Wireless in‐mold melt front detection for injection molding: A long‐term evaluation

Wireless sensing technology for injection molding is of increasing interest in literature. Recently, a purely mechanical in‐mold sensor for melt front detection was introduced. The sensor system is based on building resonant structures into the mold which are excited by the passing melt front generating structure‐borne sound, from which the melt front position is derived. A big advantage of this system is the possibility to implement a plurality of resonant structures while just having one receiver. One important aspect is the need to separate and assign the recorded impinging sounds. A novel algebraic approach was introduced separating the resonant structures by reference to their oscillatory behavior. In this article, measurement results for over 450 injection molding cycles are given proving functionality of the separation process. In addition, it is shown that the melt front detection is reliable and robust when comparing it with results obtained by cavity temperature sensors. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40346.     

Visualization of in‐mold shrinkage in injection molding process

This article presents an experimental investigation on the visualization of (material/mold) separation development during the in‐mold shrinkage of injection molded parts. The purpose is to correlate the separation times with the shrinkage values. Two cavity designs were studied: (i) a simple rectangular plate (nonconstrained plate) and (ii) a rectangular plate with an obstacle pin (constrained plate). Separation development was recorded using a high speed camera on a designed and manufactured visual mold. The results indicate that although there is a meaningful correlation between shrinkage value and separation time in the nonconstrained mold, this correlation is highly disturbed in the presence of a constraint (here, an obstacle pin). POLYM. ENG. SCI., 47:750–756, 2007. © 2007 Society of Plastics Engineers.     

Capacitive transducer for in‐mold monitoring of injection molding

A capacitive transducer is developed for online monitoring of the in‐mold material status for injection molding, particularly for measurements of melt‐front position and flow‐rate. This paper will show, in addition to fulfilling its design purposes, that such a sensor can also be effectively used for the detection of the start and end of mold filling, the time of gate freezing, and over‐packing. Polym. Eng. Sci. 44:1571–1578, 2004. © 2004 Society of Plastics Engineers.     

Model‐based melt flow virtual sensors for filling process of injection molding

Based on the model‐based virtual sensing approach, previously proposed by the authors, two melt flow virtual sensors are developed. The virtual sensors estimate the melt front position during the filling process by using easily obtained machine variables, specifically, the injection hydraulic pressure and the screw position and nozzle pressure. Both virtual sensors were theoretically analyzed and experimentally evaluated on a commercial injection molding machine. The theoretical analysis provides step‐by‐step design guidelines for the virtual sensors. Performance evaluation with a twin thin‐plate mold validates the feasibility of the proposed model‐based melt‐flow virtual sensors. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Characterization of mold fouling during elastomer injection molding

Consideration is given to the characterization and origins of mold fouling occurring during the injection molding of elastomers. Results for nitrile rubber and fluoroelastomer compounds are presented with a range of techniques, including light microscopy, scanning electron microscopy, elemental analysis by energy‐dispersive X‐ray spectroscopy, X‐ray photoelectron spectroscopy, and surface‐energy measurements with the sessile drop approach. A specially designed mold tool combined with interchangeable cavity inserts has also enabled the exploration of the effects of different metal surface treatments on the onset and extent of mold fouling. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3186–3194, 2006     

Processability study of in‐mold coating for sheet molding compound compression molded parts

In‐mold coating (IMC) is applied to compression molded sheet molding compound (SMC) exterior automotive or truck body panels as an environmentally friendly primer to make the part conductive for subsequent electrostatic painting operations. The coating is a thermosetting liquid that when injected onto the surface of the part cures and bonds to provide a smooth conductive surface. In order to identify the processability of IMC for SMC, it is essential to predict the time available for flow, that is the time before the viscosity starts to increase as well as the time when the coating has enough structural integrity so that the mold can be opened without damaging the part surface (mold opening time). In the present work, we study cure behavior of IMC based on differential scanning calorimetry and rheological experiments and show its relevance to both flow and mold opening time for the IMC process during SMC compression molding. POLYM. ENG. SCI., 59:1688–1694 2019. © 2019 Society of Plastics Engineers     

Self‐interference flow of an isotactic polypropylene melt in a cavity during injection molding. II. Morphology and crystallinity

