Abstract:
The invention relates to a method and a forming machine for working a workpiece, for example by deforming it or fixing it in another workpiece, in which the workpiece is fitted over a mandrel, at least a part of the mandrel is expanded so as to fix the workpiece, the workpiece and at least one tool, such as a forming roller, are rotated about an axis relative to each other and the workpiece is worked by means of said tool. Less than half of the expanded or expandable part of the mandrel engages portions of the workpiece that are being worked with the tool.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is a continuation of and claims priority of International patent application Serial No. PCT/NL03/00186, filed Mar. 11, 2003, and published in English the content of which is hereby incorporated by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The invention relates to a method and a forming machine for working a workpiece, for example by deforming it or fixing it in another workpiece, in which the workpiece is fitted over a mandrel, at least a part of the mandrel is expanded so as to fix the workpiece, the workpiece and at least one tool, such as a forming roller, are rotated about an axis relative to each other and the workpiece is worked by means of said tool.  
           [0003]    Expandable mandrels are known and they are e.g. locally provided with segments along their circumference, which segments can be moved outwards and inwards. When a workpiece is fixed in position on the mandrel, the segments are moved in outward direction until they engage the inner side of portions of the workpiece that are to be processed. Mandrels of this type are liable to relatively quick wear. In addition, it frequently happens that the workpiece can only be removed from the mandrel with difficulty.  
           [0004]    For the sake of completeness it is noted that International patent application PCT/NL01/00939 (not pre-published) makes mention of an expandable mandrel.  
         SUMMARY OF THE INVENTION  
         [0005]    The object of the invention is to improve the method and the forming machine as referred to in the first paragraph.  
           [0006]    To this end, the method and the forming machine according to the invention are characterized in that less than half of the expanded or expandable part of the mandrel engages portions of the workpiece that are being worked with the tool. Preferably, the expanded part of the mandrel remains substantially clear of those portions of the workpiece that are being worked.  
           [0007]    The load on the expandable part, and thus the extent of wear on the mandrel, is significantly reduced in this manner, and in the case of mandrels whose expandable part is segmented, the material of the workpiece is prevented from being pressed into the openings between the segments during the operation and thus interfere with the contraction of the mandrel.  
           [0008]    Preferably, the mandrel is provided with a stop for the workpiece. Thus, workpieces can be mounted on the mandrel in a simple manner, for example by pressing the workpiece against the stop by means of the expandable part of the mandrel, thereby defining the axial position of the workpiece.  
           [0009]    Depending inter alia on the nature of the workpiece and of the final product, it is possible to rotate the workpiece while the tool remains stationary in a rotational direction, to rotate the tool while the workpiece remains stationary in the rotational direction or to rotate both. For examples of the various methods reference is made to International patent applications PCT/NL01/00563, PCT/NL01/00564 and PCT/NL01/00565 and to the aforesaid International patent application PCT/NL01/00939.  
           [0010]    Within the framework of the invention, the term “mandrel” comprises any device that can be inserted into a workpiece and on which said workpiece can be fixed temporarily. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The invention will be explained in more detail hereinafter with reference to the appended figures, which show a number of embodiments of the method and the apparatus according to the present invention.  
         [0012]    [0012]FIG. 1 is a schematic top plan view of an example of a forming machine.  
         [0013]    [0013]FIG. 2 is a top plan view, partially in section, of a detail of the forming machine of FIG. 1.  
         [0014]    [0014]FIGS. 3A and 3B are cross-sectional views of a first embodiment of a mandrel according to the invention for use in the forming machine of FIGS. 1 and 2.  
         [0015]    [0015]FIGS. 4A-4D show four steps of an example of a method according to the present invention.  
         [0016]    [0016]FIGS. 5A-6B show two further examples of a mandrel according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    Insofar as parts are identical or have the same function in the various embodiments, said parts will be indicated by the same numerals hereinafter.  
