True strain distribution profile on sheet metal using different punch geometries
Changes are often necessary during the tryout of stamping tools. These changes may range from adjustments on die and punch designs to the selection of a new material with better formability characteristics. All these actions, however, require time and money creating the need for better initial sheet metal evaluation. Hence, increasing attention has focused on the development of laboratory tests that enable stamping companies to know more about the sheet metal stampability or that can, at least in part, ensure that their stamped products are produced without major problems. Identification of high stress region on stamping may allow for better tool stamping adjustment during tests, rendering a more uniform materials deformation and leading to the production of higher quality parts. Increasing attention has focused on the material evaluation based on the tool geometries in order to calculate the strain distribution. This study deals with an evaluation of four punch models with varied geometries in addition to the traditional Nakazima test tool. An evaluation was also made of the major true strain distribution profile at points distributed linearly from the region close to the die shoulder to the punch center.
Computer aided analysis and design of sheet metal forming processes: Part I – The finite element modeling concepts
The design of a stamping die essentially begins with the geometric development of die-faces using the process specifications in the form of part geometry, material data and stamping criterion such as the thinning limits. Succeeding the completion of the forming interface geometry; the computer aided design models for the punch, the die and the binder tools are generated using the specifications of the manufacturing tools and presses. Nevertheless, an ensuing forming interface geometry is hardly possible right at the first time, and depending on the experience and skills of the methods engineer, several iterations may be required to ensure a die-face design that deforms the blank in to the stamping part at a minimum number operation. It is hence the design for the forming interface that determines a significant part of the tooling design and production costs. The computer aided analysis based on the finite element method may, on the other hand, help the stamping methods engineer to reduce the costly trial-and-error iterations through the qualification of the sheet metal forming process in accordance with the objective stamping criteria. In order to make an utmost benefit of computer analysis in the tooling design for stamping processes, the stamping engineer should have the fundamental understanding of the computational concepts of the finite element analysis in the sheet metal process simulation. The finite elements, the deformation response of sheet metals, and the numerical procedures are key concepts for the stamping simulation engineer in this perspective. The finite element procedures and the element formulations, along with their performance comparisons in an industrial stamping applications are the subjects in this part of the study. The sheet metal deformation modeling and the die-face design concepts are presented in Parts II and III, respectively, together with a set of industrial applications. The practical connotations of the computer aided analysis and design of the sheet metal stamping dies is given and conclusions are drawn.
Recalculation of Mass Defects
THE well-known mass defect curve of the old nuclear scheme calculated with regard to α-particles and protons presented a difficulty with its minimum of binding energy for tin and an increasing portion between tin and lead. On the other hand, the mass defect values against protons give a rather smoothly decreasing curve.1 As has already been pointed out,2 the number of α-particles must be considerably reduced from the point of view of the new scheme, which does not admit any electrons in nuclei, but only neutrons and protons (presumably joined as α-particles). The curve of mass defect against protons and neutrons (perhaps with a single ‘central’ α-particle) is very similar to the old curve against protons, but decreases less rapidly. Clearly the new mass defect values relatively to α-particles, neutrons and protons must lie somewhere between the old values computed relative to protons and α-particles respectively (because the number of α-particles is decreased). We may emphasise that this new mass defect curve shows no increasing portion between tin and lead. For illustration we give two typical values: Old: 50Sn124 = 31α + 12&#38;epsiv;; mass defect = 0.158 (in mass units); 82Pb208 = 52α + 22&#38;epsiv;; mass defect = 0.035. New: 50Sn124= 25α + 24ω (ω = neutron); mass defect = 0.304; 82Pb208 = 41α + 44ω; mass defect = 0.366.