Patent Publication Number: US-6988390-B2

Title: Method and installation for making a workpiece comprising at least a tubular section

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a method and to an installation for making a workpiece comprising at least one tubular part obtained by bending a metal sheet. This method and this installation are particularly adapted to the manufacture of a shadow mask support frame for a cathode-ray display tube. 
   2. Brief Description of the Related Art 
   Such a frame is used for example in the domain of the manufacture of colour televisions. The colour display cathode-ray tubes comprise a metal foil pierced with a plurality of holes or slots, called “shadow mask” and disposed between the electron gun and the display screen. Such a shadow mask is supported by a frame, generally rectangular in shape, which holds it in position in the vicinity of the display screen and, if necessary, ensures that the mask is taut in order to limit the deformations resulting from the local overheatings created by the electron beams. 
   It is known from EP-A-0 809 272 to produce a shadow mask frame from two thin metal strips joined to each other and comprising ribs for rigidification. Such a frame is light and rigid, which allows it to be used for a taut shadow mask and for a crimped shadow mask. Application FR-A-2 790 140 discloses a shadow mask frame comprising tubular parts formed by bending a metal sheet. The sheet may be bent by different methods, in particilar by hand, but a manual bending is not compatible with high-rate industrial production. Furthermore, the known methods of bending with the aid of machines comprising an apron, sometimes called “support strap”, on which a metal sheet to be bent is held with the aid of a holding clamp, and an articulated bending flap, do not allow tubular parts to be easily manufactured. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to propose a method of bending with the aid of a bending machine making it possible to manufacture workpieces comprising at least one tubular part, particularly a workpiece constituting one or more uprights of a frame supporting a shadow mask. 
   In this spirit, the invention relates to a method for making a workpiece comprising at least one tubular section obtained by bending a metal plate along at least one longitudinal edge, characterized in that it comprises steps consisting in pre-bending the plate along at least two bending edges or lines of bending then in exerting, during bending, a clamping force along at least one part of the plate by a bending member. 
   With the invention, the metal plate is efficiently displaced by the bending member, without risk of sliding that may result in an imprecise bending along the edge or line of bending. Because of the pre-bending, the plate is maintained in position on an apron or supporting beam on which it rests, without risk of buckling during subsequent bending. The force of clamping or of holding of the plate with respect to the line of bending makes it possible to hold the plate in position with respect to its environment without resorting to fixing clips which could be used inside tubular parts only with difficulty, as they would hinder the bending operations. 
   According to advantageous but non-obligatory aspects of the invention, the method incorporates one or more of the following characteristics. 
   The pre-bending is effected by immobilizing the plate on an apron by means of a retractable holding clamp. In addition, a step of preparation of the pre-bending may be provided, by weakening the metal sheet along the lines of bending. Such weakening may be effected by marking or punching through a part of the thickness of the metal sheet, or by any other suitable method. 
   The plate is bent along different edges or lines of bending over the length of the workpiece to be manufactured, with the result that tubular sections of different basic profiles are formed. This makes it possible to produce workpieces of elaborate geometry, such as shadow mask support frames. 
   The plate is bent about at least one virtual geometrical axis defined by the cooperation of the bending member and of guiding means associated therewith. 
   The clamping force is essentially exerted on the outside of a tubular section of the workpiece, in the absence of a tightening effort or force exerted by a holding clamp or like equipment. This takes into account the fact that the use of a holding clamp is delicate with a tubular workpiece, and even impossible if it has sections of different basic profiles. 
   The clamping force is directed substantially in the direction of the bending edge or line of bending. 
   The clamping force is substantially perpendicular to the bending edge. 
   The clamping force stresses a part of the metal plate parallel to itself and perpendicularly to the bending effort exerted on this part by the bending member. 
   The clamping force is adapted as a function of the position of the bending member. This aspect of the invention makes it possible to take into account the dimensional variations of the plate in the course of the bending operation, such variations resulting in particular from the localized stresses at the edge, or line of bending, and of its radius of curvature. It also makes it possible to avoid an interference between the elements exerting a clamping force at two opposite edges, or lines of bending, of the plate. 
   The method further comprises a step consisting in causing a first part of the plate to overlap a second part thereof and in reducing the clamping force exerted on the second part before these parts are welded together. This aspect of the invention ensures that the overlapping parts are in elastic contact during welding, which allows this welding to be efficient and lasting. 
   The method also comprises a step consisting in bending the plate about at least one virtual axis defined as the geometrical axis of a cylindrical cradle for guiding the bending member. The use of a virtual axis makes it possible to move the bending member without resorting to a hinge capable of interfering with other parts of the installation and dedicated to a bending along another edge or line bending. In particular, it may be provided to bend the plate about different bending axes depending on the length of the workpiece, using bending members guided by cradles of different geometrical axes corresponding to these bending axes. 
   The method comprises a step consisting, after formation of a plurality of tubular sections, in shaping them into a closed frame by bending joining sections, between two adjacent tubular sections, perpendicularly to the principal directions of these tubular sections. 
