Abstract:
The invention relates to a method for producing a cylindrical component, particularly of turbomachines. In the process, a heated blank is provided. The blank is then formed to create a flat blank ( 2 ). The flat blank ( 2 ) is next bent and/or rolled to form a cylindrical half-shell ( 40 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a method for producing a cylindrical component in accordance with the present invention. 
         [0002]    Blanks for cylindrical housings, such as, for example, engine housings, are typically ring-rolled. In this process, the heated torus-shaped blank is rolled between a cylindrical mandrel roller arranged inside of the blank and a cylindrical main roller arranged outside of the blank, with the axes of the mandrel roller and the main roller lying parallel to the axis of the workpiece being formed. Simultaneously, two conical axial rollers are arranged above and below the blank on the side diametrically opposite to the blank. The mandrel roller and the main roller determine the radial thickness of the blank (also referred to as the wall thickness of the blank) and the two axial rollers determine the axial length of the blank. For reasons of strength, the housing has ribs, so that the wall thickness of the blank has to be at least as great as the rib height. In particular, cylindrical housings typically do not have a uniform thickness. The ribs are created in the cylindrical outer wall of the blank by machining, such as, for example, by milling, after ring rolling. This process is particularly detrimental, because a very large volume of material debris is produced. Furthermore, in the case of longitudinally divided housings, the ring has to be cut open to form a half-shell, so that an additional operating step ensues in order to be able to produce the final product. 
         [0003]    Furthermore, housings of turbomachines particularly have to satisfy the so-called containment criterion. This means that rotating components located in the housing must not penetrate through the housing in the event of a defect, such as, for example, the fracture of a rotor blade. If the housings are cast, the containment criterion can be met only by using an appropriately large mass. This entails the drawback that the housings are heavier than housings produced by machining. 
       SUMMARY OF THE INVENTION 
       [0004]    Accordingly, the present invention is based on the object of proposing a method in which less volume of material debris is created during the production of cylindrical components and which is more economical in production. 
         [0005]    The object is achieved by the method of the present invention. 
         [0006]    The invention relates to a method for producing a cylindrical component, particularly one of turbomachines. First of all, a heated blank is provided. The blank is then press-formed to create a flat blank. The flat blank is next bent and/or rolled to form a cylindrical half-shell. In the process, the blank may be heated to a temperature above the recrystallization temperature of the blank material. This offers the advantage that, in comparison to ring rolling, cutting to create a half-shell is dispensed with. 
         [0007]    In an advantageous embodiment of the invention, the flat blank is essentially rectangular in shape. This offers the advantage that little protruding material is created by press forming and the flat blank exhibits a form similar to that of the later final product. 
         [0008]    In another advantageous embodiment of the invention, the flat blank has a machining allowance on at least one of its contours. This offers the advantage that, during press forming, any lacking dimensional accuracy can thereby be compensated for. In this case, the machining allowance can be between 0 and 10 mm. In particular, the machining allowance may only be necessary on the contours that later constitute a contact surface. 
         [0009]    In another advantageous embodiment of the invention, at least one rib and/or one eyelet is formed in at least one of the surfaces of the blank. In this case, these raised areas (ribs, eyelets, or upset eyelets) are formed at the same time as the press-forming operation. This offers the advantage that these raised areas do not need to be machined out of the solid material. In comparison to ring rolling, little or no material debris volume is created. In this case, the raised areas may be produced advantageously in the surface of the blank without any machining allowance, so that the ribs, the eyelets, and the upset eyelets do not need to be post-finished. 
         [0010]    In another advantageous embodiment of the invention, at least one contact surface of the half-shell is machined, in particular milled, to a final dimension. This is especially advantageous, because, as a result, it is possible to achieve greater dimensional accuracy than is possible at all by press forming. Any final machining is then necessary only at the required places, such as, for example, the contact surfaces, so that the volume of material debris is minimized. 
