A significant percentage of energy in hot forming is used to heat the components. Especially in manufacturing hybrid components, workpieces are heated in the preceding hot-joining process in addition ...to the heating cycles. Nevertheless, previous processing steps require longer times than the following hot forming processes leading to long downtimes. With the pre-production of workpieces, the machine's capacity is fully utilized but prevents the reuse of the residual heat. Consequently, an immense amount of energy is wasted due to additionally required heating cycles. Our approach is to develop a flexible and resource-efficient process chain. We combine two hot forming processes with different cycle times in a single process chain. Therefore, we consider the process of a hybrid bevel gear with heat and time-consuming preparation and a hybrid shaft with moderate preparation effort. To compensate for the bevel gear's high cycle times, the shaft is hot-formed during the downtimes. In order to reuse the residual heat of the bevel gear, their hot-forming process run is prioritized: Whenever the bevel gear's workpiece is manufactured, it will be hot-formed immediately. Combining these process chains allows the forming machine's capacity to be fully utilized and energy utilization optimized.
•In situ Raman spectra of tungstate-bearing solutions were collected at ≤400°C and ≤60Mpa.•CO32- and HCO3- do not associate with tungstate to form carbonic tungstate species.•Polymeric tungstate ...species are stable in CO2-bearing fluids at <300°C.•Monomeric tungstate species are responsible for hydrothermal transport of W at >300°C.•The presence of CO2 favors the extraction of Fe(II) from the host rock and subsequent W-mineralization.
Knowledge on hydrothermal tungsten (W) species is vital towards a better understanding of tungsten transport and mineralization mechanisms. In this study, in situ Raman spectra of a 0.005 – 0.1mol/kg (m) K2WO4 solution containing CO2, HCl, and NaHCO3 were collected at 50–400°C and 20–60MPa. The spectra for the symmetric stretching vibration mode of the WO bond, v1(WO), were analyzed to investigate the hydrothermal tungstate species. Results showed that carbonate/bicarbonate do not associate with tungstate to form carbonic tungstate species. Nevertheless, the presence of CO2 can increase the fluid acidity, which favors the formation of polymeric tungstate species at <300°C. Above about 300°C, monomeric tungstates (e.g., WO42-, HWO4-, H2WO4 and alkali tungstate ion pairs) are responsible for the hydrothermal transport of tungsten, and the v1(WO) modes of these species are centered at ∼930 cm-1 and 950cm-1. Based on the above observations, we simulated the mineralization process in the context of fluid-rock interactions using tungstate and alkali tungstate ion pairs as the only aqueous W species. The thermodynamic simulations showed that (a) the timing of mineralization mainly depends on the W concentration in the initial mineralizing fluid and the availability of Ca2+, Fe2+ and Mn2+, with higher W concentrations generally favoring higher temperature mineralization; (b) highly W-enriched fluid is not essential for W mineralization, while extremely low contents of Fe, Mn and Ca in the magma are useful to maintain the mobility of aqueous W until favorable host rocks are encountered; and (c) a “hydrogen reservoir” effect was identified for dissolved CO2. The presence of CO2 can promote the extraction of Fe(II) from the pelitic host rocks, thereby facilitating a high-grade vein-type W mineralization.
At <∼300°C, polytungstate species, whose v1(WO) modes are centered at ∼965 – 995 cm-1, are important hydrothermal W species along with monomeric tungstates. Therefore, polymeric tungstate species should be considered in future thermodynamic modeling of W transport and mineralization at <300°C. An increase in fluid pH induced by CO2-escape and/or fluid-rock interactions will destabilize the polymeric tungstates to form WO42- and other monomeric tungstate, which interacts with metal cations to form wolframite and/or scheelite.
