PURPOSE: To effectuate stabilized quality products, reduced non-contact area, and enhanced reliability in metal explosion-contact, base and clad material strains, base and clad-on-base material synthetic strain, and the ratio of synthetic strain area to pressure-contact base material area are controlled.

CONSTITUTION: Material strains are controlled as follows: less than 1.6 mm/m for metal base material, less than 3.0 mm/m for metal to be used as clad material, and less than 2.4 mm/m for synthetic strain of clad and base materials. The ratio of the synthetic strain area to pressure-contact base material area are controlled less than 20%. In explosion contact, product contact ratio (percent of non-contact area devided by the whole contact area) are greatly affected by base material strain as well as synthetic strain of clad and base material. The above conditions have been found as the optimum control for such material and synthetic strains.