In questo lavoro sono stat e studiate le relazioni esistenti tra le condizioni di processo, la struttura e leproprietà di provini ottenuti mediante la tecnologia di micro-stampaggio a iniezione. I micro-provini consistono in"dog-bone" di dimensioni molto contenute in poliossimetilene (POM), che è un polimero semi-cristallino largamente impiegato per la realizzazione di componenti meccanici per le ottime caratteristiche meccaniche, la stabilità all'umiditàe la buona lavorabilità. In particolare, sono state ricercate le correlazioni tra le temperature di processo (temperatura del fuso polimerico e dello stampo), le caratteristiche microstrutturali del materiale e le proprietà meccaniche dei micro-manufatti. I risultati mostrano che in funzione delle temperature di processo impiegate, si ottengono microstrutture caratterizzate da diversi livelli di orientazione dei domini cristallini di POM; le differenze sono tali da riflettersi sul comportamento meccanico dei micro-provini.

This paper reports on design, fabrication, and characterization of a microfilter to be used in biomedical applications. The microfilter, with mesh of 80 ?m, is fabricated by micro-injection molding process in polymeric material (polyoxymethylene (POM)) using a steel mold manufactured by micro-electrical discharge machining process. The characteristics of the filter are investigated by numerical simulation in order to define a suitable geometry for micro-injection molding. Then, different process configurations of parameters (melt temperature, injection velocity, mold temperature, holding pressure and time, cooling time, pressure limit) are tested in order to obtain the complete part filling via micro-injection molding process preventing any defects. Finally, the component is dimensionally characterized and the process parameters optimized to obtain the maximum filtration capacity.

This paper reports on design, fabrication and characterization of a micro-filter for hearing aid, dialysis media and inhaler. The microfilter is fabricated by micro injection moulding process in polymeric material (Polyoxymethilene - POM) using a steel mould manufactured by micro electrical discharge machining process. A novel filter configuration is proposed and, in the design step, the characteristics of the filter are investigated by numerical simulation in order to define a suitable geometry for micro-injection moulding. Then, different process configuration of parameters (melt and mould temperature, injection velocity, holding time and pressure, cooling time, pressure limit) are tested in order to obtain the complete part filling. Finally the component is dimensionally characterized and the process parameters optimized to obtain the maximum filtration capacity.

Due to the sensitive nature of applications of the micro injection moulding process, such as medical and aerospace, achieving high quality parts with high dimensional accuracy is crucial. In this work, simulation and an experimental study was performed to analyse the effect of four main parameters (melt and mould temperature, injection speed and holding pressure) on dimensional accuracy of a micro feature. Moreover, the focus was also to assess the process capability of a screwless/two plungers micro moulding machine in processing polyoximethilene (POM) and liquid crystal polymers (LCP). Results showed that mould temperature and injection speed was the most effective on dimensional accuracy respectively for POM and LCP and high settings for all the parameters improved the accuracy of the ribs. For LCP achieving process reproducibility was more difficult than POM even if the obtained dimensional errors are considerably lower.

Due to its ability to produce low-cost and high repeatable micro polymeric parts, injection moulding of micro components is emerging as one of the most promising enabling technologies for the manufacturing of polymeric micro-parts in in many different fields, from IT to Healthcare, to Medicine. However, when approaching the micro-scale, different issues related to the process should be addressed, especially as the depth of the mould cavity becomes very thin. In particular, the mould roughness could affect the surface quality of the produced micro components, like in macro moulding, as well as the complete filling of the parts. Although micro-injection moulding process has been extensively studied, further research on the effect of mould roughness conditions and on non-Newtonian fluid flow in micro-cavities are required. This will shed a light and open up new paths for a deeper understanding of the moulding scenario. The main objective of the present paper is the evaluation of the influence of the mould roughness on the polymer flow during micro injection moulding process. The test parts have been realized in POM material and have thickness lower than 250 ?m. The test part design has been properly conceived in order to neglect the effect of dimensions and geometry and to highlight the roughness contribution during the filling phase of micro injection moulding process. The experimentation has been performed considering cavities with different roughness values (3 levels) and decreasing depths (3 levels), for a total of nine test parts manufactured by micro-electrical discharge machining process (?-EDM). The results of the experiments are discussed in the paper and show that cavity surface roughness affects the injection process as the moulding scale level is decreased. In particular, when the cavity depths are reduced, higher surface roughness promotes the filling of components and this finding could be ascribed to the increase of wall slip effect.

