Conductive polymer composite foams can achieve impressive absorption of electromagnetic energy through the synergistic effects of conduction and polymer loss, as well as multiple internal-scattering mechanisms driven by the material discontinuities between walls and air cells. Although it is well known that the concentration of conductive fillers affects air cell formation and growth during the foaming process, the mechanisms of powder incorporation into the solid precursor mixture warrant further investigation. In this work, a design of experiment (DoE) was developed to examine how the type of metal particles, concentration, and method of inclusion affect the chemical foaming process, morphology, and shielding effectiveness (SE) of the composite foams. For the experiments, recycled low-density polyethylene (LDPE) and reused metal particles (AISI 316 L and Maraging 300 steels, Nickel superalloy, and Copper) at two concentrations (5 % and 10 % wt) were used as the polymer matrix and fillers, respectively. Before foaming, each metal powder amount was incorporated according to two distinct approaches: (i) mixing/stirring; (ii) settling metal powder layers in two phases onto the LDPE pellets, without stirring. The morphological analysis and scanning electron microscope (SEM) images reveal that settling a smaller amount of metal powder (5 wt%) provides lighter, porous structures with distributed air cell areas and more homogeneously dispersed metal particles. Furthermore, these characteristics enable achieving an average specific Shielding Effectiveness (SSE) of more than 25 dB/g/cm3 in the X-band, especially for lower amounts of Ni superalloy or Cu, as confirmed by Analysis of Variance (ANOVA). In contrast, mixing the metal powders generally resulted in more dense structures with significantly reduced electromagnetic absorption.

Effective thermal management within injection molds is crucial for improving the process energy efficiency. This study presents a novel hybrid mold design, combining steel inserts with polymeric base plates, to enhance thermal insulation and reduce energy consumption. Two mold configurations were experimentally tested on a micro-injection molding machine without active cooling: one made of conventional mold steel and the other using Formlabs White V05 resin. Thermal behavior was analyzed through experimental measurements and finite element simulations using Comsol Multiphysics, with numerical models calibrated using real process data. The results indicate that the hybrid mold retains heat more effectively, achieving higher steady-state temperatures and improved thermal stability during machine stops. At the steady-state regime, the thermal energy stored in the traditional mold insert is estimated at 1 J, while in the hybrid mold it is 2.1 J. The difference is lost by traditional molds since it is dispersed in the surrounding environment. On a limited transient of 164 cycles starting from ambient temperature, the overall advantage of hybrid versus traditional mold in terms of stored thermal energy is estimated at ∆E=506 J (+45%). This amount of thermal energy can be harvested and reused in other phases of the process, such as raw material pre-heating or drying. These results suggest that incorporating polymers as a strategic material in mold design can lead to more energy-efficient injection molding processes.

Efficient thermal management is a key factor in improving the sustainability and productivity of injection moulding processes, particularly at the micro-scale where thermal transients strongly affect part quality and cycle stability. This work investigates the thermal behaviour of hybrid moulds composed of polymeric support plates manufactured in Precision Resin V01 and stainless-steel inserts manufactured by additive manufacturing. An experimental campaign was carried out on a micro-injection moulding machine to characterize the intrinsic thermal response of the mould under uncooled conditions. Temperatures were monitored through embedded thermocouples and used to develop and calibrate a three-dimensional transient numerical model in COMSOL Multiphysics. Particular attention was devoted to the identification and calibration of heat transfer coefficients at the injection and extraction interfaces, which were found to play a dominant role in governing insert temperature evolution. The calibrated model accurately reproduces the experimental thermal transients, with deviations below 10%, demonstrating its reliability as a predictive tool for analysing mould thermal behaviour and supporting early-stage design and process optimization. The results highlight the advantages of hybrid architectures in promoting thermal stability and provide a robust methodology for modelling heat exchange in unconventional mould configurations.

