A student just e-mailed me this question…
I am a little confused about the difference between Near Field and Far Field ultrasonic welding. Is this referring to the size of the part or the horn?
Actually, near and far field refers to the distance from the ultrasonic horn to the weld joint. Typically, when this distance is less than 0.25in or 6mm it is considered ‘Near Field’ or ‘Close Range’ ultrasonic welding. Distances greater than that are generally considered ‘Far Field’ or ‘Long Range’ ultrasonic welding.
As a general rule, the greater the distance, the more difficult it is to get the vibrational energy of the horn transferred to the point of the weld. Materials which are softer often get less polymer chain entanglement at the interface since much of the vibrational energy is absorbed by the part before it reaches the joint.
Parts being designed for ultrasonic welding should take factors such as horn location and joint design early in the design process to ensure success.