Search

A simplified column-buckling model is developed to understand the buckling mechanism of thin-walled strips restrained by uniform lateral pressure in the milling process. The strip is simplified as two rigid columns connected by a rotation spring, resting on a smooth surface, restrained by a uniform pressure and loaded by an axial force. Two loading cases are considered, i.e., the dead load and the follower load. Analytical solutions for the post-buckling responses of the two cases are derived based on the energy method. The minimum buckling force, Maxwell force and stability conditions for the two cases are established. It is demonstrated that the application of higher uniform pressure increases the minimum buckling force for the column and thus makes the column less likely to buckle. For the same pressure level, the dead load is found to be more effective than the follower load in suppressing the buckling of the system. The effect of initial geometric imperfection is also investigated, and the imperfection amplitude and critical restraining pressure that prevent buckling are found to be linearly related. The analytical results are validated by finite element simulations. This analytical model reveals the buckling mechanism of strips under lateral pressure restraint, which cannot be explained by the conventional bifurcation buckling theory, and provides a theoretical foundation for buckling-prevention strategies during the milling process of thin-walled strips, plates and shells commonly encountered in aerospace or automotive industries. [ABSTRACT FROM AUTHOR]

The adequate filling and quenching of small corner features are major challenges in manufacturing complex-shaped boron steel tubular parts during the hot metal gas forming process. Considering that the tube forming process involves closed and invisible features, a single-sided die quenching experiment of boron steel sheets was proposed to simulate the in-die quenching process of tubes. The results confirmed that for a given sheet thickness, the critical size of the non-contact zone of achieving complete martensite transformation could be determined. A simple demonstrator geometry was designed to analyze the effects of bulging temperature and pressurizing rate on the corner filling, microstructure, and mechanical properties in the hot metal gas forming process, which are then correlated with the cooling rate in single-sided die quenching experiment. The corner filling was significantly improved with the increase in the bulging temperature and the pressurizing rate. At the bulging temperature of 900 °C, when the pressurizing rate increased from 1 to 3 MPa/s, the obtainable minimum corner radius decreased only from 24 to 16 mm. Under the above increased pressurizing rate, the width of the non-contact zone was 12.23 mm, which corresponded to a cooling rate that could reach 47 °C/s in the corner zone. The limited corner filling resulted from a significant temperature drop during hot metal gas forming. Decreasing the cooling rate of the tube or increasing the pressurizing rate can extend the range of reasonable process parameters in the boron steel tubes' hot metal gas forming. [ABSTRACT FROM AUTHOR]