This paper deals with the contributions of stress and molecular orientation to the birefringence induced in an injection molded polymer strip. It is well known that the birefringence observed in polymeric materials is dominated both by the stress and by the molecular orientation produced in the polymer. This means that, in order to apply the measured birefringence for evaluation of the degree of molecular orientation, which results in anisotropic mechanical, optical and/or thermal properties of the molded strip, the stress-based birefringence and molecular orientation based birefringence must be separated from the total birefringence. In this paper, therefore, the generation of birefringence due to stress and molecular orientation was discussed on the basis of the master curve of the birefringence-strain coefficient.
Using the master curve in conjunction with the Boltzmann's superposition principle and time-temperature reducibility, the process of birefringence generation within an injection-molded polymer strip was numerically estimated. The results showed that the birefringence induced by the thermal strain is mainly due to molecular orientation in the core region, while the birefringence in the surface region is also dominated by the thermal stress. On the other hand, it was also shown that polymer melt flow during the filling stage of the injection-molding process results in the birefringence purely due to molecular orientation, and that the birefringence tends to be frozen in the surface region.

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The effects of molding conditions, such as the set temperature of the band heaters and the screw rotation rate, on the temperature history and distribution in the heating cylinder have been studied by measuring the barrel temperature and the temperature at the screw surface. The temperature history at the screw surface during the molding process was measured by using a thermocouple telemetry system. The measured results were compared with the set temperatures of the heaters. Representative PP and PS resins were used in the experiments.
The observed temperature distribution along the screw axis indicates a steep temperature rise at the feed zone, and it differs largely from the set values. The set temperature at the feed zone notably affects the temperature of the polymer melt in the compression and metering zones. The results obtained in this study will be useful for an optimum design of the heating cylinder and also for the construction of a CAE model.

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We examined two kinds of numerical analysis method for polymer melt flow in dies, that could reduce the memory capacity and the CPU time. The first method was an approximate analysis method in which the velocity field was calculated by a pure-viscous non-Newtonian model and the stress field was obtained by substituting the velocity field in a viscoelastic model. The second method was used a viscoelastic model in which the extra-stress is represented by an explicit function of the velocity and the deformation rate. It was found that both methods could reduce both the memory capacity and the CPU time. In the approximate analysis method, the stress calculation did not converge at high shear rates when we used the finite element method in previous work. But, in the present work, the stress solution could be obtained up to high shear rates using streamwise integration of the constitutive equation. The calculated results by the approximate analysis method were compared with the results obtained by a mixed method using the Giesekus model for tapered contraction flow. Both results agreed within the region where the shear and the elongational viscosities of the pure-viscous non-Newtonian and the viscoelastic models coincided with each other. But this method could not apply to a polymer with strain-thickening elongational viscosity because the pure-viscous non-Newtonian model could not represent its characteristics. In the second method, we used the Criminale-Ericksen-Filbey (CEF) model and a simplified-CEF model as the viscoelastic models in which the extra-stress was an explicit function of the velocity and deformation rate. The solutions for both models could not be obtained up to a high shear rate, but in the low shear rate region, the results using both models agreed with the results using the Giesekus model.

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Up to now, a number of CAE mold design software packages for simulating an injection molding process have been developed. For most of such software, it is necessary to know accurately the temperature of the resin injecting into the mold. It is, however, not very easy to measure the temperature due to heat generation caused by the shear flow between the resin and the thermocouple. A non-contact measuring method has been developed by using an infrared technique, but the infrared radiation is generated not only from the molten resin, but also from the surrounding solid surface. Moreover, the emissivity of the molten resin cannot be easily measured.
In this study, a method of measuring the molten resin temperature by using an ultrasonic technique has been developed. The temperature of the molten resin is related to the pressure and sound velocity, and the pressure is easily and exactly measured. Therefore, the temperature of the molten resin flowing through the nozzle and the barrel can be measured.

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This paper describes the method of measuring cavity pressure during the injection molding process. In this method, a thin metallic foil is placed on the cavity surface. The thickness of the foil is about 80μm and it must be large enough to cover the ultrasonic transducer.
From the experimental results, it was clear that the cavity pressure can be obtained by measuring the amplitude of ultrasonic waves reflected at the interface between the mold surface and the metallic foil placed on the mold surface. Moreover, it was clear that the relation between the cavity pressure and the amplitude of ultrasonic wave could be obtained if the roughness and hardness of the contact surfaces were clearly known.

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Presently, injection moldings of thermoplastics are widely used in many industries. When a crystalline or semi-crystalline thermoplastic is used, the crystallinity of the molded part can be directly related to its quality, that is, shrinkage, mechanical strength and so on. Many methods for measuring of the crystallinity have thus been proposed, although it is not very easy to measure the crystallinity.
In this paper, a new method of measuring the crystallinity of a molded part was developed. The crystallinity can be obtained in a nondestructive way by measuring the longitudinal sound velocity traveling through it because the sound velocity which is mainly related to the Young's modulus is different between amorphous and crystalline states. The measurement on a molded plate of high density polyethylene was carried out.

