No description available.

No description available.

This work is concerned with the prediction of short (SGF) and long glass fiber (LGF) orientation in a center-gated disk and end-gated plaque injection molding test geometry using a simulation method that has not been attempted previously. Previous work has used assumptions to simplify the fiber orientation geometry (assuming a thin cavity) or flow field (neglecting fountain flow and entry regions). LGF orientation is predicted in a center-gated disk injection molding geometry including the advancing front and simulating the sprue and gate region (SGM method) so that no assumption about fiber orientation at the mold entrance has to be made. Using a semi-flexible fiber model and orientation parameters obtained through rheology, increased agreement was found between predicted and experimentally obtained values of orientation using the SGM method and a semi-flexible fiber model than was found using a Hele-Shaw approximation. The SGM method was applied to the end-gated plaque to predict SGF orientation both along and away from the centerline using an objective (reduced strain closure model) and non-objective (strain reduction factor model) orientation model. The predicted values of the strain reduction factor model showed reasonable agreement with experimentally obtained values of orientation throughout the three-dimensional cavity when using orientation parameters fit to experimental orientation data. Furthermore it was found that the objective model predicted results very similar to the non-objective model suggesting that objectivity may not play a role in predicting orientation in more complex geometries such as an end-gated plaque. Finally, the SGM method was applied to the end-gated plaque geometry to predict LGF orientation using a rigid and semi-flexible fiber model. It was found that the SGM method and the semi-flexible fiber model provides orientation predictions that are similar to experimentally obtained values of orientation. / Ph. D.

Histotripsy is a nonthermal ultrasound therapy used to treat cancer noninvasively by tissue mechanical fractionation with cavitation bubble clouds. Histotripsy is conducted through focused ultrasound transducers, where the piezoceramic (PZT) plate or disc, which emits the ultrasound wave, is the fundamental unit of the transducer. For modular prototype histotripsy designs, these PZTs are housed in a 3D printed focused lens. However, 3D printing transducer components can be time consuming and expensive when scaling up manufacturing, and 3D printing is limited in material selection for transducer applications. This thesis investigates the use of a novel fabrication process for prototype focused ultrasound transducers, injection molding, with an in-house benchtop injection molding machine. Acoustic material properties for investigated injection molded materials, ABS, GPPS, 30% glass filled nylon, nylon 6/6, and nylon 101, are quantified experimentally. Single elements are constructed with injection molded lenses made from ABS, 30% glass-filled nylon, nylon 6/6, and nylon 101 on an in-house benchtop machine. Results show that injection molding is a novel feasible method for applications in focused ultrasound devices and the investigated plastics have favorable properties for developing prototype histotripsy transducers, comparable to 3D printed transducer housings. Future work aims to apply injection molding to various transducer designs and additional materials for focused ultrasound therapy devices. / Master of Science / Histotripsy is a cancer therapy that can noninvasively treat tumors without surgery. This is done through devices called focused ultrasound transducers which emit ultrasound waves to administer treatment to ablate tumors. These transducers are constructed using 3D printing methods, but this can be limiting when scaling up manufacturing or in material selection for transducer applications, therefore additional fabrication methods are needed. This thesis presents injection molding as a novel method for making transducer components with an in-house benchtop injection molding machine. Five plastic materials are investigated to determine ultrasound properties that would identify preferred transducer materials. Single element transducers are made from injection molded materials, tested, and compared with 3D printed single element transducers. Results of this thesis show that injection molding is a feasible manufacturing method capable of producing transducers for histotripsy, and researched materials have favorable properties for this application. In future research, additional injection molded materials should be investigated and multiple transducer designs created for injection molding fabrication. These injection molded transducers can be applied to histotripsy or applied to other focused ultrasound therapies.

Thesis (M.E.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / This report involves the overall design of a closed loop computer control plastic injection molding system and detailed design of the inspection portion of the system for a specific part. This project is concentrated on the inspection portion of the system. A part and its print specifications were provided. Design requirements called for 100% inspection of the critical part dimensions which were most subject to change. The main system constraints influencing the design were inspection accuracy and speed. The system also had to be designed using available hardware. A gaging system was designed to be used in conjunction with a Digital Equipment Corporation (DEC) PDP-8/I computer to inspect plastic parts produced by an Allrounder 100 injection molding machine. The design of a gage system that allows fast and automatic checking of the part requires sensitive instruments. Linear transducers were used in order that fast checking would be accomplished and allow the gage to be paced with the plastic molding machine. After the checking fixture design was completed and components ordered, a work station design was made in order to fully utilize the check fixture. Two designs were completed with one under an inspector's control and the other completely mechanized for future hookup with a computer controlled robot. A computer program was written to accept voltage signals from the transducers, convert them to part deviations, compare them to specified tolerances, and make an accept/reject decision on each part. The design is limited to one specific part, but that does not decrease the importance of the project because the parameters worked with are measured in all parts. The checking method may vary somewhat for different parts, but the basic concept will not change. The design phase is complete. It was planned that the building of the system should be completed in two successive phases and a third phase used for a critical evaluation of the system. In phase 1 the system should be completed, the computer software developed and tested, the checking fixture completed and checked out, and the manual work station designed in detail. Phase 2 would involve a balance of the work and decision making between the computer and the operator. The necessary computer hardware and software would be developed and debugged and the work station changed to allow automatic operation, thus saving an inspector's time. The final stage will be an analysis of phases 1 and 2 and possible further extension of the system to other parts so that it is more universal. The analysis will be directed at determining the economic feasibility of the system for industrial applications. / 2999-01-01