Polyether ether ketone (PEEK) is a semi-crystalline polymer known for its high mechanical strength, excellent chemical resistance, and thermal stability up to 250 °C. Still, it requires high processing temperatures and exhibits relatively low impact toughness. Moreover, due to its high melt viscosity and thermal sensitivity, it requires several precautions to be suitably processed. These drawbacks are more critical for PEEK-matrix composites, such as carbon fiber-reinforced PEEK (C-PEEK). Conversely, polyetherimide (PEI) is an amorphous thermoplastic with superior ductility, lower melt viscosity, and good dimensional stability. The blending of polymers, PEEK (or C-PEEK) and PEI, is a promising strategy to enhance processability and tune high-performance mechanical and thermal properties for demanding applications. In this paper, two blends made of C-PEEK and PEI, with two different fractions (i.e., 20 and 30 wt%) of PEI, were mixed and analyzed. Results show that the processability by injection molding of the blends is improved in comparison with the C-PEEK, due to the presence of PEI, which, however, reduces (< -26%) the mechanical properties. The processability by extrusion molding of 3D-printing filaments was also successfully tested with filaments having tolerance dimensions and good surface quality.

The injection molding process is one of the most widely used in industry to produce plastic parts. To optimize overall energy consumption, controlling thermal energy is a key factor. This can be achieved through smart modifications to the mold design. In this study, two molds made from different materials are compared, focusing on thermal analysis using numerical models. Examined materials for the mold base parts are mold steel and High Temp Resin (Formlabs), while an insert made in steel is used for both cases. The aim is to optimize the thermal energy management inside the mold. The software used is COMSOL Multiphysics for thermal characterization to evaluate thermal behaviour within the mold. Numerical models are calibrated by experimental testing. The results demonstrated that the resin's capacity to retain heat within the steel insert is superior, requiring less thermal energy to maintain the desired temperature and for thermal transients.

Ultra-high molecular weight polyethylene (UHMWPE) is widely used in orthopedic and prosthetic applications due to its excellent wear resistance and biocompatibility. However, its high molecular weight presents significant challenges in terms of processing and formability, particularly at the micro scale. This study investigates the flowability characteristics of a new melt-processable UHMWPE in micro-disc geometries to evaluate its suitability for advanced prosthetic applications. Micro-injection molding experiments assessed the material's behavior under various thermal conditions. The influence of parameters such as temperature, pressure, and disc dimensions has direct effects on the flow behavior of UHMWPE and was analyzed by simulation and experiments. Results indicate that while UHMWPE exhibits limited flow under conventional conditions, optimized processing parameters can enhance discs’ formability without compromising the material’s structural integrity, avoiding defects. These findings provide critical insights for the microfabrication of UHMWPE thin components in next-generation prosthetic devices, enabling improved design precision and functional performance.

This Special Issue on Advances in Injection Molding: Process, Materials and Applications presents a curated collection of papers highlighting the dynamic evolution of this fundamental manufacturing technology [...]

Secondary raw materials, recycled Polypropylene (PP) and metal powders retrieved after use in the Powder Bed Fusion-Laser Beam process, are used to realize composite foams for microwave absorptance through chemical foaming. Morphological characterization allowed us to estimate foams’ relative density, cell size, distribution, and circularity. The results highlighted that metal powders contributed to air cell nucleation during the process, thus influencing the final foam morphology. Then, numerical analyses were conducted on modeled PP foams to calculate Scattering (S) parameters and Shielding Effectiveness (SE), varying air cell areas, shapes, metal particle distribution, and evaluating their impacts on EM response. Based on simulation results, the S-parameters of all samples were then measured in the X-band. The calculated SE contributions, SER and SEA, showed that foams with virgin and reused metal powders behave very similarly. Finally, four samples foamed from extruded pellets were characterized morphologically and electromagnetically. The outcomes showed extruded-based foams had a slightly decreased relative density, increased air cell numbers with lower circularity, and better uniformity in the air cell distributions. Confronting SE contributions in the X-band, SEA improved by about 10%-20% compared to the mixed samples.