   The method comprises a step consisting in applying, by suction or magnetic attraction, a part of the sheet metal plate against a part of the bending member. 
   The invention also relates to an installation for carrying out the method described hereinabove and, more specifically, to an installation comprising at least one member for bending a metal plate along a longitudinal edge or bend line of a tubular section of the frame, characterized in that the bending member is equipped with means for exerting on a part of the plate a clamping force countering a sliding of a part of the plate along the bending member, while the bending member is articulated about a virtual geometrical axis located inside the corresponding tubular section. 
   According to advantageous but non-obligatory aspects of the invention, the installation incorporates one or more of the following characteristics. 
   A plurality of bending members are adapted to bend the plate along distinct lines or edges, with the result that tubular sections of different basic profiles are formed. 
   The clamping means are constituted by at least one heel forming a stop for abutment of the plate. This heel may extend over substantially the whole length of the line or edge. It is also possible to provide a plurality of heels distributed over the length of the bending line or edge and separated by spaces for receiving holding heels used for bending the plate along another line or edge. 
   The clamping means have a variable position with respect to the bending line or edge. This may come from the fact that the installation comprises means for adjusting or adapting the effort exerted by the clamping means on the plate. 
   The bending member comprises at least one surface for bearing against the plate and at least one circular-base cylindrical surface adapted to cooperate with a circular-base cylindrical surface of a cradle, these cylindrical surfaces being centered on a virtual axis of bend of the plate. The use of such a cradle makes it possible to guide the bending member without resorting to a hinge that could interfere with adjacent devices. In that case, the installation may be provided to comprise a plurality of bending members distributed over the length of the plate and cooperating with cradles of which the cylindrical surfaces have parallel geometrical axes offset with respect to each other. This makes it possible to bend the plate along distinct longitudinal lines or edges, over its length, which enables tubular sections of different geometries to be shaped, corresponding for example to distinct sides of a frame to be made. The bending member or members are advantageously equipped with an outer rib forming a cylindrical surface adapted to cooperate with the cylindrical surface of the corresponding cradle, these cylindrical surfaces being substantially of the same radii. According to an advantageous embodiment of the invention allowing tippings of great amplitude, the bending member or members are guided with respect to the cylindrical surface of the cradle by telescopic segments which slide in one another. The surfaces of the ribs, the telescopic segments and/or the surfaces of the cradles may be equipped with sliding balls or rollers. 
   The installation comprises a tool for shaping the workpiece, the tool including elements for supporting tubular sections of the workpiece provided with means for receiving and immobilizing these tubular parts, these elements being articulated with respect to one another. This tool allows the final shaping of the frame after the tubular parts have been produced. At least one of the articulated elements may be provided to be adjustable in length, which makes it possible to adapt the tool to the manufacture of frames of different dimensions. The articulated elements may also be provided to be adapted to form with one another a closed figure of predetermined geometry, corresponding to the geometry of a frame formed by the manufactured workpiece. The closed nature of the figure obtained makes it possible to obtain an increased geometrical precision thanks to a universal positioning of the different elements constituting the tool. According to an advantageous form of embodiment of the invention, at least one of the articulated elements is equipped with a member, of cross-section substantially in the form of a U and adapted to receive at least one shim for blocking a tubular section in place in the member, means being provided to immobilize the shim on this member. 
   At least one of the bending members is equipped with a blade forming shears for cutting out the plate during bending thereof. 
   Finally, the invention relates to the use of the method or of the installation mentioned hereinabove for manufacturing a shadow mask support frame for a cathode-ray tube. 
   At least one of the bending members is equipped with a blade forming shears for cutting out the plate during bending thereof. 
