Masao Matsui

Improvements in finite-element simulation for stamping and application to the forming of laser-welded blanks

Abstract During stamping-die design, the formability in sheet-metal forming process has been evaluated by the geometrical functions in ‘Die-Face CAD’, which has been developed and improved by Toyota Motor Corporation. When evaluation by these functions is difficult, formability has been estimated by performing experiments using test dies in which the forming defects are similar to those in the actual process. A numerical method has been developed in order to substitute numerical analysis for experiments using test dies for the accurate prediction of defects in sheet-metal forming. The elastic-plastic FEM with the commercial code ‘JNIKE3D’ has been improved in the areas of: (1) the material constitutive equation; (2) the consideration of the pressure distribution on the blank-holder; and (3) the evaluation of breakage initiation. Using the improved method, the square-cup drawing process and the hemming process have been analyzed. Numerical results for strain, breakage initiation, and hemming deflection were in good agreement with experimental results. The formability of laser-welded blanks and the most efficient process to form them were evaluated also using the improved method.

Microwave Heating of Ceramics and its Application to Joining

A new butt joining method for ceramics by microwave heating was developed. Ceramics were heated in a rectangular cavity. A klystron of maximum 3 kW at 6 GHz was used as the power amplifier. The heating system can control the iris, plunger and microwave power to keep a power efficiency up to 90% and a accuracy within ±10°C at 1800°C. Microwave ceramic-ceramic joining was tried by using this system. A bending strength of the joined alumina rod (92% purity) was 420 MPa without adhesive. This value was equal to the original strength. Silicon nitride ceramics were joined with adhesive, which was a sintered ceramic sheet having lower purity and larger dielectric loss factor than the base ceramics. The microwave energy was concentrated on the sheet, so that only the joining area was heated. The strengths of joined specimens were in excess of 70% of original strengths. The joined boundary line was not detected in microscopic observation, and there was little difference in microstructure between before and after joining. These results suggest that sintering aids in grain boundary phases were preferentially heated and melted or diffused, resulting in sound joining of ceramics.

Initiation and growth of buckling in the biaxial diagonal tensile test on steel sheet

Abstract Initiation and growth of buckling, a main cause of surface deflection in large steel press-formed components such as automobile outer panels, is simulated by the biaxial diagonal tensile test on square steel sheet specimens. The effects of the properties of the steel sheets and the biaxial loading conditions on the initiation and growth of buckling are examined by the tests and by FEM analysis. It is found that both the initiation and the growth of buckling are strongly affected by the yield strength of the material, σ s , and by the tensile stress in the breadth direction, p Y , and that buckling is restrained when p Y / σ s is high: this is because the compressive stress at the center of the specimen, the compressive stress area, and the development of the buckling area are largely affected by these factors.

Microwave sintering of electronic ceramics

The feasibility of microwave sintering of ceramics was examined. ZnO varistor and PZT ceramics with high densities could be obtained by microwave sintering. They had higher electric properties compared with those sintered by a conventional process.