Rapid prototyping (RP) is a supplementary additive manufacturing method to the traditional Computer Numerical Controlled (CNC) machining. The selection of the manufacturing method between RP and CNC machining is currently based on qualitative analysis and engineers’ experience. There are situations when parts can be produced using either of the methods. In such cases, cost will be the decisive factor. However, lack of a quantitative cost estimation method to guide the selection between RP and CNC machining makes the decision process difficult. This thesis proposes an automated cost estimator for CNC machining and Rapid Prototyping. Vertical CNC milling and Stereolithography Apparatus (SLA) RP technology are selected in specific, for cost modeling and process comparison. A binary questionnaire is designed to help estimate the CNC setup cost. An SLA build time estimator is implemented based on 3D systems’ SLA3500 machine. SLA post processing cost is also investigated. Based on the developed methods, a prototype software tool was created with an output to Excel chart to facilitate the selection. Five cases have been studied with the software and the predicted results are found reasonable and effective.

Rapid prototyping (RP) is a supplementary additive manufacturing method to the traditional Computer Numerical Controlled (CNC) machining. The selection of the manufacturing method between RP and CNC machining is currently based on qualitative analysis and engineers’ experience. There are situations when parts can be produced using either of the methods. In such cases, cost will be the decisive factor. However, lack of a quantitative cost estimation method to guide the selection between RP and CNC machining makes the decision process difficult. This thesis proposes an automated cost estimator for CNC machining and Rapid Prototyping. Vertical CNC milling and Stereolithography Apparatus (SLA) RP technology are selected in specific, for cost modeling and process comparison. A binary questionnaire is designed to help estimate the CNC setup cost. An SLA build time estimator is implemented based on 3D systems’ SLA3500 machine. SLA post processing cost is also investigated. Based on the developed methods, a prototype software tool was created with an output to Excel chart to facilitate the selection. Five cases have been studied with the software and the predicted results are found reasonable and effective.

Published Article / This paper identifies the most significant technological developments made in medical applications of rapid prototyping and manufacturing (RP&M) over the past decade. This assessment is based on a retrospective analysis of the research undertaken by the Medical Applications Group of the National Centre for Product Design and Development Research (PDR), based at the University of Wales lnstitute Cardiff (UWIC). UK. The paper describes the state of technology at the inception of the Group in 1998 and then highlights the significant technological developments that impacted on the activities of the Group over the decade to 2008. The paper will also discuss how these technologies have developed since their initial implementation. The paper will conclude with suggested directions future work should take in order to meet clinical and technical needs.

Mask Projection Microstereolithography (MPSLA) is an additive manufacturing process capable for fabricating true three-dimensional microparts and hence, holds promise as a potential micro-fabrication process for micro-machine components. With only a few MPSLA systems developed and studied so far, the research in this field is inchoate and experimental in nature. The process of curing a micropart using an MPSLA system has not been analytically modeled and no literature on process planning for MPSLA is available. In order to employ the MPSLA technology for microfabrication, it is necessary to model its part building process and formulate a process planning method to cure dimensionally accurate microparts. As a part of this thesis, an MPSLA system is designed and assembled. The process of curing a single layer using this system is analytically modeled as the Layer cure model. The Layer cure model is formulated in two steps. First, the irradiance received by the resin surface is modeled as a function of the system parameters (Irradiance model). Then, the resin used in the system is characterized to experimentally determine its working curve. The Irradiance model and the resin characterization enable us to compute the dimensions of any layer cured using our MPSLA system in terms of the process parameters. The Layer cure model has been validated by curing test layers on our system. Finally, the Layer cure model has been inverted to formulate a process planning method to cure layers of the required dimensions. Using this process planning method, it is possible to cure layers within a dimensional error of 3%.

In the present work superplastic forming (SPF) is used as part of a process to create medical implants out of titanium. SPF is a forming process which offers many advantages over conventional forming processes. It allows for greater complexity in shape as well as the ability to work with difficult to form metals such as titanium which is a key metal in the biomedical field. SPF has been used extensively in the aerospace and automobile industry, however in recent years it has been shown to be a viable means in creating medical implants. The current process involves manipulating CT scans in order to create templates using rapid prototyping. These templates are then used to generate SPF molds out of investment material. Three different parts based on anatomical regions referenced from a model skull have been formed successfully. The parts formed are shown to be very accurate when compared against the skull model.

