Abstract:
A method for producing a piston from an upper piston part and a lower piston part. A strip- or plate-shaped semifinished product made of a metal material is provided, from which an annular upper piston part or an annular blank is stamped out, which blank is finished to form an upper piston part, wherein the upper piston part is connected to a lower piston part to form a piston.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional of U.S. patent application Ser. No. 13/516,797, filed on Sep 12, 2012, which is the National Stage of PCT/DE2010/001483 filed on Dec. 17, 2010 which claims priority under 35 U.S.C. §119 of German Application No. 10 2009 059 658.5 filed on Dec. 19, 2009, the disclosure of which is incorporated by reference. The international application under PCT article 21(2) was not published in English. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for the production of a piston for an internal combustion engine, as well as to a piston that can be produced by means of this method. 
     2. The Prior Art 
     DE 103 11 149 A1 discloses a piston composed of an upper piston part and a lower piston part, which are fixed in place by means of a minimal number of weld points and are connected with one another by means of subsequent forging. Such pistons are characterized in that the upper piston part is produced from a particularly temperature-resistant and high-strength material, in order to prevent scaling, particularly in the region of the combustion bowl. However, production of such a piston is complicated and connected with significant costs. 
     SUMMARY OF THE INVENTION 
     The task of the present invention consists in making available a method for the production of a piston for an internal combustion engine, which method can be implemented with the least possible effort and reduced costs. 
     A first solution, according to the invention, consists in that a strip-shaped or plate-shaped semi-finished product made of a metallic material is made available, that a ring-shaped blank is punched out of the semi-finished product and subsequently finished to produce an upper piston part, and that the finished upper piston part is connected to a lower piston part, to produce a piston. 
     A second solution, according to the invention, consists in that a strip-shaped or plate-shaped semi-finished product made of a metallic material is made available, that at least one surface of the strip-shaped or plate-shaped semi-finished product is finished, that a ring-shaped upper piston part is punched out of the semi-finished product and subsequently connected to a lower piston part, to produce a piston. 
     A piston that can be produced with this method is furthermore an object of the present invention. 
     The present invention is characterized in that a particularly simple method for the production of a piston, which method can be implemented with few production steps and is therefore cost-advantageous, is made available. In particular, an upper piston part can be made available, which can be obtained, in particularly simple manner, from any desired material. In this way it is possible, for example, to make available a piston having a particularly high-strength and temperature-resistant upper piston part, in simple and cost-advantageous manner. 
     Advantageous further developments are evident from the dependent claims. 
     Preferably, a semi-finished product made from a steel material is used, so that the finished piston meets the requirements during engine operation in optimal manner. In particular, a hot-rolled or cold-rolled steel material is particularly well suited. 
     For the case that a blank is punched out of the semi-finished product, this blank is preferably machined level along at least one surface, for example by means of lathing or grinding. The level machined surface then forms the piston crown in the finished piston. 
     For the case that a finished upper piston part is punched out of the semi-finished product, preferably at least one surface of the semi-finished product is machined level before punching. The level machined surface then forms the piston crown in the finished piston. Of course, the upper piston part can be machined as needed after punching. 
     Depending on the requirements in an individual case, semi-finished products having a thickness of up to 15 mm can be used. 
     A preferred further development consists in that during punching, a circumferential lower recess is machined into the blank or into the upper piston part, and/or at least one circumferential lateral recess is machined into the blank or the upper piston part, by means of corresponding shaping of the punching tool. In the finished piston, the lower recess forms at least one part of a cooling channel. An outer recess forms part of a ring groove, for example. An inner recess can form part of a combustion bowl, for example. 
     The finished upper piston part can be connected with a lower piston part, to produce a finished piston, for example by means of soldering or welding. Of course, the piston can also be finished subsequently, as needed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention. 
