External Pressure Forming and Buckling Analysis of Tubular Parts with Ribs

Buckling and forming processes of tubes with varying slenderness ratio （ratio of length to diameter） under external hydraulic pressure were analyzed with three-dimensional finite element method （FEM） for studying tube external pressure forming （EPF）. Buckling pressures for different tube blanks without mandrel were predicted, and an EPF of a carbon steel tube onto a mandrel with six ribs was simulated. Both thickness distribution and buckling pressure from the simulations were found to be in agreement with those from experiments. Buckling pressures are shown to be a function of the slenderness ratio. The tubular part with six ribs produced by EPF has a uniform thickness distribution, whose maximum thinning rate is only 5.9%.

Influence of Microstructural Evolution on the Hot Deformation Behavior of an Fe–Mn–Al Duplex Lightweight Steel

The hot deformation behavior of Fe-26Mn-6.2A1-0.05C steel was studied by experimental hot compression tests in the temperature range of 800-1050℃ and strain rate range of 0.01-30 s-1 on a Gleeble-3500 thermal simulation machine.The microstructural evolution during the corresponding thermal process was observed in situ by confocal laser scanning microscopy.Electron backscattered diffraction and transmission electron microscopy analyses were carried out to observe the microstructural morphology before and after the hot deformation.Furthermore,interrupted compression tests were conducted to correlate the microstructural characteristics and softening mechanisms at different deformation stages.The results showed that hot compression tests of this steel were all carried out on a duplex matrix composed of austenite and fi-ferrite.As the deformation temperature increased from 800 to 1050℃,the volume fraction of austenite decreased from 70.9% to 44.0%,while that of 6-ferrite increased from 29.1% to 56.0%.Due to the different stress exponents（n）and apparent activation energies（Q）,the generated strain was mostly accommodated by δ-ferrite at the commencement of deformation,and then both dynamic recovery and dynamic recrystallization occurred earlier in δ-ferrite than in austenite.This interaction of strain partitioning and unsynchronized softening behavior caused an abnormal hot deformation behavior profile in the Fe-Mn-A1 duplex steel,such as yield-like behavior,peculiar work-hardening behavior,and dynamic softening behavior,which are influenced by not only temperature and strain rate but also by microstructural evolution.

Manufacturing of Long Products Made of Innovative Lightweight Materials

The processing of innovative lightweight materials to sheet metal components and assemblies with globally or locally defined properties is the object of this work. It takes a load-dependent design of components and assemblies, for example, based on the composition of different construction materials or a targeted setting of component areas with specified characteristics to fully exploit the lightweight potential when substituting conventionally used materials. Different process chains for the manufacturing of roll-formed long products made of magnesium alloys and high-strength steels with locally defined properties will be presented in this paper. Depending on the kind of material to be formed and the desired product characteristics, different temperature managements are needed for capable processes. Due to limited formability at room temperature, magnesium alloys require a heating of the forming zones above 200–225 °C throughout the bending process in order to activate additional gliding planes and to avoid any failures in the radii. The realization of local hardening effects requires at least one process-integrated heat treatment when roll forming manganese–boron steels. For both processes, it is imperative to realize a heating and cooling down or quenching appropriate for the manufacturing of long products with the required quality. Additionally, proper line speeds that allow a continuously operated economical production have to be considered. Research results including design, FEA, realization and experimentation of the mentioned process chains and strategies will be described in detail.