Mobile Induction Heat Treatment of Large-Sized Spur Gear—The Effect of Scanning Speed and Air Gap on the Uniformity of Hardened Depth and Mechanical Properties

Prematurely fractured teeth of SCM440 large-sized spur gear are commonly found among gears of a mechanical press machine. The macroscopic inspection and microstructure examination of a fractured tooth are established to show that the previous induction hardening process produced two serious issues; insufficient hardening in the root areas and nonuniform hardened depth along the tooth circumference. The numerical simulation is executed to replicate the previous induction hardening process, which consists of simulations for tooth-to-tooth mobile induction heating, water spray quenching, and the tempering process. This study highlights the influence of most adjustable parameters, such as the scanning speed of the inductor coil and air gap, to collect beneficial insights for further improvements. Experimental and numerical results are compared to validate the numerical model used. The adjustment of scanning speed and air gap highly affects the magnitude and uniformity of hardened depth along the tooth profile. Promising improvements can be achieved by slower, smaller scanning speeds and thinner air gaps, where the distortion is still in the allowed allowable range. This research provides a method and insights for future explorations to deal with relevant issues in the tooth-to-tooth mobile induction hardening process.