High‐frequency proximity heating for injection molding applications

High‐frequency proximity heating was used to rapidly heat injection molds. The principle is based on the proximity effect between a pair of mold inserts facing each other with a small gap and forming a high‐frequency electric loop. Because of the proximity effect, the high‐frequency current will flow at the inner surfaces of the facing pair, thus selectively heating the mold surface. With this method, the electrical insulation layer beneath the mold surface can be eliminated, resulting in a mold insert made of a single metal. A mold with a cavity of 25 × 50 mm² was constructed with careful design on its electrical, structural, and thermal performance. Air pockets with reinforcing ribs were embedded right beneath the mold surface for enhancing the heating performance. The resulting mold cavity can be rapidly heated from room temperature to about 240°C in 5 s with an apparent heating power of 93 W/cm². The new mold heating method was applied to thin‐wall molding and micromolding, and in all testing cases, short cycle times less than a minute were achieved. POLYM. ENG. SCI. 46:938–945, 2006. © 2006 Society of Plastics Engineers     

Amplification effect of platelet type nanoparticles on the orientation behavior of injection molded nylon 6 composites

The effect of platelet type nanoparticles and processing conditions; mold temperature and injection speed, on the development of local microstructure in injection molded nylon 6 parts was investigated. The molded parts exhibit two crystal forms (α and γ) of nylon 6 in varying proportions from skin to core. The γ crystals preferentially grow near the surface regions and α crystal fraction increases with distance from the surface in all molded parts. However, the spatial variation of crystal phases across the thickness in nanocomposites differs from that of unfilled nylon 6. Nanoplatelets induce high levels of orientation of the polymer matrix throughout the thickness of the molded part even at high mold temperatures where nonisothermal effects are highly suppressed and confined to very close proximity of surfaces. These high chain orientation levels observed in nanoparticle filled systems is a result of the shear amplification effect that occurs in small spaces between adjacent nanoparticles of differing velocity. The local preferential crystalline orientation of nylon 6 resin and nanoparticles across the thickness of the molded parts are investigated using a series of structure characterization techniques including microbeam wide angle X-ray, SAXS and TEM.     

Integrative Approaches for Mechanical Mold Design in Injection Molding

The injection mold faces a number of different loads during the injection molding process for plastic parts. The effect on the mechanical behavior of the mold, inserts, and adjacent processes can be complex and may cause bad final parts. By using an integrative simulation approach it is possible to take the process influence into account when calculating the solid body behavior of the mold in a structural simulation. A newly developed approach at IKV uses the advantages of the integrative approach and extends it by an automatic back coupling of deformation results during the filling simulation. This way the interaction of the melt flow and the deformation of inserts or mold components can be considered during the filling phase.     

Experimental investigation and numerical simulation of injection molding with micro‐features

Injection molding of thin plates of micro sized features was studied in order to manufacture micro‐fluidic devices for bioMEMS applications. Various types of mold inserts—CNC‐machined steel, epoxy photoresist, and photolithography and electroplating produced nickel molds—were fabricated and tested in injection molding. The feature size covers a range of 5 microns to several hundred microns. Issues such as surface roughness and sidewall draft angle of the mold insert were considered. Two optically clear thermoplastics, PMMA and optical quality polycarbonate, were processed at different mold and melt temperatures, injection speeds, shot sizes, and holding pressures. It was found that the injection speed and mold temperature in injection molding greatly affect the replication accuracy of microstructures on the metal mold inserts. The UV‐LIGA produced nickel mold with positive draft angles enabled successful demolding. Numerical simulation based on the 2D software C‐MOLD was performed on two types of cavity fillings: the radial flow and the undirectional flow. The simulation and experimental data were compared, showing correct qualitative predictions but discrepancies in the flow front profile and filled depth.     

Reinforcing and toughening isotactic polypropylene through shear-induced crystallization and β-nucleating agent induced crystallization

In this article, iPP with β-nucleating agent was molded by sequential co-injection molding (SCIM), in which skin and core melt were injected into the mold cavity one after the other. The microstructure and mechanical properties of samples were investigated by polarized optical microscope (POM), wide angle X-ray diffraction (WAXD) and mechanical property test. Results show that plastic parts molded by SCIM have double shear layers due to twice shear induced by filling flow of skin and core melt. In the shear layers especially the layer at the overlap of skin and core material, shear promoted the formation of highly oriented structures (shish-kebabs) but inhibited the produce of β-form. In core layer of skin material and core layer of core material, β crystals are predominant. The combination of oriented structures (shish-kebabs) and β crystals endow iPP with high strength and toughness. This work demonstrates a new approach to achieve high-performance polymer materials based on general plastics by manipulation strategy for morphology and structure.     

