PURPOSE: To enable the forming of the flat tube having high straightness and accuracy by forming with compression the straight pipe part of a circular pipe by the upper and lower opposing dies providing the groove with smaller width than the diameter of the circular pipe.
CONSTITUTION: The U-shaped pipe 2' with circular cross section is subjected to a compression work with pressing the outer diameter of the circular pipe with both shoulder parts of the groove by using a pair of tools 4 and 4', or 7 and 7' having the linear groove with uniform groove width. The hairpin-shaped flat pipe with the necessary good accuracy is thus formed with the work of the shoulder part of the groove so as to set he center of the circular pipe and the center of the groove and by flattening the circular pipe with its amending in linear shape even in case of its bending slightly.
OCHIAI IZUMI
NOZAWA YOSHIO
KITAYAMA YUKIO
UEHARA KATSUJI
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