Process for fixing a tubular reinforcing insert to a tubular metal structure and apparatus for carrying out the process

Abstract: A process for fixing a tubular reinforcing insert (12) to a tubular metal structure (10) includes the steps of: forming a hole (30) in the wall of the tubular structure (10) by inward deformation of a portion of the wall so that the deformed wall portion forms a collar (32), force fitting an end portion of the tubular insert (12) into the collar (32), and introducing liquid at high pressure into the tubular structure (10) so as to compress the collar (32) against the end portion (26) of the tubular insert (12).

Description: The present invention relates to a process and to an apparatus for fixing a tubular reinforcing insert to a tubular metal structure. EP-A-0 293 101 discloses a method of making a rigid angled joint between a first length of metal tubing and a second length. This method comprises the steps of first applying a rotating piercing tool under pressure to the first tube's wall. The tool thus forms a hole surrounded by an integral bush, which is formed from the displaced tube wall material and has a diameter to closely fit the external diameter of the second tube. The second tube is inserted through the bush into the interior of the first tube and is secured therein by a bolt or screw. In the field of motor-vehicle construction, the tubular structure may be the chassis of the motor vehicle, the support frame for the engine or a supporting structure in general. At present, when it is necessary to fix a reinforcing insert to the tubular structure at right angles thereto, a welding technique is used. The reinforcing insert serves as an anchorage for mechanical parts. For example, in the case of engine support frames, the reinforcing insert serves as the seat for vibration-damping supports and is subject to traction or axial-compressive stresses and/or shear forces. The object of the present invention is to provide a different system for fixing the reinforcing insert so as to avoid welding and screwing. According to the present invention this object is achieved by means of a process which includes the steps of: forming a hole in the wall of the tubular structure by inward deformation of a portion of the wall so that the deformed wall portion forms an annular collar, force fitting an end portion of the tubular insert into the said collar, and introducing liquid at high pressure into the tubular structure so as to compress the collar against the end portion of the tubular insert. This technique involves a considerable reduction in the working time compared with normal fixing by welding. Moreover, if the number of reinforcing inserts to be fixed to the main structure is increased, the working time remains constant in that the operation is carried out in a single forming tool. On the contrary, when inserts are fixed by welding, the working time increases proportionally with the number of pieces to be welded. The joint obtained by the process of the invention has greater resistance to shear forces by virtue of the greater resistant surface offered by the collar formed in the wall of the tubular structure. The dimensions of the joint are also more precise than in traditional fixing by welding. The object of the present invention is also achieved by means of an apparatus according to claim 7. Further characteristics and advantages of the present invention will become clear during the detailed description which follows, provided purely by way of non-limiting example, with reference to the appended drawings, in which: Figure 1 is a schematic section of apparatus for carrying out a process according to the invention, Figure 2 is a view of the part indicated by the arrow II in Figure 1, in greater detail, Figures 3, 4 and 5 are schematic illustrations of different steps in the process of the invention, and Figure 6 illustrates a piece obtained by the process of the invention. With reference to the drawings, a tubular structure is indicated 10 to which a tubular reinforcing insert 12 is to be fixed. Two dies, one movable relative to the other, are indicated 14 and 16 and are adapted to clamp the tubular structure 10 between them. The die 14, 16 have respective seats 18, 20 which together form a deformation chamber. The lower die 16 has a recess 22 from the base wall of which projects a cylindrical punch 24 which, in use, extends perpendicular to the axis of the tubular structure 10. The diameter of the punch 24 is substantially equal to the internal diameter of the reinforcing insert 12 so that the latter may be fitted onto the punch 24 without forcing. As is seen in particular in Figure 2, the diameter of the recess 22 is slightly greater than the outer diameter of the insert 12. Thus the insert fitted onto the punch 24 bears against the base wall of the recess 22. The punch 24 has a pointed part which projects beyond the corresponding end of the reinforcing insert 12. The insert 12 has a conical end portion 26 ending with an annular groove 28. In order to fit the insert 12 to the tubular structure 10, one proceeds as follows. The structure 10 is disposed between the two dies 14, 16 and is connected to a hydraulic circuit (not illustrated) which directs high pressure fluid into the tubular structure 10. This forming technique is known per se and is generally termed "hydroforming". As a result of the forcing of pressurised fluid into the structure 10, the portion of the structure which is located in the deformation chamber 18, 20 expands radially until it is brought into contact with the walls of the seats 18, 20 which form the deformation chamber. During the radial expansion of the wall of the tubular structure 10, the punch 24 opens a hole 30 in the wall 10 (Figure 3) causing inward deformation or a wall portion 32 which constitutes an annular collar. With the progressive radial expansion of the wall of the tubular structure 10, the reinforcing insert 12 is inserted forcibly into the annular collar 32 (Figure 4). The pressurised fluid acting in the structure 10 compresses the collar 32 against the outer wall of the insert 12 and clamps the collar 32 against the groove 28 and the end portion 26 of the insert 12. Subsequently, the pressure of the fluid in the structure 10 is lowered and the liquid is withdrawn from the structure. Figures 5 and 6 illustrate the structure 10 after the fixing of the insert 12 in the manner described above.