Fabrication of Tissue Engineering Scaffolds Using Stereolithography Benita M. Comeau 226 Pages Directed by Dr. Clifford L. Henderson New methods and materials for the fabrication of hierarchically structured, 3D tissue scaffolds using stereolithography (SL) are presented. The ability to chemically modify selected areas on a scaffold is one way to direct cell growth in deliberate patterns; which is necessary for the engineering of complex, functioning tissues. SL will allow for the building of complex 3D structures with well defined geometries, and a second level of order is created by subsequent modification of chemical groups via catalyzing a de-protection event through exposure to another wavelength of light. The investigated system utilizes an acid-catalyzed de-protection event to change the surface chemistry of an SL-made polymer, analogous to conventional chemically amplified photoresists. The chemical modification alters the surface energy, affecting how proteins interact with the material. This allows selective areas to be more favorable towards cell adhesion. The results of this work include the identification of cytocompatible photo-acid generators that are necessary for the acid-catalyzed de-protection, the demonstration that traditional photolithographic materials may be used for cell patterning, quartz crystal microbalance studies which illuminate why these patterning methods work, the design and performance of a mirror array based stereolithographic apparatus capable of multi-wavelength exposures, and the synthesis and formulation of a novel stereolithographic resin for use in this system. The findings suggest that this system has great potential for use in cell and tissue studies, and possibilities for future use and research are discussed.

The integration of multiple digitally driven processes is seen as the solution to many of the current limitations arising from standalone Additive Manufacturing (AM) techniques. A technique has been developed to digitally fabricate fully functioning electronics using a unique combination of AM technologies. This has been achieved by interleaving bottom-up Stereolithography (SL) with Direct Writing (DW) of conductor materials alongside mid-process development (optimising the substrate surface quality), dispensing of interconnects, component placement and thermal curing stages. The resulting process enables the low-temperature production of bespoke three-dimensional, fully packaged and assembled multi-layer embedded electronic circuitry. Two different Digital Light Processing (DLP) Stereolithography systems were developed applying different projection orientations to fabricate electronic substrates by selective photopolymerisation. The bottom up projection orientation produced higher quality more planar surfaces and demonstrated both a theoretical and practical feature resolution of 110 μm. A top down projection method was also developed however a uniform exposure of UV light and planar substrate surface of high quality could not be achieved. The most advantageous combination of three post processing techniques to optimise the substrate surface quality for subsequent conductor deposition was determined and defined as a mid-processing procedure. These techniques included ultrasonic agitation in solvent, thermal baking and additional ultraviolet exposure. SEM and surface analysis showed that a sequence including ultrasonic agitation in D-Limonene with additional UV exposure was optimal. DW of a silver conductive epoxy was used to print conductors on the photopolymer surface using a Musashi dispensing system that applies a pneumatic pressure to a loaded syringe mounted on a 3-axis print head and is controlled through CAD generated machine code. The dispensing behaviour of two isotropic conductive adhesives was characterised through three different nozzle sizes for the production of conductor traces as small as 170 μm wide and 40 μm high. Additionally, the high resolution dispensing of a viscous isotropic conductive adhesive (ICA) also led to a novel deposition approach for producing three dimensional, z-axis connections in the form of high freestanding pillars with an aspect ratio of 3.68 (height of 2mm and diameter of 550μm). Three conductive adhesive curing regimes were applied to printed samples to determine the effect of curing temperature and time on the resulting material resistivity. A temperature of 80 °C for 3 hours resulted in the lowest resistivity while displaying no substrate degradation. ii Compatibility with surface mount technology enabled components including resistors, capacitors and chip packages to be placed directly onto the silver adhesive contact pads before low-temperature thermal curing and embedding within additional layers of photopolymer. Packaging of components as small as 0603 surface mount devices (SMDs) was demonstrated via this process. After embedding of the circuitry in a thick layer of photopolymer using the bottom up Stereolithography apparatus, analysis of the adhesive strength at the boundary between the base substrate and embedding layer was conducted showing that loads up to 1500 N could be applied perpendicular to the embedding plane. A high degree of planarization was also found during evaluation of the embedding stage that resulted in an excellent surface finish on which to deposit subsequent layers. This complete procedure could be repeated numerous times to fabricate multilayer electronic devices. This hybrid process was also adapted to conduct flip-chip packaging of bare die with 195 μm wide bond pads. The SL/DW process combination was used to create conductive trenches in the substrate surface that were filled with isotropic conductive adhesive (ICA) to create conductive pathways. Additional experimentation with the dispensing parameters led to consistent 150 μm ICA bumps at a 457 μm pitch. A flip-chip bonding force of 0.08 N resulted in a contact resistance of 2.3 Ω at a standoff height of ~80 μm. Flip-chips with greater standoff heights of 160 μm were also successfully underfilled with liquid photopolymer using the SL embedding technique, while the same process on chips with 80 μm standoff height was unsuccessful. Finally the approaches were combined to fabricate single, double and triple layer circuit demonstrators; pyramid shaped electronic packages with internal multilayer electronics; fully packaged and underfilled flip-chip bare die and; a microfluidic device facilitating UV catalysis. This new paradigm in manufacturing supports rapid iterative product development and mass customisation of electronics for a specific application and, allows the generation of more dimensionally complex products with increased functionality.

