Evolution of Interfacial Friction Angle and Contact Area of Polymer Pellets during the Initial Stage of Ultrasonic Plasticization

Abstract

Interfacial friction heating is one of the leading heat generation mechanisms during the initial stage of ultrasonic plasticization of polymer pellets, which has a significant influence on the subsequent viscoelastic heating according to our previous study. The interfacial friction angle and contact area of polymer pellets are critical boundary conditions for the analysis of interfacial frictional heating of polymer pellets. However, the duration of the interfacial friction heating is extremely short in ultrasonic plasticization, and the polymer pellets are randomly distributed in the cylindrical barrel, resulting in the characterization of the distribution of the interfacial friction angle and contact area to be a challenge. In this work, the interfacial friction angle of the polymer pellets in the partially plasticized samples of polymethyl methacrylate (PMMA), polypropylene (PP), and nylon66 (PA66) were characterized by a super-high magnification lens zoom 3D microscope. The influence of trigger pressure, plasticizing pressure, ultrasonic amplitude, and vibration time on the interfacial friction angle and the contact area of the polymer pellets were studied by a single factor experiment. The results show that the compaction degree of the plasticized samples could be enhanced by increasing the level of the process parameters. With the increasing parameter level, the proportion of interfacial friction angle in the range of 0–10° and 80–90° increased, while the proportion in the range of 30–60° decreased accordingly. The proportion of the contact area of the polymer pellets was increased up to 50% of the interfacial friction area which includes the upper, lower, and side area of the cylindrical plasticized sample.

Modeling the Ultrasonic Micro-Injection Molding Process Using the Buckingham Pi Theorem

“…In our experimental trials (Exp. [6][7][8], not all parameter combinations successfully produced complete specimens using PP1. To ensure reliability and consistency, we have included in Table 8 only those combinations that yielded five complete specimens each.…”

Tuning Power Ultrasound for Enhanced Performance of Thermoplastic Micro-Injection Molding: Principles, Methods, and Performances

“…Additionally, Jiang et al [ 140 ] characterized the contact angle of some plastic polymer pellets (PMMA, PP, and PA66) with a super-high magnification lens zoom 3D microscope, taking into account the random stack of materials and extremely short interfacial friction heating time compared with the certain contact area of ultrasonic welding [ 151 ]. With the increasing parameter level, the proportion of interfacial friction angle in the range of 0°–10° and 80°–90° increased, while the proportion in the range of 30°–60° decreased accordingly, as shown in Figure 27 .…”

“…Theoretical research about UPMIM is currently lacking, mainly focusing on ultrasonic energy balance and heat generation mechanisms, including frictional heating [110,111,140] and viscoelastic heating [20,55]. Up to now, although the heat mechanism of ultrasonic welding has been reported [141][142][143][144], the research on the thermal mechanism of ultrasonic plasticization of polymer still needs further improvement.…”

Polymer–Metal Interfacial Friction Characteristics under Ultrasonic Plasticizing Conditions: A United-Atom Molecular Dynamics Study

“…With its benefits of rapid heat generation, low energy consumption, and high material usage rate, ultrasonic plasticization microinjection molding (UPMIM) technology has recently become an appealing version of thermoplastic microinjection molding [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. Interfacial friction in UPMIM plasticizing units has aroused researchers’ curiosity to understand the quick heat generating mechanism [ 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. Michaeli et al [ 15 ] investigated the heating mechanism during ultrasonic plasticization using theoretical analysis and determined that heat generation was mostly due to polymer damping characteristics and polymer–polymer interfacial friction.…”