Abstract: Special positioning tooling and two kinds of U-shaped inductors A and B with Π-shaped silicon steel sheet were designed. The induction hardening test of internal spline in tulip was carried out by using inductor A and B under the condition of spray protection of outer surface on the fully automatic quenching machine with frequency of 8-20 kHz and maximum output power of 300 kW. The results show that by using the method of positioning only the inner hole and end surface, the induction hardening is carried out with the U shaped inductor with Π-shaped silicon steel sheet under the condition of protective spraying on outer surface, which can meet the quenching requirements of internal spline in tulip. Compared with A type inductor, the heating power coefficient of B type inductor is lower, the heating time is shorter, and the energy saving and production increasing effect is more remarkable, which shows that the reasonable inductor design for the induction hardening of internal spline in tulip is an effective way for energy saving and production increasing.

Key words: internal spline, quenching process, inductor structure, energy conservation