A novel co-rotating electrochemical machining method is proposed for fabricating convex structures on the inner surface of a revolving part. The electrodes motion and material removal method of ...co-rotating electrochemical machining are different from traditional electrochemical machining. An equivalent kinematic model is established to analyze the novel electrodes motion, since the anode and cathode rotate in the same direction while the cathode simultaneously feeds along the line of centres. According to the kinematic equations of the electrodes and Faraday’s law, a material removal model is established to simulate the evolution of the anode profile in co-rotating electrochemical machining. The simulation results indicate that the machining accuracy of the convex structure is strongly affected by the angular velocity ratio and the radius of the cathode tool. An increase of the angular velocity ratio can improve the machining accuracy of a convex structure. A small difference in the radius of the cathode tool will cause changes in the shape of the sidewalls of the convex structure. The width of the cathode window affects only the width of the convex structure and the inclination α of the sidewall. A relation between the width of the cathode window and the width of the convex structure was obtained. The formation process for a convex structure under electrochemical dissolution was revealed. Based on the simulation results, the optimal angular velocity ratio and cathode radius were selected for an experimental verification, and 12 convex structures were simultaneously fabricated on the inner surface of a thin-walled revolving part. The experimental results are in good agreement with the simulation results, which verifies the correctness of the theoretical analysis. Therefore, inner surface co-rotating electrochemical machining is an effective method for fabricating convex structures on the inner surface of a revolving part.
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•The Xiahuolong deposit is an Early Cretaceous mesothermal Au deposit in southern Jilin Province.•The ore-forming fluids were of magmatic origin with continuous input of meteoric ...water.•Fluid immiscibility and mixing controlled the mineralization process.•The high water content and low oxygen fugacity promoted the mineralization.
The Xiahuolong gold deposit (3.05 t Au, average grade: 6.7 g/t), located in the Ji'an district of southern Jilin Province in the northeastern part of the North China Craton, contains orebodies in a Proterozoic metamorphosed sedimentary sequence. The distribution of the orebodies is controlled by NW- and NE-trending shear zones and faults, and the orebodies consist of auriferous quartz veins and auriferous altered rocks. The mineralization can be divided into four stages, namely (I) quartz-sericite, (II) quartz-pyrite-copper-gold, (III) quartz-pyrite-sphalerite-galena, and (IV) quartz-carbonate, with gold being introduced mainly during the second stage. Systematic analysis of the fluid inclusions suggests that two-phase vapor-rich (WV-type) and liquid-rich (WL-type) are the dominant types in the quartz veins. The early (stage I), main (stages II and III), and late (stage IV) fluid inclusions homogenize at temperatures of 273–367 °C, 201–346 °C, and 120–196 °C, corresponding to salinities of 0.68–0.79, 0.69–0.88, and 0.90–0.96 wt% NaCl equiv., respectively. The ore-forming fluid system evolved from CO2-H2O-NaCl ± CH4 to H2O-NaCl during ore formation, and fluid immiscibility and mixing caused the precipitation of sulfides and gold in the main stage. The H–O isotopes indicate that the ore-forming fluids were of magmatic origin, with a continuous input of meteoric water during ore formation. Two types of diorite porphyry have been identified, one cutting orebodies and the other filled with auriferous quartz veins. The diorite porphyry associated with the auriferous quartz vein yielded a zircon U–Pb isotopic age of 124.1 ± 1.9 Ma, indicating that Xiahuolong mineralization occurred in the Early Cretaceous, and that the high water content and low oxygen fugacity (ΔFMQ = -2.53 to +0.23; logƒO2 = -17.56 to -20.61) of the dioritic magma provided an important basis for mineralization. The results, combined with the deposit geology, fluid geology, H-O isotope geochemistry, timing of mineralization, and tectonic setting, suggest that Xiahuolong is a mesothermal gold deposit formed in an extensional setting characterized by lithospheric thinning related to the rollback of the subducting Paleo-Pacific Plate.
