Papers by Keyword: Sheet Metal

Abstract: A combined process of hole flanging and flange upsetting was proposed. Both elastic-plastic FEM and experiments were employed to analyze the process. A 2mm thick 08AL sheet with 120mm outer diameter and 24.6mm center hole diameter was used as the blank. The effect of the R_f and the R_c values on the flanging quality were analyzed, where R_f was defined as the ratio of the die fillet size to the workpiece thickness t and R_c was defined as the ratio of the clearance C to the workpiece thickness t. Also the effect of R_f and R_c on upsetting ratio R_u which was defined as the ratio of thickness before and after upsetting were studied. The finite element results were validated by experimental results. Also a 2mm thick flange without thinning and defects was gained in a reasonable range of R_c and a certain value of R_f.

Abstract: Roll forming is a well known bending process and sheet metals can only be machined into two-dimensional surfaces in traditional roll forming. While with more and more personalized demands, three-dimensional surfaces are widely required. Thus, flexible rollers are used to achieve three-dimensional surfaces. And in order to optimize experimental parameters and to predict experimental results, finite element method (FEM) is developed. In this paper the set-up of flexible roll-forming is described and the process of roll forming is simulated. Then the influences of forming parameters, such as the thickness and the roll velocity, on forming quality of the sheet metal in roll forming process are discussed. The results show that the analysis of flexible roller parameters is practical for the continuous and efficient forming of three-dimensional surfaces.

Abstract: Magnetorheological (MR) fluid is a kind of smart material. In this paper, magnetorheological (MR) fluid is applied as a flexible-die, the rheological properties of which can be changed rapidly under a magnetic field, in sheet metal forming process. Bulge tests using a kind of MR fluid, MRF-J01T, are carried out on self-designed experimental device. Stainless steel 1Cr18Ni9Ti combined with different process parameters are adopted to investigate the effect of property of MR fluid on the formability of material tested. The results showed that MR fluid can be utilized successfully as a pressure-carrying medium in sheet forming process. The rheological properties of MR fluid can greatly influence the dome height and thickness strain distribution of specimens.

Abstract: For the bulging of sheet metals under hydraulic pressure on concave surface, constitutive relation, static equilibrium conditions, and approximate geometrical relation were discussed about the source of calculation error. Dimensionless deflection at the center of sheet was used as the intermediate variable, and a simple but efficient nomographic algorithm addressed for strain limit is presented in this paper. The results of the calculation were compared with that of the uniaxial tensile test, the bulge test, and the Finite Element Analysis (FEA). This method has the potential for industrial applications such as pressure forming, bulge test, and rupture disc manufacturing.

Abstract: A new stretch-forming process based on discretely loading for three-dimensional sheet metal part is proposed and numerically investigated. The gripping jaw in traditional stretch-forming process is replaced by the discrete array of loading units, and the stretching load is applied at discrete points on the two ends of sheet metal. By controlling the loading trajectory at the each discrete point, an optimal stretch-forming process can be realized. The numerical results on the new stretch-forming process of a saddle-shaped sheet metal part show that the distribution of the deformation on the formed surface of new process is more uniform than that of traditional stretch-forming, and the forming defects can be avoided and better forming quality will be obtained.

Abstract: Stretch-forming based on discretely loading is a new process for manufacturing three-dimensional sheet metal part, the stretching load is applied at discrete points on the two ends of sheet metal, by controlling the loading trajectory at each discrete point, an optimal stretch-forming process can be realized, and the formed surface with the strains and stresses more uniformly distributed are obtained so that the forming defect can be avoided. The numerically investigated results on the stretch-forming process of spherical sheet metal part show that, comparing with the traditional stretch-forming, the equivalent strain in the new process is reduced by approximately 30% and equivalent stress reduced by 10%, the range of the strain and stress distributions are reduced by approximately 30%.

Abstract: The influence of used work rolls profiling on the quality of hot rolled metal was studied. The defect non-flatness is the main reason for hot rolled metal rejection to second grade at the continuous hot rolling mill 1700 of ArcelorMittal Temirtau JSC. The most optimal among studied profiling is concave profiling with average cumulative value ΣΔ=1.71mm. This is evidenced by the least volume of hot rolled metal, rejected to the second grade due to non-flatness.There were mathematical models developed, forecasting the volume of metal, rolled with the defect non-flatness with definite cumulative profiling of work rolls.

Abstract: The demands on accuracy of forming simulation rised sharply in recent years due to increasing manufacturing costs and intensive application of lightweight materials in automotive industry. The accuracy of prediction of forming simulation depends mainly on the use of material models, pre-processing parameters and friction modelling. For isolated investigation of individual parameters a new test has been developed at the Institute for Metal Forming Technology (IFU), University of Stuttgart. This buckling-bending-test allows a frictionless investigation of bending processes. Within preliminary investigation buckling-bending-tests were carried out using an aluminium sheet material. The strain on the outer skin of the specimen was measured in-situ during the test by the use of an optical measuring system. According to the experiments, a forming simulation of the buckling-bending-test was generated using LS-Dyna. The parameters necessary for the pre-processing, such as element size, refinement levels and meshing parameters were examined in a separate simulation study to determine the optimum for the subsequent simulation study. The approaches of Ludwik, Hollomon, Gosh and Swift have been used to describe the flow curve. It was found out that the best match can be achieved by an extrapolation according to Ludwik. The improvement of prediction amounts to 5 per cent. The description of the yield locus depends on the material file used for the simulation. In this investigation the material models MAT_18, MAT_36, MAT_37, MAT122 and MAT_133 have been used. It was shown that the prediction of bending loads can be approved by the use of the yield locus description of Barlat.

Abstract: With the help of an explicit finite element analysis, cutting of cold-rolled dual-phase steels for various tool clearances was studied. In the first part of the study, the influence of the element size in the shear zone of the sheet on the predicted cut edge geometry and punch force was assessed and the optimal simulation parameters were identified. In the second part, the fracture description was put into focus of the investigation. It is shown that the used mathematical description of the equivalent plastic strain at fracture as a function of the stress triaxiality does not yield accurate results for FEA-based prediction of the cut edge geometry. A need in a more accurate fracture characterisation and, possibly, a more advanced fracture description of dual-phase sheet steels and the directions of the future research are identified.

Abstract: Water jet incremental sheet metal forming is the leading research topic in sheet metal forming industry, recently. In this work, a five-axis machine for water jet incremental sheet metal forming is designed and built, which is made up of four parts, namely linear motion unit, nozzle tilt and rotation unit, fixture and seal chamber. The nozzle tilt and rotation unit has two rotation degrees of freedom and the linear motion unit has three translational degrees of freedom. Then, two types of nozzles including L type nozzle and upright nozzle are designed and built. Finally, two different kinds of fixture are designed and built for common sheet metal forming and bellows expansion joints forming, respectively.