Melt Fill Research Articles

Study on the Flow, Foaming Characteristics and Structural Strength of Polypropylene Structural Foam Injection Molding by Innovative Nitrogen and Molten Plastic Mixing Mechanism.

Plastic foam molding methods include thermoforming, extrusion and injection molding. Injection foam molding is a one-time molding method with high production efficiency and good product quality. It is suitable for foamed plastic products with complex shapes and strict size requirements. It is also the main method for producing structural bubbles. In this investigation, we developed a structural foam injection molding technology using the gas supply equipment connected to the unique plasticizing mechanism of the injection machine and studied its influence on the specimens' melt rheology quality and foam structures. In the experiment, the forming material was polypropylene (PP), and the gas for mixing/forming foaming characteristics was nitrogen (N2). Additionally, in order to observe the rheological properties of N2/melt mixing, a melt flow specimen mold cavity was designed and the change in the melt viscosity index was observed using a melt pressure sensing element installed at the nozzle position. With the nitrogen supply equipment connected to a unique plasticizing mechanism, the mixing of gas and molten plastic can be achieved at the screw plasticizing stage, where the foaming effect is realized during the melt-filling process due to the thermodynamic instability of the gas. It was also found that an increase in N2 fill content increased melt fluidity, and the trend of melt pressure and melt viscosity index showed that the higher the gas content, the lower the trend. The foaming characteristic depends on the gas thermodynamic instability and the pressure release, so it can be seen from the melt fill path that, the greater the pressure near the gate, the lower the foaming amount and the internal structure (SEM) after molding; the farther from the gate, the greater the relative increase in the foaming growth/amount. This phenomenon will be more obvious when the N2 fill content is increased.

Computational Analysis of Polymer Melt Filling in a Medical Mold Cavity During the Injection Molding Process

This study describes the results of a mold filling simulation analysis of a medical syringe performed during the thermoplastic injection molding process, which was performed using a computational Fluid Dynamic Simulation (CFD) with the Volume of Fluid Method (VOF). ANSYS Fluent was used for analysis and data collection. Medical grade polypropylene (PP) is considered in this study. The studies consider physical parameters (such as inlet position and syringe thickness) of the injection molding process. The outlet vent must be placed as far away from the inlet as possible to root out entrapped air and allow the molten PP to occupy the mold cavity. The findings revealed that syringe thicknesses ranging from 0.75 mm to 1.00 mm resulted in increased flow velocity, shorter filling time, and faster flow front advancement.

Evaluation of the Predictive Capacity of Viscosity Models in Polymer Melt Filling Simulations

Evaluation of the Predictive Capacity of Viscosity Models in Polymer Melt Filling Simulations

Water Penetration Stability in Water Assisted Injection Molded Symmetric Ribs

AbstractWater assisted injection molding technology has received extensive attention in recent years, due to its light weight, relatively lower resin cost per part, faster cycle time, and its flexibility in the design and manufacture of plastic parts. However, there are still some unsolved problems that confound the overall success of this technology. Unstable water penetration in molded symmetric channels is one of them. This report was to study the water penetration behavior in the water assisted injection molded symmetric cavity. Experiments were carried out on an 80-ton injection-molding machine equipped with a water injection unit. A plate cavity with symmetric water channels was used. The materials used were amorphous polystyrene and semi-crystalline polypropylene. Various processing variables were studied in terms of their influence on the water penetration behavior inside the symmetric parts: melt temperature, mold temperature, melt fill speed and fill pressure, short-shot size, water temperature and water pressure, and water injection delay time and water hold time. The effect of channel layout was also investigated. Tapered channels were found to mold parts with better penetration stability than flat channels. In addition, the penetration behaviors of water and gas in molded symmetric parts were also compared. The experimental results suggested that water penetration stability is more stable than that of gas in molded symmetric parts.

Shrinked bifilms in Mg-Gd-Y-Zr alloy

Mg-Gd-Y-Zr alloy has excellent mechanical properties at room and high temperatures, but its high oxidation properties can also result in a significant number of bifilm defects. However, its formation mechanism was not revealed so far, which was explored in the present work. The results showed that the surface oxide film folds into a grid-like double layer structure defect during solidification, due to the difference of thermal expansion coefficient between surface oxide film and matrix. In addition, the oxide film produces microcracks. As the magnesium alloy melt fills the crack, Zr precipitates into crystal nucleus with peritectic reaction and Y2O3 accumulates. These results would shed new lights on the understanding of shrinkage formation of bifilm defects and improving the defects control of magnesium alloy castings.

