Mechanical and Mechatronics Engineering

Permanent URI for this collectionhttps://uwspace.uwaterloo.ca/handle/10012/9912

This is the collection for the University of Waterloo's Department of Mechanical and Mechatronics Engineering.

Research outputs are organized by type (eg. Master Thesis, Article, Conference Paper).

Waterloo faculty, students, and staff can contact us or visit the UWSpace guide to learn more about depositing their research.

Browse

Now showing 1 - 3 of 3

Additive Manufacturing of Functionally- Graded Porous Biodegradable Scaffolds using Sacrificial Porogens
(University of Waterloo, 2015-04-30) Behzadian, Farid
The focus of this dissertation is on the additive manufacturing (AM) of a porous biodegradable scaffold using a fine Calcium Polyphosphate (CPP) powder, with the aid of sacrificial porogens. CPP is a member of Calcium Phosphate (CaP) bioceramic family which has shown great potential in bone tissue engineering over the past years. AM processes are fairly new technologies that have been involve in many different industries and applications, including bone tissue engineering. Not too long ago, CPP was investigated using a powder based 3D printing technique, which is an AM process, and it was revealed that this new manufacturing process offers a great potential in improving previous finding made by traditional fabrication techniques. Over the past few years there have been many different studies on 3D printing CPP substrate, but almost all of those studies were based on using a large particle CPP powder. In this study, the fabrication of CPP structures was based on using a fine CPP powder with a particle size of < 75µm. 3D printing fine dry powder has one main challenge which is flowability of the powder, and in this study a new solution has been suggested to improve the flow behavior of the fine CPP powder. Polyvinyl Alcohol (PVA) powder with a particle size of 75-106 µm was chosen as the large sacrificial particles so called porogens, to be mixed with fine CPP powder to improve the flowability. In order to improve the flow behavior of the powder in the AM process, various percentages of porogens were mixed with the fine CPP powder to fine the appropriate dosage. Furthermore, there were two different liquid binders tested in the AM process. After CPP parts were fabricated, all specimens were measured in dimensions before and after the sintering. The dimensional measurements were used to determine the shrinkage percentage. Then the sintered parts had to be tested one by one through Archimedes method to find the porosity percentage corresponding to each individual sample. Following that, uniaxial compression test was applied to evaluate the mechanical strength of each specimen. In order to look at the micro structures of samples and making sure the particle have formed good bonding/sinter necks, random specimens were chosen to me examined using Scanning Electron Microscopy (SEM). Moreover, different powders were sent to an external facility to be tested for the flow behavior and the average particle size by using a rheometer and a laser diffraction method, respectively. The results were analyzed for different categories based on the pre mixed porogens percentage. It was proven that adding porogens definitely improves the flowability of the fine powder; it also increases the shrinkage percentage of samples. Then the results were compared with previous findings that were based on using a large particle CPP powder; it was shown that some of those previous finding obtain by 3D printing large particle CPP powder, can be achieved by doing the same using the fine CPP powder. Furthermore, a new higher compressive strength was reported in this study that was not achieved in previous reports which was based on the large particle CPP powder.
Additive Manufacturing of Soft Polysiloxane-based Bio-structures with Heterogeneous Properties
(University of Waterloo, 2018-03-26) Liravi, Farzad
This thesis is concerned with the development of novel additive manufacturing (AM) systems and methodologies for high speed fabrication of complex material-graded silicone structures with controllable internal features consistently. To this end, two AM systems were developed, each pertaining to a specific phase of silicone rubber. The first system integrates material extrusion and material jetting AM systems. This system is designed to process the paste-like silicone rubbers at high viscosity levels (> 400,000 mPa.s at 10 1/s). In this system, the outer frame of each layer is made by extruding a highly uniform silicone strand at 5 mm/s printhead velocity. Once the perimeter is laid down on the substrate or the previous layer, a piezoelectric-based printhead with a translational speed of over 100 mm/s covers the internal section of layer by depositing uniform droplets of silicone at predefined locations. The printing parameters for both extrusion and jetting techniques were tuned using statistical optimization tools in order to minimize the surface waviness of printed parts. The optimized surface waviness values obtained are 8 μm and 3 μm for jetting and extrusion, respectively. Moreover, parts with solid density of over 99% and mechanical performance similar to the bulk material were manufactured by tailoring the rheology of silicone ink. A combination of powder-bed binder-jetting (PBBJ) system and micro-dispensing material extrusion form the second hybrid AM system. The three-dimensional (3D) shape forming of silicone powder is made possible for the first time using this system. The tomography results for the fabricated parts reveal a porous structure (~ 8% porosity). This AM process is introduced as a the proof-of-concept. The porosity of structures can be tuned by improving the silicone binder delivery method so that binder droplets with pico-liter volumes can be dispensed. The characterization techniques used for materials and additively manufactured parts include confocal-laser profilometry for investigating the surface quality of printed parts, differential scanning calorimetry (DSC) for investigating