Experimental characterization of heat transfer coefficients for hot stamping AA7075 sheets with an air gap
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(2020) 20:93
ORIGINAL ARTICLE
Experimental characterization of heat transfer coefficients for hot stamping AA7075 sheets with an air gap Wenchao Xiao1 · Kailun Zheng2 · Baoyu Wang3,4 · Xiaoming Yang3 Received: 23 April 2020 / Revised: 16 June 2020 / Accepted: 6 July 2020 © Wroclaw University of Science and Technology 2020
Abstract The heat transfer coefficient (HTC) is critical for hot stamping and in-die quenching. The air gap at interface is a dominant factor affecting the HTC, which is normally resulted from initial tooling clearance and thinning of deformed aluminum sheet. To precisely determine the HTCs under different air gaps, this research performed a comprehensive investigation on determining HTCs between an AA7075 blank and H13 tool steel. Hot stamping experiments were performed with different air gaps enabling HTC values were determined. Using the experimentally calibrated HTC, a finite-element model for hot stamping a door beam was established, which was successfully verified using the experimentation. The good predictions showed the reliability of the HTC values under different air gap conditions. Keywords Hot stamping · AA7075 · Heat transfer coefficient · Air gap
1 Introduction Hot stamping technology is an effective solution for manufacturing complex-shaped panel structures of high-strength aluminum alloys, enabling the drawback of poor ductility at ambient temperature to be overcome. Mohamed et al. [1] analyzed the deformation and failure features in hot stamping of AA6082, and a set of constitutive equations were established to predict the improved formability under optimized hot stamping conditions. El Fakir et al. [2] numerically * Baoyu Wang [email protected] Wenchao Xiao [email protected] Kailun Zheng [email protected] Xiaoming Yang [email protected] 1
School of Engineering and Technology, China University of Geosciences (Beijing), Beijing 100083, China
2
School of Mechanical Engineering, Dalian University of Technology, Dalian 116024, China
3
School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China
4
Beijing Key Laboratory of Metal Lightweight Forming Manufacturing, Beijing 100083, China
investigated the formability of AA5754 and found that a higher forming temperature results in significantly greater formability. Zheng et al. [3] demonstrated that hot stamping followed by cold-die quenching, which combines the stamping process with the heat treatment process, can simultaneously improve the formability of AA6082 aluminum alloys, guarantee a desirable microstructure, and satisfy the postmechanical property requirements. Furthermore, a variety of aluminum alloy grades, such as AA7075 [4], AA2024 [5], have also been demonstrated their feasibility in the hot stamping process. The interface thermal properties of tooling are of vital importance to determine the temperature fields of both the sheet and forming dies during hot stamping. Subsequently, material deformation and microstructural evolution, such as the formation of
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