How To Choose Ultrasonic Welding Parameters

Ultrasonic Welding is a common way for plastic joining, it is a process where high-frequency vibrations are used to weld two plastic parts together. These vibrations are very high and are above the range of human hearing, that’s why the technology is called ultrasonic welding. To get two plastic parts welded together, ultrasonic vibrations are used to generate heat and let the plastic parts melt and flow together, exert some pressure, and the plastic parts cool and form into one assembly.


Many important parameters in the ultrasonic welding process affect the welding results of the plastic parts which include amplitude, down speed, weld time, hold time, etc.

Today we focus on sharing the impact of three parameters on ultrasonic welding.

  1. Amplitude:

Ultrasonic Welding Amplitude

In ultrasonic welding, the amplitude is usually the peak value.  Amplitude is measured in micrometers (μm). The standard amplitude value range is between 10 and 60 micrometers (μm). Amplitude refers to the amplitude of the vibration of the welding sonotrode surface,

Amplitude = amplitude of the transducer surface * the gain of the booster * the gain of the welding sonotrode.

The greater the amplitude, the greater the welding energy. Generally speaking, semi-crystalline materials require more energy and so require larger amplitudes than amorphous resins. Plastics with higher melting points require higher amplitudes. Table 1 shows the recommended amplitude, near-field welding, and far-field welding performance of plastics at 20kHz.

Material20KHz Amplitude Reference GuideNear-field weldingFar-field welding
Note: 1 = easiest  5 = hardest

Table 1

  1. Down speed:

During ultrasonic welding, if the ultrasonic welding machine head down quickly, it can shorten the welding time and improve production efficiency. However, the fast pressing speed of the ultrasonic welding machine head will also cause many problems:

  1. Affects the welding consistency of the product; Down the machine head too fast will cause the ultrasonic welding machine to shake on the platform, causing inconsistent welding quality.
  2. If the ultrasonic welding machine is down too fast, the ultrasonic wave will not emit waves. If the ultrasonic welding machine is pressed down too fast, the instantaneous current of the sound will be too large, causing it to be unable to vibrate.
  3. It is easy to cause misalignment of the welding surface of the product. Excessive pressing speed will hit the plastic parts, causing the welding surface to expand outwards. Then, due to the influence of high-frequency vibration of ultrasonic welding, the product can easily become misaligned.
  4. Reduce the service life of the ultrasonic mold. Ultrasonic welding tooling consists of an upper mold and a lower mold. When welding thin plastic parts, the speed is too fast, making it easy for the upper mold to directly hit the lower mold, shortening the life of the mold.

ultrasonic plastic welder FU2025 series (2)

Therefore, when using an ultrasonic welding machine to weld products, the descending speed should be adjusted. For pneumatically controlled ultrasonic welding machines, the common specifications of the cylinder are a diameter of 63mm and a length of 75mm. That is to say, the speed is relatively fast between 0-65mm, and the buffer deceleration is reached only after reaching the end. The head of the ultrasonic welding machine should be adjusted to a certain height to allow the end buffer to play a role and achieve good welding results.


  1. Weld Time & Hold Time:

Weld time refers to the time when the ultrasonic welder head applies pressure and applies ultrasonic vibration. Welding time varies based on ultrasonic application. Small thermoplastic parts require shorter welding times than larger parts. For most applications, a good starting point for welding time would be between 0.02 – 2.0 seconds.

Hold time means after ultrasonic waves are applied to a thermoplastic part, pressure is maintained on the plastic part to ensure that the molten plastic solidifies. This time parameter allows the welding head to continue to maintain a certain pressure after applying pressure to ensure the firmness of the welding joint. Generally speaking, the hold time is usually half the welding time.

These time parameters need to be adjusted and optimized according to specific welding tasks and process requirements to ensure ideal welding results.

Ultrasonic Welding Parameters Setting

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