Heat exchanger fin with ribbed hem

A method of manufacturing serpentine fins for assembly between tubes in a heat exchanger core comprising:

• providing a flat metal strip for making heat exchanger fins, the strip having a width between opposite strip edges and a length greater than the width;
• forming in the strip, while the strip is substantially flat, multiple rows of split louvers, each row of louvers comprising louvers having openings extending in the direction of the strip length and formed in adjacent, spaced louver banks extending at least a portion across of the width of the strip, and forming in a center portion of the strip at least one central rib substantially parallel to the louver openings and extending across the pair of louver banks, the metal strip having unformed portions extending across the strip width between rows of strip louvers and the at least one central rib for forming folds across the width of the strip;
• after forming the rows of split louvers and the central rib, applying an initial pressure to the metal strip to cause the substantially flat strip to buckle in the unformed portions and begin to form folds in the strip, with at least one row of split louvers residing between adjacent folds along the length of the strip;
• thereafter applying further pressure to the metal strip to complete formation of the folds of the strip to form the serpentine fin, the distance between the adjacent folds conforming to the desired spacing distance between the heat exchanger core tubes;
• folding at least one of the strip edges to form a hem comprising a double thickness of the metal strip, the hem extending a portion of the distance inward from said at least one edge;
• and
• forming at the hem an end rib having an angled leg and a bent portion whereby the hem extends from the said at least one edge along the angled leg and at least partially follows along the contour of the end rib bent portion.