Method for making a supporting crossbar construction and a crossbar construction made according to the method

A method for making a supporting crossbar construction from metal strip, comprising the steps of:

• feeding the strip lengthwise to a punching station;
• forming in said punching station four parallel rows of slits extending lengthwise of the strip so that five parallel plate fields are formed extending lengthwise of the strip, said five plate fields being defined by said four rows of slits;
• forming in said punching station pairs of inclined slits transverse to a pair of the rows of slits, each pair of the inclined slits and the pair of the rows of slits therebetween defining a diagonal member;
• deforming each diagonal member into a tubular or C-shaped profile;
• deforming the strip so that the strip is expanded into a construction having two outer straight plate fields and a straight middle plate field between said two outer plate fields, said middle plate field being interconnected with each of said two outer plate fields by a plurality of the diagonal members that are spaced apart and are formed by deformation of the plate fields between said middle and outer plate fields, whereby said middle and outer plate fields are spaced apart from each other;
• and
• bending said middle plate field along at least one bend line extending lengthwise of the strip so as to bring together said two outer plate fields and securing said two outer plate fields together, thereby to form a supporting crossbar construction in which one flange is comprised by said middle plate field and another flange is comprised by said secured-together outer plate fields, the diagonal members being a plurality of alternatively oppositely inclined crossbars interconnecting said flanges.