       In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
         FIG. 1  is an exemplary embodiment of a piston according to the invention, in section; 
         FIG. 2  is a top view of a strip-shaped semi-finished product for use in the method according to the invention; 
         FIG. 3  is another exemplary embodiment of an upper piston part produced according to the method according to the invention, in section; 
         FIG. 4  is another exemplary embodiment of an upper piston part produced according to the method according to the invention, in section. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows an exemplary embodiment of a piston  10 . Because the invention can be used for all piston types and all piston materials, only one piston type will be used as an example in the following, to describe the present invention. 
     In the exemplary embodiment, the piston  10  is a two-part welded box piston, the structure of which is known as such. The piston  10  has an upper piston part  11  having a circumferential top land  12 . The upper piston part  11  forms a piston crown  11   a  as well as part of a combustion bowl  13 , and has a piston ring groove  14  below the top land  12 . The piston  10  furthermore has a lower piston part  15  having two piston ring grooves  16 ,  17  as well as pin bosses  18  that are set back relative to the piston ring grooves  14 ,  16 ,  17 . The pin bosses  18  are provided with pin bores  19  for accommodating a piston pin (now shown). The upper piston part  11  and the lower piston part  15  together form a circumferential cooling channel  21 . 
       FIG. 2  shows an exemplary embodiment of a semi-finished product  22 , here a strip-shaped semi-finished product, for use in the method according to the invention. The semi-finished product  22  consists, for example, of a hot-rolled or cold-rolled steel material of the type 42CrMo4, having a thickness of 10 mm. The cutting lines along which a ring-shaped blank or a ring-shaped upper piston part is punched out, according to the present invention, are indicated with  23 ,  24 . 
     For the case that the semi-finished product  22  is used without further processing, a ring-shaped blank  25  is punched out. The blank  25  is machined level along at least one surface, for example by means of grinding or lathing. This surface forms the piston crown  11   a  of the upper piston part  11  in the finished piston  10 . Subsequently, the finished upper piston part  11  is connected to a lower piston part  15 , to form a piston  10 , for example by means of soldering or welding, such as friction welding, electrode welding, or laser welding. Of course, the piston  10  can also be finished subsequently, as needed. 
     However, the semi-finished product  22  can be processed further before being punched, in that at least one of its surfaces  26  is machined level, for example by means of grinding or lathing. Subsequently, a ring-shaped upper piston part  11  is punched out. The level machined surface  26  forms forms the piston crown  11   a  of the upper piston part  11  in the finished piston  10 . Subsequently, the finished upper piston part  11  is connected to a lower piston part  15 , to form a piston  10 , as described above. 
       FIG. 3  shows an exemplary embodiment of a ring-shaped upper piston part  111  punched out of a semi-finished product  22 . The upper piston part  111  has a circumferential lower recess  127  that forms part of a circumferential cooling channel in the finished piston; see the cooling channel  21  in  FIG. 1 . The recess  127  is formed in that the punching tool is provided with a corresponding embossing shape, in known manner. Therefore the recess  127  is formed at the same time with the punching process. The central opening  113  of the ring-shaped upper piston part  111  forms part of a combustion bowl in the finished piston; see the combustion bowl  13  in  FIG. 1 . Of course, the same holds true analogously also for production of a blank from the semi-finished product  22 . 
       FIG. 4  shows another exemplary embodiment of a ring-shaped upper piston part  211  punched out of a semi-finished product  22 . The upper piston part  211  also has a circumferential lower recess  227  that forms part of a circumferential cooling channel in the finished piston; see the cooling channel  21  in  FIG. 1 . The upper piston part  211  furthermore has a circumferential outer recess  228  that forms part of a piston ring groove in the finished piston; see the piston ring groove  14  in  FIG. 1 . The recesses  227  and  228  are formed in that the punching tool is provided with corresponding embossing shapes, in known manner. Therefore the recesses  227  and  228  are formed at the same time with the punching process. The central opening  213  of the ring-shaped upper piston part  211  forms part of a combustion bowl in the finished piston; see the combustion bowl  13  in  FIG. 1 , Of course, the same holds true analogously also for production of a blank from the semi-finished product  22 . 
     Accordingly, while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.