Nowadays, the study of polymer nanocomposites is an active area of materials development because nanofillers and in particular Multi-Wall Carbon Nanotubes (MWCNTs) can significantly improve or adjust the properties of the materials into which they were incorporated such as optical, electrical, mechanical and thermal properties. MWCNTs have been adopted in quite a number of applications, but advancements in their properties are needed for spreading their potential. Moreover their behaviour and filling properties in micro injection moulding process have still to be studied.Therefore, in this work, experimental and statistical studies were performed to analyze the parameters effect on replicating capability of micro parts manufactured in POM/MWCNT by micro injection moulding process. Two compounds with different filler fraction (3 and 6 wt%) were tested and processed with different conditions and their operating range have been pointed out and compared with that of pristine POM (PolyOxyMethilene).The results show that the filler content has the effect to change slightly the operative range of the micro injection process parameters and to increase the replicating capability. The most effective parameters on replicating capability of micro ribs, evaluated by a dimensional index, are the mould temperature for the POM/MWCNT 3% and injection velocity for the 6% filler fraction.

The increasing demand for small and even micro scale parts is boosting the development of reliable micro system technologies. Micro-fabrication process capabilities should expand to encompass a wider range of materials and geometric forms, by defining processes and related process chains that can satisfy the specific functional and technical requirements of new emerging multi-material products, and ensure the compatibility of materials and processing technologies throughout these manufacturing chains. Micro injection moulding is the process of transferring the micron or even submicron precision of microstructured metallic moulds to a polymeric products. It represents one of the key technologies for micro manufacturing because its mass production capability and relatively low production cost. Polymers have relatively low cost, and offer good mechanical and thermal strength, electrical insulation, optical transparency, chemical stability and biocompatibility.In this work the authors investigate the micro injection moulding process parameters on the overall quality of a miniaturized dog-bone shaped specimen. The aim of the experimentation is to calibrate the process and set the machine for the correct filling of the component. A set of injection parameters are selected for study by experimental plan and simulation tool and then discussed. Simulation results are used to better understand the polymer flow behaviour during the filling phase. A commercial software is used and input data, collected during the micro injection moulding process, are included using as performance indicators flow front position and moulded mass. Process simulation can provide, at the present time, mostly qualitative input to the designer and process engineer. Two different polymers materials are tested and evaluated in relation to the process replication capability: Polyoxymethylene (POM) and Liquid Cristal Polymer (LCP). Finally, the moulding factors with significant statistical effects are identified. The holding pressure and holding time for POM and the holding pressure and injection velocity for LCP show the highest influence on achieving high part mass.

Due to its ability to produce low-cost and high repeatable micro-polymeric parts, micro-injection molding is emerging as one of the most promising enabling technologies in many different fields. When approaching the micro-scale, different issues related to the process should be addressed, especially as the thickness of the cavities becomes very thin. In particular, the mold roughness affects the surface quality of the micro-components produced, like in macro-molding, but this could also encompass the complete filling of the parts. The main objective of the present paper is to evaluate the roughness influence of the mold on the non-Newtonian fluid flow during the micro-injection process in thin micro-cavities where the mold surface condition could affect the process due to the phenomena neglected in macro- or mesoscale as less important boundary conditions. The part design was properly conceived in order to neglect the effect of dimensions and geometry and to highlight the roughness contribution during the filling phase. The experimentation was performed using cavities with different roughness values and decreasing depths from 200 to 50 ?m, considerably lower than 250 ?m found in literature and manufactured by the micro-electrical discharge machining (?-EDM). The results of the experiments are discussed and show that cavity-surface roughness affects the process as the molding scale is decreased. In particular, in thin cavities, higher surface roughness promotes the filling of component.

