Uniform Thickness Distribution Research Articles

К ВОПРОСУ О ПРОЧНОСТИ КОМПОЗИТНОГО ШАРОБАЛЛОНА

In modern launch vehicles, combined composite structures in the form of thin-walled spherical shells are used as pressure accumulators and tanks. Such balloons consist of an inner metal body (liner), which ensures tightness, and an outer reinforcing composite shell, which ensures the operability of the structure.The paper presents a methodology for the design calculation of a combined composite balloon by using zonal winding on a liner. An analysis of publications on this topic showed that the requirements for the strength and continuity of the tape covering the entire surface of the balloon depend on the tape geometry, its width, thickness, the ultimate strength of the bundle along the fibers, the number of zones and the angular coordinates of the beginning of the zones. The even distribution of the location of the beginning of each zone, accepted by the authors in publications, leads to the need to use an excess number of winding turns to fulfill the strength conditions than is necessary for a continuous coverage of the zone surface.A rational design of the reinforcing composite shell will be in the case when the strength conditions and the conditions of the coating continuity are met in each zone with the same number of required tape turns. The algorithm is based on a sequential calculation of zone parameters. According to the known coordinate of the beginning of the first zone, the required number of turns of the tape is determined, which is necessary to fulfill the condition of the continuity of the coverage of the zone. The strength conditions in the first zone determine the angular coordinate of the beginning of the second zone. The calculation of the parameters of each zone is made taking into account the influence of the value of the width and thickness of the wound tape. Each subsequent zone is determined in the same way, taking into account all the previous zones.The paper compares the results obtained by the proposed method with the results known in the press. The performed numerical experiments showed that the proposed engineering technique allows to reduce the weight of the composite tape by 30%, and the designed spherical shell in this case will be thinner and has a more uniform distribution of the shell thickness along the meridian.

Film Formation Control for High Performance Dion–Jacobson 2D Perovskite Solar Cells

AbstractDion–Jacobson (DJ) 2D hybrid perovskite semiconductors offer improved environmental stability and higher structural diversity in comparison with their 3D analogous. However, lacking of controlled perovskite crystallization makes it a challenge to achieve high charge transport for photovoltaic devices. Here, a detailed understanding of effects on film formation during different solution‐casting processes for the DJ perovskite (PDMA)(MA)n−1PbnI3n+1 (<n> = 4, PDMA refers to 1,4‐phenylenedimethanammonium) in the final film structure and photovoltaic outcomes is presented. Faster removal of solvent from solution via hot‐casting or antisolvent dripping results in a more uniform thickness distribution of quantum wells. This eventually enhances carrier transport greatly along perpendicular direction and increases power conversion efficiencies. A high efficiency of 15.81% is achieved for the hot‐casting devices, which is also the highest for aromatic spacer‐based DJ perovskite solar cells. This work helps to better understand the control of film formation during solution‐casting for high performance solar cells.

Formability and mechanism of pulsed current pretreatment–assisted laser impact microforming

Pulsed current treatment was introduced into the laser impact microforming technology to improve the formability of laser impact forming. A pulsed current pretreatment–assisted laser impact microforming technology is proposed, and the formability and mechanism of such composite technology are discussed. In this study, the mechanical properties of H62 brass before and after pulse treatment were tested. The effect of pulsed current treatment on the formability of the material under high strain rate was studied by a laser impact free microbulging experiment. Moreover, the mechanism of pulsed current influence on the material’s formability was analyzed from the aspects of microstructure, texture evolution process, and grain size and morphology. Results showed that the elongation of the material was increased obviously, the flow stress during the tensile process was decreased significantly after pulsed current treatment, and the fracture form of the material gradually evolved from brittle fracture to ductile fracture. The forming height of samples under high strain rate improved greatly which may be due to the high-density pulsed current treatment that significantly alleviated the dislocation entanglement in the material. Owing to the weaker orange-peel effect which is induced by smaller recrystallized grains and lower maximum density of texture, the surface quality of formed parts after pulsed current treatment increased remarkably. In addition, the more uniform section thickness distribution of formed parts was observed, which may stem from obviously refined grains after pulsed current treatment improved the fluidity of the grains in a high–strain rate deformation process.

