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This study proposes a versatile, low-cost, shape-conforming soft gripper fabricated using the self-developed high-speed multi-material vat photopolymerization process. This additive manufacturing technology consists of a rotary build plate that moves through 180° along the XY plane and multiple resin vats to accommodate different materials. A cleaning system uses pressurized air and alcohol to prevent contamination between layers and to increase the bond strength. The soft grippers are manufactured using soft (GC3D-ESK) and hard phase (AA-temp) materials to optimize the gripping force and prevent damage of the objects. Experimental results show that the tensile strength of the multi-material fabricated part (GC3D-HSK and AA-temp) is 5 times greater than that of the soft material GC3D-HSK. The multi-material specimen exhibits an elastic modulus of 89.28 MPa, which is much higher than 2.08 MPa of the soft material. The multi-material fabricated specimen exhibits high strength, high elastic modulus, and 65% longer elongation than the hard material. In addition, the specimens that are cleaned with alcohol after successive printing of each layer have 4% higher tensile strength and 30% longer ductility. A shrinkage analysis is carried out to evaluate the material compatibility. The percentage shrinkage for both GC3D-HSK and AA-temp is obtained in the range of 0.1–0.2%. The printed pneumatic soft gripper is used to lift goods of up to 200g using a maximum pressure of 34.3 kPa. The lifting efficiency of the developed gripper is evaluated to be 5.83 g/kPa which is higher than the currently existing grippers. The printed gripper can lift objects of different weights and profiles without damaging the surface. The high-speed multi-material VP 3D printer can be used for additive manufacturing to optimize the design of pneumatic soft grippers. [ABSTRACT FROM AUTHOR]

Ti-6Al-4V alloy is the most preferred alloy used in laser powder bed fusion (LPBF) and physical vapour deposition (PVD) coating may often be needed. However, whether the wear performance of the coating on the high hardness LPBF Ti-6Al-4V substrate may perform differently to that on the conventionally processed (CP) and significantly lower hardness alloy substrate has not been clear. In this study, dry sliding wear tests have been conducted on PVD TiN-coated Ti-6Al-4V samples processed either by LPBF or by CP, using WC-Co as counter material. It has been found that local fracturing of coating after being thinned to 0.4–0.5μm in both coated LPBF and CP samples is similar. The major wear mechanism leading to a gradually rapid increase in wear rate of the coated samples will be demonstrated and explained through a wear process described as thickness reduction and local fracturing of the coating before the widening of the wear track. It will be shown that the local fracturing of coating was accompanied by the local deformation in CP substrate due to its low hardness. For the LBPF substrate, the deformation was not readily observed. That the higher amount of deformation underneath the coating for the case of CP substrate has affected little the overall wear rate will be illustrated. [ABSTRACT FROM AUTHOR]

This paper deals with the deep drawing of metal cups using the Marform process. Using this technique, higher limiting drawing ratios can be obtained compared with the conventional deep drawing process. The analytical model of the process is presented initially, followed by the finite element simulations using ABAQUS software. A new friction model based on local contact conditions is presented and used in the finite element (FE) simulations of the process. Compared with traditional Coulomb friction model, the results of the FE simulations with the new friction model showed good correlation with experimental results. The results showed that the maximum thinning occurs at the punch profile portion, and by increasing the forming pressure, thinning of the sheet metal propagates from the punch profile portion to the side wall. At low forming pressures, wrinkles appear in the flange, whilst at higher pressures, fracture is the main defect of the Marform process. [ABSTRACT FROM AUTHOR]

Deep drawing of sheet metals using Maslennikov's technique has been analyzed by analytical and finite element simulation approaches. A new friction model based on local contact conditions has been used in the finite element (FE) simulations of the process. Compared to traditional Coulomb friction model, the results of FE simulations with the new friction model show good correlation with analytical calculations. The effects of key process parameters such as rubber ring thickness, ring inner diameter, die hole diameter, and die profile radius on the results have been investigated. The results showed that very deep cups without thinning in the side wall portion can be achieved with this process. Based on the results of FE analysis, it was found that the maximum drawing ratio can be achieved by adopting a combination of process parameters which correspond to points nearest to the fracture limit. [ABSTRACT FROM AUTHOR]