         [0018]    [0018]FIGS. 1-3B show a forming machine  1  comprising a chuck  2  for setting up a workpiece, such as the illustrated, already deformed metal cylinder  3 . The chuck  2  can be rotated about an imaginary axis  5 , for example by means of an electric or hydraulic motor present within the housing  4 . Disposed on either side of the workpiece  3  is a forming tool, such as a forming roller  6 ,  6 ′, which is rotatably mounted on a respective holder  7 ,  7 ′, which is fitted in an upper slide  8  in a housing  9 . The upper slide  8 , and thus the forming roller  6 , can be reciprocated over a guide present in the housing  9 , for example by means of a hydraulic servo motor or cylinder, in a (Y) direction extending at angle of e.g. 45-90° to the axis  5 .  
         [0019]    The housing  9  is mounted on a lower slide  10 , which is largely hidden from view by bellows  11  and which is mounted on a guide, which in turn forms part of a machine bed. The lower slide  10  can be reciprocated over said guide  12 , also in this case by means of a hydraulic servo motor or cylinder, for example, in an (X) direction extending perpendicularly to the direction of movement of the upper slide  8 .  
         [0020]    For more details on a suitable example of an assembly of a forming roller and the associated slide and driving means, reference is made to European patent application EP 0 125 720.  
         [0021]    In the operation that is shown in FIGS. 1-3, the cylinder  3  is rotated at a suitable speed, while the forming rollers  6 ,  6 ′ are pressed against the outer wall thereof. The forming rollers  6 ,  6 ′ are driven in such a manner that they translate reciprocatingly in the Y-direction with a frequency that has been adapted to the frequency of the rotation of the cylinder  3 , in order to thus follow and further deform the deformed part, the central axis  12  of which includes an angle with the axis  5 .  
         [0022]    Following that, the forming rollers  6 ,  6 ′ and the cylinder  3  are moved in the X-direction relative to each other, for example in such a manner that the forming rollers  6 ,  6 ′ are initially spaced from the end of the workpiece  3  by some distance and subsequently move towards said end. During this movement, the relevant part of the workpiece can be deformed by adjusting the reciprocating translating movement of the forming rollers  6 ,  6 ′. Depending inter alia on the properties of the material, the wall thickness, the extent of deformation and diameter reduction, a larger or smaller number of working passes or steps will be required.  
         [0023]    Present in the cylinder  3  is an insert piece  13 . To this end the forming machine  1  is provided with a forming head  14 , which is rotatably mounted (about the axis  5 ) in a housing  15 , which housing can be reciprocated, by means of a slide (not shown), over two guide rails  16 , which are in line with the axis  5 . The head  14  may freely rotate or be rotated about the imaginary axis  5 , for example by means of an electric motor disposed within the housing  15 , and it is provided with an eccentric, sloping mandrel  17 , on which the insert piece  13  is clamped down.  
         [0024]    During operation, the end and the edge of the end of the cylinder  3  are deformed to conform to the shape of the end and the cylindrical edge of the end of the insert piece  13  by means of the forming rollers  6 ,  6 ′, as described above, after which said edges form a strong and possibly gastight (clamped) connection.  
         [0025]    [0025]FIG. 2 schematically shows a mandrel according to the prior art, while FIGS. 3A and 3B show a mandrel  17  according to the invention, which can be used in the forming machine  1 . Said mandrel  17  comprises an outer portion  18 , within which an inner portion  19  is present, which inner portion can be reciprocated in the axial direction of the mandrel  17 . At the location of the end of the mandrel  17 , the inner portion  19  comprises a (frusto)conical portion  20 , whose circumference substantially corresponds to the circumference of the end of the outer portion  18  as regards the shape, a circularly cylindrical shape in this specific example, and the dimensions. Positioned between the conical portion  20  and the end of the outer portion  18  is an element, a ring  21  in this example, which is expandable in radial direction. Such a ring  21  may be made of an elastic, at any rate a flexible material, e.g. rubber or a metal coil spring.  
