Simultaneous dual-frequency induction heating adds a new dimension to the variables that control the induction heating process. The process requires less energy and space than earlier dual-frequency induction heating systems, as well as atmosphere furnace treating systems. It also can be more easily incorporated into an automated manufacturing line or flexible work cell. In addition, the process provides a cost benefit by allowing the use of high-carbon steels, which are ideally suited for induction hardening, compared with more expensive high-alloy steels used with thermochemical processes. The reduced overall heating associated with simultaneous frequency heat-treating technique improves the microstructure of the hardened area, has minimal effect on material core properties and, in most cases, eliminates the need for finish machining to meet dimensional specifications after hardening.
From the very beginning of the industrial application of induction heating to heat treat gears, engineers have attempted to obtain a uniform case-hardened surface on the tooth profiles of gears. Case hardening increases both the abrasion resistance of the tooth face and the fatigue properties of the root of the tooth without through hardening. However, early induction heating approaches were limited to what could be achieved using a single-frequency power supply, or two power supplies operating independently at different frequencies to sequentially heat the gear plus the mechanics necessary to switch power and move the part.