Composite tube and manufacturing method thereof

1. A composite tube manufacturing method, comprising the following steps:

providing a billet, wherein the billet comprises an inner material and an outer material, and the inner material is enveloped in the outer material;

heating the billet;

pushing the billet to a to-be-extruded position; and

performing an extrusion process, and extruding the billet to a composite tube, wherein the inner material and the outer material of the billet are respectively extruded to an inner tube and an outer tube of the composite tube, and the outer tube is bonded to the inner tube through the extrusion process;

wherein the extrusion process comprises the following step: passing through an outlet of an extrusion die by at least one mandrel, so as to change an area of a section of the outlet of the extrusion die, so that the billet is extruded to the composite tube according to a changed sectional shape of the outlet of the extrusion die, wherein the at least one mandrel comprises first to fourth mandrels, the first and the third mandrels make the composite tube have different inner diameters, and the second and the fourth mandrels make the composite tube have different outer diameters.

2. The composite tube manufacturing method according to claim 1 , wherein

the step of pushing the billet to a to-be-extruded position comprises: placing the billet in a billet container, and pushing the billet to the to-be-extruded position by using an extrusion stem; and

the extrusion process comprises the following step: extruding the billet by using the extrusion stem, so that the billet is extruded to the composite tube according to a sectional shape of an outlet of an extrusion die.

3. The composite tube manufacturing method according to claim 1 , wherein the step of pushing the billet to a to-be-extruded position comprises: placing the billet in a billet container, and pushing the billet to the to-be-extruded position by using an extrusion stem.