This article is principally concerned with the morphology and crystallinity of isotactic polypropylene (iPP) parts molded by injection molding, during which a self‐interference flow (SIF) occurs for the melt in the cavity. Scanning electron microscopy shows that a transverse flow takes place in SIF samples. Wide‐angle X‐ray diffraction and differential scanning calorimetry show that SIF moldings exhibit a γ phase, in addition to α and β phases, and high crystallinity. Meanwhile, the results for iPP moldings made by the conventional flow process, that is, conventional injection molding, are reported for comparison. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2791–2796, 2003     

Self‐interference flow of an isotactic polypropylene melt in a cavity during injection molding. I. Effect of the self‐interference flow on the properties

The self‐interference flow (SIF) of a melt in a cavity during injection molding is introduced. It comes from two streams of the melt being split by a patented mold gate called a twin gate. The effects of this flow on the static and dynamic mechanical properties, thickness distribution, and shrinkage in the transverse direction (TD) of injection‐molded isotactic polypropylene parts are discussed. SIF has an influence on the static mechanical properties, especially the impact strength. There are slight increases in the tensile strength and Young's modulus and an increase of approximately 70–90% in the impact strength in comparison with the properties of samples obtained by a conventional flow process with a common pin gate. Dynamic mechanical thermal analysis studies show an increase in the storage modulus for SIF samples. Results obtained from research into the effect of the mold temperature and injection pressure on the impact strength show that the impact strength of SIF specimens has a weaker dependence on the mold temperature and injection pressure. In addition, the flow brings a more uniform thickness distribution and a smaller shrinkage in the TD to SIF samples. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2784–2790, 2003     

No‐flow temperature in injection molding simulation

Most injection molding simulation packages use the no‐flow temperature (NFT) as a means of determining whether the polymer flows or is solid. The NFT is not well defined, and a standard method for measuring it does not exist. A sensitivity analysis of the filling stage has been carried out with two different packages [VISI Flow (Vero Software Limited, Gloucestershire, UK) and Moldflow (Autodesk, Inc., San Rafael, CA)] to estimate the influence of the NFT on the main processing parameters. The NFT has a large influence on the thickness of the frozen layer, but it does not appreciably affect the filling pressure. Because the NFT affects the frozen layer, an effect on the estimation of shrinkage and warpage is expected. Software packages have also been compared, and similar simulations have been found to produce contrasting results. A simple correlation for NFT estimation, derived from the Cross–Williams–Landel–Ferry equation, is proposed for both amorphous and semicrystalline polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Decreasing the cycle time for in‐mold coating (IMC) of sheet molding compound (SMC) compression molding

In‐mold coating (IMC) is a thermosetting liquid applied to compression molded sheet molding compound (SMC) exterior automotive or truck body panels as an environmentally friendly primer to improve surface quality and make the part conductive for subsequent electrostatic painting. The IMC is injected onto the surface of the SMC then cures and bonds to provide a smooth conductive and protective surface. In IMC as in many other reactive polymer processes, to have short cycle time while maintaining adequate flow time and pot life is required. This allows enough time to fill the mold before solidification. In this study, the effect of inhibitor (p‐benzoquinone), initiator (t‐butyl peroxybenzoate), and mold temperature on the flow and cure time of IMC materials has been experimentally investigated using differential scanning calorimeter. A cure model is developed based on experiments to predict inhibition and cure time. A multiple criteria optimization method was employed to identify the setting parameters of the controllable process variables that provide the best compromise (Pareto frontier [PF]) between flow and cure time. The analysis shows that simultaneous addition of initiator and inhibitor allows the molding to be performed at a higher temperature, which moves the PF toward the ideal location. Hence, minimizes the cure time and maximizes the flow time simultaneously. POLYM. ENG. SCI., 59:1158–1166 2019. © 2019 Society of Plastics Engineers     

Characterization of a reverse molding sequence at the mesoscale for in‐mold assembly of revolute joints

In‐mold assembly and miniature molding have been combined to realize miniature assemblies. Our previous work has shown that for realizing in‐mold assembly at the mesoscale, the molding sequence is the reverse of that used at the macroscale. Moreover, special features are needed in the mold to prevent plastic bending of the pin because of the pressure exerted by the second stage melt. This article presents novel mold designs and computational methods to enable the use of the reverse molding sequence to prevent: (1) plastic bending of the premolded component, and (2) joint jamming during the mesoscale in‐mold assembly process. The computational methods are also validated through experimentation. Results reported in this article show that for making in‐mold assembled revolute joints with the polymer combination of ABS and LDPE, a reversed molding sequence needs to be used for joints sizes less than 1.5 mm. POLYM. ENG. SCI., 50:1843–1852, 2010. © 2010 Society of Plastics Engineers     

