ABSTRACT EVALUATION OF FIT FOR 3D PRINTED RETAINERS AS COMPARED TO THERMOFORM RETAINERS By David Cole, D.M.D. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Dentistry at Virginia Commonwealth University Thesis Directors: Eser Tüfekçi, D.D.S., M.S., Ph.D., M.S.H.A. Professor, Department of Orthodontics Sompop Bencharit, D.D.S., M.S., Ph.D. Associate Professor and Director of Digital Dentistry, Department of General Practice Introduction: Despite recent advances in three-dimensional (3D) printing, little information is available on 3D printed retainers Methods: Three reference models were used to fabricate traditional vacuum formed, commercially-available vacuum formed, and 3D printed retainers. For each model, three retainers were made using the three methods (a total of 27 retainers). To determine the trueness, the distances between the intaglio surface of the retainers and the occlusal surface of the reference models were measured using an engineering software. A small difference was indicative of a good fit. Results: Average differences of the traditional vacuum formed retainers ranged from 0.10 to 0.20mm. The commercially-available and 3D printed retainers had a range of 0.10 to 0.30mm and 0.10 to 0.40mm, respectively. Conclusions: The traditional vacuum formed retainers showed the least amount of deviation from the original reference models while the 3D printed retainers showed the greatest deviation.

Plastic is widely used to shape many of the daily goods produced and consumed today. Compared to wood and metal, this versatile material was recently introduced to society. The technical advances that began in the mid 1850's led to the invention of the first cellulose plastic polymers - a naturally occurring or synthetic compound consisting of large molecules made up of a linked series of repeated simple monomer (One Look on line Dictionary, 2009) - to be used at an industrial level. Inaugurating a period in which objects could have the strength of metal or wood, while also being lighter, colorful and cheaper to be manufactured. Plastics are a material that has the ability to be easily shaped (Lefteri, 2008). For me, plastic is ideal to work with, not only because its eclectic applications in product design and manufacture, but also due to its ordinary use in our globalized society. My master's research is to design functional objects using different types of plastics. My goal is to experiment with this material and understand the industrial production process behind the manufacture of the daily functional objects that surround us. Each plastic polymer has its proper usage and constraints. These characteristics are taken into account in my design process. Conceptually I allow myself to have freedom in exploring the object's form by respecting the material`s limitations as well as the techniques I have available to design and make my pieces. In conjunction with this creative research, I am using Computer Aided Design and Computer Aided Manufacturing through Computer Numerical Control and Rapid Prototyping technologies to design and produce the pieces. Furthermore, my intention is to have a deep understanding of the uses, production, discard and, recycling procedures of plastics goods. I am interested in knowing more about biodegradable, compostable and recyclable polymers in order to enjoy this great material that is evolving rapidly (Lefteri, 2008) in the contemporary society without causing environmental damage and preserve good conditions to future habitants of the Planet.

Support materials play a vital role across the entire field of additive manufacturing (AM) technologies. They are essential to provide the ability to create complex structures and features using AM. Successful implementation of support materials in ultrasonic consolidation (UC) will provide a vast opportunity for improvement of geometric complexity. Experimentation was performed to evaluate suitable support materials and their effectiveness within UC. Additionally a fused deposition modeling (FDM) system was integrated into the UC build environment to create an automated support deposition system. Finally several unique structures were built using support materials to demonstrate the improved geometric capability and to develop design rules for use in UC.

In this study, a previously designed passive dynamic walker (PDW) is built out of aluminum and plastic. The aim of the study was to produce an asymmetrical PDW and to compare the results to a computer simulation to validate the mathematical model. It also aimed at identifying the limitations of using additive manufacturing to create components for a PDW as well as gain insights on asymmetric systems. Beginning with a five mass kneed model, parameters were varied to produce up to a nine mass kneed model solution. The nine mass model allows more variability in added mass locations and separates the zeroth, first, and second moments of inertia. To validate asymmetric gait, step length and step time of the prototype were compared to the simulation. The walker, unable to produce a steady gait, failed to match the asymmetric simulation. More than four times the amount of symmetric data was found compared to asymmetric data. Successful runs of symmetric gaits were approximately double than for asymmetric gaits. The reason for unequal successes is thought to be due to greater instability of asymmetric systems. This instability is thought to be due to inertia from a constant state of hanging motion. 3D printing proved useful in simplifying components and reducing waste but the polymers used did not have enough strength when mass was added to the system. Joining differing materials on the legs was difficult to keep in place. A smaller more robust design could solve these problems. This study focused on understanding physically asymmetric PDWs. These simple robots separate the neurological and mechanical controls of walking and are advantageous for studying physical parameters of human gait. Once a reliable asymmetric walker is built, further research could alter the foot shape or knee location to reverse the process, thus having a PDW walk symmetric. Once a walker is successfully reverted from walking asymmetrical to symmetrical, these parameters could be then applied to human subjects. An example of this would be for prosthetic foot design.

