Abstract:
A method for manufacturing hollow shafts having end portions of greater wall thickness and at least one intermediate portion of reduced wall thickness, from a tube having constant wall thickness. The method includes providing a mandrel having diameters stepped over its length, with a first longitudinal section having a smallest diameter and at least one further longitudinal section having a further larger diameter. Reducing the external diameter of a first portion of the tube over the first longitudinal section of the mandrel to produce the first end portion. Reducing the external diameter of a middle portion of the tube over the at least one further longitudinal section of the mandrel to produce the at least one intermediate portion. Reducing the external diameter of a further portion of the tube over the first longitudinal section of the mandrel to produce the second end portion.

Description:
TECHNICAL FIELD 
   The present invention relates to a method for manufacturing hollow shafts having end portions of greater wall thickness and at least one intermediate portion of reduced wall thickness, from a tube previously having constant wall thickness, using a mandrel having diameters stepped over the length, which has a first longitudinal section having a smallest diameter and at least one further longitudinal section having a further larger diameter. 
   BACKGROUND 
   A method of this type is known from U.S. Pat. No. 6,837,091. In this case, a first end portion of the tube is reduced freely in external diameter in a matrix without internal support, a middle tube portion having lesser wall thickness and larger external diameter is manufactured by stretching over an internal mandrel of constant diameter, and a second end portion of the tube is manufactured through reduction in external diameter in a matrix in the opposite drawing direction or through hammering without internal support. 
   A method of the type cited, in which a first portion of a tube is reduced over a calibration mandrel which is introduced from the tube end discussed, and in which an intermediate portion of the tube is reduced over a stretching mandrel, which is introduced from the other tube end, is known from DE 35 06 220 A1. The second end portion of the tube is reduced over the calibration mandrel again after changeover of the tube. The stretching mandrel comprises two longitudinal sections of different diameters having a conical transition area. 
   SUMMARY OF THE INVENTION 
   The present invention provides a dimensionally accurate method, which may be performed efficiently, for manufacturing hollow shafts of the above-mentioned type. 
   A method of the type cited is provided, having the following steps: reducing the external diameter of a first portion of the tube over the first longitudinal section of the mandrel to produce the first end portion of the hollow shaft; reducing the external diameter of at least one middle portion of the tube over the at least one further longitudinal section of the mandrel to produce the at least one intermediate portion of the hollow shaft; and reducing the external diameter of a further portion of the tube over another longitudinal section of the mandrel to produce the second end portion of the hollow shaft. 
   This method has the advantage that all longitudinal portions of the hollow shaft are reduced over a single mandrel, the orientation of the direction of tube and mandrel to one another remaining the same. In this case, the method is applied in such a way that in the event of one or more changes of the relative position of mandrel and tube, the entire process up to manufacturing a finished hollow shaft may occur in a uniform feed direction of mandrel and tube in relation to one another without a tool change. For this purpose, the first end portion and one or more intermediate portions of the hollow shaft, having a reduced wall thickness in each case, may be produced with unchanged axial position of the mandrel in relation to the tube. If the two end portions are to have the same cross-section, the second end portion is particularly also to be produced over the first longitudinal section of the mandrel. Furthermore, one or more further intermediate portions, each having an increased wall thickness respectively, and the second end portion of the hollow shaft may be produced with a changed axial position of the mandrel in relation to the tube in each case, drawn out from the tube step-by-step. Finally, between the above-mentioned shaping steps, at least two intermediate portions having alternating wall thicknesses, first increased in relation to the preceding wall thickness and then reduced again in relation to the last wall thickness, may be produced. The reduction of the external diameter of the tube can be performed through cold drawing using a matrix; alternatively, the reduction of the external diameter of the tube is also possible through swaging, roll bending, or rolling, however. 
   Furthermore, transitions between end portions and intermediate portions and transitions between intermediate portions of different wall thicknesses be formed by internal conical surfaces having a cone opening angle between 5 and 45°. A further embodiment provides that the wall thickness ratio between end portions and the adjoining intermediate portion of smallest wall thickness is greater than 1.6. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred exemplary embodiments for performing the method according to the present invention are illustrated in the drawing and will be described in the following. 
       FIG. 1  shows, in a method for manufacturing a hollow shaft having a uniform middle intermediate portion: 
     A) the tube in the starting state; 
     B) the tube having inserted mandrel and applied matrix; 
     C) the tube after the reduction of the first tube end to form the first end portion and the stretching of a middle intermediate portion; 
     D) the tube before the reduction of the second tube end; 
     E) after the reduction of the second tube end to form the second end portion; and 
     F) the finished hollow shaft. 
