Technical field [0001] 　The present invention relates to a method of manufacturing a mouth widened metal tube. 　This application claims priority based on Japanese Patent Application No. 2014-264337, filed in Japan on December 26, 2014, which is incorporated herein by reference. Background technique [0002] 　As a method for producing a mouth widened metal pipe, the pipe expanding punch, which tapers (punch), pressed from the open end of the metal tube (blank tube) which is a material, to push the said metal tube to the radial direction the method of forming the expanded portion to the metal pipe is known (e.g. Patent documents 1 and 2). [0003] 　However, in the above production method, due to various factors, cracks or molding defects such as buckling at the root of the expanded portion, generated in the expanded portion. Therefore, when manufacturing the metal tube widened mouth than base pipe (tube expansion metal tube), it is required to suppress molding defects occurrence of the. CITATION Patent Document [0004] Patent Document 1: Japanese Patent No. 4798875 discloses Patent Document 2: Japanese Patent No. 5221910 Publication Summary of the Invention Problems that the Invention is to Solve [0005] 　The present inventors, as a factor molding failure occurs in tube expansion of the metal pipe (pipe expanding), focused on the thickness distribution and hardness distribution in the circumferential direction of the mother tube. 　Figure 10A is a cross-sectional view showing an example of thickness distribution of the electric resistance welded steel pipe 301 which is used as a material in the tube expansion, FIG. 10B shows an example of thickness distribution of the seamless steel tube 302 which is used as a material in the tube expansion it is a cross-sectional view showing a. 11 is a graph showing the thickness distribution in the circumferential direction of the electric resistance welded steel pipe 301. 11, the horizontal axis represents an angle from the seam, i.e. the angle from the weld 305 formed on an electric resistance welded steel pipe 301. [0006] 　As shown in FIGS. 10A and 11, the electric resistance welded steel pipe 301, weld 305 angle wall thickness of the portion is about 60 ° from t1, and the thickness t2 of the portion the angle of about 150 ° is, It is smaller than the thickness t3 ~ t5 of other sites, the wall thickness deviation has occurred. The thickness t1 and t2 is of the order of 98 to 99% of the average value of the thickness. 　Further, as shown in FIG. 10B, the seamless steel tube 302 (seamless steel pipe), the wall thickness deviation as the thickness t7 (1) a hollow shell 　as the hollow shell 1, an outer diameter of 73mm, a seamless steel pipe having an average thickness of 6mm was used. The thickness of the thin portion 1a of the hollow shell 1 is 5.6 mm, the thickness of the thick portion 1b of the hollow shell 1 was 6.4 mm. [0046] 　(2) punch 　using a tube expanding punch 50 and the forming punch 60. 　Tube expanding punch 50 is a taper angle α is 4.5 °, a taper angle β is 24.6 °, the diameter of the cylindrical portion 51 was 81.2 mm. Forming punch 60, the taper angle γ is 15 °, the diameter of the cylindrical portion 61 was 81.2 mm. [0047] 　(3) fixed mold 　fixed mold 70, the inside diameter D of the side wall portion 72 (see FIG. 3) was 93.2Mm. [0048] 　(4) production process 　by pushing the tube expansion punch 50 to the hollow shell 1, the hollow shell 1 and tube expansion were produced intermediate molded article 10. In this case, the intermediate molded article 10, L1 shown in FIG. 2 was prepared as a 0.17 times L2. 　Thereafter, the intermediate molded article 10 disposed in the fixed die 70, pushing the forming punch 60 to the intermediate molded article 10 to produce a mouth widened metal tube 20. [0049] 　(5) of the molding defect evaluation 　intermediate product 10, and molding failure such as cracking in the mouth spread metal tube 20 did not occur. Further, the expansion ratio of the mouth spread metal tube 20 was 30%. [0050] 　 (1) a hollow shell 　as the hollow shell 1, an outer diameter of 90.0 mm, the electric resistance welded steel pipe of the average wall thickness 2.8mm were used. The electric resistance welded steel pipe has a tensile strength TS of 80 kgf / mm 2 is (785 MPa), hardness distribution in the circumferential direction was distribution shown in FIG. [0051] 　(2) punch 　using a tube expanding punch 50 and the forming punch 60. 　