Effects of Variable Punch Speed and Blank Holder Force in Warm Superplastic Deep Drawing Process

A cylindrical deep drawing test was conducted for the purpose of improving the drawability, product accuracy, and quality in warm deep drawing using a superplastic material with large strain rate dependence. Then, the effects of blank holding force (BHF) and punch speed (SPD) on the flange wrinkle behavior and wall thickness distribution were investigated by experiments and theoretical analysis. A Zn-22Al-0.5Cu-0.01Mg alloy superplastic material SPZ2 with a sheet thickness of 1 mm was employed as the experimental material, and a cylindrical deep drawing experiment with the drawing ratio (DR) of 3.1 and 5 was performed at 250 °C. A good agreement was qualitatively obtained between the elementary theory on the flange wrinkle limit, the fracture limit, and the experimental results. In addition, the authors examined each variable BHF and SPD method obtained from the theory and experimentally demonstrated that the variable BHF method has a great effect on uniform wall thickness distribution and that variable SPD has a great effect on shortening the processing time for superplastic materials. Furthermore, the authors demonstrated the effectiveness of the variable BHF/SPD deep drawing method that varies both BHF and SPD simultaneously.

Water-jet cavitation shocking as a novel array micro-forming technique

Micro-feature arrays and large-area complex microscopic features on thin metallic sheet play an important role in micro-components. A novel technique-submerged water-jet cavitation shocking-is presented to generate micro-feature arrays on 304 stainless foils in this paper. High-speed camera shadowgraph images of the cavitation cloud were employed to analyze the impact zone. Then the forming depth, uniformity of forming depth and the thickness distribution of the micro-feature arrays were also studied. The results show that the forming region can be categorized into the jet-impact-zone, the bubble-impact-zone and the periphery-impact-zone radially. Bubble-impact-zone peaks in the depth of array micro-forming. The forming depth increases with time while the uniformity decreases with time. The forming parts have a uniform thickness distribution.

Vacuum-free fabrication of organic solar cell on assembled glass substrates

Vacuum-free fabrication is essential to realize large-scale production of organic solar cells. Blade-coating and printing are important solution-processing techniques to realize this idea. Preparation devices on large substrates is important for mass production; however, it is not easy to handle large substrates during fabrication procedures. In this work, we demonstrate a fabrication method for all-solution vacuum-free organic solar cells on an assembled glass substrates. Small pieces of glasses were assembled into a mosaic of larger total size for device fabrication. A gap-prefilling method was also developed to realize uniform thickness distribution. For the device with blade-coated ZnO electron transport layer, blade-coated active layer, spray-coated hole transport layer and spray-coated top electrode, power conversion efficiency of 4.19% is obtained. This showed that, by combining spray and blade coating, ultimate scale of the vacuum-free fabrication of OPV on glass substrate will not be limited by the substrate size itself, and can be scaled up to multi-meter by assembling the glasses into a mosaic. A method for all-solution vacuum-free organic solar cells on an assembled glass substrates were developed. Devices fabricated by blade-coating and spray-coating with power conversion efficiency of 4.19% was obtained. • ‧A technique for all-solution vacuum-free organic solar cells on an assembled glass substrates is presented. • ‧A gap-prefilling method was also developed to realize uniform thickness distribution. • ‧Power conversion efficiency of 4.19% is obtained for the device with blade-coated PEDOT:PSS, blade-coated active layer, spray-coated hole transport layer and spray-coated top electrode.

Investigation and optimization of the ultra-thin metallic bipolar plate multi-stage forming for proton exchange membrane fuel cell

Multi-stage forming of the ultra-thin metallic sheets is a promising process for manufacturing fine width and high aspect ratio bipolar plates in proton exchange membrane fuel cell. Correlations between the processing parameters and the channel quality evaluation indicators are investigated experimentally and numerically. A novel parameter optimization method and stage number design guidance are established with the consideration of the indicator priorities and material properties. The forming depth can be increased by larger Stage II punch stroke along with smaller clearance and radius. Increasing or decreasing the Stage II punch stroke and radius simultaneously contributes to larger draft angle. Small Stage II punch stroke and radius are beneficial to greater rib width. More uniform thickness distribution can be achieved by using smaller Stage II punch stroke and clearance. Two-stage forming is enough for soft materials and three-stage forming is suitable for relatively hard materials. Both the output power density and voltage distribution uniformity of the proton exchange membrane fuel cell are improved by employing multi-sage formed bipolar plates. The relationship between the parameters and indicators, optimization method, stage number design guidelines, all serve as the design principles of the micro channel's multi-stage forming for bipolar plates with ultra-thin metallic sheets.