   Finally, the invention relates to the use of the method or of the installation mentioned hereinabove for manufacturing a shadow mask support frame for cathode-ray tube. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more readily understood and other advantages thereof will appear more clearly in the light of the following description of two forms of embodiment of an installation for manufacturing a shadow mask support frame and of its method of implementation, given solely by way of example and made with reference to the accompanying drawings, in which: 
       FIG. 1  schematically shows a shadow mask frame on which is disposed a partially shown shadow mask; 
       FIG. 2  schematically shows a perspective view of a part of an installation for manufacturing the frame of  FIG. 1 , the frame not having been shown; 
       FIG. 3  schematically shows a part of the frame of  FIG. 1  when it is in place in the installation of  FIG. 2 ; 
       FIG. 4  is a section along line IV—IV in  FIG. 2 , the frame being shown in place in the installation; 
       FIG. 5  is a section similar to  FIG. 4  during a first step of the method of the invention, prior to the configuration of  FIG. 4 ; 
       FIG. 6  is a section similar to  FIG. 4  during a subsequent step of the method of the invention, later than the configuration of  FIG. 4 ; 
       FIG. 7  is a section similar to  FIG. 4  during a second subsequent step of the method of the invention 
       FIG. 8  is a section along line VIII—VIII in  FIG. 2 , the frame being shown in place in the installation; 
       FIG. 9  is a section similar to  FIG. 8  during a subsequent step of the method of the invention; 
       FIG. 10  is a section similar to  FIG. 8  during a second subsequent step of the method of the invention; 
       FIG. 11  is a view in perspective of another part of the installation of the invention, a frame in the course of manufacture being shown above this part of the installation; 
       FIG. 12  is a view on a larger scale of detail XII in  FIG. 11 , the frame being in place on the tool; 
       FIG. 13  is a view similar to  FIG. 12  during a subsequent step of manufacture of the frame; 
       FIG. 14  is a plan view of the part of the installation shown in  FIGS. 11 to 13 , in the course of use; 
       FIG. 15  is a partial schematic representation in section of a part of a plate in the course of bending; 
       FIG. 16  schematically shows a perspective view of a part of the installation; 
       FIG. 17  is a schematic section of a part of an installation in accordance with a second form of embodiment of the invention; 
       FIG. 18  is a view similar to  FIG. 13  for the installation of  FIG. 17 , and 
       FIG. 19  is a section along line XIX—XIX in  FIG. 18 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  schematically shows a shadow mask  1  mounted on a shadow mask supporting frame  2 . The frame is generally rectangular in shape and comprises two lateral uprights  3 ,  3 ′ and two end uprights  4 ,  4 ′. The shadow mask is constituted by a thin metal foil, for example of iron-nickel alloy with a low coefficient of expansion, pierced with holes  5  and fixed by welding on upper edges  6 ,  6 ′ of the end uprights  4 ,  4 ′. Different forms of shadow mask are possible as a function of the cathode-ray tube with which it is to be associated. In the example shown, the shadow mask is substantially planar, but it may equally well be curved into a portion of cylinder. The mask I may in addition be taut, i.e. subjected to a tension parallel to the lateral uprights  3 ,  3 ′ of the frame  2 . 
   The uprights  3 ,  3 ′,  4  and  4 ′ are formed by bending a sheet metal so as each to constitute a tubular element. These four uprights may be obtained by bending a single metal plate. It is also possible to provide using one bent plate for each upright or one plate for two contiguous uprights. 
   In the example illustrated in the Figures, a single metal plate  10  is used for making the four tubular uprights  3 ,  3 ′,  4 ,  4 ′. This plate is partially visible in  FIG. 3  after steps of cutting out assembly tongues  11  and of pre-marking longitudinal edges  12  to  17 . 
   At the level of the edges  12  to  14 , the plate  10  forms the end upright  4 . At the level of edges  12  and  15  to  17 , the plate  10  forms the lateral upright  3 . In practice, the part of the plate  10  shown in  FIG. 3  corresponds to the corner  7  of the frame  2  at the level of which the join is made between the uprights  3  and  4 . 
   The plate  10  is shaped in the configuration of  FIG. 3  by operations of cut out, stamping and bending using, in particular, punches intended to create in the plate  10  an edge  12  extending over substantially the whole of its length while the edges  13  to  17  extend over only a part of the plate  10 , the edges  13  and  15  being parallel to each other but offset, i.e. distant from the edge  12  by different distances d 1  and d 2 . 
   As is more particularly visible in  FIG. 5 , the pre-bending of the plate  10  is effected by immobilizing this plate on an apron or support strap  101  thanks to a holding clamp  107  and by bending the plate  10  as represented by arrows F, which has the effect of creating the lines of bend  12  and  13 . Another holding clamp is used at the level of the upright  3 , which makes it possible to continue the creation of the line of bend  12  and to create the line of bend  15 . This second holding clamp is also configured in order to allow the creation of the lines of bend  16  and  17 . 
   These operations of pre-bending make it possible to attain the configuration of  FIG. 4  in which the holding clamp  107  is retracted or withdrawn from the interior space of the plate  10  as represented by arrow F′. It will be noted that the shape of the holding clamp  107  is compatible with its withdrawal from the interior of the plate  10  in the configuration of  FIG. 4 . 
   Thanks to this operation of pre-bending, the plate  10  is immobilized with respect to the installation of the invention, as it is in abutment along the two bending edges  12  and  13  or  12  and  15  which are substantially parallel. 
   Pre-bending may be prepared by a marking of the lines of bend, for example by a stamping through a part of the thickness of the plate  10 , in particular of 25%. 
   In general, the pre-bending of the plate  10  may be effected on the machine shown in the Figures or on another machine, without departing from the scope of the present invention. 
   In the event of an upright being made whose section has more than three sides, such as upright  3 , preliminary pre-bendings are necessary in order to make the edges of the type of edges  16  and  17 . Such a preliminary pre-bending is also used in the case of the upright  4  for making the edge  14 . 
