Investigation of heat treatment of gears using a simultaneous dual frequency inducting heating method

Abstract

A heat treatment of gears (increasing hardness in the surface layers of gear teeth) significantly enhances the quality and performance of gears in terms of resistance to ware and abrasion and fatigue strength . Recently, a simultaneous dual frequency (SDF) induction heating technology has emerged as the most effective and efficient heat treatment method . It strives to achieve "uniform" temperature distributions along the outer contour of gears by applying two input currents simultaneously [1,2] . The amplitude and frequency of both currents are regulated independently to control the hardening depth at the root and the tip of the gear teeth [3] . Obtaining the best combinations of the input frequencies and powers experimentally is very costly and time consuming . Thus, many researches have been concentrated on determining these parameters using simulation methods, but they require tremendous computational time and resources [4,5] . In an effort to reduce computational costs in determining SDF input parameters, this paper proposes a 2D FE modeling method, and it experimentally evaluates the heat treatments of gears using a SDF induction heating system with the parameters obtained with 2D FE analysis . Two physical phenomena of electromagnetic field and heat transfer should be considered in induction heating models . At each time step, the heat produced by the magnetic field of the medium frequency (MF) and the high frequency (HF) is calculated using the harmonics analysis . It is then assigned as a heat source for the transient heat transfer analysis . This algorithm continues to the end of the target time . Fig . 1 (a) shows the 2D FE induction heating model for a baseline gear used in this study (the number of teeth, module, pitch diameter and width of the gear are 18, 4, 72mm and 10mm, respectively) . For parametric studies, the frequencies from 3 kHz to 15 kHz for MF, 110 kHz for HF and currents from 2000 A to 8000 A were considered . Fig .1 (b) shows simulation results with isothermal plots for each case at 0 .1 sec . Generally, SDF heating can be completed less than 0 .5 sec . As shown in Fig . 1 (b), the isothermal lines of the 3 kHz case "uniformly" follow along the contour of the gear tooth, indicating that it would harden the surface layer of the gear tooth uniformly . For the cases with 10 kHz and 15 kHz, the heat is concentrated in the tip of the gear . Although 3 kHz is the best condition, it becomes faulty gear treatment after 0 .2 sec . So, it can be identified that process time is also an important factor . To study the effect of gear types, this study considered four different gears with the same outer diameter (Gear A-module: 2, tooth number: 38, pitch diameter: 76mm; Gear B-module: 2 .5, tooth number: 30, pitch diameter: 75mm; Gear Cmodule: 4, tooth number: 18, pitch diameter: 72mm; Gear D-module: 5, tooth number: 14, pitch diameter: 70mm) . For this study, the same input condition (HF=110 kHz, MF=3 kHz, I H =2000A, I M =8000A) was used for all gears . Fig .1(c) shows simulation results at 0 .1 ...