Abstract:
The machine ( 20 ) comprises: a supporting structure ( 24, 26 ); a movable unit ( 28 ) mounted on the supporting structure ( 24, 26 ) so that it can translate along a first working direction (Z) and along a second direction (X) towards and away from a stationary workpiece-carrying structure ( 88 ); a tool-carrying unit ( 10, 11, 12 ) carried by the movable unit ( 28 ); and a driving system for controlling the movement of the movable unit ( 28 ) in the working direction (Z). The driving system includes a first motor unit ( 60 ) for controlling the rotation of a driving shaft ( 62 ) and a mechanism for converting the rotational movement of the shaft ( 62 ) into the translational movement of the movable unit ( 28 ). The motion conversion mechanism comprises a cam member ( 76 ), which is rotatably mounted on the movable unit ( 28 ) and the rotation of which is controlled by the driving shaft ( 62 ), and a roller member ( 78 ) which is rotatably mounted on the supporting structure ( 24, 26 ) and on which the cam member ( 76 ) rests. The cam member ( 76 ) has an outline ( 76   a ) arranged to co-operate with the roller member ( 78 ), which is suitably shaped so as to cause the movable unit ( 28 ) to move along the working direction (Z) with a predetermined movement law upon rotation of the cam member ( 76 ).

Description:
This is a National Stage entry of International Application PCT/EP2004/052954, with an international filing date of Nov. 12, 2004, which was published as WO 2005/046905 A1, and the complete disclosure of which is incorporated into this application by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a machine for working sheet metal parts and to a driving system for such a machine. More particularly, the invention refers to a flanging machine for connecting by flanging sheet metal panels, such as, for example, car body panels. 
     FIGS. 1A to 1C  of the appended drawings schematically show the operation of flanging a pair of sheet metal panels  1  and  2 , that is, an outer panel and an inner panel, respectively. The two panels  1 ,  2  are first arranged ( FIG. 1A ) with respective flat edge portions  3  and  4  in contact with each other on a workpiece-carrying structure (not shown), generally formed by a bed suitably shaped in accordance with the piece to be worked. The flat edge portion  3  of the outer panel  1  has an edge  3   a  which is initially bent at a given angle (typically 90 degrees) with respect to the plane of the portions  3  and  4  ( FIG. 1A ) and is intended to be further bent and pressed on the flat edge portion  4 , thereby clamping the latter against the underlying portion  3 . The flanging operation usually includes a first phase, known as “pre-flanging”, in which the edge  3   a  is bent to a given angle (typically 45 degrees) with respect to the plane of the edge portions  3  and  4  by applying a first force F 1  preferably perpendicular to the said plane ( FIG. 1B ), and a subsequent phase, or “final flanging”, in which the edge  3   a  is further bent until it contacts the flat edge portion  4  and is then pressed against the latter by applying a second force F 2 , also preferably perpendicular to the plane of the portions  3  and  4  ( FIG. 1C ). 
   For the sake of simplicity, it will be assumed hereinafter that the two flat edge portions  3  and  4  of the panels to be flanged are arranged in a horizontal plane and therefore that the direction along which the flanging forces are applied is vertical. The terms “horizontal” and “vertical” are thus to be understood, in the description and the claims which follow, as parallel to the plane on which the edge portions of the panels to be flanged lie and as perpendicular to that plane. 
   The flanging operation described above is commonly performed with the use of a tool-carrying unit  10  of the same type as that schematically shown in  FIG. 2 . The tool-carrying unit  10  is mounted on the flanging machine (not shown) so that it can be moved vertically to perform the pre-flanging and the final-flanging operations, as well as moved substantially horizontally towards or away from the working area in order, for example, to allow the workpiece to be loaded or unloaded. 
   The unit  10  carries a first, pre-flanging tool  11  having a working surface  11   a  inclined at the pre-flanging angle (typically 45 degrees) with respect to the vertical direction, and a second, final-flanging tool  12  having a working surface  12   a  inclined at 90 degrees with respect to the vertical direction. 
