Abstract:
The hooking system of the lid ( 4 ) to the sliding plate comprises grooves ( 27 ) provided in the heating ceramic plate ( 11 ), to accommodate rails made of refractory steel. 
     These rails ( 26 ) enable on the one hand to fix the ceramic plate ( 11 ) below the metal plate ( 10 ), via tension rods ( 14 ) and, on the other hand, to hook the lid ( 4 ), using H-section parts ( 22 ) that nest into T-shaped grooves ( 25 ) of the said rails and in identical T-shaped grooves provided opposite to one another in the upper section of the lid ( 4 ).

Description:
FIELD OF THE INVENTION 
     This invention relates to the field of heating presses that enable producing sheet metal parts intended for aeronautical material or other, by supraplastic deformation at temperatures close to 1 000° C. and using appropriate tooling. 
     The invention relates, on these presses, to the arrangement of the sliding plate on which is attached the lid of the forming tools, and more especially, the hooking system of such lid. 
     BACKGROUND OF THE INVENTION 
     The sliding plate consists of a single water-cooled metal plate, integral with the working actuator(s), and of a heating ceramic plate interposed between the metal plate and the tooling lid. 
     This ceramic plate is composed of blocks that are fixed to the metal plate by appropriate tension rods. The blocks making up the plate are made of material such as vitreous silica. 
     This ceramic plate acts as a heating plate and has numerous advantages associated with its dimensional stability regardless of the temperature, its surface evenness, its low thermal inertia and its low maintenance cost. 
     The tools, and in particular the lid, are heated using heating elements such as resistive wires or heating pipes. These heating elements are inserted in holes provided in the ceramic blocks, close to the surface that is in contact with the top of the lid. 
     These heating elements are multiple, spread over one or several layers and form a compact network so that the lid of the forming tooling, on the sliding plate, is fixed generally using a hooking system arranged on the upper lateral edges of the lid, co-operating with the rims of the sliding plate. 
     This lateral hooking system has several drawbacks. It requires adaptation of the geometry of the tooling lid and, moreover, it enhances deformation of the said lid. 
     This invention provides a hooking system that enables to obviate these drawbacks thanks to a peculiar arrangement of the sliding plate. 
     SUMMARY OF THE INVENTION 
     The invention provides a hooking system for a tooling lid onto the sliding plate of a hot forming press, which sliding plate comprises a water-cooled upper metal plate and, below the latter, a ceramic plate provided with heating elements that enable to reach a temperature in the order of 1 000° C., which hooking system comprises rails made of refractory steel that are inserted in grooves in the said ceramic plate, which rails enable on the one hand to fix the said ceramic plate below the said metal plate via tension rods provided between the rails and the metal plate and, on the other hand, to hook the said lid, for example using H-section parts that nest into T-shaped grooves provided opposite to one another in the said rails and the said lid. 
     Still according to the invention, the thickness of the hooking rails is smaller than the depth of their reception grooves, in order to avoid any contact between the said rails and the top of the lid. 
     According to another embodiment of the invention, each rail is fixed to the upper metal plate via tension rods made on the one hand, of a refractory steel rod provided at its lower end with a head inserted in an appropriate cavity of the rail that is located above the T-shaped groove, and at its upper end, with a nut, and on the other hand, between the said nut and the top of the metal plate, with compensation means comprising a spring and/or a stack of single-coil spring lock washers. 
     According to another embodiment of the invention, the length of the rails is limited and should not exceed twice the distance between two adjacent tension rods that enable fastening them, in order to limit the problems associated with deformation by elongation of the said rails when subjected to high temperature. 
     According to another embodiment of the invention, when in the same groove, the rail consists of several rail sections, the ends of both sections of adjacent rails comprise a male/female arrangement to enable their nesting into one another, thereby providing continuity at, particularly, the T-shaped groove and enabling feeding H-section parts through without any problems. 
     According to another embodiment of the invention, in order to obtain good thermal distribution, heating elements are placed also close to the bottom of the reception groove of the rails, on either side of the tension rods, for some continuity of the heated surface. 
     According to another embodiment of the invention, in order to keep the same thermal inertia with respect to a conventional ceramic plate, the thickness of the ceramic plate with grooves, is increased with the thickness of the fastening rails. 
     According to another embodiment of the invention, the width of each reception groove of the rails is greater than that of the rails, whereas the said rails rest solely at the bottom of the said groove, which bottom is connected to the walls of the said groove by roundings in order to avoid initial and potential fractures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be detailed better using the following description and the appended drawings, given for exemplification purposes and in which: 
     FIG. 1 is a general view of a hot forming press using a plate according to the invention; 
     FIG. 2 represents, in a more detailed fashion, the hooking system of the ceramic plate below the metal plate; 
     FIG. 3 shows in a still more detailed fashion, the fastening rail associated with an H-section part that co-operates with a groove provided in the lid to be fixed; 
     FIG. 4 is a vertical longitudinal sectional view of the rail showing its fastening and the arrangement of the ends of both adjacent rail sections; 
     FIG. 5 is a view from beneath of the junction of two adjacent rails; 
     FIG. 6 is a perspective view of the ends of two adjacent rails; 
     FIG. 7 is a partial view from beneath of the sliding plate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The simplified press on FIG. 1 comprises a fixed lower plate  1  holding a tooling  2 , and a sliding plate  3  below which is hooked the lid  4  of the said tooling. 