Optical measurements are increasingly widely used as preferential techniques to evaluate dimensional and surface quantities in micro-products. However, uncertainty estimation is more critical on micro-products than macro, and it needs careful attention for evaluating the obtained quality, the requested tolerance, and the correct setting of experimental process settings. In this study, optical measurements characterized micro-injected products by linear and surface acquisition and considered all the sources contributing to uncertainties. The results show that the measure uncertainty could be underestimated if only the standard deviation on simple measurements is considered; this could cause a significant restriction of the estimated range covering the measured values. Furthermore, the findings confirm that the correct evaluation of the potential uncertainties contributes to accurately assessing the process behavior and improving product quality.

The massive increase in telecommunications infrastructure and devices has recently exacerbated the necessity of developing advanced electromagnetic interference (EMI) shielding solutions. Porous structures based on conductive polymer composites (CPCs) are currently promoted as feasible options for this task. In this scenario, the chemical foaming process shows suitability for easily fabricating CPC foams with closed cells and variable porosity. Nonetheless, the process and the products have not yet been fully explored in the literature for EMI shielding purposes. Hence, this work proposes the fabrication of foams made of polylactic acid with 10wf% carbon fiber (CF-PLA) via chemical foaming. After the process assessment, the morphological and dielectric characterizations of the samples were discussed in the function of the process parameters. The results show that chemical blowing agent (CBA) weight fraction % and temperature were key in obtaining target structural and dielectric requirements enabling EMI shielding. Numerical analyses on CF-PLA foams, modeled according to morphological outcomes, were performed via the integral finite difference time domain (IFDTD) method. The obtained Scattering Parameters and shielding effectiveness (SE), between 0.5 and 12 GHz, highlighted that when foam relative density and air pore density are simultaneously high, the shielding is mainly accomplished through absorption (SE A = 20dB) while reflection is minimized (SE R = 2dB). Scattering Parameters and SE were also measured in the X-band showing good agreement with the numerical findings; indeed, CF-PLA foams with higher relative density and air cell density exhibited a reduction of SE R (3dB) and a SE A with maxima up to 30dB.

In articular joint implants, polymeric inserts are usually exploited for on-contact sliding surfaces to guarantee low friction and wear, a high load-bearing capacity, impact strength and stiffness, and biocompatibility. Surface micro-structuring can drastically reduce friction and wear by promoting hydrostatic friction due to synovial fluid. Ultra-High Molecular Weight Polyethylene (UHMWPE) is a suitable material for these applications due to its strong chemical resistance, excellent resistance to stress, cracking, abrasion, and wear, and self-lubricating property. However, surface micro-texturing of UHMWPE is hardly achievable with the currently available processes. The present study investigates UHMWPE’s micro-textured surface replication capability via injection molding, comparing the results with the more easily processable High-Density Polyethylene (HDPE). Four different micro-texture cavities were designed and fabricated on a steel mold by micro-EDM milling, and used for the experimental campaign. Complete samples were fabricated with both materials. Then, the mold and samples were geometrically characterized, considering the dimensions of the features and the texture layout. The replication analysis showed that HDPE samples present geometrical errors that span from 1% to 9% resulting in an average error of 4.3%. In comparison, the UHMWPE samples display a higher variability, although still acceptable, with percentage errors ranging from 2% to 31% and an average error of 11.4%.

The use of additive manufacturing (AM) processes at the micro-scale helps to increase the development of micro-systems, thus enabling shorter tooling development to be exploited for other micro-technologies, such as micro-injection molding (µ-IM). In recent years, these process combinations have shown their capability of providing greater flexibility to micro-technologies and facilitating a high production rate, in particular allowing µ-IM to be economically feasible for low-volume production. Therefore, in order to assess the feasibility of micro-metal AM for µ-IM mold production, a set of mini- and micro-polymeric parts injected by using molds realized via the laser-powder bed fusion (L-PBF) process is discussed in this paper. The molds were manufactured in low-carbon steel and have been characterized and tested experimentally, without any post-process treatment. Two selected geometries, corresponding to a mini dogbone for tensile tests and a flexural hinge with features at the micro-scale, were designed and realized by the µ-IM process. These were replicated in order to assess the accuracy of the whole process. The obtained results of replication accuracy and mechanical tests confirm that the µ-IM process, performed with an L-PBF-made mold insert, is feasible and affordable for micro-production, although great accuracy, especially in mold design, fabrication, and assembly, is required.

