Molded Counterparts Research Articles

In-plane properties of an in-situ consolidated automated fiber placement thermoplastic composite

Automated fiber placement (AFP) has been employed to manufacture aerospace structures for decades, recently focusing on thermoplastic composites (TPC). The in-situ consolidation AFP of TPCs is pursued as an energy-efficient additive manufacturing (AM) approach for fabricating composite structures. This work compares the in-plane mechanical properties of in-situ consolidated coupons with those of compression molded counterparts to provide new insights into their failure mechanics and processing-structure relationships. Tensile and compressive properties along the fiber and transverse directions, in-plane shear properties, and short beam strength were measured for all samples. Failure modes and mechanics in tested coupons were related to AFP defects and processing, i.e., resultant crystallinities, fiber misalignment, matrix mechanical properties, porosity, and fiber–matrix interfacial strength. The findings of this study can be used to guide the manufacturing of future TPC structures and potentially open new avenues for applications where post-processing is not feasible or reduced mechanical performance is acceptable.

Direct 3D printing of a two-part silicone resin to fabricate highly stretchable structures

The direct ink writing (DIW) method of 3D-printing liquid resins has shown promising results in various applications such as flexible electronics, medical devices, and soft robots. A cost-effective extrusion system for a two-part high-viscous resin is developed in this article to fabricate soft and immensely stretchable structures. A static mixer capable of evenly mixing two viscous resins in an extremely low flow regime is designed based on the required mixing performance through a series of biphasic computational fluid dynamics analyses. The printing parameters of the extrusion system are determined empirically, and the mechanical properties of the printed samples are compared to their molded counterparts. Furthermore, some potential applications of the system in soft robotics and medical training are demonstrated. This research provides a clear guide for utilizing DIW to 3D print highly stretchable structures.

Design and Fabrication of an In Situ Short-Fiber Doser for Fused Filament Fabrication 3D Printer: A Novel Method to Manufacture Fiber–Polymer Composite

Fused filament fabrication (FFF) 3D-printed parts are mostly used as prototypes instead of functional parts because they have a weaker mechanical strength compared to their injection molded counterparts. Various methods including a fiber-reinforced polymer composite were proposed to enhance the properties of FFF 3D-printed parts. A new concept to fabricate a polymer composite via FFF 3D printing is proposed, where fiber is deposited during printing, instead of using a premixed composite filament. In order to investigate the workability of this concept, a new device is needed. Firstly, the design requirements were identified, and a fiber doser that can be mounted on a commercial 3D printer was designed. Prototype testing was conducted to improve the design. The improved fiber doser was able to deposit varied fiber contents during FFF 3D printing. Thermogravimetric analysis (TGA) was used to quantify the fiber contents of the fabricated composites. With this newly designed doser, short glass fiber–polylactic acid (PLA) composites with three different fiber contents (1.02 wt.%, 2.39 wt.%, and 4.98 wt.%) were successfully manufactured. A new technique to manufacture a polymer composite is proven; nevertheless, the mechanical and tribological properties of the newly fabricated composites are under investigation and will be reported in a subsequent article.

A comparative study for the behavior of 3D‐printed and compression molded PLA/POSS nanocomposites

AbstractBecause of the biocompatible and nontoxic character of both PLA (polylactide) and POSS (Polyhedral Oligomeric Silsesquioxane) nanoparticles, recently being a significant alternative for biomedical parts; the main purpose of this study was to investigate performance of the 3D‐printed PLA/POSS nanocomposites with respect to the compression molded PLA/POSS specimens. Due to the higher uniformity and higher homogeneity in the distribution of POSS nanoparticles in each PLA matrix layer, mechanical tests (tensile, flexural, and toughness) revealed that the improvements in the strength, elastic modulus and fracture toughness values of the 3D‐printed specimens were much higher compared to their compression molded counterparts, the benefits starting from 13% increasing up to 78%. It was also observed that there was almost no deterioration in the physical structure and mechanical properties of the 3D‐printed specimens, even after keeping them 120 days at 37°C in a physiological solution prepared by using the standard PBS (phosphate buffered saline) tablet.

Tensile and Bending Strength Improvements in PEEK Parts Using Fused Deposition Modelling 3D Printing Considering Multi-Factor Coupling.