   A flanging machine of the above-mentioned type is known, for example, from European patent application EP 0 924 005. According to this known solution, the vertical movement of the tool-carrying unit is driven by a screw mechanism controlled by an electric motor, whereas the movement towards and away from the working area (in this case, a tilting movement) is driven by a leverage controlled by a pneumatic cylinder. 
   The use of a screw mechanism for driving the vertical movement (working movement) of the flanging machine has first of all the disadvantage of a high cost, due both to the high precision required for the production of the screw and to the complexity of the electronic control system required to ensure the correct operation of the machine. Moreover, the precision of the machine, and hence the quality of the worked pieces, may tend to decrease with time as a result of the plays due to the wear of the screw mechanism. 
   German utility model DE 295 11 071 U discloses a driving sys-tem for driving a tool-carrying unit of a machine for the working of sheet metal parts, in particular a bending or punching machine, wherein the tool-carrying unit is slidably mounted along a vertical direction on a supporting structure of the machine. This known driving system comprises a driving shaft rotatably mounted on the supporting structure and carrying two cam discs engaging with two rollers mounted on the tool-carrying unit. The one cam disc and roller assembly controls the working stroke of the tool-carrying unit, while the other cam disc and roller assembly controls the return stroke of the tool-carrying unit. 
   A flanging machine for the working of sheet metal parts is known from European patent application EP-A-0 933 148. In this case, the vertical reciprocating motion of the tool-carrying unit is driven by an electric motor which is fixedly mounted on a supporting structure of the machine and operates a driving shaft rotatably mounted on the sup-porting structure and connected to the tool-carrying unit by means of a cam and lever mechanism. 
   SUMMARY OF THE INVENTION  
   It is therefore the object of the present invention to overcome the shortcomings of the prior art discussed above, by providing a machine for working sheet metal parts, in particular for performing flanging operations, which has a simple structure, a low cost and a precise and reliable operation with time. 
   The advantages of a machine according to the invention with respect to the prior art can be summarized in the following points:
         simpler construction,   more compact sizes,   lower manufacturing and working costs,   lower number of components,   higher reliability,   less frequent and easier servicing operations, and   greater working force which can be exerted, and therefore greater length which can be worked.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the invention will become apparent from the detailed description which follows, given purely by way of non-limiting example with reference to the appended drawings, in which: 
       FIG. 1A  is a side sectional view which shows a pair of sheet metal panels arranged to be connected to each other by a typical double-phase flanging operation; 
       FIG. 1B  is a side sectional view which shows the two panels of  FIG. 1A  after the 45-degrees pre-flanging phase; 
       FIG. 1C  is a side sectional view which shows the two panels of  FIG. 1A  at the end of the final-flanging phase; 
       FIG. 2  is a side sectional view which shows a tool-carrying unit adapted to carry out the flanging operation illustrated in  FIGS. 1B and 1C ; 
       FIG. 3  is a perspective view from above and from the rear side which shows a flanging machine according to the invention; 
       FIG. 4  is a perspective view from above and from the front side which shows the flanging machine of  FIG. 3 , without tool-carrying unit; 
       FIG. 5  is a front elevation view of the flanging machine of  FIG. 3 ; 
       FIG. 6  is a side sectional view of the flanging machine of  FIG. 3 ; 
       FIG. 7  is a perspective view from above which shows a stationary base of the flanging machine of  FIG. 3 ; 
       FIG. 8  is a perspective view which shows a section of a crank mechanism of the flanging machine of  FIG. 3  designed to control the longitudinal horizontal movement of the machine towards and away from the workpiece; 
       FIG. 9  is a perspective view from above which shows a main body and a movable unit of the flanging machine of  FIG. 3 , in the assembled condition; 
       FIG. 10  is an exploded perspective view which shows the main body and a shaft and cam assembly for controlling the vertical movement of the movable unit of the flanging machine of  FIG. 3 ; 
       FIG. 11  is a plan view which shows the outline of the cam of the flanging machine of  FIG. 3 ; 
       FIGS. 12A to 12K  are partial side views which illustrate schematically the work-cycle of a flanging machine according to the invention; and 
       FIGS. 13 to 17  show the angular positions of the cam of a flanging machine according to the invention at respective characteristic points of the work-cycle illustrated in  FIGS. 12A to 12K . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring first to  FIGS. 3 to 10 , a flanging machine ac-cording to the invention, generally indicated  20 , comprises: 
   a stationary base  22 , intended to be fixed to the floor or mounted on a proper support plane (not illustrated) arranged parallel to the plane in which the edge portions of the sheet metal panels to be connected by flanging lie; 
   a movable base  24 , mounted on the stationary base  22  so as to be movable parallel to the latter towards or away from the working area (double arrow X), hereinafter indicated as longitudinal direction; 
   a main body  26  fixed to the movable base  24  and having substantially a portal-like structure; 
   a movable unit  28 , mounted on the main body  26  so as to be movable vertically (double arrow Z), that is, perpendicularly to the plane of the two bases  22 ,  24 ; and 
   a tool-carrying unit  10  of the same type as that described above with reference to  FIG. 2 , which is fixed onto the movable unit  28 . 
