Abstract:
To make tailored tubular blanks the circumferential weld seam and the longitudinal weld seam are so arranged that the seams do not intersect but only form an interface. In this way tailored tubular blanks that have better formability are produced.

Description:
[0001]     Applicants hereby claim foreign priority benefits under 35 U.S.C. § 119 of Swiss Patent Application No. 522/00 filed 23 March 2000 and PCT Application No. PCT/CH0 1/00122, filed 26 February 2001, the disclosures of which are herein incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Technical Field  
         [0003]     The invention relates to tailored tubular blanks and methods for manufacturing them in general, and in particular to tailored tubular blanks having at least one circumferential weld seam and at least one longitudinal weld seam, and methods for manufacturing the same, in particular.  
         [0004]     2. Background Information  
         [0005]     Tailored tubular blanks are welded open-ended bodies either in the shape of a simple tube, or alternatively with a non-circular cross-section or a cross-section that varies along the length, which can result in a cylindrical or conical or irregular form lengthways. The shape given to them depends on their subsequent intended purpose and is designed with the latter in mind. For simplicity&#39;s sake these bodies, including those that are irregularly shaped, will be referred to as “tubes”. Tailored tubular blanks are characterised by the fact that they are made from two or more metal sheets of different thickness and/or grades of material and/or coatings. The way in which such tailored tubular blanks are constructed from metal sheets with different characteristics produces tubes the sections of which are specifically adapted to the requirements concerned. These tailored tubular blanks may be used as such or in the main example of their use further processed by shaping them, notably using hydraulic shaping (hydroforming), to make hollow bodies with complex shapes. Such hollow bodies or shaped parts are for instance employed in automotive engineering, for example as load-bearing components in the vehicle body (pillars, roof rail, sill beam sections, etc.) and in the undercarriage (running gear, chassis rails, cross-members, muffler and catalyst housings, etc.). Application fields other than automotive engineering are also possible, notably wherever spatially complex specialist parts are to be employed. The specialist term “tailored tubular blanks” is used generally in the technical terminology and therefore also in this patent application; by analogy with the conventional plane “tailored blanks” (rendered in German inter alia as “belastungsangepasste Platinen”), “tailored tubular blanks” may inter alia be rendered in German as “belastungs-angepasste Rohre”.  
         [0006]     Tailored tubular blanks are joined using beam welding techniques (laser welding, electron beam welding or resistance arc welding), involving firstly rounding a tailored blank in the conventional way to make a tube, and then making the weld seam longitudinally along the tube.  FIGS. 1   a - 1   c  and  2   a  -  2   c  show two different variants of tailored tubular blanks taken from the prior art.  FIGS. 1   a - 1   c  show a first variant having parallel longitudinal seams, with  FIG. 1   a  showing the plane tailored blank  1  from metal sheets  1  and  2  with the weld seam  3 .  FIG. 1   b  shows the welded tube (tailored tubular blank) from above with the tube&#39;s longitudinal weld seam  4 , and  FIG. 1   c  shows a cross-section taken through the tube. The present invention does not relate to such tailored tubular blanks having weld seams running exclusively lengthways, but to tailored tubular blanks as seen in  FIGS. 1   a -  2   c  with a circumferential and a longitudinal seam.  FIG. 2   a  shows the corresponding tailored tubular blank with the metal sheets  1  and  2  and the weld seam  3 , which after being formed into a tube as shown in  FIG. 2   b  (tailored tubular blank) forms the circumferential weld seam  3  which intersects the weld seam  4  running the length of the tube.  FIG. 2   c  shows a cross-section through such a tailored tubular blank in the region of metal sheet  2 . Tailored tubular blanks with a transverse division, as shown in  FIGS. 2   a  - 2   c , can exhibit drawbacks during the subsequent shaping operation (e.g. hydroforming) because the welding stresses are concentrated at the point of intersection and the heat-affected zones (the margins of the weld zone proper) of the two seams overlie one another. There is also an increased risk of welding defects at the point where the seams intersect. By controlling the welding process to maximum effect it has up till now been attempted to avoid these drawbacks as far as possible, or at least to minimise them to the extent that they make no difference in the metal forming operation. However, depending on the characteristics of the metal sheets it is difficult to select and observe suitable welding parameters.  
