Melt Fill Research Articles

Numerical Simulation of Melt Filling and Gas Penetration in Gas Assisted Injection Molding

The governing equations of two-phase flows including gas and polymer melt are presented, which are solved using finite volume and domain extension methods with SIMPLEC technology. The melt filling and primary gas penetration in gas-assisted injection molding (GAIM) process are simulated, where the Cross-viscosity model is employed to describe the melt rheological behavior, and the CLSVOF(coupled Level Set and Volume of fluid) method is employed to capture the moving interfaces. In order to test and verify the coupled methods, melt filling in a rectangular plate with an insert is simulated, and the numerical results are in good agreement with those of the experiment. As a case study, the melt filling and gas penetration processes in a ring-shaped channel are simulated. The numerical results successfully depict some important phenomena, such as race-tracking effect, corner effect and the flow asymmetry of the gas penetration, which can deepen the understanding and studying of the GAIM process.

Interface study of carbon fibre reinforced Al–Cu composites

The application of continuous carbon fibre-reinforced aluminium matrix composites (C f/Al) in aerospace, automobile, and electric power cable industries is of considerable interest because of their high specific strength, specific modulus, and low coefficient of thermal expansion. In this paper, we report the study on the alloy contribution to the interface of a carbon fibre reinforced aluminium alloy matrix composite. The composites were produced using squeeze casting technology. An Al–Cu alloy was used as the matrix material. Detailed investigations revealed that the aluminium alloy melt fill in the gaps between fibres. The important feature is that the solidification microstructure of Al–Cu matrix alloy is altered by the presence of carbon fibre. The surface of carbon fibre acts as the nucleation site of Al 2Cu phase. Al 2Cu phase prefers to form at the interface between carbon fibre and Al–Cu alloys. Ni coated on carbon fibre does not change the feature.

Simulation of Fluid Flow and Oscillation of the Argon Oxygen Decarburization (AOD) Process

The oscillation of argon oxygen decarburization (AOD) converters is flow related and depends on the process parameters (e.g., vessel geometry, melt fill height, process gas type and blowing rate, vessel tilting angle, as well as geometry, number, and arrangement of the side-wall nozzles). For a 120-ton AOD converter with seven submerged side-wall nozzles, plant tests, physical simulations on a 1:4 scale water model, and computational fluid dynamics simulations have been done. The investigations show that the penetration depth of an inert gas jet into the melt does not exceed approximately 0.4 m. The plumes are located close to the nozzle-side converter wall and induce a large-scale primary vortex as well as intensive surface movements; both are responsible for the oscillation. Several process mechanisms were investigated. The oscillation is highest in the last stage of the dynamic blow and is still high during the reduction stage. As the amount of inert gas increases, the vibration level also increases. Inert gas has a greater influence on the oscillation than oxygen. Tilting the converter around 8 deg clearly leads to more intensive oscillations. Increasing the blowing rate increases the forces and torques acting on the vessel, whereas the oscillation frequency remains nearly constant. A varying fill level does not influence the vibration level the same way as the blowing rate. The operational test shows, for example, that the maximum torque does not depend on the heat size when the latter varies between –8 pct and +21 pct of the nominal heat size. The water model test shows decreasing forces and torques with a rising fill level.

Visualization Analysis of Melt Filling Behavior from Submarine-gate in Ultra-High-Speed Injection Molding

Visualization Analysis of Melt Filling Behavior from Submarine-gate in Ultra-High-Speed Injection Molding

Microinjection moulding: The influence of runner systems on flow behaviour and melt fill of multiple microcavities

To increase productivity and thus reduce the unit cost, often micro moulding tools incorporate multiple cavities and the selected runner design and applied pressure are very important for achieving satisfactory moulding results. The main function of the runner system is to facilitate the flow of molten material from the injection nozzle into the mould cavity. Therefore, the microinjection filling process depends on the optimum design of runner systems and this is an important prerequisite for the production of high quality parts. In this context, the paper reports on an experimental study that investigates the flow behaviour of the polymer melts in microcavities with a particular focus on the relationship between the filling of micro parts and the size of the runner system. In particular, the runner size effects on the microinjection moulding process were investigated by focusing the research on only the filling stage of the process. The filling performance of spiral-like micro cavities was studied as a function of runner size in combination with melt temperature, mould temperature, injection speed, and holding pressure time employing the design of the experiment approach. In addition, the results were analysed further with melt flow simulation to identify the effects of the runner size together with flow properties of the polymers, PP and ABS, on the behaviour of the microinjection moulding process.