Initial microstructure influence on Ti–Al–Mo–V alloy's superplastic deformation behavior and deformation mechanisms

Superplastic forming is an effective way to manufacture complex-shaped parts of titanium-based alloys. This paper studies the influence of the initial microstructure and its strain-induced evolution on superplastic deformation behavior and the formability of a titanium-based alloy. Two types of Ti–Al–V–Mo alloy samples having a different fraction of recrystallized grains before the start of the superplastic deformation were studied. The deformation behavior, including strain hardening and strain rate sensitivity of the flow stress, was analyzed in a temperature range of 775 °C–900 °C and a strain rate range of 10−5 to 10−2 s−1. Strain-induced changes of the microstructure within the bulk of the samples and on the surface of the pre-polished samples were studied during superplastic deformation with a constant strain rate. The dynamic recrystallization and dynamic grain growth in the volume of the samples and the multiple slip bands on the samples' surface were revealed after superplastic deformation. The grain structure evolution and slip bands localization depended on the samples’ initial microstructure. The results showed that the samples with an increased fraction of recrystallized grains exhibited better superplasticity and higher quality of the formed parts with a more uniform thickness distribution across the section than the samples with a lower initial recrystallized fraction.

Influences on the extended length and performance of push bending for the GH4169 superalloy tube with small bending radius of 1D

It is extremely difficult to eliminate the defects like wrinkling, which is generated in the bending of tube with small bending radius. In this thesis, the push-bending process of the GH4169 superalloy tube with a large diameter-thickness ratio of 60 and small bending radius of 1D is studied by numerical simulations and experiments, aiming to eliminate wrinkles on the inside of the tube and obtain enough extended length (e) of straight segment as well as minimal changes in the wall thickness. Three influencing factors, such as the inclined angle (α) at the initial end, the reverse thrust (P) of polyurethane blocks, and the lubrication, are investigated in the simulation. According to the simulations, the proposed experiment is successfully implemented on an independent development of push-bending equipment. The results are in good agreement with the simulation. The optimum parameters for the GH4169 superalloy alloy tube with a large diameter-thickness ratio of 60 and small bending radius of 1D are simulated. And then α is optimized to 45° and P is optimized to 48 MPa. And differential lubrication is used for longer extended length of straight segment and more uniform distribution of wall thickness on both sides of the deformed elbow.

Research on combinatorial optimization of multidirectional sheet postures for forming thickness uniformity

To solve the problem of the uneven thickness distribution of a formed part caused by a large difference between the forming angles and the different curvatures of the surfaces in CNC incremental forming, a combinatorial optimization method of multidirectional sheet postures was proposed based on particle swarm optimization. In this method, an infinite number of optional sheet postures at each point in the forming area are taken as the combined object. The optimization goal is to make the forming angles of the entire sheet part be smaller than the forming limit angle and to minimize the difference between them; then find the optimal combination of the multidirectional sheet postures that can be selected at each point in the forming area. Case studies of the algorithm and the actual forming experiment show that not only can the optimized multidirectional sheet metal postures determined by the proposed method realize the non-fracture forming of the sheet metal parts with different forming angles and different curvature of the surface, but also obtain a more uniform thickness distribution of the formed parts.

The effect of the initial pipe thickness on the final thickness of the part during gas molding

Examines the impact of the factory-supplied a pipe round cross-section on the final wall thickness distribution steeply curved pipe. The purpose of this study is to obtain a more uniform distribution of the wall thickness. Studies have shown that using the factory-supplied billets at orientation in the die cavity can be reduced by forming a level difference thickness obtained items by 17%.

