Which Plastics are Suitable for Ultrasonic Welding?

Materials made of the same plastic and materials made of different plastics can be connected using multiple methods. For example, welding is a common joining process. Especially when the adhesive cannot guarantee sufficient or long-lasting connection. Plastic welding is not a surface bond; This is a strong material bond. However, this only applies to so-called thermoplastic materials (which can be formed when heated).

1. Thermoplastic materials: mainly composed of linear molecular chains, they slide against each other when heated, giving the plastic ductility and weldability.
2. Elasticity: Composed of a wide network of molecular chains, they will return to their original state once the heat is reduced. Therefore, it cannot be formed through welding process.
3. Thermosetting resin: composed of tightly interlocked molecular chains. Heat will destroy their structure, which means melting and welding are impossible.

Thermoplastic materials

Only the same thermoplastic material can be uniformly (uniformly) welded. All thermoplastic materials except PTFE can be welded. However, there are material specific differences between plastics:

1. ABS (Acrylonitrile Butadiene Styrene)
It can be easily welded. The welding temperature is between 270 and 310 ° C.
2. PS (polystyrene)
It can also be easily welded. The welding temperature is between 270 and 310 ° C.
3. PP (polypropylene)
Due to the rapid combustion of PP, it is necessary to closely monitor the temperature and heating time. The welding temperature is between 230 and 280 ° C.
4. PE (polyethylene)
It can be easily welded, but conventional adhesives cannot be used for bonding. The welding temperature is between 220 and 280 ° C.
5. PVC (polyvinyl chloride)
Close attention must be paid to temperature and heating time, as PVC burns very quickly and forms hydrochloric acid. The welding temperature is between 250 and 280 ° C.
6. PMMA (polymethyl methacrylate)
Commonly known as acrylic glass. It can be easily welded. The welding temperature is between 120 and 180 ° C.
7. PC (polycarbonate)
It can also be easily welded. The welding temperature is between 270 and 310 ° C.

Decisive material properties

The characteristics of materials play an important role in precise and effective welding processes:

1. The elastic module (e-madult) describes the tension and expansion of plastic when force is applied. The larger the electronic module, the better the sound transmission of the material.
2. Shock absorption describes the degree to which plastic absorbs and converts mechanical vibrations. The greater the damping of J, the stronger the heat generation, as more vibration energy is converted into heat.
3. The point at which a melting point material changes from a solid to a liquid. It determines how much heat is required for the welding process.
4. Melt viscosity: How fast is the flow rate of the melted part of plastic. Tougher melts tend to remain in the connection area, resulting in a more uniform process.

influence factor

Various external factors can affect the weldability of plastics:

Negative effect
1. Fire resistant additives: Additives can prevent plastic from degrading due to external influences. However, this also means that additives make it more difficult to treat plastics with ultrasound.
2. Moisture (especially polyamide): If the moisture content of plastic is high, it will evaporate during the welding process. This will cause bubbles to appear in the connection area, leading to porous welding joints.

Positive impact
1. Fiberglass: increases the stiffness, toughness, and strength of plastics, thereby improving the conductivity of sound, especially in semi crystalline plastics.
2. Glass beads: increase the pressure resistance of plastic, thereby improving the conductivity of sound, especially in semi crystalline plastics.