Professor Induction column of February issue of HTRro eNews reviewed the case study illustrating how numerical computer modeling helps optimizing design of induction coil and heating process recipe for SpinductionTM Welding of pistons. It has been shown that since induction pre-heating provides over 95% of the weld energy input, it is critical part of SpinductionTM Welding technology. An ability to obtain required temperature uniformity is imperative for a success of this process. FEA modeling helps determining geometry of inductor that allows achieving the heat balance when heating complex geometry component such as piston, take into consideration a complexity of electro-magnetic field distribution as well as subtleties of dissimilar heat sink effects experienced by different weld zones.
It is important to remember that immediately after completion of the heating stage, the inductor must be quickly retracted from the heating position allowing the two piston’s halves to be rapidly pressed together forming sound weld. Even though the time of retraction of inductor is a fraction of a second, it might be sufficient to noticeably distort temperatures of pre-heated weld faces noticeably affecting thermal condition of the welding process.
An ability to simulate soaking / cooling stage is as important as an ability to computer model the heating stage. An analysis show that only 1 sec of an inductor retraction time can result in temperature reduction of weld faces that exceeds 250deg.C/450deg.F. Therefore, it is important to have clear understanding regarding an effect of time delay between end of heating and beginning of welding.
As an example, Figure below shows dramatic variation of temperature distribution in the proximity to weld faces during 1 second of soaking / cooling on air helping determining the most appropriate maximum time of inductor retraction.
1. V.Rudnev, D.Loveless, C.Ribeiro, J.Boomis, Unleashing a superior induction heating design with computer modeling, Industrial Heating, August, 2009, p.43-47.
2. V. Rudnev, et al., Handbook of Induction Heating, Marcel Dekker, NY, 2003, 800p.
3. V. Rudnev, Simulation of Induction Heating Prior to Hot Working and Coating, ASM Handbook, Vol. 22B: Metals Process Simulation, editors D.U. Furrer and S.L. Semiatin, ASM International, 2010, p.475-500.