Double-headed tube forming method and double-headed tube structure

A double-headed tube forming method, comprising the following steps:

• step 1, a tube body being sleeved on a first mold, a first tube head being placed at a first end portion of the tube body to locate inside the first end portion of the tube body, the first end portion of the tube body and the first tube head being sealedly welded together so as to securely fix together, the first mold being removed;
• step 2, a second mold that is different from the first mold being inserted through an opening of the first tube head to extend through an interior space of the tube body to reach a second end portion of the tube body, an annular retaining member being fitted on one end portion of the second mold and located inside the second end portion of the tube body;
• step 3, a second tube head that includes an opening being placed at the second end portion of the tube body, the second end portion of the tube body, the annular retaining member and the second tube head being sealedly welded together, the second mold being removed,
• wherein the annular retaining member is interposed between the one end portion of the second mold and an inside surface of the second end portion of the tube body, such that the second mold is located inside the tube body and is spaced from the inside surface of the tube body by the retaining member and the annular retaining member supports the inside surface of the tube body to prevent the tube body from deforming.