PURPOSE: To manufacture the branch pipe in uniform thickness with a high branch pipe part by pulling a burring punch out of a prepared hole by heating the whole pipe blank and passing the mandrel for straightening to the inner part by reheating the pipe blank on the deformation of the pipe blank.
CONSTITUTION: In the case of forming the branch pipe part of H/d≥0.5 by taking the height of the branch pipe part as H and the outer diameter as (d), the oblong hole becoming a prepared hole is pierced at the specified position of a pipe blank 2 to insert a burring punch 3 into the inner part of the pipe blank 2. The part shown by an alternate long and two short dashes line is then heated to a work temp. and the branch pipe part 1 is formed by performing burring by loading a specific work force on the burring punch 3 by an actuator, etc. In order to straighten the deformed pipe blank 2 the mandrel 4 for straightening in complete roundness is inserted into the pipe blank 2. The part shown by an alternate long and two short dashes line is then heated to a work temp., a specific work force is loaded on the mandrel 4 by the actuator, etc., and said part is straightened in a round shape by pulling out or extruding the mandrel 4.