Melt Flow Behavior Research Articles

Mechanical, thermal, melt-flow and morphological characterizations of bentonite-filled ABS copolymer

PurposeThis study aims to investigate the mechanical, thermal, melt-flow and morphological behavior of acrylonitrile-butadiene-styrene (ABS)-based composites after bentonite inclusions. Melt mixing is the most preferred production method in industrial scale and basically it has very near processing parameters compared to 3D printing applications. Rheological parameters of ABS and its composites are important for 3D applications. Melt flow behavior of ABS effects the fabrication of 3D printed product at desired levels. Shear thinning and non-Newtonian viscosity characteristics of ABS make viscosity control easier and more flexible for several processing techniques including injection molding, compression molding and 3D printing.Design/methodology/approachABS copolymer was reinforced with bentonite mineral (BNT) at four different loading ratios of 5%, 10%, 15% and 20%. ABS/BNT composites were fabricated by lab-scale micro-compounder followed by injection molding process. Mechanical, thermo-mechanical, thermal, melt-flow and morphological properties of composites were investigated by tensile, hardness and impact tests, dynamic mechanical analysis (DMA), thermo-gravimetric analysis (TGA), melt flow index (MFI) test and scanning electron microscopy (SEM), respectively.FindingsMechanical tests revealed that tensile strength, elongation and hardness of ABS were enhanced as BNT content increased. Glass transition temperature and storage modulus of ABS exhibited increasing trend with the additions of BNT. However, impact strength values dropped down with BNT inclusion. According to MFI test measurements, BNT incorporation displayed no significant change for MFI value of ABS. Homogeneous dispersion of BNT particles into ABS phase was deduced from SEM micrographs of composites. Loading ratio of 15% BNT was remarked as the most suitable candidate among fabricated ABS-based composites according to findings.Research limitations/implicationsThe advanced mechanical properties and easy processing characteristics are the reasons for usage of ABS as an engineering plastic. Owing to the increase in its usage for 3D printing technology, the ABS became popular in recent years. The utilization of ABS in this technology is in filament form with various colors and dimensions. This is because of its proper rheological features.Practical implicationsMelt-mixing technique was used as preparation of composites, as this processing method is widely applied in industry. This method is also providing similar processing methodology with 3D printing technology.Originality/valueAccording to the literature survey, to the best of the authors’ knowledge, this study is the first research work regarding the melt-flow performance of ABS-based composites to evaluate their 3D printing applications and processability. ABS and BNT containing composites were characterized by tensile, impact and shore hardness tests, DMA, TGA), MFI test and SEM techniques.

Theoretical and Computational Analysis on the Melt Flow Behavior of Polylactic Acid in Material Extrusion Additive Manufacturing under Vibration Field

Material extrusion (ME), an extrusion-based rapid prototyping technique, has been extensively studied to manufacture final functional products, whose forming quality is significantly influenced by the melt flow behavior (MFB) inside the extrusion liquefier. Applied vibration has a great potential to improve the MFB, and thereby promote the forming quality of the built product. To reveal the mechanism, a dynamic model of the melt flow behavior (DMMFB) is established based on fluid dynamics, Tanner nonlinear constitutive equation and Newton’s power law equation. The MFB, i.e., pressure drop, shear stress and apparent viscosity, is investigated without and with different vibration applied. The corresponding finite element analysis (FEA) is then carried out. From the comparison between DMMFB and FEA results, it is concluded that the proposed model is reliable. When vibration is applied onto the extrusion liquefier, the time-domain MFB will change periodically. Its effective value decreases significantly, and further decreases with the increase of vibration frequency or amplitude. This paper provides the theoretical basis to improve the MFB by applied vibration, and thereby to enhance the forming quality of ME products.

