Assessing a stepped sonotrode in ultrasonic molding technology

Ultrasonic molding is a new technology used to process polymeric micro-molded parts. An ultrasonic horn, or sonotrode, transmits ultrasonic energy which melts the material and pushes it into a mold cavity to configure a shape. Sonotrode design - and any transformations to the dimensions or shape caused by tool wear - strongly affects efficient operation. The sonotrode may go beyond the generator operating frequency range, thus affecting process performance. This paper assesses two issues involving a stepped sonotrode employed in ultrasonic molding: (i) a design procedure that can predict the sonotode's behavior during the molding process and (ii) a method for creating a sonotrode operating frequencies map which will facilitate the design of new sonotrodes and be able to determine the extent to which they can be re-machined after a certain period of wear. Numerical simulations carried out by finite element methods were compared to experimental measurements performed to capture the sonotrode frequency vibrational modes. A frequency map provides the dimensional range within which the sonotrode can be re-machined in order to eliminate tool wear and allow the sonotrode to work properly again, thus extending the lifecycle of the tool.