       FIG. 2  shows, in a method for manufacturing a hollow shaft having a multiply stepped intermediate portion: 
     A) the tube in the starting state; 
     B) the tube having inserted mandrel and applied matrix; 
     C) the tube after the reduction of the first tube end to form the first end portion and a first intermediate portion and the stretching of a middle intermediate portion; 
     D) the tube before the reduction of a second intermediate portion; 
     E) the tube after the reduction of a second intermediate portion; 
     F) the tube before the reduction of the second tube end; 
     G) the tube after the reduction of the second tube end to form the second end portion; and 
     H) the finished hollow shaft. 
       FIG. 3  shows, in a method for manufacturing a hollow shaft having a multiply stepped intermediate portion in a second embodiment: 
     A) the tube in the starting state; 
     B) the tube having inserted mandrel and applied matrix; 
     C) the tube after the reduction of the first tube end to form the first end portion and a first intermediate portion and the stretching of a first thin-walled intermediate portion; 
     D) the tube before the reduction of a thick-walled intermediate portion; 
     E) the tube after the reduction of the thick-walled intermediate portion and the stretching of a second thin-walled intermediate portion; 
     F) the tube before the reduction of the second tube end; 
     G) the tube after the reduction of the second tube end to form the second end portion; 
     H) the finished hollow shaft. 
   

   DETAILED DESCRIPTION 
     FIG. 1A  shows an illustration a of a tube  11  in the starting state, in which a first tube end  12  is identified on the left and a second tube end  16  is identified on the right, while a middle portion is identified by  14 . 
   It may be seen in  FIG. 5B  that a matrix  31  is applied to the left first tube end  12  and a mandrel  21  is inserted into the interior of the tube, which essentially terminates with the left first tube end  12  and projects out of the right second tube end  16 . The mandrel  21  has a first longitudinal section  22  having minimal diameter and a further longitudinal section  24  having a diameter which is essentially seated fixed in the tube  11 . A conical transition section  27  is located between the first longitudinal section  22  and the further longitudinal section  24 . 
     FIG. 1C  shows how two phases of the shaft manufacturing have already been finished through a relative movement of matrix  31  (to the right) and mandrel  21  (to the left). Using the matrix  31 , the first tube end has been reduced in external diameter while increasing the wall thickness to produce a first shaft end  12 ′ over the longitudinal section  22  of the mandrel  21 . Furthermore, the middle portion has been reduced to form an intermediate portion  14 ′ of the hollow shaft  11 ′ over the second longitudinal section  24  of the mandrel  21 . An internal conical transition area  17  has been formed over the transition section  27 . 
   In  FIG. 1D , the mandrel  21  has been pulled back into a second axial position in relation to the matrix  31 , the first longitudinal section  22  of the mandrel  21  being inserted axially into the second tube end  16 . 
   In  FIG. 1E , the tube  11  is shown after the completion of a third phase of the shaft manufacturing, the second tube end having been reduced in external diameter to manufacture a second shaft end  16 ′ with wall thickness increased, the tube being supported radially on the inside on the longitudinal section  22  of the mandrel  21 . An internal conical transition area  20  between the intermediate portion  14 ′ and the second end portion  16 ′ of the hollow shaft  11 ′ is formed for this purpose solely by reducing the external diameter without internal support. 
   In  FIG. 1F , the finished hollow shaft  11 ′ having the two strengthened shaft ends  12 ′,  16 ′ and the intermediate portion  14 ′ of reduced wall thickness is shown, two internal conical transition areas  17 ,  20  being recognizable. 
   In  FIG. 2A , a tube  11  of constant wall thickness is shown in the starting state. 
   In  FIG. 2B , a matrix  31  is applied to the tube  11 , while a mandrel  21  is inserted into the interior of the tube, which comprises a first, a second, and a further longitudinal section  22 ,  23 ,  24  and conical transition sections  27 ,  29  lying between them, which increase in diameter from the free end on the left to the end on the right. The matrix  31  is applied to the left tube end  12 . The right tube end  16  may be axially supported. 
   In  FIG. 2C , a partially finished hollow shaft  11 ′ is shown after performing three manufacturing phases. By reducing the external diameter while increasing the wall thickness, a first shaft end  12 ′ has been produced, which is supported radially on the inside on the first longitudinal section  22  of the mandrel  21 . A first intermediate portion  13  has also resulted with reduction of the external diameter and simultaneous stretching, which is supported on the longitudinal section  23  of the mandrel  21 , and a second intermediate portion  14 , which is supported on the longitudinal section  24  of the mandrel  21 , has resulted with reduction of the external diameter. 
   In  FIG. 2D , the mandrel  21  is pulled back into an axial position in relation to the matrix  31  in which the longitudinal section  23  of the mandrel  21  is inserted into the second tube end  16  of the tube  11 , which has not yet been shaped. The tube  11  is held axially in the matrix  31 . 
     FIG. 2E  shows how a further intermediate portion  15  has resulted through reduction of the external diameter with partial stretching, whose wall thickness and length corresponds to the first intermediate portion  13  of the hollow shaft  11 ′ and which is supported radially on the longitudinal section  23  of the mandrel  21 . 
