Influence Of Thickness Reduction Research Articles

Influence of thickness reduction on the forming results in the three-dimensional surface rolling process with rigid arc-shaped rollers

Three-dimensional surface rolling with rigid arc-shaped rollers (TSRRAR), a new method for manufacturing double-curved metal sheets, can be used to realize the rapid forming of 3D surface sheets. The non-uniform roll gap is generated by a pair of rollers with different axial radii with appropriately reduced sheet thickness. After passing through the roll gap, a flat sheet is bent in the rolling direction. Meanwhile, it deforms perpendicular to the rolling direction, resulting in a three-dimensional surface part with curvatures in both directions. The work adopted the elastic-plastic finite element (FE) method to simulate aluminum alloy sheets with different maximum thickness reductions. The results showed that the longitudinal curvature of sheets rose as the reduction increased. Moreover, a slightly increased reduction caused a significant variation in the longitudinal curvature radius of sheets. Different bending curvatures of sheets could be obtained by changing the reduction, indicating the flexible forming of three-dimensional curved surface metal sheets. Also, the changing trend of longitudinal curvatures of testing parts obtained by rolling experiments was substantially in agreement with the FE simulation results. Therefore, the established FE models can be used for exploring the manufacturing process of TSRRAR.

Influence of thickness reduction on forming limits of mild steel DC01

The Forming Limit Diagram (FLD) is an essential tool to assess sheet metal formability in sheet metal deep drawing. In FLDs/FLC (Forming Limit Curve) is representation of material formability limits at which material is not able to withstand higher deformation. In this work, different methodologies for FLC determination of mild steel DC01 are investigated. The Nakajima test is a well-known experiment for FLC determination but, however, contact conditions that can appear in the form of either friction or pressure may perturb the results. The former may cause the need for repetitions for different widths by altering the necking location, whereas the latter may be responsible for overestimation of the material formability. Another method for FLC determination without those effects is to use the cruciform specimen test under biaxial loading conditions. As the first step, Necking has to be induced at the center of cruciform specimen by thickness reduction or groove. Therefore, in this work, the cruciform geometry under biaxial loading is optimized using FEM through the comparative analysis. The goal of simulation was to induce the necking just in the thinner gauge, not adjacent zone. Thereupon, different loads on biaxial machine’s axes can provide different strain paths at the thinner gauge of the optimized specimen. After reviewing of various researches in connection with thickness reduction effect on sheet metal deformation, it was found that thickness reduction might not influence the material formability during uniaxial and plane strain tensions, but it was observed that there is gradual decrease of limit strains with decreasing the thickness for equi-biaxial tension.Manufacturing process like milling, cause small defects on material surface and local instability takes place at lower level of deformation. Besides, it was found that existence of through thickness normal stress leads to higher value of FLC. Deformation during Nakajima and cruciform experiments were captured by Digital Image Correlation (DIC) system. The execution and evaluation of those experiments are explained in detail and Time Dependent Method (TDM) was applied to detect the beginning time of instability. Experimental strain paths are compared with consideration of strain rates and, as it was expected, FLC from cruciform specimen is lower than Nakajima one, especially on the right hand side of FLD. The remarkable difference can be attributed to defects in the material and existence of through-thickness normal stress, which leads to overestimation of the material formability during Nakajima experiment.

Influence of Thickness Reduction in Base Plate on Elastic Stress State of Patch Plate Joint by Combination of Welding and Bonding

Influence of Thickness Reduction in Base Plate on Elastic Stress State of Patch Plate Joint by Combination of Welding and Bonding

Influence of thickness reduction in base plate on elastic stress state of patch plate joint by combination of welding and bonding

ABSTRACT For investigating the influence of thickness reduction in base plate on elastic stress state of patch plate joint by combination of welding and bonding, a series of experiment and analysis were conducted. A static tensile loading experiment was carried out. The thickness reductions of 2.5 mm were applied to both top and bottom surfaces of a base plate with a thickness of 12 mm. The thickness-reduced parts of the base plate were covered by the patch plates with a thickness of 6 mm. The joining methods of patch plates were only fillet welding, only bonding and the combination of welding and bonding. The load-carrying effect at the centre of the joint was improved by the combination of welding and bonding compared to the case with only welding. However, the stress reduction effect around the welded part could not be clearly confirmed from the experimental result. The 2D elastic analysis was performed for simulating the experiment and examining the stress reduction effect around the welded part in detail. Furthermore, the influence of the degree of thickness reduction in base plate on the stress state around the welded part was investigated. The results indicated that the stress reduction effect by the combination of welding and bonding was larger around the weld root rather than the weld toe.

