How to choose between 35khz and 20khz ultrasonic welding machine?

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Introduction of ultrasonic welding machines

Ultrasonic metal welding has gained immense popularity in various industries for its ability to create strong, reliable, and clean welds without the need for additional materials such as solder or adhesives. Two common frequencies used in ultrasonic metal welding are 35khz and 20khz. Selecting the right frequency for your specific application is crucial to ensure optimal performance and results. In this article, we will mainly introduce the difference between the two, how to distinguish them and some applications examples for your reference which can better help you choose the suitable ultrasonic welding machines for your business.

The difference between 35khz and 20khz ultrasonic welding machines


35khz: This ultrasonic welding machine operates at a higher frequency of 35,000 cycles per second. Higher frequencies result in shorter wavelengths and smaller amplitudes. This means that the vibrational motion applied to the materials is faster and more precise.

20khz: In contrast, the 20khz ultrasonic welding machine functions at a lower frequency of 20,000 cycles per second. Lower frequencies produce longer wavelengths and larger amplitudes, which generate more substantial mechanical vibrations.


35khz: Due to its higher frequency, a 35khz machine typically has smaller amplitudes. Smaller amplitudes are ideal for delicate or thinner materials as they create less stress during the welding process.

20khz: Conversely, the 20khz machine offers larger amplitudes, making it well-suited for thicker and more robust materials. The increased amplitude results in more significant plastic deformation, ensuring a strong bond between the materials.

Welding Speed

35khz: Machines operating at 35khz frequencies generally achieve higher welding speeds. The smaller amplitude allows for quicker energy transfer and, thus, faster weld cycles. This makes them a preferred choice for applications where speed is critical, such as high-volume production.

20khz: On the other hand, 20khz machines are slower in terms of welding speed but compensate with increased energy output. This slower pace is often advantageous for applications that prioritize weld quality and strength over speed.

Weld Strength

35khz: While 35khz machines offer efficient and speedy welding, their welds may have slightly less overall strength compared to 20khz machines. However, they are more than adequate for many applications, especially those involving thinner materials.

20khz: 20khz machines deliver greater energy during welding, resulting in exceptionally strong bonds. If your application demands robust welds, such as in heavy-duty manufacturing, 20khz machines are the preferred choice.

Material Thickness

35khz: Thin materials, like foils, thin sheets, and fine wires, benefit from 35khz machines due to their ability to create precise welds without causing material damage.

20khz: Thicker materials, such as heavy metals and thicker sheets, are better suited for welding with 20khz machines, as the higher energy output ensures proper bonding in these scenarios.


35khz: If your application requires high precision and accuracy, 35khz machines excel due to their smaller amplitudes and faster vibrational motion.

20khz: While 20khz machines may not be as precise as their 35khz counterparts, they make up for it with greater weld strength and versatility.


In terms of cost, 35khz machines are generally more budget-friendly than 20khz machines, making them an attractive option for businesses with limited budgets.

How to distinguish between 35khz and 20khz ultrasonic welding machines?

Machine appearance

Examine the transducer and horn of the machine. 35khz machines will generally have smaller transducers and horns compared to 20khz machines due to their higher frequency. Or check the control panel or user interface. Some machines may label the frequency setting clearly, helping you identify whether it’s 35khz or 20khz.

Mold Size

The horn and fixture of a 20khz machine are usually larger to accommodate the longer wavelength of lower frequencies. Conversely, 35khz machines have smaller horns and fixtures.


Review the machine’s specifications for voltage and current requirements. 20khz machines tend to require higher power due to their larger amplitudes, so they may have higher voltage and current ratings.

Amplitude Adjustment

Check if the machine offers amplitude adjustment. 20khz machines often provide a wider range of amplitude adjustment settings to accommodate different material thicknesses and welding requirements.

Key considerations in choosing between 35khz and 20khz

In addition to a few points we have already mentioned in the difference between 35khz and 20khz ultrasonic welding machines, here are more points you need to consider when choosing between 35khz and 20khz ultrasonic welding machines:

Weld Strength and Quality

The desired weld strength and overall quality of the bond are crucial considerations in choosing the right frequency.

35khz: Opt for a 35khz machine if your priority is achieving high welding speeds while maintaining acceptable weld strength and quality. These machines are ideal for applications where speed is critical, such as mass production lines.

20khz: For applications demanding exceptionally strong welds with superior quality, especially in industries like automotive or aerospace, a 20khz machine is the preferred choice. The increased energy output at lower frequencies ensures robust bonds.

Material Compatibility

Consider the specific properties of the materials you’re working with. Some materials may respond better to 35kHz frequency due to their composition and thickness, while others may benefit from the greater energy output of a 20kHz machine.

Application examples of 35khz and 20khz ultrasonic welding machines

35khz Ultrasonic Welding Machines

  • Electrical Connector Manufacturing

Material: For the production of electrical connectors, which often consist of thin metal pins and sockets.

Why 35kHz: A 35kHz ultrasonic metal welding machine is well-suited for delicate electrical connector manufacturing. It offers the precision required to weld these small, intricate components without damaging them, ensuring a reliable electrical connection.

  • Battery Tab Welding in Electronics

Material: In electronics and battery assembly, thin metal tabs or leads need to be welded to battery cells or other components.

Why 35kHz: The 35kHz machine is ideal for this application due to its ability to create precise, low-impact welds on thin metal tabs without causing thermal damage to sensitive electronic components.

20khz Ultrasonic Welding Machines

  • Automotive Fuel Tank Seam Welding

Material: Fuel tanks in automobiles are typically made from thick metal sheets that need to be securely sealed.

Why 20kHz: 20kHz ultrasonic metal welding machines are employed in the automotive industry for their ability to handle thicker materials. They generate the high energy required to create strong, hermetic seals on fuel tanks.

  • Sheet Metal Joining in HVAC Systems

Material: HVAC (heating, ventilation, and air conditioning) systems often involve joining various sheet metal components.

Why 20kHz: The 20kHz machine is well-suited for HVAC applications, where the welding of thicker sheet metal is common. It provides the strength and durability needed for these components to withstand environmental stresses.


Choosing between a 35kHz and a 20kHz ultrasonic metal welding machine involves careful consideration of material thickness, desired weld strength, welding speed, precision requirements, budget, and material compatibility. There is no one-size-fits-all answer, as each frequency offers distinct advantages depending on the application.

Ultimately, the right choice will depend on your specific needs and goals. By thoroughly evaluating these factors and seeking expert advice when necessary, you can make an informed decision that ensures efficient and effective ultrasonic metal welding in your production processes.

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