Compared with laser-based 3D printing, fused deposition modelling (FDM) 3D printing technology is simple and safe to operate and has a low cost and high material utilization rate; thus, it is widely used. In order to promote the application of FDM 3D printing, poly-ether-ether-ketone (PEEK) was used as a printing material to explore the effect of multi-factor coupling such as different printing temperatures, printing directions, printing paths, and layer thicknesses on the tensile strength, bending strength, crystallinity, and grain size of FDM printed PEEK parts. The aim was to improve the mechanical properties of the 3D printed PEEK parts and achieve the same performance as the injection molded counterparts. The results show that when the thickness of the printed layer is 0.1 mm and the printing path is 180° horizontally at 525 °C, the tensile strength of the sample reaches 87.34 MPa, and the elongation reaches 38%, which basically exceeds the tensile properties of PEEK printed parts reported in previous studies and is consistent with the tensile properties of PEEK injection molded parts. When the thickness of the printed layer is 0.3 mm, the printing path is 45°, and with vertical printing direction at a printing temperature of 525 °C, the bending strength of the sample reaches 159.2 MPa, which exceeds the bending performance of injection molded parts by 20%. It was also found that the greater the tensile strength of the printed specimen, the more uniform the size of each grain, and the higher the crystallinity of the material. The highest crystallinity exceeded 30%, which reached the crystallinity of injection molded parts.

Comparative study on the electrical, thermal, and mechanical properties of multiwalled carbon nanotubes filled polypropylene and polyamide 6 micromoldings

AbstractIn this work, a series of carbon nanotubes filled polypropylene (PP/CNT) and polyamide 6 (PA6/CNT) composites were prepared by melt blending and subsequently molded by compression molding and microinjection molding (μIM), respectively. Electrical conductivity results indicate that the percolation threshold of corresponding microparts shifted to higher filler concentrations when compared with that of compression molded counterparts, suggesting the prevailing shearing conditions in μIM is unfavorable for the construction of conductive pathways. In addition, Raman spectral analysis shows that there is a preferential alignment of CNTs along the flow direction of microparts. Thermal properties of both melt blended samples and subsequent microparts were evaluated using differential scanning calorimetry and thermogravimetric analysis. The mechanical properties of subsequent microparts are greatly affected by filler concentration, which might be related to the structural change that induced by the state of dispersion of CNTs.

Mechanical behaviour of additively manufactured bioactive glass/high density polyethylene composites

Bioactive glass (BAG) is a well-known biomaterial that can form a strong bond with hard and soft tissues and can also aid in bone regeneration. In this study, BAG is added to a polymer to induce bioactivity and to realize fused filament fabrication (FFF) based printing of polymer composites for potential orthopaedic implant applications. BAG (5, 10, and 20 wt%) is melt compounded with high density polyethylene (HDPE) and subsequently extruded into feedstock filament for FFF-printing. Tensile tests on developed filaments reveal that they are stiff enough to resist forces exerted during the printing process. Micrography of printed HDPE/BAG reveals perfect diffusion of raster interface indicating proper selection of printing parameters. Micrography of freeze fractured prints shows the homogeneous distribution and good dispersion of filler across the matrix. The tensile, flexural, and compressive modulus of FFF-printed HDPE/BAG parts increases with filler addition. BAG addition to the HDPE matrix enhances flexural and compressive strength. The tensile and flexural behaviour of FFF-prints is comparable to injection molded counterparts. Property maps exhibit the merits of present study over the existing literature pertaining to desired bone properties and polymer composites used in biomedical applications. It is envisioned that the development of HDPE/BAG composites for FFF-printing can lead to possible orthopaedic implants and scaffolds to mimic the bone properties in customised anatomical sites or injuries.

Reinforcing silicone with hemp fiber for additive manufacturing

This study explores the 3D printability of a new material based on silicone and hemp fibers from renewable, sustainable and non-petroleum resources with the aim of enhancing mechanical properties of silicone. Incorporation of fibers improved the mechanical properties of the silicone matrix, but it also adversely affected the printability of silicone due to the high viscosity. Therefore, an additional solvent is added into the composition to alter the viscosity. To mature the composite printing technology, this research aims to find out the desired mixing composition of silicone, hemp fiber, and solvent. The behavior of the new engineered material was analyzed using rheological study to obtain a printable material. The composition containing 15 wt% hemp fibers and 20 wt% solvent with enhanced mechanical properties displayed the desirable printability. Moreover, the mechanical properties of the 3D printed and molded samples were studied. The results revealed that 3D printed samples outperformed the molded counterparts. Finally, a honeycomb structure and a simple gripper were fabricated to demonstrate the application of the developed material.

