To prevent deformation generated n the cross section of thick part formed at the time of executing local thickening work and heat treatment to a metallic tube such as a square tube.
By preliminarily setting a die 10 for heat treatment in the square tube 1 to be thickened, forming a heated part 5 by locally heating the square tube with a heating device 4 under the state where compressive force is added to the square tube 1 with a compressing device 3 and moving the heated part 5 in the longitudinal direction to the square tube, thick part 1A thickened is continuously formed, the heated part 26 for heat treatment is formed by heating the thick part 1A with an auxiliary heating device 9 and heat treatment of the whole thick part is executed by moving the heated part 26 for heat treatment in the longitudinal direction of the thick part. At the time of these thickening work and heat treatment, deformation on the verge of generating in the thick part 1A is prevented with the die 10 for heat treatment which is set inside the square tube 1 and the thick part 1A having a good cross-sectional shape is formed.
NAGANO TOSHIO
MINAGAWA TSUGIO
FUKUDA AKIRA
DAI ICHI HIGH FREQUENCY CO LTD