The surface quality of injection molded parts depends on the processing conditions, the cavity surface structure, the runner system, the used polymer and the part geometry. Different replication of the cavity surface structure to the molded part influences its surface function and visual appearance. A descriptive model of the replication process has been developed, taking into account the thickness of the frozen layer during injection. The expected dependencies were proven by systematic injection molding tests with geometric surface micro structures, having depths of 45 or 100 μm and widths from 400 to 2000 μm, that were replicated into high-crystalline polypropylene (HCPP) and polycarbonate (PC). The volumetric structure replication ratio increased with rising mold temperature, melt temperature and cavity pressure. As expected, the mold temperature was dominant for very small micro features. The RMS roughness, determined by confocal microscopy and atomic-force microscopy, was found to be a suitable replication parameter for draw-polished to mirror-finished stochastic cavity surface structures. An abrupt change in wall thickness decelerated the flow front velocity, thus decreased the replicated polymer surface roughness and increased the surface gloss. Moreover, a several micrometer high “surface step” remained, due to the different thickness-dependent shrinkage. This step always ascended from the thicker to the thinner part area. The replication of a mirror-finished mold surface into HCPP was dominated by morphological effects. Local micro shrinkage differences led to micro sink marks, which affected the surface gloss much more than the mold surface structure.

This study aimed at optimizing the injection molding process of an automotive oil filter housing made from PA6.6. Mass accumulations in its design intensely increased the cooling time. In a first successful approach, a copper alloy mold insert (λ = 106 Wm−1 K−1) that contains two externally cooled heat‐conducting copper pins (λ = 310 Wm−1 K−1) was installed. We hypothesized that a biomimetic cooling channel structure in a steel mold insert would even perform superior. Using simulation software Sigmasoft® v5.0, the mold insert materials (steel Bohler X20Cr13, Ampcoloy® 83), the plastics grade PA66‐GF35 (λ = 0.27 Wm−1 K−1 or λ = 0.40 Wm−1 K−1), and three cooling designs were evaluated for their impact on cooling the hot spots in the part: the copper pin‐system, a conformal cooling channel, and blood‐vessel like channels. In the latter, the major artery branches into two sub‐arteries, which further divide into two capillary tubes each. The capillaries merge into two sub‐veins and those fuse in the major vein again. As expected, the plastics heat conductivity dominates the cooling. The biomimetic (blood‐vessel) channels, as hypothesized, cooled the major hot spot more efficient than the conformal channel and the copper pin system do. In detail, compared to the heat‐conductive insert, the cycle time may be reduced by 10 s, in spite of the lower heat conductivity λ (23.5 Wm−1 K−1) of the steel insert. Using the biomimetic (blood‐vessel) structure in a heat‐conductive mold insert would reduce the cycle time by a further second. However, raising the heat conductivity of the plastics would save another 15s. Experimental tests proved the cooling efficiency. Nevertheless, cooling channels only perform well, if they are close enough to the mass accumulation. In conclusion, transferring biologic cooling structures to injection molding seems to be promising. Ongoing advances in Additive Manufacturing will help to efficiently implement these structures into mold inserts for injection molding. POLYM. ENG. SCI., 59:E180–E188, 2019. © 2018 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers.

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Structural characterization in polymer nanocomposites is usually performed using X-ray scattering and microscopic techniques, whereas the improvements in processing and mechanical properties are commonly investigated by rotational rheometry and tensile testing. However, all of these techniques are time consuming and require quite expensive scientific equipment. It has been shown that a fast and efficient way of estimating the level of reinforcement in polymer nanocomposites can be performed by melt extensional rheology, because it is possible to correlate the level of melt strength with mechanical properties, which reflect both the 3D network formed by the clay platelets/polymer chains as well as final molecular structure in the filled system. The physical network made of silicate filler and polymer matrix has been evaluated by X-ray diffraction and transmission electron microscopy. Extensional rheometry and tensile testing have been used to measure efficiency of the compatibilizer amount in a polypropylene-nanoclay system.

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