Optimisation of process conditions in powder injection moulding of microsystem components using a robust design method: part I. primary design parameters

Powder injection moulding (PIM) is a net fabrication technique that combines the complex shape forming ability of plastic injection moulding, the precision of die casting, and the material selection flexibility of powder metallurgy. For this study, the design issues related to PIM for the fabrication of thin walled, high aspect ratio geometries were investigated. These types of geometries are typical to the field of microtechnology based electro chemical, mechanical and biological systems, which are multiscale (sizes in at least two or more different length scale regimes) fluidic devices working on the principle of heat and mass transfer through embedded micro- and nanoscale features. Stainless steel was the material chosen for the investigations because of its high temperature resistivity and chemical inertness necessary for typical microfluidic applications. The investigations for the study were performed using the state of the art computer aided engineering design tool, PIMSolver. The effect of reducing part thickness on the process parameters, including melt temperature, mould temperature, fill time and switchover position, during the mould filling stage of the injection moulding cycle was investigated. The design of experiments was conducted using the Taguchi method. It was found that the process variability generally increased with reduction in thickness. Mould temperature played the most significant role in controlling the mould filling behaviour as the part thickness reduced.

Analysis and Numerical Simulation of Polymer Melt Filling in Micro Injection Molding

The theoretical models of melt flowing characterictics in microscale channels are constructed by model modification method according to the macroscopic rheological theories and the modeling technology for polymeric melt.Moreover,the influences of microscale viscosity,wall slip and convection heat transfer coefficient between polymer melt and mold wall on micro melt flowing are investigated by using numerical simulation method and compared with the existing experimental data.The results indicate that the viscosities of polymeric melt flowing in microchannels are obviously lower than those calculated with the conventional viscosity model and are proportional to the characteristic dimensions of microchannel.With the decrease of the characteristic dimensions of microchannel,the slip coefficients arc obviously reduced,while the slip velocities of polymeric melt on the wall are increased.In addition,considering the surface convection heat transfer coefficients the distribution of melt temperature in microchannels is subject to the size effect.The flowing behaviors of polymeric melt in microchannels are different from those in macrochannels in some aspects.

Development of Measurement Method for Melt Filling Patterns in Injection Mold by Gate Shutting System

In this study, the authors aimed to develop a simple and highly precise method of measuring inmold melt filling patterns in order to verify the accuracy of CAE analysis in injection molding. Specifically, the measurement method proposed obtains accurate melt filling patterns in the mold by forcibly stopping melt flow at the mold gate using a small air pressure cylinder in the short-shot molding process to prevent melt flow into the cavity after injection process completes. Experiments were then conducted to evaluate the method. The results of measuring melt pressure in the runner and cavity confirmed that the gate shutting system works accurately. From the measurement of the melt filling patterns, it was confirmed that when the conventional short-shot method is applied, errors may occur in the flow front length and shape. These results verify the validity of the short-shot method using the gate shutting system developed.

Measurement and Analysis of Cavity Pressure and Melt Filling Capacity During Injection Molding

Using an online measure system consisted of a high sensitivity pressure sensor, a spiral channel mold and a data collecting/analysis series. The cavity pressure and flow length response under different injection pressure, injection velocity, mold temperature and different vibration condition was measured and analyzed in this study. The results show that the cavity pressure and flow length increased with the increase of injection pressure, injection velocity and mold temperature. In vibration assisted injection molding (VAIM), the cavity pressure and flow length increased as a result of imposing vibration. The change of amplitude and frequency in VAIM had more distinct effect on flow length than injection pressure. The results also indicate that the measure system established in this study can accurately monitor and record the changes of cavity pressure, and could be used in the study of melt's filling capacity in injection molding process.

Investigation of micro-injection moulding: Factors affecting the replication quality

Micro-injection moulding is one of the key technologies for micro-manufacture because of its mass-production capability and relatively low component cost. The surface quality in replicating micro-features is one of the most important process characteristics and constitutes a manufacturing constraint in applying injection moulding in a range of micro-engineering applications. This research investigates the effects of three processing and one geometric factor on the surface quality of micro-features in three different polymer materials. In particular, the following factors are considered: barrel temperature, mould temperature, injection speed and distance between micro-features. In this investigation, the mould temperature was set in the conventional range. The study revealed that in general, increasing the barrel temperature, mould temperature and the injection speed improves the polymer melt fill in micro-cavities. However, the effects of these factors on the process replication capabilities are not consistent for different polymer materials, and could be adverse in specific conditions. Varying the distance between micro-features does not affect the melt fills.

