Members of the elderly population is disproportionately prone to experiencing mobility impairment due to their aging bodies and as a result have frail bodies that are at a higher risk of grave injury due to falling. In order to combat this assistive mobility devices such as exoskeletons have been developed to help patients enhance their range of motion. With additive manufacturing techniques, such as fused deposition modeling (FDM), becoming a more mainstream form of design, the inclusion of lightweight polymers such as nylon 12 as primary construction materials for these devices has increased. In this thesis computer aided design (CAD) software was used to design a prototype lower body exoskeleton and simulation software was used to give the device the characteristics of Stratasys' nylon 12 carbon fiber FDM material to verify it if could be used as the primary construction material for this device when extruded from a FDM printer on either the XZ or ZX printing plane. From the simulations it was found that the material printed along the XZ plane could create a device that could withstand the weight of an average elderly male patient (200 lbs.) as well as the 35 lbs. of force applied to the device by a linear actuation motor that would be used to extend and contract the exoskeleton leg.

Multi-material 3D Printing allows the ability to fabricate parts with tuned mechanical properties, multi-process 3D printing widens the choices of available fabrication materials. The objective of this study is to build a custom 3D printing test bed that is capable of printing multi-material parts with fused deposition modeling and direct ink writing techniques. A 3D printer, controlled by an industrial motion control system, with FDM and DIW capabilities was built by combining FDM extruders with a pneumatic dispensing system on a single platform. By utilizing the Direct Ink Writing function, we expand the number of printable materials to include some off the shelf silicones and epoxies, as well as custom, user made, materials. This study will further expand the manufacturing and research capabilities within the additive manufacturing discipline.

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This project was initiated by Dr. Sasan Dadbaksh upon listening to the requirements I presented for my master thesis. My requirements were to do a master thesis project in the field of additive manufacturing specifically fused deposition modeling that should not only involve the research work but should also present an opportunity to develop hardware and should involve experimental testing. Then Sasan came up with the idea of developing a system capable to perform 3D printing with the extruder fixed in one position and the motion required for 3D printing will be provided by the robotic arm. The title of developing green build strategies for robot assisted plastic 3D printing came into being. The main concept behind the title of developing robot assisted plastic 3D printing platform is to develop such a system that can offer additive manufacturing services, specifically of fused deposition modeling 3D printing, as an inbound process during the manufacturing of any part through subtractive processes with the help of a robotic arm along with the repair of any kind of parts with the assistance of fused deposition modeling 3D printing. The main objectives of the master thesis include building a stationary filament extrusion module to interact with a robot hand and establishing a strategy for a robot hand to move the part to appropriate locations to complete building a part on a preform without support structures. The targets that were achieved with the completion of this thesis project includes the development of the complete hardware that consists of a mechanical structure with the option of mounting the components required to run the extrusion setup, learning the basic working of the software that are able to simulate the 3D printing process with the robotic arm (Robot Studio and Robo DK), creation of the simulation of the whole process, achieving communication between the robotic arm and the microcontroller of the extruder and finally the printing of a simple part for the demonstration. The components needed to be installed on the structure includes the motor, extruder, hot end, nozzle, filament. The structure also accumulated the required electronics that includes power supply, microcontroller, and an LCD to monitor the extrusion parameters. The developed machine runs on the state-of-the-art components that belong to the few of the best manufacturers of the technology.

Today's commercial rapid prototyping systems (i.e., solid freeform fabrication, layered manufacturing) rely on human intervention to load and unload build jobs. Hence, jobs are processed subject to both the machine's and the operator's schedules. In particular, first-in-first-out (FIFO) queuing of such systems will result in machine idle time whenever a build job has been completed and an operator is not available to unload that build job and start up the next one. These machine idle times can significantly affect the system throughput, and, hence, the effective cost rate. This thesis addresses this problem by rearranging the job queue to minimizing the machine idle time, subject to the machine's and operator's schedules. This is achieved by employing a general branch-and-bound search method, that, for efficiency, reduces the search space by identifying contiguous sequences and avoiding reshuffling of those sequences during the branching procedure. The effectiveness of this job scheduling optimization has been demonstrated using a sequence of 30 jobs extracted from the usage log for the FDM 1600 rapid prototyping system in the Department of Mechanical Engineering at Virginia Tech. / Master of Science

