Forming-based geometric correction methods for thin-walled metallic components:a selective review

Geometric correction processes contribute to zero-defect manufacturing for improved product quality. Thin-walled metallic components are widely used in numerous applications such as electric vehicles and aircraft due to the lightweight feature, facilitating to achieve zero-emission goals. However, many components suffer geometric imperfections and inaccuracies such as undesired curvatures and twists, seriously affecting subsequent manufacturing operations, for example, automatic welding and assembly. Geometric correction techniques have been established to address these issues, but they have drawn little attention in the scientific community despite their wide applications and urgent demands in the industry. Due to the strict geometric tolerances demanded in high-volume automated production, it is urgent to increase the knowledge needed to develop new techniques to address future industrial challenges. This review paper presents an overview of typical geometric defects in thin-walled components and clarifies the associated underlying generation mechanisms. Attempts have also been made to discuss and categorize geometric correction techniques based on different forming mechanisms. The challenges in correcting complex thin-walled products are discussed. This review paper also provides researchers and engineers with directions to find and select appropriate geometric correction methods to achieve high geometric accuracy for thin-walled metallic components.</p

Design of Magnesium Phosphate Cement Based Composite for High Performance Bipolar Plate of Fuel Cells

In this work, we report a comprehensive study on a magnesium phosphate cement (MPC) based composite as the construction material for high performance bipolar plates of fuel cells. MPC with partial replacement of fly ash was employed as the binding matrix. Some carbon-based materials, such as graphite, carbon black, carbon fiber, and multi-walled carbon nanotubes were used to construct the conductive phase. A simple hot-press process was applied to produce the composite. The formula and the structure of the composite was modified and adjusted to optimize the properties of the composite to meet the US DOE 2015 technical targets, including the introducing of a reinforcement support. Finally, all the technical targets such as electrical conductivity (\u3e100 S cm-1), the flexural strength (\u3e25 MPa), the corrosion resistance ( \u3c 1 μA cm-2), and gas permeability ( \u3c 10-5 cm3 (s cm2)-1) were achieved as well as low cost ( \u3c 5 $ per kW). The optimized formula and the detailed procedures to fabricate the MPC based composite were concluded

Precambrian tectonic evolution of Central Tianshan, NW China: constraints from U-Pb dating and in-situ Hf isotopic analysis of detrital zircons

International audienceThe Tarim Block is an important geologic unit in the reconstruction of the tectonic evolution of the Central Asian Orogenic Belt and the Precambrian Columbia and Rodinia supercontinents. In order to examine the evolution and crustal generation of the Tarim Block, we performed detrital zircon U-Pb dating and in-situ Hf isotopic analysis of Devonian sandstones of the Baluntai area in Central Tianshan, which is part of the Tarim Block. Most analyzed zircon grains show oscillatory zoning and have Th/U ratios >0.4, suggesting that they were mainly derived from igneous rocks. A total of about 400 detrital zircon analyses yielded five age populations, namely, early Paleoproterozoic (peak at 2470 Ma), middle Paleoproterozoic (peak at 1858 Ma), early Mesoproterozoic (peak at 1541 Ma), early Neoproterozoic (peak at 952 Ma), and late Neoproterozoic (820 to 750 Ma). These peak ages are remarkably consistent with the polyphase tectonothermal events that occurred in the Tarim Block. The peak at 2470 Ma indicates the presence of late Neoarchean to early Paleoproterozoic magmatism in the Tarim Block. The two peaks at 1858 Ma and 952 Ma coincide with the two periods of assembly of the Columbia and Rodinia supercontinents. This further suggests that the Tarim Block was part of these two supercontinents. In fact, the age peak of 1541 Ma correlates with the breakup of Columbia, and the age range of 820 to 750 Ma is interpreted to represent the time of the breakup of Rodinia. The zircon Hf model ages suggest three major stages of crustal evolution at 1.0-1.4 Ga, 1.8-3.3 Ga, and 3.4-3.8 Ga. The zircons exhibit a huge range of var epsilonHf(t) values from −33 to +51, suggesting that they were derived from highly diverse protoliths. However, since most detrital zircons show negative var epsilonHf(t) values, the protoliths of the Baluntai sandstones of Central Tianshan probably comprise rocks of Archean to Proterozoic crust. Owing to the similar Precambrian basement, lithology and age spectra between Central Tianshan and Tarim, it is argued that Central Tianshan belonged to the Tarim Block in the Precambrian time. Furthermore, euhedral zircons with high Th/U ratios (>0.4) yielded a prominent peak of 447 Ma. This can be correlated with an early Paleozoic arc development in Central Tianshan