In‐plane anisotropic permeability characterization of deformed woven fabrics by unidirectional injection. Part I: Experimental results

Because of the increasing use of polymer composites in a wide variety of industrial applications, the manufacturing of complex composite parts has become an important research topic. When a part is manufactured by liquid composite molding (LCM), the reinforcement undergoes a certain amount of deformation after closure and sealing of the mold. In the case of bidirectional woven fabrics, this deformation may significantly affect the resin flow and mold filling because of changes in the values of permeability. Among other considerations that govern the accuracy of numerical simulations of mold filling, it is important to predict the changes of permeability as a function of the local shearing angle of the preform. The resin flow through a fibrous reinforcement is governed by Darcy's law, which states that the fluid flow rate is proportional to the pressure gradient. The shape of the flow front in a point‐wise injection through an anisotropic preform is an ellipse. Part I of this article describes a new methodology based on the ellipse equation to derive the in‐plane permeability tensor from unidirectional injection experiments in deformed woven fabrics. Part II presents a mathematical model that predicts the principal permeabilities and their orientation for sheared fabrics from the permeability characterization of unsheared fabrics. Unidirectional flow experiments were conducted for a nonstitched, balanced, woven fabric for different shearing angles and fiber volume fractions. This article presents experimental results for deformed and undeformed fabrics obtained by unidirectional flow measurements. A comparison of the proposed characterization methodology with radial flow experiments is also included. POLYM. COMPOS. 28:797–811, 2007. © 2007 Society of Plastics Engineers.     

Spatial distribution of molecular orientation in injection molded iPP: influence of processing conditions

In this paper, the influence of processing conditions on the spatial distribution of the molecular orientation was determined within the depth of the thickness of injection molded isotactic polypropylene (iPP) plates. Small 35 μm-thick slices were microtomed from the surface to the core of 1 and 3 mm-thick plates. The orientation functions along the three crystallographic axes were determined on the slices from IR dichroism measurements and WAXS pole figures. It was found that the orientation of the amorphous phase was low and the crystalline orientation had a maximum in the shearing layer, which was solidified during the filling stage. The plate thickness seemed to govern the global level of orientation, while the injection speed determined the thickness of the shearing layer without changing the maximum of orientation. Changing the mold temperature from 20 to 40 °C did not modify the molecular orientation. A specific bimodal crystalline orientation was found in the shearing layer. This crystalline structure continued in the post-filling layer, but the local symmetry axes tilted towards the core.     

基于Moldflow的车载导航面板注塑模具设计

以车载导航面板为研究对象,结合塑件的结构特点和精度要求,设计了一副一模一腔的高精度注塑模具。利用Moldflow软件进行模流分析,确定了模具浇注系统与冷却系统设计的正确性。该模具采用牛角式潜伏浇口的半热流道走胶方式和直孔隔水板局部强冷的冷却水路设计,考虑塑件内部侧凹、骨位等特征特点,分别设计了3组斜导柱式侧抽机构、3组分体式斜顶机构、模具镶件和"推杆+推管+推板"的联合推出机构。结果表明,该模具结构设计先进合理,有利于降低模具成本,可用于指导生产。     

Effects of inserts on the injection molding process

Injection molds often contain blocks of dissimilar material for improved cooling; they may also contain blocks of movable metal as a means of ejecting large parts from the mold. In this case, the blocks of metal are made of the same material, but the resistance at the interface between them has a marked influence on the cooling in the local area near the interface. In many other cases, inserts may be required because of wear in a particular mold section, or because efficient mold design is needed to produce similar parts. Hence, any mathematical model for analysis of heat transfer in injection molds must be general enough to apply to interfaces with and without gaps (i.e., with and without resistance to the flow of heat at the interface) for similar, as well as dissimilar, materials. A new and accurate model for prediction of heat transfer in heterogeneous (zoned) molds is presented in this paper. Through the solution of real problems with this model, the effects of differing material properties and interfacial thermal resistance are studied and the results are reported. It is observed that inserts have both local and global effects on the injection molding process; the overall ejection time for a part may be shortened, and the surface appearance of a part may be improved by correct placement of inserts.     

Effect of processing conditions on the structural gradients developed in injection-molded poly(aryl ether ketone) (PAEK) parts. I. Characterization by microbeam X-ray diffraction technique

Depending on the processing conditions, poly(arylene ether ketone) exhibits unique structural gradients as a result of its thermomechanical history when it is injection-molded. Gapwise structure gradients change from a fully amorphous to multilayer amorphous–semicrystalline–amorphous and, finally, to a uniformly semicrystalline one when mold temperature is increased. When injection speed is decreased, the crystallized layers become thicker, and at very slow injection speeds, the crystalline layers developed near the two surfaces of the parts approach each other at the core. These structure variations were characterized by differential scanning calorimetry, optical microscopy, and a matrixing microbeam X-ray diffraction (MMBX) technique developed in our laboratories. The relationship between the structure gradients developed and the processing variables and the cavity geometry are discussed. © 1993 John Wiley & Sons, Inc.     