   In order to guide the translational movement of the movable base  24  along the direction X, the base is provided with a pair of longitudinal rails  30  (one of which can be partially seen in the sectional view of  FIG. 6 ) arranged to slide on respective guide surfaces  32   a  provided by two pairs of sliding blocks  32  mounted on the stationary base  22  ( FIG. 7 ), The translational movement of the movable base  24  is driven by an electric geared motor unit  34  through a crank mechanism  36  ( FIG. 8 ) which converts the rotational movement into rectilinear movement. 
   With reference to  FIGS. 7 and 8 , the crank mechanism  36  comprises a vertical input shaft  38  connected at its top to the geared motor unit  34  so as to rotated by the latter. The shaft  38  is rotatably mounted by means of a bush  46  on a support body  40 , which is fixed by screws  44  to the movable base  24  in a flange-like portion  42  thereof. The shaft  38  forms at its bottom a cylindrical extension  48  acting as a crank, which is placed eccentrically with respect to the axis of rotation of the shaft and on which a roller  50  is rotatably mounted. The roller  50 , together with the associated extension  48 , extends downwards into a through opening  52  provided in the movable base  24  ( FIG. 9 ) and is guided between a pair of vertical surfaces  54   a  which are oriented perpendicularly to the longitudinal direction X and are provided by respective guide members  54  secured to the stationary base  22 . 
   In this way, when the geared motor unit  34  drives the rotation of the shaft  38 , the roller  50  rolls along the guide surfaces  54   a  of the stationary base, while as a reaction the movable base  24 , which is fast for translation with the shaft  38 , moves longitudinally with respect to the stationary base  22  along the longitudinal guides  30 ,  32 . The direction of the longitudinal movement of the movable base  24  is evidently set by suitably controlling the direction of rotation of the shaft  38 . 
   In order to guide the translational movement of the movable unit  28  along the direction Z, the unit is provided with a pair of vertical rails  56  ( FIG. 9 ) arranged so as to slide on respective guide surfaces provided by two pairs of sliding blocks  58  (which can be partially seen in the sectional view of  FIG. 6 ) mounted on the main body  26 , in a similar manner as that described above in connection with the movable base  24 . 
   The vertical translational movement of the movable unit  28  is driven by an electric geared motor unit  60  configured to rotate a driving shaft  62 . The geared motor unit  60  is fastened to the movable unit  28  by means of screws  64 , on the opposite side with respect to the working area. The shaft  62 , which extends longitudinally, is supported for rotation in a support body  66  fitted in a through hole  68  of the movable unit  28 . 
   The shaft  62  forms an end portion  70  ( FIG. 6 ) which has an outer eccentric-shaped surface and projects from the support body  66  towards the working area. Onto the eccentric portion  70  is secured an annular member  72  the outline of which extends parallel to that of the outer eccentric surface of the portion  70 . Alternatively, there may be provided a cylindrical end portion  70  coaxial with the shaft  62  and an annular eccentric-shaped member  72 . 