Influence of thickness reduction per pass on strain, microstructures and mechanical properties of 7050 Al alloy sheet processed by asymmetric rolling

The influences of thickness reduction per pass (TRPP, 13–75%) on the macro-deformation, strain distribution, microstructural evolution, mechanical properties and their through-thickness uniformities of 7050 Al alloy sheets processed by a series of asymmetric rolling (ASR) are investigated using finite element (FE) and experimental methods. With decreasing TRPPs, the shear distances in rolling direction (RD) between top and bottom surfaces of rolled sheets are increased, resulting in much more shear and equivalent strains, and their homogeneous distribution throughout the thickness of ASR-processed sheets. The quantity of micro-shear bands comprising fine sub-grains with average size <0.5μm through the thickness of rolled sheets is increased with decreasing TRPPs. In addition, the size of the sub-grains with well-defined boundaries is increased with increasing TRPPs while the dislocation density in their interior is decreased, which could be mainly attributed to the insufficient deformation and more recovery occurred during rolling as well as after. After annealing/recrystallization, the grain sizes as well as their through-thickness homogeneity are improved greatly using smaller TRPPs, which also contributes to the good through-thickness homogeneity of mechanical properties.

Influence of high deformation on the microstructure of low-carbon steel

Low-carbon steel sheets DC04 used in the automotive industry were subjected to cold rolling for thickness reduction from 20% to 89%. The desired thickness was achieved by successive reductions using a rolling mill. The influence of thickness reduction on the microstructure was studied by scanning electron microscopy. Microstructure evolution was characterized by the distortion of grains and the occurrence of the oriented grain structure for high cold work. A mechanism of grain restructuring for high cold work was described. The occurrence of voids was discussed in relation with cold work. The evolution of voids at the grain boundaries and inside the grains was also considered. To characterize the grain size, the Feret diameter was measured and the grain size distribution versus cold work was discussed. The chemical homogeneity of the sample was also analyzed.

Study of the cooperativity at the glass transition temperature in PC/PMMA multilayered films: Influence of thickness reduction from macro- to nanoscale

In multilayered polymer films, the influence of thickness reduction on the glass transition temperature (Tg) and cooperatively rearranging region (CRR) size was investigated using temperature modulated differential scanning calorimetry (TMDSC). The materials used in this work are multilayered films comprising tens to thousands of alternating layers of two polymers, Bisphenol A Polycarbonate (PC) and polymethyl-methacrylate (PMMA) fabricated by layer multiplying coextrusion technique. The TMDSC measurements enable the calculation of the average values of CRR parameters at the dynamic glass transition temperature (Tg) using Donth’s method. The molecular mobility in each polymer is found to be altered in entirely different ways as the thickness of each component became thinner than 125 nm, whereby the polymers exist as two dimensional layers under those conditions. PC exhibits a drastic decrease in cooperativity volume at the glass transition while slight modifications are observed for PMMA. These observations are discussed in regard with the role of the large interface amount between the two different polymers and the evolution of the macromolecule conformations.

Improving strip cleanliness after cold rolling

Strip cleanliness in the industrial cold rolling mill must be controlled by optimizing the roll, strip, lubricant and process parameters. Obtained experimental evidence in this work shows which of these parameters have a significant influence on strip cleanliness. The experiments were carried out on a plate-out tester and on cold rolling pilot mills. New findings were the influence of thickness reduction on strip cleanliness: a high reduction in the first stands of a tandem mill results in poor strip cleanliness, but in the latter stands a high reduction results in a better strip cleanliness than a low reduction. Furthermore the beneficial influence of a chrome coating on the work roll was shown to be related to the better adherence of oil to this type of work roll. This article provides a concise overview of the experimental results achieved and their interpretation.

Effects of Liquid Core Reduction during Solidification of Pb2.5wt%Sb Thin Slabs

The influence of thickness reduction during solidification of Pb2.5wt%Sb thin slabs in the microstructure was experimentally analyzed using a physical simulator consisted of a water cooled mould with a moveable sidewall, driven by a hydraulic piston, to squeeze the liquid core during the solidification. Experiments were carried out in order to obtain slabs without thickness reduction and with thickness reduction of about 20% and 40%. The microstructures are revealed in order to analyze the influence of the thickness reduction applied in the formation of central equiaxial structure and in the secondary dendrite arm spacing. From the results it was observed that increasing the thickness reduction increases the extension of the equiaxial structure.