Ultrasonic Welding – Definition, Working Principle, Applications

In this article, we will learn ultrasonic welding along with definition, meaning, working, principle, applications, advantages, disadvantages, etc.

What are Ultrasonic Welding?

Let’s learn ultrasonic welding with basics, definition & history.

Ultrasonic Welding Basics

You might have seen in the classic movies when a singer sings in a high tone all the champagne glasses in the room shatter due to its acoustic vibrations. This shows how a high-pitched noise or sounds can break a material, but do you know a similar principle can be used to join the material like welding two different layers.

Ultrasonic welding is a method that is used to weld items from a variety of sectors, including medical equipment, sporting shoes, and cars.

  • Fasteners such as nails, screws, or thread are commonly used to join materials.
  • This applies to metals, wood, textiles, and polymers.
  • Glues are utilized for various plastics; glues establish chemical connections between the glue and the surfaces of the bound plastic components.
  • Heating other metals as a bonding agent, such as lead solder in electrical connections and weld sticks can hold metals together.

The metals can be directly melted together (welding), and the metals will bind together once the molten metal surfaces cool. Welding often necessitates the use of an open flame or torch to produce the high temperatures required to melt the metal surfaces together.

History of Ultrasonic Welding

  • In the 1940s, a new, less expensive welding technique was invented. Ultrasonic welding is a method of joining metals that involves high-frequency sound waves and pressure rather than conventional welding.
  • From the 1950s through the 1990s, ultrasonic metal welding evolved as the electronics in the equipment got more complex and computers could manage the operation. Since then, the method has been extended to plastics, where it has grown in popularity.

In this blog, we will go through the working principle of ultrasonic welding, various parts, its application, advantages, and disadvantages of this welding method.

What is the Ultrasonic Welding Technique?

  • When ultrasonic vibrations are used to weld two different workpieces then it is called the ultrasonic welding process.
  • Ultrasonic welding is a method that is widely utilized in various industries for welding tiny components at high production rates.
  • Welding is accomplished by the use of high-frequency vibration in the range of 20kHz to 40kHz.
  • It is similar to a spot welding process in which the welding is performed using mechanical vibrations and intermolecular bonding.

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Working Principle of Ultrasonic Welding

Ever rubbed your hands together in winter? It gets heated up, right! Similarly, if you strike repeatedly on a metallic surface with a hammer or a metallic block you notice that the temperature increases. Now imagine doing these processes at a speed of thousand times per second – enormous amounts of heat will be generated.

  • The above mentioned principle is used in the ultrasonic welding process. The frictional heat created can dramatically boost the temperature in a relatively short period of time.
  • High-frequency sound (ultrasound) essentially produces fast vibrations within the materials to be welded.
  • The vibrations cause the materials to rub against each other, and the friction raises the temperature of the surfaces that come into contact. This fast frictional heat is what causes the materials to bond together.

Parts of Ultrasonic Welding Machine

The parts of the ultrasonic welding machine are as follows,


It’s used to provide pressure on the two plastic parts that are going to be connected or welded. It might be pneumatic or electrically powered. Press is used to apply pressure on the parts fixed on the fixtures.

Fixtures or Anvil

It’s a clamping mechanism that holds and clamps the two plastic parts together. It enables high-frequency vibration to be directed to the interface between the two components.

Ultrasonic stack

It is made up of three parts: a converter or piezoelectric transducer, a booster, and a horn or sonotrode. These three components are adjusted to function on a resonant frequency of 15 kHz, 20 kHz, 30 kHz, 35 kHz, or 40 kHz.

A transducer is a piece of equipment that transforms electrical impulses into mechanical vibrations. A Transducer is used in ultrasonic welding equipment to transform high-frequency electrical impulses into high-frequency mechanical vibrations.


The booster functions as an amplifier, amplifying the mechanical signals acquired from the transducer. This is an essential factor since the booster provides the amplitude necessary to generate a weld.

