We studied a method of evaluating the strain distribution of a steel sheet after forming, using high-frequency ultrasonic wave. We used JIS No.5 test pieces which applied arbitrary strain with 590 MPa class steel and 980 MPa class steel. The longitudinal wave sound velocity in the material was measured using high-frequency ultrasonic wave, visualization of the strain received by the material was found to be possible. It was found that there is a correlation between the amount of strain added to the material and the increase in sound velocity.
The micro extrusion process is one of the microforming technologies for the fabrication of microparts such as micro-gear shaft and micro pins for electronic parts. This paper focuses on the frictional behavior and plastic deformation observed at various die angles and friction conditions of lubricants and die coatings, and presents the friction models effects and geometry effects of micro extrusion 6063 aluminum alloy billets. The extrusion force increases with increasing die angle. From the results for various die angles, the backward extrusion length was found to increase with increasing die angle. The high kinematic viscosity and low friction coefficient can reduce extrusion force when the material flow is an external-shear type. However, the extrusion force increases with increasing kinematic viscosity and acts only in the backward extrusion part when the material flow is an internal-shear type. Three friction models were considered: Coulomb friction, plastic shear friction, and combined (Coulomb and plastic shear) friction. The finite element simulation was carried out and the results showed that the combined friction model accurately predicted the micro extrusion results.
The numerical simulations of sheet metal forming are used practically in production preparation for automotive parts. Breakage and wrinkles are evaluated in most of the sheet metal forming by FEM analysis. The wrinkles are controlled by the restraining force with drawbeads. If the force is too large, a breakage occurs. Thus, the adjustment of the drawbeads are important in deforming the sheet metal without defects. The drawbead size is much smaller in comparison with the whole of automotive panels. If the whole panel is divided into finite elements with the mesh sizes corresponding to the shape of the drawbeads, the analysis takes several days. Therefore, the FE models of drawbead parts in the panels are normally omitted and drawbead force is given as the boundary condition, instead. A new calculation method of drawbead properties, in which a material and friction models conforming to the actual phenomenon were implemented, was proposed to improve the accuracy of sheet metal forming analysis. The difference between the predicted drawbead forces and the experimental values has been decreased to less than 10% at maximum. As a result of the application of these values to the calculation of forming an actual panel and a comparison with experimental results, the validity of the proposed method was verified.
It is known that a burr of a blank produced by sheet metal shearing falls off during a subsequent process and causes problems. The authors became interested in this problem and carried out deep drawing experiments using a blank with a stepped edge as a substitution for burr. As a result, there was no rupture at the blank edge, but the stepped flange edge wrinkled regularly depending on the design of the step. The authors considered this deformation to have a new industrial value, for example, the structure of the waveform is effective in bonding at an insert molding. Therefore, we decided to examine the fundamental characteristics of this wavy deformation. Furthermore, we thought that the numerical approach to this deformation may provide a hint for elucidating the burr elimination problem in the actual process. Hence, FEM analysis was also carried out to obtain the damage value and maximum principal stress, and the possibility of fracture was discussed.