Highly dense cellulose acetate specimens with superior mechanical properties produced by fused filament fabrication

The extrusion based Fused Filament Fabrication (FFF) enables to build up components of thermoplastic materials by using a layer-by-layer strategy. Typically, the layered structure results in an internal porosity limiting the mechanical performance. In this work, using a commercial 3D-printer specimens of the polymer cellulose acetate (CA) were produced having porosities as low as 1–3 %. Quasi-static tensile tests demonstrate that these highly dense specimens reach similar or even higher strength values in comparison to their injection molded counterparts. The influence of the temperature management was studied by using different hot-ends, namely a standard one and a novel hot-end having a modified heat-block. Using the latter one, a homogeneous internal structure was achieved as observed with scanning electron microscopy (SEM). The very low porosities can be assigned to the elevated specimen temperature maintained during printing which is slightly above the materials glass transition temperature. Processing of CA at such temperatures leads to a slight loss of plasticizer as proved with NMR spectroscopy. This favorable change in material composition during printing additionally contributes to the mechanical strength of the test specimens. We conclude that the porosity is the key parameter (which has to be measured and minimized) to realize FFF components with good mechanical performance. Whereas we demonstrated FFF for the first time for CA as an industrially relevant thermoplastic material, our results can be easily applied to amorphous polymers in general.

Electrical, thermal, and mechanical properties of polypropylene/multiwalled carbon nanotube micromoldings

AbstractIn this paper, properties of microparts molded from polypropylene/multiwalled carbon nanotubes (PP/CNT) composites were studied in detail. Results indicated that the percolation threshold of PP/CNT microparts shifted to higher filler concentrations when compared with their compression molded counterparts. Morphology observations revealed that the distribution of CNT is not uniform along the flow direction, which can significantly affect the properties of microparts. The thermal properties of PP and PP/CNT composites as well as corresponding microparts were investigated using differential scanning calorimetry and thermogravimetric analysis, respectively. Moreover, the mechanical properties of microparts were evaluated by nanoindentation analysis. Multicycling measurements indicated that the mechanical properties of microparts are both depth and location dependent. Both the hardness and elastic modulus increased with corresponding filler loading concentration of CNT below 3 and 7 wt%, respectively. Above those concentrations, both properties decreased with an increase of CNT concentration. This could be related to the state of filler distribution within the microparts.

Evaluation of 3D Printed Soft Robots in Radiation Environments and Comparison With Molded Counterparts.

Robots have an important role during inspection, clean-up, and sample collection in unstructured radiation environments inaccessible to humans. The advantages of soft robots, such as body morphing, high compliance, and energy absorption during impact, make them suitable for operating under extreme conditions. Despite their promise, the usefulness of soft robots under a radiation environment has yet to be assessed. In this work, we evaluate the effectiveness of soft robots fabricated from polydimethylsiloxane (PDMS), a common fabrication material, under radiation for the first time. We investigated gamma-induced mechanical damage in the PDMS materials' mechanical properties, including elongation, tensile strength, and stiffness. We selected three radiation environments from the nuclear industry to represent a wide range of radiation and then submerged a 3D printed hexapus robot into a radiation environment to estimate its operation time. Finally, to test the reliability of the 3D printed soft robots, we compared their performances with molded counterparts. To analyze performance results in detail, we also investigated dimensional errors and the effects of fabrication methods, nozzle size, and print direction on the stiffness of PDMS material. Results of this study show that with increasing exposure to gamma irradiation, the mechanical properties of PDMS decrease in functionality but are minimally impacted up to 20 kGy gamma radiation. Considering the fractional changes to the PDMS mechanical properties, it is safe to assume that soft robots could operate for 12 h in two of the three proposed radiation environments. We also verified that the 3D printed soft robots can perform better than or equal to their molded counterparts while being more reliable.

Electrical and morphological properties of microinjection molded polypropylene/carbon nanocomposites

ABSTRACTA series of different carbon (carbon black, carbon nanotubes, and graphite nanoplatelets) filled polypropylene nanocomposites were prepared by melt blending, then followed by compression molding or microinjection molding (µIM). Direct current electrical conductivity measurements and melt rheology tests were utilized to detect the percolated structure for compression molded polypropylene/carbon nanocomposites. For µIM, a rectangular mold insert which has a three‐step decrease in thickness along the flow direction was adopted to study the effect of abrupt changes in mold geometry on the electrical and morphological properties of subsequent micromoldings (µ‐moldings). Results indicated that the µ‐moldings exhibited a higher percolation threshold when compared with their compression molded counterparts. This is largely due to the severe shearing conditions that prevail in the µIM process. The morphology of µ‐moldings containing different carbon fillers was examined using scanning electron microscopy. The development of corresponding microstructure is found to be strongly dependent on the types of carbon fillers used in µIM, which is crucial to the enhancement of electrical conductivity for the resulting µ‐moldings. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45462.

