Amplitude, Time and Pressure
In order for thermoplastic to be ultrasonically welded, there must be a correct balance between amplitude, time and pressure.
Amplitude is the vertical, vibratory, peak-to-peak movement produced by the convertor, modified by the booster and fine-tuned by the horn. This vertical motion (usually between 20-100 microns) applied under pressure causes molecular friction at the interface of the thermoplastic parts being joined. This friction causes the plastic to melt and flow through the joint. When the amplitude and pressure are released from the parts, the plastic resolidifies and the parts are welded. Certain ultrasonic welding applications require different amounts of amplitude in order to get a desired result. For example, ultrasonic staking requires more amplitude then ultrasonic inserting. Thermoplastics require different amplitude settings in order to get them to weld. As a general rule, amorphous polymers require less amplitude then crystalline polymers because of the difference in molecular structure.