A subluxação atlantoaxial em cães miniatura culmina em compressão da medula espinhal e mielopatia cervical de graus variáveis. Frequentemente o tratamento cirúrgico se faz necessário, sendo os implantes transarticulares uma das opções terapêuticas. Convencionalmente a passagem desses implantes baseia-se em pontos anatômicos de referência e ângulos genéricos preestabelecidos, todavia, devido ao estreito corredor ósseo o posicionamento ideal é desafiador. O desenvolvimento de métodos de planejamento cirúrgico individualizados poderia aumentar a acurácia na aplicação de implantes atlantoaxiais. O presente estudo teve como objetivo desenvolver um guia cirúrgico paciente-específico (GCPE) para colocação de pinos atlantoaxiais em cães miniaturas e comparar a eficácia desses dispositivos em relação a técnica cirúrgica convencional. Para tanto, dezesseis cadáveres de cães de até seis quilogramas foram dispostos aleatoriamente em dois grupos de oito cães, para serem submetidos a cirurgia de estabilização transarticular atlantoaxial com pinos lisos de 1,6 mm. Nos cães do Grupo A (GrA) a aplicação dos pinos foi guiada por um GCPE, desenvolvido com base em imagens de tomografia computadorizada (TC), a partir de técnicas de prototipagem rápida e impressão 3D por modelagem por fusão e deposição. Os cães do Grupo B (GrB), foram submetidos ao procedimento operatório convencional, sendo a passagem dos pinos guiada por referências anatômicas. Posteriormente ambos os grupos foram submetidos à exame de TC para avaliação da acurácia dos pinos. Para a avaliação do posicionamento dos implantes criou-se uma escala que ponderou a manutenção nos corredores seguros e os classificou de acordo com a estabilidade oferecida e a segurança da aplicação. Observou-se que não houve diferença significativa entre o método com GCPE e a cirurgia convencional, sendo que ambos grupos tiveram resultados expressivos de pinos inadequadamente aplicados, incluindo violação de corticais com obliteração do forame vertebral em 3 (37,5%) cães do GrA e 4 (50%) cães do GrB e obliteração do forame transverso em 3 (37,5%) animais do GrA e 1 (12,5%) do GrB. A aplicação de pinos em posição adequada bilateralmente foi observada em apenas 2 (25%) cães de cada grupo. Concluímos que a confecção de um GCPE para pinos transarticulares em cães miniaturas é viável, todavia, o modelo criado não foi capaz de aumentar a eficácia e segurança da cirurgia em relação à técnica convencional. / The atlantoaxial subluxation in miniature dogs leads to spinal cord compression and cervical myelopathy in several degrees. Commonly the surgical treatment is necessary, and one of therapeutic options are the transarticular fixation. Conventionally the passage of these implants is based on anatomical reference points and generics pre-established angles, however, due to the narrow bony corridor the ideal positioning is challenging. The development of individual surgical planning methods could improve the accuracy of atlantoaxial implants application. The present study aimed to develop a patient-specific surgical guide (PSSG) for placement of atlantoaxial pins in miniature dogs and to compare the efficacy of these devices related to the conventional surgical technique. Sixteen cadavers of dogs, up to six kilograms, were randomly placed in two groups of eight dogs each, to undergo atlantoaxial transarticular stabilization with Kirschner wires. On the Group A (GrA) the application of Kirschner wire were guided by a PSSG, developed based on computed tomography (CT) images, using rapid prototyping and fused deposition modeling 3D impression technique. The dogs of Group B (GrB) were submitted to conventional procedure, with the passage of the Kirschner wires guided by anatomical references. After surgeries, dogs in both groups were submitted to a CT scan to evaluate the accuracy of the implants. To evaluate the implants position a scale was created and considered the maintenance of the pins in the safe corridors and classified them according to the stability and safety of the application. It was observed that there was no significant difference between the PSSG method and the conventional surgery, and that both groups had expressive results of inappropriately applied pins, including obliteration of vertebral foramen in 3 (37.5%) dogs from GrA and 4 (50%) dogs from GrB and obliteration of the transverse foramen in 3 (37.5%) dogs from GrA and 1 (12, 5%) dog of GrB. The bilaterally application of pins in a suitable position was observed in only 2 (25%) dogs of each group. We concluded that the development of a PSSG for transarticular pins in miniature dogs is feasible, however, the model that we design was not able to increase the efficacy and safety of the surgery, compared to the conventional surgical technique.