Shear amplification and re-crystallization of isotactic polypropylene from an oriented melt in presence of oriented clay platelets

In this study, we first prepared isotactic Polypropylene (iPP)/organoclay nanocomposite specimens via twin-screw extruder and by adding compatibilizer (maleic anhybride grafted PP). Then PP and the composites were subjected to dynamic packing injection molding, in which the melt was firstly injected into the mold then forced to move repeatedly in a chamber by two pistons that moved reversibly with the same frequency as the solidification progressively occurred from the mold wall to the molding core part. The dispersion and orientation of layered organoclay in the nanocomposite were estimated by transmission electron microscopy (TEM) and 2d-wide angle X-ray scattering (2d-WAXS). A much higher degree of orientation of PP was found in the composites compared with the pure PP. This was explained by so called shear amplification in that a great enhancement of local stress occurred in the small interparticles region of two adjacent layered tactoids with different velocities. Furthermore, re-crystallization of isotactic polypropylene (iPP) by melting the dynamic packing injection molded samples has been investigated by polarizing light microscopy (PLM). A highly oriented threadlike crystallites was observed for the first time when crystallization occurs by melting the dynamic packing injection molded samples at 180 °C. However, spherulitic morphology is always obtained once PP crystallizes from an isotropic melt by melting the samples at 200 °C. The shear amplification mechanism and the formation mechanism of oriented threadlike crystallites have been discussed in detail.     

Injection molding using a generalized eulerian lagrangian formulation

A mathematical and a numerical approach to model the injection mold filling stage is presented. The approach is based on a Generalized Eulerian Lagrangian (GEL) formulation. In purely Lagrangian formulations the solution is obtained at mesh points which follow the local fluid velocity. On the other hand, in Eulerian formulations the mesh is fixed and the solution is obtained at fixed spatial locations. In injection molding different parts of the flow domain are best analyzed by one but not both formulation methods. The Generalized Eulerian Lagrangian formulation combines the advantages of both formulations: In the same flow problem but different regions the GEL formulation allows the selective application of an Eulerian, Lagrangian, or a mixture of the two formulations. In this work the melt is described using the White-Metzner constitutive relation and results are shown and discussed for the filling of a cavity from a single gate and from a fully open end under different process conditions.     

Numerical and experimental investigations on polymer melt flow phenomenon in a vario‐thermal mold cavity

Mold temperature is one of the key factors affecting the morphology and quality of plastic parts. This article explores the melt flow phenomena in a vario‐thermal mold cavity. A coupled numerical method, considering the conjugate heat transfer between the mold and melt, is developed for the melt flow simulation. Mold temperature variations and melt flow phenomena for short shot injection in an electrical heated mold cavity are numerically studied and verified by experiments. The results indicate that the melt flow length and cavity filling ratio increase significantly with the elongation of the preheating time before injection. Melt filling ratio increased nearly linearly with the increasing of electric heating time. The smaller the injection pressure is, the bigger the relative filling ratio increment is. Therefore, polymer melt can flow much longer or the mold cavity can be filled up with a smaller injection pressure when the cavity is preheated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45193.     

Formation mechanism of high-pressure water penetration induced fiber orientation in overflow water-assisted injection molded short glass fiber-reinforced polypropylene

Recently, there has been growing interest in water-assisted injection molding (WAIM) not only for its advantages over gas-assisted molding (GAIM) and conventional injection molding (CIM), but also for its great potential advantages in industrial applications. To understand the formation mechanism of water penetration induced fiber orientation in overflow water-assisted injection molding (OWAIM) parts of short glass fiber-reinforced polypropylene (SGF/PP), in this work, the external fields and water penetration process within the mold cavity were investigated by experiments and numerical simulations. The results showed that the difference of fiber orientation distribution in thickness direction between WAIM moldings and CIM moldings was mainly ascribed to the great external fields generated by water penetration. Besides, fiber orientation depended on the position both across the part thickness and along the flow direction. Especially in the radial direction, fiber orientation varied considerably. The results also showed that the melt temperature is the principal parameter affecting the fiber orientation along the flow direction, and a higher melt temperature significantly facilitated more fibers to be oriented along the flow direction, which is quite different from the results as previously reported in short-shot water-assisted injection molding (SSWAIM). A higher water pressure, shorter water injection delay time, and higher melt temperature significantly induced more fibers to be orderly oriented in OWAIM moldings, which may improve their mechanical performances and broaden their application scope.     

