Papers by Keyword: Sheet Metal

Abstract: In Thailand, the sheet metal products that were produced by rolling process have high demand and the consumption trend to grow in the future. Many new products, which made from rolling steel sheet, had been developed with various design. Thus the manufacturers have to improve the productivity through the investigation and analysis of different process parameters, which affect to the quality during the production. In this paper, finite volume method FVM had been applied to analyze different effects of processes parameters such as temperature, roller speed, friction, size and capacity of rolling machine. The commercial software MSC.SuperForge was used in the modeling and simulation of metal deformation under the flat rolling process. Considering the predicted results compared with the experimental data, the different in dimension error data were within an acceptable range of quality specification. The error in width of finished steel sheet was 1.17%, the length was error of 1.50%, and the thickness was error of 2.32%. By using this technique, different factors affected during rolling process can be investigated and controlled such as the metal flow, the distribution of stress and strain, and the deformation zone.

Abstract: Sheet metal forming forms in numerous industries like vehicle depend on the yielding of the sheet metals when strained. Yielding is portrayed by plastic flow of the materials when strained. The yield point if there should be an occurrence of uniaxial tension can be effectively decided from the pressure strain diagram, yet if there should arise an occurrence of multi axial Stresses it gets complicated. A connection between the principal stresses is required determining the conditions under which plastic flow occurs. This intricacy is tended to by the anisotropic yield capacities. Likewise, the tests used to acquire yield loci might be costly and time taking in such case these yield capacities end up being exceptionally viable. The yield criteria additionally help in deciding planar distribution of yield stresses and anisotropic coefficients, which gives a decent gauge of these mechanical parameters without having to through the pain of trial assurance. This project aims at using Hill 1948 criterion to obtain the Yield surface Diagrams for SS304 in annealed and original state and subsequently obtain the planar distribution of the uniaxial yield stress and anisotropic coefficient. Also, the performance evaluation of both the distributions will be done using accuracy index.

Abstract: A sixth order yield function was used to analyze the anisotropic plasticity behavior of sheet metal forming. Based on a complete sixth order homogenous polynomial in plane stress, the yield function was implemented as user material subroutines in the FE code ABAQUS Explicit and Standard. The associated flow rule and isotropic hardening were assumed. Material parameter values in the yield function were decided by uniaxial yield stresses and plastic strain ratios along 7 different loading orientations and plane strain yield and equal biaxial stresses and plastic strain ratio. To show the superiority of the sixth order yield function, the hole expansion test by Kuwabara et al.[1] was considered. The results of finite element simulation using the sixth order yield function showed a better agreement with the test results than YLD2000-2D yield function with M=6.

Abstract: Nowadays, there are several grades of sheet metal used in the automotive industry. Highstrength steel sheets, particularly, have been widely used in order to reduce the weight of vehicles,which is strongly related to their fuel consumption rate. However, it is generally known that thestrength of the sheets, which is relatively higher than that of the conventional carbon steel sheets,results in their low formability. In this work, the limiting drawing ratio and forming behavior of sheetmetal that is conventionally used for automobile parts were evaluated by test using cylindrical cupwith hole. The feasibility to use limiting cup height for comparing formability of sheet metal was alsoincluded in the investigation. The sheet materials used in the experiments are aluminium, cold rolledsteel, high strength steel and advanced high strength steel. The process parameters for this study weredie corner radius and blank holder force. Workpiece materials were prepared with a circular shapeand with a diameter of 80 millimetres. In the center of the circular workpiece, a 12-millimetrediameter hole was drilled to observe the formability of each of the materials. The advantage of usingan initial blank with a hole in the center by the cylindrical cup drawing test is that the cup does notfail from changes of the thickness of material near the punch radius at the bottom of the cup. Thelimiting cup height of the investigated materials were evaluated by test using the cylindrical cup withhole. The results show that the limiting cup height values have a relationship to the limiting drawingratio values of the investigated materials. Testing using cylindrical cup with hole by evaluating thelimiting cup height value is feasible for comparing the formability of sheet metals.

