what is ultrasonic welding plastic

Ultrasonic welding of plastics is a cold welding process that uses the piezoelectric effect of piezoelectric ceramics to convert electrical energy into ultrasonic waves and uses the high-frequency vibration of ultrasonic waves to weld thermoplastic plastics.

how does ultrasonic plastic welding work

Ultrasonic welding of plastics converts electrical energy into acoustic energy through the piezoelectric effect of ceramic plates. The ultrasonic waves are transmitted to the plastic parts via a welding horn, causing high-frequency vibrations. During these high-frequency vibrations, the temperature of the plastic parts rises to the glass transition temperature or melting point, causing the molecular chains of the plastic to start moving and recombining. Finally, applying pressure and cooling achieves a welding effect with a strength comparable to that of the raw material.

Key advantages of ultrasonic welding plastic

  • High Efficiency: Short welding time (0.1–5 seconds), suitable for automated production lines.
  • Clean Process: No need for solders or solvents, eliminating chemical contamination.
  • Precision: Welding area can be controlled to millimeter-level accuracy, with no obvious surface damage.
  • Energy Saving: Energy consumption is only 30–50% of traditional thermal welding processes.

what materials can be ultrasonically welded

Ultrasonic welding is applicable to most thermoplastics, which are categorized into amorphous plastics and semi-crystalline plastics. These two types require different welding conditions:
  • Amorphous Plastics (e.g., PS, PC, PMMA):
    When heated by high-frequency vibrations to their glass transition temperature (Tg), the molecular chains within the plastic start to slide and recombine. After cooling under pressure, a new molecular structure forms, achieving the welding effect.
  • Semi-Crystalline Plastics (e.g., PE, PP, PA (Nylon)):
    Semi-crystalline plastics have both amorphous and crystalline regions. The amorphous regions allow molecular movement at  glass transition temperature (Tg), while the crystalline regions require heating to their melting point (Tm) for melting and welding. However, rapid cooling after melting may reduce weld strength due to crystalline shrinkage. Therefore, higher ultrasonic amplitudes or specialized energy-directing structures are typically needed to concentrate heat and ensure optimal welding results.

Common plastics that can be welded and their properties

Plastic TypeCharacteristics & WeldabilityTypical Applications
Polypropylene (PP)Low melting point (approx. 160-170°C), good weldability, commonly used for non-structural components.Automotive parts, packaging containers, toys, etc.
Polyethylene (PE)High flexibility, low melting point (approx. 120-130°C), suitable for thin-walled or flexible components.Plastic bags, hoses, plastic bottle seals, etc.
Polystyrene (PS)High rigidity, easy to melt but brittle, suitable for applications with low strength requirements.Electronics casings, stationery, transparent parts (e.g., lamp covers), etc.
ABS PlasticExcellent comprehensive performance (high strength, impact resistance), higher melting point (approx. 210-230°C), requires higher welding energy.Household appliance casings, automotive interiors, 3C products, etc.
Polymethyl Methacrylate (PMMA, Acrylic)High transparency, good sealing after welding, but temperature control is required to prevent yellowing.Optical devices, advertising light boxes, medical instruments, etc.
Polyoxymethylene (POM, Acetal)High rigidity, wear-resistant, higher melting point (approx. 175°C), precise parameter control needed to avoid degradation.Gears, bearings, precision mechanical parts, etc.
Nylon (PA)High toughness, heat-resistant (melting point approx. 220-260°C), hygroscopic – drying required before welding.Automotive components, electrical connectors, sports equipment, etc.
Polycarbonate (PC)High transparency, impact resistance, high melting point (approx. 220-230°C), requires higher energy and prone to stress cracking.Optical lenses, electronic device casings, safety equipment, etc.
PET (Polyethylene Terephthalate)Good chemical resistance, commonly used for transparent or semi-transparent components, temperature control critical during welding.Beverage bottles, packaging boxes, electronic component trays, etc.

Can PTFE be ultrasonically welded?

PTFE (polytetrafluoroethylene) can be welded by ultrasonic welding. PTFE is a high-performance plastic with excellent chemical stability and a low coefficient of friction. Although PTFE has a low surface energy and high crystallinity, and as a non-polar polymer, it can only form weak dispersion forces with other materials, resulting in poor adhesion, and it has a high melting point (approximately 400°C), which usually makes it a difficult material to weld, the welding effect of ultrasonic welding on PTFE can be ensured by optimizing the equipment and process of ultrasonic welding and adjusting parameters such as ultrasonic amplitude, applied pressure, and welding time according to specific conditions.

hyusonic ultrasonic plastic welder

ultrasonic plastic welding machine 8800st

Ultrasonic Plastic Welding Machine Standard Type
ST Series

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ultrasonic plastic welder 2000iq

Ultrasonic Plastic Welding Machine Intelligent Typ
iQ Series

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ultrasonic plastic welding machine-2000X-1

Ultrasonic Plastic Welding Machine High-end Type
X Series

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