An extrusion-molding apparatus of a differential thickness pipe having a solid part, which comprises a mandrel having a predetermined shape, a sleeve having a predetermined shape, a container in which a container hole that is a penetration hole having a predetermined shape is formed, and a drive mechanism configured so as to push said mandrel and said sleeve into said container hole, and which is configured so as to mold the differential thickness pipe having a solid part from a material having a predetermined shape by extrusion processing, wherein:
- said material is a member comprising a first hollow part that is a circular cylindrical part which has a first hollow hole that is a circular columnar space opened at an end surface on a base end side that is an upstream side in an extrusion direction and having a first inner diameter that is a predetermined inner diameter formed therein and has a first thickness that is a predetermined thickness and a first solid part that is a circular columnar part which is located between an end surface on a tip end side that is a downstream side in said extrusion direction and said first hollow part, and having a circular columnar outer shape having a first outer diameter that is a predetermined outer diameter as a whole,
- said differential thickness pipe is a member comprising a second hollow part that is a circular cylindrical part which has said first outer diameter and said first thickness, a third hollow part that is a cylindrical part which is located adjacent to said second hollow part on said tip end side and has an outer diameter changing from said first outer diameter to a second outer diameter that is a predetermined outer diameter smaller than said first outer diameter and a thickness changing from said first thickness to a second thickness that is a predetermined thickness smaller than said first thickness from said base end side toward said tip end side, a fourth hollow part that is a circular cylindrical part which is located adjacent to said third hollow part on said tip end side and has said second outer diameter and said second thickness, and a second solid part that is a circular columnar part which is located between an end part on said tip end side and said fourth hollow part and has said second outer diameter, and having a second hollow hole that is a circular columnar space opened at an end surface on said base end side and having said first inner diameter formed continuously from said second hollow part to said fourth hollow part,
- said mandrel is a member internally fitted in said sleeve coaxially and slidably in an axial direction and having a circular columnar shape which has a third outer diameter that is a predetermined outer diameter corresponding to said first inner diameter,
- said sleeve is a member externally fitted with said mandrel coaxially and slidably in an axial direction and having a circular cylindrical shape which has said first outer diameter and a second inner diameter that is a predetermined inner diameter corresponding to said third outer diameter,
- said container hole comprises a large inner diameter part that is a part formed on said base end side and having a third inner diameter that is an inner diameter corresponding to said first outer diameter, a small inner diameter part that is a part formed on said tip end side and having a fourth inner diameter that is an inner diameter corresponding to said second outer diameter, and an inner diameter decreasing part that is a part formed between said large inner diameter part and said small inner diameter part and having an inner diameter decreasing from said third inner diameter to said fourth inner diameter as approaching from said large inner diameter part to said small inner diameter part, and
- said extrusion-molding apparatus is configured so as to mold said differential thickness pipe by carrying out:
- a first process in which said material is inserted in said large inner diameter part of said container hole to bring an end part on said tip end side of said material into contact with said inner diameter decreasing part of said container hole, said sleeve is brought into contact with an end part on said base end side of said material, said mandrel is inserted into said first hollow hole of said material, and a tip-to-tip distance that is a relative distance in said extrusion direction between an end part on said tip end side of said sleeve and an end part on said tip end side of said mandrel is fixed at a first distance that is a predetermined distance,
- a second process in which extrusion processing is performed by advancing said sleeve and said mandrel toward said extrusion direction while maintaining said tip-to-tip distance at said first distance by cooperative driving of said mandrel and said sleeve to push said material into said small inner diameter part through said inner diameter decreasing part of said container hole, and the advance of said sleeve and said mandrel is continued until a first time point that is a time point when said end part on said tip end side of said mandrel arrives at an end part on said base end side of said inner diameter decreasing part of said container hole,
- a third process in which said sleeve and said mandrel are advanced toward said extrusion direction while maintaining said tip-to-tip distance at said first distance after said first time point, and
- said bottom part of said first hollow hole of said material is not in contact with said mandrel at least at said second time point.