Influence of blank holder-die gap on micro-deep drawing of SUS304 cups

Micro-deep drawing (MDD) is a promising micro-manufacturing technology. Size effects complicate and signify the influence of the blank holder-die gap on MDD, which was investigated in this study. Annealing of SUS304 foils of 50 µm thick was conducted to obtain various grain sizes. Micro-tensile testing was carried out to acquire the stress-strain curves of the foils, followed by MDD experiments. Advanced FE models were developed to simulate the MDD process taking into account material inhomogeneity and surface morphology of the foils at micro-scale. Bending dominates the early stage of MDD. A combination of proper gap size and punch/die corner radius may incur in-process springback before the occurrence of the maximum drawing force, benefiting the MDD process. A relatively small gap is favourable to a uniform distribution of wall thickness without obviously increasing the risk of fracture. It also improves the overall shape accuracy of outer surface whilst may result in the inner surface distortion. The complex development of the shape accuracy in three defined areas on the drawn cup can be attributed to the integrated effect of the gap size, material inhomogeneity and surface morphology of the foil. The combined design and multi-object optimisation of the gap size and the corner radii of punch and die should be conducted for improving the MDD process.

Influences of Blank Holder Force in The Multi-Step Deep Drawing Process of Aluminum Sheets

In recent decades, the use of aluminium alloys is developed in the automotive industry with regard to the need for lightweight and anti-corrosion components, one of which is AA7075 Al alloy. In this study, the multi-step deep drawing process of AA7075 aluminium sheets under various blank holder forces is investigated through a numerical simulation and is then validated with experimental results. Simulations were conducted by ABAQUS finite element software, and the influences of the blank holder force on the wrinkling height, rupture occurrence and thickness distribution of the sheet were studied. The optimum amount of blank holder force at each drawing step is determined so that the height of wrinkling, and the thinning percentage do not exceed the permissible value. Based on the results, the blank holder force magnitude should be considered descending during the four successive steps to achieve more uniform thickness distribution, and also the wrinkling height could be reduced by increasing the blank holder force in the analysed force range. The optimum amount of blank holder force in the four drawing steps was 28000, 2500, 1500 and 600 N, respectively. In general, the minimum thickness was created in the corner of the punch. The results also showed that an excessive increase in the blank holder force in order to eliminate the wrinkling caused the thinning percentage to increase. Finally, a good accordance between the experimental and numerical results was observed.

Study on AlxGa1-xAs nanocones with variable Al composition structures for highly efficient light trapping

In this study, various AlxGa1-xAs nanostructure arrays with variable Al composition are proposed and designed for highly efficient light capture. The optical properties of the proposed nanocone array with variable Al composition have been numerically investigated by COMSOL Multiphysics package based on the finite element method (FEM), and compared with the counterparts of cylinder and conical frustum. The results show that the variable composition AlxGa1-xAs nanocones with uniform sublayer distribution thickness can obtain an ultimate efficiency of 37.3%, which is higher than that of the cylindrical and conical frustum structures under the same conditions. In addition, the effects of geometric parameters of nanostructures on the light absorption of nanoarrays with different shape changing components are studied. Taking the variable component AlxGa1-xAs nanocone structure as an example, increasing the Al component range in the axial direction of the nanocone can significantly improve the absorption of short-wavelength light, which increases the overall absorption efficiency. In addition, for a specific Al composition distribution range, a uniform thickness distribution design of unit sub-layer in nanocone along the z-axis direction can provide optical absorption enhancement of more than 1.8% and 0.9% over than the decreasing and increasing distribution design. The design principles proposed in this work will provide a reference for selecting appropriate parameters in solar cell applications.