Claims: A process for fixing a tubular reinforcing insert (12) to a tubular metal structure (10) comprising forming a hole (30) in the wall of the tubular structure (10) by inward deformation of a portion of the wall so that the deformed wall portion forms an annular collar (32), characterised in that it includes the following steps: force fitting an end portion (26) of the tubular insert (12) into the said collar (32), and introducing liquid at high pressure into the tubular structure (10) so as to compress the collar against the end portion (26) of the tubular insert (12). A process according to Claim 1, characterised in that the hole (30) and the collar (32) are formed by the force insertion of a punch (24) into the wall of the tubular structure (10). A process according to claim 2, characterised in that it further includes the step of radially expanding a portion of the tubular structure (10) in correspondence with the anchoring point for the insert (12) due to the effect of the introduction of pressurised liquid into the tubular structure (10), the insertion of the punch (24) into the wall of the tubular structure (10) being caused by the radial expansion of the wall. A process according to Claim 2 or Claim 3, characterised in that the tubular insert (12) is located on the punch (24) before the step of insertion of the punch (24) into the wall of the tubular structure (10), the punch (24) having a pointed end which projects beyond the end of the insert (12). A process according to Claim 1, characterised in that the said end portion (26) of the insert (12) is conical. A process according to Claim 1, characterised in that the tubular insert (12) has an annular groove (28) over which the collar (32) is closed during its compression against the end portion (26) of the insert (12). Apparatus for fixing a tubular reinforcing insert (12) to a tubular metal structure (10), wherein: a) the apparatus comprises a pair of dies (14, 16) suitable for clamping the tubular structure (10) between them; b) one of the dies (16) has a recess (22) in its base wall, a punch (24) being fixed in the recess (22) with its free end projecting beyond the base wall, a cylindrical cavity suitable for accommodating the reinforcing insert (12) being defined between the punch (24) and the wall of the recess (22); c) the punch (24) includes a pointed part at its free end, the point part being suitable for opening a hole (30) in the wall of the tubular structure (10) and inwardly deforming the wall portion opened when the punch (24) and the wall are moved relatively towards each other, the punch (24) being so shaped, that during continued relative movement between the punch (24) and the wall, the material around the hole (30) is progressively expanded in radial direction into an annular collar; and that d) the apparatus comprises means for introducing liquid at high pressure into the tubular structure (10). Apparatus according to Claim 7, characterised in that the dies (14, 16) define a deformation chamber (18, 20) with larger dimensions than those of the corresponding portion of the tubular structure (10) before the introduction of the pressurised liquid into the structure itself so that the introduction of the liquid into the tubular structure causes the radial expansion of the portion of this structure within this chamber (18, 20) and the penetration of the punch (24) into the wall of the structure (10).

Inventors: DA RE MARIO, GUIDOBONI PAOLO GIUSEPPE, DA RE', MARIO, GUIDOBONI, PAOLO GIUSEPPE
Applicants: FIAT AUTO SPA, FIAT AUTO S.P.A.
Application year: 1993
Main classification: B21D39
IPC codes: B21D39, B21D26