Ultrasonic Welding Technology for Plastics

Ultrasonic plastic welding is a kind of welding technology where current is converted into a high-frequency electric energy by the ultrasonic generator. It is the joining or reforming of thermoplastics through the use of heat generated from high-frequency mechanical motion. Ultrasonic welding of plastic materials creates a molecular bond within the weld seam.
Ultrasonics activates the plastic molecules – friction heat is generated
Ultrasonics activates the plastic molecules – friction heat is generated
Ultrasonic vibrations are focused by means of special design of the components or tools. This specific geometry within a component is referred to as energy director. The contact points in the joining area are actively molded by means of energy input to achieve elastic deformation. Friction occurring between the contact surfaces and within the molecule chains generates heat that causes the material to melt.

Parts of the ultrasonic welding

Ultrasonic plastic welding machine principle

  • Generator(Power supply): A high-frequency ultrasonic welding machine requires a high voltage power supply.
  • Converter (Transducer) : Converter takes the high voltage current and converts it to high-frequency vibrations.
  • Booster: It works like an amplifier where it takes the high frequencies and then makes them even more powerful.
  • Sonotrode or Horn: A sonotrode or horn as it is commonly known is the medium between the materials to be welded and the machine. It focuses the ultrasonic vibrations to a localized point.

The materials to be welded is commonly fixed on anvil or some type of fixtures that hold them together. A pneumatic press is often attached to the machine so that the pressure can be transferred to the materials using the horn.

The basic principle of ultrasonic welding

The basic principle of Ultrasonic Welding Technology for Plastics
The basic principle of ultrasonic plastic welding
  • Step 1 – Parts in fixture: The two thermoplastic parts to be assembled are placed together, one on top of the other, in a supportive nest called a fixture.
  • Step 2 – Horn contact: A titanium or aluminum component called a horn is brought into contact with the upper plastic part.
  • Step 3 – Pressure applied: A controlled pressure is applied to the parts, clamping them together against the fixture.
The basic principle of Ultrasonic Plastics Welding
The basic principle of ultrasonic plastic welding
  • Step 4 – Weld time: The horn is vibrated vertically 20,000 (20 kHz) or 40,000 (40 kHz) times per second, at distances measured in microns, for a predetermined amount of time called weld time. Through careful part design, this vibratory mechanical energy is directed to limited points of contact between the two parts.The mechanical vibrations are transmitted through the thermoplastic materials to the joint interface to create frictional heat. When the temperature at the joint interface reaches the melting point, plastic melts and flows, and the vibration is stopped. This allows the melted plastic to begin cooling.
  • Step 5 – Hold time: The clamping force is maintained for a predetermined amount of time to allow the parts to fuse as the melted plastic cools and solidifies. This is known as hold time
  • Step 6 – Horn retracts: Once the melted plastic has solidified, the clamping force is removed and the horn is retracted. The two plastic parts are now joined as if molded together and are removed from the fixture as one part.

The widely use of our ultrasonic plastic welding

Ultrasonic plastic welding is suitable for virtually all thermoplastics. When planning welds between semi-crystalline plastic pieces of work, it is important to remember that the weld behaviour of these plastics differs considerably from that of amorphous plastics.

Ultrasonic welding of plastics is widely used in the electronic, food, plastics, packing and automotive industries. For example, the packaging industry uses this technique to make films, assemble tubes and blister packs.

application of Ultrasonic Plastics Welding
Ultrasonic plastic welding machine application

Advantages of ultrasonic plastic welding

  • Does not need external heat source: The primary advantage of ultrasonic plastic welding is that it doesn’t need an external heat source. The heat is self-generated between the materials.
  • Fast: Since the frequency of vibrations is very high, ultrasonic plastic welding is one of the fastest welding methods available in the industry.
  • Clean and strong joint: The contact surfaces melt/fuse upon welding, and it produces a very clean and strong joint.
  • Safety: Ultrasonic plastic welding does not require flammable fuels and open flames, so compared to other welding methods, it’s a safer process.

Easy to implement: This welding technology is also easy to implement in a production process and has a low fault rate, continuous production without interruption

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