Study on Rheological and Dimensional Properties of Polypropylene on End-Of-Life Vehicles

As the global population increased, the production of vehicles also has increased. It is estimated that the population of vehicles in the world has exceeded 1.32 billion units at the end of 2016. The increased vehicle production brings a lot of negative impact to the environment such as noise pollution and the increase of end-of-life vehicles (ELVs). This study aims on the potential of recycled polypropylene that has been used in ELVs. The recycled materials are obtained from vehicles dismantling center at DRB-HICOM Environmental Services Sdn Bhd. The materials were then cleaned and crushed into the pellet before undergoing rheological test at the heat treatment laboratory, Faculty of Mechanical Engineering in Uitm Shah Alam. The purpose of rheological test is to study the melt flow behavior of recycled polypropylene in order to obtain the optimum temperature to be applied in plastic injection molding process. The graph of shear viscosity vs. shear rate represents the behavior of both materials at 190°C, 200°C and 210°C. Then materials are produced as a new product. The process of plastic injection molding is carried out at Sheikh Brothers Industries Sdn Bhd in Pelabuhan Klang.

Role of thermal fluid dynamics in alloying element distribution and weld porosity in powder feeding-based laser welding of Al alloy

This work develops a model incorporating the powder transport, laser heating, and molten pool dynamics to describe the mixing process of alloying element and reveal the mechanisms of bubble dynamics in powder feeding-based laser welding. Simulation results show that the different roles of recoil pressure: driving the molten metal flow at the rear part of keyhole in partial penetration and maintaining the stable keyhole profile in full penetration, are responsible for the difference between their melt flow behaviors. Driven by the melt flow, the alloying element transport path can be generalized as the shallow areas, the rear areas, the central and bottom areas in partial penetration. It permits a relatively uniform silicon distribution. However, two vortices rotating in the opposite direction in full penetration results in a higher concentration of Si in the upper part. Meanwhile, we conclude three steps for the bubble dynamics: bulge formation, bubble formation, bubble being captured by re-formed keyhole or being captured by the solid-liquid interface or escaping from the free surface. Such phenomena manifest that the contributions to the processing quality and metallurgy quality of welded joints come from the complex melt flow behaviors, which are confirmed by a series of experiments.

Migration behavior of IMC layer in twin-spot laser welding-brazing of aluminum to steel

The migration behavior of intermetallic compound (IMC) layer with some distance to the interface was observed in twin-spot laser welding-brazing of AA7075-T5 aluminum to DP590 galvanized steel. The microstructure characterization of different types of IMCs was systematically discussed using scanning electron microscopy, focused ion beam and transmission electron microscopy methods. It was found that the dense plate-like IMC layer formed at the interface was η-Fe2Al5 phase and the acicular IMC was θ-FeAl3 phase, while the sparse plate-like IMC layer that migrated into the weld metal was the mixture of the θ-FeAl3 phase and molten Al. A 3D thermo-fluid numerical model was developed to predict the melt flow behavior and analyze the mechanism of the migration behavior of the IMC layer. The simulation results revealed that the downward violent flow under the twin-spot center impacted the sparse IMC layer and entered into the gap between the steel and IMC layer, forming a broken migrated IMC layer. The joint strength increased with maximum migration distance and the maximum joint strength of 133.14 MPa was obtained. Thicker and sparse IMC was formed at the interface when the migration distance increased, which was adverse to the joint strength.

Modeling non-linear rheology of PLLA: comparison of Giesekus and Rolie-Poly constitutive models

ABSTRACT Rheological models for biobased plastics can assist in predicting optimum processing parameters in industrial forming processes for biobased plastics and their composites such as film blowing, or injection stretch-blow molding in the packaging industry. Mathematical descriptions of polymer behavior during these forming processes are challenging, as they involve highly nonlinear, time-, temperature-, and strain-dependent physical deformation processes in the material, and have not been sufficiently tested against experimental data in those regimes. Therefore, the predictive capability of two polymer models, a classical Giesekus and a physically-based Rolie-Poly, is compared here for extensional and shear rheology data obtained on a poly(L-lactide) (PLLA) across a wide range of strain rates of relevance to those forming processes. Generally, elongational and shear melt flow behavior of PLLA was predicted to a satisfactory degree by both models across a wide range of strain rates (for strain rates 0.05–10.0 s−1), within the strain window up to 1.0. Both models show a better predictive capability for smaller strain rates, and no significant differences between their predictions were found. Hence, as the Giesekus model generally needs a smaller number of parameters, this class of models is more attractive when considering their use in computationally demanding forming simulations of biobased thermoplastics.

