Abstract:
A method for producing highly dimensionally accurate, deep-drawn half shells with a base region, a body region and a flange region, includes firstly forming a pre-formed half shell from a blank and then shaping the pre-formed half shell into a finally formed half shell, wherein the pre-formed half shell has excess blank material due to its geometric shape and wherein, owing to the excess material during the shaping of the pre-formed half shell into its final shape the half shell is compressed into the finally formed half shell by at least one further pressing process. The method requires that the pre-formed half shell has excess blank material in a transition region between the body region and flange region.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of and priority to German patent application no. DE 10 2008 037 612.4-14, filed on Nov. 28, 2008. The disclosure of the above application is incorporated herein by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to a method for producing highly dimensionally accurate, deep-drawn half shells with a base region, a body region and a flange region, wherein a pre-formed half shell is firstly formed from a blank and is then shaped into the finally formed half shell, wherein the pre-formed half shell has excess blank material due to of its geometric shape and wherein owing to the excess material during the shaping of the pre-formed half shell into its final shape the half shell is compressed into the finally formed half shell by at least one further pressing process. The invention also relates to a tool set for producing a highly dimensionally accurate deep-drawn half shell with flange regions with a first tool for producing a pre-formed half shell, the first tool comprising a first bottom die, and with a second tool for producing the finally formed half shell, the second tool comprising a second bottom die, the shape of which substantially corresponds to the negative of the outer shape of the finally formed half shell. 
       BACKGROUND 
       [0003]    Closed hollow profiles, which have cross-sections and material thicknesses specially adapted to the application are increasingly being used in motor vehicles. Closed hollow profiles were previously generally produced in that firstly a tube is formed, the tube is subjected to corresponding bending and pre-forming processes and then a hydro-forming of the pre-bent or pre-formed tube into the final shape of the closed hollow profile takes place. On the one hand, not all components can be produced in this manner as in hydro-forming local elongations of the material are exceeded and thus cracks may form. In addition, there may be a non-manageable formation of folds during the hydro-forming. Moreover, the method steps previously used to produce a closed hollow profile adapted to the application are very complex and therefore expensive. A closed hollow profile may, in principle, also be produced from two deep-drawn half shells. During the deep-drawing of a blank, stresses are, however, introduced into the blank and lead to a spring-back of the half shell. The spring-back of the half shells makes the precise positioning of the half shells in a bottom die for welding the half shells into a closed hollow profile more difficult. 
         [0004]    Assembling half shells which spring back strongly in a vehicle structure is very complex, however, because of the strong distortion. These parts alternatively have to be straightened and this entails very high costs. 
         [0005]    A method for press-forming half shells, which are then welded to form a closed hollow profile, is known from the published European patent application EP 1 792 671 A1. The object of the European patent application mentioned is to provide half shells with thickened edge regions between the base region and the body. For this reason, a pre-formed half shell is firstly produced from a blank which provides excess material which is pressed during shaping into the final form from the base region into the edge regions between the body and the base region of the half shell. In comparison, the present invention deals with reducing the spring-back of deep-drawn half shells. 
       SUMMARY OF THE INVENTION 
       [0006]    Proceeding from this, the present invention is based on the technical problem of providing a method and a tool set for producing highly dimensionally accurate flanged half shells, with which, with a low outlay for apparatus, highly dimensionally accurate flanged half shells can be economically produced. 
         [0007]    This technical problem is achieved according to the invention in that the pre-formed half shell has the excess blank material in the transition region between the body region and flange region. This transition region is taken to mean the body region adjoining the flange region and the flange region adjoining the body region. When producing half shells by simple deep drawing, strong geometrical deviations from the intended shape frequently occur in the transition region. This transition region is therefore particularly critical when producing highly dimensionally accurate flanged half shells. For example, deep drawing in the transition region may lead to the formation of cracks or premature material fatigue. Such problems are reliably avoided by the excess material in the transition region. 
         [0008]    According to a preferred embodiment, the pre-formed half shell has the excess blank material at least in the base region and in the body region or in the base region and in the flange region, so the half shell is highly dimensionally accurate after the second pressing process in its entire cross-section and a spring-back is prevented. Furthermore, the finally formed half shell has a shape corresponding very precisely to the geometry of the second bottom die. The invention is based on the recognition that to produce highly dimensionally accurate flanged half shells, it is necessary to compress the pre-formed half shell over its entire cross-section. Therefore, the excess material required for compression also has to be available over the entire cross-section. 
         [0009]    The excess blank material is provided in a further preferred embodiment of the invention in that the central flange radius in the transition region between the body region and flange region in the pre-formed half shell is greater or smaller than in the final shape. The central flange radius is taken to mean the radius of the circle, with the periphery of which the course of the half shell best coincides in the transition region between the body region and flange region. It is thus unnecessary for the transition region of the half shell between the body region and flange region to actually be arc of a circle-shaped. Thus, the transition region may, for example, have the shape of an elliptical arch, a parabola or another shape. The provision of excess blank material is achieved in a very simple manner by this embodiment. 
