Ultrasonic riveting technology
Principle of ultrasonic riveting: A method of fixing a thermoplastic part to another part of a different material. Rivets or bosses should have a very large radius or rounded corners at the bottom to prevent cracks or melting. In order to concentrate the ultrasonic energy, the top of the boss should be designed to minimize the initial contact with the welding head. The top of the boss can be flat or conical, and the semi-crystalline or filled polymer is preferably conical. The integrity of ultrasonic riveting depends on the precise capacity relationship between the rivet and the welding head.
Standard riveting-flat head rivets with a diameter of 1.6-4.0mm. Rigid and flexible non-wearing thermoplastics are recommended for standard shapes.
Hemispherical riveting-rivets with a diameter less than 1.6mm are recommended for hemispherical riveting. It is suitable for wear-resistant plastics.
Overflow riveting welding-Overflow riveting welding is used in applications where the surface is required to be flat or raised and the thickness of the locking part is allowed.
Hollow riveting-Boss or rivets with diameter greater than 4mm can produce blind bosses after core removal.
When no through holes are allowed in the mating parts, the ultrasonic welding equipment can also form a mechanical interlock. Molded plastic rivets and blind chamfers in mating parts can form true mechanical joints based on tolerances.
Material factors of ultrasonic welding:
1. Amorphous polymers, especially those that are out of glass at room temperature, are usually good candidates for welding processes. The glassy amorphous polymer has good transmission properties, allowing successful welding with near-field and far-field welding techniques. When the material is soft, the ultrasonic welding of the open-shaped material becomes a problem. For example, welding high impact ps will generally require more energy and additional amplitude than welding general ps.
2. Semi-crystalline polymers are generally more difficult to weld with ultrasonic energy. Increase the energy value emitted by the welding system (that is, increase the amplitude); shorten the distance between the welding head/workpiece contact surface and the joint interface; use near-field ultrasonic welding technology; use a welding head with an amplitude of up to 0.05-0.15mm. These high welding amplitudes require the use of titanium welding heads. When high-strength, sealed assembly is required, both shear joints and ramp joints are suitable for semi-crystalline polymers.
3. Welding hygroscopic polymers: weld the parts immediately after molding (while they are still dry); dry the parts before welding; store the parts in a desiccator before welding.