       DISCLOSURE OF THE INVENTION  
       [0007]     It is therefore the object underlying the invention to create tailored tubular blanks having a circumferential seam and a longitudinal seam which do not incur the stated drawbacks or at any rate only to a greatly reduced degree.  
         [0008]     In the case of tailored tubular blanks of the type mentioned in the introduction, this object is achieved by a tailored tubular blank that has at least one circumferential weld seam and at least one longitudinal weld seam, wherein the circumferential weld seam and the longitudinal weld seam do not intersect one another when they meet at the joint.  
         [0009]     The fact that the circumferential seam (or circumferential seams if more than one is provided) do not intersect the longitudinal seam (or longitudinal seams if more than one is provided) means that the aforementioned drawbacks are largely not applicable. Non-intersecting seams merely abut one another, with the result that they may be referred to concretely as T-joints, although as a rule the seams do not meet at a right angle. Such T-joints have a low concentration of welding stresses in the vicinity of the welded joints than is the case with intersecting seams, which results in better formability. Also the risk of welding defects when joints are being welded is smaller than when welding intersecting seams. The interfaces of the seams can also be more systematically positioned at locations that are subject to little stress in metal-forming terms.  
         [0010]     It is a further object of the invention to create a process for producing tailored tubular blanks that do not have the stated drawbacks.  
         [0011]     This object is achieved by a process for, or method of, making a tailored tubular blank that has at least one circumferential weld seam and at least one longitudinal weld seam, wherein the circumferential weld seam and the longitudinal weld seam are arranged in such a manner that the seams meet at a joint. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Exemplary embodiments of the invention will now be explained in detail with reference to the Figures, wherein:  
         [0013]      FIGS. 1   a - 1   c  show a tailored blank, a tailored tubular blank in a plan view and a cross-section through the latter under the prior art;  
         [0014]      FIGS. 2   a  - 2   c  also show a tailored blank, a tailored tubular blank and a cross-section under the prior art;  
         [0015]      FIGS. 3   a  - 3   c  show a first exemplary embodiment of the invention, likewise with a tailored blank, a tailored tubular blank and a cross-section;  
         [0016]      FIGS. 4   a  - 4   c  show a further exemplary embodiment, in which tubular sections are joined at their ends;  
         [0017]      FIGS. 5   a  and  5   b  show a further exemplary embodiment with a tailored blank and tailored tubular blank in a plan view;  
         [0018]      FIGS. 6   a  and  6   b  show a further exemplary embodiment with a tailored blank and tailored tubular blank;  
         [0019]      FIG. 7  shows an exemplary embodiment of a tailored blank; and  
         [0020]      FIG. 8  shows another exemplary embodiment of a tailored blank. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]      FIGS. 1   a - 1   c  show an example, already explained above, of prior art tailored tubular blanks the embodiment of which does not form a subject-matter of the present invention.  FIGS. 2   a  - 2   c  show an exemplary embodiment of prior art tailored tubular blanks having a longitudinal seam and a circumferential seam, the improved version of which does form a subject-matter of the present invention.  
         [0022]      FIG. 3   a  shows a first exemplary embodiment of tailored tubular blanks in accordance with the invention, with  FIG. 3   a  showing the tailored blank  10  from which the tubular can body will be shaped, using any conventional tube shaping process, and then welded to make the tube. The tailored blank  10  is formed by welding two metal sheets  11  and  12  which are joined to one another by means of a diagonal weld seam  13 . The metal sheets  11  and  12  may be any desired conventional metal sheets of different thickness and/or with different sheet metal characteristics, as is fundamentally known in making tailored tubular blanks. When the tailored blank is formed into the tube by working the edges  16  and  17  of the tailored blank out of the drawing plane and away from the observer, the result is a tubular can body as in the plan view seen in  FIG. 3   b , in which the edges  16  and  17  have already been joined together by a weld seam  18 . The weld seam  13 , which runs at the end points  14  and  15  into the edges,  16  and  17  respectively, then forms with the weld seam  18  two interfaces,  14  and  15  respectively, which are spaced apart from one another by a predetermined distance. The spacing results from the oblique position of the weld seam  13  and can be selected in a correspondingly free manner and, for example, be from a few millimetres to several centimetres in size. This means that each end of weld seam  13  is only butted up to weld seam  18  and does not continuously intersect the latter, which brings about the advantages outlined above.  FIG. 3   c  shows a cross-section through the tube  20  in the vicinity of the metal sheet  12 .  
