On-line ultrasonic monitoring of injection molding of polyethylene and die casting of aluminum is studied using pulse-echo techniques. The flow front of molten materials including the polymers and aluminum inside the mold has been probed by a multiple-channel probing system with a time resolution of about 1 ms. This information can be used to control the plunger movements. The gap development which is important for the understanding of the thermal contact between the mold and the part due to the shrinkage is also monitored. Gap formation time periods versus different packing pressure and at different part locations with different part thickness have been investigated. The ultrasonic velocity inside the part during the solidification has been also measured for the interpretation of the solidification process.;For monitoring the die casting of aluminum with a melt temperature above 690°C, novel high performance buffer rods together with cooling channels are integrated into the die thus the ultrasonic measurement such as flow front and gap formation can be carried out with high signal-to-noise ratio signals for the first time at such elevated temperature.
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