As the complexity of micro-products increases, the micro-manufacturing processes, tool setups, and measurement processes have to be more precise and efficient. Combining them in a multi-stage process chain can effectively improve production accuracy and performance and reduce limitations and production costs. This paper focuses on the process chains for the manufacturing of micro-products and presents the state of the art, highlighting the specific characteristics of the existing models of process chains for micro-manufacturing. Based on the critical review of these characteristics, an evolution of the process chain model for micro-manufacturing is proposed, considering machining, measurement/characterization, referencing processes, and their combination into a suitable sequence. The proposed model accounts for relevant aspects of micro-manufacturing, such as size effects and technological fingerprints at the microscale. This paper also discusses the hierarchical properties of multiple micro-manufacturing process chains and some specific techniques to address the critical issue of referencing processes. Furthermore, some relevant case studies involving micro-electrical discharge machining, micro-injection molding, additive manufacturing, and micro-milling are presented to demonstrate how the micro-manufacturing potentiality can be increased using process chains.

The effects of micro texturing on several surface characteristics, i.e. biofouling, wetting, lubrication, cell adhesion, have been widely investigated. In the healthcare sector, and specifically medical devices, micro-structured surfaces are exploited to improve tribological properties or foster the osseointegration of surgical implants. Polymeric components in joint implants substitute cartilages of natural joints guaranteeing biocompatibility, low friction and wear, high load bearing capacity, impact strength and stiffness. Among these, tribological properties are very important for their direct impact on the implant lifespan. Micro-structuring of on-contact sliding surfaces can drastically reduce the friction and wear by promoting hydrostatic friction due to synovial fluid at the components interface. In these applications, Ultra-High Molecular Weight Polyethylene (UHMWPE) is a successful material but its current manufacturing process hinders surface micro-texturing. In this scenario, a production process chain, combining micro-injection molding of UHMWPE with molds made by Stereolithography (SLA) can be a successful option for investigating several micro-structuring designs reducing time and cost for the analysis. In this work, the micro-texturing surface manufacturing capability of an SLA technology is investigated through four micro-textures, two mold materials, three orientations in 3Dprinting and two micro-features heights. Micro-texturing patterns are realized and characterized on the molds. The same molds are then used for injection molding of parts, studying the process parameters and the replication capability on molded samples. The results show that dimension of the micro-textures brings the SLA to its limit, with good agreement on pin height and an error on the pin diameter between 24 and 108µm. The 3Dprinting orientation can improve both pin shape and surface roughness. The injection molding experimentation allows to obtain a good replication capability.

Hybrid polymer composites are very promising for applications in a wide variety of sectors, such as automotive, aerospace, robotics, energy and construction. These materials consist of a polymer matrix and two or more fillers, which synergically interact resulting in enhanced specific properties and performance. Among hybrid polymer composites, those based on carbon fibers reinforced poly(ether ether ketone) (C-PEEK) are gaining a primary role for their excellent mechanical and chemical properties; zirconium oxide (ZrO2) nanoparticles can further enhance these properties, improving also the wear resistance. In this paper, a new hybrid C-PEEK+ZrO2 composite has been studied and its mechanical properties compared with its reference composite C-PEEK.

Quality evaluation of micro injection molded products is a complex task, in particular when instruments basing on contact methods are used and issues in measurements could arise due to the contact tool dimension not fitting well with extremely narrow features. Therefore, in these cases, optical methods may be preferred for the evaluation of molded products' dimensions and surface quality, especially for parts devoted to applications requiring functional purposes. In this context, the present paper proposes the use of surface parameters as a quality index for the evaluation of both the micro injection molding process and the resulting products. To this aim, two experimental procedures were implemented to allow for: (i) the evaluation of the most suitable surface parameters identified in relation to the process parameters; (ii) comparisons of the surface parameters findings with those obtained by classic dimensional quantity via a designed experimental plan (DoE). The results show that the surface parameters, evaluated in critical areas of the components, can ensure reliable estimates for the surface quality of the molded parts and can be preferred in comparison to linear measurements.

