Ultrasonic welding and welding horn having indenter

A method of joining includes disposing a second workpiece adjacent to a first workpiece. The method further includes identifying a determined hardness parameter of at least one of the first and second workpieces at a welding position. The determined hardness parameter is determined by at least one of estimation, calculation, and measurement. The method includes selecting a weld schedule based on the determined hardness parameter and welding the first and second workpieces together using the selected weld schedule. A welding horn includes a shank and a tip having an end face, the tip being disposed at an end of the shank and configured to contact a workpiece and to transmit energy to the workpiece. Knurls are disposed on the end face, each knurl having a distal end. A curved indenter extends from the end face beyond the distal ends of the knurls.