ABB Corporate Research was looking to redevelop one product to be manufactured via polymer additive manufacturing (AM), as opposed to its previously traditionally manufacturing method. The current product is cylindrical in shape and must withstand a certain amount of hydrostatic pressure. Due to the pressure and the current design, the cannister is prone to buckling failure. The cannister is currently produced from two cylindrical tube parts and two spherical end sections produced from solid blocks of the same material. For assembly, an inner assembly is inserted into one of the tube parts and then all parts are welded together. This product is also custom dimensioned for each purchase order. The purpose of investigating this redevelopment for AM is to analyse if an updated inner design unique to additive manufacturing is able to increase the performance of the product by increasing the pressure it can withstand from both a material failure standpoint and a buckling failure. The redevelopment also aims to see if the component count and process count can be decreased. Ultimately, two product solutions are suggested, one for low pressure ranges constructed in ABS and one for high pressure ranges constructed in Ultem 1010. To accomplish this, relevant literature was referred to gain insight into how to reinforce cylindrical shell structures against buckling. Design aspects unique to AM were also explored. Iterations of these two areas were designed and analysed, which led to a final design choice being decided upon. The final design is ultimately based on the theory of strengthening cylindrical structures against buckling through the use of ring stiffeners while also incorporating AM unique design aspects in the form of hollow network structures. By utilizing finite element analysis, the design was further developed until it held the pressure required. Simulation results suggest that the ABS product can withstand 3 times higher pressure than the original design while being protected against failure due to buckling. The Ultem simulation results suggest that the product can withstand 12 times higher pressure than the current design while also being protected against failure due to buckling. Part count and manufacturing processes are also found to have decreased by half. Post-processing treatments were also explored, such as the performance of sealants under pressure and the effects of sealants on material mechanical properties. Results show that one sealant in particular, an acrylic spray, is most suitable to sealing the ABS product. It withstood a pressure of 8 bar during tests. The flexural tests showed that the sealant did indeed increase certain mechanical properties, the yield strength, however did not affect the flexural modulus significantly. This work gives a clear indication that the performance of this product is feasibly increased significantly from redeveloping it specifically to AM.

Les tanins condensés sont largement répandus et très abondants dans la nature. Au cours des dernières décennies, ces tanins ont été abondamment utilisés pour la production de formulations thermodurcissables (par exemple, les adhésifs pour le collage du bois, les matériaux en mousse) en raison de leur réactivité chimique. Cependant, ils présentent également un grand potentiel en tant que composants pour la conception de matériaux polymères innovants en raison de leurs propriétés physico-chimiques (p. ex. antioxydantes, antimicrobiennes et stabilisantes). Afin d’étendre les domaines d’utilisation des tanins aux matériaux polymères, le principal verrou scientifique et technique réside dans leur incompatibilité avec les polymères hydrophobes. À cette fin, trois voies de modification ont été mises au point pour améliorer la compatibilité des tanins avec les matrices PP ou PLA. Dans la première partie, les PP/ tanins ont été modifiés avec du glyoxal par vulcanisation dynamique. Après extrusion réactive, les tanins vulcanisés présentent une meilleure compatibilité avec la matrice PP et des propriétés anti-UV. La deuxième approche consiste en une modification par estérification à l'aide d'anhydride acétique. Avec cette méthode, des teneurs élevées en AT ont pu être incorporées au PLA, jusqu'à 30 % en poids et jusqu'à 20 % sans diminution notable des propriétés mécaniques ni impact sur la morphologie de surface. Ces composites PLA/AT sont imprimables en impression 3D par dépôt de matière fondue. Dans la troisième partie, une compatibilisation réactive a été réalisée avec succès pour améliorer l'adhésion interfaciale entre PLA et les tanins condensés en utilisant du 3-aminopropytriéthoxysilane, du diisocyanate de méthylène diphényle et du peroxyde de dicumyle (DCP). / Condensed tannins are widely distributed and highly abundant in nature. In the past decades, such tannins have played an important role in thermosetting systems (e.g. adhesives for wood bonding, foam material) because of their chemical reactivity. However, they also exhibit great potential as a component of polymeric materials because of their physicochemical properties (e.g. antioxidant, antimicrobial and stabilizing properties), which are promising for material preparation. In order to transform tannins from traditional application to a broaden application in polymeric materials, the main challenge facing tannins are their incompatibility with hydrophobic polymer. For this purpose, three modification pathways were developed to improve the compatibility of tannins with PP or PLA matrix. In the first part, PP/ tannins were modified with hexamine or glyoxal via dynamic vulcanization technique. After vulcanized extrusion, vulcanized tannins present better compatibility and UV protective performance in PP matrix. The second approach is CTs modified with acetic anhydride. With this method, up to 30 wt% acetylated tannin (AT) can be well incorporated with PLA while PLA containing up to 20 wt% AT did not deteriorate the mechanical property and surface morphology. This PLA/AT composites are printable via fused deposition modeling process. In the third part, the efficient reactive compatibilization have been successful used to improve the interfacial adhesion between PLA and CTs by using 3-aminopropytriethoxysilane, methylene diphenyl diisocyanate, and dicumyl peroxide (DCP).

