Ultrasonic welding process in welding of automobile plastic parts
Ultrasonic automotive plastic welding Ultrasonic welding definition: Ultrasonic welding is a high-tech technology for welding mature plastic plastic products. Since the application of this technology can replace the flux, adhesive, studs or other mechanical fixing methods in the past, the production efficiency is improved and the cost is reduced. The principle of ultrasonic welding is to convert high-frequency electrical energy into high-frequency mechanical motion through an ultrasonic generator, and then the mechanical motion is transmitted to the welding head through a set of amplitude modulator devices that can change the amplitude. The welding head transfers the received vibration energy to the joint of the workpiece to be welded. In this area, the vibration energy is converted into heat energy through friction to melt the plastic. Ultrasound can be used not only to weld hard thermoplastics, but also to process fabrics and films.
Advantages and disadvantages of ultrasonic welding in the automotive industry: Advantages of ultrasonic welding: fast and automatic. Disadvantages of ultrasonic welding: limited by size, shape and material (ultrasonic welding is mostly for PP, PC, ABS, PA, PS, AMMA plastics)
The design of the ultrasonic welding surface is inclined surface welding to achieve a complete surface connection. Since uniform heat energy and larger welding area can be obtained, the welding strength is high and the air tightness is good. Successive joining belongs to shear welding, and uniform heat is obtained from the surface contact joint in the vibration direction, and its air tightness and welding strength are very good. However, the flash generated after welding will stay on the surface, especially when flash is not allowed, be careful. Shear joining is between the above-mentioned bevel joining and successive joining. Because of its good airtightness, it can effectively weld shapes other than circles, so it is often used. Energy-oriented joining is a joining design method where energy is concentrated on the convex part of the triangle called directional, and the heat generated by repeated impacts. The advantage is that the shape is simple and the restriction of the joint part is small. However, for crystalline plastics, excessive local heating will cause softening and melting, which will lead to pressure welding stress loss and poor airtightness, which must be paid attention to.
Ultrasonic welding conditions: As the conditions of ultrasonic welding, the important thing is the length of time (vibration, welding time) and pressure applied to welding energy. Of course, other conditions are also very important. Welding temperature The viscous flow temperature of the ultrasonic welding material. Otherwise the material will not melt. Related to the amplitude, the higher the amplitude, the higher the temperature rise. The pressurizing force uses a cylindrical tool to pressurize the molded product. Generally, the compressed air pressure is 0.1-0.3MPa (pressure gauge), sometimes higher. However, if high pressure is used, the cylindrical vibration will be hindered. The welding time varies depending on the type of material and the shape of the product, and the welding time of some molded products is only 0.2 seconds. Too long time will cause excessive welding and produce a lot of flash and bubbles, which will lead to poor airtightness, so attention must be paid. Cooling (holding) time For crystalline plastics, if the temperature is below the melting point, the connecting part will be solidified, and the pressure time is usually maintained between 0.1 and 0.2 seconds.
Ultrasonic welding machine requirements: the welding head is divided into three parts from bottom to top: welding head, amplifier and transducer. The three are enlarged according to a certain ratio. If the amplitude of the transducer is 6MM, the amplifier can amplify three times to 18MM, and the amplitude to the welding head can be increased to 36MM. Of course, as the amplitude increases, the life of the welding head will decrease. Different materials to be welded require different amplitudes. There are generally three types of welding head materials: Titanium: expensive, good performance, good toughness, and difficult to process. The friction loss is small, and the amplitude can reach 60MM; aluminum alloy: cheap, fast wear, amplitude cannot exceed 30MM, easy to process; steel: very hard, not suitable for welding head, amplitude cannot exceed 25MM, suitable for cutting, need to increase blower pipe, Easy to cool.
Ultrasonic automotive welding applications: automotive door panels, automotive door panel sound insulation felt, automotive non-woven interior parts spot welding, automotive dashboards, automotive dashboards, automotive plastic parts riveting, automotive bumpers, automotive tire covers, automotive roofs, automotive trunks Non-woven fabrics, non-woven fabrics for car seat cushions, car engine covers, car taillights, car lampshades, car bearing cages, car glove boxes, car filters, car plastic valves, car air commutators, car airflow detectors Wait. For the welding of automotive plastic parts, non-standard ultrasonic welding equipment is mostly used, multi-head multi-station design, with PCL program control and LCD display operation, welding of large-scale automotive complex workpieces, including welding surfaces in different directions, and multiple locations need to be welded at the same time .