In a metal-working process, the friction between the material and the tools influences the process by modifying the strain distribution of the workpiece. This frictional behavior is often taken into account by using a constant coefficient of friction in the finite element simulations. However, friction coefficient varies in time and space with many parameters. This paper aims at modeling of friction in dry contacts which happens at metal-forming processes in the lack of lubricant. The coefficient of dry friction in this model is a function of contact area ratio (which is a function of surface contact characteristics) and strain hardening exponent (material property). The V-bending process of aluminum alloy 6061-T4 sheets was studied experimentally and numerically using ABAQUS/Standard with two kinds of friction models: Coulomb friction and newly developed dry friction models. The results clearly showed that the developed dry friction model has better results in predicting load-stroke curves and springback compared to traditional Coulomb friction model. The FE prediction error for 6061-T4 AA is 16.9% using Coulomb friction model and 9.2% using dry friction model. [ABSTRACT FROM AUTHOR]

The biaxial bulge test is a material test for sheet metals to evaluate formability and determine the flow stress diagram. Due to the biaxial state of stress induced in this test, the maximum achievable strain before fracture is much larger than in the uniaxial tensile test. A new dynamic bulge testing technique is simulated and analyzed in this study which can be performed on a conventional split Hopkinson pressure bar (SHPB) system to evaluate the strain-rate dependent strength of material at high impact velocities. Polyurethane rubber as pressure carrying medium is used to bulge the OFHC copper sheet. The use of hyperelastic rubber instead of fluid as a pressure medium makes the bulge test simple and easy to perform. The input bar of SHPB is used to apply and measure the bulging pressure. The finite element simulation using ABAQUS/explicit and analytical analysis are compared and show good correlation with each other. The results clearly show that as the strain-rate increases, the strength of the OFHC copper increases. From the study, a robust method to determine the material behavior under dynamically biaxial deformation conditions has been developed. [ABSTRACT FROM AUTHOR]

The Stribeck friction model was investigated in this study to predict springback of high-strength steel sheets. The coefficient of friction in Stribeck curve depends on sliding velocity and contact pressure. The plane-strain bending process is simulated in ABAQUS/Standard. The influence of forming speed, over-pressing and holding time on springback behaviour of sheets was studied numerically. By plotting the variation of bending angle with punch stroke, we found that the loading curve of finite element analysis showed similar results to the experiments. The unloading curves of FE analysis with friction models based on Stribeck curve and Coulomb law showed good agreement with experiments with error less than 1.5%. Forming speed of up to 50 mm/s does not have significant effect on springback. The effect of holding time on reducing springback is small, but over-press has large effect on reducing springback. The results showed that Stribeck model is suitable for sheet metal forming simulations, especially at higher forming speeds and pressures. [ABSTRACT FROM AUTHOR]

In a metal working process, the friction between the material and the tools influences the process by modifying the strain distribution of the workpiece. From a numerical point of view, a constant coefficient of friction (Coulomb’s friction) is commonly used in finite element simulations to model the frictional behaviour of contacting solids. However, friction coefficient varies in time and space with many parameters. We presented here a theoretical model of static friction in rubber/metal contact which allows the determination of the static coefficient of friction as a function of local contact conditions. Simulations using finite element software ABAQUS/Explicit were carried out for an axisymmetric tube bulging operation using the defined friction model. We compared the computed tube thickness related to the constant coefficient of static friction with the defined friction model. The results clearly showed that the new friction model provides better agreement between experiments (Girard, Grenier, Mac Donald, J Mater Process Technol 172:346–355, ) and results of numerical simulations. [ABSTRACT FROM AUTHOR]