To address the materials processing challenges resulting from high levels of heat input in wire arc additive manufacturing (WAAM), a novel wire arc metal additive manufacturing method using pulsed ...arc plasma (PAP-WAAM) was developed in this study. In this method, the pulsed arc plasma generated by the pulsed voltage was used as the heat source. Owing to the applied pulsed voltage, the arc plasma was alternately ignited and extinguished during additive manufacturing. By adjusting the relative positions of the tungsten electrode, filler wire, and substrate, the arc plasma was ignited between the tungsten electrode and the filler wire. This increased the proportion of discharge energy allocated to the filler wire, thus reducing the overall heat input required for material deposition. Furthermore, no heat was transferred to the deposited material because the arc plasma was extinguished during the discharge interval. Consequently, the previously deposited material was rapidly cooled. Preliminary experimental results showed that the newly developed PAP-WAAM process used 37 % less heat input than the conventional gas tungsten arc welding-based WAAM (GT-WAAM) process at the same wire feed speed of 350 mm/min. The PAP-WAAM process yielded smaller melt pools, higher cooling rates, and less heat accumulation than the GT-WAAM process, which was mainly attributed to the combined effects of low heat input and efficient heat dissipation by the pulsed discharge during PAP-WAAM. As a result, PAP-WAAM produced finer geometric features and microstructures as well as greater tensile strength than GT-WAAM.
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•A wire-based AM method using pulsed arc plasma generated by pulsed voltage as a fusion source was proposed.•The newly developed process used 37 % less heat input than the GT-WAAM process at the same wire feed speed of 350 mm/min.•The mechanisms for the reduced heat input required for material deposition during PAP-WAAM was investigated.•The influencing mechanisms of thermal behaviors on microstructural evolution and mechanical properties were investigated.
Micropattern forming process is an efficient and low‐cost process for fabricating multifunctional surfaces in electronics, energy, and biomedical products, but this process of creating microdimples ...on the surface of zirconium alloys has not been investigated. Currently, there are few models describing the micropattern forming process, and these existing models have not considered the effect of roughness on forming. The influence of roughness on micropattern forming process is not to be neglected due to the size effect, especially the plowing effects caused by asperities in surface roughness during sliding process. In this article, a micropattern forming process model is developed by combining a rough plane indentation model and a plowing effects model, and the experimental study of the forming process is conducted, which can quantitatively evaluate the effects of different process parameters and different roughness of forming die on forming process. The applicability range of the developed model is obtained, and the model is capable of predicting the forming process with various process parameters and surface roughness of forming die by comparing the experiment results with the model results, which is of great significance to the design of the forming die and the improvement of the forming process.
The micropattern forming process on Zr‐4 zirconium alloy (Zr‐1.5Sn‐0.2Fe‐0.1Cr) surface with consideration of roughness is investigated. A model for micropattern forming process is developed by a rough plane normal indentation model and a tangential plowing effects model. In comparison with the experiments, the models can quantitatively evaluate the effects of different roughness and process parameters on forming.
The present study is conducted on forming of the metallic bipolar plates made of 316 stainless steel sheet with a parallel serpentine flow field. The plastic deformation of straight and curved ...microchannels, forming limit criteria, and deformation mechanics during the process are investigated partially to present a reliable model for estimating fracture initiation. For this purpose, experimental stamping tests are employed to fabricate metallic bipolar plates and the process is simulated by finite element software. The validity of simulation results is examined by comparing thickness distribution and force-displacement curves reflecting 4.76% and 3.85% error rates, respectively. According to experimental observations, fracture starts at a channel depth of 0.610 mm. Hence, for determining the forming limit and predicting the fracture during the process, the deformation mechanic is studied at different points of the microchannels. Results of stress states analysis indicate that the stress state of plane-strain tension up to biaxial tension governs this process. Despite the presence of different loading paths during the process, the critical element in each channel is deformed under plane-strain tension. Therefore, a fracture model is developed based on thinning percentage and equivalent strain to predict the instability of metallic bipolar plates. According to the results, both the equivalent strain and thinning percentage criteria with critical limits of 0.56 and 33.45%, respectively, are considered as an allowable range of plastic deformation during the conventional stamping process of bipolar plates. Results indicate that maximum thinning in all directions is lower than 33.45% by using the modified stamping process.
