| 摘要 |
PROBLEM TO BE SOLVED: To provide a necking method of a round metallic tube by which the occurrence of internal cracks in the parallel part where is made at the nose of the necking is suppressed even in the case a die system which is simple in an equipment mechanism is used and the round metallic tube is made of a material having high deformability or comparatively low deformability and the necking rate (D0-D1)/D0 at the nose of the round metallic tube having a high thickness ratio t0/D0 is increased. SOLUTION: This necking method of the round metallic tube has a necking stage where the necking is performed by moving the round metallic tube 1 to a die having a necking part for necking the round metallic tube 1 and a plug 3 for holding and pressing the round metallic tube 1 from the outer peripheral surface and the inner peripheral surface together with the necking part. The necking stage is performed so that the thickness draftγin the necking part where the necking is applied in the round metallic tube 1 is≥14%. Where,γ= (tc-t1)/tc×100 (%). ( In the equation, tc is the average value of the thickness in the necking part in the case the plug is not arranged and t1 is the average value of the thickness in the necking part in the case the plug is arranged.). COPYRIGHT: (C)2006,JPO&NCIPI
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