Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Lomolding is a new process similar to injection moulding. In this thesis a numerical model of the polymer flow into the cavity is presented. The model is used to compare the two processes with each other. Lomolding and injection moulding were modelled numerically with the finite element method. The model was an axisymmetric model and takes phenomena such as generalised Newtonian flow, free surfaces, moving boundaries and solidification into account. The processes’ characteristics that were compared are the cavity pressure, shear rate and shear stress. Improvements in these characteristics will result in lomolding having smaller machines, less fibre breakage and a better potential for in-mould-decoration. The thesis shows that lomolding has substantially lower shear rates and shear stresses than injection moulding. The model was also used to investigate certain machine design aspects, and to gain a better understanding of the polymer flow in lomolding. / AFRIKAANSE OPSOMMING: Lomoldering is ’n nuwe proses soortgelyk aan inspuitgiet. Hierdie tesis beskou ’n numeriese model van die polimeervloei soos dit in die gietholte invloei. Die model word gebruik om die twee prosesse met mekaar te vergelyk. Lomoldering en inspuitgiet is numeries gemodeleer met die eindige-elementmetode. Die model is aksiaal-simmetries en neem verskynsels soos Newtoniese vloei, vrye oppervlakke, bewegende grense en stolling in ag. Die proses-karakteristieke wat vergelyk is, sluit die gietholtedruk, vervormingstempo en skuifspanning in. Verbeterings in hierdie karakteristieke sal meebring dat lomoldering kleiner masjiene nodig sal hê, minder veselskade sal veroorsaak en meer versoenbaar met in-gietholte-versierings sal wees, vergeleke met inspuitgiet. Die tesis toon dat lomoldering laer vervormingstempo’s en skuifspanning het, in vergelyking met inspuitgiet. Die model is ook gebruik om sekere masjienontwerpaspekte te ondersoek, en om die polimeervloei in lomoldering beter te verstaan.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Rectangular components were produced by both standard injection moulding and by a process called Lomolding. Both moulding grade polypropylene homopolymer and glass-filled polypropylene were used. The effect of processing parameters on material properties, as measured by tensile and impact strength, and warpage were determined for both injection moulding and lomolding, for both unfilled and glass-filled polypropylene materials. Sampling of the components allowed for critical evaluation of processing parameters’ effect on material properties at points close to and distant from the injection point, as well as in the direction of materials flow and transverse to material flow. Glass-filled components were also evaluated in terms of glass fibre length and fibre distribution (post-injection). Overall conclusions could be drawn with respect to the 2 different processes and the materials used. It was seen, inter alia, that the specimen orientation had no effect on the mechanical properties when using unfilled polypropylene, but that the orientation of the glass fibres in the testing direction resulted in an increase in the tensile strength and the impact strength for the injection moulded samples. Similar results were seen for lomolded samples, except that the fibre orientation effects were different. In the same vein, other notable differences could be observed for samples produced by lomolding and injection molding. Fibre length and distributions obtained by polymer burn-off experiments served to help explain differences in properties of glass-filled products produced by the two processes.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / This dissertation describes the design analysis of a lomolder (a machine similar to an injection moulding machine). It focuses on key design aspects that will drive the purchase cost of the machine and that will also influence the maintenance and operating cost. The main objective of the study is to provide an understanding of the key factors that influence the cost of a lomolder as well as the factors that contributes to a quality manufactured part. A semi-analytical flow model was developed to predict cavity pressure drops for a range of part sizes. This model was necessary to eliminate time consuming numeric simulations required for machine optimisation. Numerous machine concept designs were developed and a final layout design chosen. A parametric CAD model was built for the lomolder. Layout designs for different sized lomolders can be generated with this model. The dissertation concludes with a cost study that focuses on the purchase cost of a lomolder unit. Key elements such as choice of actuator and piston to part area ratio are described.

published_or_final_version / Business Administration / Master / Master of Business Administration

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by James R. Rinderle. / M.S.

Thesis (M.S.M.E.)--University of Delaware, 2006. / Principal faculty advisor: James Glancey, Dept. of Bioresources Engineering. Includes bibliographical references.

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.

Thesis (M.B.A.)--University of Hong Kong, 1980.

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