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3. Experimental StudyIn the hot runner experiment, the mold structure is same as in Fig. 1.The injection molding process is conducted cycle by cycle. Table 2shows the molding parameters. The temperature measuring will beapplied after five shots to make sure that the melt temperature reachesmore stable state.4. Results and DiscussionsThe simulating results are shown and discussed first, including melttemperature distribution inside of the melt channel and moldbase. Inthe experimental result, the melt temperature as function of the certainlocations is measured and plotted. The simulating result is comparedwith that from the experiment. The comparison shows the goodagreement both in trend and magnitude.4.1 Simulation ResultsFig. 4 displays the simulating melt temperature field inside therunner or melt channel at the end of ten injection molding cycles. Thesensor node 2 (as shown in Fig. 2) detects higher melt temperaturearound the area with the bottom heating coil. The sensor node 10detects much lower melt temperature not only because of the coolingchannel and heat conduction contact with the metal mold but alsobecause of the gate area. In Fig. 4(a), since the first sensor node (1A) location is too close the cooling channel, the melt temperature is alwayslower than 278oC. The first heating coil is always turned on. From thefirst cycle to the 10th cycle, the first heating coil keeps going togenerate heat to melt system, around the first coil area has beenaccumulated too much heat. The temperature profile of melt is around81-453oC. It is not a good setting for industrial operation. The impropersetting will damage polymer melt, and will further impact the productquality significantly. Moreover, in Fig. 4(b), when the sensor nodesgroup for the heating coil setting is changed to 1B, 2B, and 3B, thetemperature control is in a good shape. The temperature profile of meltis around 81-300oC with no damage for melt.4.2 Experimental ValidationThe figure 5 shows the experimental melt temperature distributionsas function of locations using controlling sensor nodes 1A, 2A, and 3A.The temperature was measured after five injection molding cycles andassumed to reach steady state in the real mold trials. The simulatingresult is also plotted together and compared with the experimental one.The profile can be pided into three zones: the low-temperautre zonenear the gate area, the high-temperature with the bottom coil (610 W),and the flat zone close to 280 degree. The figure 6 shows theexperimental melt temperature distributions as function of locationusing controlling sensor nodes 1B, 2B, and 3B. In the experimentresult, there is no obvious high-temperature region at the position of60 mm. The simulation result also indicates this phenomenon. This isdifferent with the previous case. The profile in this case can be onlypided into two zones: the low-temperautre zone near the gate area
and the zone close to 280 degree. The high-temperature zone can beremoved completely.In the above two cases with different sets of controlling sensornodes, the comparisons between the simulating and experimentalresults indicate good agreement in both trend and magnitude.5. ConclusionsTo realize the mechanism of hot runner, we have performed bothnumerical simulation and experimental studies in a single melt channelsystem. The numerical results are compared with the experimentalresults. The simulating results are in a good agreement with those fromthe experimental in both trend and magnitude. Moreover, some keypoints we can summarize are as follows:1. Conventionally, the melt temperature (quality) along the meltchannel is assumed in a good uniformity. In reality, it is stronglydependent of the runner design and the temperature sensor andcontrol system.2. In a single melt channel hot runner, the temperature sensor andcontrol is very important for melt quality control. Even the impropersensor node installation, some melt temperature variation can beover one hundred degree (see Fig. 4(a) and (b)). The poor meltquality will further affect product quality and life cycle, but it isvery difficult to detect.3. For many real hot runner designs, they are more complicated toinclude manifold, multiple melt channels, and complex heatingzones. How to make sure that the melt uniformity is good to savematerial is one of the crucial topics for further study. And CAEtechnology is a good method to help us visualize the insidemechanism.