BACKGROUND OF THE INVENTION : In structural applications of thin metal tubes such as steel tubes, it is desirable to have a tube with thickened ends. The ends are either joined with other tubes or structures in most applications and the strength of these joints will depend upon the thickness of the metal tubes in the joining region. Often tube thickness is specified based on the strength or thickness requirements at the zones of joint.

PRIORART Conventional method of producing thin walled metal tubes with thickened ends for structures is by taking a tube having the required end thickness and cold drawing the tube to make the wall thickness of the tube thinner except at the end zones. The cold drawing process of metal tube to obtain thin wall metal tube with thicker end zones is cumbersome and expensive. The invention provides a simple method of producing thin wall metal tubes with thickened ends which can be used for structural applications.

OBJECT OF THE INVENTION :

The primary object of the invention is to produce a thin wall metal tube with prescribed thickness at the end zones. The method according to the invention allows the end zones to be thickened either keeping the same inside diameter throughout the tube or keeping the same outside diameter throughout the tube depending upon the requirement. Thickening may also be done wherein both the inner and outer diameter are simultaneously varied at the ends.

Thus the invention provides a method of producing thin wall metal tube with thickened ends comprising the steps of holding a thin wall metal tube of desired length within the jaws, a clamp, introducing two punches having a step configuration from both ends of the tube and applying pressure from both ends so that the stepped portion of the punches buckle the end zones of the thin wall metal tube and allow the flow of metal to thicken the end zones at both ends of the tube, removing the punches from the ends and releasing the clamp to obtain a thin wall metal tube with thickened ends.

BRIEF DESCRIPTION OF THE DRAWINGS :

Figure 1 shows the relative positions of gripping jaws, thin wall metal tube and the punches at both ends before compaction.

Figure 2 shows the thin wall metal tube held by the gripping jaws.

Figure 3 shows the thin wall metal tube held by the gripping jaws and the end portion of the punches introduced at the ends of the tube. Figure 4 shows the thin wall metal tube held by the gripping jaws with pressure applied at the end zones through the punches.

Figure 5 shows the thin wall metal tube held by the gripping jaws after the pressure is applied to the ends through the punches.

Figure 6 shows the relative positions of gripping jaws, thin wall metal tube and end punches after the thickening of end zones.

DETAILED DESCRIPTION

The thin wall metal tube (T) is held between the gripping jaws (J) of a clamp. Two punches (P) having a step configuration is introduced from the ends (E) of the tubes. In order to obtain a metal tube with thickened end zones (Zl) and uniform outer diameter, diameter of the end portion (A) of the punch (P) may be kept less than the inner diameter of the metal tube and middle portion of the punch (P) may be provided with a diameter equal to the outer diameter of the metal tube (T). For obtaining a metal tube with thickened ends having uniform inner diameter at the end zones (Zl), the diameter of the end portion (A) of the punch (P) may be kept almost equal to the inside diameter of metal tube (T) and clearance may be provided between the gripping jaw (J) at end zones (Zl) of the tube. The diameter of the end portion (A) of the punch (P) may be kept less than the inner diameter of the metal tube (T) to achieve inside thickening of the tube ends and obtain tube with uniform outer diameter. The clearance between the end portion (A) of the punch (P) and the inner wall of the tube will determine the thickness at the ends of the metal tube after thickening the ends. The outer diameter and inner diameter in the region of the thickened ends may also be varied independently or simultaneously within required limits.

The method according to the invention is simple and economical compared to methods known for producing metal tubes with thickened ends.