Method for manufacturing an extruded article changing in cross-section and an apparatus for extruding said extruded article

An apparatus for manufacturing an extruded article which has at least one spiral hollow portion and changes in cross-section along a direction of an extrusion axis, said apparatus comprising:

• a container in which a billet is loaded;
• a punch for applying a forward pressure to said billet;
• a die for defining an outer periphery of said extruded article;
• and
• a mandrel for defining an inner periphery of said hollow portion, wherein said mandrel has a tip end portion asymmetrical to a rotary axis of said mandrel, and wherein said mandrel is capable of rotating about said extrusion axis and moving relative to said die when said punch is advancing,
• whereby said extruded article is formed by advancing said punch to extrude said billet while controlling a movement of said mandrel relative to said die.

A method for manufacturing an extruded article which has at least one hollow portion and a closed end portion and changes in cross-section along a direction of an extrusion axis, the method including the steps of:

• applying a pressure to a billet by a punch in a state in which a bearing hole of a die for defining an outer periphery of said extruded article is closed so as to fill said bearing hole with materials of said billet to thereby form said closed end portion;
• releasing a closing of said bearing hole;
• and then moving a mandrel for forming said hollow portion and;
• advancing said punch to extrude said billet to thereby form said extruded article.

An apparatus for manufacturing an extruded article which has at least one hollow portion and a closed end portion and changes in cross-section along a direction of an extrusion axis, said apparatus comprising:

• a container in which a billet is loaded;
• a punch for applying a forward pressure to said billet;
• a die having a bearing hole for defining an outer periphery of said extruded article;
• a mandrel for defining an inner periphery of said hollow portion, said mandrel being capable of moving relative to said die;
• and
• a closing member detachably disposed at an outlet side of said bearing hole so as to close said bearing hole,
• whereby a pressure is applied to said billet in a state in which a bearing hole of said die is closed by said closing member to fill said bearing hole with materials of said billet to thereby form said closed end portion, then a closing of said bearing hole is released by detaching said closing member from said die, and thereafter said punch is advanced to extrude said billet while controlling a movement of said mandrel relative to said die to thereby form said extruded article having said hollow portion.