A method for manufacturing of a tubular element comprising a tube with a fixedly arranged flange

BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to a method for manufacturing of a tubular element which comprises a tube with a fixedly arranged flange, wherein the tube is manufactured of a tubular blank and that the flange is manufactured of a flange blank having a through hole.

Advantageously, tubes having a complicated shape are manufactured by a hydroforming process. Many times such tubes are pro- vided with a flange at an end portion such that they are connectable to associated components or tubes. The flange is often fastened to the tube by welding or soldering after that it has been hydroformed to its final shape. The work to fasten flanges to tubes demands a great deal of work and is time wasting. Therefore, the manufactur- ing cost for manufacturing of such tubular elements is relatively high.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for manufacturing of a tubular element, which comprises a tube with a fixedly arranged flange, in a simple and effective manner such that the manufacturing cost for such a tubular element will be relatively low.

This object is achieved by the method of the initially mentioned kind, which is characterized by the steps of moving the flange blank into said hole of the tubular blank, placing the tubular blank and the flange blank, in this state, in a hydroforming tool, and providing a hydroforming process with such a high internal pressure in the tubu- lar blank that it expands plastically to said tube at the same time as the expansion of the tubular blank widens the opening of the flange blank during the process in an at least partly elastic manner such

that a permanent state of tension is created in the final flange, which state exerts a compressive force on the tube in a connecting area such that a fixed connection is accomplished between the flange and the tube. Consequently, a tubular element can here be manufactured with a fixedly arranged flange during a hydroforming process. A condition for enabling a tubular element to be used to transport gaseous and liquid media is that a completely sealed connection can be created between the flange and the tube in the connecting area. By a suitable dimensioning of the included compo- nents and a suitable pressure during the hydroforming process, it is possible to create a state of tension in the flange which exerts a pressure on the tube such that a completely sealed and fixed connection is created between the tube and the flange.

According to an embodiment of the present invention, the method comprises the step of performing a hydroforming process where the tube is provided with at least one radially projecting portion in connection to the connecting area with the flange, which radially projecting portion has a shape and location such that a displacement of the flange in relation to the tubular element is prevented in at least one axial direction. Thereby, the risk is substantially completely eliminated that axial displacement motions of the flange in relation to the tube arise in this direction. The tube may be provided with radially projecting portions such that the risk for motions in both the possible axial directions is eliminated.

According to another embodiment of the present invention, the method comprises the step of using a flange blank having a through hole which has a shape differing from a circular shape such that the outer surface of the final tube provides a corresponding shape in the connecting area, which results in a shape connection being created in the connecting area which prevents turning motions of the flange in relation to the tube. By providing the flange blank with a through hole which has a shape differing from such a circular one, a shape connection between the tube and the flange is created, during the hydroforming process, which also differs from a circular shape. Thus, the risk is substantially completely eliminated that

turning motions will arise in the tubular element between the tube and the flange. The original tubular blank does not need to be round for the hydroforming process to work. It may be square, oval etc. The tubular blank may, for example, also be conical in its longitudi- nal direction without that influencing the process.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following preferred embodiments of the invention are de- scribed by way of example with reference to the attached drawings in which:

Fig. 1 shows a tubular blank and a flange blank for manufacturing of a tubular element according to the present invention,

Fig. 2 shows a tubular blank and a flange blank applied in a hydroforming tool,

Fig. 3 shows the finally manufactured tubular element,

Fig. 4 shows the manufacturing of an alternative tubular element,

Fig. 5 shows the alternative tubular element in a finally manufactured state,

Fig. 6 shows the manufacturing of a further alternative tubular element and,

Fig. 7 shows a tubular blank applied in an octagonal hole of a flange blank.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention relates to a method for manufacturing of a tubular element with a fixedly connected flange. Fig. 1 shows a tubular blank 1 and a flange blank 2 by means of which the tubular element is manufactured. The flange blank 2 is provided with a through hole 2a which is larger than the circumference of the tubular blank 1. The method is initiated by moving the tubular blank 1 into the hole 2a of the flange blank 2, which is shown in Fig. 1.

