The horn in ultrasonic welding has several primary functions, including:

1. Amplifying the high-frequency vibrations produced by the ultrasonic transducer to the workpiece.
2. Transferring the mechanical energy generated by the transducer to the joint area between the workpieces.
3. Focusing the mechanical energy to the specific area of the workpiece where welding is required.
4. Controlling the amplitude, frequency, and duration of the ultrasonic vibrations applied to the workpiece.
5. Ensuring that the mechanical energy is evenly distributed across the joint area, resulting in a strong and consistent weld.
6. Providing support and stability to the entire ultrasonic welding system.

The shape, size, and material of the horn are critical factors that affect the performance of the ultrasonic welding process. The design of the horn is specific to the part being welded, and various horn configurations are available to suit different welding requirements.