   The installation  100  of the invention comprises the apron  101  on which is placed a central part  21  of the plate  10 . Studs, of which only one is visible in the Figures with reference  102 , extend from this plate  101  and are intended to traverse openings  22  provided in the part  21 , so as to position the plate  10  on the base plate  101 . 
   From the part  21  there extend two flanges  23  and  24  of the plate  10  intended to form the upright  4 . From this same same central part  21  there extend two other flanges  25  and  26  intended to form the upright  3 . 
   The flanges  23  and  25  are connected to the part  21  along the edge  12 . The flanges  24  and  26  are respectively connected to the part  21  along the edges  13  and  15 . The flange  23  is connected to a border  27  by the line of bend or edge  14  while the flanges  25  and  26  are both divided into two panels  25   a ,  25   b  and  26   a ,  26   b  respectively, by the lines of bend or edges  16  and  17 . 
   The installation  100  comprises a bending jaw  103  intended to bend the flange  23  down in the direction of part  21  thanks to an effort represented by arrow F 1 . The jaw  103  comprises plate  103   a  whose length, parallel to a longitudinal axis X–X′ of the installation  100 , is adapted to the length of the flange  23 . The face  103   a   1  of the plate  103   a  intended to be in contact with the flange  23  is substantially planar. The plate  103   a  is equipped, on its face  103   a   2  opposite the face  103   a   1 , with two ribs  103   b  extending opposite the flange  23  in directions substantially perpendicular to axis X–X′. These ribs  103   b  each form a convex surface  103   c  in the form of a portion of cylinder with circular base centred on a virtual axis a. “Virtual” is understood to mean the fact that the axis a is not defined by a hinge, but as being the geometric focus joining the centres of curvature of the surfaces  103   c . This axis is located inside the upright  4  and is parallel to axis X–X′. 
   The installation  100  also comprises a cradle  113  defining a cylindrical inner surface  113   c  and with circular base against which the ribs  103   b  are in sliding abutment by their surfaces  103   c . The axis of symmetry of the surface  113   a  is also the axis a. The radii of curvature R 103  and R 113  of the surfaces  103   c  and  113   c  are equal. It is thus possible to pivot the jaw  103  in the cradle  113  about the axis a, as represented by arrow F 2  in  FIG. 4 , by relative slide of the surfaces  103   c  and  113   c.    
   A second jaw  104  comprises a plate  104   a  intended to come into abutment, by a face  104   a   1 , against the flange  24  and to exert thereon an effort F 3  making it possible to bend it down in the direction of the base plate  101  and of the central part  21 . The plate  104   a  is provided, on its face  104   a   2  opposite the face  104   a   1 , with ribs  104   b  of which an outer or convex surface  104   c  is cylindrical with circular base and adapted to come into abutment against an inner or concave cylindrical surface with circular base  114   c  of a cradle  114 . c denotes the common central geometrical axis of the surfaces  104   c , this axis being parallel to axis X–X′ and located in the interior volume of the upright  4 .  114   c  and R 104  and R 114  denote the respective radii of the surfaces  104   c  and  114   c , these radii being of the same length. The jaw  104  may pivot about the axis c being guided by the cradle  114 , as represented by arrow F′ 2 . 
   Referring more particularly to  FIGS. 4 ,  6  and  7 , it will be understood that it is possible to shape the plate  10  in a tubular section with substantially triangular base thanks to efforts F 1  and F 3 . 
   However, from the position of  FIG. 4 , if the efforts F 1  and F 3  are exerted while the flanges  23  and  24  rest respectively against the plates  103   a  and  104   a  without any other effort, the plate  10  risks rising in the direction of arrow F 4  in  FIG. 4 , because the flanges  23  and  24  risk sliding along the surfaces  103   a   1  and  104   a   1 , as respectively represented by arrows F 5  and F 6 . This might result in an imprecise bending at the level of the edges  12  and  13  of which the centre of curvature would in that case no longer merge with the geometrical axes a and c. 
   In order to avoid relative movements between the flanges  23  and  24  and the surfaces  103   a  and  104   a , the jaws  103  and  104  are each equipped with a heel  103   f ,  104   f  adapted to exert on the flanges  23  and  24  an effort, respectively denoted F 7  and F 8 , directed substantially towards the edges  12  and  13 , i.e. countering a slide of the flanges  23  and  24  in the direction of arrows F 5  and F 6 . The efforts F 7  and F 8  therefore constitute efforts of clamping or of holding of the flanges  23  and  24  with respect to the jaws  103  and  104 . In particular, the flanges  23  and  24  do not risk projecting radially outside the jaws  103  and  104 . 
   In other words, the heels  103   f  and  104   f  form stops to the displacement of the flanges  23  and  24  in the direction of arrows F 5  and F 6 . 
   It will be noted that the efforts F 7  and F 8  are exerted by the outside of the upright  4 . In this way, the plate  10  is maintained on the apron  101  without using an added element, such as a holding clamp, this being favourable as a holding clamp would be delicate to place in position and to remove once the plate is bent. In addition, a holding clamp could not be extended up to the level of the upright  3 . 
