Shrinkage behavior and mechanical performances of injection molded polypropylene/talc composites

In this research, the influences of adding talc mineral particles of 10 μm particle size on the shrinkage and the mechanical properties of injection molded polypropylene (PP)/talc composites were investigated. PP has a crystalline molecular structure and hence it possesses nonisotropic shrinkage along and across the flow directions. Addition of the talc mineral filler to PP induced an isotropic shrinkage in the molded part because of the nonisotropic shape of talc particles. The results of experiments indicated that the maximum flexural strength, maximum impact strength, and isotropic shrinkage were achieved by adding 10, 20, and 30 by weight percent of talc respectively. By incorporating of 10 wt% of talc particles into the PP matrix, the tensile strength was hardly affected but the occurrence of cold drawing phenomena in the tensile test was hindered considerably. The flake‐shape structure of talc filler played an important role in determining the molded part shrinkage and mechanical properties. POLYM. ENG. SCI., 47:2124–2128, 2007. © 2007 Society of Plastics Engineers     

Shrinkage anisotropy in fiber reinforced injection molded products

This paper includes a systematic study of the effect of fiber concentration and molding conditions on fiber orientation and shrinkage in injection molded composites. Closed-form expressions were derived to relate shrinkage and internal stresses to the molding pressure and fiber orientation. The shrinkage predictions were seen to agree well with experimentally measured shrinkages.     

A novel method for improving the surface quality of microcellular injection molded parts

Microcellular injection molding is the manufacturing method used for producing foamed plastic parts. Microcellular injection molding has many advantages including material, energy, and cost savings as well as enhanced dimensional stability. In spite of these advantages, this technique has been limited by its propensity to create parts with surface defects such as a rough surface or gas flow marks. Methods for improving the surface quality of microcellular plastic parts have been investigated by several researchers. This paper describes a novel method for achieving swirl-free foamed plastic parts using the microcellular injection molding process. By controlling the cell nucleation rate of the polymer/gas solution through material formulation and gas concentration, microcellular injection molded parts free of surface defects were achieved. This paper presents the theoretical background of this approach as well as the experimental results in terms of surface roughness and profile, microstructures, mechanical properties, and dimensional stability.     

灯具注塑件真空镀膜附着力等检查方法

检查灯具注塑件真空镀膜附着力是验证镀膜零部件表面膜层质量水平的一项重要指标,镀膜附着力的好坏直接影响镀膜零部件的防蚀性和使用效果。本文应用国家标准的和结合实际的情况,介绍了镀膜附着力测试方法和其他测试项目对附着力作用的阐述,旨在帮助大家对真空镀膜附着力检查,以正确选用方法进行镀膜附着力等测定,保证镀膜质量。     

Reduction of internal stresses in injection molded parts by metallic fillers

The build-up of internal stresses in injection molded parts is due to the combined effect: of a low thermal conductivity (diffusivity) of normal polymer melts and their rapid cooling in the mold cavity. The present paper shows that increasing the thermal diffusivity of the polymer by the addition of relatively small amounts of metallic fillers resulted in a substantial reduction in the internal stress level. The filler content was of the order of a few percent by volume. The average internal stress (σ_i) was determined by a stress relaxation method. The modulus, tensile strength, and other mechanical properties of the samples were not influenced by the filler addition. The impact strength, however, decreased sharply, as no adhesion pro-motors were used. The observed improvements in mold shrinkage, thermal shrinkage, hardness, and stress-cracking tendency could be related to a decreased σ_i level. In comparative experiments with other fillers (MgO, glass powder), a good correlation was found between the σ_i level and the thermal diffusivity of the filler.     

