Prediction of SLS parts properties using reprocessing powder

Purpose: Owing to the operating principle of powder bed fusion processes, selective laser sintering (SLS) requires effective management of the mixture ratio of processed material previously exposed to the high temperatures of processing with new virgin material. Therefore, this paper aims to fully understand the effect that the successive reprocessing has in the powder material and to evaluate its influence on the properties of SLS parts produced at different building orientations. Design/methodology/approach: Polyamide 12 material with 0%, 30% and 50% of virgin powder and parts produced from them were studied through five consecutive building cycles and their mass, mechanical, thermal and microstructural properties were evaluated. Then, the experimental data was used to validate a theoretical algorithm of prediction capable to define the minimum amount of virgin powder to be added on the processed material to produce parts without significant loss of properties. Findings: Material degradation during SLS influences the mass and mechanical properties of the parts, exhibiting an exponential decay property loss until 50% of the initial values. The theoretical algorithms of reprocessing proved the appropriateness to use a mixture of 30% of virgin with 70% of processed material for the most common purposes. Practical implications: This paper validates a methodology to define the minimum amount of virgin material capable to fulfil the operational specifications of SLS parts as a function of the number of building cycles, depending on the requirements of the final application. Originality/value: The use of theoretical models of prediction allows to describe the degradation effects of SLS materials during the sintering, ensuring the sustainable management of the processed powder and the economic viability of the process.The authors acknowledge the financial support given by FCT – Portuguese Foundation for Science and Technology through the reference project UID/CTM/50025/2019 and the European Structural and Investment Funds in the FEDER component, through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) [Project n0 037902; Funding Reference: POCI-01-0247-FEDER-037902]

Evaluating the electromagnetic shielding of continuous carbon fiber parts produced by additive manufacturing

Electronic devices are sensitive to electromagnetic (EM) emissions, and require electromagnetic shielding protection to ensure good operation, and prevent noise, malfunctioning, or even burning. To ensure protection, it is important to develop suitable material and design solutions for electronic enclosures. Most common enclosures are made with metal alloys using traditional manufacturing methods. However, using thermoplastic composites combined with additive manufacturing (AM) technologies emerges as an alternative that enables the fabrication of complex parts that are lightweight, consolidated, and oxidation- and corrosion-resistant. In this research, an AM technique based on material extrusion was used to print 2 mm-thick specimens with a multi-material made of micro-carbon fiber (CF)-filled polyamide that was reinforced at specific layers using continuous carbon fibers stacked with a 90° rotation to each other. The specimens’ electromagnetic shielding effectiveness (EMSE) was evaluated in the frequency band of 0.03–3 GHz using the coaxial transmission line method. Depending on the number of CF layers, the EM shielding obtained can be up to 70 dB, with a specific shielding up to 60 dB.cm3/g, predominantly by the absorption mechanism, being 22 times higher than without the CF layers. These findings promote this innovative approach to lightweight customizable solutions for EM shielding applications.ERDF - European Regional Development Fund(47108

Design and development of an Automatic Optical Inspection (AOI) system support based on digital manufacturing

Visual inspection of components, subassemblies and final products is an essential step to ensure the quality control of ready-to-market electronic components. In many manufacturing plants, including Bosch Car Multimedia S.A., typically automated systems for automatic optical inspection (AOI) are implemented at several workstations to perform visual verification and validation in between critical production tasks. At Bosch Car Multimedia S.A., the AOI system includes a metallic support frame that accommodates a series of components for the function of AOI. The support frame is attached to a robotic arm for controlled movement. As the AOI is a rather fast-moving process, deformation of components may occur during monitoring due to the high acceleration of the robotic arm while operating. In addition to this issue, the existent AOI system includes a high number of components and connections which increase complexity for assembly and disassembly operations. This paper presents the redesign for enhanced performance and functionality of a AOI metallic support frame by resourcing to the generative design (GD) exploration method. Furthermore, additive manufacturing technology, based in selective laser sintering (SLS) of polymeric powders, was used for the production of a new lightweight and reliable version of an AOI support frame. The alternative AOI support frame configuration consists of a single consolidated polymeric component that enabled an overall weight decrease above 30% and a reduction of main components and total number of parts of approximately 89% and ~77%, respectively.FEDER - Federación Española de Enfermedades Raras(undefined)European Structural and Investment Funds in the FEDER component, through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) [Project nº 039479