   The invention therefore allows a bending of the plate  10  into a tubular structure without introduction of a wedging device inside its different sections. 
   The heel  103   f  is in one piece with the plate  103   a , this heel being intended to cover the border  27  of the flange  23 . This heel  103   f  extends over the whole length of the jaw  103  parallel to axis X–X′, which guarantees that the upper edge of the upright  4 , on which the mask  5  is intended to be stretched, is bereft of irregularities. To that end, the heel  103  presents a regular surface towards the border  27  as the heel  103   f  serves for forming this border which must be as regular as possible for the mask  1 , which is stretched on the upper edge of the upright  4 , not to present a wave or element in relief capable of disturbing the image generated in the cathode-ray tube. 
   The  104   f , which extends over the length of the jaw  104 , is capable of moving perpendicularly to the plate  104   a  and to the flange  24 , as represented by arrow F 9  in  FIG. 4 . 
   Functioning is as follows: 
   When the plate  10  has been positioned on the apron  101  and pre-bent thanks to the holding clamp  107 , the jaw  104  is displaced by a pneumatic, electric or hydraulic jack, with the result that, thanks to the effort F 3  exerted by the plate  104   a , it bends the plate  24  down in the direction of the part  21 . The heel  104   f  exerts on the flange  24  an effort F 8  directed towards the edge  12 , which guarantees a correct positioning of the flange  24  with respect to the jaw  104 . The position of  FIG. 6  is then attained, where the angle α between the flange  24  and the part  21  is less than 90°. From this position, the jaw  103  is actuated so that it bends the flange  23  down in the direction of the part  21  by exerting the effort F 1 , as shown in  FIG. 7 . The jaws  103  and  104  are guided in their displacements F 2 , and F′ 2  thanks to the cooperation of the convex cylindrical surfaces  103   c ,  104   c  and concave ones  113   c ,  114   c.    
   In order to avoid an interference between the heels  103   f  and  104   f , the heel  104   f  is moved away from the flange  24 , as represented by arrow F′ 9  in  FIG. 7 . In effect, it is possible to eliminate the effort F 8  in the configuration of  FIG. 6  as no displacement of the flange  24  is necessary between the configurations of  FIGS. 6 and 7 . Moreover, the fact that the angle α is less than 90° ensures an efficient positioning of the flange  24 , including in the event of elimination of the effort F 8 . 
   In other words, in the configurations of  FIGS. 6 and 7 , the effort F 8  is not indispensable as the plate  104   a  efficiently holds the flange  24  in position with respect to axis c. 
   According to a variant embodiment of the invention, it is possible to provide for a plurality of heels  104   f  to be distributed over the length of the plate  104   a , parallel to axes X–X′ and c. 
   Reference will now be made to  FIG. 15  which is an enlargement of the detail XV in  FIG. 4 . The plate  10  has a non-zero thickness e. The passage from the position shown in solid lines to the position shown in dashed and dotted lines, which corresponds substantially to that of  FIG. 7 , has the effect of reducing the height h of the flange  23  in the configuration in dashed and dotted lines with respect to the length l of this flange in the solid line configuration as the neutral axis f of the plate  10  forms an arc of circle centred on the axis a in the configuration shown in dashed and dotted lines. If it is considered that axis a is located inside the zone intended to form the edge  12  with a distance d with respect to the neutral axis f and taking the example of a plate curved from a planar configuration to arrive at a configuration bent at 90°, the difference between the height h and the length l is ½ πd. In the present case, it is less insofar as the edge  12  is already pre-marked in the configuration of  FIG. 4 . However, it is not zero. 
   Taking into account this difference in values between the height h and the length l, the value of the effort F 7  should be adapted so that it efficiently immobilizes the plate  10  in the zone of the edge  12  all along the movement of rotation of the jaw  103  about axis a. To that end, the heel  103   f  is provided to be elastically loaded in the direction of axis a or of the edge  12 . In that case, the heel  103   f  is not in one piece with the plate  103   a . According to another approach, a cam system may be provided to allow the intensity of the effort F 7  to be varied as a function of the angular orientation of the jaw  103  about the axis a, in the course of the pivoting F 2 . 
   According to another approach, it is possible to compensate this difference in value between the height h and the length l by offsetting the pivot axis a in a direction perpendicular to the principal plane of the apron  101 . In that case, the heel  103   f  may be in one piece with the plate  103   a  of the jaw  103 . 
   Of course, the heel  104   f  may also be provided with means for varying the intensity of the effort F 8  as a function of the position of jaw  104  about axis c in the course of pivoting F′ 2 . In a variant, the position of the axis c may also be provided to be variable in order to compensate the variations in length and/or height of the flange  24 . 