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•MBPP with higher depth/width is studied for raising power density and efficiency.•Detailed study of deformation mechanics of metallic bipolar plates is conducted.•An appropriate forming and fracture limit criteria is proposed.•Process is modified regarding thinning and equivalent plastic strain analysis.
As a crucial component of proton exchange membrane fuel cells (PEMFC), bipolar plates (BPPs) facilitate the transport of reactant gases, collection of current, and management of heat and water. This ...research provides a novel design and roll forming fabrication method for air-cooled metal BPPs. Furthermore, the application of carbon pre-coated 316L stainless steel can enhance manufacturing efficiency and reduce production costs. A 20-cell air-cooled PEMFC stack was fabricated with such metallic BPPs and its performance evaluations at different hydrogen inlet pressures were conducted. The testing results revealed that the stack could reach average output power of 299.4 W (power density 311.8 mW/cm2@0.535V) at a hydrogen inlet pressure of 0.06 MPa, during 50 h operation without significant degradation.
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•A novel design of metallic bipolar plates is provided.•The metallic bipolar plates are fabricated by roll forming process.•A 20-cell air-cooled PEMFC stack was assembled with the metallic bipolar plates.•The 20-cell stack operates for 50 h with an output power of around 300 W.
Skarn Cu deposits are one of most important deposit-type in Middle-Lower Yangtze River region, eastern China, but skarn formation process remains unclear. Mineralogical, morphological and in situ ...geochemical data from the skarn stage of Tongguanshan skarn Cu deposit in Tongling region are systemically investigated, to reveal the timing, physical-chemical conditions, and fluid evolution during the skarn formation. The Tongguanshan garnets can be identified homogeneous and unzoned early generation garnet (GrtI), and oscillating zoned late generation garnet (GrtII) with the Fe-rich core (GrtII-Fe) and Al-rich edge (GrtII-Al). Garnet U–Pb dating results show that the Tongguanshan Cu mineralization was formed in 145.6 ± 4.4 Ma. In situ elemental composition results of the garnet samples indicate that they belong to grossular-andradite solid solution series, and are a magmatic-hydrothermal origin. The distinctly geochemical characteristics (e.g., Sn and U contents, (La/Yb)N, δEu and Y/Ho values) reveal that the physiochemical conditions from GrtI to GrtII-Fe, and GrtII-Fe to GrtII-Al stages in the Tongguanshan skarn formation were an increase and a decrease of fluid salinity and oxygen fugacity, closed to open and then to closed of fluid environment, and neutral-weakly acidic to acidic and acidic to neutral-weakly acidic of fluid pH, respectively. A comprehensive discriminant analysis indicates a fluid boiling occurred in the GrtI to GrtII-Fe stage of the Tongguanshan skarn Cu deposit, and there is little or no external fluid mixed during the skarn stage.
Metallic bipolar plates are important components of the proton exchange membrane fuel cell. To achieve higher performance of fuel cells, dozens of fine flow channels with the width of approximately ...1 mm and a high aspect ratio of over 0.3 are required for bipolar plates. Those functional demands push the forming process of bipolar plates to the limit of material and tools, making the rupture sensitive to even a tiny deviation of the tools' geometric dimensions and material properties. To address that, a robust design method is established in this work to analyze the rupture probability by introducing the stochastic variation of material properties and tools’ geometric dimensions. Utilizing the method, the rupture probability is decreased from 19.14% to 0.18% during the practical forming of metallic bipolar plates by parameters control. The yield rate is also verified to be over 99.5%.
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•A robust design method is established for forming metallic bipolar plates.•The stochastic deviation of material properties and tool dimensions are considered.•Criteria of those factors are provided for the fracture-free stamping process design.•High-quality metallic bipolar plates are fabricated with a yield rate of over 99.5%.
•An alternative to the conventional cold roll forming process is developed.•Feasibility is evaluated using UHSS sheets.•Computational modeling based on the finite element method is ...performed.•Dimensional accuracy and quality are assessed for automotive component.
In this study, an alternative to the conventional cold-roll-forming process was developed. The new in-line incremental die forming process is a continuous manufacturing process that can provide rapid prototyping of automotive components. This new process combines the pressing and drawing operations. The feasibility of using ultra-high-strength steel (UHSS) sheets to manufacture real automotive components usually produced with the conventional cold-roll forming process was evaluated. Finite element simulations incorporating the mechanical properties of plasticity and ductile fracture were conducted to validate the new process. The results demonstrated that the proposed forming process efficiently produced automotive components with consistent shapes and lengths, and the simulation outputs were in good agreement with the experimental data in terms of dimensional accuracy and quality. Additionally, sensitivity analyses of process parameters such as friction and die design provide valuable insights for optimizing the newly proposed formation process of UHSS sheets.
