First, let’s discuss the principle of ultrasonic welding machines: They convert 50/60 Hz electrical current into high-frequency electrical energy (such as 15, 20, 30, or 40 KHz) through an ultrasonic generator. This electrical energy is then transformed into mechanical motion of the same frequency by a transducer. The mechanical motion is transmitted to the workpieces to be welded via an amplitude transformer and a welding horn. The welding horn delivers the vibrational energy to the joint area of the workpieces, where it is converted into heat through friction, causing the plastic or other materials to melt. Under pressure, the molten materials fuse together, forming a strong intermolecular bond. In simple terms, the high-frequency vibrations of the ultrasound cause the two plastic workpieces to generate heat through friction, and under pressure, they fuse together.
Observation: Detailed changes in plastic products during ultrasonic welding. From the images above, we can see that after the ultrasonic friction generates heat, the temperature has reached the melting point of the plastic parts, causing the fusion between molecules. From this, we can derive two key points:
1. The two plastic parts should ideally be made of the same material or materials with similar melting points.
2. Plastic welding involves the fusion of molecules, which ensures the strength of the bond after fusion.
From the images, it is observed that the width of the welding zone depends on the welding pressure. Under the same conditions, the larger the welding line, the greater the pressure required for welding. The welding line mentioned here refers to the ultrasonic welding line or ultrasonic guide line. Depending on the product structure and welding requirements, we design different ultrasonic welding lines. This is also a critical factor in determining whether the desired welding effect can be achieved in the subsequent process.
As previously mentioned, the working principle of an ultrasonic welding machine involves high frequency, vibration, friction generating heat, followed by pressure and cooling. So, through which components does the ultrasonic welding machine accomplish this process?
How is the vibration generated in ultrasonic welding?
The components of an ultrasonic welding machine include an ultrasonic generator, a transducer, an amplitude transformer, and a welding horn. The generator produces high-frequency, high-voltage signals, the transducer converts these signals into high-frequency mechanical vibrations, the amplitude transformer modifies the amplitude, and finally, the welding horn delivers the vibrational energy to the joint area of the workpieces to be welded. During this process, the mechanical motion generates heat through friction on the workpiece surface and between molecules. When the temperature reaches the melting point of the workpiece, the joint area rapidly melts and cools under pressure, achieving the purpose of welding.
An ultrasonic transducer is an energy conversion device that transforms input electrical power into mechanical power (i.e., ultrasonic waves) and transmits it, while consuming only a small portion of the power itself.
Heat is initially generated in the welding zone.
Heat is produced at the interface of the welding horn.
Heat is generated in the surrounding areas.
The entire part experiences minor heat generation.
What factors influence this ultrasonic process?
Firstly, high-frequency vibration—what frequency is used? A vibration of 15,000 times per second is referred to as a 15 kHz ultrasonic welding machine, while a vibration of 20,000 times per second is referred to as a 20 kHz ultrasonic welding machine.
Secondly, the coordination between the ultrasonic horn and the transducer, also known as the fixture.
The two plastic parts should have the same or similar melting points.
The design of the plastic parts’ structure, including the design of the ultrasonic welding line.
Post time: Mar-04-2025