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ABSTRACT
A recently developed infrared (IR) local heating method is fairly effective to reduce springback of advanced high strength steel in manufacturing processes of car chassis. Although parabolic heaters, consisting of an IR lamp located on the focus of a parabolic reflector, can reduce springback in stamping processes, non-negligible temperature changes are generated in the heated area. For this reason, an improved heater has been required for the IR heating method. In this work, an overlapping heater array is designed to solve the problem of the parabolic heater for the IR local heating method. The overlapping heater array can reduce the temperature change in the heated area. In the overlapping heater array, the parabolic heaters are connected in series. The connected parabolic heaters are then placed on both sides of a thin sheet metal and intersected to reduce the temperature change. In order to design a more efficient overlapping heater array, a simple design parameter was employed. The numerical and experimental verifications have shown that the overlapping heater array drastically reduces the temperature change in the heated area.
Nomenclature
| a | = | Distance between lamps in the overlapping heater array (m) |
| d | = | Width affected by the direct radiation (m) |
| dA1, dA2 | = | Each infinitesimal area per unit length (m) |
| DP | = | Dual-Phase |
| fl | = | Vertical distance between the lamp and the heated surface (m) |
| FEM | = | Finite element method |
| I0 | = | Irradiance of the lamp (W/m) |
| I1, I2 | = | Each energy intensity incident on dA1 and dA2 (W/m2) |
| IR | = | Infrared |
| k0 | = | Thermal conductivity of the used DP 980 steel sheet (W/m·K) |
| k | = | Artificial value of the thermal conductivity for the numerical study (W/m·K) |
| mn | = | Central point of the nth lamp (m) |
| = | Unit normal vector to a surface | |
| r | = | Distance between the lamp and the target point (m) |
| T | = | Temperature (K) |
| w | = | Effective heating width of the overlapping heater (m) |
| x | = | Distance from the center in the heated area |
Greek symbols
| dα | = | Infinitesimal angle (°) |
| θ | = | Angle between the normal vector and the IR ray incident on the target point (°) |
| μ | = | Absorptivity of a heated surface |
| τ | = | Measure of temperature change: average change of the temperature per unit length in the effective heating width (K/mm) |
| Φdirect(x) | = | Direct radiation : absorbed IR heat flux from the heat flux incident on the heating surface after being directly emitted from one IR lamp (W/m2) |
| Φaovl(x) | = | Overall heat flux from the multiple lamps (W/m2) |
| Ψ | = | Measure of flux change: average change of the heat flux per unit length in the effective heating width (W/mm2/mm) |
Subscripts
| direct | = | IR rays directly emitted from a IR lamp |
| max | = | maximum |
| min | = | minimum |
| n | = | nth lamp |
| ovl | = | Summation of IR rays from multiple lamps |
Superscripts
| a | = | Distance between lamps in the overlapping heater array (m) |
| = | Vector |
Additional information
Notes on contributors
Eun-Ho Lee
Eun-Ho Lee received Ph.D. degree from the department of mechanical engineering at KAIST in 2015, then he worked at General Motors R&D center in Detroit, USA. His research interest is thermal-mechanical analysis and applications in mechanical engineering. He has several published papers and patents in the field. He is now working at Handong Global University as an assistant professor.
Dong-Yol Yang
Dong-Yol Yang received his M.S. and Ph.D. degrees on metal forming theory and applications in mechanical engineering, respectively, in 1975 and 1978 from Korea Advanced Institute of Science and Technology (KAIST). He has been working as professor in mechanical engineering department at KAIST since 1978. He has published over 600 technical publications in academic journals and international conference proceedings. His research interest lies in net shape manufacturing in general, including metal forming and rapid prototyping covering nanostereolithography.