Characteristics and mechanisms of polymer interfacial friction heating in ultrasonic plasticization for micro injection molding

With the capability of plasticizing just the small amount of polymer melt required for micro parts, ultrasonic plasticization is believed to be a promising alternative solution for micro injection molding. However, the heat generation mechanism during ultrasonic plasticization process has not been fully understood yet. In this paper, the research focus was put on the heat generation mechanism, specifically the interfacial friction heating mechanism. Experimental and numerical schemes were designed and conducted to understand the characteristics of the interfacial friction heating phenomenon and the influence mechanism of process parameters such as the ultrasonic amplitude and the applied plasticizing pressure. The results indicate that the interfacial friction heating of polymer granulates is a transient process with inhomogeneous temperature field around the interface. The interface could have a steep temperature increase up to polymers flow temperature in 0.078 s in the case of polymethyl methacrylate granulates. The interfacial friction heating phenomenon occurs and lasts only until the interfaces disappear, meaning that it acts only at the initial stage of ultrasonic plasticizing process. The interfacial friction heating flow rate increases with increased ultrasonic amplitude. In comparison, the ultrasonic amplitude was confirmed to have more significant impact than the plasticizing pressure on the interfacial friction heating.