In making the die of automotive outer panels, the most difficult process is fixing surface deflection. To fabricate
high-quality outer panels without modifying dies, it is important to develop an evaluation method and a numerical
analysis method for the surface deflection of outer panels. In this study, we developed a new evaluation method that
uses the maximum value of curvature, calculated using reflecting curves in the surface. This made the examiner
evaluation conform to digital evaluation. The method shows better agreement with the examiner evaluation than the
conventional method. We proposed a new analysis method of predicting surface deflection correctly. By the proposed
method, plastic deformation is calculated in consideration of stress in the thickness direction, and restriking conditions
are examined. We applied our methods to the fabrication of automotive outer panels and verified that they were useful
Metallic glass (MG) has unique mechanical properties, combining high strength and low Young’s modulus. By
applying MG to the fabrication of fastening bolts, high resistance against bolt loosening is expected. However, MG
components are thought to be brittle because MG exhibits poor ductility when subjected to uniaxial loading at room
temperature. We have developed hexagonal cap bolts made of zirconium-based MG by cold thread rolling. The MG
bolt showed a 1.6% plastic strain with a tensile strength of more than 1550 MPa. In addition, the load-strain curve was
similar to that of a strain hardening material although MG itself is free of strain hardening. In this study, we attempt to
clarify the reasons for the behavior, which are advantageous for bolts in terms of toughness and reliability. Various
experiments and numerical analysis indicate that residual stress plays an important role in the behavior.
Methods by which smooth and high-precision cut surfaces of high strength steel sheets with strength of up to
980MPa class have been investigated using a servo press in which the average punching speed can be varied from 2 to
140mm·s-1. A method called finish blanking has been performed, and the other method called press shaving has also
been conducted to obtain either smooth cut surfaces or highly precise product shapes and dimensional sizes. The
results show that both methods can yield good cut surfaces if appropriate working parameters including punch/die
clearance, edge radius and punching speed are used. However, as regards shape and dimensional accuracies, the
press shaving method yielded the most satisfactory results.
In the roll forming of high-strength electric-resistance-welded pipes, the work hardening and springback of strips
should be clarified. In this study, the effects of roll type, roll diameter and sheet strength on such operations in a single
bending stand are examined by finite element analysis and experiment. Two kinds of roll are used. One (Type A) is a
roll stand that pinches strips entirely in the circumferential direction by top and bottom rolls. The other (Type B) is a
roll stand that pinches strips only at the edge part of the strips. The springback in Type A is smaller than that in Type B.
However, in the case for Type B, overbending occurs owing to the hollow of the bottom roll, and the final circumferential
curvature is almost the same as that in the case for Type A. The amount of work hardening in the case for Type A is larger
than that in the case for Type B because of the transfer of the longitudinal top roll shape.
The fracture toughness of cemented carbide for cold forging dies is necessary for predicting the fracture of a die
insert. It is generally measured by the hardness indentation method. In the present study, it was measured by the
three-point bending test using a test piece with a precrack generated by the EC method. Seven types of cemented
carbide were used. It was found that the fracture toughness increases with an increase in WC grain size or Co mass
percent. It was also found that the bending test using a test piece with a precrack gives good results compared with the
hardness indentation method. It was shown that cemented carbides could be destroyed macroscopically under a 160
MPa tensile stress as analyzed by FEM simulation using a test piece model without a precrack.
Continuous blanking was carried out using polycrystalline diamond (PCD) tools without a lubricant with the aims
of developing the technologies required to apply these tools to shearing and of putting them to practical use. The
adhesion of an A5052 aluminum alloy sheet subjected to blanking to the PCD tools was markedly reduced compared
with that in the case of conventional SKD11 tools. It was also clarified that a high-precision sheared surface with
properties similar to those obtained in the first blanking can be obtained even after 10,000 times of blanking. In
addition, the adhesion of a SUS304 stainless-steel sheet to the PCD tools was prevented during the blanking, and the
wear resistance of the PCD tools was markedly improved as compared with that of conventional tools. The
properties of the sheared surface obtained after blanking 200,000 times were similar to those of the sheared surface
obtained in the first blanking. The burr height and inner and outer diameters of the workpiece obtained after
blanking 200,000 times did not change, demonstrating that high-precision sheared surfaces can be stably obtained.
The above results show that PCD tools can be practically used in blanking.