Stereolithography

The stereolithography (SLA) process and its methods are introduced in this chapter. After establishing SLA as pertaining to the high-resolution but also high-cost spectrum of the 3D printing technologies, different classifications of SLA processes are presented. Laser-based SLA and digital light processing (DLP), as well as their specialized techniques such as two-photon polymerization (TPP) or continuous liquid interface production (CLIP) are discussed and analyzed for their advantages and shortcomings. Prerequisites of SLA resins and the most common resin compositions are discussed. Furthermore, printable materials and their applications are briefly reviewed, and insight into commercially available SLA systems is given. Finally, an outlook highlighting challenges within the SLA process and propositions to resolve these are offered

Response surface method for optimisation of SLA processing parameters

In the current study, response surface method (RSM) was applied to correlate stereolithography (SLA) process parameters such as layer thickness, hatch overcure, and part orientation to SLA part characteristics such as density, surface finish and ultimate tensile strength (UTS). The results showed that density was directly proportional to the hatch overcure but inversely affecting the layer thickness. Besides, the hatch overcure was shown to have a positive effect on the UTS, while the layer thickness was found to influence the UTS adversely. Furthermore, the relationship between the layer thickness and surface roughness was suggested to be directly proportional. The optimised values of process parameters indicated by the response surface model were 90°, 0.12 mm and 0.1 µm for the part orientation, hatch overcure and layer thickness, respectively. The corresponding predicted density, UTS and surface roughness of an SLA part were 1,098 kg/m3, 42.8 MPa and 5.31 µm, respectively

Continuous, Non-Destructive Detection of Surface Bacterial Growth with Bioinspired Vascularized Polymers

Reducing or eliminating bacteria on surfaces is vital for medical devices, drinking water quality, and industrial processes. Evaluating surface bacterial growth at buried interfaces can be problematic due to the time-consuming disassembly process required for obtaining standard surface samples. In this work, a continuous, non-destructive, and reusable method was developed to detect surface bacterial growth at buried interfaces. Inspired by vascular systems in nature that permit chemical communication between the surface and underlying tissues of an organism, bacterial-specific signals diffusing from cells on the surface were detected in channels filled with an inert carrier fluid embedded in a polymer matrix. The carrier fluid was analyzed using conductivity, ultraviolet-visible (UV-vis) spectroscopy, and high-performance liquid chromatography (HPLC); methods that ranged in sensitivity and accessibility. A second iteration prototype was developed that addressed delamination and contamination issues. Carrier fluid from the second prototype vascularized polymers with surface Escherichia coli growth recorded greater values in conductivity (9.32 ± 0.22 mS/cm) against controls with no bacteria (7.86 ± 0.29 mS/cm) after 24 hours. Additionally, sample carrier fluid absorbance (0.535 ± 0.041 a.u.) was greater than control carrier fluid absorbance (0.430 ± 0.016 a.u.) after 24 hours. HPLC analysis detected two matrix-specific peaks in carrier fluid from controls and the appearance of a bacterial-specific peak in carrier fluid from samples. Extracting and refilling the vascular channels with new carrier fluid allowed for the system to continuously monitor surface bacterial growth over time and measure early detection. Differences in conductivity, absorbance, and HPLC were observed at 8 hours of surface bacterial growth. Clinically relevant bacterial strains, Staphylococcus aureus and Pseudomonas aeruginosa, were tested and yielded significant increases in carrier fluid in conductivity, absorbance, and HPLC peak areas. This work lays the foundation for the use of vascularized polymers as an adaptive system for the continuous, non-destructive detection of surface bacteria along with multiple methods for analysis

Modelling, inspection, and post-processing of layer-based additive manufacturing surfaces to maintain product quality