Engineering flame retardant biodegradable polymer nanocomposites and their application in 3D printing

Flame retardant, environmentally sustainable nanocomposites were made by melt blending poly (lactic acid) (PLA) with melamine polyphosphate (MPP) and Cloisite 30B (C-30B). The composition of the nanocomposite was highly specific and guided by interfacial energy minimization principals which balanced enthalpic and mechanical contributions. In this critical range, even small changes in the filler concentration can have a large impact on the performance of the material. We showed that while addition of 17% MPP can increase the flame resistance of PLA, (achieving a UL-94 V2 rating) the mechanical properties were significantly degraded. Addition of only 1% C-30B reversed these effects and yielded a nanocomposite with enhanced mechanical properties and passing the UL-94 V0 flame test. This compound was able to be extruded and fed into a Makerbot Replicator 2X Fused Deposition Modeling (FDM) 3D printer, where the printed samples were indistinguishable mechanically from their molded counterparts and also achieved the UL-94 V0 rating. The enhanced performance occurred only within a very narrow composition window. Cone calorimetry revealed that while a significant decrease in the heat release rate, accompanied by the formation of an intumescent char, was achieved by the addition of 1% C-30B to the MPP/PLA blend, a very poor char, corresponding the increase in the heat release rate, was obtained with addition of 2% C-30B. These results were explained in view of the altered phase morphology observed in Transmission Electron Microscopy (TEM).

Properties and antioxidant activity of soy protein concentrate films incorporated with red grape extract processed by casting and compression molding

Self-standing transparent soy protein concentrate (SPC) films plasticized by glycerol (30% w/w SPC dry basis) and supplemented with red grape extract (RGE) as natural antioxidant (0–10% w/w SPC dry basis) were prepared by two methods: casting and intensive mixing followed by compression molding. The influence of RGE on key film properties was analyzed at the light of the specific stabilizing interactions of SPC films. The addition of RGE had a favorable effect on moisture content, total soluble matter, water vapor permeability and percentage of elongation of casted films compare with compression molded counterparts. RGE induced a redistribution of hydrogen interactions of casted films replacing protein-protein hydrogen interactions by protein-polyphenol ones with no variations in disulfide bridges, while these last interactions were significantly reduced in compression molded films in favor of hydrophobic and hydrogen interactions, as disclosed by differential solubility assays and infrared spectroscopy. The antioxidant activity of the SPC films in terms of scavenging activity of the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power, increased significantly irrespective of the manufacturing method, being the release of antioxidants from casted films lower than that from compression molded films in accordance with the strong interactions between SPC matrix and polyphenols.

Performance Limitations in Polymer Laser Sintering

Abstract Commercial laser sintering (LS) machines have been used for years in a variety of rapid prototyping applications. Emphasis in the LS research community has moved towards rapid manufacturing: the creation of engineered structural components. However, the mechanical properties of LS parts are often inconsistent compared to their molded counterparts. This is due to a variety of factors including feedstock uniformity, microstructure evolution due to LS processing, and the overall ability of commercial LS machines to reliably form structural parts without thermal degradation of the feedstock powder. This paper will review the current state of the art of commercial LS machines, and discuss the resulting implications for rapid manufacturing. Particular focus will be paid to the role of part bed temperature variations due to non-uniform heating, unsteady cooling due to natural convection currents in the part chamber, and how these and other phenomena may impact the design of laser control systems.

Polymer multilevel lab-on-chip systems for electrochemical sensing

The authors present a scheme intended for production of large quantities of lab on chip systems by means of Si dry etching, electroplating, injection molding, and pressure-assisted thermal bonding. This scheme allows for the fabrication of large numbers of samples having a combination of structures with depths as small as tens of nanometers and as big as hundreds of microns on the same polymer chip. The authors also describe in detail the fabrication procedure of polymer substrates with embedded Au and pedot:tosylate electrodes for electrochemical applications. The electrode fabrication process is simple and fit for integration in a production scheme. The electrode–substrates are then bonded to injection molded counterparts to be used for electrochemical applications. A dimensional and functional characterization of the electrodes is also presented here.

Influence of graphite nodules on the particles erosion of spheroidal graphite cast irons

The influence of graphite nodules on the normal angle erosion of the spheroidal graphite cast irons with four different matrices, namely ferrite, upper bainite, lower bainite and martensite, was investigated. The results indicate that, in the range investigated (10–15 area pet), graphite nodules (with variations in area percent and size) did not exert any influence in the irons with ferrite or upper bainite matrix. However, in the case of the spheroidal graphite cast iron with martensitic matrix, both increasing area percent and decreasing diameter of graphite nodules did in fact raise the erosion rate; moreover, those cast in metal molds consistently experienced higher erosion rate than those cast in sand molds. For the irons with a lower bainite matrix, increasing the amount of graphite nodules raises the erosion rate for those cast in sand molds, but did not affect the erosion rate for those cast in metal molds; furthermore, the erosion rate of the sanded-molded irons was consistently higher than their metal molded counterparts. The different roles of graphite nodules on the erosion rates of the spheroidal graphite cast irons are discussed.