What Is the Principle of Ultrasonic Cleaning?
The key principle of ultrasonic cleaning is cavitation.
When ultrasonic waves travel through a liquid, they create alternating high-pressure and low-pressure cycles.
During the low-pressure phase, countless tiny bubbles form in the liquid. When the pressure rises again, these bubbles collapse instantly, releasing localized high pressure and high-speed micro-jets.
These microscopic implosions impact the surface of the workpiece, dislodging attached contamination layers while enhancing the chemical action of the cleaning solution. As a result, the overall cleaning effect becomes more uniform and thorough.
You can imagine cavitation as countless “invisible tiny brushes” in the liquid. When the bubbles collapse, they act like they are brushing away surface contamination.
Why Can Ultrasonic Cleaning Clean So Thoroughly?
Compared with manual wiping or high-pressure spray cleaning, ultrasonic cleaning offers the following advantages:
It can reach fine gaps and blind holes to remove contamination that is difficult to access by hand.
The cleaning force is uniform and consistent, regardless of the shape or position of the workpiece.
It requires fewer chemical agents, making it more environmentally friendly and energy-saving.
It can be combined with filtration and circulation systems to maintain stable cleanliness over long operating periods.
It can be fully automated, reducing manual labor and human error.
Through liquid flow, it can effectively carry away detached oil, dirt, and fine particles.
This makes ultrasonic cleaning widely used in automotive and motorcycle parts, electronics, optics, semiconductors, medical devices, molds, and precision parts cleaning.
Common Frequencies Used in Ultrasonic Cleaning
Different ultrasonic frequencies affect bubble size and cleaning intensity.
The following are common ultrasonic frequency ranges and their applications:
28 kHz
Strong cavitation force and high cleaning power, but relatively rough. Suitable for automotive and motorcycle parts, heavy oil contamination, and metal parts.40 kHz
A general-purpose frequency that balances cleaning power and cleaning fineness. Suitable for electronics, precision mechanical parts, and molds.68–80 kHz
Gentle cleaning, suitable for fine structures. Commonly used for optical lenses and medical instruments.120 kHz and above
Ultra-fine cleaning, suitable for high-precision parts. Commonly used in semiconductors, optoelectronics, and high-end processes.
In Taiwan’s industrial applications, the commonly used ultrasonic cleaning frequencies are around 28 kHz and 40 kHz because these two frequencies provide a good balance of cleaning efficiency and stability.
Advantages and Limitations of Ultrasonic Cleaning
Advantages:
Reaches blind holes and fine gaps for thorough cleaning.
Short cleaning time and high efficiency.
Reduces labor and chemical usage.
Can be combined with filtration and pure water systems to ensure stable quality.
Suitable for high-volume processes or applications requiring high cleanliness.
Limitations:
Not suitable for very thin or easily damaged materials. For example, soft aluminum or plated parts may require power adjustment.
Excessive contamination in the liquid may reduce cleaning performance, so regular filtration and liquid replacement are required.
Large or heavy workpieces may require lifting fixtures or rotating mechanisms for assistance.
Applications of Ultrasonic Cleaning
Automotive and motorcycle industry: engines, clutches, fuel injectors, and metal parts.
Electronics and semiconductor industry: wafers, PCBs, pins, and lead frames.
Optical and precision machinery: lenses, molds, cutting tools, and bearings.
Medical and laboratory applications: surgical instruments, glassware, and laboratory parts.
Metal surface treatment: pre-plating cleaning, wax removal after polishing, and degreasing processes.