Abstract The claim in additive manufacturing (AM) changes from simply producing prototypes as show objects to the fabrication of final parts and products in small volume batches. Thereby the focus is on freedom of material, dimensional accuracy and mechanical component properties. A novel extrusion-based AM technology has been developed focusing on these issues. The working principle is to form spheres from a thermoplastic polymer melt and build parts by single droplets. The material preprocessing is similar to the injection molding technology and enables a wide range of different thermoplastic polymers as build materials. With the droplet-based working principle high mechanical component properties and dimensional accuracy can be reached compared to similar processes. Further improvements to the process need a detailed knowledge of the physical effects during the build process. The temperature distribution during the manufacturing process determines at which temperature material is fused and how solidification takes place and shrinkage can occur or is suppressed. Thus, it has a significant influence on the mechanical properties and warpage effects of produced parts. In this work a thermal model is presented that describes the heat transfer during the build process. The necessary input data are the material properties and a print job description including the part geometry and building strategy. The basic idea is to simulate each single droplet deposition by applying a dynamic Finite Element Method. All relevant heat transfer effects are analyzed and represented in the model. The model was validated with measurements using a thermal imaging camera. Several measurements were performed during the build process and compared to the simulation results. A high accuracy could be reached with an average model error of about 4° Celsius and a maximal error of 10° Celsius.

Abstract In this paper, the impact of recycling and remanufacturing on the behavior of low-density polyethylene/multi-walled carbon nanotube (LDPE/MWCNT) composites is investigated. LDPE/MWCNT composites with 0.1–5 wt.%, previously manufactured by injection molding, were mechanically recycled and remanufactured by injection molding and 3D filament extrusion, and the rheological, electrical, and mechanical properties were analyzed and compared with those of virgin composites under the same conditions. Experimental results demonstrate that the recycled LDPE/MWCNT composites have similar rheological, electrical, and mechanical properties to virgin composites, if not better. Therefore, the recycled LDPE/MWCNT composites have a great potential for being used in engineering applications, while reducing the environmental impact.

Injection Molding is among the most popular processes in plastic parts production. Through this process, burn marks and shrinkage play the most significant role in decreasing surface quality as well as increasing costs, especially when manufacturers use this method in order to produce thin-walled plastic parts. In this paper, a new strategy to remove the defects caused by shrinkage and burn marks has been proposed for the injection molding process of a specific plastic part which is used to keep the doors of an automobiles open during the painting process. Burn marks caused by the trapped air inside thin walls of the part were first simulated in MOLDFLOW 2010 software. Next step is to compare the simulation results to results that are obtained from experimental analysis. Then, Burn marks and shrinkage effects were eliminated by optimization of the process which includes mold design revision by means of SOLIDWORKS software, modification of the simulation in MOLDFLOW and the mold modification in workshop environment by improvising some ejector pins in certain points. Furthermore, shrinkage amount of the part after cooling process was calculated by applying Finite Element Method (FEM) and obtained results were used to optimize the design of the mold. Results demonstrate that mold design optimization would be possible through designing flawless molds that contain certain points for trapped air discharge and calculating shrinkage amount by FEM for optimization of design procedure. Results consequently decrease costs as well as providing surface quality improvement.

In this study, the structure-property relationships in thermoplastic polyurethane (TPU) filled with multi-walled carbon nanotubes (MWCNTs) were investigated. Firstly, the contribution of MWCNTs to the melt shear viscosity and the pressure-volume-temperature (pVT) behavior was investigated. Secondly, injection-molded samples and 2 mm diameter filaments of TPU/MWCNT composites were fabricated and their mechanical and electrical properties analyzed. It was found that the melt processability of TPU/MWCNT composites is not affected by the addition of a small amount (1–5 wt.%) of MWCNTs, all composites displaying shear-thinning at high shear rates. The mechanical and electrical properties of the TPU/MWCNT composites were substantially enhanced with the addition of MWCNTs. However, the conductivity values of composites processed by injection molding were two and three orders of magnitude lower than those of composites processed by extrusion, highlighting the role of melt shear viscosity on the dispersion and agglomeration of nanotubes.

