The four stages of ultrasonic welding
In recent decades, with the large-scale application of plastics and composite materials in industrial production and daily life, as well as the rapid development of the electronics industry and the emergence of new high-power transducers, plastic ultrasonic plastic welding machines are characterized by their fast welding speed and welding seam. The advantages of good quality, easy automation, and suitability for mass production have been widely used and become the most commonly used plastic welding method.
1. The principle and process of ultrasonic welding
The basic principle of ultrasonic plastic welding machine is to use ultrasonic frequency mechanical vibration (frequency is 10~70kHz, amplitude is 1~250μm) to act on plastic parts, causing local heating under pressure (heating is due to the combined effect of surface and molecular friction) The result) and melting to form a weld. The ultrasonic welding process is divided into 4 stages:
Phase 1: The welding head contacts the part, pressurizes and starts to vibrate. The heat of friction melts the energy-conducting ribs, and the melt flows into the joint surface. As the distance between the two parts decreases, the welding displacement (the decrease in the distance between the two parts due to the flow of melt) begins to increase. The welding displacement increases rapidly at first, and then slows down when the melted energy guide bars spread out and contact the surface of the lower part. In the solid state friction stage, heat is generated due to the friction energy between the two surfaces and the internal friction in the part. Friction heating causes the polymer material to heat up to its melting point. The calorific value depends on the frequency of action, amplitude and pressure.
The second stage: the increase of the melting speed causes the increase of the welding displacement and the contact between the surfaces of the two parts. A thin melted layer is formed at this stage, and the thickness of the melted layer increases due to continuous heating. The heat at this stage is generated by viscous dissipation.
The third stage: the thickness of the solution layer in the weld remains unchanged and with constant temperature distribution, steady state melting occurs.
Stage 4: After a set time or a specific energy, power level or distance is reached, the power is cut off, the ultrasonic vibration stops, and the fourth stage begins. The pressure is maintained so that part of the extra melt is squeezed out of the bonding surface. The maximum displacement is reached when the weld is cooled and solidified, and intermolecular diffusion occurs.