Experimental Investigation on Thermal Effects in Ultrasonic Joining of Thin Poly(ethylene terephthalate) Films Using Torsional Vibrations

Abstract

The authors previously determined that thermal effects are not a dominant factor in the ultrasonic joining of very low density polyethylene (VLDPE) films using torsional vibration. Now, to confirm that the plastic materials are not ''melted'' by mechanically generated heat in the joining, they have conducted joining experiments for thin poly(ethylene terephthalate) (PET) films. The temperature at the interface of two PET films of 0.1 mm thickness only increased to approximately 100 C, and no trace of liquidation of the material was observed at the interface under a polarizing microscope. Investigation using a differential scanning calorimeter (DSC) revealed that the ''melting point'' of PET is about 260 C, and an ultrasonically joined specimen showed no significant difference in thermal characteristics compared with an intact PET film. It was also determined that the PET films cannot be joined even after being pressed together for a period of 30 min or longer at approximately 150 C. From the results obtained using the microscope and the DSC, the authors conclude that melting of the materials plays essentially no role in ultrasonic plastic joining.

Experimental elucidation on the mechanism of ultrasonic joining of thin polyethylene films using torsional vibrations

“…Since the early 1990s, we have been striving to elucidate the mechanism of ultrasonic plastic joining, [1][2][3][4] which had begun to get used practically no later than the mid-1960s and is still one of the most sophisticated fabrication techniques in production engineering. We have already found that the thermal effect of high-amplitude ultrasonic vibrations is not a dominant factor in ultrasonic plastic joining and have decisively concluded that the plastic materials were actually not "melted" or welded at the joining interface by the ultrasonically generated heat during those joining processes in the previous studies.…”

“…We have already found that the thermal effect of high-amplitude ultrasonic vibrations is not a dominant factor in ultrasonic plastic joining and have decisively concluded that the plastic materials were actually not "melted" or welded at the joining interface by the ultrasonically generated heat during those joining processes in the previous studies. 3,4) Hence, molecular entanglement at the joining interface has been considered the core of the effect since then. However, despite the diligent efforts of a few researchers, [1][2][3][4][5][6][7][8] the joining mechanism has not been completely clarified yet and further development of this valid technology has thus been hampered.…”

“…3,4) Hence, molecular entanglement at the joining interface has been considered the core of the effect since then. However, despite the diligent efforts of a few researchers, [1][2][3][4][5][6][7][8] the joining mechanism has not been completely clarified yet and further development of this valid technology has thus been hampered.…”

Ultrasonic splicing of polymer optical fibres

“…SC, LC), which results in inconvenient on-site handling as well as insufficient mechanical strength for some applications where a large strain is applied. However, ultrasonic welding is known as a technique for fusing and connecting polymer materials [8,9]. With this technique, rapid well-sealed connections can be achieved without any consumable tools (including glue and solvent) because of the high repeated stress of the ultrasonic waves.…”

Molding and bonding of thermoplastic microfluidic devices

“…In this thesis, the interfacial temperature variation under ultrasonic actuation was measured by a pre-embedded sheathed thermocouple with junction-tip diameter of 197.8 (±11.2) μm. Though this method has been adopted in many related works [167,170,[250][251][252][253], several technical issues have been overlooked, such as vibration and movement of the embedded thermocouple joint, friction between the thermocouple joint and the surrounding polymer. In fact, it is exceedingly difficult to obtain accurate measurement of interfacial temperature under ultrasonic vibration.…”