<p>Matlab Simulink is a commonly used tool in the design process of control systems. To further take advantage of the Matlab Simulink models it is desirable to translate them for realtime use together with the possibility to read/write physical signals. </p><p>Real-Time Workshop is an extension to Simulink that automatically generates code from a model to a variety of target platforms. RTAI and RTLinux are hard realtime operating systems, making use of Linux. </p><p>To make automatically generated code run on RTAI and RTLinux an adaptation of the generation of code is necessary. </p><p>To control, for example, an automotive engine a data acquisition card with an appropriate device driver is required. Comedi, an open source project, provides a number of device drivers for data acquisition cards. </p><p>The developed system makes use of Simulink, Real-Time Workshop, RTAI or RTLinux, and the standard data acquisition card NI 6035E using a Comedi device driver. The Simulink models may be executed at frequencies up to 50 kHz on ordinary PC hardware. </p><p>The evaluation of the system consisted of measuring the interrupt latency of the used motherboard's bus, measuring computation times running Simulink models with known complexity, running models developed at Vehicular Systems and a comparison of interfacing Simulink/Real-Time Workshop between RTAI and RTLinux. </p><p>The recommended realtime operating system is RTAI due to the open source community support of it as a target platform for Real-Time Workshop.</p>

This paper introduces an alternative technique for the development of microfluidic systems for biotechnology based on mechanical machining and ultrasonic welding. Advantages of this approach over existing prototyping approaches involving the rapid development of tooling include: (a) short cycle time, (b) design flexibility, and (c) low cost manufacturing. In addition, the process provides a migration path to high volume production. A limitation of this system is that it cannot practically produce microchannels smaller than about 250 μm (0.010 in). However, for many biological cell-based biosensors, this feature scale seems well suited based on cell viability results. Several issues are discussed relevant to this approach, including bond strength, seal leakage, and sterilization. / Graduation date: 2002

An algorithm was developed to enable efficient segmentation of dimensionally-large objects into smaller components that can be fabricated within the given Rapid Prototyping (RP) machine workspace. The algorithm uses vertical and horizontal flat plane cuts, as well as feature-based volume decomposition. Due considerations were given to the optimisation of the surface accuracy, the build time, the strength and the number of segments generated by the segmentation process. A computer-aided design (CAD) application programme that interfaces with Unigraphics (UG) was also developed to allow import of objects in Standard Triangulated Language (STL) files into UG without loss of accuracy. In addition, the application software provides the functions that facilitate the implementation of the segmentation algorithm in UG. Two case studies were carried out using the algorithm in a Selective Laser Sintering (SLS) RP system. The resulting objects had properties that matched the research objectives with which the proposed algorithm was validated. / Singapore-MIT Alliance (SMA)

The purpose of this study was to investigate the implications of additive manufacturing on industrial design profession and designers through an explorative study. Through a literature survey, implications of additive manufacturing technologies on industrial designers and industrial design profession were explored. Expanding literature survey with on-line searches, several experimental and commercial application examples of rapid manufacturing of products were identified. These identified examples were then used for a qualitative evaluation on the implications of additive manufacturing for the industrial design profession and designers through semi-structured interviews conducted with seven professional industrial designers having experience with rapid manufacturing in Istanbul Turkey. The research concluded with significant implications of additive manufacturing having the potential to cause paradigm shifts in industrial designer&rsquo / s role, definition of the profession and design process. The conclusions derived include suggestions to exploit the potential brought by these technologies and their applications.