The extrusion blow molding process is an important polymer processing operation which involves a complex thermo-mechanical history. / Specimens were obtained from two commercial, blow molding grade, high density polyethylene resins, employing an instrumented Impco reciprocating screw blow molding machine. High speed cinematography was employed in conjunction with a parison pinch-off mold and a transparent blow mold to characterize the dimensional changes of the parison during the parison formation and the clamping and inflation stages. The contact temperature and the heat removal rate were measured during the cooling stage. Numerical methods were employed to investigate the thermal history during various stages. After molding at various operating conditions, the molded specimens were extensively characterized in relation to the distribution of thickness, crystallinity, orientation and impact behavior. / The distributions were analyzed in relation to the data obtained regarding the thermo-mechanical history during the molding process and some theoretical considerations of the relevant flow and heat transfer phenomena.

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This paper documents the investigation into injection molding, or die casting, a bulk metallic glass (BMG). A BMG is an amorphous metal of a thickness greater than 25 ��m, according to leading researchers in the field. This critical thickness differentiates a normal metallic glass from a "bulk" metallic glass. The impetus for studying the ability to process lies in the material properties of the BMG, which has twice the strength of steel and the ability to be formed much like a thermoplastic. An initial discussion of processing options and history precedes a detailed description of the machine concept and design, including the governing parameters placed on the design. An account of methods and materials used has been included, along with problems encountered and resultant remedies. The initial results consist of the verification of the machine concept and the ability to replicate nanometer-sized surface features from a mold. Design issues are addressed and the corresponding revisions described. The final machine revision shows an increase in process repeatability. A presentation of photographs, which show results of forming the BMG against both copper and stainless steel, is offered as a qualitative assessment of the processing capability. A discussion of considerations and paths forward has been included for future research using the machine that was developed, but these processing theories could also be carried over to other experiments. In the end, this study proves the ability to form extremely small surface features in cast BMG parts and makes suggestions on research avenues that may give a better understanding of the variables involved in processing BMG from the molten state. / Graduation date: 2003

A novel process based on the principle of layered photolithography has been proposed and tested for making real three-dimensional micro-structures. An experimental setup was designed and built for doing experiments on this micro-fabrication process. An ultraviolet (UV) excimer laser at the wavelength of 248 nm was used as the light source and a single piece of photo-mask carrying a series of two dimensional (2D) patterns sliced from a three dimensional (3D) micro-part was employed for the photolithography process. The experiments were conducted on the solidification of liquid photopolymer from single layer to multiple layers. The single-layer photolithography experiments showed that certain photopolymers could be applied for the 3D micro-fabrication, and solid layers with sharp shapes could be formed from the liquid polymer identified. By using a unique alignment technique, multiple layers of photolithography was successfully realized for a micro-gear with features at 60 microns. Electroforming was also conducted for converting the photopolymer master to a metal cavity of the micro-gear, which proved that the process is feasible for micro-molding. / Singapore-MIT Alliance (SMA)

After the operation of medium-power and low-power radio stations being made to public access, the competition among broadcasting companies has reached its peak. As a result, considerable quantities of so-called ¡¥medicine-selling¡¦ broadcast hosts extensively stimulate the audience to buy advertised products by molding the settings. This research intends to study how broadcast hosts; as the main characters in broadcast programs, mold the settings by means of charisma, styles and techniques. Furthermore, this research intends to explore how the application of settings inspires audience¡¦s purchasing desire. The following three questions are designed to meet the research purpose. 1. Which techniques are used by broadcast hosts to mold the setting in the act of marketing merchandise? 2. Which interaction patterns are used by broadcast hosts to mold the setting in the act of marketing merchandise? 3. Which methods of molding the setting are used by broadcast hosts to serve the purpose of marketing merchandise? The author has adopted in-depth interviewing as the main method for this study, and interviewed five broadcast hosts from five different broadcasting companies. The analysis of these interviews has revealed that broadcast hosts don¡¦t necessarily need to exaggerate the effectiveness of the merchandise to increase sales. As a matter of fact, since the audiences¡¦ level of education has ascended, the old-fashioned hawking way is not that well-adopted nowadays. It is found that the relationship between the host and audience is similar to the one shared among family. That is to say the audiences¡¦ purchasing behavior results from the trust and dependency on the hosts. The audiences not only buy the medicine, but also seek empathy from the hosts. In addition, the exaggeration of effectiveness and gift give-aways are not the most effective ways any more. It is also found that phone-in are the fastest way to mold the interactive setting, and the host sharing personal experiences is the most effective way to increase sales.