In this work, the moldability via micro-injection molding (mu IM) of nano-filled polyamide 6 (PA6) based systems and the microstructural characteristics of the micro-injected parts were investigated and compared to those observed via traditional injection molding (IM). Two types of nano-fillers, different in nature and geometry, were examined, namely carbon nanotubes and silicate layers. The presence of nano-fillers did not impair the mold replication capability of PA6 in the mu IM process. A micro-rib and a standard dumbbell specimen for tensile tests were used as reference micro- and macro-injected part, respectively. Transmission Electron Microscopy, Wide and Small Angle X-ray Scattering and Differential Scanning Calorimetry analyses showed that, due to the different thermomechanical histories during mu IM and IM, the micro- and the macro-parts have different microstructures, influenced also by the filler type. Both nano-filler dispersion and PA6 crystallinity were influenced.

At the present time, there is a growing interest in additive manufacturing (AM) technologies and their integration into current process chains. In particular, the implementation of AM for tool production in micro injection molding (µ-IM), a well-established process, could introduce many advantages. First of all, AM could avoid the need for the time-consuming and expensive fabrication of molds for small series of customized products. In this work, the feasibility, quality, and reliability of an AM/µ-IM process chain were evaluated by designing and fabricating mold inserts for µ-IM by stereolithography (SLA) technology; the mold inserts were characterized and tested experimentally. The selected geometry is composed of four thin cavities: This particular feature represents an actual challenge for both the SLA and µ-IM perspective due to the large surface-to-volume ratio of the cavity. Two different materials were used for the mold fabrication, showing sharply different performance in terms of endurance limit and cavity degradation. The obtained results confirm that the µ-IM process, exploiting an SLA fabricated mold insert, is feasible but requires great accuracy in material choice, mold design, fabrication, and assembly.

Micro-applications, especially in biomedical and optical sectors, require the fabrication of thin polymeric parts which can be commonly realized by micro-injection molding process. However, this process is characterized by a relevant constraint regarding the tooling. Indeed, the design and manufacturing of molds could be a very time-consuming step and so, a significant limitation for the rapid development of new products. Moreover, if the design displays challenging microfeatures, their realization could involve the use of more than one mold for the fabrication of a single thin part. Therefore, proper integration of different manufacturing microtechnologies may represent an advantageous method to realize such polymeric thin microfeatures. In this work, a micromanufacturing process chain including stereolithography, micromilling, and micro-injection molding is reported. The mold for the micro-injection molding process was fabricated by means of stereolithography and micromilling, which allowed us to produce low-cost reconfigurable modular mold, composed of insert support and a removable insert. The assessment of the proposed process chain was carried out by evaluating the dimensions and the surface finishing and texturing of the milled mold cavities and molded components. Finally, a brief economic analysis compares three process chains for fabricating the micromold showing that the proposed one reduces the manufacturing cost by almost 61% with the same production time.

Currently, the increasing interest in the study of Polylactic acid (PLA) polymer has been motivated by the potential of such material for consumer and biomedical applications. PLA is a thermoplastic polymer, biodegradable, compostable and deriving from renewable natural sources as starch and sugar. Injection molding is the most widely used process for thermoplastic micro-featured parts for to its capacity to manufacture low-cost and high repeatable micro-parts. The use of PLA for injection molded micro components is still not well stabilized due to the slow crystallization kinetics, not suitable for high performance applications. In this work, preliminary experimental studies have been performed to analyze the filling ability of PLA in a meso and a micro parts using different molding conditions to evaluate process parameters influence. The experiments results are discussed in the paper and show that injection molding proved to be suitable for meso-micro PLA product manufacturing.