         [0010]    Furthermore, a very simple first bottom die can be used to produce the pre-formed half shell. The formation of a larger flange radius is advantageous, in particular, in the case of large drawing depths and leads to a smaller wall thinning of the pre-formed half shell in the body region. Formation of a smaller flange radius is advantageous for the lateral wall ironing of the flange region and thus reduces the spring-back of the pre-formed half shell. To reduce the spring-back of the pre-formed half shell, additional measures may also be provided in both variants, such as, for example, body wall ironing, via flange moderation by means of moderating crimps/beads and/or by adjusting the forces of the holding-down device. 
         [0011]    A further improvement of the dimensional accuracy of the half shell, in particular in the flange region, is achieved in a further preferred embodiment in that the material flow of the half shell at the flange edges of the half shell is blocked, at least intermittently, during the pressing process. This means that no blank material is pressed out of the pressing region and thus the entire excess blank material is completely compressed into the finally formed half shell, so the half shell is reinforced in particular at the critical points for the dimensional accuracy. 
         [0012]    The blocking of the material flow of the half shell to the outside can be achieved in a particularly preferred manner by a blocking wall provided on the calibration top die used for the pressing process. This, on the one hand, has the advantage that no additional moveable component has to be provided to block the material flow to the outside. On the other hand, it is thus achieved that the blocking wall blocking the material flow travels into the position provided for blocking precisely during the pressing process bringing about the material flow. 
         [0013]    In a further preferred embodiment, the pre-formed half shell is trimmed in the flange region before or during the pressing process in the same bottom die. This means that the half shell already has its completely finished final shape after the pressing process. This saves a working step and therefore time and costs. 
         [0014]    The precision and cleanness of the trimming of the half shell is achieved in a further preferred embodiment in that the pre-formed half shell is fixed by a holding-down device in the flange region before trimming. This prevents a change of the position of the half shell during trimming and therefore the formation of an unclean cutting edge. An advantageous control of the material flow in the half shell is achieved by maintaining the fixing during the pressing process with simultaneous blocking of the material flow to the outside. Thus the fixing during the pressing process leads to a material flow of the excess material from the flange region into the transition region between the body region and flange region. Furthermore, the pre-formed half shell is reliably held in the second bottom die by the fixing so the calibration top die of the second bottom die can travel more precisely into the bottom die. 
         [0015]    A particularly precise and clean cutting edge in the flange region of the half shell is achieved in a further preferred embodiment by the use of a laser for trimming the flange region. 
         [0016]    The blocking of the material flow of the half shell to the outside is blocked in a further preferred embodiment by the cutting top dies carrying out the trimming. If the half shell in the second bottom die is trimmed, this is particularly advantageous as no additional components are necessary to block the material flow to the outside. This allows the method to be carried out more easily, faster and more economically. 
         [0017]    The method according to the invention is particularly suitable for producing half shells made of steel or a steel alloy. Therefore, the blank to produce the pre-formed half shell in a preferred embodiment consists of steel or a steel alloy. 
         [0018]    The technical problem is furthermore achieved by a tool set in that the bottom die of the first tool in the transition region between the body region and flange region differs from the shape of the bottom die of the second tool in such a way that the pre-formed half shell in the transition region has more material than is required for the finally formed half shell. During deep-drawing, in particular in the transition region between the body region and flange region of the half shell, strong geometric deviations frequently occur. The tool set according to the invention means that the half shell pre-formed in the first bottom die differs, in particular in this region, from the shape of the second bottom die and therefore excess material is available in the second bottom die during the pressing process and leads to a high dimensional accuracy in this region. 
         [0019]    According to a first embodiment, the bottom die of the first tool deviates at least in the base region and in the body region or in the base region and in the flange region from the shape of the bottom die of the second tool in such a way that the pre-formed half shell in the base region and in the body region or in the base region and in the flange region has more material than is required for the finally formed half shell. In the pressing process, a material flow of the excess blank material is produced in the second bottom die in order to orientate the stresses in the blank material which then counteract an uncontrolled spring-back. Moreover, the half shell is to be reinforced by the material flow in the regions otherwise thinned by the deep-drawing. This leads to a high dimensional accuracy of the finally formed half shell. The deviations of the shape of the first bottom die from the shape of the second bottom die can thus be formed as undulating, convex or concave, inward or outward bulges. 