The Low Breaking Fiber Mechanism and Its Effect on the Behavior of the Melt Flow of Injection Molded Ultra-Long Glass Fiber Reinforced Polypropylene Composites.

In this study, fiber breaking behavior, fiber orientation, length variation, and changes in melt flow ability of long glass fiber reinforced polypropylene (L-FRP) composites under different mold cavity geometry, melt fill path, and plasticization parameters were investigated. The matrix material used was polypropylene and the reinforcement fibers were 25 mm long. An ultra-long-fiber composite injection molding machine (with a three-stage plunger and injection mechanism design) was used with different mold cavity geometry and plasticization parameters. Different screw speeds were used to explore the changes in fiber length and to provide a reference for setting fiber length and parameter combinations. Flow-length specimen molds with different specimen thickness, melt fill path, and gate design were used to observe the effect of plasticizing properties on the flow ability of the L-FRP composite materials. The experimental results showed that the use of an injection molding machine with a mechanism that reduced the amount of fiber breakage was advantageous. It was also found that an increase in screw speed increased fiber breakage, and 25 mm long fibers were shortened by an average of 50% (to 10 mm). Long fibers were more resistant to melt filling than short fibers. In addition, the thickness of the specimen and the gate design were also found to affect the filling process. The rounded angle gate and thick wall product decreased the flow resistance and assisted the flow ability and fiber distribution of the L-FRP injection molding.

The Feasibility of an Internal Gas-Assisted Heating Method for Improving the Melt Filling Ability of Polyamide 6 Thermoplastic Composites in a Thin Wall Injection Molding Process.

In thin wall injection molding, the filling of plastic material into the cavity will be restricted by the frozen layer due to the quick cooling of the hot melt when it contacts with the lower temperature surface of the cavity. This problem is heightened in composite material, which has a higher viscosity than pure plastic. In this paper, to reduce the frozen layer as well as improve the filling ability of polyamide 6 reinforced with 30 wt.% glass fiber (PA6/GF30%) in the thin wall injection molding process, a preheating step with the internal gas heating method was applied to heat the cavity surface to a high temperature, and then, the filling step was commenced. In this study, the filling ability of PA6/GF30% was studied with a melt flow thickness varying from 0.1 to 0.5 mm. To improve the filling ability, the mold temperature control technique was applied. In this study, an internal gas-assisted mold temperature control (In-GMTC) using different levels of mold insert thickness and gas temperatures to achieve rapid mold surface temperature control was established. The heating process was observed using an infrared camera and estimated by the temperature distribution and the heating rate. Then, the In-GMTC was employed to produce a thin product by an injection molding process with the In-GMTC system. The simulation results show that with agas temperature of 300 °C, the cavity surface could be heated under a heating rate that varied from 23.5 to 24.5 °C/s in the first 2 s. Then, the heating rate decreased. After the heating process was completed, the cavity temperature was varied from 83.8 to about 164.5 °C. In-GMTC was also used for the injection molding process with a part thickness that varied from 0.1 to 0.5 mm. The results show that with In-GMTC, the filling ability of composite material clearly increased from 2.8 to 18.6 mm with a flow thickness of 0.1 mm.

The Measurements of the Shear Stress Distribution at the Cavity Surface during Melt Filling in an Injection Mold

Measurement of shear stress distribution is important for examining phenomena occurring in the interface between the mold cavity surface and molten resin in injection molding. The authors developed a high precision measurement technique for shear stress distribution using a movable block and 3-component force transducer. In this study, we analyzed the influence of resins, cavity surface properties, and cavity thicknesses on shear stress distribution. The results are summarized below：

Characterization of siloxane-infiltrated ceramics microstructure by spectral scattering in the near infrared

