Aiming at robotic manipulators subject to system uncertainty and external disturbance, this paper presents a novel adaptive control scheme that uses the time delay estimation (TED) technique and ...reinforcement learning (RL) technique to achieve a good tracking performance for each joint of a manipulator. Compared to conventional controllers, the proposed control scheme can not only handle the system parametric uncertainty and external disturbance but also guarantee both the angular positions and angular velocities of each joint without exceeding their preset constraints. Moreover, it has been proved by using Lyapunov theory that the tracking errors are uniformly ultimately bounded (UUB) with a small bound related to the parameters of the controller. Additionally, an innovative RL-based auxiliary term in the proposed controller further minimizes the steady state tracking errors, and thereby the tracking accuracy is not compromised by the lack of asymptotic convergence of tracking errors. Finally, the simulation results validate the effectiveness of the proposed control scheme.
Uniaxial tensile tests were conducted to investigate the hot tensile deformation behavior of 6061 aluminum alloy under various temperatures and strain rates. Fields−Backofen equation was employed to ...establish the constitutive model of 6061 aluminum alloy, which was used to construct the finite element model for multi-bosses formed by plate forging process at elevated temperature. In the combination of numerical simulations and experimental tests including micro-hardness and electron back-scattered diffraction (EBSD) examination, the influence of two main process parameters, namely deformation temperature and counter-punch force, on the boss deformation and microscopic characteristics of multi-bosses formed at elevated temperature was discussed. The results show that the constitutive equation adopted is adequate to predict the deformation behavior in the plate forging process. While a higher temperature can improve the formability due to the reduction of plastic deformation resistance, a higher counter-punch load is favorable to increase the boss height and risk of fracture around the punch radius at the same time. In addition, it is favorable to promote recrystallization and fabricate the cylindrical component with a more homogeneous microstructure at a higher deformation temperature. From a comprehensive consideration, the 623 K is taken as the optimized deformation temperature for the selected 6061 aluminum alloy.
To minimize the earing incurred by the planar anisotropic properties of sheets, a non-uniform die clearance model was proposed for the cup drawing process. The theoretical earing profile height model ...with non-uniform die clearance was developed based on the combination of radial strain and thickness strain. The Hill 1948 yield criteria was applied to predict geometric earing profile and the anisotropic parameters were calibrated by optimization. It is observed that the predictions of the theoretical model are in agreement with the results of the cup drawing experiments, and the earing profile height is increasingly decreased by the non-uniform die clearance model. Further to this, a numerical model of the deep drawing process was also carried out using the commercial finite element software Abaqus. The results show that the cup drawing with non-uniform die clearance can not only minimize the earing profile height but also reduce the opening springback and twist springback in the split-ring process.
The forging of hollow parts faces a great challenge as folding and buckling always occur during the forging process. To overcome these problems, a novel tube forging process combining upsetting and ...shear forging is developed to manufacture hollow parts with an inner flange at an arbitrary location. Firstly, two flow modes are introduced to analyze the deformation behavior of a hollow cylinder during internal thickening by upsetting, where the geometric limits associated with different deformation modes and the critical upsetting ratio with no folding defects are determined. The results clearly show the occurrence of a mode transition for some cylinders during the upsetting process; furthermore, the cylinder is less prone to folding in some cases due to the appearance of a third deformation zone located mid-way up the cylinder. Then, the forming mechanism of this novel process is analyzed, and its feasibility is demonstrated through finite element simulations and experiments. Results show that the flange can be moved to an arbitrary location on the inner wall in the height direction by controlling the stroke of the punch, and shear deformation can enhance the strength of the flange. Additionally, it is found that the shear depth, corner radius of the counter punch, and supporting force on the counter punch are the key parameters affecting the product quality.
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•A new tube forging process combined upsetting and shear forging was proposed.•Two flow modes were introduced to analyze the deformation behavior in upsetting.•The deformation mode and critical folding limits during upsetting were determined.•Deformation characteristics in shear forging process were analyzed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Hot deformation in 6063 aluminum alloys was investigated by hot compression testing over the temperature range of 573–723 K with strain rates of 0.01–10 s−1 using a Gleeble 3500 thermal-mechanical ...simulator. Based on the experimental results, constitutive equations compensated with strain were developed to model the hot deformation behavior. The intrinsic workability was further analyzed by establishing three-dimensional processing maps. These maps were constructed based on dynamic materials model to delineate variations in power dissipation efficiency and flow instability domains. Combined with microstructure observation, recommended processing domains are predicated to be within the temperatures range of 673–723 K and strain rates range of 0.01–0.1 s−1. Under such conditions, the main softening mechanism is dynamic recrystallization. The results from these processing maps agree well with microstructure observation.
