Ultrasonic Welding (USW) is a welding technique that uses ultrasonic vibration of high frequency to weld the two pieces together. It is most commonly used to weld thermoplastic materials and dissimilar materials. Metal with a thin section can also be welded with USW.
A high frequency (20 kHz to 40 kHz) ultrasonic vibration is used to join two plastic pieces together. The high-frequency vibration generates heat energy at the interface of the two pieces and melts the material. The melted material fused with each other to form a strong weld on cooling and solidification.
The typical frequency used is 15, 20, 30, 35 or 40 kHz.
The various main parts or components of ultrasonic welding are
- A Press: It is used to apply pressure on the two plastic pieces to be joined. It may be of pneumatic or electric driven type.
- Nest or anvil or fixture: It is a clamping device that is used to hold and clamp the two plastic pieces together. It allows the high-frequency vibration directed to the interface of the two pieces.
- An Ultrasonic Stack: It consists of the three components, a converter or piezoelectric transducer, a booster and a horn or sonotrode. These three elements are tuned to work on resonate frequency of 15 kHz, 20 kHz, 30 kHz, 35 kHz or 40 kHz.
- Converter: It converts the electrical signals into high-frequency mechanical vibration. And it does so through the piezoelectric effect.
- Booster: It modifies the amplitude of vibration mechanically. In some standard systems, it is used to clamp the stack in the press.
- Horn or Sonotrode: It vibrates at high frequency and transmits the mechanical vibration to the two pieces to be welded. It also modifies the amplitude mechanically. It takes the shape of the part. The horn is made of titanium or aluminum.
- An Ultrasonic Generator: It generates and delivers high-frequency electrical signals matching the resonance frequency of the stack.
- Controller: It is used to control the movement of the press and delivery of the ultrasonic energy.
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Working Process of Ultrasonic Welding
- The two plastic pieces to be joined are assembled in the nest ( anvil or fixture)
- The horn is made to contact at upper part of the piece.
- A pressure is applied to the two pieces against the fixture. The pressure is applied through the pneumatic or electric driven press.
- Horn is vibrated vertically at very high frequency (20 kHz to 40 kHz), transmits the mechanical vibration to the two plastic pieces. This generates heat energy at the contact tip of the two surfaces and melts them.
- A clamping force is applied to the two pieces for a predetermined amount of time to fuse them together to form a strong weld on cooling and solidification.
- After solidification, the clamping force is removed and horn retracted. The welded plastic part is taken out of the fixture as one piece.
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It is mostly used in computer and electrical, aerospace and automotive, medical, and packaging industries.
- Computer and Electrical Industries: Here it is used to join wired connections and to create connections in small delicate circuits.
- Aerospace and Automotive Industry
In automotive industries, it is used to assemble large plastic and electrical components such as door panels, instrument panels, air ducts, lamps, steering wheels, and upholstery and engine components.
In aerospace, it is used to join thin sheet gauge and lightweight materials like aluminum.
- Medical Industry
It does not introduce any contaminants or degradation into the weld. That’s why it is used in medical industries.
Items such as anesthesia filters, arterial filters, blood filters, dialysis tubes, pipettes, blood/gas filters, cardiometry reservoirs, etc. can be made using ultrasonic welding method.
4. Packaging Industry
It is used to package different materials in food industries.
It is used for packaging dangerous materials like explosives, fireworks, and chemicals.
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- It is a fast welding process.
- It has Quick drying time i.e. the pieces do not remain for a long time in the fixtures to dry
- It can be easily automated.
- It produces a clean and precise joint.
- It exhibits clean weld sites and does not require and touch-up work.
- It produces a low thermal impact on the materials.
- It cannot be used to produce large joints (greater than 250 x 300 mm).
- It requires specially designed joints, so it can make tip contact during the welding process.
- High tooling cost for the fixtures.
- The ultrasonic welding process is restricted to the lap joints.