Ultrasonic Welding of Metals (Definition, Process & More)

Ultrasonic Welding of Metals

What is Ultrasonic Welding?
Definition: Ultrasonic Welding is defined as a solid state welding process in which the joining of metals occurs due to heat and pressure energy produced by the application of a high frequency vibrator (frequency >20000 Hz).

No filler material or filler rod is used during the ultrasonic welding process of metals

During the ultrasonic welding of metals, the temperature of the metal remains below its melting point, hence there will not be any noticeable change in the properties of metals that arises due to excessive heat.

This was just a simple overview. Now further I have discussed the process involved in Ultrasonic Welding of Metals as well as its advantages, disadvantages and applications.

So let’s dive right into it.

Ultrasonic welding process (How does ultrasonic welding work?)

Ultrasonic Welding of Metals

The diagram for ultrasonic spot welding is shown in the above picture.

The ultrasonic welding system consists of two main components.

  • Power source and
  • Transducer

The power source used in ultrasonic welding is a frequency converter that converts the input power (having 60 Hz) into a high frequency electric power.

The transducer converts this high frequency electric power into mechanical vibrations.

The ultrasonic vibrations are produced by an oscillator which sets the output frequency.

The amplifier is used in ultrasonic welding in order to step up the input power to as high as 25000 watts. After this, the transducer converts this electrical power into mechanical vibrations.

There are basically two types of transducers.

  • Piezoelectric transducer and
  • Magnetostrictive transducer

When the current passes through the piezoelectric transducer, it vibrates at a natural resonant frequency.

Magnetostrictive transducer contains laminations of nickel or nickel alloy, surrounded by coil of wire.

This lamination of nickel expands and contracts with the vibrations from the amplifier. This is because the deformation of nickel takes place upon heating.

In ultrasonic welding of metals, the two workpieces which are to be joined are clamped together under a static pressure.

As shown in the above diagram, the static pressure is maintained at the surface normal to the flat lower support and the upper electrode (known as sonotrode).

The sonotrode is connected to the transducer which oscillates at a very high ultrasonic frequency (more than 20000 Hz or 20000 cycles/sec.)

At this time, the pressure is applied to the sonotrode from the top (see diagram).

Due to this pressure and high frequency vibrations of the sonotrode, the metal molecules heat up and they start to deform. 

Because of the pressure acting on the deformed workpiece, the workpiece starts to fuse with each other and finally solid weld is obtained.

The range of frequency and pressure required for the ultrasonic welding process depends on the type of metals as well as size of metals.

Ultrasonic bonding occurs due to a combination of pressure and high frequency vibrations.

In the ultrasonic welding process of metals, the pressure is applied on two sides of the workpiece (upper side and lower side).

The piston or any other mechanical equipment is used to push the vibrating sonotrode towards the workpiece.

Ultrasonic welding does not involve melting of metal as well as it does not involve any filler rods.

It does not even involve high pressure and the entire ultrasonic process can be completed within a short time.

Ultrasonic welding is used to weld the metals of thickness ranging from 0.0005 mm to 1 mm.

Aluminum sheets up to 3 mm can also be welded using an ultrasonic welding process.

So, this is how ultrasonic welding works. Now let’s see the advantages and disadvantages of ultrasonic welding.

Advantages of ultrasonic welding

Advantages of ultrasonic welding process are mentioned below.

  • The ultrasonic welding equipment is simple in construction and the welding process is also simple.
  • Time consumption in ultrasonic welding is comparatively less.
  • Filler material or flux are not required during the ultrasonic welding of metals.
  • Less skilled welders can also operate the machine.
  • Dissimilar metals can also be welded by using ultrasonic welding.

Disadvantages of ultrasonic welding

Disadvantages of ultrasonic welding process are mentioned below.

  • Life of ultrasonic welding equipment is less.
  • This process is not suitable for welding thick plates.
  • Sometimes the workpiece gets welded to the sonotrode or anvil.
  • Not economical as compared to other types of welding process.

Applications of ultrasonic welding

Applications of ultrasonic welding process are mentioned below.

  • Ultrasonic Welding is used in;
    • Aircraft industries
    • Fine wire assemblies
    • Building of transistors
    • Welding of aluminum foil for packaging purpose.
  • It is used for joining thin sheets to thick sheets.
  • Also applicable for joining various electrical components.
  • Ultrasonic welding is also used for joining plastics.

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