1,074,208. Corrugating. TECHNIGAZ, and G. FOURNIER. June 30, 1964 [Jan. 13, 1964], No. 26961/64. Heading B3E. Apparatus for forming, in a metal sheet having a first series of substantially parallel corrugations, a second series of substantially parallel corrugations intersecting the first series comprises means to hold those portions of the sheet not to be altered in shape and punch and die means operable to fold the sheet to form said second corrugations without any stamping action. Metal sheet formed with one series of corrugations is held between upper plates P1, P2, having projections F to engage the formed corrugations, and lower plates P3, P4 having complementary projections I. The upper plates P1, P2 are linked by members hinged at (S1), (S2), (S3), Fig. 4 (not shown), and the lower plates P3, P4 by members hinged at (C1), (C2) (C3), (C4), (C5). In operation, the plates P1, P3 and P2, P4 are moved towards a centre line (MM 1 ) so that the edges (S2), (C2), (C5) effect a corrugation crossing the initial series of corrugations at right-angles. Alternatively, Fig. 6 (not shown), three V-shaped tools (S2), (C2), (C5) may be used. In a further embodiment, Fig. 7 (not shown), the descent of an upper plate causes, through cam means, the left and right-hand gripping members P1, P3 and P2, P4 to move towards one another and, through further cam means on the members P3, P4, lower projections to move towards one another.