Today???s Additive Manufacturing (AM) is mostly layer-based. Despite AM???s great capabilities in fabrication of complex geometries, product???s surface roughness is a limiting factor in many industrial applications. Therefore, application of AM parts in industrial services highly relies on appropriate modeling, inspection, and post-processing of the fabricated surfaces. A thorough investigation of surface roughness to improve surface quality of AM products is the focus of this thesis by developing methodologies to complete the three tasks of modelling, inspection, and post-processing of AM surfaces. A theoretical formulation to model surface roughness of layer based manufactured parts is developed by defining centerline using a Total Least Square (TLS) approach and the model is validated experimentally. The developed model is also used for surface topography of AM parts as a new metrology approach. Optical scanning data point cloud of Fused Deposition Modeling (FDM) parts are used to conduct inspection based on the developed methodology. 3D topography of the surfaces are reconstructed when a good agreement with the corresponding 2D profilometer inspection is observed. Acetone vapour bath smoothing is used for post-processing of FDM parts. The number of smoothing cycles, and the duration of each cycle are considered as the main smoothing parameters. Effect of geometric complexity and smoothing parameters are studied and the best smoothing settings are proposed for a desired level of smoothing requirement. The developed experimental models allow engineers to plan the smoothing process based on the build orientation and geometric complexity of the product

Desenvolvimento de uma máquina de limpeza e de cura para peças impressas em SLA

A manufatura aditiva (MA) tem crescido nos últimos anos. A sua inicial função de prototipagem rápida e aceleramento do processo de desenvolvimento de produto é ainda a sua principal função, embora existam desenvolvimentos no sentido de usar estas técnicas para o fabrico de produtos de utilização final como já se começa a verificar em várias empresas. Devido às suas características, os processos de manufatura aditiva parecem ter o seu espaço no mercado, em especial na produção de pequenas séries e produtos personalizados. As peças fabricadas por MA com a tecnologia Stereolithography (SLA), após serem retiradas da impressora, encontram-se revestidas de resina não curada e as próprias peças estão apenas parcialmente curadas, pelo que nesta fase devese utilizar um solvente para retirar toda a resina não curada da superfície de modo a obter um melhor acabamento superficial. Após as peças estarem limpas é necessário curar totalmente as peças para estas obterem as suas propriedades finais. Esta dissertação aborda o desenvolvimento de uma máquina que realiza a limpeza e cura de peças impressas pela tecnologia SLA, construída com uma combinação de peças obtidas por MA e processos convencionais. A impressora utilizada durante a prototipagem foi a Original Prusa i3 MK3. A metodologia de desenvolvimento de produto foi aplicada com estabelecimento de necessidades e especificações que levaram à geração e seleção de conceitos. Foi produzido um protótipo do conceito mais promissor e este foi testado para estabelecer as especificações finais. Por fim, foi desenvolvido um custo de prototipagem com o material e energia utilizados para calcular o custo total unitário do protótipo e realizar uma aproximação de um eventual produto final, através de duas opções apresentadas

Capacitive ultrasonic transducers fabricated using microstereolithography

Air-coupled thin-membrane capacitive ultrasonic transducers have been developed that use microstereolithography fabrication with architectures comprised entirely of partially metalised photopolymer. These devices derive considerable advantages from rapid prototyping technology, in that they are cheap to produce, and benefit from the design-to-product lead times inherent in the production of components using stereolithography. To date membranes have been produced with thicknesses ranging from 30 to 90 μm with aspect ratios in the range of 100 - 1000. These devices have been shown to operate both as transmitters and as receivers of ultrasound, and have a bandwidth approaching 100% with a centre frequency of 100 kHz. The method of fabricating these devices allows for easy modification for various applications including structural health monitoring and immersion, as well as affording the possibility of integrated focussing or wave-guiding architecture and packaging that can be incorporated into a single build. Fundamental or subtle changes to a given transducer design may be achieved incurring little additional cost or time. This novel approach to transducer fabrication enables the bespoke manufacture of specific transducer architectures from a computer aided design package using polymers that exhibit different material properties to materials used in silicon micromachining, but at the same time allow for fabrication on a scale that is approaching that of microfabrication. The versatility of 3-D rapid prototyping allows the realisation of more complicated structures than was possible previously. This work examines these transducers in terms of their characterisation and their operation in conjunction with other transduction architecture, such as focussing parabolic mirrors that were also produced using the same manufacturing technology. In addition, their operation in contacting acoustics and the reception of surface acoustic waves has been demonstrated. Immersion studies using these devices have found that that they hold promise for operation in a variety of different media. These transducers are seen as an important prototype development tool in the field of capacitive ultrasonic transduction and microphone-speaker design