Effect of energy density on defect evolution in 3D printed Zr-based metallic glasses by selective laser melting

In this study, the defects in 3D printed Zr-based bulk metallic glasses (BMGs) fabricated by selective laser melting (SLM) under different energy densities have been investigated via both experimental and simulation approaches. Different defects, including balling, interlayer pores, open pores and metallurgical pores, are detected in the 3D-printed Zr-based MGs depending on the energy inputs. Balling mainly occurs at a relatively low energy density ( E 8.33 J/mm3) due to the incomplete melting of particles, while interlayer pores and open pores are formed at modest energy densities ( E =13.89-16.67 J/mm3) because of incomplete welding and insufficient filling of molten liquid between layers. Fine metallurgical pores appear on the upper surface at relatively high energy densities ( E =20.83-27.78 J/mm3), which originate from gas escaping from molten pools during rapid solidification of the melt. Computational fluid dynamics (CFD) simulations are carried out to verify the experimental observations. The CFD simulations reveal that the various defects formed in the 3D-printed Zr-based BMG are related to the melt flow behaviours in the molten pools under different energy densities. The present work provides in-depth understandings of defect formation in the SLM process and provides methods for eliminating these defects in order to enhance the mechanical performance of 3D printed BMGs.

In-situ full-field mapping of melt flow dynamics in laser metal additive manufacturing

Melt flow plays a critical role in laser metal additive manufacturing, yet the melt flow behavior within the melt pool has never been explicitly presented. Here, we report in-situ characterization of melt-flow dynamics in every location of the entire melt pool in laser metal additive manufacturing by populous and uniformly dispersed micro-tracers through in-situ high-resolution synchrotron x-ray imaging. The location-specific flow patterns in different regions of the melt pool are revealed and quantified under both conduction-mode and depression-mode melting. The physical processes at different locations in the melt pool are identified. The full-field melt-flow mapping approach reported here opens the way to study the detailed melt-flow dynamics under real additive manufacturing conditions. The results obtained provide crucial insights into laser additive manufacturing processes and are critical for developing reliable high-fidelity computational models.

Influence of Laser Processing Strategy and Remelting on Surface Structure and Porosity Development during Selective Laser Melting of a Metallic Material

316L samples were fabricated by selective laser melting (SLM) with different laser powers and scanning strategies/patterns. The porosity distribution and surface structures of the as-fabricated samples were characterized using optical microscopy and scanning electron microscopy. This combined with a mathematical modeling of the SLM process aims to understand the formation mechanism of pores in a newly built layer and the role of remelting of previous layers on internal porosity development. It is shown that the surface structure and the formation of pores in a newly built layer are mainly associated with melt flow behavior, but the formation of pores within bulk samples, particularly those at interlayer interfaces, were largely dictated by the extent of remelting of previous layers during SLM. Laser melting of a powder layer tends to develop rough surfaces and open pores on the uppermost layer. With laser remelting of a newly built layer, the sample surfaces become much smoother and the pores within the uppermost layer can be completely eliminated. During SLM processing, sufficient remelting of previous layers leads to development of good bonding at the interlayer interfaces, whereas less extent of remelting of previous layers results in an increased number of pores at the interlayer interfaces. Laser power or energy density shows a much more dominant role than the laser scanning strategy in porosity development, which is attributed to the fact that laser power or energy density shows greater influence on the extent of remelting as compared with the latter. The mechanism on how remelting affects the evolution of pores is also demonstrated through modeling.