Injection molding of micro components is more and more an emerging technology for its ability to manufacture low cost and high repeatable micro polymeric parts relevant to many different fields, from IT to healthcare, to medicine. In particular, micro injection molding of thin cavities is an interesting challenge due to the large surface to volume ratio that characterizes the process. This condition emphasizes the heat transfer at the polymer/mold interface, especially when the depth of the mold cavity becomes very thin. Furthermore, the boundary conditions, neglected in macro scale, affect the process and hence the mold surfaces show high influence during products filling and not only on their final quality. Thus, the mold roughness should be considered in evaluating the polymer flow behaviour in filling micro thin cavities. In this work, three inserts were designed to evaluate roughness contribution during molding and were manufactured by micro electrical discharge machining process obtaining three thin cavities (depth of 100µm and different roughness values). These inserts were used for molding polymeric micro plates and the flow lengths, reached inside these parts, were measured as process quality response. The results show that the cavity roughness affects the micro injection process favouring the filling of the thin cavities. In fact, the samples, molded with the insert having the highest roughness, show the longest flow length. Finally, wettability measurements were performed on the mold inserts and also these results sustain the occurred relation suggesting a decrease of the heat transfer in the process at the increase of mold surface roughness.

Injection moulding of micro components is becoming more and more important for applications of micro system technologies in different fields (IT, Healthcare, Medicine) due to its ability to produce low-cost and high repeatable micro polymeric parts. However, when approaching micro scale level, different issues related to the process should be addressed, especially as the depth of the mould cavity becomes very thin. In particular, the mould roughness could affect not only the surface quality of the produced micro components, like in macro moulding, but also the complete filling of the moulded parts. This work aims to identify experimentally the effect of the roughness of thin mould cavity on filling capability in micro injection moulding process. Preliminary results of the experiments, carried out using POM material, are discussed in the paper and show that the surface roughness favours filling of the micro cavity.

The large surface area to volume ratio that characterized the micro injection molding process makes interfacial phenomena particularly critical and fundamental for the overall effectiveness of the process. This is more evident for micro injection molding of thinner part, where the roughness is comparable to at least one between the overall dimensions of the cavity. In this case, the contact situation between polymer and mold, significantly affects the heat transfer at interface, which strongly influences the polymer flow behavior. Therefore, in this paper, the effects of the polymer-tool interface on polymer flow were investigated. In particular, the filling of a representative micro part with a thickness of 100 ?m was studied as a function of surface roughness and mold wettability

Micro injection moulding process represents a key technology for realizing micro components and micro devices used in several fields: IT components, biomedical and medical products, automotive industry, telecommunication area and aerospace. The development of new micro parts is highly dependent on manufacturing systems that can reliably and economically produce micro components in large quantities. In this work the authors investigate the process parameters on the overall quality of a miniaturized dog-bone shaped specimen. The factors affecting micro flow behavior and components mass were studied byexperimentation (designed using DoE methodology) and simulation tool and then discussed. Different polymer materials, particularly indicated for the injection molding applications due to their flowability and stability, are tested and evaluated in relation to the process replication capability.It has been found that the holding pressure and holding time for Polyoxymethylene (POM) and holding pressure and injection velocity for Liquid Cristal Polymer (LCP) have the higher influence on achieving high part mass.

The increasing demand for small and cheap parts is boosting the development of reliable micro-system technologies. Fabrication process capabilities should expand to encompass a wider range of materials and geometric forms, which can satisfy the specific requirements of new emerging micro-products, and ensure the compatibility of new materials and processing technologies. Polymeric composites are very promising materials, since they offer new combinations of properties not available in traditional homogeneous materials. Because of their advantageous light weight, high strength, fatigue life, and corrosion resistance, they are forecast to replace conventional materials in several applications. Among the plastic process technologies, injection moulding is one of the key technologies for manufacturing miniaturised components due to its mass production capability and relatively low production cost. Micro-injection moulding allows to transfer micron and even submicron precision features to small products. Since final product properties strongly depend on materials and production processes and parameters, the process conditions of compounding as well as of product manufacturing have to be carefully studied and controlled. This is particularly important for the manufacturing of micro-products, since, at the micro-scale, some phenomena negligible at the macro-scale (as hesitation effect or capillarity forces for examples) can become important. However, only few studies concern the micro-injection of nanocomposites. Therefore, in this paper the micro-injection of two composites made of polyoxymethylene and carbon nanotubes has been studied. First, the electrical properties of the compounds have been measured; the fillers are dispersed in the matrix and form a network that dramatically increases the conductivity of the composites in comparison with the pristine resin. Then the compounds have been injected using a micro-injection machine and the components have been analysed. The mechanical analysis, based on tensile tests and dynamic-mechanical experiments on miniaturised dog-bone specimens, shows a slight reinforcing effect of the filler; however, the ductility is considerably reduced. This is likely due to a scarce adhesion of the carbon nanotubes and the polymer and the presence of some agglomerates. Moreover, as expected, the mould temperature affects the mechanical properties of the specimens, probably due to its effect on the internal structure of the solidified materials. The dimensional analyses carried out on micro-rib specimens show that replication capability is increased by the presence of the filler and using high values of the process parameters. Finally, microscopic analyses have been done in order to verify the dispersion and orientation of the fillers in the compounds. These effects have been observed only when high shear rates are involved.