The purpose of the present study is to develop techniques for manufacturing anatomically-shaped substrates of implants made from calcium polyphosphate (CPP) ceramic. These substrates have tissue-engineered cartilage growing on their top surfaces and can be used as implants for osteochondral focal defect repair. While many research groups have been fabricating such substrates using standard material shapes, e.g., rectangles and circular discs, it is considered beneficial to develop methods that can be integrated in the substrate fabrication process to produce an implant that is specific to a patient’s own anatomy (as obtained from computer tomography data) to avoid uneven and/or elevated stress distribution that can affect the survival of cartilage. The custom-made, porous CPP substrates were fabricated with three-dimensional printing (3DP) and computer numerically controlled (CNC) machining for the first time to the best of the author’s knowledge. The 3DP technique was employed in two routines: indirect- and direct-3DP. In the former, 3DP was used to fabricate molds for pre-shaping of the CPP substrates from two different powder size ranges (<75 μm and 106-150 μm). In the latter, CPP substrates were produced directly from the retrofitted 3DP apparatus in a layer-by-layer fashion from 45-75 μm CPP powder with a polymeric binder. The prototyped samples were then sintered to obtain the required porosity and mechanical properties. These substrates were characterized in terms of their dimensional shrinkage and density. Also, SEM images were used to assess the particle distribution and neck and bond formations. The substrates produced using the indirect-3DP method yielded densities (<75 μm: 66.28 ± 11.62% and 106-150 μm: 65.87 ± 6.12%), which were comparable to the substrates used currently and with some success in animal studies. Geometric adjustment factors were devised to compensate for the slight expansion inherent in the 3DP mold fabricating process. These equations were used to bring the plaster molds into true dimension. The direct-3DP method has proven to be the ultimate choice due to its ability to produce complex anatomically-shaped substrates without the use of a chemical solvent. In addition, it allows for precise control of both pore size and internal architectures of the substrates. Thus, the direct-3DP was considered to be superior than the indirect-3DP as a fabrication method. In the alternative CNC machining approach to fabrication, the ability to machine the CPP ceramic was feasible and by careful selection of the machining conditions, anatomically-shaped CPP substrates were produced. To develop strategies for optimizing the machining process, a mechanistic model was developed based on curve fitting the average cutting forces to determine the cutting coefficients for CPP. These cutting coefficients were functions of workpiece material, axial depth of cut, chip width, and cutter geometry. To explore the utility of this modelling approach, cutting forces were predicted for a helical ball-end mill and compared with experimental results. The cutting force simulation exhibits good agreement in predicting the fundamental force magnitude and general shape of the actual forces. However, there were some discrepancies between the predicted and measured forces. These differences were attributed to internal microstructure defects, density gradients, and the use of a shear plane model in force prediction that was not entirely appropriate for brittle materials such as CPP. The present study successfully developed 3DP and CNC fabrication methods for manufacturing anatomically-shaped CPP substrates. Future studies were recommended to explore further optimization of these fabrication methods and to demonstrate the utility of accurate substrates shapes to the clinical application of focal defect repair implants.

The proliferation of electric machines has drastically increased in recent years and is likely to increase into the future. This interest in the production of advanced, high power density electrical machines that are small in size has heightened the need for flexible manufacturing processes to produce their laminated components during short batch and prototyping production runs. A means of cost effective, accelerated prototyping of these machines will have a substantial impact on their design and optimization, reducing time requirements to produce and test a given design. A review of the current manufacturing methods for prototyping electric machines was conducted. In particular, laser cutting, electric discharge machining, and abrasive waterjet (AWJ) machining were researched as competitive processes. Each of these methods exhibits marked advantages and disadvantages that present the opportunity for a new process to compete. This work investigates the applicability of high throughput profile milling (HTPM) for the prototyping of advanced electric machines, specifically, the process parameter space for milling of electrical steels. The material response will be determined by characterizing its specific cutting energy and utilizing this to develop a model to predict cutting forces during the milling process. Optimal process parameters will be investigated to obtain maximum productivity and minimal burr formation. Finally, the impact of HTPM processing on the magnetic properties of electrical steels will be compared to that of a leading prototyping technology, AWJ machining.