A study on ultrasonic welding of thermoplastics with significant differences in physical properties under different process parameters

Thermoplastics such as polypropylene (PP) and polyamide6 (PA6) with large different physical properties are difficult to welding. The novel ultrasonic welding device introducing the interlayer solder sheet (ISS) and interfacial compatibilization can realize the fusion bonding between PP and PA6. So it is necessary to discuss the influence factors on various process parameters for the mechanical welding performance of these materials. The better weld strength and morphology are related to weld time, weld load, and ISS components. When the process parameters vary in these ranges: welding time: 4-6 s, welding load: 5-7 N, PP-g-MAH contents: 30-70 %, the welding strength shows the better value, while the fracture surface and microstructure of welding interfaces show a perfect welding area with a much more smooth and defect-free uniform microstructure. The ISS with PP-g-MAH contents lower than 50 % has better plasticity, promoting the molecular chain inter-diffusion at the interface, which is beneficial to ultrasonic energy converting to the viscoelastic heat of the material. In addition, too short a weld time (<= 2 s) or load (0-2 N) result in lower weld strength with a small welding area for lower interfacial temperature, while too long a weld time (8 s) leads to defective structures at the weld interface, such as bubbles, holes, etc.

Automated summary

This study investigates the mechanical welding performance of thermoplastics (PP and PA6) using ultrasonic welding, and finds that weld time, weld load, and interlayer solder sheet components have significant effects on weld strength and morphology.