Enhancing the mechanical integrity of Polylactic acid components via ultrasound-assisted rotary friction welding for sustainable medical device fabrication

Abstract

Polylactic acid is extensively utilized in the fabrication of medical devices due to its biocompatibility and degradability. However, the dimensional limitations of additive manufacturing platforms necessitate segmenting large medical devices into multiple components for printing, followed by post-fabrication assembly. Currently, mechanical fasteners such as nuts and bolts are commonly used in laboratory settings to join these printed segments. However, this approach faces critical challenges, including loosening or detachment of fasteners due to repetitive movements in large medical devices, leading to compromised structural integrity and reliability. To address these challenges, this study focuses on developing an advanced joining method for PLA polymer rods using ultrasound-assisted rotary friction welding (UARFW). The proposed technique significantly enhances joint strength while aligning with sustainable development goals through its high energy efficiency and reduced environmental impact. The ultrasonic waves applied during UARFW promote the flow of molten material within the weld zone, which is crucial for achieving superior mechanical properties. This research demonstrates that the positioning of the ultrasonic oscillator along the Z-axis of the CNC lathe critically affects the weld quality. Optimal joint performance is achieved at a 5 mm displacement, resulting in a 97 % increase in bending strength due to enhanced molten material flow. Fracture analysis indicates that failures predominantly occur within the base material rather than at the weld interface, confirming that the weld interface exhibits superior strength. Moreover, the surface hardness of the weld interface increases by up to 25.7 % compared to conventional rotary friction welding without ultrasonic-assisted micro-vibrations. Numerical simulations are employed to model the temperature distribution within the weld bead, and the results show excellent agreement with experimental data, with a deviation of only 0.6 %. These findings validate the reliability of the proposed numerical approach and highlight the potential of UARFW as a robust and sustainable joining method for the assembly of larger medical devices.