   A cam  76  is also fastened by means of screws  74  to the end portion  70  of the shaft  62  and has an outer surface  76   a  with an outline suitably shaped so as to control the vertical movement of the movable unit  28  according to a predetermined law, as will be described in detail further on. The cam  76  rests with its outer surface  76   a  on the outer cylindrical surface of a lower roller  78  rotatably mounted about a stationary shaft  80  of longitudinal axis, which is supported by a support member  82  attached to the movable base  24  ( FIGS. 4 and 6 ). 
   An upper roller  86  ( FIGS. 5 and 6 ) is rotatably mounted in a support portion  84  attached to a workpiece-carrying structure  88  (schematically illustrated in  FIGS. 12A to 12K ), the outer cylindrical surface of the roller co-operating with the outer surface  76   a  of the cam  76  during the pre-flanging phase, as will be explained in detail in the following part of the description. 
   According to a preferred embodiment of the invention, the flanging machine  20  is configured to perform a flanging operation of the type of that described in the introductory part of the description, that is, an operation consisting of a first, pre-flanging phase and a second, final-flanging phase. With reference to  FIGS. 12A to 12K  the work-cycle performed by the machine  20  will be described now. 
   The flanging machine is arranged first in a “loading/unloading” position ( FIG. 12A ), in which the movable unit  28  is longitudinally spaced from the workpiece-carrying structure  88  so as to allow the loading of the workpieces to be flanged (for example, the panels  1  and  2  shown in  FIGS. 1A to 1C ). 
   Next ( FIG. 12B ), the movable unit  28  is longitudinally moved towards the workpiece-carrying structure  88  (as indicated by arrow B X ) until the pre-flanging tool  11  is brought into contact with, or at least close to, the upper, 90-degree-bent edge  3   a  of the panel  1 . The position so reached by the machine is indicated as “pre-flanging start” position. 
   At this time ( FIG. 12C ), the pre-flanging phase is performed by vertically moving the movable unit  28  downwards (arrow C Z ) until the edge  3   a  of the panel  1  is bent up to 45 degrees. The position so reached by the machine is indicated as “pre-flanging end” position. 
     FIG. 12D  shows the machine in a “detachment after pre-flanging” position, reached by vertically moving the movable unit  28  upwards (arrow D Z ) so as to move the pre-flanging tool  11  away from the edge  3   a  of the panel  1 . 
   The movable unit  28  is then moved away from the workpiece-carrying structure  88  by a longitudinal movement (arrow E X ) and reaches again the “loading/unloading” position shown in  FIG. 12E . 
     FIG. 12F  shows the flanging machine in a “preparation for final flanging” position, reached by vertically moving the movable unit  28  upwards (arrow F Z ) until the working surface  12   a  of the final-flanging tool  12  is brought to a higher level than the upper end of the edge  3   a  of the panel  1 . 
     FIG. 12G  shows then the machine in a “final-flanging start” position, reached by longitudinally moving the movable unit  28  towards the workpiece-carrying base (arrow G X ) until the working surface  12   a  of the final-flanging tool  12  is brought above the edge  3   a  of the panel  1 . 
   At this time ( FIG. 12H ), the final flanging is performed wherein the movable unit  28  is vertically moved downwards (arrow H Z ) until the edge  3   a  of the panel  1  is further bent by 45 degrees and is finally pressed against the underlying edge  4  of the other panel  2 . At the end of this phase, the machine is in a position indicated as “final-flanging end” position. 
     FIG. 12J  shows the machine in a “detachment after final flanging” position, achieved by vertically moving the movable unit  28  upwards (arrow J Z ), so as to move the final-flanging tool  12  away from edge  3   a.    
   Finally ( FIG. 12K ), the movable unit  28  is again moved away from the workpiece-carrying structure  88  by a longitudinal movement (arrow K X ), thereby getting back in the “loading/unloading” position. 
   This work-cycle is performed by imparting a predetermined sequence of commands to the geared motor units  34  and  60  which control the longitudinal and vertical movements, respectively, of the movable unit  28 . The vertical movements of the unit  28  are also determined by the shape of the outline  76   a  of the cam  76 . 