The sheet metal industry has seen more technological advances than any other since the last century. Right from hand-forming processes to finite element based simulation, the transformation is very ...significant. They have prominent industrial applications especially in automotive industries. This may be attributed to the ease with which the final component with desired shape and appearance can be produced using simple tools. Due to wide range of applications, the process of forming the sheet metal into various shapes leads to classification of the forming processes based on specific operation. This classification involves bending, blanking, stretch forming and deep drawing. Each process has some parameters that define the quality of the work achieved. This paper aims at scattering light on the recent research and developments in the sheet metal forming processes over the last two decades. Most of the literature available on sheet metal forming focuses on the parameters that influence the quality and economic factor of the final product. The influence of process parameters based on geometry such as punch nose radius, blank temperature, and blank holding force, tooling dimensions, blank thickness and punch depth is significant. Similarly, the parameters based on the material properties like elastic strength, yield strength, plasticity and anisotropy have as much influence as the geometry based parameters. The literature raises the issue of defects in the formed parts. Defects such as wrinkling, tearing, springback, local necking and buckling in regions of compressive stresses have been analysed using both experimental and simulation techniques. Springback, the most predominant defect, has been researched thoroughly while considering sheet thickness, punch force, nose radius, binder force, die opening, punch velocity, punch height, sheet anisotropy, clearance, elastic limit and yield strength of the blank material as input parameters. Lastly, this paper also aims at reviewing the finite element based tool design, experimental and numerical investigations into sheet metal forming processes.
In this study, the forming of metallic bipolar plates micro-channel was investigated. Rubber pad forming process was employed to fabricate the parallel micro-channels. According to the experimental ...observation, the onset of failure was the main limiting factor during the deformation of micro-channels. Therefore, the fracture behavior was studied during rubber forming processes. Experimental analysis with the finite element model (FEM) simulation was adopted to investigate the fracture mechanism. Three different fracture criteria were used to predict the fracture. Critical damage values were determined through conducting the uniaxial tension test. The fracture surface was constructed using ductile fracture criteria, and the most accurate fracture prediction was obtained via normalized Cockroft-Latham fracture criterion (9.14% fracture prediction error). The effect of process parameters on stress triaxiality and normalized Lode angle parameter was analyzed by FEM simulation results. According to the results, process parameter variation did not significantly affect the stress state. Thus, the normalized Cockroft-Latham fracture criterion was employed to investigate the onset of fracture in different forming conditions and the effect of process parameters on damage evolution. Based on the findings, draft angle, corner radius, and the ratio of w/h should be set to 15°, 0.2 mm, and 1.6 in order to achieve 100% filling percentage.
•Fracture defect in the rubber pad forming of metallic bipolar plates is investigated.•The normalized Cockroft-Latham is able to accurately predict fracture in the metallic bipolar plate.•The effects of process parameters on stress state and damage evolution are investigated.•The optimum value of the draft angle, corner radius, and width to channel depth ratio are obtained using the developed model.
The Resistive Random Access Memory (RRAM) is a new type of non-volatile memory based on the resistive memory device. Researchers are currently moving from resistive device development to memory ...circuit design and implementation, hoping to fabricate memory chips that can be deployed in the market in the near future. However, so far the low manufacturing yield is still a major issue. In this paper, we propose defect and fault models specific to RRAM, i.e., the Over-Forming (OF) defect and the Read-One-Disturb (R1D) fault. We then propose a March algorithm to cover these defects and faults in addition to the conventional RAM faults, which is called March C*. We also develop a novel squeeze-search scheme to identify the OF defect, which leads to the Stuck-At Fault (SAF). The proposed test algorithm is applied to a first-cut 4-Mb HfO 2 -based RRAM test chip. Results show that OF defects and R1D faults do exist in the RRAM chip. We also identify specific failure patterns from the test results, which are shown to be induced by multiple short defects between bit-lines. By identifying the defects and faults, designers and process engineers can improve the RRAM yield in a more cost-effective way.
•Fracture onset in the roll forming of AA6061 Aluminum Alloy was investigated.•Effects of damage weighting functions and calibration tests on fracture prediction were studied.•The most accurate ...fracture prediction was obtained using the Ayada fracture criterion calibrated by the plane-strain tension•Stress-Strain states analysis during both the roll forming process and the tension tests were studied in detail.