   Referring more particularly to  FIGS. 8 to 10 , it is noted that the lateral upright  3  is of quadrangular section. A jaw  105  is provided to cooperate with the flange  25  and comprises a base plate  105   a  of which one face  105   a   1  in contact with the flange  25  makes it possible to exert an effort F 11  to bend the flange  25  down in the direction of elements  21  and  101 . Like jaw  103 , the jaw  105  is equipped with ribs  105   b  defining cylindrical convex surfaces  105   c  centred on the axis a and making it possible to cooperate with a cradle  115  defining a concave surface  115   c  for slide of the surfaces  105   c , the surface  115   c  being, like surfaces  105   c , of circular base and centred on axis a. The jaw  105  is equipped with a plurality of heels  105   f  distributed over its length parallel to axis X–X′, these heels being provided to come into contact with the flange  25  at the level of edge  17 , constituting a stop for a possible slide of the flange  25 . The heels  105   f  exert on the flange  25  a clamping effort F 12  directed towards the edge  12  and parallel to panel  25   a . The effort F 12  has the same function as the efforts F 7  and F 8  evoked previously. It makes it possible to efficiently position the flange  25  with respect to the axis a all along the operation of bending effected thanks to the effort F 11 . 
   In the same way, a jaw  106  is provided to cooperate with the flange  26  and comprises a plate  106   a  forming a face  106   a   1  for abutment against the flange  26  and equipped with ribs  106   b  whose convex outer radial surfaces  106   c  cooperate with a concave surface  116   c  of a cradle  116 . The surfaces  106   c  and  116   c  are centred on a geometrical axis or virtual axis b constituting the centre of the edge  15  and located, like axis a, in the interior volume of the upright  3 . 
   The jaw  106  is equipped with heels  106   f  making it possible to retain the flange  26  in position with respect to the plate  106   a  in the course of bending of the edge  15 . The plate  106   a  is not planar but forms a concave zone for receiving the panels  26   a  and  26   b , the plate  106   a  itself being formed by two panels oriented one with respect to the other with an angle β corresponding to the angle of orientation of the panels  26   a  and  26   b  with respect to one another. The heels  106   f  are disposed in order to come into abutment against the free edge  26   c  of the panel  26   b.    
   The heels  106   f  are distributed over the length of the plate  106   a.    
   The heels  105   f  on the one hand and  106   f  on the other hand, are positioned in quincunx with respect to each other, being offset along the axis X–X′, a heel  105   f  being opposite a free gap  106   g  defined between two heels  106   f , while a heel  106   f  is disposed opposite a free gap  105   g  defined between two heels  105   f.    
   The bending of the upright  3  may be explained with reference to  FIGS. 8 to 10 . In the configuration of  FIG. 8 , an effort is exerted on the jaw  105  by any appropriate means, with the result that it is displaced and exerts the bending effort F 11  of the flange  25  in the direction of the part  21 , the heels  105   f  overlapping the zone of join  25   c , defined between the panels  25   a  and  25   b  and which includes the edge  17 . The effort F 11  makes it possible to bend the flange  25  down as far as the position of  FIG. 9  where the panel  25   a  is substantially perpendicular to the part  21 , the panel  25   b  being substantially parallel to this part. In the course of the bending operation made between the configurations of  FIGS. 8 and 9 , the effort F 12  efficiently retains the flange  25  in position with respect to the jaw  105  and to the edge  12 . 
   The jaw  106  is in that case activated, in order to pass from the position of  FIG. 9  to that of  FIG. 10 , an effort F 13  of bending of the flange  26  in the direction of the part  21  being exerted by the plate  106   a  while an effort F 14  is exerted by the heels  106   f  on the flange  26  parallel to this flange and substantially in the direction of the edge  15 . 
   As previously, the efforts F 12  and F 14  may be modulated as a function of the orientation of the jaws  105  and  106  about axes a and b. In a variant, the axes a and b may be offset with respect to their representation in  FIGS. 8 to 10  in order to compensate the variations in length of the flanges  25  and  26 . 
   In addition, in the configuration of  FIG. 10 , the effort F 12  may be released or reduced by a movement of the heel  105   f  in a sense of moving away with respect to the edge  12 , with the result that, due to the elasticity of the plate  10 , the panel  25   b  comes into firm elastic abutment against that face of the panel  26   b  oriented towards the part  21 . It is in that case possible to spot weld the panels  25   b  and  26   b  thanks to a high energy beam directed between two adjacent heels  105   f  and  106   f.    
   In order to attain the elastic abutment of the panels  25   d  and  26   d , it is also possible to provide for the angle of bend between the panels  25   a  and  25   b  to be slightly more open than that obtained in the configuration of  FIG. 10 , with the result that an elastic abutment is obtained in this configuration without it being necessary to release the effort F 12 . 
   As is more clearly visible in  FIGS. 11 to 14 , the frame  2  is conformed, after shaping of the different uprights  3 ,  3 ′,  4  and  4 ′, by bending. When the tubular uprights have been made, the plate  10  extends substantially in the direction X–X′ in four sections joined by zones of join  8 ,  8 ′ and  8 ″. A tool  20  is provided for shaping the frame  2  and comprises four flaps  201 ,  202 ,  203  and  204  intended each to receive one of the uprights  3 ,  3 ′,  4  or  4 ′. 
