sentences:  Much of this work took place at the frequencies of 1920 and 3000 Hz as these were the easiest frequencies to produce with the equipment available.As with many technology-based fields it was the advent of World War II which led to huge developments in the utilization of induction heating in the production of vehicle parts and munitions.Over time, the technology advanced and units in the 3 to 10 kHz frequency range with powers outputs to 600 kW became common place in induction forging and large induction hardening applications.