         [0026]    In FIG. 3A the inner portion  19  is pressed away from the end of the outer portion  18  against the action of a spring  25  by pressure means  22 , in this example a pneumatic or hydraulic stamp  23  which cooperates with a rocker  24 . As a result, the ring  21  is hardly loaded, if at all, in the axial direction, and said ring  21  has an external diameter that corresponds to or is smaller than the largest external diameter of the cone  20 . In this condition it is possible to slide the insert piece  13  over the mandrel  17 . Once the insert piece  13  has reached the desired axial position, the force that is exerted on the inner part  19  with the aforesaid pressure means is reduced to such an extent that the conical portion  20  is moved in the direction of the outer portion  18  by the spring  25 . As a result, the ring  21  is compressed in the axial direction, causing it to expand in the radial direction and engage the inner side of the insert piece  13  just behind the cylindrical edge to be worked.  
         [0027]    The insert piece  13  that is shown in the examples consists of an inner housing  26  or a part thereof for catalytic converter units for passenger cars and the like. The insert piece  13  that is shown in FIG. 2 moreover comprises a so-called catalytic brick or substrate  27  provided with an insulating casing  28 .  
         [0028]    [0028]FIGS. 4A-4D show four steps of a method in which the cylinder  3 , an insert piece  13  and a mandrel  17 , which is again provided with an expandable ring  21  in this example, are positioned on the same axis  5 . The mandrel  17  is moreover provided with a ring-shaped stop  29  in this example. The insert piece  13  substantially consists of a rotationally symmetrical cone, which cone terminates in a circularly cylindrical end.  
         [0029]    In a first step, the insert piece  13  is slid over the mandrel  17  in the axial direction until it butts against the stop  29 . Then the ring  21 , which is positioned near the transition between the cone and the end at that point, is expanded in the radial direction (cf. FIGS. 3A and 3B), with the ring  21  engaging the inner side of said parts and in addition pressing the insert piece  13  firmly against the stop  29 . Then the insert piece  13 , whose position relative to the mandrel  17  is fixed at that point, is placed into the cylinder  3  and accurately positioned relative to a part that is present therein, for example a substrate  27 , by means of said mandrel  17 . Following that, the end of the cylinder  3  can be closed by means of forming rollers (not shown), with the (axial and radial) positions of the insert piece  13  relative to the substrate  27  and the cylinder  3  remaining constant. As soon as the cylinder  3  is closed, the expansion of the ring  21  is undone and the finished or semi-finished product thus obtained can be removed from the mandrel  17 .  
         [0030]    [0030]FIGS. 5A and 5B show the position of the rest and the expanded position of a variant of the mandrel  17  according to FIGS. 4A-4D. This variant comprises a hollow ring  21  made of an elastic, at any rate a flexible material, which can be filled with a gas or a liquid via a pipe  30  so as to cause the circumference of the ring to increase in the radial direction.  
         [0031]    [0031]FIGS. 6A and 6B show a variant, in which one or more brackets  31  are arranged along the circumference of the end of the mandrel  17 , being rotatable about a point located near their centre. The rear end of each of said brackets  31  extends radially inwardly. When a pressure is exerted on said rear ends by means of a stamp  32 , the front end of said brackets  31  will move outwardly until they engage the inner side of a workpiece  13 .  
         [0032]    Although the examples as described above are combinations of workpieces in all cases, the forming machines and the methods according to the invention are also suitable for working one-part workpieces, of course.  
         [0033]    The forming machines according to the invention preferably comprise a control unit. Such a control unit is for example arranged for controlling the means for moving the rollers in the X-, Y- and radial directions according to a control programme stored in a memory, in such a manner that the forming rollers will follow one or more desired paths for deforming the workpiece into the desired finished or semi-finished product.  
         [0034]    The invention is not limited to the embodiments as described in the foregoing, which can be varied in several ways within the scope of the invention as defined in the claims. Thus, the mandrel can be adapted to products having different shapes. Besides the concentric and sloping mandrels as described above, it is also possible to use a mandrel whose central axis extends eccentrically with respect to the central axis of the (second) workpiece, for example.