Bubble growth in reaction injection molded parts foamed by ultrasonic excitation

Processing of microcellular foam was studied for polyurethane. Assuming that the bubble growth is controlled by diffusion, theoretical prediction was carried out numerically to understand the bubble growth mechanism in the cavity during mold filling. Final bubble sizes were also predicted by considering the gelation time and the diffusion boundary. Viscosity change of the mixed polyurethane resin during polymerization reaction was predicted by considering reaction kinetics. The gelation time was determined to terminate the numerical calculation. The diffusion boundary was predicted based on the number of nucleated bubbles that had been determined both theoretically and experimentally. For processing of polyurethane foam by reaction injection molding, ultrasonic excitation was applied to the mixture of polyol and isocyanate. The polyol resin was supersaturated with nitrogen gas at an elevated pressure and ultrasonic excitation was applied to the mixture after impingement mixing of two components of the selected polyurethane system. Bubble nucleation was induced by the ultrasonic excitation and the bubbles were grown as the gas was supplied to the bubble from the resin.     

基于注塑件翘曲优化及影响因素分析

随着信息产品和电子产品的发展,对注塑制品的质量提出了更高的要求,如轻便、小巧等,这就促使了薄壳制品的出现。由于制件的壁薄（一般为1-2mm）,所以更容易出现收缩、翘曲、残余应力等缺陷。对于薄壳制品而言,翘曲变形形严重影响制品的质量。本文就翘曲变形进行探讨分析。     

Nondestructive and fined characterization of injection molded ceramic parts by industrial computed tomography

Nondestructive testing technology of industrial computed tomography(ICT) is introduced to investigate the injection molded bodies (green body, debinded body and, sintered part) in this study. The results show that ICT can characterize the defects qualitatively and quantitatively by comparing and analyzing the gray distribution of ICT images. The size, numbers and location of pores can be characterized precisely and the density distribution of the green body is quantitatively evaluated. The structure difference and evolution related with processing parameters is also analyzed by this technique. In addition, an image processing method is introduced to three-dimensional reconstruct the two dimensional images after threshold segmentation, and observe the internal structure and spatial morphology of the green body.     

Integrated simulation to predict warpage of injection molded parts

Injection molding analysis programs were developed for CAE (Computer Aided Engineering) in injection molding of thermoplastics. The programs consist of mold cooling, polymer filling-packing-cooling, fiber orientation, material properties and stress analyses. These programs are integrated to predict warpage of molded parts by using a common geometric model of three dimensional thinwalled molded parts. The warpage is predicted from temperature difference between upper and lower surfaces, temperature distribution, flow induced shear stress, shrinkage, and anisotropic mechanical properties caused by fiber orientation in the integrated simulation. The integrated simulation was applied to predicting warpage of a 4-ribbed square plate of glass fiber reinforced polypropylene for examination of its validity. Predicted saddle-like warpage was in good agreement with experimental one.     

Flow behavior of LCP melts and its influence on morphology and mechanical properties of injection molded parts

The flow behavior of two commercial liquid crystalline polymers (LCP), Vectra B 950 and Vectra L 950 (Ticona GmbH), was investigated using a capillary rheometer with a new double slit die. The influence of pre‐shearing of the melt on its viscosity and the apparent geometry dependence of its flow behavior were analyzed. The dependence of flowability on the part was determined with a modular spiral mold in which the thickness of the channel was varied. The influence of processing parameters and part geometry on the mechanical properties and morphology of molded parts was also studied.     

Molded geometry and viscoelastic behavior of film insert molded parts

Virgin injection‐molded tensile specimens without any inserted film and four kinds of film insert molded (FIM) tensile specimens were prepared. They were annealed at 80°C to investigate the effect of residual stresses and thermal shrinkage of the inserted film on thermal deformation of tensile specimens. The FIM specimens with the unannealed film were bent after ejection in such a way that the film side was protruded and the warpage was reversed gradually during annealing and the film side was intruded. Warpage of the FIM specimen with the film annealed at 80°C for 20 days was not reversed during annealing. Processing of the FIM specimens have been modeled numerically to predict thermoviscoelastic deformation of the part and to understand the warpage reversal phenomenon (WRP). Nonisothermal three‐dimensional flow analysis was carried out for filling, packing, and cooling stages. The flow analysis results were transported to a finite element stress analysis program for prediction of deformation of the FIM part. The WRP was caused by the combined effect of thermal shrinkage of the inserted film and relaxation of residual stresses in the FIM specimen during annealing. It is expected that this study will contribute towards the improvement of the FIM product quality and prevention of large viscoelastic deformation of the molded part. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Evaluation of polymer injection molded parts via density-based magnetic levitation

