Sheet hydroforming using high- and ultra high-strength steel has the potential to realize the manufacture of lightweight and complex car parts. In this study, forming characteristics and limits in sheet hydroforming with the material inflow of welded double blanks (double sheet hydroforming) without a blank holder are investigated by finite element (FE) analysis. On the basis of the obtained results, technology of welded triple blanks (triple sheet hydroforming) is demonstrated in experiments. The main results are as follows. (1) In double sheet hydroforming, wrinkles occur owing to the difference between the upper and lower material inflows. (2) The limits of wrinkle occurrence depend on the differences between the upper and lower die circumferences, the upper and lower sheet tensile strengths, and the upper and lower sheet thicknesses. (3) The formable range of double sheet hydroforming using dies with concave and convex beads differs, even in the same upper and lower die circumferences. (4) Two methods of triple sheet hydroforming are proposed. Experimental products have no defects. It is confirmed that the new methods are effective in reinforcing automotive parts.

The surface modification of aluminum alloy by shot lining and laser irradiation was investigated to form a hard Fe-Al intermetallic compound having excellent corrosion resistance. A centrifugal-type peening machine with an electrical heater was employed. The shot medium was high-carbon cast steel. The substrate was a commercial aluminum alloy. The sheet was commercially available pure aluminum, and the powder was an electrolytic iron. The shot lining process was carried out at 573 K in air using a peening machine. The top surface of the lined workpiece was melted by laser beam irradiation. The intermetallic Fe-Al layer was formed on the irradiated surface. The lined substrates exhibited a harder layer of aluminum-rich intermetallic in the irradiated part. The present method could be used for the formation of functional films on aluminum alloy.