   These flaps  201  to  204  are each formed by two massive pieces  201   a ,  201   b ,  202   a ,  202   b ,  203   a ,  203   b ,  204   a ,  204   b  joined by a screw/nut system  201   c ,  202   c ,  203   c  or  204   c  for adjustment of the flaps  201  to  204  in length. Guide rods  201   c ′,  202   c ′,  203   c ′ and  204   c ′ are associated with the systems  201   c  to  204   c . The length of each flap  201  to  204  is adjusted, parallel to its largest dimension X 1  to X 4 , to the length of the upright that it must receive. The flaps  201  to  204  are provided to be adjustable in length in order to allow frames  2  of different sizes to be manufactured. 
   The pieces  201   a  and  201   b  are respectively provided with angles  201   d ,  201   e  for receiving the upright  4 . Jaws  201   f ,  201   g  are provided to immobilize the upright  4  against the angles  201   d  and  201   e . In the same way, the flaps  202 ,  203  and  204  are respectively equipped with angles  202   d  to  204   e  and with jaws  202   f  to  204   g . As is more particularly visible in  FIGS. 11 and 12 , the jaws are shaped as a function of the geometry of the flanges  24  and  26 . 
   The flaps  201  and  202  are articulated together about an axis Y 1  essentially perpendicular to the principal direction X–X′ of the uprights  3 ,  4 ,  3 ′ and  4 ′. The axis Y 1  is also perpendicular to the direction X 1  along which the flap  201  is adjustable in length. In the same way, the flaps  202  and  203  are articulated together about an axis Y 2  while the flaps  203  and  204  are articulated together about an axis Y 3 , these axes Y 2  and Y 3  being substantially perpendicular to axis X–X′ and to the directions X 1 , X 2 , X 3  and X 4  for adjusting the different flaps in length. 
   Three jacks  205 ,  206  and  207  respectively join the flaps  201  and  202 , the flaps  202  and  203  and the flaps  203  and  204 , with the result that they are adapted to exert thereon efforts or forces of closure represented by arrows F 16 , F 17  and F 18  in  FIG. 14 . These efforts make it possible to take the tool  200  into a substantially rectangular configuration in a plane perpendicular to axes Y 1  to Y 3 , which makes it possible to bend the frame  2  at zones  8 ,  8 ′ and  8 ″ and to form corners such as corner  7 , as represented in  FIGS. 12 and 13 . In effect, the effort or force F 17  has the effect of bringing together the sides of the flaps  202  and  203  joined by the jack  206 , which results in a bending of the plate  10  along a line  18  parallel to axis Y 2 . The tongues  11  arranged on the upright  4  are thus made to overlap the edge  3   a  of the upright  3 , these tongues and this edge in that case being able to be welded by a high energy beam. 
   In the configuration of  FIG. 14 , the tool  200  forms a rectangle whose flaps  201  to  204  constitute the four sides. This rectangle is closed at the level of a zone of join between the flaps  201  and  204  where there are provided locking means (not shown) associated with guiding means, likewise not shown. In this way, the rectangle shown in  FIG. 14  is defined precisely by the cooperation of the flaps  201  to  204 , with the result that the geometry of the frame  2  thus obtained is also defined precisely. 
   According to an advantageous aspect of the invention shown solely in  FIG. 16 , the jaw  106  is equipped with a blade  106   h  forming shears with the plate  101  and making it possible to cut out, during the bending of the upright  3 , the plate  10  in the zone of join of the uprights  3  and  4  so as to create a notch  19  visible in  FIG. 11  compatible with the movement of bend about axis Y 2 . Due to the use of the blade  106   h , the notch is created after the operations of shaping the tubular uprights  3 ,  3 ′,  4  and  4 ′. Before the use of this blade, the plate  10  presents a continuity in the zones  8 ,  8 ′ and  8 ″ of join between the uprights  3  and  4 . In other words, the incorporation of the blade  106   h  on the jaw  106  enables the notch  19  to be made just before the use of the tool  200 , which avoids too great stresses at the level of the line  18  during production of the tubular parts. In practice, the blade  106   h  may be with double cutting edge, with the result that it makes it possible to cut out the plate  10  along two parallel lines  28  and  29  defining therebetween the notch  19  up to a bore  30  previously made in the plate  10 . Of course, the jaws  103 ,  104  and  105  may also be equipped with blades forming shears. 
   As a function of the geometry of the frame  2 , i.e. as a function, in particular, of the length of the uprights and of their cross-section, different sets of jaws  103  to  106  and of cradles  113  to  116  may be used, the jaws and the cradles being placed in position jointly in the installation  100 , which makes it possible to effect a rapid standard exchange of the assembly of the bending members of this installation. 