The quality of polymer injection molded parts is definitely related to the molding process. Polymer injection molded parts with different properties differ in density and internal density distribution. This paper proposes a novel evaluation method for polymer injection molded parts through magnetic levitation (MagLev) to detect the differences among products by means of their densities and density distributions. Three cases of polycarbonate lenses are employed as samples in the experiments: lenses produced at different processing parameters, lenses obtained from different cavities in one mold, and those with different interior defects. The lenses obtained at different processing parameters differ in density, and those with different defects exhibit different behaviors during the levitation. The MagLev testing method shows its capability in distinguishing minute differences among the densities (< 0.0005 g cm−3) that even the subtle distinctions among the lenses formed from different cavities in one mold can be detected. Further analysis demonstrates that minute changes in thickness (2.5 μm) can also be detected. The theoretical analysis and experimental results indicate that the MagLev testing method is applicable to the evaluation of polymer injection molded parts. Moreover, the method affords advantages, such as high accuracy, high sensitivity, and convenience. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48431.     

Thermoset injection molding dynamics and the distribution of cure in thermoset molded parts

A detailed characterization of a commercial-filled unsaturated polyester molding compound has been carried out to determine the kinetics of cure and the rheological behavior of the material at various temperatures and shear rates. Molding experiments were conducted in a 2 1/3 oz, 68 ton reciprocating screw injection molding machine, in conjunction with a simple rectangular cavity. The cavity and nozzle were equipped with pressure transducers to determine, the variation of pressure with position throughout the injection molding cycle. The injection speed was determined with the help of a position transducer. Finally, the moldings were analyzed to determine the distribution of cure states and tensile properties in the molding at various cure times. Significant differences have been observed. It is expected that studies of this type should be helpful in obtaining a better understanding of the thermoset injection molding process and the development of mathematical models to simulate this process.     

The influence of knit-lines on the tensile properties of injection molded parts

When injection molding complex parts, often knit-lines are formed during the mold filling stage. These knit-lines are well-known as particularly critical regions in the mold when mechanically loaded. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter and the effects of the knit-lines on the tensile properties of injection molded plates with holes is quantified by the variation of a socalled knit-line-factor a_k1. Finally, for PS a comparison of the influence of knit-line-formation by a splitted melt stream and by multi-gating on the mechanical level is given.     

Some relationships between injection molding conditions and the characteristics of vitrified molded parts

The various mold filling phenomena influencing the characteristics of fabricated parts are surveyed. The phenomena leading to jetting in injection mold filling are considered. These are associated with the magnitude of swell by the melt as it exits the gate into the mold. Special attention is given to the influence of non-isothermal runner flow. A theory of extrudate swell of polymer melts with temperature profiles is developed using Tanner's unconstrained recovery theory. In the. absence of jetting, mold filling by a simple advancing front takes place. The hydrodynamics of the advancing front and the stress fields in the flowing melt are determined. Analysis and modeling are presented based on the use of hydrodynamic lubrication theory involving a solid layer along the mold wall and a hot isothermal melt core. This theory is compared with experimental measurements of pressure losses in mold filling. The development of birefringence in injection molding processes is analyzed. Birefringence distributions are due to frozen-in flow birefringence. A new experimental study is presented and its results compared with theoretical predictions. The problem of thermal stresses in injection molded parts is considered.     