Improvement on formability and forming accuracy in electromagnetic forming of deep-cavity sheet metal part using a dual-coil system

A dual-coil electromagnetic forming (EMF) method assisted by radial Lorentz force was proposed herein to achieve the die forming of deep-cavity sheet metal parts. The objective of this study was to certify the extent to which the formability and forming accuracy can be improved by the proposed method. For comparative study, a single-coil EMF system without radial Lorentz force was also utilized. To develop the deformation process, the experiments and simulations of deep-cavity aluminum workpieces under a wide range of voltage combinations were conducted by the single-coil and dual-coil EMF, respectively. The experimental results showed that the dual-coil EMF resulted in the formation of the deep-cavity workpiece with high forming accuracy, maximum die-fitting gap of 0.35 mm, and more uniform thickness distribution. In contrast, the workpiece tended to crack without contacting the die by the single-coil EMF. Based on the simulation results, dynamic deformation behaviors of the deep-cavity workpieces were demonstrated and the underlying mechanisms of the improved formability and forming accuracy were explained. Moreover, the process window of die-fitting gap control indicated that the fittability could be controlled by adjusting the voltage combinations of the dual-coil EMF, and the corresponding optimum voltage of Coil-2 (V2) that contributed to high forming accuracy decreased with the increase of the voltage of Coil-1 (V1). Therefore, the proposed dual-coil EMF exhibits more flexibility and efficiency for producing the deep-cavity sheet metal part with a higher forming accuracy than the single-coil EMF, extending the potential application of the conventional EMF due to the utilization of multiple coils.

Improvement of a scraper heat exchanger for pre-heating plant-based raw materials before concentration

When heating liquid and paste-type products, enterprises in the food industry commonly use scraper heat exchangers, which, given their high heat treatment intensity, make it possible to retain the original properties of the treated raw materials. Most heat exchangers demonstrate an unstable stabilizing effect: the vapor pressure ‒ the temperature that leads to damage to raw materials, under conditions of significant energy- and metal capacity. It is possible to eliminate these drawbacks by using a temperature-stable flexible film resistive electric heater of the radiating type as a heater in an improved scraper heat exchanger. We have proposed applying a hinged blade with a cutting edge (with a reflective heating surface) as a stirring element of the heat exchanger to obtain the uniform distribution of a product layer thickness at the working surface and to additionally heat by the blade's reflective surface. The heat exchanger can be supplemented with a cooling shell with ring channels to pass the refrigerant, which is placed on the outer surface of the non-thermally insulated flexible electric heater. Such a solution provides the possibility of cooling to −15 °C and it simultaneously serves the additional air thermal insulation in the absence of the carrier in it. We have determined the uniformity of heat flow distribution over the heating surface of the model design of the improved unit (60.3...60.5 °C) and at the reflective surface of the hinged blade with a cutting edge (60.0...60.3 °C). The total thickness of a liquid layer has been established depending on the shaft rotation frequency of the proposed hinged blade with a cutting edge: at 50 min –1 – 1–2.65 mm, at 350 min –1 –1.5 mm, compared with a standard hinge blade (a layer thickness is from 5.0 mm to 1.5 mm), in terms of product consumption W=50 l/h. The improved scraper heat exchanger is characterized by a 1.48-time decrease in the specific energy consumption (170.4 kJ/kg), used to heat a product volume unit, compared to the heater with a steam shell – 252.6 kJ/kg. The research result is the confirmed efficiency of using the improved scraper heat exchanger, as well as its proposed structural scheme

A novel multi-step strategy of single point incremental forming for high wall angle shape

Single point incremental forming (SPIF) is a die-less manufacturing technology using a numerical controlling system for complex and customized parts. However, single-step SPIF cannot achieve high wall angle shapes due to the formability limit of the material. As wall angle gets larger, local thinning becomes severe, and cracking occurs easily. Generally, a multi-step strategy is used to get a hard-to-form deep drawing shape. However, inappropriate multi-step strategies can cause a stepped feature (corrugation). In this study, a novel parameterized multi-step strategy is proposed to solve the local thinning and stepped feature issues of forming high wall angle shape. Both experimental and simulation results showed this strategy not only improves the formability of a high wall angle, by avoiding over-thinning in the local region and redistributing the thickness of the material, but also minimizes geometric deviation by stepped feature. The multi-step strategy made the local thickness increase from 0.47 mm to 0.68 mm, preventing both cracking observed in a single-step strategy and the occurrence of the stepped feature. With the good agreement between experimental and simulation results, simulations with different parameters in a parameterized multi-step strategy were carried out to compare thickness distribution at each step, the stepped feature at the bottom and the ductile failure tendency. The comparison reveals that the locally large plastic strain, which was caused by the mismatch between the tool radius and vertical displacement, is the main reason for uneven thickness distribution, obvious stepped feature, and high failure tendency. With appropriate parameters, a multi-step strategy results in a more uniform thickness distribution, higher geometric accuracy, and lower failure tendency.

