Most advanced technologies developed nowadays focus on issues such as minimizing manufacturing cost and improving product quality. Cooling system design is one of the most critical factors to reduce cycle time. Conformal cooling is the concept which can reduce cooling time and improve product quality as well. However, cooling system layout is restricted by traditional molding method. For cavities with irregular geometry, the distance between cooling channels and cavity may vary throughout the part. This causes local heat accumulation and some product defects such as sink mark and warpage. By using some non-conventional methods such as laser sintering, cooling channels can get closer to the cavity surface than using traditional method. This leads to a shorter cooling time. The current study uses a true three dimensional simulator to predict cooling time and compare the results from a conventional and a conformal cooling design. The results also show flow behavior inside cooling channels which provide important indices for cooling system design revision. With a shorter cycle time and an improved product quality, conformal cooling has a great potential in injection molding industry.

An effort was made to study the damage mechanisms in both thermoplastic and thermoset composites in response to repeated low-velocity impacts. An instrumented falling-dart impact tester was used that provided the load-deflection and energy-deflection curves plus other numerical data on material properties. Both poly(phenylene sulfide) (PPS) and epoxy composites prepared from different preform styles and stacking sequences were tested. For any composite with given dimensions a threshold incident impact energy (Ec,) could be identified above which delamination would occur at the first impact. As a consequence, both the stiffness and the strength of this composite were reduced and these properties could be measured using the same impact tester as a function of impact cycles. If instead a subcritical incident energy (Ein < Ec) was imposed on the material, no appreciable property loss would be observed until a critical number of impact cycles (Nc) was reached. In this subcritical stage, matrix cracking preceded delamination as impacts were repeated. Both the number and size of delamination cracks were then found to increase as the number of repeated impacts was increased. An elastic strain energy approach was developed to predict the threshold incident energy values of various composites and the prediction was found to be in good agreement with the experimental data. Distinct failure mechanisms were found to exist between epoxy and PPS composites.

In recent years, the use of long fiber‐reinforced thermoplastics (LFRT) has become one of the most popular materials in lightweight applications. However, the microstructure of the fiber inside the plastic matrix is quite complex, making it hard to fully control the fiber effect in the injection molding process. On the other hand, the screw structure and operation will affect the residual fiber length significantly. However, the mechanism of how the screw influences the fiber breakage is still not yet clear. Thus, in this study, we apply the screw plastication in the injection molding process to investigate the fiber microstructure mechanism. The results show that more severe fiber breakage occurs when the compression force increases abruptly. Generally speaking, the breakage increases from the compression to the metering section. One effective method to reduce the fiber breakage is to increase the channel depths in both the feeding and the metering sections while taking the plastic melt quality into consideration. Moreover, the fiber breakage phenomena for two types of fibers are also investigated. Evidently, carbon fiber is easier to be broken. Its length distribution has a higher peak at the exit of the screw. This discovery is consistent with the experimental results of the current literature studies. POLYM. ENG. SCI., 58:452–459, 2018. © 2017 Society of Plastics Engineers

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