Sonotrode or Horn

Titanium or aluminium is used to make the horn. It vibrates at a high frequency and sends mechanical vibration to the two welded components. It also mechanically changes the amplitude. It adopts the form of the component.


The ultrasonic generator creates and transmits high-frequency electrical impulses that correspond to the stack’s resonance frequency.


To deliver alternating current to the transducer, a transformer is needed. The principle of mutual inductance is used to accomplish this.


The beam used to support the transformer and transducer-horn combination is the column. The column must be stiff enough to withstand the mechanical vibrations and hold the components being welded.


In the case of ultrasonic welding equipment, a cast iron foundation is installed. This foundation works as a damper, absorbing the produced vibrations. This helps in the stabilization of the complete structure.

Ultrasonic Welding Process

Steps for Ultrasonic Welding

Following steps are followed while welding two components together:

  • Parts to be welded together are placed and clamped in the fixture or anvil.
  • The horn is lowered to make a contact between the parts and horn.
  • A pneumatic or hydraulic press is used to apply pressure on the horn to make sure that the horn is in contact with the welded parts, and it holds them together.
  • To heat the materials, the horn emits ultrasonic vibrations. Vibrations travel less than a millimeter up and down and side to side.
  • The welding process is completed, and the parts are now welded together.
  • The horn is now lifted and retracted, and the parts welded together can be removed and the process is completed.

A computer or microprocessor within the welding apparatus controls the welding – time, pressures, and temperatures. And what happens during the welding process is determined by the composition of the materials.

  • In metals, ultrasonic vibrations are supplied parallel to the material’s plane. The frictional heat raises the temperature of the metal surfaces to roughly one-third of the melting point but does not melt the metals.
  • Heat, on the other hand, removes metal oxides and coatings from the surfaces. Metal atoms can travel between the two surfaces and create intermolecular bonds that hold the metals together.
  • While performing ultrasonic welding on plastics the vibrations are transmitted through the parts perpendicularly and enough heat is generated due to friction that can melt the plastic surface. The plastic molecules bond, when the plastic surfaces cool, they are welded together. Although weld durations vary, welds can occur in as little as 0.25 seconds.

Factors Influencing Ultrasonic Welding

  • The frequency of the sound waves, which is generally 20, 30, or 40 kHz,
  • The pressure provided to keep the materials together, and
  • The duration during which the ultrasound is delivered, which can range from fractions of a second to more than one second

Advantages of Ultrasonic Welding

Due to its versatility to be utilized on thermoplastics and other materials, ultrasonic welding has gained significant acceptance across a variety of sectors. There are a variety of other reasons why ultrasonic welding may be superior to traditional welding and joining processes. The advantages in detail are as given below:


  • One of the major advantages of ultrasonic welding is that it is an extremely quick welding technique. The horn’s ability to transmit high-frequency ultrasonic acoustic vibrations allows the material to heat, weld, and cool rapidly.
  • The welding process takes only a few seconds in most situations, providing for maximum productivity and quick response.

Low cost of material

In terms of material use, the ultrasonic welding method is highly cost-effective. Since no connecting bolts, solder, or adhesive material are used in the procedure, the project’s material expenditure is reduced.

  • Part scrapping is also kept to a minimum since ultrasonic welding is very accurate and generates high-quality welds.
  • Labor expenses are kept to a minimum by minimizing human intervention during and after the welding process using automation in assembly lines.

Quality of weld

  • Ultrasonic welding creates a smooth, accurate weld. Ultrasonic welding technology, when utilized properly, generates no plastic flash or distortion, resulting in a clean, virtually undetectable joint that does not require touch-up work.

High reliability

Ultrasonic welding equipment will work with a high level of reliability once it has been constructed and calibrated.

The procedure can even be automated, allowing for the efficient welding of thousands of components with minimum human interaction.