Thermoforming behavior of 3D-printed PLA sheets

Abstract Fused deposition modeling is one of the most well-known additive manufacturing methods. It might be considered the easiest way to produce particle reinforced composites or unreinforced sheets which are biodegradable and used in the packaging industry as well as for custom products. In this study, polylactic acid (PLA) sheets were produced by 3D printing and thermoformed using a lab-scale thermoforming machine. This article aims to determine the deformation behavior of 3d printed PLA sheets during thermoforming. In addition to experimental work, finite element analysis was performed to investigate the prediction capabilities of Mooney-Rivlin and Ogden models for PLA sheets. In addition, the initial thickness of the sheet was optimized using FEA and a python script to obtain final uniform thickness distribution. Thanks to 3D printing’s capability for printing sheets of variable thickness, sheets of variable thickness were printed to verify the material models. As a result, based on the thickness distribution obtained from the experimental study, Mooney-Rivlin and Odgen material models were found to be inadequate for representing the actual deformation behavior of PLA sheets.

Manufacturing of a hemispherical component combining incremental forming and superplastic forming

The interest towards magnesium (Mg) alloys for the fabrication of light weight components has been continuously increasing, especially for transportation, since the payload is strictly related to the energy (fuel or electricity) consumption. Super plastic forming (SPF) and single point incremental forming (SPIF) are viable processes for manufacturing light weight parts since they allow to produce components with superior characteristics and quite complex geometries, even in the case of the poorly formable Mg alloys. But, since both the processes are characterized by stretching, thinning is a key issue to be addressed. On the other side, in order to fulfil the structural and corrosion resistance characteristics required by aerospace and automotive applications, components with a uniform thickness distribution have to be produced. Such an aspect is even more important when the shape complexity of the component increases. SPF and SPIF have never been combined or hybridized so far but, in order to produce parts with a uniform thickness distribution, a possible strategy based on the blank pre-forming by SPIF prior to the SPF has been proposed in the present paper. In particular, the initial blank shape to be obtained by SPIF was designed using a numerical optimization approach and effectively created using the sine law to predict the wall angle and design the tool path. A hemispherical component in AZ31B-H24 was used as case study. The thickness profile of the component obtained by SPF revealed to be highly uniform in a large area (the portion from the centre of the sample to its periphery corresponding to about 70%) being characterized by a thickness equal to about 0.5mm. The quality in terms of finishing of the component produced by SPF resulted to be good, irrespective of the roughness increase exhibited by the blank after the pre-forming by SPIF.

Effective improvement of electrochemical performance of electrodeposited MnO2 and MnO2/reduced graphene oxide supercapacitor materials by alcohol pretreatment

Abstract In this work, basing on the traditional electrodeposition method, we improve the structure and electrochemical performance of MnO2 and MnO2/reduced graphene oxide (MnO2/RGO) electrode materials by alcohol infiltrated substrate process that introduces ethanol oxidation reaction on nickel foam substrate surface. After alcohol treatment, the deposited MnO2 on substrate obtains more uniform thickness and looser distribution, RGO obtains larger deposition area with compact distribution. In addition, the capacity, rate, specific energy, specific power and cycle performance have been greatly improved. MnO2 electrode shows the specific capacitance increasing from 153 and 103 F g − 1 to 270 and 190 F g − 1 at the current densities of 1 and 5 A g − 1, respectively. MnO2/RGO electrode shows specific capacitance increasing from 343 to 254 F g − 1 to 467 and 307 F g − 1 at 1 and 5 A g − 1, respectively. Moreover, the specific capacitance of MnO2 and MnO2/RGO electrodes keep 83.9% and 93.1% retention after 2500 cycles at the large current density of 5 A g − 1, respectively. Based on some scientific universals, we look forward to the proposed alcohol infiltrated substrate process for this work, which may be favorable for the performance enhancement of a series of MnO2-based supercapacitor materials, not only for MnO2 and MnO2/RGO.