Tube expanding punch 50 is a taper angle α is 4.5 °, a taper angle β is 24.6 °, the diameter of the cylindrical portion 51 was 112.4Mm. 　Forming punch 60, the taper angle γ is 15 °, the diameter of the cylindrical portion 61 was 112.4Mm. [0052] 　(3) fixed mold 　fixed mold 70, the inside diameter D of the side wall portion 72 (see FIG. 3) was 117 mm. [0053] 　(4) production process 　by pushing the tube expansion punch 50 to the hollow shell 1, the hollow shell 1 and tube expansion were produced intermediate molded article 10. In this case, the intermediate molded article 10, L1 shown in FIG. 2 was prepared as a 0.17 times L2. 　Thereafter, the intermediate molded article 10 disposed in the fixed die 70, pushing the forming punch 60 to the intermediate molded article 10 to produce a mouth widened metal tube 20. [0054] 　(5) of the molding defect evaluation 　intermediate product 10, and molding failure such as cracking in the mouth spread metal tube 20 did not occur. Further, the expansion ratio of the mouth spread metal tube 20 was 30%. [0055] 　 　(1) a hollow shell 　as the hollow shell 1, using the same electric resistance welded steel pipe as in Example 2. [0056] 　(2) punch 　using a tube expanding punch 50 and the forming punch 60. 　Tube expanding punch 50 is a taper angle α is 7.5 °, a taper angle β is 21.9 °, the diameter of the cylindrical portion 51 was 129.4Mm. 　Forming punch 60, the taper angle γ is 15 °, the diameter of the cylindrical portion 61 was 129.4Mm. [0057] 　(3) fixed mold 　fixed mold 70, the inside diameter D of the side wall portion 72 (see FIG. 3) was 135mm. [0058] 　(4) the manufacturing process 　to produce an intermediate molded article 10 in the same manner as in Example 1 and 2. In this embodiment, the intermediate molded article 10, L1 shown in FIG. 2 was prepared as a 0.33 times L2. [0059] 　(5) of the molding defect evaluation 　intermediate product 10, and molding failure such as cracking in the mouth spread metal tube 20 did not occur. Further, the expansion ratio of the mouth spread metal tube 20 was 50%. [0060] 　 　(1) a hollow shell 　using the same electric resistance welded steel pipe as in Example 2. 　(2) punch 　unlike the first to third embodiments, without using a pipe expanding punch 50, using only forming punch 60. 　(3) stationary mold 　using the same fixed die 70 as in Example 2. 　(4) production process 　the hollow shell 1 is arranged in the fixed die 70, by pushing the forming punch 60, the hollow shell 1 and tube expansion were produced mouth spread metal tube. 　(5) molding defect evaluation 　expansion ratio of the metal tube widened opening is 30%, the molding defects such as cracking in a metal tube widened mouth occurred. In the present embodiment, because the expansion ratio was as low as 30%, even without using a pipe expanding punch 50, it is considered defective molding did not occur. [0061] 　 　(1) a hollow shell 　using the same electric resistance welded steel pipe as in Example 2. 　(2) punch 　unlike the first to third embodiments, without using a pipe expanding punch 50, using only forming punch 60 (i.e., the same as in Reference Example 1). 　(3) mold 　using the same fixed die 70 as in Example 2. 　(4) production process 　the hollow shell 1 is arranged in the fixed die 70, by pushing the forming punch 60, the hollow shell 1 and tube expansion were produced mouth spread metal tube. 　(5) molding defect evaluation 　expansion ratio of the metal tube widened mouth was the 50%, mouth spread cracks in the metal pipe occurred. [0062] 　According to Examples 1-3, the hollow shell 1, and the deformation resistance is small low deformation resistance portion along the circumferential direction, there is a high deformation resistance portion deformation resistance is greater than the low deformation resistance portion Nevertheless, without burdening the low deformation resistance portion, it was possible to suppress molding defects such as cracking. 　