Abstract:
The invention concerns a perforating device comprising a cutting tool ( 10 ), means for rotating ( 11 ) the cutting tool ( 10 ) and means for translating ( 12, 14 ) the cutting tool ( 10 ), the ratio between the rotational speed and the translational speed being variable during rotation of the cutting tool ( 10 ). It comprises a gear train ( 16, 17; 18, 19 ) for synchronizing the rotating means ( 11 ) with the translating means ( 12, 14 ). The speed ratio between a driving pinion ( 16; 18 ) of the gear train, rotationally linked to the means ( 11 ) for rotating the cutting tool ( 10 ) and a transmission pinion ( 17; 19 ) of the translating means is reversed at least once during one rotation of the cutting tool ( 10 ). The invention is useful for fragmenting the resulting shavings.

Description:
BACKGROUND 
     The present invention concerns a perforation device. 
     The present invention relates generally to the field of perforation, including in particular the techniques of perforation, but also the techniques of milling. 
     Generally speaking, the present invention concerns a perforation device, comprising a rotating cutting tool, such as a drill. 
     In this type of perforation technique, the quality of the result obtained depends on many parameters and especially the proper removal of the chips formed during the perforation. In fact, if this removal is not effective and some of the chips remain in place, they may then become entrained by rotation of the cutting tool and thereby degrade the geometry or the surface condition of the hole produced. 
     In particular, when a perforation device comprises a cutting tool driven by a part in rotation and another part in translation, the regular feed of the cutting tool in the course of the perforation process has the effect of producing long chips which are difficult to remove. 
     Document U.S. Pat. No. 5,342,152 describes a device comprising a cutting tool driven in rotation and in translation and subjected to an oscillation along the axis of rotation, allowing one to vary the thickness of the chips and to cut these chips. 
     The ratio between the speed of translation and the speed of rotation of the cutting tool is variable during the rotation of said cutting tool. 
     Thus, by modifying the ratio between the speed of translation and the speed of rotation during the rotation of the tool, the thickness of the chips formed is modulated in such a way that the resulting chip becomes fragile. 
     These irregular chips are thus more easy to remove, especially by breaking up these chips. 
     BRIEF SUMMARY 
     The purpose of the present invention is to propose a perforation device making it possible to ensure a satisfactory removal of the chips by using precise and reliable means. 
     For this purpose, the present invention contemplates a perforation device having a cutting tool, means of driving this cutting tool in rotation and means of driving the same cutting tool in translation, the ratio between the speed of rotation and the speed of translation being variable during the rotation of the cutting tool. 
     According to the invention, the perforation device has a gear train adapted to synchronize the means for driving in rotation with the means for driving in translation, the speed ratio between one driving pinion of the gear train connected in rotation to the means for driving the cutting tool in rotation and one transmission pinion of the means for driving in translation being inverted at least once during one rotation of the cutting tool. 
     By intervening directly at the pinions of a gear train of the tool, it is possible to modify and periodically cancel the speed of translation of the cutting tool. 
     According to one characteristic of the invention, the speed of rotation or the speed of translation of the cutting tool is variable for not more than one rotation of the cutting tool. 
     One thus avoids the formation of helical chips, which are harder to remove. 
     In practice, the speed of translation of the cutting tool is zero at least once during a rotation of the cutting tool. 
     The chip thus formed during the feed of the tool is broken up during the rotation of the tool, thanks to the feed of the cutting tool in consecutive stages. 
     The pieces of chip of short length are thus more easily removed. 
     In practice, the means for driving in translation comprise a threaded spindle, joined in rotation to the means for driving the cutting tool in rotation and a tapped pinion mounted on the threaded spindle, the speed ratio between an input pinion joined to the threaded spindle and the tapped pinion being inverted at least once during one rotation of the input pinion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and benefits of the invention will appear more clearly in the following description. 
