About Ultrasonic Welding
22 January 2017 · 2 min read · News
Ultrasonic Welding Technology
Ultrasonic welding is an industrial process where electrical energy is converted into mechanical vibration.High frequency (ultrasonic) sound waves, called acoustic vibrations, and transmitted through a plastic part (held together under pressure) to the joint interface. These ultrasonic vibrations create friction and locally heat the joint area causing the parts to become welded together. No other consumables are required. The two parts are ultrasonically welded to each other. The process is extremely fast (cycle times generally within 1 second) and very energy efficient.
For assembly of complex thermoplastic moulded parts, ultrasonic welding equipment can easily be applied to join parts by welding. Strong structural welding can easily be achieved. Ultrasonic tooling is customised to fit the exact specifications of the parts being welded. Plastic parts are sandwiched between a customised fixed nest (anvil) and the work horn (sonotrode). Common ultrasonic welders operate at frequencies between 20 kHz to 70 kHz. Often the joint interface can require a special 'joint design' to assist the melt and flow of the plastics. The ultrasonic energy melts the contact points of the parts, creating a weld.
Ultrasonics can also be used to weld metals. Ultrasonic metal welding is generally limited to thin 'white metals' in applications such as 'wire splicing', 'spot welding' and sealing of copper tubes. Ultrasonic Weldable metals include: aluminum, copper, nickel.
Ultrasonic welding of thermoplastics causes local melting of the plastic due to absorption of vibrational energy along the joint line. In metals, welding occurs due to high-pressure dispersion of surface oxides and local motion of the materials.
The benefits of ultrasonic welding:
Ultrasonic welding is very fast and very energy efficient. No consumables (adhesives or solvents) are required. Ultrasonic welding can be automated by easy integration into exisiting packaging lines, or handling and manipulation by multi axis robotics.
Documents
Brochure Rinco Ultrasonics Product OverviewCommon questions
Ultrasonic welding FAQ
What is ultrasonic welding?+
Ultrasonic welding is a joining process that uses high-frequency mechanical vibration (typically 20–70 kHz) and pressure to create friction heat at the interface between two thermoplastic parts. The plastic melts locally at the joint line and fuses into a permanent, homogeneous weld — usually in well under one second, with no adhesives, fasteners or external heat.
What materials can be ultrasonically welded?+
Thermoplastics — plastics that melt when heated. Amorphous polymers such as ABS, polystyrene, polycarbonate and acrylic weld most readily. Semi-crystalline polymers such as polypropylene, polyethylene and nylon are weldable with correct joint design and higher amplitude. Both parts must be chemically compatible, ideally the same polymer. Synthetic textiles and non-wovens can also be welded and cut. Thermoset plastics, which do not re-melt, cannot be ultrasonically welded.
How long does an ultrasonic weld take?+
Typical weld times are 0.1 to 1.0 seconds, plus a short hold phase. Complete machine cycles — load, weld, hold, unload — commonly run two to three seconds, which is why ultrasonic welding dominates high-volume plastic assembly.
What is the difference between 20 kHz and 35 kHz welding?+
20 kHz machines deliver higher amplitude and power to larger horns, suiting bigger parts and tougher materials. 35 kHz machines run smaller amplitudes with finer control and less audible noise, suiting small, delicate or cosmetic parts. As frequency rises, maximum practical horn size falls. 70 kHz hand units serve the most delicate work.
Is ultrasonic welding strong?+
A well-designed ultrasonic weld is a homogeneous fusion of the parent material — with correct joint design the weld can approach the strength of the surrounding part. Strength depends on material compatibility, joint design (energy directors or shear joints) and process control.
Do I need special part design for ultrasonic welding?+
Joint design matters. Most joints use a small triangular energy director moulded onto one part, or a shear-interference joint for semi-crystalline materials and hermetic seals. Rinco publishes joint design guidelines, and Techspan reviews part designs for manufacturers in New Zealand before tooling is cut.