Available in 20 and 40 kHz versions, portable ultrasonic plastics welding systems can be set to weld in digital time (0.1 to 9.9 sec) and/or constant energy (0 to 999,999 J) modes as well as continuous duty mode for optimal control. Each 500 W, MPU-controlled hand gun, designed for welding, staking, inserting, and spot welding applications, also has autotune circuitry, frequency display, digital amplitude control, ultrasonic power load meter, and upper/lower weld limit settings.