Polymeric microsensors using microtechnologies

Tese de Doutoramento - Programa Doutoral em Ciência e Engenharia de Polímeros e CompósitosThe work present here aims to combine advanced and specialized polymeric materials and microtechnologies with silicon based microtechnologies to develop an innovative concept for a thermal convective accelerometer with improved performance while also overcoming existing limitations. Thermal convective accelerometers have a transduction mechanism based in heat transfer by convection over a working fluid. The thermal accelerometer is a relatively recent technology and although research focused in improving many properties, parameters and processing techniques, thermal accelerometers still present some drawbacks regarding the power consumption caused by thermal losses through the fabrication material (typically silicon based) and limited third sensing dimension (planar silicon based microtechnologies). New developments towards the optimization of the existing thermal accelerometers may limit the power consumption and allow an easy integration of a Z-axis sensitive dimension. The methodology from the development of a concept to the actual fabrication and characterization requires a series of steps that need to be followed in a sequential way, namely: design and simulation analysis of the device concept (considering the electrical, thermal and fluidic domains), based on CAD and FEM techniques (using a FSI approach); development (project and simulation analysis) of tools based on CAD and CFD techniques; definition and optimization of a fabrication methodology (combination of polymeric and silicon based microtechnologies); and a full characterization of the fabricated device (sensitivity, bandwidth, dynamic range, and power). A three-axes thermal convective accelerometer was fully manufactured containing two main components: a polymeric based external structure fabricated my means of microinjection moulding technology that generates an isolated chamber from outside influences while supporting the second component, a polymeric flexible membrane that sustains and protects the metallic heating and sensing elements fabricated by microtechnologies. The proposed solution for the fabrication of a three-dimensional polymer based thermal accelerometer based in convection is innovative and the main contribution will be the use of polymeric materials not commonly used in microsystem technology and in electronic and instrumentation systems that are suitable to solve the main problems related to the current stateof- art of thermal accelerometers. Fabricated accelerometers were fully tested and characterized presenting a XY-axes sensitivity around 8 mV/g, a Z-axis sensitivity of 2.2 mV/g, and a 4 Hz bandwidth for a power of 45 mW. Thermal tests performed show that the heater can sustain up to 280 ºC without overheating the remaining structures and damaging the device. The developed technology has huge potential for functional highly complex threedimensional geometries at the micro-scale.O trabalho aqui apresentado tem como intuito combinar materiais e microtecnologias poliméricas avançadas e especializadas com microtecnologias à base de silício para o desenvolvimento de um conceito inovador para um acelerómetro térmico convectivo com um desempenho melhorado superando também as limitações existentes. Os acelerómetros térmicos convectivos tem um mecanismo de transdução baseado na transferência de calor por convecção através de um fluído funcional. O acelerómetro térmico é uma tecnologia relativamente recente e embora os estudos científicos se tenham focado na otimização de diversas propriedades, parâmetros e técnicas de processamento, os acelerómetros térmicos ainda apresentam algumas desvantagens relativas ao consumo energético provocado pelas perdas térmicas através do material de fabrico (normalmente à base de silício) e também uma terceira dimensão sensível limitada (microtecnologias planares à base de silício). Novos desenvolvimentos no sentido da otimização dos existentes acelerómetros térmicos podem limitar o consumo energético e permitir uma integração mais fácil da dimensão sensível do eixo dos ZZ. A metodologia desde o desenvolvimento do conceito até à atual fabricação e caracterização requere uma série de etapas que necessitam de ser seguidas de uma forma sequencial, nomeadamente: projeto e análise por simulação do conceito do dispositivo (considerando os domínios elétrico, térmico, e fluídico), com base em técnicas CAD e FEM (através de uma abordagem FSI); desenvolvimento (projeto e análise por simulação) de ferramentas com base em técnicas CAD e CFD; definição e otimização de uma metodologia de fabrico (combinação de microtecnologias de polímeros com microtecnologias à base de silício); e uma caracterização completa do dispositivo fabricado (sensibilidade, largura de banda; gama dinâmica, e energia). Um acelerómetro térmico convectivo com três eixos foi inteiramente fabricado contendo dois componentes principais: uma estrutura externa à base de polímeros fabricada através da tecnologia de moldação por microinjeção gerando uma câmara isolada de influências externas que suporta o segundo componente, uma membrana polimérica flexível que sustem e protege os elementos metálicos de aquecimento e sensoriais fabricados por microtecnologias. A solução proposta para o fabrico de um acelerómetro térmico polimérico tri-dimensional baseado em convecção é inovativa e a principal contribuição consiste no uso de materiais poliméricos não comumente utilizados na tecnologia de microsistemas e na electrónica e instrumentação de sistemas que são adequados para solucionar os principais problemas relacionados com o atual estado da arte dos acelerómetros térmicos. Os acelerómetros fabricados foram testados e caracterizados apresentando uma sensibilidade de cerca de 8 mV/g para os eixos XY e 2.2 mV/g para o eixo ZZ, e uma largura de banda de 4 Hz para uma energia de 45 mW. Foram realizados testes térmicos demonstrando que a resistência de aquecimento consegue suportar até 280 ºC sem sobreaquecimento das restantes estruturas e sem danificar o dispositivo. A tecnologia desenvolvida apresenta um grande potencial para geometias tri-dimensionais altamente complexas e funcionais à escala micro.Portuguese Fundação para a Ciência e a Tecnologia (FCT), for the financial support under the PhD scholarship SFRH/BD/78372/2011). The work was supported by FEDER through COMPETE and national funds through FCT in the framework of the project PTDC/EEA-ELC/099834/2008. The author would like to acknowledge the doctoral program in Science and Engineering of Polymers and Composites for supporting this work

