This dissertation presents work involving the manufacture and analytic modeling of microcantilever parts (length-width-thickness of roughly 500-100-10 microns). The manufacturing goals were to devise a means for and demonstrate repeatable production of microcantilevers from techniques not used in the integrated-circuit field, which are the exclusive means of current microcantilever production. The production of microcantilevers was achieved via a solvent casting approach and with injection molding, which produced parts from various thermoplastic polymeric materials (amorphous, semi-crystalline, fiber- and nanoclay-filled) in a repeatable fashion. Limits of the injection molding process in terms of the thinnest cantilevers possible were examined with 2 microns being the lower bound. Subsets of the injection-molded parts were used in a variety of sensing applications, some results were successful (e.g., vapor-phase, resonance- and deflection-based sensing), while others showed poor results, likely due to experimental shortcomings (e.g., fluid-phase, deflection-based sensing). Additionally, microcantilever parts with integrated tips were injection-molded and showed to function at the same level as commercial, tipped, silicon-nitride parts when imaging an optical grating; this experimental work was the first demonstration of injection-molded parts for chemical sensing and force spectroscopy. The scientific results were (i) the derivation of a length scale dependent bending stiffness and experimental evidence showing that such an effect was observed, (ii) the development of a new microcantilever experimental mode (surface stress monitoring via microcantilever bending resonant frequencies) and experimental validation of the technique, and (iii) a new method for determining microcantilever geometry based upon measurement of a bending, lateral, and torsional mode and experimental validation of the procedure.

This thesis describes the fabrication of plastic microneedle devices, their fabrication by injection molding, and analysis of the penetration mechanics. Injection molding is an economical mass-production technique that may encourage widespread adoption of microneedles for drug delivery. Four polymers were injection molded into hexagonal and square patterns of between 91 and 100 needles per array. The patterns and geometries were chosen to study the effect of needle spacing and array design on penetration force. Two needle spacings of approximately 1 mm and 1.5 mm were employed for both patterns. Molded parts showed tip radii below 15 microns, heights of 600 to 750 microns, and an included angle of approximately 30 degrees. An economic analysis performed of the injection molded polymer devices showed that they can be manufactured for approximately $0.10 - $0.179 per part, which should be low enough to gain market acceptance. The added benefits of low pain perception, improved drug delivery for certain treatments, and the possibly of being recyclable make injection molded micro-needle devices a desirable alternative to silicon or metal microneedles. Penetration tests were performed with plastic micro-needle arrays and arrays of steel needles of the same spacings and patterns. Silicone rubber with mechanical properties similar to human skin was used as a skin simulant. The results showed that the micro-needles penetrated skin to depths between 120 and 185 microns depending on pattern, spacing, tip radius and needle length. This depth is sufficient to deliver drug therapies, but not so far that they stimulate the nerve endings present beyond 130 microns inside the dermis layer in human skin. An analytical model was developed to estimate the effects of various microneedle and skin characteristics on penetration force. The model was based on literature sources and derived from test results. The model accounted for coefficient of friction, tip radius, tip angle, and needle spacing, as well as the skin mimic's mechanical properties such as elastic modulus, mode I fracture toughness, and puncture fracture toughness. A Monte Carlo simulation technique was used to correct for errors in needle length and testing angle. Comparison of the experiments to the model showed good agreement.

Fuel cells are electrochemical energy conversion devices that convert chemical energy to electrical energy efficiently. Bipolar plates form an integral part of a fuel cell and their high manufacturing cost and low production rate have hindered the commercialization of fuel cells. Bipolar plates require high electrical conductivity, strength, chemical resistance and thermal conductivity. This thesis presents efforts to manufacture bipolar plates which meet these requirements using compression or injection molding. Compression or injection molding processes allow cost-effective, large-scale manufacturing of bipolar plates. A variety of material systems for the fabrication of bipolar plates are processed, molded and characterized. / text

published_or_final_version / Industrial and Manufacturing Systems Engineering / Doctoral / Doctor of Philosophy