Effects of mold surface conditions on flow length in injection molding process

In this study, to clarify the influence of a mold on thin‐wall molding, the effect of different mold surface conditions on the flow length and mobility (i.e., ease with, which melted plastics can be filled into the mold) in an injection molding process was investigated. Three different coatings were used for the mold surface. Several degrees of roughness were also selected for the mold surface. The results were evaluated by comparing flow length with interfacial tensions, which were derived from Young's formula. Although the interfacial tension exhibited different values, the influence on flow length was generally found to be small. On the other hand, in the mold that gives surface roughness, though the change of interfacial tension was small compared with coatings, the flow length increased linearly with the surface roughness when the roughness exceeded a certain level roughness. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

An experimental and theoretical investigation of transient melt temperature during injection molding

An in-depth study of the effect of molding parameters on melt temperature was carried out, in which the melt temperature was measured with infrared probes. The effect of screw speed, back pressure, shot size, and polymer viscosity on melt temperature during plastication was determined. The melt temperature was not constant during injection, and was found to be as much as 44°C above the barrel temperature. The temperature rise results from viscous dissipation during plastication and adiabatic compression during injection. Measured temperatures are in qualitative agreement with a first order model of the process.     

微注塑成型过程塑料熔体流动的偏移行为

采用集成式热电偶传感器温度测量系统和可视化全息示踪技术, 对多型腔微注塑成型过程熔体流动前沿在型腔内的偏移现象进行观察和分析。结果表明, 当注射速度为140~220 mm·s^-1时, 主流道内的塑料熔体前沿呈“U型流”状态分布, 分流道内塑料熔体前沿向上侧偏移;当注射速度为10~70 mm·s^-1时, 主流道塑料熔体前沿呈“喷泉流”状态分布, 分流道熔体前沿向下侧偏移;当注射速度为80~120 mm·s^-1时, 主流道和分流道熔体前沿均没有明显的偏移。说明微注塑时注射速度不同, 产生的剪切热也不同, 熔体前沿偏移情况也不同。为此, 引入非平衡流动系数λ, 来判断熔体前沿的流动和偏移情况。     

Visualization analysis of the filling behavior of melt into microscale V‐grooves during the filling stage of injection molding

With the rapid increase in the applications of polymer microreplication, it has become important to understand the replication process. Visualization is clearly the most direct and definite method of determining the replication process. In our experiment, the behavior of melt flowing over a stamper with V‐grooves was observed through a prism glass installed in the mold; an ultrahigh‐speed video camera connected with a long‐distance microscope was used. As a result, when molding with an open cavity having V‐grooves with a pitch of 100 μm and at an injection rate of 50 cm³/s, the filling of the melt into the V‐grooves was generally completed during the first several milliseconds after the melt flowed over the grooves. However, as the pitch of the V‐grooves decreased to 50 μm, the filling process slowed, thereby decreasing the filling ratio. In all cases, the filling of the melt into the V‐grooves was accelerated when the injection rate increased, and this was followed by an increase in the filling ratio. In addition, the effects of mold temperature and cavity thickness on the filling behavior were also investigated. This visualization analysis offers a unique opportunity to understand and improve the replication process by injection molding. POLYM. ENG. SCI., 46:1590–1597, 2006. © 2006 Society of Plastics Engineers.     

塑料杯成型工艺及注塑模设计

本文对水杯的技术要求和工艺结构进行了分析,确定了工艺方案及模具形式。而且对水杯进行了相关数据的分忻与计算,根据分析结果选注塑机和注塑工艺,从而确定聚丙烯水杯设计思路及方案,最后在设计过程中运用Pro／E、Auto CAD软件进行注塑模结构设计与计算并绘制出模具总装图以及部分非标准图形。     

Simulations of a full three‐dimensional packing process and flow‐induced stresses in injection molding

