Closed-Loop, Rapid Polymer Welding Using Radio-Frequency Heating

Polymer components are becoming more prevalent in load-bearing applications due to their superior strength-to-weight ratio. Thermoplastics, particularly, have gained traction in recent years due to their ability to be molded, recycled, and reused. Effective welding and joining methods are essential to facilitate the assembly of intricate thermoplastic parts; but these manufacturing processes are energy expensive and depend on the processed materials. We have developed and energy efficient closed-loop method that utilizes a recent discovery that radiofrequency (RF) fields rapidly heat up carbonaceous materials. We developed a machine capable of monitoring the material's pressure, deformation, and thermal response during the assembly process; this closed-loop system does not require human intervention to process the materials. In this work, we will show that the closed-loop machine can rapidly weld thermoplastics using RF heating at the bondline; to process these materials, we can control the pressure or displacement of the welds to ensure desired mechanical properties. Our initial experiments showed that we can successfully weld polylactic acid (PLA) coupons with graphitic RF susceptors at the bond line in less than 2 minutes, utilizing less than 50 W of RF power. The weld properties show no significant variation within a 0 to 0.3 MPa pressure range. However, an increase in out-of-plane welding displacement enhances the modulus and strength of the weld. This work introduces an energy-efficient, automated system for welding polymer composites using RF fields, showing promise for diverse manufacturing applications. The machine can be used in three control settings: hold, displacement, and pressure control. We saw excellent RF heating response of conductive carbonaceous coatings on polymers; this rapid heating was used for RF processing and bonding thermoplastics using less than 50 W of RF input powers in an automated manner.