Patent ID: 6993838

Claim:
A method for manufacturing a header for a heat transfer apparatus, comprising: providing a tube having an outside diameter (D), and outside radius (D/2), and a wall thickness (s); punching the tube without an internal die (i) to form a slot in the tube, (ii) to provide a tube having a ratio (D/2:s) of the tube's outside radius (D/2) to the tube wall thickness (s) of less than 5, and (iii) to provide a tube having a ratio (D:D 1 ) of the tube outside diameter (D) outside of the region of the slot to the tube diameter in the region of the slot (D 1 ) of between 1.02 and 1.5 spot heat treating and/or mechanically weakening the tube in the region to be punched before the step of punching.