When ultrasonic waves act on the contact surface of the thermoplastic, the ultrasonic welding machine generates tens of thousands of high-frequency vibrations per second. This high-vibration vibration reaches a certain amplitude, and the ultrasonic energy is transmitted to the weld zone through the upper weldment. The area, that is, the junction of the two weldments, has a large sound resistance, so local high temperature will occur, and because of the poor thermal conductivity of the plastic, it can not be dissipated in time and gather in the weld zone, causing the contact surfaces of the two plastics to melt rapidly, plus a certain pressure. To make it merge into one. When the ultrasonic wave stops, let the pressure last for a few seconds to make it solidified, thus forming a strong molecular chain for welding purposes, and the welding strength can be close to the strength of the raw material.
The quality of ultrasonic plastic welding depends on the three factors of the amplitude Ca of the transducer welding head, the applied pressure P and the welding time T. The welding time T and the welding head pressure P are adjustable, and the vibration Um is determined by the transducer and the horn.
The energy required for its welding
These three quantities should have an appropriate value for each other. When the energy E exceeds an appropriate value, the amount of melting of the plastic is large, and the welded material is easily deformed. If E is small, it is not easy to weld the car. P should not be too large. This optimum pressure is the product of the side length of the welded portion and the optimum pressure per 1 mm of the edge. When welding polystyrene, AS, ABS and other plastics, the optimum pressure is about 1.47-2.94 N/m.
Although there is a rough calculation about the welding conditions (power and pressure), depending on the type of welding machine or the nature and shape of the plastic, there is only one general criterion for putting it. In addition, the type of plastic, the necessary amplitude in welding and the pressure per unit length on each side, for example, the radio box for welding ABS, when the material is acrylic resin, the side length is 400 mm, the applied pressure is 1.47 N/mm × 400×2=1176N; the welding time is slightly longer, the amplitude is 45m-, as shown in Figure 3.2, then the power needs about 1kW. In view of increasing the output, the welding time must be shortened, which increases the pressure and amplitude, so the power is also I added it. Assuming that the pressure is still 1176N and the amplitude is increased to 55m, then the power of 1.4kW can be found from the curve in Figure 3.2. In the same case of pressurization, different materials require different power. For example, in the case of pressurization of 70 kg, the ABS requires an amplitude of 50 m. Nilon requires an amplitude of 70m, so the welding ABS power is 700W, while the welding Nilon requires a power of 1400W. At the same pressure, the power required to solder ABS is only half that of Nile. The above briefly introduces the three main conditions of welding. Other influences are further explored based on the type of plastic and the shape of the weld. In the ultrasonic welding of thermoplastic materials, it has been found that the rigidity of the reflected sound electrode of the workpiece also plays an important role. When the rigidity is suitable, the high-frequency welding is obtained in a short time by the amplitude vibration.