Due to its high efficiency for the large scale production of polymeric parts, micro injection moulding is one of the key technologies of the new millennium. Although a lot of researches have been conducted to identify the most effective processing conditions for micro injection moulding, the comprehension of the influence of all parameters on the quality, the properties and the reliability of the moulded parts is still an issue. In this context, this study aims to evaluate the effects of the micro injection moulding process conditions on the tensile properties of micro parts, investigating the influence of three main process parameters: the injection speed, the mould temperature and the melt temperature. A full factorial plan has been applied to study the contributions of these parameters and a second study has been performed to understand the synergic interaction between the two temperatures on the tensile strength. Due to its high level of potential crystallinity, a typical semi-crystalline thermoplastic resin was used in the experiments. The results of the analysis showed a great influence of the mould temperature (T mould) on the ultimate tensile strength and of the melt temperature (T melt) on the deformation at the point of breaking; whereas the injection speed was significant on the overall mechanical performance. A new studied factor (T melt-T mould) could affect the resulting molecular structure and consequently the mechanical behaviour, but itself is not sufficient to thoroughly explain the observed behaviour. Moreover, the visual inspection of the deformation mechanism at break shows three distinctive trends demonstrating the great variability of the mechanical properties of micro-injected specimens due to process conditions.

Many research efforts have gone in the production of carbon nanotubes (CNT) composites for functional and structural applications and many processing methodologies have been experimented. Twin-screw extrusion appears to be the most suitable way from the perspective of production scale up and commercialization of these composites. At the same time, micro-injection molding process is considered as the key manufacturing technology for the mass production of miniaturized components and devices. Despite the massive literature about nanocomposites and microinjection molding process, few articles focus on the interaction between the compounding process and the following micro-injection molding transformation processes. This article aims at analyzing the influence of the screw configuration used in compounding process on the rheological and technological properties of the resulting nanocomposites. Two different combinations of screw elements have been tested to incorporate CNTs in two different resins: LCP (liquid crystal polymer) and POM (polyoxymethylene) typically used in micro-injection molding. The effects of the process set up have been observed studying first the rheology and then the moldability of nano-compounds microinjected ribs with high aspect ratio. The nanofiller dispersion has been evaluated via light and transmission electron microscopy. The results confirm that, the screws show different capacity at promoting the dispersion of the nanofiller, which affects the moldability of micro-injected CNT nanocomposites. The viscosity of the polymer seems a critical factor as well, because it influences first the dispersion of CNT bundle during extrusion and then the injection moldability of the composites in the micro-channels. POLYM. COMPOS., 38:349-362, 2017. © 2015 Society of Plastics Engineers. © 2015 Society of Plastics Engineers

Injection moulding of micro-featured plastic parts is becoming more and more important for applications of micro system technologies in different fields (IT, healthcare, medicine) due to its capacity to produce low-cost and high repeatable micro polymeric parts. However, approaching the micro world, different issues related to the process should be addressed, especially as the depth of the mould cavity becomes very thin. In particular, the characteristics of mould surface could affect not only the surface quality of micro components, but also the filling of injected parts. This work aims to identify the effect of the superficial texture on the filling capability of thin cavity in micro injection moulding process, and to evaluate the influence when the texture is obtained by different machining processes. The results of the experiments, carried out using a polymeric material, are discussed in the paper and show that, when the surface has an isotropic texture, the filling is proportional to the increase of the surface roughness, whereas an oriented direction of the texture longitudinal to the flow front favours the injection process.