   The shape of the outline  76   a  of the cam  76  according to a preferred embodiment of the invention and the sequence of commands imparted by the geared motor unit  60  to the cam in order to perform the work-cycle described above will be explained now in detail, with reference to  FIG. 11  and  FIGS. 13 to 17 . 
   The outline  76   a  of the cam  76  is shown in  FIG. 11 , where the centre of rotation of the cam is indicated O. On the other hand,  FIGS. 13 to 17  illustrate the angular positions reached by the cam  76  in the different working positions previously mentioned. 
   In a first phase, the two panels to be flanged are loaded onto the workpiece-carrying structure  88 , while the machine is in the “loading/unloading” position illustrated in  FIG. 12A . In a second phase, the movable unit  28  is moved longitudinally to the “pre-flanging start” position illustrated in  FIG. 12B . During these first two phases the movable unit  28  is not moved vertically, but the cam  76  is held in the initial position shown in  FIG. 13 , in which the cam contacts the lower roller  78  in a point P AB  of its outline. 
   In a third phase, the pre-flanging is performed, whereby the movable unit  28  is vertically moved downwards until it reaches the “pre-flanging end” position illustrated in  FIG. 12C . This third phase is comprised of the following three steps. 
   The cam  76 , which rests on the lower roller  78  together with the whole movable unit  28  drivingly connected thereto, is first caused to rotate counter-clockwise in such a manner that its point of contact with the roller  78  moves from point P AB  specified above to a second point P C1 . The segment of cam outline  76   a  comprised between points P AB  and P C1  is shaped in such a manner that it causes the movable unit  28  to move downwards until the working surface  11   a  of the pre-flanging tool  11  is brought into contact with the 90-degree-bent edge  3   a  of the sheet metal outer panel  1 . 
   The outline portion  76   a  of the cam  76  following point P C1  would correspond to a further downward movement of the movable unit  28 , if this latter continued to rest with the cam  76  on the lower roller  78 . As a matter of fact, by causing the cam  76  to rotate counter-clockwise again, the movable unit  28  remains “suspended” on the edge  3   a  of the panel  1  with its tool  11 , while the cam  76  disengages from the lower roller  78  and starts to engage with the upper roller  86 , drivingly connected to the workpiece-carrying structure  88 , starting approximately from a point P C1 * opposite point P C1  or from a following adjacent point. This second step provides for a rotation through nearly 60 degrees, until the cam  76  comes into contact with the upper roller  86  in a point P C2 . Since the outline segment comprised between points P C1 * and P C2  is an arc of circumference, no vertical movements of the movable unit  28  take place during this second step. 
   As the cam  76  continues to be rotated, it engages with the upper roller  86  along the outline segment  76   a  comprised between point P C2  and a point P C3  and finally reaches the position shown in  FIG. 14 . Since this outline segment provides for an increase in the radial distance from the centre of rotation O, the cam  76  is urged downwards dragging with it the movable unit  28  and the tool-carrying unit  10  mounted thereon. The pre-flanging tool  11  can thus perform the pre-flanging operation, by exerting on the edge  3   a  of the panel  1  a bending force which is the sum of the weight of the movable unit  28  and of the downward load brought about by the interaction of the cam  76  with the upper roller  86 . 
   In a fourth phase, the movable unit  28  is moved vertically upwards until it returns into the “pre-flanging start” position. To this end, the cam  76  is caused to rotate clockwise until it returns into the initial position shown in  FIG. 13 , in which it contacts the lower roller  78  in point P AB . 
   In a fifth phase, the movable unit  28  is moved longitudinally until it reaches the “loading/unloading” position illustrated in  FIG. 12E , while the  1   a  cam  76  is held stationary in the initial position of  FIG. 13 . 
   In a sixth phase, the movable unit  28  is moved vertically upwards until it reaches the “preparation for final flanging” position illustrated in  FIG. 12F . To this end, the cam  76  is caused to rotate clockwise whereby the point of contact with the lower roller  78  moves along the outline segment comprised between point P AB  and a point P F  (which coincides with point P C3  previously identified), as shown in  FIG. 15 . 