the curing mechanism of heat-curable silicone inks, Fourier transform infrared (FTIR) spectroscopy for controlling the curing kinetics and surface cohesion of UV-curable silicones, dynamic mechanical analysis (DMA) tests for tuning the rheological properties of silicone inks under different shear stresses, rheometry for establishing the viscosity threshold for jetting of silicone inks at different temperatures, scanning electron microscopy (SEM), particle size analysis, and powder rheometry for establishing guidelines for the size, shape, cohesiveness, flow, and shear stress resistance of silicone powders, uniaxial tensile test, tearing test, and durometry for identifying the mechanical characteristics of 3D printed parts, and computed-tomography (CT) scanning for quantifying the porosity of parts. The systems and fabrication methods introduced in this research, with high commercialization readiness levels, were concluded to have great impact on the manufacturing of functionally-graded complex bio-structures. This has been validated through high speed fabrication of multiple heterogeneous bio-structures. Moreover, the proposed techniques can be used for the fabrication of other silicone-based products.
Process Mapping and Optimization of Titanium Parts Made by Binder Jetting Additive Manufacturing
(University of Waterloo, 2018-01-08) Wheat, Evan
Additive manufacturing (AM) has recently seen an increase in adoption outside of its traditional role of rapid prototyping and is being used more and more for the production of functional components. The increased adoption is due in part to better systems and a better understanding of the AM process. Binder jetting additive manufacturing (BJAM), however, has seen significantly less adoption compared to other AM technologies and that is likely because there has been comparatively less work done on improving and understanding the process. For BJAM to see more widespread use, a more thorough understanding of the process both during printing and sintering is required. One area where BJAM can see more substantive adoption is in the medical and dental fields. Porous parts, especially implants, can have highly beneficial properties compared to solid parts. However, the porosity in these components needs to be tailored depending on the application. BJAM allows for this level of control, as the density of sintered parts can be controlled anywhere from around 50% to nearly 100%. Tailoring these properties requires controlling the density of the green parts (through printing) and subsequently the final parts (through sintering), as many part properties are directly linked to density. Previous studies in the group focused on the printing of commercially pure titanium components. This thesis adds onto that work by examining the effects of powder sizes and sintering on green and final densities. Five sample types were produced to evaluate the sintering process. The powder size distribution was varied between samples while the printing parameters were kept fixed. This was done in order to isolate the effects of the powder size distribution from the printing parameters. Two mono-modal distributions were used (45-106µm and 106-150µm) as well as three bi-modal distributions (0-45µm/45-106µm, 0-45µm/106-150µm and 45-106µm/106-150µm). The completed work focuses on two main areas. The first area is more traditional sinter theory and sinter structure analysis, which is done to gain insight into how different particle sizes and the specific powder systems seen in BJAM parts affects the sintering process. This analysis is done using computed tomography (CT), where both the green and sintered parts are scanned and compared. Four major features are evaluated from the CT scans, which are bulk porosity, porosity per layer, particle size and pore size. Parts are sintered at 1000°C and 1400°C to produce parts that undergo only non-densifying and densifying sintering respectively. From the results, it was found that samples with the fine powder additions (0-45µm) sintered with substantially higher levels of densification (at both 1000°C and 1400°C) compared to the other powder types comprised of larger particles. All of the samples showed a periodic density change corresponding to the height of the printed layers. Parts were found to be the most dense within a layer and least dense at the layer interfaces. After sintering, the relative density variation was unchanged for samples with larger particles and exacerbated for samples made with finer particles. Samples with the finer particles were able to achieve bulk densities of 82.7% and 84.6% when sintered at 1400°C. However, the density fluctuated from nearly 100% within layers to approximately 60% at the layer interfaces. The second area of focus is on the development of a tool to predict the final density of sintered parts. The development of this tool drew heavily from existing information on the sintering of powder metallurgy components. From a literature review, the master sinter curve (MSC), a powder metallurgy technique based on the combined stage sinter theory, was deemed to be an excellent basis for developing a predictive tool. The MSC is constructed using experimental dilatometry results, avoiding the need for a more comprehensive analysis of the powders used. To generate MSCs for each powder type, samples were sintered in a dilatometer from room temperature up to 1550°C at various heating rates and then cooled quickly. The dilatometry results are then processed to create MSCs. Reliable MSCs could not be made from the dilatometry results. The specific push-rod dilatometry analysis that was used as part of this work (required due to the system configuration) gave poor shrinkage results. These results could not be used to make good quality MSCs and prevented the generation of the predictive tool. However, since the general process has already been made as part of this work, only new dilatometry measurements are required to be able to create proper MSCs.

Browse

Browsing Mechanical and Mechatronics Engineering by Subject "3D Printing"