In this paper, gap voltage and discharge current waveforms occurring during micro-EDM milling of micro-channels realized in a Si3N4-TiN workpiece are monitored and discriminated. The analysis is performed by implementing a design of experiment for the identification of the relationship existing among process parameters, machining performance and pulse type distribution. A pulse classification algorithm gathers gap voltage and current waveforms into four defined pulse types: short, arc, delayed and normal. The micro-channels are manufactured using an energy level corresponding to the finishing regime and varying pulse width, frequency and gap. The results show that material removal rate (MRR) benefits from the increase of normal and delayed pulses as expected. However, also arcs seems to increase MRR. Tool wear ratio (TWR) grows when normal pulses increases, whilst no particular influence is observed by delayed pulses. The peculiarity in TWR is found when arcs are considered: the values slightly decreases when arcs are more frequent, according to MRR behavior, but on the contrary with previous analysis done on different workpiece materials. This issue is currently under investigation

Achieving high quality parts is a crucial task for the micro injection moulding process due to the sensitive nature of applications as medical and aerospace. In this work, simulation and an experimental study are performed to analyse the effect of four main parameters (injection speed, melt and mould temperature, and holding pressure) on replicating capability of a micro feature by injection moulding process that is the main focus of the present paper. This work also assesses the performance of a screwless-two plungers micro moulding machine in processing polyoximethilene (POM) and liquid crystal polymers (LCP). Results show that mould temperature and injection speed are the most effective parameters on replicating capability respectively for {POM} and {LCP} and high parameters setting improved the dimensions of the feature and thus the quality. For LCP, achieving process reproducibility is more difficult than for {POM} even if the obtained replication fidelity is considerably higher.

Micro injection moulding process represents a key technology for realizing micro components and micro devices used in several fields: IT components, biomedical and medical products, automotive industry, telecommunication area and aerospace. The development of new micro parts is highly dependent on manufacturing systems that can reliably and economically produce micro components in large quantities. In this work, the authors investigate the process parameters on the overall quality of a miniaturised dog-bone-shaped specimen in order to determine the process constraints. The factors affecting parts aspects and mass are studied by experimentation designed using DoE methodology and then discussed. Two polymer materials (polyoxymethylene and liquid crystal polymer), particularly suitable for injection moulding applications due to their flowability and stability, are tested and evaluated in relation to the process replication capability. It has been found that the holding pressure and holding time for POM and holding pressure and injection velocity for LCP have the highest influence on achieving high part mass. Differently, melt temperature has the highest influence on minimising the process variability for both tested polymers. A further investigation has been carried out on the relationship between the holding pressure and the part mass and dimensions demonstrating the existence of a linear correlation between specimens mass and dimensions.

A desert dust episode in June 2007 and its radiative effects on the energy budget have been studied at three Italian stations (Rome, Lecce and Lampedusa) with the aim of investigating the interactions with different conditions and aerosol types over the Mediterranean. The three sites are representative for urban (Rome), sub-urban/rural (Lecce), and marine (Lampedusa) environment, respectively in the central Mediterranean region. Measured ground-based column-averaged aerosol optical properties and aerosol extinction profiles were used to initialize the MODTRAN4 radiative transfer model. The radiative transfer model was used to estimate the shortwave aerosol radiative forcing (ARF) and its forcing efficiency (FE) at two different solar zenith angles (20° and 60°) in the 280-2800 nm spectral range.The goal was to investigate the role of different aerosol types in the atmospheric boundary layer on the radiative budget during a dust event. During the event the aerosol optical depth was moderately high and similar at the three stations, with a maximum value of about 0.6. The Ångström exponent was found to increase with the distance from the source (0.21, 0.36, and 0.43 at Lampedusa, Rome, and Lecce, respectively). Differences in the aerosol optical properties were observed, also depending on the aerosol type assumed in the boundary layer. The estimated direct aerosol forcing appears to depend on the changes in aerosol properties and to the surface albedo. The results show that the desert dust produces a cooling effect at both surface (largest ARF of -224 W m-2 at 20° solar zenith angle at Rome) and top of the atmosphere (largest ARF of -19 W m-2 at 20° solar zenith angle at Lecce). The cooling is largest in the rural and smallest in the marine environment. The surface forcing efficiency appears to be strongly affected by the aerosol absorption in the BL. Large differences exist between our results and the FE determinations by AERONET, derived considering a single layer with homogeneous optical properties and prescribed vertical distribution. The FE deviations are around 20, 60, and 40% at the surface, TOA, and in the atmosphere, respectively. These results suggest that the detailed description of the vertical distribution of the aerosol properties is needed for an accurate determination of its radiative effects.