A modular rotary anvil for mounting on an ultrasonic welding machine. The modular rotary anvil includes a first end segment configured to attach to the ultrasonic welding machine, a second end segment configured to attach to the ultrasonic welding machine, and at least one insert having a first side and a second side. Each of the first side and the second side is configured to attach to at least one of other inserts, the first end segment, and the second end segment.