   In a seventh phase, the movable unit  28  is moved longitudinally towards the workpiece-carrying structure  88  until it reaches the “final-flanging start” position illustrated in  FIG. 12G , while the cam  76  is held stationary in the angular position shown in  FIG. 15 . 
   In an eighth phase, the final flanging is performed by moving the movable unit  28  vertically downwards up to the “final-flanging end” position illustrated in  FIG. 12H . To this end, the cam  76  is caused to rotate clockwise until it reaches the angular position shown in  FIG. 16 . As well as for the pre-flanging phase, the final-flanging phase also is comprised of three steps. 
   First the cam  76  is caused to rotate clockwise in such a manner that its point of contact with the lower roller  78  moves from point P F  specified above to a point P H1 . The outline segment  76   a  of the cam comprised between points P F  and P H1  is shaped in such a manner that it brings about a downward movement of the movable unit  28  until the working surface  12   a  of the final-flanging tool  12  is brought into contact with the 45-degree-bent edge  3   a  of the sheet metal outer panel  1 . 
   As the cam  76  continues to be rotated clockwise, it disengages from the lower roller  78 , while the movable unit  28  remains “suspended” on the bent edge  3   a . At the same time, the eccentric annular member  72 , which is fast for rotation with the cam  76 , starts to engage with an abutment surface  90  provided by the workpiece-carrying structure  88 , namely by the support portion  84  fixed to this structure (which can be seen in the side-sectional view of  FIG. 6 ). 
   In a similar way to what has been described with reference to the pre-flanging operation, as a result of the interaction between the outline of the eccentric annular member  72  and the abutment surface  90 , the movable unit  28  and the tool-carrying unit  10  mounted thereon are urged downwards until they reach the “final-flanging end” position. During this third step, the final-flanging tool  12  exerts on the edge  3   a  of the panel  1  a bending force which is the sum of the weight of the movable unit  28  and the downward load produced by the interaction of the eccentric annular member  72  with the abutment surface  90 . 
   By suitably dimensioning the annular eccentric member  72 , the load which is obtained during the final flanging phase is advantageously far higher (for example, nearly four times higher) than that exerted during the pre-flanging phase. Moreover, since the bending force exerted by the tool  12  on the edge  3   a  is substantially aligned with the contact force between the annular eccentric member  72  and the abutment surface  90  (as is visible from the side sectional view of  FIG. 6 ), these forces do not produce a torque which could adversely affect the working precision. 
   In a nine phase, the movable unit  28  is moved vertically upwards until it gets back in the “final-flanging start” position. To this end, the cam  76  is caused to rotate counter-clockwise until it gets back in the angular position shown in  FIG. 16 , in which it contacts the lower roller  78  in point P F . 
   A tenth phase follows, in which the movable unit  28  is moved away longitudinally from the workpiece-carrying structure  88  until it reaches the “loading/unloading” position illustrated in  FIG. 12K , while the cam  76  is held stationary in the angular position of  FIG. 16 . 
   In a last phase, the movable unit  28  is moved vertically downwards so as to get back in the cycle start position of  FIG. 12A . To this end, the cam  76  is caused to rotate counter-clockwise until its point of contact with the lower roller  78  is brought at point P AB  of its outline, as shown in  FIG. 18 . At this time, with the movable unit  28  held in position, the worked piece is unloaded. 
   Naturally, the principle of the invention remaining unchanged, embodiments and manufacturing details may vary widely from those described and illustrated purely by way of non-limiting example. 
   In particular, although there is described and illustrated a preferred embodiment of a flanging machine arranged to perform a double-phase flanging operation (45-degree pre-flanging and 90-degree final-flanging), it is clear that the same machine can be easily modified in a suitable manner for performing any other type of flanging operation, for example with a different pre-flanging angle or without the pre-flanging phase, or again with a different final-flanging angle. 
   Moreover, it is clear that a machine according to the invention can also be used to perform other types of working which provide for the application of a bending force in a given direction. By suitably modifying the outline of the cam, in fact, it is possible to make the tool-carrying unit to move according to a movement law suitable for the particular type of working to be performed.