In particular, the comparison between Example 1 and Comparative Example 3, in the conventional method of high expansion ratio which cracking had occurred product was confirmed to be produced without causing cracks. [0063] 　Having described the embodiments of the present invention, these embodiments have been presented by way of example, the scope of the present invention is not limited only to these embodiments. These embodiments described herein may be embodied in other various forms, without departing from the spirit of the invention, various omissions, substitutions, and changes can be made. Such embodiments and modifications as would fall within the scope and spirit of the invention, and are included in the invention and the scope of their equivalents are claimed. [0064] 　For example, in the first embodiment, by using the pipe expanding punch 50, it shows a case of molding a hollow shell 1 to the intermediate molded article 10. However, different by using a plurality of tube expanding punch having an outer diameter, the hollow shell 1 stepwise (plural times) may be formed. [0065] 　Further, for example, in the first embodiment, by using a forming punch 60, the intermediate molded article 10 shows a case of molding a mouth widened metal tube 20. However, without using the forming punch 60, the intermediate molded article 10 may be a metal tube widened mouth obtained by tube expansion punch 50. In this case, it is possible to obtain the eccentric mouth spread metal tube. Industrial Applicability [0066] 　According to the present invention, when manufacturing the mouth spread metal tube from a hollow shell having a site relatively deformation resistance is small, it is possible to suppress molding defects occurrence of breakage, the mouth widening method for producing a metal tube it is possible to provide a. DESCRIPTION OF SYMBOLS [0067] 1: a hollow shell 1a: thin portion (low deformation resistance portion) 1b: thick portion (high deformation resistance portion) 10: intermediate product 20: mouth spread the metal tube 50: tube expansion punch 60: forming punch 70: stationary mold we claim:- [Claim 1] 　From hollow shell having a plurality of sites deformation resistance different when viewed along the circumferential direction, a method for producing a mouth widened metal tube having an expanded portion, 　the plurality of sites, relatively deformable the low resistance region with identifying as a low deformation resistance unit, a first step and identifying the sites relatively deformation resistance than the low deformation resistance portion is greater as the high deformation resistance portion; 　a tube expanding punch into the hollow shell press fit to the second step of tube expanding the hollow shell; has, 　in the second step, the low deformation resistance of the wall thickness reduction rate, than the wall thickness reduction rate of the high deformation resistance portion small mouth spread method for producing a metal tube, characterized in that. [Claim 2] 　The tube expanding punch, 　　has a first contact surface abutting on said low deformation resistance portion of the hollow shell, and a second contact surface abutting on the high deformation resistance portion of the hollow shell, the tube expansion inclination angle of the first abutting surface relative to the central axis of the punch is smaller than the inclination angle of the second contact surface with respect to the central axis, 　in the second step, 　　the first abutment surface of the tube expansion punch is brought into contact with the low deformation resistance portion of the hollow shell, while the second abutment surface of the tube expansion punch is brought into contact with the high deformation resistance portion of the hollow shell, the hollow element the tube expansion punch press-fitted into the tube mouth spread method for producing a metal tube according to claim 1, characterized in that. [Claim 4] 　The second step,　the tube expansion punch was pressed into the hollow shell, and the tube expanding punch press-fitting to obtain an intermediate molded article than said hollow shell, 　　said the intermediate molded article, the expanded pipe portion of the mouth spread metal tube a forming punch press-fitting step of press fitting the forming punch, having a shape matching the inner surface having a mouth widened method for producing a metal tube according to claim 2 or 3, characterized in that. [Claim 5] 　The pipe expansion punch press fitting process, as diameter of the low deformation resistance portion of the hollow shell becomes 0.5 times less than the diameter of the high deformation resistance portion of the hollow shell, the tube expansion press-fitting punch into the hollow shell mouth spread method for producing a metal tube according to claim 4, characterized in that. [Claim 6] 　The hollow shell is electric resistance welded steel pipe or seamless steel pipe mouth spread method for producing a metal tube according to any one of claims 1 to 5, characterized in that.