Intrinsic Factors Affecting the Ultrasonic Welding Performance of Plastic Parts
Plastic properties:
Plastics are divided into thermoset plastics and thermoplastics.
Thermoset plastics are plastic but irreversible. When heated for the first time, the flow can be melted, heated to a certain temperature, and a chemical reaction occurs. The cross-linking solidifies and hardens to form a solid; but this change is irreversible, and the thermosetting plastic cannot be melted again when it is reheated. Therefore, ultrasonic welding cannot weld thermosetting plastics.
Thermoplastics are plastic and reversible. When the first heat forms a solid, its internal structure undergoes only a change in morphology and is reversible; when reheated and pressurized, it can be remelted and solidified again. Ultrasonic welding is capable of welding most thermoplastics.
Thermoplastics are further divided into amorphous plastics and semi-crystalline plastics.
Due to the different molecular structure and arrangement of the two, the ultrasonic welding performance of the two is different.
The molecular structure of amorphous plastics is randomly distributed, without a clear melting point Tm, which gradually softens, melts and flows over a wide range of temperatures; instead of melting from solids immediately upon heating to a certain temperature, then immediately Cured. This property of amorphous plastics is very easy to conduct ultrasonic vibration and enables ultrasonic welding over a wide range of pressures and amplitudes.
The molecular structure of semi-crystalline plastics is regularly distributed locally, with a clear melting point Tm. The semi-crystalline plastic remains solid until the temperature reaches the melting point; when the temperature reaches the melting point, the entire molecular chain begins to move immediately and solidifies immediately.The difference in the melting process between amorphous plastics and semi-crystalline plastics is shown in the figure below.