Effect of cavity surface roughness and wettability on the filling flow in micro injection molding

The surface to volume ratio in micro injection molding is quite large and this makes interfacial phenomena particularly crucial for the effectiveness of the process. This criticality is more evident for thin parts molding, where the influence of roughness on the thermal boundary conditions is not negligible. In this case, the contact between polymer and mold significantly affects the heat transfer at the interface and consequently it strongly influences the polymer melt flow behavior. In this paper, the effects of the polymer-mold interface on polymer flow were experimentally investigated. In particular, the filling of a representative micro part with a thickness of 100 μm was studied in relation to surface roughness and mold wettability. The results showed that the state of the polymer-mold interface plays a fundamental role in the filling of thin-wall micro injection molding. In particular, the flow length increases with both the mold roughness and the contact angle between the molten polymers and the cavity surface.

Time-dependent behavior of melt flow in the industrial scale silicon Czochralski growth with a transverse magnetic field

The time-dependent behavior of the silicon melt flow in the industrial scaled 300-mm diameter silicon Czochralski growth with a transverse magnetic field was investigated by both the experiment and numerical simulation. The measured temperatures at multiple positions in the melt showed oscillation with the same period but different amplitudes. The calculated results by the fully three-dimensional numerical simulation represented the measurement results and provided a qualitative explanation to this phenomenon. The periodic change of melt flow pattern occurred via the generating, descending, and vanishing of the cold plume. This behavior was driven by the buoyancy, which was similar to the flow under the non-magnetic field reported by Ozoe and Sung.

Magnetic-Field-Induced Partial-to-Full Penetration Evolution and Its Mechanism During Laser Welding

The geometry and tensile strength of magnetic-field-assisted laser-welded Ti-6Al-4V joints have been studied. Due to the effects of the magnetic field on the melt flow behavior during welding, the weld penetration depth increased from 4.27 mm (partial penetration) to 5.00 mm (full penetration) and the curvature of the weld cross-section decreased, improving the weld tensile strength. The fusion zone was enlarged, showing a maximum increase of 53.4% in area when the magnetic field intensity was 90 mT. The increased penetration depth and fusion zone area suggest that application of a magnetic field can improve the energy utilization of the laser during laser butt welding. The mechanism of the magnetic-field-induced penetration depth evolution is discussed. This study provides a new energy-saving method to obtain a full-penetration weld using laser welding at lower power.

Influence of rotational speed and aspect ratio on the flow patterns of different fluids subjected to rotation about vertical axis

The quality of the Centrifugal cast primarily depends on flow behavior of the melt during its rotation in addition to other process parameters.The opaque nature of mold and melt posses problems in the analysis of fluid behavior.The present investigation therefore focus on cold modeling experiments for vertical centrifugal casting in which permanent fluids such as water, SAE90 and Glycerine were subjected to vertical axis of rotation in a transparent mould at room temperature, in which the fluid flow patterns were observed with respect to variation in the process parameters such as thickness of the cylindrical fluid, viscosity, aspect ratio and rotational speed of mould.For high aspect ratio and maximum thickness the fluid cylinder was observed to be conical in shape. In a mould having aspect ratio 0.5 and 1.0, for different fluid thickness, the complete fluid cylinder was formed in the range of 350–450 rpm. The maximum G value required either to form complete fluid cylinder or the fluid to reach extreme point of the cylindrical mould was found to be in the range of 10G–28G,14G–39G using mould of aspect ratio 0.5 and 1.0 respectively and the lift of of the fluid was found to be easier in case of high viscous fluid. Also the melt flow behaviour has been studied by obtaining cast of Al-12%Si at diffetent rotational speeds. The results obtained in cold modeling experimentation were validated by CFD simulation using ANSYS Fluent software also compared with actual cast.