The present study evaluates the fracture behavior of the AA6061-T6 aluminum alloy during the roll forming process using ductile fracture criteria. Three criteria including Ayada, Rice-Tracey, and normalized Cockroft-Latham were utilized to develop an accurate fracture model for predicting fracture onset during the roll forming process. To this end, the fracture criteria were calibrated using uniaxial, plane-strain, and notched tension tests. The model was developed by integrating the calibrated fracture criteria into the numerical analysis (commercial finite element code Abaqus/Explicit) through an appropriate user subroutine. Based on the results, the damage weighting function and calibration procedures had a significant effect on the accuracy of the fracture prediction during the process. When the uniaxial tension test was used as the calibration test, the normalized Cockroft-Latham and Rice-Tracey ductile fracture criteria were not able to predict the fracture onset during the roll forming process and the Ayada fracture criterion could only predict the bending angle of the forming station where the fracture initiated. On the other hand, calibrating ductile fracture criteria using the plane-strain tension test led to higher accuracy in predicting fracture. The most accurate prediction was obtained using the Ayada fracture criterion calibrated by the plane-strain tension test with an error of 7.85%. Overall, the Ayada fracture criterion and plane-strain tension test can be considered as the most appropriate ductile fracture criterion and calibration method for predicting fracture in the roll forming process, respectively.
High-voltage nanosecond pulses are widely used in scientific research, but their wider adoption in industry requires compact, cost-effective, and easy to use generators to be developed. This article ...presents the modeling and experimental investigations into one method of producing such pulses-a spiral generator with a solid-state-thyristor-based input switch. It includes how the pulses are formed within the spiral, why a high-speed input switch is required, and how the geometry of the spiral dictates its output characteristics and the effects of different loads. Using thyristors, often connected in series to increase the operating voltage of the spiral, enables the spiral generators to have low jitter, high repetition rate, and long lifetime. Modeling of the circuit used a combination of telegraph equations to account for the wave propagation along the spiral and a lumped circuit exchanging charge between the spiral and the input switch and load. The model is verified by the detailed experimental results with the relative error being < 10% in most cases. The output voltage pulse was often observed to have an initial peak of much lower magnitude than the subsequent peak(s)-which can only be fully explained by considering wave propagation effects. Lower input switch inductance, shorter switching time, larger mean diameter of the spiral, and increasing the width of the copper tape that makes up the spiral can all increase the voltage multiplication efficiency. Although increasing the number of turns that makes up the spiral can increase the output voltage, it can also lower the multiplication efficiency. By understanding the effects of different geometries, the spiral can be optimized to drive different loads-three applications of such spiral generators are then presented-pulses with 10 kV amplitude and 10 kHz repetition rate for driving dielectric barrier discharge plasma, pulses with amplitude of 10 kV and 10 kV/ns rising rate for triggering of advanced solid-state switches, and pulses with -50 kV amplitude and 50 ns rising time for triggering high-current gas switches through field distortion.
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The final quality of complex conical-section rings depends on co-design of multiple processes in forming process chain. In this study, for a complex aeroengine casing ring with a ...large slope and a flange on its end, a co-design method of the forming process chain is put forward towards the objective of precision forming, which not only proposes a standard process route composed of multiple processes of upsetting, punching, rectangular ring rolling, loose tooling forging and profiled ring rolling, but also presents co-design methods of dies and blanks for all the processes. For profiled ring rolling, a design method of preformed blank that makes the blank and the target conical-section ring have the same axial volume distribution is proposed. By the method, the axial metal redistribution during the process can be alleviated greatly thus improving the forming stability and precision of the ring. Based on the geometric features of designed preformed blank, design methods of blanks and dies for loose tolling forging, rectangular ring rolling, punching and upsetting are proposed sequentially. In view of the key roles of loose tooling forging (manufacturing the preformed blank) and profiled ring rolling on the final quality of the conical ring parts, inherited FE simulations for these two processes are performed to verify the proposed design methods and determine appropriate design parameter. It is demonstrated that the proposed design method has significant advantages in improving forming precision. Besides, a suggestive value 1.5 of the rolling ratio for profiled ring rolling (a key design parameter) is given based on comprehensive consideration of multiple indicators such as ring roundness, deformation uniformity and forming load. The corresponding industrial experiments performed illustrate that a high forming precision of the conical-section aeroengine casing ring is achieved.
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