     The sliding plate  3  is carried by a girder  5 , via actuators  6  that enable controlling the said and applying the pressure necessary to the closing of the tooling, for the forming operation. 
     This forming operation takes place in hot condition, in order to work on sheet metal parts, at a temperature close to 1 000° C., which enables supraplastic deformation. 
     Taking the temperature into account, and to avoid any wastage, the central zone where the tooling lies, is closed laterally; moveable walls  7  serving as doors or traps to enable insertion and evacuation of the parts to be formed and, possibly, of the bottom  2  of the tooling. 
     The base plate  1  and the sliding plate  3  comprise a metal section and a section made of ceramic material. 
     FIG. 2 shows a section of the sliding plate  3  comprising two plates: a metal plate  10  integral with the ends of the actuators  6  and, beneath this metal plate, a plate  11  of ceramic material that enables insulating the metal plate  10  from the hot section, and in particular from the lid  4  of the tooling. 
     The metal plate  10  comprises a cooling system  12  in which water is circulating for example. 
     The ceramic plate  11  comprising blocks, as detailed below in relation with FIG.  7 . These blocks are made of a material such as vitreous silica; they are integral with the metal plate  10  using simple tension rods  13  or as detailed below in connection with FIGS. 2 and 3, via tension rods  14  fulfilling a complementary function associated with hooking the lid  4  of the tooling. 
     The ceramic blocks, as represented on FIG. 7, are variable in sizes, adopted to the dimension of the metal plate. They are peripheral blocks  15  fixed to the lid  10  by the tension rods  13 , and blocks  16  that are in contact with the lid  4  whose space requirements are represented by thin dotted points. These blocks  16  are fixed to the lid  10  either with simple tension rods  13  or with tension rods  14 . 
     The contact surface  17  of the ceramic plate  11 , to which is fixed the lid  4 , is perfectly plane and this surface is brought to high temperature, 1 000° C. for example, using heating elements  20  in the form of resistive wires or heating pipes accommodated in rows of orifices provided on one or several layers, as represented on FIG.  2 . 
     The lid  4  is fastened to the ceramic plate  11  via H-section parts  22 , as represented on FIG. 3, which parts usually called “dogbones”, are interposed between a T-shaped groove  24  provided on the top of the lid  4  and a T-shaped groove  25  provided in a rail  26 . These H-section parts  22  are in fact small parts whose length is in the order of a few centimeters, between 5 and 10 for example. 
     This rail  26  is provided in a groove  27  cut into the thickness of the ceramic plate  11 , from the contact surface  17 . This rail  26  contributes to the fastening of the ceramic plate  11  to the metal plate  10 , using tension rods  14  mentioned previously. 
     The space or the pitch between the rails  26  is defined in relation to the dimensional stresses of the toolings. 
     In order to avoid heat losses at the rails  26 , heating elements  31  have also been provided above the groove  27 , on either side of the tension rods  14 . 
     The thickness of the ceramic plate is determined on the basis of heating elements  31 , and consequently, with respect to a conventional ceramic plate (without any grooves), the thickness of the plate according to the invention is greater by a value that corresponds to the depth of the grooves  27 . 
     The tension rods  13 ,  14  and the rails  26  are made of a refractory material. The thickness of the rail  26  is slightly smaller than the depth of the groove  27 ; its width is also smaller than the width of the groove  27  and it comprises chamfers  29  at the bottom  32  of the groove. The bottom  32  and the lateral walls  33  are connected via ample roundings to avoid initial fractures. 
     The rail  26  rests on the bottom  32  and solely this bottom. 
     The tension rod  14  comprises a head  34  that nests into an appropriate orifice  35  provided in the rail  26 . This head is located above the T-shaped groove  25 . At its upper section, the tension rod  14  comprises a thread that accommodates a nut  36  with, interposed between the said nut and the upper section of the plate  10 , elastic compensation means such as springs  37  and/or stacks of washers/springs. The upper section of the tension rod  14  is for example embedded in an orifice provided at the upper section of the metal plate  10 . 
     The spring  37  enables to keep constant tension regardless of the oven temperature. The pre-stress tension is adjusted by tightening the nut  36  in order to enable lifting the lid  4  of the tool and maintaining the ceramic plate in contact with the metal plate  10 . 
     The rails  26  are subjected to elongation deformations because of temperature. In the same groove  27 , they consist preferably of several sections whose length does not exceed twice the distance between two adjacent tension rods  14 . 
     FIG. 7 shows in the grooves  27  a first rail section  26  with two tension rods  14  and a portion of a second rail section with one of its tension rods  14 . 
     FIG. 4 shows a sectional view along  4 — 4  of FIG. 7 showing two rail sections  26  whose ends correspond to the junction plane  41  of two blocks  16  of the ceramic plate  11 . 
     Each rail  26  comprises, as detailed on FIGS. 5 and 6, a male end  261  and a female end  262 . The end  261  comprises a finger-shaped arrangement  41  making up an extension of the upper section of the rail. The end  262  of the adjacent rail comprises a slotting shaped arrangement  42  whose sizes are adapted to those of the finger  41  to enable guiding both ends  261  and  262  in relation to one another and in particular centring for keeping the alignment of the T-shaped grooves of each rail. 
     The inlets and outlets of the T-shaped grooves and in particular those of the lower rims  43 , are provided with inlet slopes  44  that avoid all difficulties as the parts  22  are fed through.