Welding by position or absolute distance in ultrasonic welding refers to controlling the weld process based on the actual position or distance between the horn and the workpiece. This method is typically used when the parts being welded are not of uniform size or shape, or when the positioning of the parts is critical to the final product.

In this method, the position of the horn is measured and controlled using sensors, which can be optical, mechanical, or electromagnetic. The distance between the horn and the workpiece is also measured and controlled using similar sensors. This allows for precise control of the welding process and ensures that the parts are joined in the correct position and with the correct amount of pressure and energy.

Welding by position or absolute distance is commonly used in the production of complex parts and assemblies, such as automotive components, medical devices, and electronics.