The document describes several case studies where Fluxtrol helped optimize induction heating processes by developing new induction coil designs and magnetic flux concentrator profiles. In each case, computer simulations identified issues with existing processes, and new coil designs with customized Fluxtrol concentrators achieved more uniform heating and resolved production problems. The optimized solutions improved part quality, increased production rates, and extended coil lifetimes.

1. Chapter VII. Case Stories

3. Case Story 1. Design of Stress Relieving Coil and Process

6. Step 2: Simulation of Existing Process Flux 2D program 1 2 Temperature evolution in Outside (1) and Inside (2) seam points Temperature color map at the end of heating These results are close to experimental data and very far from specifications

7. Step 3: Initial Inductor Design Using Power Ramping Results are much better but specifications are still not met The easiest way to improve temperature distribution is to use power profiling along the coil length. It may be achieved by variation of concentrator geometry. 1 2

9. Temperature Evolution with New Coil Temperature profile along the pipe OD surface at the end of heating Temperature evolution in Outside (1) and Inside (2) seam points for optimized process Minimum temperature in HAZ (point 2) reached required value without material exceeding maximum acceptable temperature 1 2

10. New Inductor Sketch (Top and Side Views) Concentrator has full C-shaped profile at ramping stage. When maximum permissible temperature was reached, concentrator shape started to change by cutting pole length and then complete removal of concentrator. Top view of concentrator (hatched) Side view of induction coil Fluxtrol concentrator Fluxtrol concentrator

12. Case Story 2. Wheel Hub Heat Treating

16. Step 3: Development of New Induction Coil Using Computer Simulation Predicted hardness pattern Temperature distribution in part with new coil design Flux 2D program

18. Case Story 3. Surface Hardening of Truck Axle

21. Step 2a: Simulation of the Process with Existing Single Turn Coil . Temperature distribution and magnetic field lines at the end of dwelling period Flux 2D program Simulation of the process with a single-turn coil without a magnetic flux controller clearly showed overheating of the stem near fillet area (in good agreement with tests results)

22. Step 2 a: Temperature Distribution at the End of the Dwell Results: Marginal depth in the radius, severe overheating in the area above the radius (temperature over 1150 C, which would continue to grow in the beginning of the scanning process) Temperature range 20 – 1150 C Temperature range 800 – 1150 C

23. Step 2b: Simulation of the Process with Existing Two-Turn Coil Temperature distribution and magnetic field lines at the end of dwell Flux 2D program

24. Temperature Distribution at the End of the Dwell with Two-Turn Coil Results : Insufficient depth in the radius and short pattern on fillet, severe overheating in the area above the radius (temperature over 1130 C, which would continue to grow in the beginning of the scanning process). Temperature range 20 – 1135 C Temperature range 800 – 1135 C

25. Step 3: Development of Optimized Coil Temperature distribution and magnetic field lines at the end of dwell Based on results of computer simulation and previous experience it was decided to design a two-turn coil with Fluxtrol concentrator on the lower turn. This design provides a favorable temperature distribution with required hardness depth on fillet and well controlled preheating of the stem area by the upper turn. Optimal temperature distribution was achieved by variation of cross-sections of copper and magnetic concentrator made from Fluxtrol “A” .

26. Temperature Distribution at the End of the Dwell with Optimized Coil Results: Good depth in the radius, no significant overheating in the area above the radius (temperature less than 1020 C); high scan speed/production rate Temperature range 20 – 1020 C Temperature range above 800 C corresponding to a total hardness depth

27. Case Story 4. Induction Brazing of Aluminum Heat Exchanger

29. System Geometry Description Existing inductors had a “horseshoe hairpin” shape for simple part loading. The coils consisted of two hair-pin sections connected in series with diagonal cross-over. Geometry is clearly 3D with multiple components (pipe, tube, header, coil copper, magnetic controllers). Due to planes of symmetry it was possible to simulate only ¼ of system. Non-symmetry due to crossovers was neglected. Geometry prepared for simulation using Flux 3D program

30. Step 1: Simulation of Existing Process Current density distribution in joint area for diagonal crossover. Left – no electrical contact Right – good electrical contact Coil currents direction and magnetic generic field lines for horseshoe coil with diagonal crossover On a base of process analysis it was assumed that the main non-controlled variable was an electrical contact between pipe and tube. These components are preliminarily coated with flux and electrical contact between them is unstable. When the joint is filled with molten filler metal, contact is good. Computer simulation confirmed this theory. With no electrical contact there is a strong heat concentration on the tube edge closest to the coil. Overheating of this area is a common defect of brazing. With good contact current flows from tube to pipe resulting in heat pattern change. It is not possible to balance these two patterns achieving stable quality. + +

31. Step 2: Development of Induction Coil with Horizontal Crossover Current density distribution in joint area for horizontal crossover. Left – no electrical contact Right – good electrical contact Coil currents direction and magnetic generic field lines for horseshoe coil with horizontal crossover For a coil with horizontal crossover currents flow mainly inside of each component for good and no contact conditions. However, computer simulation showed that heating of pipe and tube is very weak compared to the heat exchanger header. Small heating of header is useful for support of temperature profile in the tube, but main power must be delivered to pipe and tube in a correct proportion. + . +

32. Final coil design for one of the brazing joints Optimized power distribution in brazing joint components Step 3: Optimal Coil and Process Design Additional magnetic controller was placed between the coil bottom and header surface. Variation of magnetic flux controllers made of Fluxtrol “A” material allowed the process to achieve optimal power distribution between all three heat exchanger components. Laboratory tests confirmed stable process flow and good quality of brazed parts. Additional consideration: It was noticed that change of crossover resulted in much stronger electrodynamic forces. Coil tends to “open” when power is turned ON. To reduce effect of electrodynamic forces, an additional fiberglass connector was installed on the coil.