Gelatin methacrylate (GelMA) is a ubiquitous biocompatible photopolymer used in tissue engineering and regenerative medicine due to its cost-effective synthesis, tunable mechanical properties, and cellular response. Biotechnology applications utilizing GelMA have ranged from developing cell-laden hydrogel networks to cell encapsulation and additive manufacturing (3D printing). However, extrusion based 3D printing is the most common technique used with GelMA. Mask projection microstereolithography (MPµSL or µSL) is an advanced 3D printing technique that can produce geometries with high resolution, high complexity, and feature sizes unlike extrusion based printing. There are few biomaterials available for µSL applications, so 3D printing GelMA using µSL would not only add to the repertoire materials, but also demonstrate the advantages of µSL over other 3D printing techniques. A novel GelMA resin was tested with µSL to create a porous scaffold with a height and print time that has not been displayed in the literature before for a scaffold of this size. The resin consists of GelMA, deionized water, lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP, photoinitiator), and 2-Hydroxy-4-methoxybenzophenone-5-sulfonic acid (sulisobenzone, UV blocker) and can be processed at room temperature. Four resins were tested (w/w %) and characterized for µSL printing: 20% GelMA 0.5% UV blocker, 20% GelMA 1.0% UV blocker, 30% GelMA 0.5% UV Blocker, and 30% GelMA 1.0% UV blocker. Swell testing, working curve, photo-rheology, photo-DSC (dynamic scanning calorimetry), 3D printing, and cell culture tests were performed and results showed that 30% GelMA 1.0% UV blocker had the best 3D print fidelity among resin compositions. / Master of Science / Three dimensional (3D) printing is a widely used technology to rapidly produce structures with varying degrees of complexity. 3D printing of biological components is of interest because as the world population increases, there is a lack of donors available to compensate for organ loss and tissue replacement. 3D printing offers a solution to great custom scaffolds and structures that mimic physiological geometry and properties. One printing technique is known as microstereolithography, or µSL, which uses a projector-like system to pattern ultraviolet (UV) light in specific arrangements to generate complex geometries and 3D parts. Gelatin is a material of interest for this technology because gelatin is derived from collagen, which is the most abundant protein found in the body. Gelatin can be modified so that it is reactive with UV light, and can be processed with µSL to generate 3D structures. In this work, gelatin was modified into the form of gelatin methacrylate (GelMA) in order to develop and test resin formulations for use with µSL. Four different resins were tested and characterized and the results indicated that one GelMA resin produced prints with greater fidelity and resolution than other formulations. This resin has been identified for potential applications in tissue engineering and 3D printed organ development.

Although stereolithography (SL) is a remarkable improvement over conventional prototyping production, it is being pushed aggressively for improvements in both speed and resolution. However, it is not clear currently how these two features can be improved simultaneously and what the limits are for such optimization. In order to address this issue a quantitative SL cure process model is developed which takes into account all the sub-processes involved in SL: exposure, photoinitiation, photopolymerizaion, mass and heat transfer. To parameterize the model, the thermal and physical properties of a model compound system, ethoxylated (4) pentaerythritol tetraacrylate (E4PETeA) with 2,2-dimethoxy-2-phenylacetophenone (DMPA) as initiator, are determined. The free radical photopolymerization kinetics is also characterized by differential photocalorimetry (DPC) and a comprehensive kinetic model parameterized for the model material. The SL process model is then solved using the finite element method in the software package, FEMLAB, and validated by the capability of predicting fabricated part dimensions. The SL cure process model, also referred to as the degree of cure (DOC) threshold model, simulates the cure behavior during the SL fabrication process, and provides insight into the part building mechanisms. It predicts the cured part dimension within 25% error, while the prediction error of the exposure threshold model currently utilized in SL industry is up to 50%. The DOC threshold model has been used to investigate the effects of material and process parameters on the SL performance properties, such as resolution, speed, maximum temperature rise in the resin bath, and maximum DOC of the green part. The effective factors are identified and parameter optimization is performed, which also provides guidelines for SL material development as well as process and laser improvement.

abstract: Stereolithography files (STL) are widely used in diverse fields as a means of describing complex geometries through surface triangulations. The resulting stereolithography output is a result of either experimental measurements, or computer-aided design. Often times stereolithography outputs from experimental means are prone to noise, surface irregularities and holes in an otherwise closed surface. A general method for denoising and adaptively smoothing these dirty stereolithography files is proposed. Unlike existing means, this approach aims to smoothen the dirty surface representation by utilizing the well established levelset method. The level of smoothing and denoising can be set depending on a per-requirement basis by means of input parameters. Once the surface representation is smoothened as desired, it can be extracted as a standard levelset scalar isosurface. The approach presented in this thesis is also coupled to a fully unstructured Cartesian mesh generation library with built-in localized adaptive mesh refinement (AMR) capabilities, thereby ensuring lower computational cost while also providing sufficient resolution. Future work will focus on implementing tetrahedral cuts to the base hexahedral mesh structure in order to extract a fully unstructured hexahedra-dominant mesh describing the STL geometry, which can be used for fluid flow simulations. / Dissertation/Thesis / Masters Thesis Aerospace Engineering 2014