Prediction of fiber orientation in injection molded parts of short-fiber-reinforced thermoplastics

Fiber orientation induced by injection mold filling of short-fiber-reinforced thermoplastics (FRTP) causes anisotropy in material properties and warps molded parts. Predicting fiber orientation is important for part and mold design to produce sound molded parts. A numerical scheme is presented to predict fiber orientation in three-dimensional thin-walled molded parts of FRTP. Folgar and Tucker's orientation equation is used to represent planar orientation behavior of rigid cylindrical fibers in concentrated suspensions. The equation is solved about a distribution function of fiber orientation by using a finite difference method with input of velocity data from a mold filling analysis. The mold filling is assumed to be nonisothermal Hele-Shaw flow of a non-Newtonian fluid and analyzed by using a finite element method. To define a degree of fiber orientation, an orientation parameter is calculated from the distribution function against a typical orientation angle. Computed orientation parameters were compared with measured thermal expansion coefficients for molded square plates of glass-fiber-reinforced polypropylene. A good correlation was found.     

Crystal distribution and molecule orientation of micro injection molded polypropylene microstructured parts

Polypropylene (PP) microstructured part which comprises micro columns array and a macroscopical base plate was manufactured by micro injection molding. The morphology distribution in micro columns is quite different from that of the base plate. This article investigates the crystal distribution and molecule orientation of the microstructured part by X‐ray diffraction. The hardness of shear zone of micro columns was evaluated by Nano Indenter. Test results show that both micro columns and macroscopical base plate contain α and β phase. However, the relative proportion of β phase in micro columns is markedly higher than that of the base plate. β phase distributes only in the shear zone of the microstructured part. So, the mechanical properties of micro columns must differ from that of the base plate. In addition, the orientation of Ø100 μm micro columns is slight, which indicates that the mechanical anisotropy of micro columns induced by orientation could be ignored. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Evaluation of molecular orientation in injection molded parts with microscale features by Raman spectroscopy

Molecular orientation of polycarbonate (PC) in injection‐molded parts with microscale features was characterized by means of polarized Raman spectroscopy, and the relationship between microstructure and replication was discussed. The microscale feature size of continuous v‐groove was 20 μm in depth and 50 μm in width. PC injection‐molded parts were molded with various molding conditions. The molecular orientation distribution along flow direction on the cross‐section of molding parts were evaluated by the intensity ratio of the bands at 635 to 703 cm^?1 (I₆₃₅/I₇₀₃) in the Raman spectra. Molecular orientation along the flow direction inside the v‐groove was higher than that of the core and the opposite surface region. In particular, the highest molecular orientation was at the surface of the v‐groove. Among the injection molding conditions, the mold temperature showed significant effect on the molecular orientation and replication. Higher mold temperature caused high replication and low molecular orientation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characteristics of thermoplastics containing electrically conducting asymmetric particles: Anisotropic electrical conductivity of injection molded parts and extrusion behavior

The characteristics of compounds of acrylonitrile-buta-diene-styrene and high impact polystyrene resins, filled with carbon fibers, steel fibers, carbon black, and aluminum flakes have been investigated with special emphasis on electrical conductivity and flow behavior in a capillary rheometer. Compression and injection molded compounds were found to be highly electrically anisotropic. The components of the electrical conductivity tensor, K₁₁, K₂₂ and K₃₃, were measured, Generally K₁₁, the flow direction conductivity, has the highest value and the thickness direction, and K₃₃ has the lowest. The injection molded parts were usually electrically heterogeneous with the conduetivities highest at the greatest distances from the gate. The results were interpreted in terms of particle orientation and distribution. Shear viscosities were measurable for all but the aluminum flake compounds which exhibited fluctuating pressure drops. The flow of these compounds through dies was investigated. Examination of material from the die entrance indicated streamline flow without entrance vortices. Sometimes high entrance concentration of particulates were observed especially for the aluminum flakes. Extrudates were found to contain oriented particles.     

Foam formation in gas-assisted injection molded parts: Theoretical and experimental considerations

This article is concerned with a physico-mathematical model to describe the foaming phenomenon in gas-assisted injection molded parts. The investigations have been conducted on polycarbonate grades to begin with. When parts are produced by gas injection molding, foam has the effect of weakening the residual wall thickness and also of impairing optical quality. It would thus be an advantage if a parameter constellation could be defined in advance, which would ensure the suppression of foam formation.