Packing processing parameters, including packing pressure and packing time, have significant impact on the internal molecular orientations, mechanical properties and optical performance of injection molded polymeric products. One of the limitations of cold-runner injection molding machines is the lack of real-time control of packing processing parameters during an injection molding cycle. As a result, a new melt modulation device has been developed and experimentally validated to control melt flow and manipulate processing parameters during cold-runner manufacturing. The use of the integrated melt modulation device has shown enhancement of physical properties and optical performance of injection molded polymeric products. Numerical simulations and experimental results of common thermoplastic optical polymers, such as PMMA, PC, and GPPS have been conducted and briefly demonstrated herein.

In the near future, carbon nanotubes containing plastic parts are likely to enter the environment in large quantities and, due to their resistance to degradation, the environmental impact may be even more important than that of similarly shaped plastic products. Thus, there is an immediate need to examine and understand the effect of recycling on the properties of polymer/carbon nanotube composites in order to develop sustainable recycling technologies. In this paper, polypropylene filled with different levels of multi-walled carbon nanotubes (MWCNTs) manufactured by injection molding was closed-loop recycled in order to investigate the effect of recycling and reprocessing on its rheological, electrical and mechanical properties. Preliminary results show that the PP/MWCNT composites keep the flow performance after mechanical recycling. Moreover, the stress and strain at break increase after one reprocessing cycle (mechanical recycling coupled with injection molding) whereas no statistically significant changes in electrical conductivity, Young modulus and tensile strength of the PP/MWCNT composites filled with 1, 3 and 5 wt.% were observed.

In this work, the advantages of Thermoplastic Polyurethane (TPU) filled with multi-walled carbon nanotubes (MWCNTs) were combined with those of the over injection molding process in order to obtain two-component (2k) structures with very different but high mechanical and electrical properties. TPU/MWCNT composites with different MWCNTs wt.% were over-molded onto Acrylonitrile Butadiene Styrene (ABS) substrates, under different processing conditions, and the adhesion was assessed by T-peel tests at room temperature. Since adhesion is also related to flow behavior, the rheological properties were studied with a capillary rheometer at shear rates similar to those of the injection molding process (10 2 ∼10 4 s −1 ). Experimental results indicated that the most effective way to control the adhesion between the ABS substrate and the over-molded TPU/MWCNT composite is to increase the melt temperature. The addition of carbon nanotubes improves adhesion in the vicinity of 0.5 wt.% MWCNTs.

As American vehicle fuel efficiency requirements have become more stringent due to the CAFE standards, the auto industry has turned to fiber reinforced polymer composites as replacements for metal parts to reduce weight while simultaneously maintaining established safety standards. Furthermore, these composites may be easily processed using established techniques such as injection molding and compression molding. The mechanical properties of these composites are dependent on, among other variables, the orientation of the fibers within the part. Several models have been proposed to correlate fiber orientation with the kinematics of the polymer matrix during processing, each using various strategies to account for fiber interactions and fiber flexing. However, these all require the use of empirical fitting parameters. Previous work has obtained these parameters by fitting to orientation data at a specific location in an injection-molded part. This ties the parameters to the specific mold design used. Obtaining empirical parameters is not a trivial undertaking and adds significant time to the entire mold design process. Considering that new parameters must be obtained any time some aspect of the part or mold is changed, an alternative technique that obtains model parameters independent of the mold design could be advantageous. This paper continues work looking to obtain empirical parameters from rheological tests. During processing, the fiberpolymer suspension is subjected to a complex flow with both shear and extensional behavior. Rather than use a complex flow, this study seeks to isolate and compare the effects of shear and extension on two orientation models. To this end, simple shear and planar extension are employed and the evolution of orientation from a planar random initial condition is tracked as a function of strain. Simple shear was imparted using a sliding plate rheometer designed and fabricated in-house. A novel rheometer tool was developed and fabricated in-house to impart planar extension using a lubricated squeeze flow technique, where a low viscosity Newtonian lubricant is applied to the solid boundaries to minimize the effect of shearing due to the no-slip boundary condition. The Folgar-Tucker model with a strain reduction factor is used as a rigid fiber model and compared against a Bead-Rod model (a semi-flexible model) proposed by Ortman. Both models are capable of predicting the data, with the Bead-Rod model performing slightly better. Orientation occurs at a much faster rate under startup of planar extension, and also attains a much higher degree of flow alignment when compared with startup of steady shear.