•Constitutive equations compensated with strain were established for 6063 alloy.•Optimum processing parameters were determined by 3D processing maps.•The intrinsic workability of 6063 alloy was investigated.•The occurrences of DRV and DRX were discussed briefly by TEM.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Based on UG10.0 software as the secondary development platform, the UG/MenuScript and UG/KF (knowledge fusion) language are used in this paper to develop a computer-aided design system for casting ...process (CAD-CP). The CAD-CP system is divided into five parts: information acquisition module, riser design module, runner design module, sprue cup design module, and subsidized design module. To test the effectiveness of the designed system, a typical disk part of flywheel casting process is investigated by the CAD-CP system, where the process structures are designed and the process parameters are obtained. Besides, the numerical simulation of flywheel casting by ProCAST software and experiment are carried out, and the results show that the experiment is consistent with the numerical simulation. It indicates that the as-designed CAD-CP system would meet the standard of the casting process, where the design workload of the casting process is reduced effectively as well as the design efficiency is improved.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Friction has always been an urgent problem in metal forming process. Considering the coefficient of friction as a constant in the cold forging process tends to predict a larger stress–strain, this ...will lead to an inaccurate prediction result. This study takes AISI-1025 carbon steel with zinc phosphate coating as the research object, and a combination of finite element simulations and experiments is used to develope a pressure-dependent variable friction model. On the one hand, as the interface pressure is less than the critical pressure, it is still at a low friction level, and the friction factor can be measured by the sliding friction test; on the other hand, the friction factor is logarithmically increased with the interfacial pressure because of the rupture of the zinc phosphate coating. The variable friction model is then programmed into the finite element software as a subroutine and used to simulate the solid boss extrusion experiment. The predicted results are compared with the pressure-dependent variable friction model, the constant friction model, and the experimental validation results, which demonstrate that the variable friction model has a good prediction of deformation characteristic in cold forging process.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The surface roughening behavior under uniaxial tension is manifested as newly added micro-valleys and micro-mountains. The total strain experienced by the material during plastic deformation is an ...important factor in determining surface roughness. The surface roughness of DP590 increases with the increase in strain. Moreover, the inhomogeneity of the initial orientation of the experimental material leads to the incompatibility of the strain between adjacent grains during the plastic deformation process, which affects the surface morphology of the material, and the roughening of the surface is closely related to the (112)
1
1
¯
0
orientation. Furthermore, the friction behavior under lubricated conditions is almost the same whether the surface is rough or not: The frictional stress increases linearly with the average pressure, then shows a slight decrease, and finally increases linearly again.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Using tung oil as the raw material, a new bio-based prepolymer was successfully synthesized by reacting with acrylic-modified rosin (-acryloyl nutrient ethyl) ester (ARA)/acrylic-2-hydroxyethyl ester ...(HEA) followed by the use of the above composite material as the matrix and then reacting with the active diluent (2-HEMA, TPGDA) and the photoinitiator TPO and Irgacure1173 to successfully synthesize a new type of bio-based prepolymer-acrylate-epoxy tung oil polypolymer (AETP). The tung oil monomer before and after the epoxy formation was compared by proton NMR spectroscopy, and the chemical structure of AETP was analyzed by Fourier transform spectroscopy. Tung oil has an acid value of 1.5 mg KOH per g, an epoxy value of 5.38%, an iodine value of 11.28 g/100 g, and a refractive index of
n
25
= 1.475. Composite-based 3D printing resins (like AETP) were cured using digital light treatment, while some samples were also post-treated
via
ultraviolet (UV) light treatment. The AETP-based 3D printing resin has excellent thermal and mechanical properties, and the viscosity of its system is 313 mPa s; exposure time 4.5 s; the tensile strength, flexural strength and flexural modulus were 62 MPA, 63.84 MPa and 916.708 MPa, respectively; Shore hardness was 80 HD and shrinkage was 4.00%. The good performance of the AETP-based 3D printing resin is attributed to the rigidity of their tightly crosslinked structure. This study pioneered a method for producing photoactive acrylates (
e.g.
, tung oil-based acrylate oligomer resins) from renewable, low-cost biomass for light-curing 3D printing.
Using tung oil as the raw material, a new bio-based prepolymer was synthesized by reacting with ARA/HEA as the matrix and then reacting with the diluent and photoinitiator to synthesize a new bio-based prepolymer-acrylate-epoxy tung oil polypolymer.
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IJS, KILJ, NUK, UL, UM, UPUK
During the sheet metal forming, one of the major causes for die failure is transfer and accumulation of adhered material to the die surface, generally referred to as galling behavior. In the present ...work, the galling mechanism in sheet metal forming is investigated by a multi-scale approach. Firstly, the macro-galling behavior in square cup drawing of high-strength steel is examined by laboratory experiment and numerical simulation. Then, the first-principle calculations are used to present an insight to the atomic level galling at TiC/bcc-Fe interface. As a result, the macro-galling behavior in sheet metal forming is dominated by the critical contact pressure and the effective sliding distance. At atomic scale, the theoretical modeling using perfect crystals suggests that the separation most likely occurs at TiC/bcc-Fe interface or within the sub Fe slab, where the initiation galling would be arose and then formed as micro-adhesion.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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