         [0020]    The deviations of the shape of the first bottom die from the shape of the second bottom die are achieved in a further preferred embodiment in that the bottom die of the first tool in the transition region between the body region and flange region has a larger or smaller flange radius than the bottom die of the second tool. The pre-formed half shell inserted into the second bottom die, in the transition region between the body region and the flange region, thus does not rest on the second bottom die, but has a deviating course with an increased material quantity. The latter is produced in the case of a larger flange radius owing to the extended flange region, and with a smaller flange radius, owing to the relatively large curvature length in the transition region between the body region and flange region. During the pressing process, the half shell is pressed onto the second bottom die and the excess blank material reinforces the half shell above all in the transition region. 
         [0021]    So that the excess blank material remains completely in the second bottom die during the pressing process and thus leads to a reinforcement and therefore higher dimensional accuracy of the half shell, the second tool comprises means in a preferred embodiment which block the material flow to the outside, at least intermittently during the pressing process of a half shell to be shaped into the final shape on the flange edges of a component inserted into the second tool. 
         [0022]    This can be achieved in a further preferred embodiment in that the second tool comprises a calibration top die and a blocking wall for blocking the material flow or a cutting top die for the flange trimming with an integrated blocking wall. The calibration top die and the blocking wall may, in this case, form a unit or be moved separately. When providing a cutting top die, the half shell is directly trimmed in the second bottom die. The work sequence can thus be reduced by one working step. The cutting top die is also suitable, in particular, for the integration of the blocking wall, as the latter thus does not need to be moved individually. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    Further features and advantages of the present invention are described in more detail in the description of some embodiments, reference being made to the accompanying drawings, in which: 
           [0024]      FIG. 1  shows an embodiment of the first tool of a tool set according to the invention for producing a pre-formed half shell from a blank, 
           [0025]      FIG. 2  shows a half shell pre-formed in the first bottom die, 
           [0026]      FIG. 3  shows a first embodiment of the second tool of a tool set according to the invention with a pre-formed half shell inserted therein, produced with a first tool of a tool set according to the invention, 
           [0027]      FIG. 4  shows a first embodiment of the second tool from  FIG. 3  with a pre-formed half shell inserted therein, produced with a further first tool of a tool set according to the invention, 
           [0028]      FIG. 5  shows a second embodiment of the second tool of a tool set according to the invention with a pre-formed half shell inserted therein, produced and trimmed with a first tool of a tool set according to the invention, 
           [0029]      FIG. 6  shows a third embodiment of the second tool of a tool set according to the invention with a pre-formed half shell inserted therein, produced and trimmed with a first tool of a tool set according to the invention and 
           [0030]      FIG. 7  shows a finally formed half shell produced with a tool set according to the invention. 
       
    
    
     DESCRIPTION 
       [0031]    The first tool  2  of an embodiment of a tool set according to the invention for producing a pre-formed half shell from a blank  4 , shown in  FIG. 1 , comprises a first bottom die  6  and a deep-drawing top die  8 . The general shape of the inside  10  of the bottom die  6  is similar to the shape of the outside of the finally formed half shell to be produced with the tool set. In the transition region  14  between the body region  16  and the flange region  18  of the bottom die  6  and in the base region  12 , the inside  10  of the bottom die  6  deviates with respect to its shape, however, from the shape of the outside of the finally formed half shell to be produced with the tool set. Thus, the inside  10  of the bottom die  6  in the base region  12  has an undulating shape. Alternatively, a simple concave or convex shape or another shape deviating from the intended shape of the base region or the finally formed half shell is also conceivable. Furthermore, the flange radius in the transition region  14  and the height of the shape, in other words the distance between the base region  12  and the flange region  18 , is increased. Alternatively, a bottom die is conceivable, in which the flange radius is reduced, but the height is not increased. The deep-drawing top die  8  has a shape adapted to the shape of the bottom die  6 , so the blank  4  is deep drawn by lowering the deep-drawing top die  8  into the bottom die  6  to form a pre-formed half shell. 
         [0032]      FIG. 2  shows a pre-formed half shell  24  after deep drawing with the first tool shown in  FIG. 1 . The outside  26  of the pre-formed half shell  24  substantially corresponds to the inside  10  of the bottom die  6 , but deviates through spring-back from the precise shape of the inside  10  of the bottom die  6 . In the transition region  30  between the body region  32  and the flange region  34 , the pre-shaped half shell  24  has an enlarged flange radius  36 . The base region  28  of the pre-formed half shell  24  is undulating in accordance with the shape of the base region  12  of the bottom die  6 . 