Effects of Lignocellulosic Fillers from Waste Thyme on Melt Flow Behavior and Processability of Wood Plastic Composites (WPC) with Biobased Poly(ethylene) by Injection Molding

Wood-like plastic composites were manufactured with a thermoplastic matrix polymer from renewable resources, i.e. high-density poly(ethylene) from bioethanol and a lignocellulosic filler obtained as a byproduct of the industrial distillation of thyme. The potential manufacturing of these composites by injection molding was studied. For this purpose, an in depth study of the effects of the lignocellulosic loading (comprised between 10 and 50 wt%) on the rheological properties of these composites was carried out by using capillary rheometry and model fitting with the Cross-WLF rheological model. In addition, a side by side comparison of the experimental results and those obtained by simulations with MoldFlow® was provided. In addition, the values of the pressure in the cavity and in the sprue were measured and collected by two selectively mounted pressure sensors and the results were compared with those predicted by MoldFlow® with the inputs provided by the Cross-WLF fitting model. The results showed a remarkable increase in viscosity with increasing lignocellulosic filler content, which has a negative effect on overall processability. This phenomenon specifically intense at low shear rates. However, this phenomenon could be potentially minimized using high shear rates because of the shear thinning effect of pseudoplastic fluids. Both the experimental and simulated results suggest the need of higher pressures to fill the cavity with these WPC, specifically for those with high filler content of up to 50 wt%. The results of the study indicate that melt viscosity is highly linked to the cavity pressure which is the dominant factor determining the quality of the final product in plastic injection molding.

Numerical and experimental study on keyhole and melt flow dynamics during laser welding of aluminium alloys under subatmospheric pressures

Porosity defects was highly related to the keyhole and melt flow dynamic during laser welding process. In this paper, a novel 3D numerical model was developed to describe the keyhole dynamic and melt flow behaviors during laser welding of 5A06 aluminium alloy under subatmospheric pressures. The effect of ambient pressure on laser welding process was taken into consideration by optimizing the boiling point of aluminium alloy and recoil pressure of evaporated metallic vapor jets based on vapor–liquid equilibria calculation and Wilson equation. A moving hybrid heat source model was employed to describe the laser energy distribution under subatmospheric pressures. Numerical results indicated that a wider and deeper keyhole with less humps was produced under subatmospheric pressure comparing with that of atmospheric pressure. The vortices in the rear keyhole wall became unapparent or even disappeared with the decrease of ambient pressures. The melt flow velocity on the keyhole wall was larger under a lower pressure. A smaller difference between boiling point and melting point was produced and this led to the formation of a thinner keyhole wall and improved the stability of molten pool. Larger recoil pressure produced under subatmospheric pressure was responsible for the weakened vortices and enhanced melt flow velocity. Bigger keyhole opening size, larger melt flow velocity, thinner keyhole and the weakened vortices all resulted into the reduction of porosity defects during laser welding of aluminium alloys. Based on the simulation results, the plasma distribution, weld formation and porosity defects had been demonstrated. The compared results showed that the simulation results exhibited good agreements with the experimental ones.

Investigations on the melt flow behaviour of aluminium filled ABS polymer composite for the extrusion-based additive manufacturing process

In extrusion-based additive manufacturing (AM) process, the melt flow rate (MFR) of material plays a significant role in determining the suitable process parameters for printing parts. MFR of the polymers varies on the addition of fillers which eventually leads to alteration in the pre-set values of process parameters. The present study deals with the evaluation of MFR of aluminium (Al) filled acrylonitrile butadiene styrene (ABS) polymer matrix composite using melt flow index tester for extrusion-based AM process. L16 Taguchi OA method was used to design the experiments considering three factors and four levels. Extrusion temperature, extrusion load and filler loading (wt.% of Al) were considered as the input factors, while MFR was selected as the measured response. Furthermore, the significance of each factor was determined using analysis of variance (ANOVA) and signal-to-noise (SN) ratio techniques. Experimental results indicated the improvement in the MFR for 10 wt.% Al filled ABS composite. However, the opposite trend in MFR was observed for other combinations of ABS/Al. Based on obtained MFR results, process parameters were established to print parts of developed ABS/Al composite through a customised extrusion-based AM process. The present study may be useful in the fabrication of customised lightweight conductive structures.

