In contemporary society, various plastic products have penetrated into every area of ​​people's daily life, and they have also been widely used in aviation, ships, automobiles, toys, electronics and other industries. However, due to factors such as the injection molding process, a considerable part of plastic products with complex shapes cannot be injection molded at one time, which requires bonding, and plastic bonding and heat sealing processes that have been used for many years are quite backward, not only inefficient, but also bonded. The agent also has certain toxicity, causing problems such as environmental pollution and labor protection. Traditionally, this kind of technology can no longer meet the development needs of the modern plastics industry, so a novel plastic processing technology—ultrasonic plastic welding stands out for its superiority of high efficiency, high quality, aesthetics, and energy saving.
Ultrasonic plastic welding machine welding plastic products, that do not add any adhesive, filler or solvent, nor consume a lot of heat, with simple operation, welding speed, high welding strength, high production efficiency. Therefore, ultrasonic welding technology has become more and more widely used.
First, the working principle of ultrasonic plastic welding machine.
When the ultrasonic wave acts on the thermoplastic plastic contact surface, it will generate tens of thousands of high-frequency vibrations per second. This kind of high-frequency vibration reaches a certain amplitude, and the ultrasonic energy is transmitted to the weld zone through the upper weldment, since the weld zone is two. The welding interface has a large acoustical resistance and therefore generates local high temperatures. Because of the poor thermal conductivity of plastics, they can not be distributed in time and accumulate in the weld zone, causing the two plastic contact surfaces to melt quickly and add a certain pressure to fuse them into one. When the ultrasonic wave ceases to function, let the pressure persist for a few seconds to allow it to solidify and form a solid molecular chain so that the welding can be achieved. The welding strength can be close to that of the raw material. The quality of ultrasonic plastic welding depends on the amplitude of the transducer weld head, the applied pressure and the welding time. The welding time and welding head pressure can be adjusted. The amplitude is determined by the transducer and the horn. These three quantities have a suitable value for each other. When the energy exceeds the suitable value, the amount of plastic melting is large, and the welding material is easily deformed; if the energy is small, the welding is not easy and the applied pressure cannot be large. This optimum pressure is the product of the side length of the welded part and the optimal pressure per 1 mm of the edge.
Second, ultrasonic plastic welding method
1. Welding ultrasonic vibration with the welding head conducts the ultrasonic wave to the weldment. Due to the large acoustic resistance at the two weldments, local high temperatures are generated and the interface of the weldment melts. Under certain pressure, the two weldments achieve a beautiful, fast, and strong welding effect.
2. Insert the nut or other metal into the plastic workpiece. First, the ultrasonic wave is transmitted to the metal, and after high-speed vibration, the metal material is directly embedded in the molded plastic, and the plastic is melted at the same time.
3. The riveting method is intended to join metal and plastic or two plastics with different properties. Ultrasonic riveting can be used to make the weldment less brittle, beautiful and strong.
4. The spot welding method uses small welding heads to spot weld two large plastic products, or the entire row of toothed welding heads directly presses on two plastic workpieces to achieve the effect of spot welding.
5. The forming method utilizes ultrasonic waves to instantaneously melt the plastic workpieces. When the plastic is solidified, it can make the metal or other material plastic firm.
6. The resection method utilizes the special design method of the welding head and the base. When the plastic workpiece has just been injected, it directly presses on the plastic trunk and achieves the effect of removal through ultrasonic conduction.
Third, the sound wave plastic welding machine composition and its role
Ultrasonic plastic welding machine consists of pneumatic transmission system, control system, ultrasonic generator, transducer, tool head and mechanical device.
1. Pneumatic transmission system
Including: helium devices, pressure reducing valves, oil misters, commutators, throttle valves, cylinders, etc.
During the work, the air compressor is used to drive the stroke cylinder to drive the ultrasonic transducer vibration system to move up and down. The pneumatic pressure is set according to the welding requirements in the middle and low power ultrasonic welding.
2, the control system
The control system consists of a time relay or integrated circuit time timer.
The main functions are: First, control the pneumatic transmission system to make it open under the time control of the welding gas valve, the cylinder pressure to make the welding head down, press the object to be welded with a certain pressure, when the welding pressure after a period of time The control system then reverses the pneumatic valve to allow the welding head to lift and reset. The second is to control the working time of the ultrasonic generator. This system enables the entire welding process to be automated. When the operation only starts the button to generate a trigger pulse, it automatically finishes. In this welding process. The sequence of the entire control system is: the power source starts a trigger control signal pneumatic transmission system, the cylinder pressurizes the welding head down and presses the welding to trigger the ultrasonic generator, emits the ultrasonic and maintains a certain welding time to remove the ultrasonic emission, and maintains a certain pressure time to depressurize , welding head recovery welding end.
3, ultrasonic generator
1) Ultrasonic plastic welding machine with large power, the generator signal adopts phase-locked frequency automatic tracking circuit, so that the output frequency of the generator is basically the same as the resonant frequency of the transducer.
2) The generator used in ultrasonic plastic welding machines with power above 500W uses a self-excited power oscillator and also has a certain frequency tracking capability.
4. Acoustic systems used in ultrasonic plastic welding machines
1) Transducer
The acoustical system for ultrasonic plastic welding machines consists of three parts: 1 Driving part 2 The fixing part 3 working part. In the above three components, the drive is the core, generally using a bolt-clamped longitudinal vibration transducer, in which a half-wavelength longitudinal oscillator and a quarter-wavelength longitudinal oscillator, a half-wavelength longitudinal vibration and a half-wavelength concentrator The connections form a full-wavelength plastic welding transducer, and a quarter-wavelength longitudinal oscillator is connected to a quarter-wavelength concentrator to form a half-wavelength transducer.
2) Tool head
Different tool heads are required for different welding objects. Whether it is near-field welding or transmission welding, only a half-wavelength tool head can achieve the maximum amplitude of the welding end face. The tool head has two types, with amplitude amplification and without amplitude amplification. The head of the acoustic welding system for plastic welding machines is usually made of aluminum alloy. The end face is plated with a carbide, and when the power is high, it is also made of titanium alloy. As a result, the fatigue strength of this material is more than double that of aluminum alloy.
Fourth, ultrasonic plastic welding machine model and specifications
Ultrasonic plastic welding machine because of different occasions and welding materials, welding size is not the same, its specifications are also varied. Its output power ranges from a few tens of watts for manual welding machines to a few kilowatts for mainframes, typically in the range of 15 KHz to 40 KHz.