Physical Modeling of Metalworking Processes—I: Determination of Large Plastic Strains

This article discusses the application of the visioplasticity method to the evaluation of large plastic strains such as those occurring in metalforming. Although this method can be used for any mode of deformation, its application to plane-strain deformation is treated here. The distortion of a quadrilateral element of a grid is tracked to compute strains during deformation. In each case any two lines of the quadrilateral can be used (length before and after deformation and direction cosines before deformation) to determine strains in the element. The method has been verified by application to basic cases of deformation such as uniaxial compression, tension, pure shear, and rotation of elements. The effect of choice of lines upon the results of strain calculation is also discussed

Physical Modeling of Metalworking Processes—I: Determination of Large Plastic Strains

This article discusses the application of the visioplasticity method to the evaluation of large plastic strains such as those occurring in metalforming. Although this method can be used for any mode of deformation, its application to plane-strain deformation is treated here. The distortion of a quadrilateral element of a grid is tracked to compute strains during deformation. In each case any two lines of the quadrilateral can be used (length before and after deformation and direction cosines before deformation) to determine strains in the element. The method has been verified by application to basic cases of deformation such as uniaxial compression, tension, pure shear, and rotation of elements. The effect of choice of lines upon the results of strain calculation is also discussed

Physical Modeling of Metalworking Processes—II: Comparison of Visioplastic Modeling and Computer Simulation

The analytical modeling of physical processes is an integral part of scientific and technical research. Physical build-and-test procedures used for designing forging dies are prohibitively expensive and result in long lead times in obtaining satisfactory designs. In the present study the wedge test was advanced to the level of a standard laboratory test in order to verify the analytical results of a viscoplastic finite-element program, ALPID (Analysis of Large Plastic Incremental Deformation), which was developed to simulate the metal flow in deformation processes such as forging and extrusion. Wedge-shaped specimens were machined from plates of 1100-F and 6061-T6 aluminum alloy and the grids engraved on the meridian plane by means of a CNC engraver. The specimens were compressed in segmented dies at room temperature. The undeformed and deformed grids were digitized, and the true effective strains were calculated using a computer program developed for that purpose. The effective strains were then displayed as contour plots for comparison with the ALPID-generated strain values. Comparison of the experimental and ALPID results indicates that the values predicted by the ALPID code are very near the experimental values. The minor differences in the results are attributed to unavoidable experimental errors

Physical Modeling of Metalworking Processes—II: Comparison of Visioplastic Modeling and Computer Simulation

The analytical modeling of physical processes is an integral part of scientific and technical research. Physical build-and-test procedures used for designing forging dies are prohibitively expensive and result in long lead times in obtaining satisfactory designs. In the present study the wedge test was advanced to the level of a standard laboratory test in order to verify the analytical results of a viscoplastic finite-element program, ALPID (Analysis of Large Plastic Incremental Deformation), which was developed to simulate the metal flow in deformation processes such as forging and extrusion. Wedge-shaped specimens were machined from plates of 1100-F and 6061-T6 aluminum alloy and the grids engraved on the meridian plane by means of a CNC engraver. The specimens were compressed in segmented dies at room temperature. The undeformed and deformed grids were digitized, and the true effective strains were calculated using a computer program developed for that purpose. The effective strains were then displayed as contour plots for comparison with the ALPID-generated strain values. Comparison of the experimental and ALPID results indicates that the values predicted by the ALPID code are very near the experimental values. The minor differences in the results are attributed to unavoidable experimental errors

Extrusion Through Controlled Strain Rate Dies

The workability of a material during deformation processing is determined by (a) the die geometry which, in turn, determines the flow field during deformation, and, (b) the inherent workability of the material under the imposed processing conditions of strain rate and temperature. Most common alloys have good inherent workability and can be successfully formed over wide ranges of temperature and strain rate. Products can be successfully formed from these alloys even with dies which impose large variations in strain rate during deformation. However, many of the new alloys and composites can be deformed only in very narrow processing regimes, and control of the strain rate during deformation of such materials becomes important. For example, extrusion of a whisker-reinforced aluminum alloy composite is possible only when the strain rate is controlled to within one order of magnitude. This paper describes the development of a method for obtaining preliminary shapes of controlled strain rate extrusion dies, a special case being the constant strain rate die. The theoretical basis for such die design processes is presented, followed by some examples of die geometries. Since this design procedure ignores the material flow properties, the designed die shapes must be verified using the finite element method or physical modeling. Results of simulations with the program ALPID are also presented

Extrusion Through Controlled Strain Rate Dies

The workability of a material during deformation processing is determined by (a) the die geometry which, in turn, determines the flow field during deformation, and, (b) the inherent workability of the material under the imposed processing conditions of strain rate and temperature. Most common alloys have good inherent workability and can be successfully formed over wide ranges of temperature and strain rate. Products can be successfully formed from these alloys even with dies which impose large variations in strain rate during deformation. However, many of the new alloys and composites can be deformed only in very narrow processing regimes, and control of the strain rate during deformation of such materials becomes important. For example, extrusion of a whisker-reinforced aluminum alloy composite is possible only when the strain rate is controlled to within one order of magnitude. This paper describes the development of a method for obtaining preliminary shapes of controlled strain rate extrusion dies, a special case being the constant strain rate die. The theoretical basis for such die design processes is presented, followed by some examples of die geometries. Since this design procedure ignores the material flow properties, the designed die shapes must be verified using the finite element method or physical modeling. Results of simulations with the program ALPID are also presented