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Products manufactured by injection molding sometimes show unexpected defects and lack of precision in dimensions due to residual stress that occurs during the molding process. In order to optimize molding methods and conditions, it is necessary to clarify the mechanism generating this type of stress. The authors previously proposed a thermo-viscoelastic model with a dual-layered construction to explain the occurence of residual stress through the thickness of extrusion-molded products made of polyethylene. Based on accurate measurements of the material properties, the mechanism generating residual stress through the thickness was clarified in terms of thermally induced and distributions of material properties induced factors. In the present work, the thermo-viscoelastic model has been advanced from a dual-layered to a three-layered model in order to take into account the heat history and layered construction that are typically found in the thickness direction of injection molded products. This model demonstrated the generation mechanism of residual stress during the injection molding process and indicated that the factors inducing residual stress can be divided into the categories of thermally induced and distributions of material properties induced factors. The validity of the model was confirmed by comparing the results of quantitative calculations made with the finite element method and stress measurement data obtained from the layer removal method.

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When crystalline thermoplastic is used as an injected material, the crystallinity of the moldings depends on the cooling rate of the resin in the cavity. Therefore, a number of CAE software packages for simulating the cooling behavior of the filled resin have been developed, by assuming constant temperature of the resin through the nozzle. On the other hand, it is clear that the temperature of the resin injected from the nozzle into the cavity is not always constant. Moreover, the influence of the temperature variation of the injected resin on the crystallinity distribution in the moldings has not also been made clear.
In this paper, the temperature behavior of the resin injected into the cavity was related to the barrel temperature distribution and nozzle temperature. It is clear that the crystallinity distribution of the molded resin depends on the temperature behavior of the injected resin. From these experimental results, it is clear that the crystallinity distribution of the molded resin becomes nearly constant when the injected resin temperature through the nozzle is high at the initial injection stage, and becomes low after the initial stage.

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Warpage of two injection molded parts with similar geometry was investigated to clarify the key parameters for determining the qualitative warpage mode in injection molding. The geometry of one part (Case 1) included small ribs in addition to the geometry of the other part (Case 2). The basic geomerty of Case 1 and Case 2 were plate with three rectangular ribs, and were identical to each other. PET compounded with 30 weight % short glass fiber was used in the study. It was experimentally found that the warpage mode of Case 1 did not qualitatively coincide with that of Case 2. From thermal stress analysis and buckling analysis, it was shown that the difference of the fiber orientation states between Case 1 and Case 2 was not adequate for generating a qualitative difference in warpage mode between the two parts. The numerical analysis indicated that the Case 2 warpage was caused by the anisotropic material properties which were induced from the fiber orientation state. On the other hand, the buckling analysis indicated that the measured Case 1 warpage required an external force applied to the part during the injection molding. The possiblity was shown that external force influences to the warpage modes of injection molded parts. The detail investigations on the existence of the external force and on how the external force affects to the part warpage are left for the future study.

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A simultaneous composite injection molding (SCI. molding) process is a new process of molding composite parts in which two different melts are injected into one mold cavity simultaneously through two channels. This molding process has the outstanding advantages of high resin/resin bonding strength and low production cost compared with the conventional two-color injection molding. The sandwich injection molding process as well as two-color injection molding uses two injection units. However, since they use one common nozzle, some problems remain such as the limitation in the selection of materials. The SCI. molding process can solve these problems with the conventional sandwich injection molding.
In this study, we fabricated fiber reinforced thermoplastics articles with sandwich structures using the SCI. molding process. The effect of molding conditions on the sandwich structure was discussed. Two different materials with large differences in melting temperature can be fabricated. Bending tests were carried out, and composite beam theory and laminated beam theory were applied to predict the bending modulus. It was confirmed that sandwich composite injection molding has various unique properties i.e. high strength, low cost, low weight etc. The bending modulus of the sandwich beam showed good agreement with the theoretical value obtained by composite beam theory. This result suggested that a very strong interface could be formed between two different materials.

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This paper describes an experimental study of the wear of injection molded acetal gears on tooth flank.
For the driving gear, general-purpose acetal copolymer is used, while for the driven gear, 12 kinds of acetal resin for friction performance are used. The gear parameters are module=1.0mm, number of teeth=37, pressure angle=20° and face width=6.0mm. The gear precision for the driving and driven gears are JGMA Grade 0 to 3. The conditions of this experiment are as follows; fixed torque=0.3N·m, rotation rate=1000rpm, total number of revolutions=1×10⁶ times.
This experiment concentrated on the following 4 points. 1) Amount of wear, 2) Change on tooth flank, 3) Gear accuracy, 4) State of tooth surface (using a SEM).
The above observation shows that low friction coefficient acetal gears, with a few exceptions, are effective for wear decrease generally in proportion to their mechanical properties. Grading by JIS and by JGMA standards for gear accuracy do not always coincide, because these methods are basically different. Furthermore, a significant change in the tooth surface is seen around the pitch and this change depends on the combination of intermeshing gears. Lubrication of the driven gear also plays an important role in the state of wear and in friction performance. Therefore it is evident that the choice of the gear material has a great influence on the usage.

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