An experimental study of the water-assisted injection molding of glass fiber filled poly-butylene-terephthalate (PBT) composites

The purpose of this report was to experimentally study the water-assisted injection molding process of poly-butylene-terephthalate (PBT) composites. Experiments were carried out on an 80-ton injection-molding machine equipped with a lab scale water injection system, which included a water pump, a pressure accumulator, a water injection pin, a water tank equipped with a temperature regulator, and a control circuit. The materials included virgin PBT and a 15% glass fiber filled PBT composite, and a plate cavity with a rib across center was used. Various processing variables were examined in terms of their influence on the length of water penetration in molded parts, and mechanical property tests were performed on these parts. X-ray diffraction (XRD) was also used to identify the material and structural parameters. Finally, a comparison was made between water-assisted and gas-assisted injection molded parts. It was found that the melt fill pressure, melt temperature, and short shot size were the dominant parameters affecting water penetration behavior. Material at the mold-side exhibited a higher degree of crystallinity than that at the water-side. Parts molded by gas also showed a higher degree of crystallinity than those molded by water. Furthermore, the glass fibers near the surface of molded parts were found to be oriented mostly in the flow direction, but oriented substantially more perpendicular to the flow direction with increasing distance from the skin surface.

Three-dimensional Simulation of Melt Filling and Gas Penetration in Gas-Assisted Injection Molding Process Using a Finite Volume Formulation

Article Three-dimensional Simulation of Melt Filling and Gas Penetration in Gas-Assisted Injection Molding Process Using a Finite Volume Formulation was published on July 1, 2006 in the journal Journal of Polymer Engineering (volume 26, issue 5).

Micro-injection moulding: Factors affecting the achievable aspect ratios

Micro-injection moulding is one of the key technologies for micro-manufacture because of its mass-production capability and relatively low component cost. The aspect ratios achievable in replicating micro features are one of the most important process characteristics and constitute a major manufacturing constraint in applying injection moulding in a range of micro-engineering applications. This research studies the effects of five process and one size factors on the achievable aspect ratios, and the role they play in producing micro components in different polymer materials. In particular, the following factors are considered: barrel temperature, mould temperature, injection speed, holding pressure, the existence of air evacuation and the sizes of micro features. The study revealed that the barrel temperature and the injection speed are the key factors affecting the aspect ratios of micro features replicated in PP and ABS. In case of POM, in addition to these two factors, the mould temperature is also an important factor for improving the replication capabilities of the micro-injection moulding process. For all three materials, an increase of feature sizes improves the melt flow. However, the melt fill of micro features does not increase linearly with the increase of their sizes.

Visualization Analysis of Melt Filling Phenomena in a Boss-shaped Cavity Using 3-D Visualization Mold

Visualization Analysis of Melt Filling Phenomena in a Boss-shaped Cavity Using 3-D Visualization Mold

Weldline strength in injection molded HDPE/PA6 blends: Influence of interfacial modification

AbstractMost injection molded objects contain defects known as weldlines. This defect may introduce an element of weakness affecting the object's performance. Weldlines are particularly problematic in multiphase materials where the situation may be exaggerated by component mismatch on the two sides of the interface that results in additional weakening when the two components do not adhere well to each other. In addition, weldline behavior is influenced by orientation and morphological effects. This paper deals with relationships between the structure and the mechanical properties in injection molded high density polyethylene polyamide‐6 blends. The weldline effect is investigated in detail. Two molds were used to generate weldlines: a double‐gated tensile bar cavity in which the weldline results from the meeting of two melt fronts flowing into each other from opposite directions, and a film‐gated rectangular plaque mold with a circular insert that divides the melt front in two. Following the recombination of the fronts, there is additional flow as the melt fills the mold cavity. Two preparations containing 75 vol % of polyamide‐6 and 25 vol % of polyethylene with and without compatibilizer were studied. In the first case, a compatibilizer was incorporated into the polyethylene prior to compounding with the polyamide‐6. In the directly molded tensile bar the minor phase is strongly oriented parallel to flow. Only in the core, which represents about 10% of the sample thickness, do the dispersed phase particles assume spherical shape. The morphology of the weldline is closely related to that of the skin: the elongated structures are oriented parallel to the weldline plane. The effect of the compatibilizer on the mechanical properties (without the weldline) of the directly molded tensile bars is minor: It is overshadowed by the flow‐induced morphology. The weldline strength loss is about 40% in the noncompatibilized blend. The introduction of the compatibilizer has restored the material's ability to yield and the properties are close to those measured without the weldline. For the second type mold, the effect of the weldline is less pronounced and the effect of the distance from the insert is negligible. The anisotropy is quite pronounced in the noncompatibilized blend. In compatibilized blends, all tensile properties are unaffected by the presence of weldline, except for the 2‐mm‐thick plaque in the position close to the insert. The properties in the direction parallel to flow are similar to the type I mold and not affected by the increase of plaque thickness. Consequently one may question the utility of the directly molded tensile specimens in studying various aspects of the mechanical behavior of multiphase materials where the flow‐generated structure is very different from that found in “real” injection molded parts. © 1995 John Wiley & Sons, Inc.