         [0033]    The second tool  42  shown in  FIG. 3  of a tool set according to the invention comprises a second bottom die  44 , a calibration top die  46  and a holding-down device  48 . A pre-formed half shell  50 , which was produced by the tool shown in  FIG. 1 , is inserted into the bottom die  44 . The shape of the inside  52  of the bottom die  44  corresponds to the shape of the outside of the finally shaped half shell to be produced. The half shell  50  therefore does not rest completely on the inside  52  of the bottom die  44 , but stands away from the inside  52  of the bottom die  44 , in particular, in the base region  54  owing to its undulating shape and, in the transition region  56  between the body region  58  and flange region  60  and in the flange region  60  owing to the greater flange radius in the transition region  56 . The height of the pre-formed half shell  50  is thus greater than the height of the finally formed half shell to be produced. The pre-formed half shell  50 , owing to these regions standing away, has excess blank material which is distributed during the lowering of the calibration top die  46  by a material flow on the half shell and leads to a high dimensional accuracy of the finally shaped half shell. The calibration top die  46  has a shape corresponding to the inside of the half shell to be produced. A cutting top die  62  with a cutting edge  64  is integrated into the calibration top die  46 . When lowering the calibration top die  46 , the pre-formed half shell  50  is thus trimmed in the flange region  60  by the cutting edge  64  on the edge  65  of the bottom die  44  to the intended size. The bottom die  44 , in the region of the cutting top die  62 , has a recess  66 , so the cutting die  62  can be lowered and the cut-off piece of the pre-shaped half shell can fall down. The pre-formed half shell  50  in the flange region  60  is fixed by the holding-down device  48  and this leads to a very clean trim of the pre-formed half shell  50  by the cutting edge  64 . In a preferred manner, the calibration top die  46  with the cutting top die  62  is firstly positioned at an adequate height above the pre-formed half shell  50  in the bottom die  44 . It thus has no contact with the base region and the flange region of the pre-formed half shell  50 . The holding-down device  48  is then moved down, for example, by means of sleeves let into the calibration top die and fixes the pre-formed half shell  50  in the flange region  60 . When using a pre-formed half shell  50  with the greater flange radius this leads to an arcuate deformation of the pre-formed half shell  50  in the flange region. With a pre-formed half shell  50  with a smaller flange radius no such deformation occurs and there is therefore a cleaner trim. This is advantageous, in particular in the case of greater sheet metal thicknesses. Finally, the calibration top die  46  and the cutting top die  62  move down completely. In the process, the cutting top die  62  firstly cuts off the projecting flange region of the pre-shaped half shell  50  and blocks the material flow of the blank material to the outside during the further downward movement. The pre-formed half shell  50  is compressed over its entire cross-sectional area by the calibration top die  46  into the finally formed half shell by the excess blank material in the transition region  30  as well as in the base region  54  and in the flange region  60  or in the base region  54  and in the body region  58  of the half shell  50 . Said half shell can only change with respect to its sheet metal thickness during the compression process and is therefore formed with good dimensional accuracy. 
         [0034]      FIG. 4  shows the second tool  42  from  FIG. 3 . A pre-formed half shell  72  produced by means of a second embodiment of the first tool of a tool set according to the invention is inserted into the bottom die  44 . The pre-formed half shell  72  differs from the pre-formed half shell  50  shown in  FIG. 3  in that the transition region  74  between the flange region  76  and the body region  78  has a smaller flange radius than the bottom die  44 . Furthermore, the height of the pre-formed half shell  72  coincides with the height of the finally formed half shell to be produced and therefore with the depth of the bottom die  44 . Owing to the smaller flange radius, the pre-formed half shell  72  in the transition region  74  does not rest on the inside  52  of the bottom die  44 . Thus, excess blank material is available at this point owing to the extended curvature region during the lowering of the calibration top die  46 . 
         [0035]    The second tool of a tool set according to the invention shown in  FIG. 5 , in contrast to the second tool  42  shown in  FIG. 3 , has no holding-down device and no cutting edge. Instead of a cutting top die, the calibration top die  86  has a blocking wall  88 . A pre-formed half shell  92  is inserted into the bottom die  90 . In contrast to the pre-formed half shell  50  shown in FIG.  3 , the pre-formed half shell  92  in the flange region  94  already has the size of the finally formed half shell to be produced. This is achieved, for example, in that a pre-formed half shell produced by a first tool is trimmed in a separate working step before insertion into the bottom die  90 . In this manner, the structure of the second tool and the method sequence are simplified, as no holding of the calibration or cutting top die in an intermediate position is necessary to lower the holding-down device. 
         [0036]    The second tool  102  of a tool set according to the invention shown in  FIG. 6  differs from that shown in  FIG. 5  in that the blocking wall  104  is configured as a separate part from the calibration top die  106  and can be moved independently of the calibration top die  106 . 
         [0037]    A finally formed half shell  112  produced by a tool set according to the invention is shown in  FIG. 7 . In particular in the transition region  114  between the body region  116  and flange region  118  as well as in the transition region  120  between the base region  122  and flange region  118 , it has high dimensional accuracy and great stability.