   The use of the jaws  103  to  106  that may slide on cradles  113  to  116  of different geometrical axes, such as axes a and c, makes it possible to produce non-aligned edges, such as the edges  13  and  15 , which would not be possible with conformation jaws articulated on common hinges. 
   In the Figures, the jaws  103  and  105  and the cradles  113  and  115  have been shown as two distinct units. However, it might be question of the same unit forming bending member at the same time for uprights  3  and  4 , as the axis of bend a is the same for the whole edge  12  over the length of the plate  10 . This is why the plates  103   a  and  105   a , on the one hand, and the cradles  103   d  and  105   d , might be constituted in one piece. 
   When the plate to be bent is thin and in order to avoid a phenomenon of buckling of its flanges under the effect of the clamping efforts, it may be provided to apply the metal sheet against the plates  103   a  to  106   a  of the jaws  103  to  106  by suction or by magnetic attraction. To that end, the jaws  103  to  106  may be provided with channels opening out on the faces  103   a   1 ,  103   a   2 ,  105   a   1  and  106   a   1  and connected to a source of vacuum. The jaws may also be equipped with permanent magnets or with electro-magnets allowing an immobilization of the flanges  23  to  26 . 
   As shown in  FIG. 17  for an installation according to a second form of embodiment of the invention, the jaws, such as jaws  104  may be guided by cradles, such as cradle  114  thanks to telescopic circular segments  1041  and  1042  which make it possible, for a given geometry of a cradle  114 , to obtain an efficient guiding for a movement F 20  of pivoting of the jaw  104  about axis c of high amplitude. The segment  1041  is fast with the jaw  104  while it is fitted inside the segment  1042 , this segment  1042  itself being mobile in abutment against the inner cylindrical surface  114   c  of the cradle  114 . 
   The segment  1042  is hollow while segment  1041  is solid and of width less than the width of the inner volume of the segment  1042 . 
   The segment  1042  is provided with rollers  1042   g  disposed along its inner surface  1042   h  and adapted to cooperate with the edge  1041   c  of the segment  1041 . These rollers facilitate the relative slide between the segments  1041  and  1042 . Moreover, the edge  1042   c  of the segment  1042  is also provided with rollers  1042   i  adapted to cooperate with the inner surface  114   c  of the cradle  114 . This facilitates pivoting of the segment  1042 . 
   According to variants of the invention (not shown), the segment  1041  and/or the cradle  114  may be equipped with balls or rollers for slide. 
   The invention has been described, with reference to the first form of embodiment, with jaws equipped with ribs of which the end surfaces  103   c ,  104   c ,  105   c  and  106   c  are provided to slide against the cylindrical surfaces  113   c  to  116   c  of the cradles  113  to  116 . However, the ribs  103   b  to  106   b  may be equipped with runners incorporating balls or rollers, such balls or rollers being provided to roll on the surfaces  113   c  to  116   c.    
   Other modes of guiding the jaws by the cradles may be envisaged. 
   As is more particularly visible in  FIGS. 18 and 19 , the angles  201   d  to  204   e  and the jaws  201   f  to  204   g  of the first form of embodiment may be replaced by profiles of cross-section substantially in U-form, of which two are shown in  FIG. 18 , with references  202   m  and  203   m . These profiles have a cross-section suitable for receiving the uprights  3  and  4 ′respectively, being fixed on flaps similar to flaps  202  and  203  of the first embodiment. 
   Shims  202   p  and  203   p  are respectively associated with the sections  202   m  and  203   m  for wedging the uprights  3  and  4 ′ in position. These shims have a substantially triangular section with a truncated angle, i.e. in fact a trapezoidal section. When the uprights  3  and  4 ′ have been placed in position in the profiles  202   m  and  203   m , the shims are introduced in the profiles as represented by arrows F 20 , the geometry of the shims  202   p  and  203   p  being such that they are each provided with a surface  202   g ,  203   g  adapted to rest against certain flanges  24  or  26  of the profiles  3  and  4 ′. 
   Each shim  202   p  or  203   p  is provided with a blind hole  202   r ,  203   r  for receiving a pin  202   s ,  203   s  provided to pass through an orifice  202   t ,  203   t  of the profiles  202   m  and  203   m . The introduction of the pin  202   s  in the orifice  202   t  and the blind hole  202   r  is represented by arrows F 21 . Once the pins  202   s  and  203   s  are in place in the holes and orifices  202   r ,  202   t ,  203   r  and  203   t , the shims are immobilized on the profiles  202   m  and  203   m  and maintain the uprights  3  and  4 ′ in place. 
   The invention has been shown with jaws whose inner surfaces  103   a   1  to  106   a   1  are planar while the flanges  23  to  26  are also planar. Of course, these surfaces and these flanges may be skew as a function of the geometry desired for the uprights  3 ,  3 ′,  4  and  4 ′. 
   The invention has been shown when employed for manufacturing shadow mask support frames. Such frames may be made in one, two or four parts, each part forming one, two or the four uprights of the frame.