Interface Oral Health Science 2016: Innovative Research on Biosis–Abiosis Intelligent Interface

Dentistry; Oral and Maxillofacial Surgery; Regenerative Medicine/Tissue Engineerin

Automatic Determination of Part Build Orientation for Laser Powder Bed Fusion Additive Manufacturing

Laser powder bed fusion is one of the key and most widely used additive manufacturing processes. The use of this process to build a part includes a set of continuous activities, where process planning is an indispensable one. This activity refers to a systematic planning of the build orientation, supports, slices, laser scanning path and process parameters to build a part using a laser powder bed fusion machine. It includes four successive steps, where build orientation determination is the first step. At present, most of the determination tasks in real workshops are manually completed by process planners according to their production knowledge and experience. Different process planners could determine different build orientations for an identical part under the same conditions. This would increase the build time and build cost and have a negative influence on the quality and production stability of the built part. To this end, a study on automatic determination of part build orientation for laser powder bed fusion additive manufacturing is carried out in this thesis. This study divides build orientation determination into alternative orientation generation and optimal orientation selection. Firstly, an automatic alternative orientation generation method based on facet clustering for laser powder bed fusion is presented. A set of fuzzy aggregation operators for evaluating the values of attributes of alternative orientations are then constructed. Using the constructed operators, an automatic optimal orientation selection method based on multi-attribute decision making for laser powder bed fusion is proposed. Finally, an automatic part build orientation determination method for laser powder bed fusion is developed via combining and implementing the alternative orientation generation method and optimal orientation selection method. Case studies are presented to illustrate the application of the developed method. The effectiveness, efficiency and advantages of the method are evaluated via theoretical analysis, experimental analysis and comparisons. The completed research work in the thesis is expected to realise a transformation of part orientation for laser powder bed fusion from a manual mode to a computer-aided mode. It can easily be extended to other additive manufacturing processes and can provide effective ideas and methodology for study of computer-aided process planning for additive manufacturing

Capacitive ultrasonic transducers fabricated using microstereolithography

Air-coupled thin-membrane capacitive ultrasonic transducers have been developed that use microstereolithography fabrication with architectures comprised entirely of partially metalised photopolymer. These devices derive considerable advantages from rapid prototyping technology, in that they are cheap to produce, and benefit from the design-to-product lead times inherent in the production of components using stereolithography. To date membranes have been produced with thicknesses ranging from 30 to 90 μm with aspect ratios in the range of 100 - 1000. These devices have been shown to operate both as transmitters and as receivers of ultrasound, and have a bandwidth approaching 100% with a centre frequency of 100 kHz. The method of fabricating these devices allows for easy modification for various applications including structural health monitoring and immersion, as well as affording the possibility of integrated focussing or wave-guiding architecture and packaging that can be incorporated into a single build. Fundamental or subtle changes to a given transducer design may be achieved incurring little additional cost or time. This novel approach to transducer fabrication enables the bespoke manufacture of specific transducer architectures from a computer aided design package using polymers that exhibit different material properties to materials used in silicon micromachining, but at the same time allow for fabrication on a scale that is approaching that of microfabrication. The versatility of 3-D rapid prototyping allows the realisation of more complicated structures than was possible previously. This work examines these transducers in terms of their characterisation and their operation in conjunction with other transduction architecture, such as focussing parabolic mirrors that were also produced using the same manufacturing technology. In addition, their operation in contacting acoustics and the reception of surface acoustic waves has been demonstrated. Immersion studies using these devices have found that that they hold promise for operation in a variety of different media. These transducers are seen as an important prototype development tool in the field of capacitive ultrasonic transduction and microphone-speaker design.EThOS - Electronic Theses Online ServiceGBUnited Kingdo