Thereafter, the tubular blank 1 and the flange blank 2 are placed, in this state, in a hydroforming tool, which is shown in Fig. 2. The hy- droforming tool consists of an upper tool half 3a and a lower tool half 3b which are movably arranged in relation to each other be- tween an open position and a closed position. The tools halves 3a, b have, in the closed position, inner wall surfaces which define the outer surface of the hydroformed product. The tool halves 3a, b have, in this case, been configured with a groove 4 having a size and a shape adapted to receive the flange blank 2. However, the groove 4 has a somewhat larger extension in a radial direction than the flange blank 2. The tool halves 3a, b comprise laterally arranged openings in which end feed cylinders 5 are applied during the hydroforming process. However, only one lateral opening is shown in the figures.

During the hydroforming process, a liquid with a very high pressure is directed in through the opening to an inner space 6 of the tubular blank 1 by means of the end feed cylinder 5. The liquid pressure is so high that it causes the tubular blank 1 to flow and be formed plastically after the inner wall surfaces of the tool halves 3a, b to a final tube 1 '. However, the final tube Y has a somewhat larger outer diameter than the hole 2a of the flange blank. During the hydroforming process, an outer surface of the tubular blank 1 will thus come into contact in a connecting surface 7 with the surface which de- fines the hole 2a of the flange blank. However, the hydroforming pressure is so high that the tubular blank 2 provides a continued expansion even in this connecting area 7 such that the opening 2a of the flange blank is widen. Since the tool halves 3a, b have been provided with a surrounding groove 4 which is somewhat larger in a radial direction than the flange blank 2, the flange blank can expand in a radial direction into the groove 4. This expansion occurs more or less elastically. When the hydroforming process has been finished, the tubular blank 1 has been expanded plastically to a tube 1 ' with a desired shape and size, which is shown in Fig. 3. At the same time, the flange blank 2 has been expanded at least partly in an elastic manner such that a permanent state of tension has been created in the final flange 2'. The final flange 2' will thus exert a ra-

dially inwardly directed compressive force on the tube Y in the connecting area 7. With a suitable choice of, among others, material, dimensions of the included components and pressure during the hydroforming process, a compressive force can be created which provides a very firm and tight connection between the tube Y and the flange 2'. Consequently, the final product picked out from the tool halves 3a, b consists of a tubular element in the form of a tube Y with a fixedly arranged flange 2'.

Fig. 4 shows the manufacturing of an alternative tubular element which has a further strengthened connection between the tube Y and the flange 2'. In this case, the tool halves 3a, b also have been provided with a recess 8 in connection to the groove 4. Thus, a correspondingly shaped projecting portion 8' is created on the tube Y in connection to the flange 2' during a hydroforming process. The tool halves 3a, b comprise a recess 9 in connection to an opposite side of the groove 4. Thus, a correspondingly shaped projecting portion 9 is created on the tube 1 ' in connection to the flange 2' during the hydroforming process. The final tubular element with tube Y and flange 2' is shown in Fig. 5. The projecting portions 8', 9' prevent an axial displacement motion of the flange 2' both to the left and to the right in the figure. A sealing material 1 1 has here been applied in the gap between the tubular blank 1 and the flange 2 before the hydroforming process is started. Thus, the sealing material 1 1 forms an ensurely sealed connection between the tube 1 ' and the flange 2' in the contact surface 7 of the final tubular element. Alternatively, such a sealing material may consist of an O-ring which is applied in a groove of the flange blank 2.

Fig. 6 shows a flange blank 2 having a radial recess 10 in the surfaces which define the hole 2a. During the hydroforming process with such a flange blank 2 in a tool 3a, b, the tubular blank 1 is pressed into the radial recess 10. The hydroformed tube Y will thus get a radially protruding portion which protrudes into the recess 10 of the final flange 2'. By means of such a form fitting between the tube Y and the flange 2' in the connecting area 7, the flange 2' is

prevented from being displaced axially on the tube 1 ' in both directions.

Fig. 7 shows a flange blank 2 having a through hole 2a with an oc- tagonal shape. During a hydroforming process with such a flange blank 2, the tubular blank 1 will expand such that the outer surface of the final tube V provides, in a connecting area 7, an octagonal shape corresponding to the final flange 2'. A shape connection is thus created in the connecting area between the tube 1 ' and the flange 2', which connection prevents turning motions of the flange 2' in relation to the tube V. Such a shape connection can be created by means of a flange blank having a through hole 2a with a shape differing from a circular shape. Thereby, the fixed connection between the tube V and the flange 2' of a tubular element may be further strengthened.

The present invention is not in any way restricted to the above- described embodiments on the drawings but can be modified freely within the scope of the claims.