Introduction of ultrasonic amplitude measuring instrument
Ultrasonic amplitude usually refers to the amplitude of ultrasonic welding equipment. The difficulty of measurement lies in the high frequency and small amplitude. Usually the frequency is between 10kHz and 60kHz, and the amplitude is between 1μm and 100μm. Because of the high frequency, it exceeds the frequency range of most measuring instruments. The small amplitude puts forward high requirements on measurement accuracy. Commonly used testing methods are powerless to it, so it is difficult to measure. Generally, only a laser vibrometer can be used for measurement, and good results can be obtained. However, laser vibration measurement equipment is expensive and complicated to operate. Not to mention general production units, even professional research and design units are rarely equipped, and it is impossible for them to be widely used.
As we all know, for any ultrasonic welding, whether it is ultrasonic plastic welding or ultrasonic metal welding, four parameters can be used to describe. In other words, the effect of ultrasonic welding only depends on four parameters, namely frequency, time, pressure, and amplitude. Among them, the first three parameters are easy to control, adjust and display. Both equipment manufacturers and equipment users understand and pay enough attention to them. They are also adjustment parameters in the daily operation of equipment. The amplitude (displacement) of ultrasonic vibration is a key indicator of ultrasonic equipment, and it is also a physical quantity that is *difficult to measure and *difficult to understand. In addition to experts and scholars, let alone the users of the equipment, even most equipment manufacturers do not care much about it. We have counted most of the manuals of ultrasonic random equipment, and there is very little description of ultrasonic amplitude, including the physical meaning of amplitude, the control and adjustment of amplitude, and the relationship between amplitude and welding quality.
The amplitude of ultrasonic vibration directly represents the size of ultrasonic output energy, and is also related to the strength of related materials and the service life of the whole machine. Whether for manufacturers of ultrasonic equipment or users who use ultrasonic equipment, the importance of it cannot be overemphasized.
For the ultrasonic vibration system, from the perspective of energy transfer, the main indicator is called the ultrasonic sound intensity I. It refers to the energy transferred per square centimeter per second in the direction perpendicular to the propagation direction of the traveling wave, namely
I=1/2ρcω2ξ2
Among them: ρ is the density of the material; c is the speed of ultrasonic propagation in the material;
ω is the angular frequency;
ξ is the ultrasonic amplitude;
Obviously, as the ultrasonic amplitude increases, the ultrasonic energy increases exponentially in a squared relationship.
In the ultrasonic welding process, if the amplitude is too small, the welding energy is not enough, and the welding place will not be welded firmly. Even if the pressure is increased or the welding time is prolonged, there is no good effect. If the amplitude is too large, it will cause over welding, glue flow or welding through. Similarly, reducing the pressure or shortening the time has little effect. If the mold design is unreasonable and the amplitude distribution is uneven, the welding will be uneven and the quality will be greatly reduced.
In the design and production process of ultrasonic equipment, if the vibration system amplitude design is too large, the internal stress of the material is correspondingly too large, exceeding the tensile strength and fatigue strength of the material itself, and the result is the mold, horn or transducer material Cracked. Generally speaking, we recommend that customers control the amplitude parameters of the corresponding components within a reasonable range when designing the ultrasonic system to ensure that the ultrasonic system can work safely and reliably.
