What Is A Sonotrode In Ultrasonic Welding?

Sonotrode definition:

The ultrasonic welding machine sonotrode, also known as the ultrasonic welding horn, is an important part of the ultrasonic welding machine.

The ultrasonic horns are used to transmit high-frequency mechanical vibration of the ultrasonic transducer to the plastic components. Its resonant frequency must match the ultrasonic sensor. The end of the welding head must conform to the welding joint design of the welding object. The design of the ultrasonic welding machine mold will directly determine the welding effect of the workpiece.

Ultrasonic Sonotrode Material

Daily sonotrodes mostly use titanium alloy, aluminum alloy, and steel as raw materials.

Titanium alloy: High hardness, good metal fatigue, excellent acoustic performance, but expensive and difficult to process.

Aluminium alloy: Low cost, excellent acoustic performance, but low hardness and poor metal fatigue, the surface of the welding head is generally hard anodized to improve hardness and corrosion resistance.

Steel: High hardness but high acoustic impedance and is difficult to process. Generally only suitable for small welding heads and small amplitude welding

Now, most of the sonotrodes use high-quality imported 7075 aluminum alloy, which has good mechanical strength, hardness, thermal conductivity, and reasonable price. It is the preferred material for ultrasonic plastic welding machine sonotrodes. Titanium alloy has good performance, but the price is relatively expensive, secondly, steel is used for sonotrodes with high requirements for strength and wear resistance.

sonotrode material
sonotrode structure

Ultrasonic Sonotrode Structure

Usually, the sonotrode of ultrasonic plastic welding machines is generally divided into two parts: upper and lower sonotrodes. The upper sonotrode is connected to the transducer, and the lower sonotrode is fixed on the base of the ultrasonic plastic welding machine.

The upper sonotrode is used to transmit ultrasonic energy, so the frequency must be the same as that of the ultrasonic generator. The frequency is the same, otherwise, it will damage the sonotrode. The lower sonotrode is mainly used to fix the plastic workpiece, and it can play the effect of fixing the workpiece.



Ultrasonic Sonotrode Frequency

The frequency of the ultrasonic sonotrode is calculated by the manufacturer through professional software analysis according to the material, size, and shape of the workpiece. The frequency of each sonotrode must be tested and matched with the equipment. Usually, the frequency of the ultrasonic plastic welding machine sonotrode is divided into 15kHz, 20kHz, 28kHz, 30kHz, 35kHz, 40kHz, etc. The higher the frequency, the shorter the sonotrode.

ultrasonic sonotrode frequency

Ultrasonic Sonotrode Maintenance

ultrasonic horn
ultrasonic mold

A well-maintained ultrasonic sonotrode has a service life of one-half longer and is not prone to oxidation and cracks. So please be sure to maintain the ultrasonic mold regularly.
rec  Avoid knocking and rasping the upper sonotrode to prevent frequency or vibration changes.
rec  When connecting the transducer and sonotrode, please use standard tool accessories.
rec  If the sonotrode without hardening surface treatment is not used for a long time, please wrap it with the oil cloth to prevent oxidation of aluminum-titanium alloy.
rec  When installing the sonotrode, please apply a thin layer of butter on the bottom (the joint surface of the vibrator) to facilitate the transmission of the ultrasonic sonotrode.

Can An Ultrasonic Horn Go Bad

Ultrasonic welding heads sometimes have the following faults:

  1. Fever
    During the working process of the welding head, heat will be generated due to the mechanical loss of the material itself and the heat conduction of the weldment. The standard for judging whether the welding head heats up normally is that it continuously emits ultrasonic waves for more than half an hour without load (without contacting the workpiece), and the temperature cannot exceed 50-70°C. If the heat is severe, it means that the welding head is damaged or the material is unqualified.
  2. Howl
    When the welding head whistles when working, please stop the machine immediately and check
    ① Check whether the installation screws are loose
    ② Whether there are cracks in the welding head
    ③ Whether the welding head is in contact with unknown objects.
  3. Overload
    When an overload alarm occurs, you can troubleshoot as follows:
    ① During the no-load test, if the working current is normal, it may be that the welding head has come into contact with an object that it should not have touched or there is a fault in the parameter adjustment between the welding head and the welding base. .
    ② When the no-load test is abnormal, you should first observe whether there are cracks in the welding head and whether the installation is firm. Then remove the welding head and conduct a no-load test to rule out whether there is a problem with the transducer or the horn. If not, replace the welding head with a new one and test.
    ③ Sometimes even if the no-load test is normal, it may not work properly. It may be that internal changes in sound energy components such as welding heads cause poor sound energy transmission. The surface of a normally working welding head has a very uniform amplitude and feels very smooth. When sound energy is not transmitted smoothly, there will be bubbles or burrs to the touch. The same situation will occur when the generator is abnormal because the input waveform when detecting the transducer should be a smooth sine wave under normal circumstances. This phenomenon can also occur when there are spikes or abnormal waveforms on the sine wave.
replace the ultrasonic sonotrode
When is the best time to replace the welding sonotrode?

The ultrasonic welding machine sonotrodes need to be replaced after a period of use. This is to better complete the welding work, improve production efficiency and ensure quality. The sonotrodes need to be replaced in the cases:

  1. When the welding sonotrode is worn, the resonant frequency of the welding sonotrode will increase. When the frequency change exceeds the working range of the generator, the sonotrode needs to be replaced.
  2. The metal material itself has a certain fatigue resistance. When the welding sonotrode has been used for a long time or has defects, the welding sonotrode will produce fatigue cracks, and when the cracks extend to a certain length, it will cause a fracture, and it needs to be replaced at this time.
  3. The welding sonotrode generally has lines. When the lines are worn and cannot meet the friction coefficient requirements, the sonotrode needs to be repaired or replaced.

Different Sonotrode Materials

Advantages and disadvantages of different materials sonotrode

There are three common ultrasonic sonotrode materials: steel alloy, aluminum alloy, and titanium alloy.
1. Steel Alloy Ultrasonic Sonotrode:
Advantages: After production, the hardness is improved after heat treatment, which is the most wear-resistant material among the three.
Disadvantages: The cutting process is difficult, the mold itself generates a lot of heat, and it is easy to cause damage to other parts.
2. Aluminum Alloy Ultrasonic Sonotrode:
Advantages: Due to the low hardness, it is suitable for cutting or engraving processing, the mechanical conductivity is also superior to that of steel alloy molds, and the heat generation is small.
Disadvantages: The problem of the material itself and the matching problem of machine performance will lead to a relatively short service life (partially), low hardness, and poor wear resistance.
3. Titanium Alloy Ultrasonic Sonotrode:
Advantages: Mechanical conductivity, the hardness is higher than that of aluminum alloys, and the wear resistance of steel alloys is higher than that of aluminum alloys.
Disadvantages: the high cost of raw materials and wear resistance is not as good as steel alloys.



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