3 axis polymeric accelerometer and method of production

Patente de Invenção Nacional n.º 105759 (submetida)The present invention consists in a thermal accelerometer capable of detecting acceleration in multiple axes. The accelerometer is made of four microinjected polymeric parts, which can be two identical top parts and two identical central parts or four different parts, which are assembled with active polymeric membranes to construct the 3-axis acceleration sensing device. The microinjected parts provide mechanical support for the heater and temperature sensors that are placed on the membranes. The device operating gas medium is hermetically sealed by the polymer parts and electrical current applied to the heater causes the air to heat and external acceleration imposes a gradient of temperature sensed by the thermal sensing elements.Fundação para a Ciência e a Tecnologia (FCT

New concepts in flexible packaging

A new approach based in a flexible packaging is being analysed to replace a commercial package for the internal transport of variable electrostatic discharge sensitive devices at Bosch Car Multimedia facilities. During the design and fabrication process of a packaging, special attention is given to the handling, by the final consumer, in order to avoid an unusable or inefficient product. This paper presents an exploratory and comparative usability test performed to evaluate the satisfaction concerning several prototype handles, in real context of use. A quantitative evaluation was achieved by means of a specially developed questionnaire with a seven level Likert scale answer, and a qualitative analysis based in the feedback given by the company collaborators. The results indicate that the handle of the actual packaging is inefficient and inadequate for the tasks to be performed, and that two of the developed handle designs are more comfortable and ergonomic.(undefined)info:eu-repo/semantics/publishedVersio

Development of functionalised foam for electrostatic discharge applications

Electrostatic discharge-sensitive devices (ESDS) consist of electronic systems that are easily damaged by electrostatic fields or discharges. To safely stow and transit the ESDS, Bosch Car Multimedia S.A. resorts to thermoformed trays with a specific design for each product configuration. Although efficient, the solutions’ specificity arose logistic issues that created the need for an alternative approach. This paper reports the investigation for the development of a flexible tray, based on an electrostatic-dissipative integral skin foam. First, a commercial integral skin polyurethane foam was evaluated by varying components mixing ratio. Once achieved a suitable combination of hardness and density, post-formulation additives (colour and anti-static) were investigated. Free expansion foaming stages were assessed and cured foams were characterised in terms of electrostatic discharge protection. Moulded foams with variable patterns were developed and evaluated considering the application purpose requirements. Real-scale prototypes of the most adequate concept design were produced and analysed.This work is funded by FCT – Portuguese Science and Tech nology Foundation, Reference ID/CTM/50025/2019, and by FEDER, through COMPETE 2020 [Project n° 039479; Funding Reference: POCI-01-0247-FEDER-039479