Investigations on the melt flow behaviour of aluminium filled ABS polymer composite for the extrusion-based additive manufacturing process

Investigations on the melt flow behaviour of aluminium filled ABS polymer composite for the extrusion-based additive manufacturing process

Flow Behavior of a Polypropylene Melt in Capillary Dies

Abstract Using capillary dies having different diameters, D, and length-to-diameter L/D ratios, a full rheological characterization has been carried out for a polypropylene melt, and the experimental data have been fitted both with a viscous model (Cross) and a viscoelastic one (the Kaye – Bernstein, Kearsley, Zapas/Papanastasiou, Scriven, Macosko or K-BKZ/PSM model). Particular emphasis has been given on the pressure-dependence of viscosity. It was found that only the viscoelastic simulations were capable of reproducing the experimental data well, while any viscous modeling always underestimates the pressures, especially at the higher apparent shear rates and L/D ratios.

Additive manufacturing and recycling by a laser-induced drop jet from a sheet edge

A new technique for additive manufacturing was recently presented by depositing droplets as a continuous track on a substrate, where the droplets were ejected from laser remote fusion cutting of a metal sheet. For the here presented approach, the droplets are instead ejected from the sheet edge, termed the machining mode, which is compared to cutting. Here, the transmitted part of the laser beam does not hit and interact with the deposited track because of lateral dislocation. High speed imaging has shown that laser-induced boiling, which drives the melt downwards, causes asymmetric conditions in the machining mode by lateral pushing of the generated drop jet under the sheet, where the melt can even attach. Compared to machining, the cutting mode keeps less deviation of the drop trajectories, higher precision, and a smoother surface finish. It was demonstrated that the edge conditions after machining are sufficient to repeat the process. This enables additional technique opportunities, including recycling of a whole sheet of waste metal. By the aid of high speed imaging from two different perspectives, the melt flow behavior, the drop jet precision, and process trends with respect to parameters, drop ejection, and deposition were studied.A new technique for additive manufacturing was recently presented by depositing droplets as a continuous track on a substrate, where the droplets were ejected from laser remote fusion cutting of a metal sheet. For the here presented approach, the droplets are instead ejected from the sheet edge, termed the machining mode, which is compared to cutting. Here, the transmitted part of the laser beam does not hit and interact with the deposited track because of lateral dislocation. High speed imaging has shown that laser-induced boiling, which drives the melt downwards, causes asymmetric conditions in the machining mode by lateral pushing of the generated drop jet under the sheet, where the melt can even attach. Compared to machining, the cutting mode keeps less deviation of the drop trajectories, higher precision, and a smoother surface finish. It was demonstrated that the edge conditions after machining are sufficient to repeat the process. This enables additional technique opportunities, including recycling...

Wall Slip of Linear Polymer Melts During Ultrasonic‐assisted Micro‐injection Molding

The wall slip of linear polymer melts under ultrasonic vibration is investigated by correcting the slip mechanism, and melt flow behaviors in ultrasonic‐assisted micro‐injection molding (UμIM) method are discussed. Based on the effect mechanism of ultrasonic vibration on the melt, theoretical models of the critical shear stresses for the onset of weak and strong wall slip during UμIM are established, and the change in rheological properties due to the onset of wall slip under ultrasonic vibration is experimental investigated by a built measurement system. The results show that the onset of weak and strong wall slip of the melt in micro cavity are promoted by ultrasonic vibration, which agree with the built theoretical models, and the melt filling capability in micro cavity is enhanced by reducing apparent viscosity and releasing shear stress of the polymer melt, which improves the molding quality of micro polymer parts via UμIM method. POLYM. ENG. SCI., 59:E7–E13, 2019. © 2018 Society of Plastics Engineers