Abstract: A two-step rotary rim-thickening process of disc-like blanks was investigated by FE simulation and spinning experiments. The preforming shape of cross section for first step was designed as trapezium before forming rectangular-shape rim in the second step. The main factors influencing the blank forming in the first step were groove bottom height h₁ and the inclination angle α of the roller. With the increase of h₁ and α of the roller in FE simulation, the workpiece will be more prone to lose stability and cause defects. The forming limit diagram was obtained in first step, including stable forming zone, unstable forming zone and failed forming zone. Considering the stability and efficiency of thickening, four groups of h₁ and α were selected for the second step simulation. Maximum rim thickness (h₂) after second-step forming was 9 mm, obtained by trial and error in FE simulations. The spinning experiments were carried out to verify the validity of numerical simulation.

Abstract: A commercially available laser marking system based on diode-pumped Nd:YVO₄ laser was used for creating grid patterns for forming strain analysis of three different multiphase steels. The aim was to determine and analyze the influence of laser working parameters on the formability of the investigated sheet materials by means of an in-depth characterization of this induced microstructural and geometric inhomogeneity. The electrochemical etching served as the reference method without the negative effect of generating inhomogeneity. The formability was evaluated using the cupping test according to Erichsen. While the quantification of geometric inhomogeneity was based on the determination of the notch factor, microhardness measurement was used for the evaluation of micro-structural inhomogeneity. The results showed that multiphase steels exhibit similar values of the mark depth under the same creating parameters by means of laser. Furthermore, only the induced geometric inhomogeneity had a marked influence on the material formability. Finally, a method for the prediction of the optimal values of the grid pattern mark depth was developed from the perspective of its good visual recognizability and associated with the microstructure based material sensitivity to stress concentrators.

Abstract: The present study aims to determine stress-strain curves at large strains of sheet metals under the uniaxial stress state by using the in-plane stretch-bending test. The combined Swift-Voce model, which describes the large-strain work-hardening of materials by means of a weighting coefficient μ, was used for FE simulation of the stretch-bending. The coefficient μ was determined by minimizing the difference in punch stroke vs. bending strain responses between the experimental data and the corresponding experimental results. By using this inverse approach, stress-strain curves of two levels of high-strength steel sheets of a precipitation hardening type, 590R and 780R, in three sheet directions (0, 45 and 90^o from rolling direction), were determined.

Abstract: Short Cycle Stretch Forming (SCS) is an innovative stretch forming technology developed at the Institute for Metal Forming Technology (IFU) at the University of Stuttgart. The SCS technology combines plane pre-stretching of blank and subsequent deep drawing operations within the same stroke of press ram. The sheet metal thickness is reduced while denting resistance and yield stress increases due to hardening effects.Current research work focuses on applying SCS-technology to rotational-symmetrical bodies. A process simulation for SCS-Cupping process was performed for food cans. Based on these results a tool was manufactured and commissioned. The results showed that the thickness of cup bottoms of two-piece drawn and ironed (D&I) steel cans can be reduced. Therefore, it is possible to save material costs in serial production based on a reduced blank diameter.In this paper the different effects leading to the thinning of steel can bottom and failure types, such as, wrinkling and cracking are observed in a number of experimental series. Based on these results, the tool geometry was optimized and an advanced tool was manufactured. The results of this paper show that SCS-Cupping offers promising potential to save material, as well as outlining the main effects for this technology.

Abstract: This paper focuses upon zigzag-shape bending for suppression of defects, including dent and springback. A series of finite element analyses was carried out in order to optimize the bending condition for suppression of these defects. As a result, it was clarified that a diagonal movement of the upper die was effective for suppression of dents while a rather vertical movement of the upper die was effective for suppression of springback. In order to suppress dent and springback at the same time, this paper proposes another method of bending method, whereby the upper die with special shape moves in a diagonal way. Moreover, the stability of the method against variation of tool dead position, which would be caused by elastic deformation of supporting members, was studied by FEM, followed by experimental verification.

Abstract: Different geometries of shear test specimens were experimentally and numerically investigated. They are used for calibration of a virtual model, to be used for sheet metal blanking. Different specimen configurations were simulated in order to determine the strain and stress fields and the potential of producing pure shear failure. Tensile and shear tests were performed using DC01 steel material. The experimental data are used later to calibrate a material with Johnson-Cook elastic-plastic model.