         [0011]    In another advantageous embodiment of the invention, the press forming is accomplished by drop forging. In this method, the form of the forged piece (blank) is reproduced as a negative in the top and bottom forging dies. Preferably, closed forging dies are used. This offers the advantage that the blank material is handled in a very material-saving manner, because the volume of the blank is only somewhat greater than that of the finished half-shell. 
         [0012]    In another advantageous embodiment of the invention, a housing comprises two half-shells. These half-shells exhibit identical outer contours after press forming. This offers the advantage that the top half-shell of a housing can be produced by using the same forging dies as those used for the bottom half-shell of the housing, so that only one set of forging dies is needed. This saves tool costs. The various half-shells can have different eyelets for the attachment of holders. These differences are machined into the corresponding half-shells only after press forming is complete. 
         [0013]    Additional advantageous embodiments of the invention are set forth in detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0014]    In the following, preferred exemplary embodiments of the invention will be described in detail on the basis of the schematic drawing. Shown therein are: 
           [0015]      FIG. 1  is a plan view of a blank according to the invention, and 
           [0016]      FIG. 2  is an oblique view of a half-shell according to the invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0017]    Shown in  FIG. 1  is a plan view of an essentially rectangularly shaped blank  2  according to the invention. Preferably, the flat blank  2  is drop-forged beforehand using a closed forging die. The blank  2  has a top lengthwise edge  4  and a bottom lengthwise edge  6 , which are joined at their ends via a first cross edge  8  depicted on the left in  FIG. 1  and a second cross edge  10  depicted on the right in  FIG. 1 . The outer face  12  can be seen between the edges  4  to  10 . A first flange projection  14  is formed on the outer face  12  along the top lengthwise edge  4  and has the maximum thickness d m  of the blank  2 . Furthermore, a second flange projection  16  is formed on the outer face  12  along the bottom lengthwise edge  6  and likewise can have the maximum thickness d m  of the blank  2 . The blank  2  is designed to be somewhat thinner between the two flange projections  14  and  16  and exhibits a thickness d R  that is less than the maximum thickness d m . 
         [0018]    The front first contact surface  13  borders the bottom lengthwise edge  6  on the outer face  12 . The rear second contact surface  15 , which is not depicted, borders the top lengthwise edge  4  on the outer face  12 . The third contact surface  17  borders the first cross edge  8  on the outer face  12 . The fourth contact surface  19 , which is not depicted, borders the second cross edge  10  on the outer face  12 . 
         [0019]    A plurality of cross ribs  18  to  30  lie between the flange projections  14  and  16  and, in this case, are parallel to the cross edges  8  and  10 . The position of the ribs is typically defined by the strength requirements. In this case, all cross ribs  18  to  30  have the same thickness d R . Molded between the cross ribs  22  and  24  are two upset eyelets  32  and  34 , which can be bored out in a latter processing step. It is also conceivable that, instead of the upset eyelets  32  and  34 , eyelets can be produced directly by press forming. This would save a later machining step (for example, boring) that produces material debris. 
         [0020]    The cross ribs  26  to  30  can be joined to one another via a lengthwise rib  36 , if this is required for reasons of structural mechanics, for example. 
         [0021]    The outer face  12 , together with all corresponding contours, such as ribs and/or upset eyelets or eyelets, may be produced advantageously without any machining allowance during drop forging, so that any later machining of this outer face  12  is dispensed with. 
         [0022]    The blank  2  is than bent or rolled, so that the essentially cylindrical half-shell  40  depicted in  FIG. 2  is created. In this process, particularly the lengthwise edges  4  and  6  are bent, so that the first and second contact surfaces  13  and  15  describe a semicircle, with the outer face  12  constituting the jacket surface of the half-cylinder. Once bending is complete, the individual contact surfaces  13 ,  15 ,  17 , and  19  may be additionally finished, preferably by machining them, so as to obtain the required dimensional accuracy. Thus, a particularly high planarity of the contact surfaces  17  and  19  is required if two such half-shells are to be assembled to form a housing. As a result, it is then ensured that the required tightness is achieved between two half-shells  40  at the contact surfaces  17  and  19 . Various indentations  44  may be present on the inner face  42  of the half-shell  40 .