Injection molding technology is utilized for a wide range of applications from mobile phone covers to bumper fascia of automotive vehicles. Foam injection molding (FIM) is a branched manufacturing process of conventional injection molding, but it was designed to take advantage of existing foaming technology, including material cost saving and weight reduction, and to provide additional benefits such as improvement in dimensional stability, faster cycle time, and so on. Gas-assisted injection molding (GAIM) is another supplemental technology of injection molding and offers several advantages as well. This thesis study takes the next step and develops innovative gas-assisted foam injection molding (GAFIM) technology, which is the result of a synergistic combination of two existing manufacturing technologies, FIM and GAIM, in order to produce a unique thermoplastic foam structure with proficient acoustic properties. The foam structure manufactured by GAFIM consists of a solid skin layer, a foam layer, and a hollow core; and its 6.4-mm thick sample outperformed the conventional 22-mm thick polyurethane foam in terms of the acoustic absorption coefficient. With respect to foaming technology, GAFIM was able to achieve a highly uniform foam morphology by completely decoupling the filling and foaming phases. Moreover, the additional shear and extensional energies from GAFIM promoted a more cell nucleation-dominant foaming behavior, which resulted in higher cell density and smaller cell sizes with both CO2 and N2 as physical blowing agents. Lastly, it provided more direct control of the degree of foaming because the pressure drop and pressure drop rate was controlled by a single parameter, that being the gas injection pressure. In summary, innovative, gas-assisted foam injection molding technology offers not only a new strategy to produce acoustically functioning thermoplastic foam products, but also technological advantages over the conventional foam injection molding process. Gas-assisted foam injection molding can become the bedrock for more innovative future applications.

Injection molding technology is utilized for a wide range of applications from mobile phone covers to bumper fascia of automotive vehicles. Foam injection molding (FIM) is a branched manufacturing process of conventional injection molding, but it was designed to take advantage of existing foaming technology, including material cost saving and weight reduction, and to provide additional benefits such as improvement in dimensional stability, faster cycle time, and so on. Gas-assisted injection molding (GAIM) is another supplemental technology of injection molding and offers several advantages as well. This thesis study takes the next step and develops innovative gas-assisted foam injection molding (GAFIM) technology, which is the result of a synergistic combination of two existing manufacturing technologies, FIM and GAIM, in order to produce a unique thermoplastic foam structure with proficient acoustic properties. The foam structure manufactured by GAFIM consists of a solid skin layer, a foam layer, and a hollow core; and its 6.4-mm thick sample outperformed the conventional 22-mm thick polyurethane foam in terms of the acoustic absorption coefficient. With respect to foaming technology, GAFIM was able to achieve a highly uniform foam morphology by completely decoupling the filling and foaming phases. Moreover, the additional shear and extensional energies from GAFIM promoted a more cell nucleation-dominant foaming behavior, which resulted in higher cell density and smaller cell sizes with both CO2 and N2 as physical blowing agents. Lastly, it provided more direct control of the degree of foaming because the pressure drop and pressure drop rate was controlled by a single parameter, that being the gas injection pressure. In summary, innovative, gas-assisted foam injection molding technology offers not only a new strategy to produce acoustically functioning thermoplastic foam products, but also technological advantages over the conventional foam injection molding process. Gas-assisted foam injection molding can become the bedrock for more innovative future applications.

Thesis (Ph. D.)--University of Hong Kong, 1996. / Includes bibliographical references.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2009. / The objective of this project was to measure the performance of high-strength aluminium alloys as injection mould material compared against conventionally used tool steel.

Mathematical models of heat flow and elastic stress generation based on the finite-element method have been developed and utilized to analyze the Epic-3 Monofrax-S casting process (Monofrax-S is primarily composed of 47-57% A1₂O₃, 34-41% ZrO₂ and 10-15% SiO₂). The results of the mathematical analysis, in conjunction with information obtained from a comprehensive industrial study, has led to the development of mechanisms for the formation of the various crack types found in this casting process. Thermal stresses have been predicted to be generated early in the solidification process in association with rapid cooling of the refractory surface as it contacts the initially cool mould and again later in the solidification process in conjunction with the tetragonal-to-monoclinic phase transformation which occurs in the zirconia component of Monofrax-S. The mathematical analysis has also helped to identify indirectly a potential mechanism for the generation of mechanical stresses. Based on an understanding of the generation of tensile stresses, recommendations have been made for modifications to the moulding and casting procedures in order to reduce the propensity for the formation of cracks. The modifications have included changes to the mould construction and geometry to reduce the generation of mechanical stresses and changes to the moulding materials to impact on the flow of heat at key times during solidification and cooling. With the recommendations in place, the casting process has been re-examined with the mathematical models to verify the impact of the modifications. The predictions show that the modifications have acted to reduce tensile stresses associated with the formation of Type-A and -B cracks. Preliminary industrial trials with the modified mould have yielded blocks free of these defects. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

This thesis is focused on design of equipment for injection molding. The work discusses current state of technology for injection molding. In the work is conducted structural design of horizontal injection press for plastics processing with horizontal closing movement. Injection molding machine is designed to form the parting plane of maximum dimension 350 x 350 mm.