Additive manufacturing is gaining popularity at a rapid rate and has been a resourceful production process to reduce material usage, wastage (scrap) and manufacturing costs for various applications. The project conducted, emphasizes on Thermoplastic Elastomer (TPE SE6300C-65A) material, which is a highly versatile compound, and has the ability to exhibit properties of both rubber (Elastomers) in terms of flexibility and plastic (Polymers) in terms of recyclability. Cost reduction without compromising quality is one of the important factors for industries. The project involves the use of TPE pellets to extrude filaments that could be used for 3D Printing. Filament extrusion involves process variables like Nozzle Temperature, De-humidification of pellets, Diameter of the nozzle, Distance of collection, Cooling and Angle of inclination of the extruder. These process variables are optimized to accomplish the desired quality of filament. The filament produced through extrusion is further used to make products using Fused Deposition Modeling (FDM). FDM also involves numerous process variables like Layer Thickness, Build Orientation, Print Infill, Print Speed etc. In this study, different test specimens, in terms of geometrical shapes are printed from the material, TPE SE6300C-65A and tested in order to understand how the surface features as well as the dimensional accuracy change with different process variables. It is observed that the surface topography produced throughout FDM process is majorly affected by the angle of orientation of the printed part. The main goal of this thesis is to give the reader a better understanding on which process variable, such as layer thickness, temperature and print speed affect the surface roughness of the models and also a comparison between these three variables, highlighting which is more or less affecting. It is also observed the dimensional accuracy of the real specimen deviate from the value input into the CAD software. The results obtained in this study clearly suggest that there is a lot of opportunities for future improvements especially regarding the dimensional accuracy, it is imperative to achieve the highest precision possible in order to have commercial values for the FDM 3D printing.

The ease of manufacturing complex geometries using fused deposition modeling (FDM) 3D-Printing reduces the overall production cost compared with the traditional manufacturing techniques. Because of the benefits of 3D printing technologies, it is proposed to be used in the manufacturing of different products. But there is still no definite characterization of the surface quality of objects manufactured by 3D printing. Hence in order to define the texture of the surfaces produced, measurements from different samples are taken and quantified.In this study, a 3D test model consisting of various slopes is printed at different layer thicknesses and different print speeds using different 3D printers.Thus, the effect of the surface orientation on the surface roughness was studied in relation to the different layer thicknesses and different print speeds. The study samples are measured using the state of the art equipment at Halmstad University.This thesis studies the surface roughness at different slopes of FDM models.A related study on the dimensional variation between the CAD model and the actual3D printed model, and causes/reasons for the variations are analyzed.It is observed that FDM produced part surface topography is directly affected by the orientation of the surface. Also, the surface roughness increases with increase in layer thickness. The observed correlations between surface roughness and layer thickness and surface orientation could be used to better understand the behavior of FDM surfaces, thus to better quantify the surface roughness. To improve quality, it must first be quantified. It is well observed that dimensional inaccuracy exists between the CAD model and the printed part. These results suggest that there is a lot of work and improvements to be done in order to close the gap of dimensional inaccuracy and achieve a high precision commercial FDM 3Dprinting.