Papers by Author: Liang Wang

Abstract: The conduction heating overcomes shortage of the radiation heating because of rapid heating and high energy efficiency. It is suitable for heating of blanks with an appropriate length/width ratio. In this study, a conduction heating system was developed in terms of Joule’s Law. Sensitivity of blank shapes on temperature distribution of hot stamping boron steel during conduction heating was investigated. Heating experiments of boron steel blanks with irregular-shapes, such as ladder, joist and rectangle with variable cross-section were implemented on the system. The results showed that the steady temperature was decided by the shape of the blanks. It was indicated that the steady temperature of the tested blanks was inversely proportion to the sectional area.

Abstract: Hot stamping ultra-high strength steel not only plays an important role in automotive field, but also has potential application in transmission line fittings industry. According to the current development status of Chinese electrical power fittings and the demand for new technique, combined with hot stamping technology, a new solution for reduction of weight in transmission line fittings has been proposed. This paper focuses on a new lightweight connection fitting with multilayer stack structure of ultra-high strength boron steel, and the key issue in design and manufacturing process of the deep U-shaped hot stamping stacked steel sheet. Numerical simulation method combining the experimental data is also used to predict mechanical performance of the new connection fitting, which provides guidance for the manufacturing process.

Abstract: One of the fundamental problems in scientific computing is to find solutions for linear equation systems. For finite element problem, Cholesky factorization is often used to solve symmetric positive definite matrices. In this paper, Cholesky factorization is massively parallelized and three different optimization methods - highly parallel factorization, tile strategy and memory scheduling are used to accelerate Cholesky factorization effectively. A novel algorithm using OpenCL is implemented. Testing on GPU shows that performance of the algorithm increases with the dimension of matrix, reaching 785.41GFlops, about 50x times speedup. Cholesky factorization is remarkably improved with OpenCL on GPU.

Abstract: In order to meet the requirements of improving hot stamping process, the temperature distribution of high strength steel (HSS) sheets should be observed. However, the accurate measurement of temperature field in transfer where the temperature falls rapidly proves to be difficult due to the limitation of thermocouple. The infrared thermography could be used for accurate measurement of temperature field but the emissivity which is crucial to the accuracy and reliability of measurement results is not available. In this paper, a method to calibrate emissivity of HSS blank was developed for temperature measurement in hot stamping using infrared thermography. Experiments were performed on the emissivity calibration of the HSS Advanced 1500 in hot stamping. Emissivity dependence on temperature was investigated, so was the impact of little variation in emissivity on the temperature measurement. The validation tests were made and the results reveal that this calibration method of emissivity is accurate and feasible. This method is also appropriate for the calibration of emissivity in other temperature measurement situations.

Abstract: Hot stamping has become the main technology to produce complex-shaped high-strength steel components. However, hot sheet metal forming can cause high rates of die wear and the scratching of the productions. A hot drawing tribo-simulator was designed to investigate the friction and wear behavior of high strength steel at elevate temperature. The value of the friction coefficient was obtained to examine the function of the tribo-simulator. The results prove that the coefficient of friction in hot stamping can be measured using this tribo-simulator. Moreover, the coefficient of friction is able to be used in finite element simulation to improve the accuracy of the modeling results and it is also an important indicator to evaluate the tribological behavior between the die and sheet metal.