Fiber orientation simulation is conducted for the Center-Gated-Disk (CGD) geometry and compared with experimental data. Long-fiber thermoplastic composites (LFTs) possess competitive advantages over short glass fiber composites in terms of their mechanical properties while retain the ability to be injection molded. Mechanical properties of LFTs are highly dependent on the microstructural variables imparted by the injection molding process including fiber orientation and fiber length distribution. As the fiber length increased, the mechanical properties of the composites containing discontinuous fibers can approach those of continuous fiber materials. Several researchers have reported that flexural, creep and charpy impact properties increase as fiber length increases, while tensile modulus will plateau for glass fibers above 1 mm in length. Fibers less than the 1 mm threshold have been considered to be short while fibers with lengths greater than 1 mm are considered long. For long fibers, they will have the ability to deform, bend and even break during any stage of polymer processing. There is a lack of knowledge about the effects of fiber length and fiber length variation on fiber orientation kinetics. This lack of information provides an opportunity to understand the length effect inherent to long fibers systems. The Bead-Rod fiber orientation model takes into account the flexibility of semi-flexible fibers that show small bending angles. In this model, a flexibility parameter representing the resistive bending potential is fiber length dependent (detailed explanation can be found in the reference) 1 . This work is concerned with the effect of fiber length on the performance of the Bead-Rod fiber orientation model which takes into account the flexibility of semi-flexible fibers. Different averaging techniques are used to represent the average fiber length for the population of fibers, which give different fiber length parameters for the Bead-Rod model. The sensitivity of the Bead-Rod model is evaluated with regard to the fiber flexibility parameter, k, and length parameter, l b . The other phenomenal parameters within the orientation model are obtained via basic rheological measurements using simple shear flow. As the value of average fiber length L av increases and the corresponding flexibility parameter value decreases, the core regions become wider and the flow direction orientation gradually decreases especially near the walls for the Bead-Rod model predictions. In addition, as the parameters favor longer fiber lengths, the predicted extent of fiber bending increases. The simulation results are also compared with the experimental obtained fiber orientation at different flow length along the thickness direction. The Bead-Rod model shows improvement over the rigid rod model.

Metal injection moulding (MIM) has over the past decade established itself as a competitive manufacturing process to produce in large quantities small precision components with complex shape which would be costly to produce by alternative methods (Enneti, 2012). MIM is a process which combines the versatility of plastic injection moulding with the strength and integrity of machined, pressed or otherwise manufactured small, complex metal parts. MIM consist in shaping powder particles in injection process and then sintering them. MIM make use of the plastic moulding concepts to shape powder-polymer feedstock into the required geometry. During the injection phase, segregation appears in the feedstock and defects will be appear in the component during the sintering. To limit this effect a vast variety of binder systems have been developed (Enneti, 2012) to improve the homogeneity of feedstocks and limit segregation. Binder is formulated as a mixture of different organic or inorganic substances with several functions. Binder has the main commitments of giving the necessary rheological behavior to the feedstocks for injection moulding to transport the powder particles into the mould cavity and the cohesion of the green part (Enneti, 2012). The goal of this study is to characterize and understand the chemical behavior of feedstocks during the phases of mixing and injection. First the binder was studied. Then based on these results the characterization of the feedstock was made. For this a study of the chemical behavior and interactions on feedstocks based on polyethylene glycol (PEG) and Inconel 718 powder was investigated by Fourier Transform InfraRed spectroscopy (FTIR) (Hidalgo et al., 2013). That methodology was also investigated to study the thermal behavior of the binder at a temperature close to the temperature of mixing and injection. Analyzes shows the thermal degradation of the PEG is not affect by the components of the feedstocks. No chemical interactions between the powder and the binder are revealed. The thermal degradation of the PEG appears during the mixing process and change the rheological behavior of the binder. This result shows the necessity to develop another formulation of binder to preserve the PEG.