Gap Distribution Between Fragile Insert and Mold in Plastic Boundary Injection Forming

Plastic inserts may enhance the performance of a product, enlarge its application scope or make it possible to apply plastic in situations where this material may not have been applied previously. The type of insert may vary from metal to plastic, ceramic, glass, or fireproof materials on a macro-scale. Glass is a typical type of fragile material. As an insert, this fragile part is easily broken or scraped during the processing of PVC injection molding, and flashes may occur at the shared boundaries of PVC and insert. The proper gap should be set between the core or cavity and the insert. In this paper, the function of the pressure attenuation and the shear flowing distribution variation along the runner is set to get the optimal gap distribution. First, two types of power loss functions are set. These functions relate pressure and shearing flow during transverse filling in a runner. Second, the summation of the two types of power loss is obtained using functions that are proportional and inversely proportional to the mold gap. Third, by discretizeing the long and narrow runner, according to the pressure distribution, the optimal gap is obtained at each point. Next, the simplified algorithm and the post-processing calculations of the fitting gap at arbitrary points are proposed. As an application, the experimental procedures and results of injection forming circular freeform materials which are used in vehicles as PVC-lined safety inserts are described in detail. Through geometrical measurement and mechanical testing on PVC and glass, we have shown that the mold gap distribution and the processing operations can ensure the technical requirement of the plastic part with fragile insert.     

一种单腔双色多功能注塑模具设计

介绍了一种特殊的单色、双色集成式家族两板注射模具。模具的布局为1模2腔,其中的一个单色模腔用于塑件的单色注射成型,另一个单腔双色模腔用于塑件的双色注射成型。单腔双色模腔只用一个模腔即能实现塑件的双色注射成型,其功能实现的方式为：在单色模腔的基础上,通过改变型腔镶件的形状及位置、以及第二胶浇口成型件的位置,达到单腔进行双色注射成型的目的。结合浇注系统的改造,模具能实现5种注射成型功能,分别为：单色塑件单腔注射功能、单色塑件双腔注射功能、单腔双色注射功能、单色+双色家族式注射功能,以及单模中注射两种不同颜色的同款塑件。模具结构新颖,简单实用,能有效降低多要求注射成型塑件的模具制造成本,有较好的设计参考价值。     

Presentation of a novel sensor based on acoustic emission in injection molding

Injection molding is the most important process to produce plastic parts. Because of increasing complexity of the plastic parts and the aim to reach zero‐defect production it is a must to control the dynamic injection molding process. Therefore information from the inside of the mold, measured with sensors, is necessary. State of the art is to implement wired mold cavity pressure sensors as well as wired cavity temperature sensors. This article presents a novel wireless measurement setup which uses structure borne sound as transport medium. The sound is generated by an acoustic actor which is activated by the passing flow front at certain predetermined positions in the cavity (or cavities). Beside the mechanical setup of the sensor proof of concept measurements with a prototype setup are shown in this article. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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     

Investigation of the Effect of Molding Variables on Sink Marks of Plastic Injection Molded Parts Using Taguchi DOE Technique

The quality of an injection molded part is affected by material properties, mold geometry, process conditions etc. Obtaining optimum process conditions and mold design is the key problem to improve the part quality. Sink mark is one of several important flaws of injection molded parts. In this article, numerical simulation is combined with Taguchi design-of-experiment (DOE) technique to investigate the influence of process conditions and cavity geometry on sink mark of the injection molded part and optimize process conditions and cavity geometry. An L18(3⁷) orthogonal array based on the Taguchi method was conducted to minimize the sink marks of injection molded parts, and the significance of each factors on sink mark was investigated. For the factors selected in the main experiments, part thickness, holding pressure, melt temperature and mold temperature were found to be the principal factors affecting the sink marks of the injection molded parts.     

Crystallization phenomena in the injection molding of poly ether ether ketone and its influence on mechanical properties

A basic experimental investigation of structure development in the injection molding of poly ether ether ketone (PEEK) is presented. It is shown that, dependent upon processing conditions, especially mold temperature, PEEK may be injection molded to form glassy or crystalline parts or parts consisting of intermediate structures such as a glassy surface and one with an internal crystalline link. In general, cold molds produce glassy parts and hot molds crystalline parts. This behavior is carefully characterized using optical microscopy, differential scanning calorimetry, and wide angle X-ray diffraction techniques. The mechanical properties of these injection molded parts is characterized as a function of the crystalline and glassy contents and types of structural gradients developed in the parts.