         [0023]      FIGS. 4   a  - 4   c  show another form of embodiment of tailored tubular blanks in accordance with the invention, exemplified by depicting a tube  30  which has a continuous circumferential seam  33  adjoined by two longitudinal seams  31  and  32  which do not intersect at the joint, with the interfaces being identified as  34  and  35  respectively. Here, too, the interfaces are spaced a preselected distance apart from one another.  FIG. 4   c  shows the two tubes  36  and  37  which serve as starting parts with longitudinal weld seams  31  and  32  for tailored tubular blanks as seen in  FIG. 4   a . The tubes  36  and  37  are preferably in turn constituted by metal sheets of different thickness and/or having different material characteristics. The tubes  36  and  37  are then joined together contiguously with one another by welding the continuous circumferential seam  33 , thereby producing the tailored tubular blanks as seen in  FIG. 4   a .  FIG. 4   b  shows a cross-section taken through the tailored tubular blank  30  from  FIG. 4   a , in the vicinity of the tube  37 . Unlike the per se known construction of tubes from tube sections, where as a rule the longitudinal seams are in alignment with one another but there may be greater or lesser or undefined deviations in the alignment of the longitudinal weld seams due to inaccuracies in the production process, in the present case relating to the construction of tailored tubular blanks the starting tubes  36  and  37  are deliberately joined together with a preselected offset “d” of the longitudinal weld seams in an industrial field and with as constant an offset “d” as possible, with the result that the manufacturing process produces a set of tailored tubular blanks with the same offset. These are also tubes  30 , or rather tailored tubular blanks, which are made up of different tube parts  36  and  37 .  
         [0024]      FIGS. 5   a  and  5   b  show another exemplary embodiment similar to the one in  FIGS. 3   a  and  3   b , in which, however, the tailored blank  40  is made up of three metal sheets  41 ,  42  and  43 , to which end the weld seams  44  and  45  are provided. Corresponding interfaces  46 - 49  are constructed in the case of the tailored tubular blank  50  with its longitudinal weld seam  51 . Here, too, all three metal sheets  41 - 43  may have different thicknesses and/or material characteristics or two of the metal sheets, say  41  and  43 , may be identical sheets and metal sheet  42  may be a sheet with different characteristics. This can result, for instance following the reshaping of the tailored tubular blanks  50 , for example by means of hydroforming, in a side rail that exhibits high strength at its centre and a lower strength, or desired upsetting behaviour, at its ends. Naturally, too, just one of the seams  44  and  45  may run diagonally and the other seam may run straight, as in the prior art, and thus intersect the longitudinal seam if that is what is wanted.  
         [0025]      FIGS. 6   a  and  6   b  show another exemplary embodiment in which the tailored blank  60  is once again made up of three metal sheets, with one seam  65  in this case forming a longitudinal weld seam on the corresponding tailored tubular blank  69  and the obliquely situated weld seam  64  forming the circumferential seam. The metal seams  65 ,  62  and  63  may in turn exhibit different thicknesses and material characteristics and, as in the examples already depicted, the interfaces  66  and  67  which are created in the case of the tailored tubular blanks have the stated advantages over an intersecting path of the weld seams under the prior art.  
         [0026]      FIG. 7  shows another tailored blank in which it is readily apparent that in this instance the interfaces  74  and  75  of the weld seam  73  which connects the metal sheets  71  and  72  lie at a right angle to the longitudinal weld seam in the case of the tailored tubular blanks. This may be referred to as a T-shaped joint, although this designation may also be used for the other interfaces in accordance with the invention even if the seams do not meet exactly at right angles.  
         [0027]      FIG. 8  shows another example of a tailored blank  80  with three welded metal sheets  81 ,  82  and  83 , the interfaces of the weld seams  84  and  86  likewise exhibiting a predetermined offset from the longitudinal weld seam along the longitudinal weld seam of the can body constituted by this tailored blank, or by tailored tubular blanks to be welded subsequently, and forming a non-intersecting joint with the longitudinal weld seam. In place of metal sheet  83  it would also be possible to provide a recess that forms a recess on the tailored tubular blank.  
         [0028]     Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and the scope of the invention