Ultrasonic welding is primarily applicable to thermoplastics, which are characterized by softening or even melting when heated, and solidifying again after cooling. This makes it possible to achieve bonding through frictional heat generated by high-frequency vibrations. However, the molecular structure, melting point, crystallinity, and damping characteristics of different plastics directly affect the welding efficiency and the quality of the final product.

1. Easier-to-Weld Plastics (Wide Welding Window, High Stability)
These materials have moderate melting points and good internal damping, effectively converting ultrasonic energy into thermal energy:

• ABS: Stable welding, good appearance, commonly used in electronic enclosures and consumer products.

• PP: Lightweight, cost-effective, but requires good weld line design.

• PE: Low energy requirement, suitable for thin part welding.

• PS: Fast melting speed, short welding time.

• PC: High welding strength, suitable for structural components.

• PMMA (Acrylic): Achieves good transparency but requires amplitude control to avoid cracking.
  👉 Characteristics: Welding parameters are relatively easy to set, yielding high success rates, ideal for mass production and automation.

2. Fiber-Reinforced or Engineering Plastics (Require Higher Energy and Precision Control)
These materials, due to the addition of glass fiber or high crystallinity, affect energy transfer and melting behavior:

• PA (Nylon) + Glass Fiber

• PBT + Glass Fiber

• PEEK (High-performance Engineering Plastic)
  👉 Welding Characteristics:

• Glass fibers absorb or disperse ultrasonic energy.

• Higher melting points require higher amplitude, pressure, or welding time.

• The design of the welding head, fixture, and weld line is critical.
  👉 Recommendation:
  Use low-frequency, high-energy systems (such as 15–20 kHz) and conduct welding trials to optimize parameters.

3. Materials Not Suitable for Ultrasonic Welding
These materials cannot effectively melt or have low energy conversion efficiency, resulting in poor welding performance:

• Thermosetting Resins (Thermosets)
  ◦ Examples: Phenolic resins, epoxy resins
  ◦ Do not re-melt when heated, only carbonize or decompose.

• Materials with Excessive Rubber Content
  ◦ High elasticity absorbs vibration energy, preventing focus on the welding interface.
  👉 Alternative Solutions:
  Consider hot-melt, adhesive bonding, mechanical fastening, or other composite joining methods.

4. Key Factors Affecting Plastic Weldability (Additional Explanation)
Even for weldable materials, the following factors should be considered:

• Whether the materials are homogeneous or compatible.

• Whether the melting point difference is too large.

• The thickness of the parts and the weld line (Energy Director) design.

• Whether there are oils, release agents, or additives on the surface.

Ultrasonic welding is not "suitable for all plastics." The thermal properties and structural design of the material itself directly affect the welding quality and stability. By selecting the right materials and setting the correct parameters, welding strength and production efficiency can be significantly improved.