Experimental Platform Design for the Determination of the Heat Transfer Coefficient in the Hot Stamping Process
Date Issued
2014
Date
2014
Author(s)
Tsai, Pei-Wu
Abstract
As the raise of environmental awareness and demand of carbon reduction, the automobile companies have dedicated to reducing the weight of automobile structure to achieve higher fuel efficiency. Due to the low formability, springback and twisting defects by raising the strength of steels, there still exists difficulties in manufacturing and cost reduction. Hot stamping has become the solution for these problems instead. Through a series of hot stamping stages leads the microstructure to Martensite transformation. The tensile stress can reach over 1400MPa with thinner blank. Therefore, hot stamping can achieve both objects of lightweight and high strength.
Through finite element analysis, performance and process designs of products can be predicted effectively before production. And the heat transfer coefficient (HTC) is one of the most critical parameter for numerical simulation. In order to improve simulation accuracy, the experimental platform and the method of calculating HTC are established. By measuring the temperature history both in die and blank, the HTC can be computed and used in CAE analysis of hot stamping components.
Influential factors associated with HTC are listed by reviewing recent development of hot stamping and research of HTC. In order to confirm the importance and necessity of HTC, the effects of cooling rate, thinning percentage and transformation of microstructure through U-shape simulation with different HTC from references are discussed.
The experimental platform is evaluated and designed by CAE analysis which includes the positions of measurement, shape of the specimen and design of cooling system. Finally, the axial symmetric circular die is employed with the experimental parameters containing different contact pressure, gaps and the various initial temperatures. Based on the history of temperature measurement, Newton’s cooling law and inverse technique are utilized to compute HTC. The HTC increases with higher contact pressure, lower gap and higher initial temperature.
Finally, different forming processes and various gaps between die and blank are discussed in door beam to investigate the effects on thinning percentage and cooling rate. The proper parameters and HTC from previous experiment are employed in the door beam analysis. By comparison of the temperature and the thickness between simulation and experiment, the result shows that there exists high consistence. Therefore, it reveals that the HTC has actual application and the hot stamping analysis of door beam can be employed in evaluation of die design.
An experimental method and computing techniques of heat transfer coefficient have been set up in this research. And it also applies in analysis of automobile components. In the future, more factors on HTC can be further investigated and discussed.
Subjects
熱沖壓成形
介面熱傳係數
接觸壓力
牛頓冷卻定律
有限元素分析
防撞樑
Type
thesis
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