Maximum safety

  • When compared to other welding processes, ultrasonic welding is highly safe. The ultrasonic energy is precisely focused, avoiding the risk of electrical energy overload.
  • Also, the heat is subjected to the parts to be welded for a very short amount of time thus avoiding heat damage to the surrounding equipment.

The following advantages make ultrasonic welding the perfect choice for industries looking for a quick and reliable process for mass production parts.

Disadvantages of Ultrasonic Welding

While ultrasonic welding has a number of benefits, it is not the best welding method for all kinds of applications. This type of welding has a number of disadvantages that may be a challenge for certain types of manufacturers. The following are a few of its drawbacks:

High initial investments

  • Ultrasonic welding equipment is considerably more expensive than regular welding equipment, and the prices only rise when automation is added.
  • If a company tries to save money by purchasing inexpensive machines, then that isn’t a viable choice either as – low-cost machines rarely provide any feedback or automation capabilities, and they may be less dependable owing to lower-quality machinery.
  • The only option left if one wants to install ultrasonic welding is to go for high-end machines having automation and feedback features owing to more efficient and reliable operations.

Limitations based on weld design

  • This welding can only be done on lap joints, which are specially engineered connections where pieces immediately overlap with a flat surface.
  • This method cannot properly weld corner joints, butt joints, tee joints, or edge joints.

Specific materials can only be used

Many thermoplastics are suitable for ultrasonic welding; however, it is not suitable for all. The ultrasonic welding method necessitates that the materials being welded have a limited moisture content.

  • Vibration welding, which is a completely distinct process, is required for materials with high moisture content.
  • Extremely strong, rigid thermoplastics are considerably more difficult to work with when employing this method.

Customized tool for every job

  • Every new project for an ultrasonic welding application requires unique tooling as part of the customized construction demands of ultrasonic welding.
  • Fixtures for components must be produced to properly match workpieces, which necessitates the use of high-quality CNC tooling.
  • This may not be an issue for full-service shops with CNC machines and toolmakers on staff, but it might be a problem for smaller businesses with limited space and manpower.

Large parts cannot be welded

  • While ultrasonic welding is ideal for a variety of thermoplastics and metals, it is not suitable for all applications using these materials.
  • To begin with, ultrasonic energy is insufficient to create massive joints larger than 250 mm in length.
  • The transducer’s power output is insufficient to handle anything bigger than that.
  • Furthermore, as thick materials are difficult to vibrate with mechanical vibration energy, ultrasonic vibration is an inefficient welding process for thick components.

High lead time

  • You won’t be able to start pumping out components right away if you decide to incorporate ultrasonic welding equipment into your production processes.
  • All ultrasonic tooling configurations must be custom-built for each item that is to be welded, which necessitates fixture and process development as well as many rounds of testing.
  • Tools for every new component to be welded are custom built, thus fixtures and processes need to be developed for new parts undergoing production.
  • This implies that new ultrasonic welding setups may not be deployed right away, and new ultrasonic welding projects may take a little longer to complete.

Applications of Ultrasonic Welding

The most common application of this type of welding is found in computer and electrical components including aerospace, automotive, medical, and packaging.

  • In computers and electronic circuits, it is used to weld wired connections and circuit boards.
  • In automotive applications it is used to put together big plastic and electrical components including door panels, instrument panels, air ducts, lights, steering wheels, upholstery, and engine parts.
  • It is used in aircrafts manufacturing industries to connect thin sheet gauge and lightweight materials such as aluminium.
  • It introduces no impurities or deterioration into the weld. That is why it is used in the medical field. Ultrasonic welding technique is used for manufacturing various types of medical equipment involving various types of filters like blood/gas, artery, anesthetic filters, dialysis tubes, cardiometry reservoirs, etc.
  • It is also used in the packaging of hazardous items like explosives, fireworks, chemicals, etc.


Hence, we have learned what is ultrasonic welding, it’s definition, meaning, working principle, applications, advantages, disadvantages, etc.

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