In this paper, the development of a new mixture, called feedstock, based on nickel super-alloys for Metal Injection Molding (MIM) is presented. This feedstock, which will be used to obtain metallic parts for the aeronautic industry, is a mixture of the appropriate, environmentally friendly polymers and metallic powders. Many scientific problems should be taken into account. For example, it requires tight control of the process to achieve the strict chemical and physical properties, because of the application in aeronautic industry. Another difficulty is the large dimension and functional requirement of manufactured components, which subject to the high mechanical and thermal constraints. Additionally, the use of a biodegradable polymer makes the process more delicate because of its thermo-physical properties.

The objective of this paper was to investigate the electrical and rheological behaviors of polypropylene (PP) filled with 1.0, 3.0 and 5.0 wt.-% multi-wall carbon nanotubes (MWCNTs). The flow behavior was analyzed in terms of the melt flow index measured at temperatures relevant for the injection molding process and the flow activation energy was calculated using an Arrhenius type equation. The electrical behavior of PP/MWCNTs composites was examined by DC resistance measurements on injection molded samples. The experimental results have shown that the incorporation of MWCNTs effectively enhances the electrical conductivity of the injection molded PP/MWCNTs composites. The composites under analysis can be classified as semi-conductors with the conducting network arranged in 4 dimensions, i.e. the critical exponent of the power-law dependence of the conductivity on the wt.-% MWCNTs is 2.37. The increased conductivity is explained by the orientation of the MWCNTs along the melt flow and the increased nanotubes-to-nanotubes contact after the formation of the percolation network.

In this article, the effects of nanoclay (CN) on the rheological behavior of polylactic acid (PLA)/polyhydroxybutyrate–valerate (PHBV) blends was investigated. The rheological behavior of PLA/PHBV blends showed a Newtonian plateau that converted to strong shear thinning behavior over the full range of frequency by the incorporation of nanoclay. The results indicate that the storage modulus and complex viscosity of PLA/PHBV blends were sensitive to nanofillers. An obvious pseudo-solid-like behavior over a wide range of frequency in PLA/PHBV/CN nanocomposites showed that the strong interaction between the PLA/PHBV blend and the nanoclay restricted the relaxation process of the polymer chains. Therefore, the PLA/PHBV/CN nanocomposites possess a higher modulus and greater melt strength, which are desirable for creating an improved foamed structure when manufactured via microcellular injection molding.

In this paper we investigated the direct-adhesion of Thermoplastic Polyurethane (TPU) to Acrylonitrile-Butadiene-Styrene (ABS). Specimens with an initial pre-crack were obtained by overmolding the TPU onto ABS substrates, at different melt and mold temperatures. The interfacial adhesion between these two dissimilar polymers, represented by the peeling force, was measured directly by using the standard T-peel test at room temperature and at a crosshead speed of 254 mm/min. The peeled fracture surfaces were observed under optical microscope to identify the failure mechanism (adhesive or cohesive). A qualitative correlation was established between the adhesion strength and the injection molding parameters.

This paper focuses on the in-mold monitoring of temperature and cavity pressure. The melt contact temperature and the cavity pressure along the flow path were directly measured using two pressure sensors and two temperature sensors fitted into the cavity of a spiral mold. Three melt temperatures and dies of different heights (1.0, 1.5 and 2 mm) were used to achieve a wide range of practically relevant shear rates. In order to analyze the extent to which the numerical simulation can predict the behavior of the molten polymer during the injection molding process, molding experiments were simulated using the Moldflow software and the simulation results were compared with the experimental data under the same injection molding conditions.

