ACOUSTIC TOOLING & ULTRASONIC ASSEMBLY

Ultrasonic Plastic Welding Horn & Acoustic Sonotrode Vector Guide

Ultrasonic plastic welding utilizes high-frequency acoustic vibrations ($20\,\text{kHz} - 40\,\text{kHz}$) transmitted through an acoustic stack (piezoelectric transducer, booster, and custom sonotrode horn) under pneumatic clamping pressure to generate frictional intermolecular heat at joint interfaces.

1. Acoustic Half-Wavelength Resonant Length ($L$)

Sonotrodes must be tuned so their longitudinal axial dimension equals exactly one half acoustic wavelength: $L = c / (2f)$, where $c = \sqrt{E/\rho}$ is the speed of sound in the material and $f$ is the system frequency. At $20\,\text{kHz}$, nominal half-wave length is $\approx 126.7\,\text{mm}$ in Titanium Ti-6Al-4V and $\approx 127.0\,\text{mm}$ in Aluminum 7075-T6.

2. Joint Design: Energy Directors vs Shear Joints

3. 2D CNC Turning Profile Prepress Checklist

• Continuous Spline Tangency: Ensure sonotrode profile CAD drawing uses single-span G02/G03 blend arcs or smooth NURBS splines at step transitions to avoid high-cycle acoustic fatigue failure.
• Nodal Clamping Ring: Position O-ring isolation mounting grooves precisely at the nodal displacement zero ($Z = L/2$).
• Contact Face Matching: Vectorize mating part contours with $0.05\,\text{mm}$ precision to ensure uniform contact pressure without localized burning or decoupling cavitation.