The spectral scattering technique is considered to estimate the scatterers (pores) size distribution. It is based on the fitting of spectral scattering coefficients determined by Mie theory and radiative transfer inverse problem solution. The previously proposed method was improved for multiphase system analysis. The spectral directional-hemispherical reflectances of slabs of not less than two different geometrical thicknesses are used for inverse radiative transfer problem solution. Semitransparent ceramics with less than 10–15% of total porosity, that contains homogeneously distributed close to solid sphere scatterers, is the application object of the proposed technique. General expressions for multiphase systems were simplified to three-phase ones to reduce the number of optimization variables and adapted to the evaluation of semitransparent ceramics infiltrated by the polymer.The proposed technique was implemented for the evaluation of silica ceramics with 10% porosity before and after the infiltration by the methyl-phenyl-spirocyclosiloxanol followed by the polyfunctional condensation to obtain the polymethyl-phenyl-spirocyclosiloxane. Two techniques of ceramics infiltration with the low-molecular polymer viz by the solution and by the melt were compared. Size distributions of the polymer-filled pores was shown to be affected by the infiltration procedure and polymerization regime. It was shown that less than 25% of the initial pore volume appears to be polymer-filled in the case of ceramics infiltration by the solution. Infiltration from the melt fills not less than 80% of the pore volume. The mean pore diameter of air-filled pores was estimated by gas/mercury porometry and spectral scattering technique. Both methods are shown to be in a rather good agreement. By these techniques air-filled pores mean diameters were shown to be 0.37 and 0.44 µm respectively for ceramics before the infiltration and 0.54 and 0.55 µm for the ceramics infiltrated through the solution. The spectral scattering technique shows mean diameter of polymer-filled pores to be 0.11–0.17 and 0.49 µm in the cases of ceramics infiltration by the solution and by the melt respectively. Thus, sizes of polymer-filled pores are shown to be shifted to the higher values because of infiltration by the melt. The obtained data on polymer-filled pores sizes may be useful for the analysis of ceramics strengthening by the polymer infiltration and infiltration procedure optimization.

Wetting behavior and reaction mechanism of molten Si in contact with silica substrate

The photovoltaic silicon ingot is currently grown in silica (SiO2) crucible. However, adhesion between Si ingot and SiO2 crucible occurred frequently, leading to cracking in Si ingot. To solve these problems, it is important to understand the Si/SiO2 interfacial wetting behavior and reaction mechanism at high temperature. In this paper, the sessile drop technology and microstructural analysis method were used to study the Si/SiO2 interfacial wetting behavior and reaction mechanism at high temperature. The results show that the contact angle of Si drop on SiO2 substrate is 83.5 ± 2°. The interfacial reaction occurs between Si melt and SiO2 substrate at high temperature, causing uneven surface of substrate with many grooves. The Si melt fills grooves at high temperature and expands during solidification, which results in interlock structure and adhesion at Si/SiO2 interface. Finally, adhesion and cracking phenomena are interpreted by analytical models.

Precise Fabrication of Fresnel Flash Lens Featured with V-Grooved Microstructures

Abstract A Fresnel lens is characterized by a micrometer-sized v-grooved structure, and its microstructure quality and curvature accuracy strongly influence its illuminance performance. In this study, a mold is designed for fabricating a Fresnel flash lens involving injection compression molding (ICM). The Taguchi method and parametric analysis are applied to examine the effect of process parameters (mold temperature, melt temperature, injection speed, packing pressure, compression pressure, and time) on the molding quality. Increasing the mold temperature and packing pressure generally improves the polymer melt fill in microsized cavities. ICM enables the realization of v-grooved microstructures with an accurate height replication rate (96.1%) as well as high curvature accuracy (6 μm), creating good optical qualities of the fabricated Fresnel lens with respect to maximum illuminance and illuminance uniformity.

Melt Filling Behaviors and Primary Si Particle Distribution on Horizontal Centrifugal Casting in B390 Aluminum Alloy

Both computational and experimental methods were employed to study the behavior of melt flow and distribution of primary Si particles of B390 aluminum. The rotational frequency of the mold has a dominant effect on the melt flow and distribution of primary Si particles. As the rotational frequency of the mold increased, the speed of melt flow increased, leading to a turbulent flow. The numerical estimation of 1200 rpm rotational frequency for the homogeneous distribution of primary Si particles across the wall of the cylinder showed good consistency with the experiment results. As the rotational frequency of the mold increased, the functionally graded materials (FGM) microstructure of Si particles was more evident toward the inner side of the cylinder.

Numerical Investigation on the Effect of Pressure and Temperature on the Melt Filling During Injection Molding Process

Molding development and fabrication is costly and always involves part modification. The cost-effective pre-molding analysis is advantageous to engineer and designer prior to the mold design and before mass production. Computer-aided techniques are identified as virtuously cost-effective for pre-molding analysis. The numerical simulation analysis of the injection molding process using ANSYS FLUENT 14 was carried out in the study. The setting pressure and operating temperature were considered for investigation. Influence of these two process parameters to the injection molding process in terms of filing time, flow front advancement, velocity profile were studied. The injection molding and rheological experiments were carried out to substantiate the predictions of ANSYS FLUENT 14 in solving injection molding problems. The results revealed the system pressure is dominant to filling time, flow front advancement and velocity profile. Inversely, operating temperature only vaguely affects the current injection molding process, due to the small variations of polypropylene viscosity at temperature 185–195\({^{\circ} {\rm C}}\). The discrepancies of the simulation and experimental results were only 4.35 and 2.21% for system pressure and temperature, respectively.

