Literatura académica sobre el tema "Injection molding of plastics"

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1993 and Thesis (M.S.)--Massachusetts Institute of Technology, Sloan School of Management, 1993.<br>Includes bibliographical references (leaves 196-197).<br>by Daniel John Berkery.<br>M.S.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2004.<br>Includes bibliographical references (leaves 218-244). Also available in electronic version. Access restricted to campus users.

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, 2003<br>Injection moulding is a process by which molten polymer is forced into an empty cavity of the desired shape. At its melting point, polymers undergo a volumetric expansion when heated, and volumetric contraction when cooled. This volumetric contraction is called shrinkage. Once the mould cavity is filled, more pressure is applied and additional polymer is packed into the cavity and held to compensate for the anticipated shrinkage as the polymer solidifies. The cooling takes place via the cooling channels where the polymer is cooled until a specific ejection criterion is met. Heat from the polymer is lost to the surrounding mould, a part of this heat reaches the cooling channel surfaces, which in turn exchange heat with the circulating cooling fluid. Due to the complexity of injection moulded parts and the cooling channel layout, it is difficult to achieve balanced cooling of parts. Asymmetric mould temperature distribution causes contractions of• the polymer as it cools from its melting temperature to room temperature. This results in residual stresses, which causes the part to warp after ejection. Given the understanding of the mathematical model describing the heat transfer process during the cooling stage, the objectives of this study were three fold. Firstly, an alternative numerical model for the heat transfer process was developed. The proposed model was used to investigate the cooling stress build-up during the injection moulding process.

Thesis (Ph. D.)--Ohio State University, 2004.<br>Title from first page of PDF file. Document formatted into pages; contains xxi, 238 p.; also includes graphics Includes bibliographical references (p. 231-238). Available online via OhioLINK's ETD Center

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.