Transformation of polymers in a stream of low‐temperature arc discharge plasma

AbstractSpraying of polymer materials in a low‐temperature plasma stream is a very efficient way of depositing polymer coatings on large surfaces. The deposition of powdered polymers by an arc discharge plasma flow and spraying from the bulk have been compared. The properties of powdered polymers do not change considerably during transportation by the stream because of the short residence of the particles in the plasma. When spraying from the bulk, polymers are transported in the form of melt droplets (polyethylene, polycarbonate) or in gaseous phase (polytetrafluoroethylene); autohesion of the droplets or secondary polymerization occurs, respectively, on the substrate surface. This process offers high‐quality thin films and coatings whose structure depends significantly on the characteristics of the substrate as well as on the structure of the source polymer. Obtained polymer coatings contain nitrogen and oxygen entrapped from the atmosphere as well as (on the glass surface) the products of glass etching. This fact enables one to vary widely the properties of the coatings. Furthermore, the problem of obtaining combined protective coatings in which polymer melt fills the pores between metal particles can be solved successfully in a united technological cycle including plasma spraying of the polymer and the metal. © 1995 John Wiley & Sons, Inc.

Combustion of Porous Samples with Melting and Flow of Reactants

Abstract We formulate and analyze a model describing the combustion of porous condensed materials in which a reactant melts and spreads through the pores of the sample. Thus there is liquid motion relative to the porous solid matrix. Our model describes the cases when the melt either fills all the pores or when some gas remains in the pores. In each case the melt occupies a prescribed volume fraction of the mixture. We employ both analytical and numerical methods to find uniformly propagating combustion waves, to analyze their stability and to determine behavior in the instability region. The principal physical conclusion which follows from our analysis is that the flow of the melted component can result in nonuniform composition of the product. Unlike models which do not take into account the relative motion of the components, this model exhibits a dependence of the structure of the product on the mode of propagation of the combustion front. Thus, if the initial mixture is uniform, models which do not al...

Melt Filling Behavior During Die Casting Under the Reduced Pressure

Melt Filling Behavior During Die Casting Under the Reduced Pressure

Formation and behavior of BGaVAs complex defects in gallium arsenide grown by liquid-encapsulated Czochralski method

The effect of wafer annealing on lattice parameter of liquid-encapsulated Czochralski (LEC) grown undoped semi-insulating GaAs crystals is investigated, showing that wafer annealing increases the lattice parameter from an anomalous state below that predicted by Vegard’s law. The sheet-carrier concentration of a silicon-implanted layer formed on undoped semi-insulating GaAs increases with the increase in lattice parameter caused by the wafer annealing. The reduction of BGaVAs complex defects is a reasonable explanation for the increase in lattice parameter and sheet-carrier concentration. In LEC-grown silicon-doped GaAs crystals, no anomalous reduction of lattice parameter is observed in as-grown crystals. It is speculated that the silicon introduced into the crystal from the melt fills the VAs vacancies in the GaAs crystal before BGaVAs forms. BGaVAs complex defects in undoped GaAs crystal must be formed during the post-growth cooling process.

Electroplating on crystalline polypropylene. II. Injection molding and adhesion

AbstractThis paper describes the effect of injection molding conditions (melt temperature, mold temperature, and fill time) and etch conditions on metal adhesion in electroplated isotactic polypropylene (PP). It is found that injection molding PP homopolymer produces a lamellar surface morphology which can consistently develop after‐plated peel strengths of 30 lb/in or better as measured by the Jacquet peel test. Surface etching of PP homopolymer prior to plating develops crack patterns characteristic of injection molding; a directional crack pattern is always evident in specimen surfaces crystallized under shear. The surface pattern is developed in the oxidative process by swelling of amorphous material, followed by oxidative dissolution and oxidative stress cracking. Additionally, the depth and number of the surface cracks is a function of the solvent swell and acid etch times. Crack depth increases in lamellar surfaces as the sample immersion times are increased; however, as crack depth increases, crack density decreases.Metal‐to‐polymer adhesion, as measured by the peel test, represents a balance between crack depth and diminished surface strength incurred in the oxidative cracking process. Although peel adhesion usually increases with crack depth, overetching may actually reduce adhesion even though the crack depth has been increased. Any advantage from deeper cracks may, therefore, be offset by a loss in the surface strength of the polymer. Comparison of the surface and cross‐sectional crack patterns in TiO2‐filled PP indicates that the surface morphology is similar to that of unfilled polymer. Molding conditions that produce the desired morphology is similar to that of unfilled polymer. Molding conditions that produce the desired morphology are important for high peel adhesion values but appear to be less critical than in unfilled PP. A propylene–ethylene copolymer (90/10) developed 12–15 lb/in. peel adhesion—50% lower than for the filled and unfilled homopolymer when molded under similar conditions; peel adhesion in this composite system is, however, relatively insensitive to changes in molding conditions. Aging of 2–3 weeks after plating is required for maximum peel adhesion in all samples studied.