Factors Affecting Ultrasonic Plastic Welding Process
Factors Affecting Ultrasonic Plastic Welding Process – Cheersonic
How much do you know about the main process factors that affect ultrasonic plastic welding?
With the development of modern industry, the replacement of metal materials by plastics and composite plastics as structural materials has become a market demand. The application of plastics and polymer materials in various fields of manufacturing is growing day by day, in machinery manufacturing, aerospace, automotive, electronics, and daily chemicals. All industries have products made of plastics and composite materials.
Traditional method
In the production of complex thermoplastic parts, it is usually a cost-effective way to connect multiple injection molded connections together. You only need to choose a variety of connection methods, such as mechanical clamping and melting connection, ie welding. . Due to the short welding process time, high production efficiency and high connection strength, it is especially suitable for the connection of heat shrinkable plastics. In welding technology, traditional methods are still used, mainly thermal contact welding and hot air welding. It has been unable to meet the needs of modern industrial development, especially the requirements of industrial production automation. Ultrasonic plastic welding has the advantages of high efficiency and high quality to stand out and occupy the market. It is imperative. It is a new process and technology that is economical, efficient and environmentally friendly. It almost completely overcomes the shortcomings of traditional plastic welding methods, has foreseen an excellent future development trend, and basically covers all fields of manufacturing. strength.
However, there is still a lack of research on the basic principles of ultrasonic plastic welding, which cannot meet the needs of industrial applications of ultrasonic plastic welding. Ultrasonic plastic welding machinery and acoustics, electronic technology, computers, measurement technology, mechanical polymer materials, automatic control and other disciplines . It is a multi-disciplinary cross field, so it brings considerable difficulty to the research of ultrasonic plastic welding. The method of combining the mechanism of ultrasonic plastic welding with theoretical analysis and experiment is to study the welding behavior of materials in the ultrasonic plastic welding area, which lays the foundation for establishing ultrasonic welding process specifications and improving welding strength.
Ultrasonic plastic welding requirements
1. The thermal resistance must reach the melting point of the workpiece
After the ultrasonic transducer converts electrical energy into machinery, it is conducted through the material molecules of the workpiece. The acoustic resistance of ultrasonic sound waves in solids is much smaller than that in the air. When the sound waves pass through the joints of the workpiece, the acoustic resistance in the gap is large. , The heat generated is quite large. The temperature first reaches the melting point of the workpiece, and a certain pressure is applied to weld the seam. The other parts of the workpiece will not be welded due to low thermal resistance and low temperature.
2. The two workpieces must be weldable
Some of the different materials can be welded better, some are basically fused, and some are not fused. The melting point of the same material is the same, and it can be welded in principle, but when the melting point of the workpiece to be welded is greater than 350°C, ultrasonic welding is not suitable. Because ultrasound melts the molecules of the workpiece instantly, the judgment is based on the fact that it cannot be welded well within 3 seconds, and other welding processes should be selected. Such as hot plate welding. Generally speaking, ABS materials are the easiest to weld, and nylon or PP materials are the most difficult to weld.
3. There are certain requirements for the joint area
When the instantaneous energy is generated, the larger the joint area, the more serious the energy dispersion, the worse the welding effect, and even the welding is impossible. In addition, ultrasonic waves propagate longitudinally, and the energy loss is proportional to the distance. Long-distance welding should be controlled within 6 cm. The welding line should be controlled between 30-80 wire, and the wall thickness of the workpiece should not be less than 2 mm, otherwise it will not be well welded, especially for products that require airtightness.
4. Output power must be constant
The output power of the ultrasonic welding machine is determined by the diameter and thickness, material and design process of the piezoelectric ceramic sheet. Once the ultrasonic transducer is finalized, the maximum power is also finalized. Measuring the output energy is a complicated process. The larger the ultrasonic transducer, the more ultrasonic power tubes used in the circuit, and the greater the output energy. It requires a very complicated amplitude measuring instrument to accurately measure its amplitude.
Influencing factors
1. Amplitude: The mechanical amplitude output by the acoustic system is the primary process parameter selected for ultrasonic plastic welding. From the perspective of plastic heating, due to its different properties, the heating rate and surface temperature rate of the plastic welding amplitude are different, and each material has In order to achieve the minimum amplitude of melting temperature, if the amplitude is not enough, it is difficult for the plastic to reach the temperature to melt it.
Therefore, the welding strength of plastics is closely related to the amplitude. The amplitude required for ultrasonic plastic welding is adjusted by the shape and material of the horn. In addition, different welding forms require different horns. For example, the amplitude required for inserting and riveting is too large, and the amplitude required for plane welding is small. That is, the amplitude of the welding output will vary with the type of workpiece and the welding form.
2. Ultrasonic time: Ultrasonic time is the time from the start of the ultrasound to the end of the ultrasound. The longer the ultrasound time, the more energy is transferred to the workpiece, the higher the temperature rise of the workpiece, and the greater the amount of melting, but too strong The welding time will cause the surface temperature of the workpiece to be too high to cause excessive damage, overflow glue, damage the surface of the part, and cause “sticking” on the non-welded surface of the in-situ welding zone on the workpiece. If the ultrasonic time is too short, the plastic cannot be melted or the amount of melting is too high. At least, the workpiece cannot be welded reliably.
3. Holding pressure time: The holding pressure time refers to the time that the ultrasound has stopped, allowing the welded parts to adhere to each other and solidify under pressure. The purpose of maintenance is that the weldments are in close contact with each other under a certain pressure, so that the melted materials on the contact surfaces of the two weldments will fuse and cool and solidify, so that the two workpieces can be welded together well.
4. Trigger pressure: Trigger pressure refers to the maximum pre-pressure applied by the welding head on the workpiece before the ultrasonic energy is transmitted to the workpiece.
After the welding head descends to contact with the workpiece, pressure is built up on the workpiece, and when the joint surfaces are in close contact, the ultrasonic welding machine starts to generate ultrasonic waves.
If the trigger pressure is too small, the contact surface cannot be in close contact with the ultrasonic wave, and the workpiece contact surface surface cannot be melted, resulting in a joint with higher strength.
5. Welding pressure: Generally speaking, adequate pressure should be applied to the workpiece so that the entire bonding surface has a better contact pressure. If it is too low, the welding time will be prolonged. This will cause welds on the workpiece and poor quality. High will make the weld rupture, make the interface fusion poor, affect the welding strength and welding quality
6. Frequency tracking: In view of the influence of welding position and welding pressure in the welding process, it may lead to the change of ultrasonic frequency. Frequency tracking is to select an adaptive method to track the frequency of ultrasonic, so that its foundation remains unchanged.