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Recently, field measurements show that corrugations are generated on curved tracks and that its wavelength varies with fasteners. The phenomenon that corrugations are generated on curved tracks can ...be explained with the assumption that corrugation is generated by the torsional vibration of wheelset. This assumption, however, has not been investigated in details yet. In this research, a finite element model including the nonlinear friction-creepage characteristics is developed to analyse the unstable vibration of a wheelset negotiating a curved track, and the results show that the friction induced torsional vibration between inner wheel and rail is most likely to be generated, which can verify the assumption. Furthermore, a mathematical model is developed to illustrate the forming process of rail corrugation, and the results indicate that the corrugation generated on curved track can be attributed to the periodical fluctuation of frictional power due to torsional vibration. Based on the results above, a forming process model of rail corrugation is formulated, which can be applied to explain why wavelength of corrugation varies with fasteners: the vertical dynamics affected by fasteners determine the frequency of torsional vibration and further affect the wavelength of corrugation, indicating the reliability and effectiveness of this forming process model.
•That torsional vibration tends to be generated on a curved track is verified by FEM.•Periodical variations in frictional power of torsional vibration cause corrugation.•Vertical dynamics affect corrugation wavelength in the form of torsional vibration.•A forming process model of corrugation based on torsional vibration is developed.•This model can illustrate why the wavelength of corrugation varies with fasteners.
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•The Maojun laterite Mn–Fe deposit is an unusual one originating from the weathering of dolomite;•Detailed research on the geology and mineralogical evolution of laterite Mn–Fe ...deposit in South China is reported for the first time;•A four-stage ore-forming process is proposed.
Laterite Fe–Mn deposits are widespread in South China, with the majority of Fe–Mn ore being present in residual quaternary clay beds. However, detailed geological data on the lateritization of low-iron-content carbonate rocks are rare. In this study, we present new results on the mineralogy and geochemistry, as well as a genetic model, of the Maojun laterite Fe–Mn deposit in the Lanshan area, Hunan Province, South China. The profile sequence of laterite consists of an eroded bedrock horizon at its base, an intermediate black–brown clay layer containing earthy Fe–Mn ore, and a reddish-brown clay layer with nodular ferromanganese ore in contact with reddish-brown or yellowish-brown clay on top. Field evidence and chemical analysis indicated that during lateritization, the Mn-Fe-containing carbonate rocks of the Huanggongtang (D2h) and Shetianqiao formations (D3s) saw a more significant removal of mobile elements (Mg, Ca, and Na) whilst insoluble elements (Fe, Mn, Si, Al, Pb, and Zn) exhibited persistent enrichment in situ. Discriminative diagrams of Fe–Mn mineralization, as well as the assemblage-related enrichment of Y, U, Mo, Pb, and Zn and depletion of high-field-strength elements Zr, Nb, and Th, imply that subsequent hydrothermal circulation overprinted on the previously formed hydrogenous deposit. Mineralogical studies conducted using XRD, EPMA, HR-TEM, and TIMA indicated the predominance of iron and manganese oxides; hematite, goethite, limonite, and hollandite were identified as major oxide phases and cryptomelane, pyrolusite, and coronadite were present in minute quantities. Similar minerals constitute the upper ferromanganese nodule horizons, although they possess distinct textures and concentrations. The mineralogy, geochemical associations, and Ti mass balance show a continuous vertical evolution from top to bottom in the lateritic profile. Ferromanganese concretions from the drenching zone with poorly crystallized Al–goethite, Al–hematite, limonite, Fe–kaolinite, Fe–Mn oxides and hollandite predominate in shallow parts, and microcrystalline hematite, goethite and hollandite were found in deeper layers. Mn2+ can be rapidly oxidized and precipitated on the surface of hematite and limonite as high-valence-state (Mn4+) manganese oxides and binds strongly with mobile elements (Ba, K, Pb, Zn, Ca, and Ni). Petrographical, mineralogical, and geochemical studies show that three stages comprised the formation of the Maojun laterite Fe–Mn deposit.