The objective of this research is the development of condition diagnosis model for injection molding process based on wavelet packet decomposition (WPD), feature extraction from cavity pressure, nozzle pressure and screw position signals and probability neural network (PNN) method. The node energies from the WPD of cavity and nozzle pressure signals are identified. In addition, five (5), seven (7) and two (2) critical features are extracted from the cavity pressure, nozzle pressure and screw position signals via the new feature extraction algorithm. The node energies and critical features are input to the PNN based condition diagnosis model for the injection modeling process. A series of injection modeling experiments are conducted and their results are used to validate the model. It is demonstrated that the proposed model is applicable to diagnose the injection molding process conditions. In particular, it is also shown that the utilization of cavity pressure and screw position signals in the model can result in higher diagnosis accuracy from the case studies.

Sustainable manufacturing systems use processes, methodologies, and technologies that are energy efficient and environmentally friendly. To create and maintain such systems, well-defined measurement methodologies and corresponding manufacturing information models play a crucial role to consistently compute and evaluate sustainability performance indicators of manufacturing processes that will result in reliable decision support. However, when it comes to describing sustainability of product manufacturing, the presently available methods and tools do not account for manufacturing processes explicitly and hence result in inaccurate and ambiguous decisions between alternate systems. Furthermore, there are no formal methods for acquiring and exchanging sustainability-related information that help establish a consolidated sustainability information base for decision support. This paper presents a study on the scope of the currently available manufacturing information models to incorporate sustainability. Identifying the requirements for information models that cater to sustainable manufacturing was done utilizing an earlier developed Systems Integration for Manufacturing Applications (SIMA) reference architecture model. We propose an extension to the SIMA architecture considering sustainability and refer to it as a GreenSIMA architecture. We present injection-molding unit manufacturing process as an example.

In this paper, we investigated the effect of injection molding parameters on the mechanical properties of thin-wall injection molded parts. A four-factor (melt temperature, mold temperature, injection speed and packing pressure) and three-level fractional experimental design was performed to investigate the influence of each factor on the mechanical properties and determine the optimal process conditions that maximize the mechanical properties of the part using the signal-to-noise (S/N) ratio response. The mechanical properties (e.g., elastic modulus, yield strength and strain at break) were measured by tensile tests at room temperature, at a crosshead speed of 5 mm/min, and compared with those of the injection-molded specimens. The experimental results showed that the tensile properties were highly dependent on the injection molding parameters, regardless of the type of the specimens. The values of Young modulus and yield strength of the injection-molded specimens were lower than those of the injection-molded parts, while the elongation at break was considerably lower for the injection-molded parts. The optimal process conditions were strongly dependent on the measured performance quantities (elastic modulus, yield strength and strain at break).

A novel combination approach to producing quality foamed injection molded parts has been investigated. By combining extruded, gas-laden pellets with microcellular injection molding, the processing benefits and material characteristics of using both N 2 and CO 2 blowing agents can be realized, thus yielding features superior to that of using either N 2 or CO 2 alone. Using an optimal content ratio for the blowing agents, as well as the proper sequence of introducing the gases, foamed parts with a much better morphology can be produced. In particular, extruding N 2 gas-laden pellets, followed by microcellular injection molding with higher amounts of CO 2 , produces a cellular structure that is very fine and dense. In this paper, the theoretical background is discussed and experimental results show that this combined approach leads to significant improvements in foam cell morphology for low density polyethylene (LDPE), polypropylene (PP), and high impact polystyrene (HIPS) using two different mold geometries.

Predicting friction forces present between part and mold surfaces in injection molding of thermoplastics is considered an important step in the design of the ejector system. However, this requires calculating the coefficient of friction at the contact surfaces, which is usually a complex task. In this study, an empirical model is developed in an attempt to estimate the coefficient of friction as applicable for the injection molding of thermoplastics. It is assumed in this model that the coefficient of friction is a sum of two correlated effects: adhesion effect and surface roughness effect. Both effects are treated as functions of mold surface’s average asperity slope.