

Titanium based bone implants production using laser powder bed fusion technology

Additive manufacturing (AM) enables fully dense biomimetic implants in the designed geometries from preferred materials such as titanium and its alloys. Titanium aluminum vanadium (Ti6Al4V) is one of the pioneer metal alloys for bone implant applications, however, the reasons for eliminating the toxic effects of Ti6Al4V and maintaining adequate mechanical strength have increased the potential of commercially pure titanium (cp-Ti) to be used in bone implants. This literature review aims to evaluate the production of cp-Ti and Ti6Al4V biomedical implants with laser powder bed fusion (L-PBF) technology, which has a very high level of technological matureness and industrialization level. The optimization of L-PBF manufacturing parameters and post-processing techniques affect the obtained microstructure leading to various mechanical, corrosion and biological behaviors of the manufactured titanium. All of the features are considered in the light of specifications and needs of bone implant applications. The most critical disadvantages of the L-PBF technology, such as residual stresses and leading deformations are introduced and the potential solutions are discussed. Moreover, the manufacturability of porous bone implants that causes benefit and harm in L-PBF applications are assessed.Peer ReviewedObjectius de Desenvolupament Sostenible::3 - Salut i BenestarPostprint (published version

Experiences in Agile R&D Project Management for New Product Design and Development in the Automotive Industry

In the past 20 years technology has advanced at incredible speed. Product life cycle has decreased tremendously. Innovation in product and process has become essential for companies’ survival. Products are not longer simple, they integrate different and new technologies and therefore manufacturing process is evolving towards intelligent, virtual, sustainable and high performance factories. In spite of all these changes in manufacturing, R&D project management has not evolved at the same pace. The authors have approached a new way of conducting R&D projects that can integrate IT Agile Project Management and Innovation Management best practices. As a result the present paperformulates a methodology for agile new product and process development that can match the actual product cycle development requirements, shortening project life cycles but keeping space for innovation and creativity. The methodology has been applied in R&D projects for the automotive industry to develop new automated manufacturing cells for production lines. The experience allowed to identify the key processes with more risk during the project execution and helped us to gather information to keep improving the methodology.Postprint (published version

Biological responses of ceramic bone spacers produced by green processing of additively manufactured thin meshes

Bone spacers are exclusively used for replacing the tissue after trauma and/or diseases. Ceramic materials bring positive opportunities to enhance greater osteointegration and performance of implants, yet processing of porous geometries can be challenging. Additive Manufacturing (AM) opens opportunities to grade porosity levels in a part; however, its productivity may be low due to its batch processing approach. The paper studies the biological responses yielded by hydroxyapatite with ß-TCP (tricalcium phosphate) ceramic porous bone spacers manufactured by robocasting 2-layer meshes that are rolled in green and sintered. The implants are assessed in vitro and in vivo for their compatibility. Human bone marrow mesenchymal stem cells attached, proliferated and differentiated on the bone spacers produced. Cells on the spacers presented alkaline phosphatase staining, confirming osteogenic differentiation. They also expressed bone-specific COL1A1, BGAP, BSP, and SPP1 genes. The fold change of these genes ranged between 8 to 16 folds compared to controls. When implanted into the subcutaneous tissue of rabbits, they triggered collagen fibre formation and mild fibroblastic proliferation. In conclusion, rolled AM-meshes bone spacers stimulated bone formation in vitro and were biocompatible in vivo. This technology may give the advantage to custom produce spacers at high production rates if industrially upscaled.Postprint (published version

Re-design of a component of a lower-limb robotic exoskeleton for integrating sensing capacity and enhancing multi-material direct additive manufacturing

The quest for the materialisation of advanced products is expanding the need for intelligent components and devices. One of the fields of application for such products is the medical technology industry, in which many value-added products could benefit from extending its embedded functionalities. To this regard, the obtention of such products via Additive Manufacturing Technologies would be very beneficial, providing that the design requirements could be met in a seamless and direct manner. In this context, the present article develops and analyses three design iterations of a component of a lower-limb robotic exoskeleton for integrating sensing capacity on it via multi-material direct additive manufacturing. In subsequent steps, the component geometry is optimised for additive direct manufacturing, and different functionalities are incorporated (padding for comfort and circuitry for sensing). For each iteration, the design is validated by means of finite element analysis and the main manufacturing parameters are assessed to compare the different times and costs yield. The third redesign incorporates three different materials (ABS, TPU and PE+Cu), but still it is possible to be 3D printed with a two extruder-head FDM 3D printer. The design and manufacturing results obtained could be implemented in further biomedical products or other parts requiring advanced functionalities.Peer ReviewedObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraObjectius de Desenvolupament Sostenible::3 - Salut i BenestarPostprint (published version