Numerical investigations of a full three‐dimensional (3D) packing process and flow‐induced stresses are presented. The model was constructed on the basis of a 3D nonisothermal weakly compressible viscoelastic flow model combined with extended pom‐pom (XPP) constitutive and Tait state equations. A hybrid finite element method (FEM)–finite volume method (FVM) is proposed for solving this model. The momentum equations were solved by the FEM, in which a discrete elastic viscous stress split scheme was used to overcome the elastic stress instability, and an implicit scheme of iterative weakly compressible Crank–Nicolson‐based split scheme was used to avoid the Ladyshenskaya–Babu?ka–Brezzi condition. The energy and XPP equations were solved by the FVM, in which an upwind scheme was used for the strongly convection‐dominated problem of the energy equation. Subsequently, the validity of the proposed method was verified by the benchmark problem, and a full 3D packing process and flow‐induced stresses were simulated. The pressure and stresses distributions were studied in the packing process and were in agreement with the results of the literature and experiments in tendency. We particularly focused on the effects of the elasticity and pressure on the flow‐induced stresses. The numerical results show that normal stress differences decreased with incremental Weissenberg number and increased with incremental holding pressure. The research results had a certain reference value for improving the properties of products in actual production processes. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polymer flow length simulation during injection mold filling

The maximum flow length of a polymer for a given set of processing conditions is important in injection molding to avoid incomplete mold filling. Experimental analysis, using various processing conditions, can generate the actual influence of processing conditions on the maximum flow length. However, the experimental determination of the flow length for all known industrial polymers would be time consuming and expensive. A non-Newtonian, nonisothermal model of mold filling was developed to evaluate the flow length without requiring large amounts of computation time. The model implements the use of both a temperature and shear rate–dependent viscosity as well as viscous heating. This paper presents the model and its numerical implementation, followed by simulation results. The model is compared with other simulation programs and experimental results using both an amorphous Styron 484-27 polystyrene and a semicrystalline 640I polyethylene in a spiral mold geometry. Good agreement between the three is observed.     

In situ flow state characterization of molten resin at the inner mold in injection molding

Online viscosity information on processing lines can reflect the material flow resistance and offer valuable guidance for manufacturing across various industries. Considering the accuracy, devices, and processes involved in injection molding, characterizing the melt's flow state during material processing poses a significant challenge. To reduce investment in viscometers, avoid influencing the components' surface aesthetics due to the installation of sensors, and make the flow state detect online in mold, this study designs a rheometric mold with cylindrical runners for identifying the in situ viscosity of molten resin during injection molding. The detection conditions of injection speed and cavity pressure variations, the entrance effect, and the viscous dissipation for Polycarbonate are analyzed under various conditions. The in situ viscosity is identified and compared with the standard cross-WLF model. The result shows that the melt velocity and cavity pressure variations during the filling process create a stable environment for in situ rheological characterization and the detected viscosity is related to the shear rate, melt temperature, and channel dimension in injection molding. The designed mold with cylindrical runners for determining the in situ thermal-rheological behavior of polymer is distinguished successfully and exhibits prospects for the development of low-cost, nondestructive, and inner-mold measurement in manufacturing applications.     

Validation of three on‐line flow simulations for injection molding

Polymer process control is limited by a lack of observability of the distributed and transient polymer states. Three simulations of varying complexity are validated for on‐line simulation of an injection molding process with a two drop hot runner system to predict the state of the polymer melt in real time and thereby improve product quality in situ. The simplest simulation is a Newtonian model, which predicts flow rates given the inlet and outlet pressures. An intermediate non‐Newtonian and nonisothermal simulation utilizes a modified Ellis model that expresses the viscosity as a function of the shear stress in which the modeling of the heat transfer utilizes a Bessel series expansion to include effects of heat conduction, heat convection, and internal shear heating. A numerical simulation was also developed that utilizes a hybrid finite difference and finite element scheme to simultaneously solve the mass, momentum, and heat equations. Numerical verification indicates that the flow rate predictions of the described simulations compare well with the results from a commercial mold filling simulation. However, empirical validation utilizing a design of experiments indicates that the described analyses are qualitatively useful, but do not possess sufficient accuracy for quantitative process and quality control. Specifically, off‐line validation using optimal transducer calibration with well characterized materials provided a coefficient of regression, R², of ～0.8. However, blind validation with previously untested materials and no transducer re‐calibration provided a regression coefficient of ～0.4. While the direction of the main effects was usually correct, the magnitudes of the effects were frequently outside the confidence interval of the observed behavior. Several sources of variance are discussed, including sensor calibration, constitutive modeling of the polymer melt, and numerical analysis. POLYM. ENG. SCI. 46:274–288, 2006. © 2006 Society of Plastics Engineers