Three Dimensional Numerical Simulation of Melt Filling Process in Mold Cavity with Insets

This paper presents a level set function, named shape function, to describe and treat the irregular surface of mold cavity. With the aid of the shape function, the continuity, momentum and energy equations can be extended for solving two-phase flows with an immersed solid surface. The governing equations are solved by using the finite volume solver with the coupled level set and volume of fluid (CLSVOF) method to track the polymer melt front. As case studies, the melt filling processes are simulated in mold cavities with cylindrical insets. The numerical results show that the mathematical model can successfully depict the phenomenon of race-tracking and fountain, which are very helpful for determining processing conditions and designing mold cavities.

Defect formation induced by seed-joints during directional solidification of quasi-mono-crystalline silicon ingots

In this work, the growth behavior inside and above seed gaps during directional solidification of monocrystalline lab-scale silicon ingots was investigated. It will be shown that the silicon melt fills the gaps rapidly and monocrystalline growth starts in most cases at the seed side walls toward the gap center. During this process, dislocations were induced at the seed edges and in the gap center by the thermal shock caused by the hot melt and the coalescence of the two growth interfaces, respectively. The dislocations originating from the gap are propagating more or less parallel to the growth axis toward the top of the crystal. These dislocation bundles fan out in dependence of the growth height and axial seed orientation, respectively. It was found that <100> is the most suitable growth direction in comparison to <111> and <110> to avoid defect clusters above the seed gaps which is probably due to the orientation of the preferential glide systems.

Formation of electrocontact plugs of anodes of metallurgical production

A method for making electrocontact plugs (ECPs) in anodes for aluminium and magnesium electrolyzers using the pulsed magnetic field (PMF) action on the metal melt was proposed. Different variants of plug construction are presented. Technology for making ECPs under laboratory conditions was developed. IFU brand coal-coke material was used in the experiments as an anode material; a casting aluminium alloy of an Al-Si system was used for ECPs. The results of experimental investigations are given and an assessment of the quality of the electric contact was carried out. It was found that the contact resistance of the contact produced under the action of the PMF is much lower than when conventionally pouring the melt. The reduction of this factor depends on the fact that the melt fills the pores and microirregularities of the carbon block of the anode under the pressure of the PMF, which results in an increase in the physical area of the contact.

Influence of Mold Temperature on Melt Filling Process of a Thin Plate Part with Microstructures in Injection Molding

Influence of Mold Temperature on Melt Filling Process of a Thin Plate Part with Microstructures in Injection Molding

Formation of pseudotachylitic breccias in the central uplifts of very large impact structures: Scaling the melt formation

