What is Ultrasonic Welding Process – An Overview

What is Ultrasonic Welding?

Ultrasonic Welding is a type of solid state welding process that utilizes very high vibrations (20 kHz to 40 kHz) and pressure to weld metal and plastic parts. This welding technique is most commonly used to weld thermoplastic materials and metals with thin sections.

Welding Equipment
This image shows Components of Ultrasonic Welding Machine.

An Ultrasonic welding machine has majorly following components that are used to create welding joint.

Ultrasonic frequency generator

It is used to generate high frequency electrical signals. These signal needs to be in accordance with the resonance frequency of the ultrasonic stack (Convertor, Booster and Horn). It has provision to change the frequency.

Pneumatically controlled press

It is used to apply pressure on parts to be welded and control the movement of the horn.

Convertor

It is used to convert electrical signal into high frequency mechanical vibrations using piezoelectric effect.

Booster

Used to change the amplitude of the vibrations and clamp horn and convertor with the press.

Horn

It is used to transfer high frequency vibrations to the part to be welded.

Fixture

Fixtures are used to align and hold parts to be welded. Alignment of part with horn is very important for the success of the ultrasonic welding.

Control Panel

It is used to setup Weld & hold time, pressure and height and the movement of the press.

Basic Principle and Working of Ultrasonic Welding

Ultrasonic Welding works by generating heat and fusing materials by friction and pressure. In ultrasonic welding, very high vibration and pressure is applied to the part for defined time. These vibrations cause the material to be welded rub against each other and frictional forces raises the temperature of the welded section significantly.

Ultrasonic welding is done in following steps:

Step-1: Parts to be welded are placed in the fixture. Fixture is aligned with the horn. Alignment of part, fixture and horn is very critical for the success of the welding.

Step-2: Titanium or Aluminum horn is brought in contact with the top part.

Step-3: Controlled required pressure is applied to the parts to be welded.

Step-4: Ultrasonic horn is vibrated for required weld time in the frequency range of 20 kHz to 40 kHz. Weld time depends on the part design and vibration frequency. These vibrations are transferred to the parts contact area from the horn and heat is generated in contact area due to frictional forces.

Step-5: Afterwards horn is held for some time to allow parts to fuse.

Following factor affect the ultrasonic weld quality.

  1. Part design
  2. Horn and Fixture Design
  3. Welding Frequency
  4. Weld time
  5. Welding pressure
  6. Hold time etc.
Advantages
  • Fast, clean and efficient process
  • Welding process is repeatable
  • Additional additives or filler material are not required to weld parts
  • Different materials can be welded.
  • Low initial investment.
  • Low part welding cost.
  • Automation is possible.
Disadvantages
  • Initial setup is a time consuming process. Therefore ultrasonic welding is recommended for high production volume parts.
  • Part design guidelines for ultrasonic welding need to be followed.
  • High horn and fixture cost.

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