     FIG. 2F  shows how the mandrel  21  is again pulled to the right out of the matrix  31 , in which the hollow shaft  11  is held axially, the first longitudinal section  22  of the mandrel  21  now being inserted into the last unshaped portion of the right tube end  16 . 
   In  FIG. 2G , it may be seen how a second shaft end  16 ′ has been manufactured by reducing the external diameter using the matrix  31 , which is supported internally on the longitudinal section  22  of the mandrel  21  with wall thickness reduction and whose length and dimensions correspond to the first shaft end  12 ′ in the present case. 
   The finished hollow shaft  11 ′ is shown in  FIG. 2H , in which the two shaft ends  12 ′,  16 ′ and the intermediate portions  13 ′,  14 ′,  15 ′ may be seen. The transitions are each formed by internal conical transition areas  17 ,  18 ,  19 ,  20 . The external diameter of the entire hollow shaft  11  is constant over the length, corresponding to the active diameter of the matrix  31 . 
   For both embodiments, it is to be noted here that in the practical application, the matrix  31  can be held axially fixed, while the entire relative motion is performed by the mandrel  21  having the tube  11  seated. Specifically, a cylindrical intake area  32 , an internal conical reduction and stretching area  33 , and an outlet cone  34  may be differentiated on the matrix. Instead of the cold drawing shown here using the matrix, milling or swaging or rolling of the external surface of the tube may also be applied, the particular tool being axially displaced in the corresponding phases in relation to the mandrel in the direction corresponding with the matrix in each case. 
   In  FIG. 3A , a tube  11  of constant wall thickness is shown in the starting state. 
   In  FIG. 3B , a matrix  31  has been applied to the tube  11 , while a mandrel  21  has been inserted into the interior of the tube, which comprises a first, a second, and a further longitudinal portion  22 ,  23 ,  24  and conical transition areas  27 ,  29  lying between each of them, which increase in diameter from the free end on the left to the end on the right. The matrix  31  is applied to the left tube end  12 . The right tube end  16  may be axially supported. 
   A partially finished hollow shaft  11 ′ is shown in  FIG. 3C  after three manufacturing phases have been performed. A first shaft end  12 ′ has been produced by reducing the external diameter while increasing the wall thickness, which is supported radially on the inside on the first longitudinal section  22  of the mandrel  21 . A first intermediate portion  13  has resulted, also with reduction of the external diameter and simultaneous stretching, which is supported on the longitudinal section  23  of the mandrel  21 , and a first thin-walled intermediate portion  14   1 , which is supported on the longitudinal section  24  of the mandrel  21 , has resulted with reduction of the external diameter. 
   In  FIG. 3D , the mandrel  21  is pulled back in relation to the matrix  31  into an axial position in which the longitudinal section  23  of the mandrel  21  is inserted into the second, still unshaped tube end  16  of the tube  11 . The tube  11  is held axially in the matrix  31 . 
     FIG. 3E  shows how a thick-walled intermediate portion  15 , which is supported radially on the longitudinal section  23  of the mandrel  21 , has resulted through reduction of the external diameter with partial stretching. Furthermore, a second thin-walled intermediate portion  14   2 , which is supported radially on the longitudinal section  24  of the mandrel  21 , has resulted through stretching of an adjoining longitudinal portion over the longitudinal section  24  of the mandrel  21 . 
     FIG. 3F  shows how the mandrel  21  has again been pulled out to the right from the matrix  31 , in which the hollow shaft  11  is held axially, the first longitudinal section  22  of the mandrel  21  now being inserted in the last unshaped portion of the right tube end  16 . 
   In  FIG. 3G , it may be seen how a second shaft end  16 ′, which is supported on the inside on the longitudinal section  22  of the mandrel  21  with wall thickness reduction and which corresponds in length and dimensions to the first shaft end  12 ′ in the present case, has been manufactured by reducing the external diameter using the matrix  31 . 
   The finished hollow shaft  11 ′ is shown in  FIG. 3H , in which the two shaft ends  12 ′,  16 ′ and intermediate portions  13 ′,  14 ′,  15 ′,  14   2 ′ may be seen. The transitions are each formed by internal conical transition areas  17 ,  18   1 ,  19   1 ,  18   2 ,  19   2 . The external diameter of the overall hollow shaft  11  is constant over the length, corresponding to the active diameter of the matrix  31 . 
   For these embodiments, it is to be noted here that in the practical application, the matrix  31  can be held axially fixed, while the entire relative motion is performed by the mandrel  21  having the tube  11  seated. Specifically, a cylindrical intake area  32 , an internal conical reduction and stretching area  33 , and an outlet cone  34  may be differentiated on the matrix. Instead of the cold drawing shown here using the matrix, milling or swaging or rolling of the external surface of the tube may also be applied, the particular tool being axially displaced in the corresponding phases in relation to the mandrel in the direction corresponding with the matrix in each case.