Abstract– The processes leading to formation of sometimes massive occurrences of pseudotachylitic breccia (PTB) in impact structures have been strongly debated for decades. Variably an origin of these pseudotachylite (friction melt)‐like breccias by (1) shearing (friction melting); (2) so‐called shock compression melting (with or without a shear component) immediately after shock propagation through the target; (3) decompression melting related to rapid uplift of crustal material due to central uplift formation; (4) combinations of these processes; or (5) intrusion of allochthonous impact melt from a coherent melt body has been advocated. Our investigations of these enigmatic breccias involve detailed multidisciplinary analysis of millimeter‐ to meter‐sized occurrences from the type location, the Vredefort Dome. This complex Archean to early Proterozoic terrane constitutes the central uplift of the originally &gt;250 km diameter Vredefort impact structure in South Africa. Previously, results of microstructural and microchemical investigations have indicated that formation of very small veinlets involved local melting, likely during the early shock compression phase. However, for larger veins and networks it was so far not possible to isolate a specific melt‐forming mechanism. Macroscopic to microscopic evidence for friction melting is very limited, and so far chemical results have not directly supported PTB generation by intrusion of impact melt. On the other hand, evidence for filling of dilational sites with melt is abundant. Herein, we present a new approach to the mysterium of PTB formation based on volumetric melt breccia calculations. The foundation for this is the detailed analysis of a 1.5 × 3 × 0.04 m polished granite slab from a dimension‐stone quarry in the core of the Vredefort Dome. This slab contains a 37.5 dm3 breccia zone. The pure melt volume in 0.1 m3 PTB‐bearing granitic target rock outside of the several‐decimeter‐wide breccia zone in the granite slab was estimated at 5.2 dm3. This amount can be divided into 4.6 dm3 melt (88%), for which we have evidenced a limited material transport (at maximum, ≈20 cm) and 0.6 dm3 melt (12%) with, at most, grain‐scale material transport, which we consider in situ formed shock melt. The breccia zone itself contains about 10 dm3 of matrix (melt). Assuming melt exchange over 20 cm at the slab surface, between breccia zone and surrounding melt‐bearing host rock volume, the outer melt volume is calculated to contain the same amount of melt as contained by the massive breccia zone. Meso‐ and microscopic observations indicate melt transport is more prominent from larger into smaller melt occurrences. Thus, melt of the breccia zone could have provided the melt fill for all the small‐scale PTB veins in the surrounding target rock. Extrapolating this melt capacity calculation for 1 m3 PTB‐bearing host rock shows that a host rock volume of this dimension is able to take up some 52 dm3 melt. Scaling up 1000‐fold to the outcrop scale reveals that exchange between a host rock volume of 2 m radius around a 37 m3 breccia zone could involve some 10 m3 melt. These results demonstrate that large melt volumes (i.e., large breccia zones) can be derived, in principle, from local reservoirs. However, strong decompression would have to apply in order to exchange these considerable melt volumes, which would only be realistic during the decompression phase of impact cratering upon central uplift formation, or locally where compressive regimes acted during the subsequent down‐ and outward collapse of the central uplift.

Injection molding and injection compression molding of thin‐walled light‐guided plates with V‐grooved microfeatures

AbstractIn this study, we investigated the feasibility of injection molding (IM) and injection compression molding (ICM) for fabricating 3.5‐in. light‐guided plates (LGPs). The LGP was 0.4 mm thick with v‐grooved microfeatures (10 μm wide and 5 μm deep). A mold was designed to fabricate LGPs by IM and ICM. Micromachining was used to make the mold insert. The Taguchi method and parametric analysis were applied to examine the effects of the process parameters on the molding quality. The following parameters were considered: barrel temperature, mold temperature, packing pressure, and packing time. Mold temperature in this investigation was in the conventional range. Increasing the barrel temperature and mold temperature generally improved the polymer melt fill in the cavities with microdimensions. The experimental results for the replication of microfeatures by IM and ICM are presented and compared. The height of the v‐grooved microfeatures replicated by ICM was more accurate than those replicated by IM. Additionally, the flatness of the fabricated LGPs showed that ICM was better than IM for thin‐walled molding. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Fully Coupled Transient Heat Transfer and Melt Filling Simulations in Rapid Heat Cycle Molding with Steam Heating

Rapid heat cycle molding (RHCM) is a novel injection molding technology, in which injection mold is rapidly heated to a high temperature, usually higher than the glass transition temperature of the polymer material, before melt-injection and rapidly cooled down to solidify the shaped polymer melt in mold cavity for ejection. Since the elevated mold temperature can eliminate the unwanted premature melt freezing during filling stage, the melt flow resistance is greatly reduced and the filling ability of the polymer melt is also significantly improved. As a result, plastic parts with excellent surface appearance can be obtained. In this study, a three-dimensional numerical model coupled with heat transfer analysis and melt-filling processes for RHCM with steam heating was established. The thermal response analysis for the heating stage of RHCM process was performed by solving heat conduction equations. The heat transfer analysis results right after the mold cavity surface is heated up to the required temperature are taken as initial temperature conditions of the mold cavity for the following melt filling simulation. The pressure implicit splitting of operations solution algorithm was used to solve the pressure-velocity coupled Navier-Stokes equation for melt filling process. The moving interface between melt and air was captured by using the volume of fluid method. The energy equations for melt filling process were solved in a coupled manner for the cavity and mold domain at the matrix level. The proposed fully-coupled numerical model was applied in simulation of the molding processes, including a two-dimensional rectangular cavity with different heating times and a three-dimensional large scale LCD panel with a stem-heated stationary mold. The results show that the fully coupled numerical method provides reliable temperature and flow field predictions with the thermal response analysis and melt flow estimation.