       In the enclosed drawings, given as nonlimiting examples: 
         FIG. 1  is a schematic view illustrating a perforation device according to one embodiment of the invention; 
         FIG. 2  is a schematic view in three consecutive positions of a gear train implemented in the perforation device of  FIG. 1 , according to a first embodiment; 
         FIG. 3  is a curve illustrating the relative speed of the pinions of the gear train of  FIG. 2 ; and 
         FIGS. 4A and 4B  are schematic views in two positions of a gear train implemented in the perforation device of  FIG. 1 , according to a second embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     We shall now describe a perforation device according to one embodiment of the invention, making reference to  FIG. 1 . 
     The perforation device comprises a rotating tool  10 , such as a drill, or a milling cutter, adapted to perform a perforation or a milling in a metal sheet. 
     The cutting tool  10  is mounted in rotation about an axis A. 
     For this purpose, the perforation device has a motor  11 , adapted to drive the cutting tool  10  in rotation about the axis A. 
     A threaded spindle  12  is mounted in joint rotation on the axis of rotation A. The motor  11  thus drives the cutting tool  10  and the threaded spindle  12  in rotation at the same time. 
     The cutting tool  10  is likewise adapted to move in translation. For this purpose, a transmission box  13  in this embodiment makes it possible to transmit the rotational movement at the exit of the motor  11  to a tapped pinion  14  mounted on the threaded spindle  12 . 
     This tapped pinion  14  is locked in translation with respect to the axis A, such that the relative rotation of the tapped pinion  14  and the threaded spindle  12  makes it possible for this threaded spindle  12  to move in translation along the axis A. 
     In this respect, in order to produce a feed motion of the cutting tool  10 , it is necessary for the threaded spindle  12  and the tapped pinion  14  to turn at different speeds. 
     As a nonlimiting example, if the threaded spindle  12  and the tapped pinion  14  each have a right thread pitch of 1 mm, and if the threaded spindle  12  is driven in rotation to the right, at a speed of 1000 rpm, and the tapped pinion  14  is likewise driven in rotation via the transmission box  13  at a rotational speed of 900 rpm, the threaded spindle will move along axis A by an amount equal to 100 times the thread pitch of 1 mm, that is, at a speed of 100 mm/min. 
     This speed of translation corresponds to a feed of the cutting tool  10  of 0.1 mm per rotation. 
     If this transmission speed of the cutting tool  10  is regular during the rotation of the tool, the chips formed are of regular thickness and great length, so that they are hard to remove. 
     To remedy this drawback, the invention modifies the speed of translation, or rather the speed of rotation of the cutting tool  10  during the rotation of this tool  10 , so as to form irregular chips, more easy to remove. 
     In this embodiment, the speed of translation of the cutting tool, that is, of the threaded spindle  12  along the axis A, is modified thanks to a modification in the region of the transmission box  13 . 
     In practice, the transmission box makes it possible to transmit the movement of rotation at the exit from the motor  11 , in the region of an input pinion  15 , to the tapped pinion  14  so as to allow for governing the speed of rotation of the tapped pinion  14  with respect to the speed of rotation of the threaded spindle  12 . 
     A gear train such as that illustrated, for example, in  FIG. 2 , can be provided in the region of the transmission box  13  to synchronize the movement of the input pinion  15  with the rotational movement of the tapped pinion  14 . 
     In this embodiment, as illustrated in  FIG. 2 , the gear train comprises two pinions  16 ,  17 . These pinions  16 ,  17 , for example, can be of identical diameter and have at their periphery a series of teeth distributed regularly over the periphery of each pinion  16 ,  17 . 
     The input pinion  15  meshes, for example, with a driving pinion  16 , which drives the pinion  17 , and the latter transmits via one or more transmission gear wheels its movement to the tapped pinion  14 . 
     These pinions  16 ,  17  are mounted in an off-center manner with respect to their respective axis of rotation  16 ′,  17 ′. They are off center by the same amount relative to their axis of rotation  16 ′,  17 ′, and the distance D between the axes of rotation  16 ′,  17 ′ is constant during the rotation of the pinions  16 ,  17 . 
     Thus, considering, for example, pinion  16  to be a driving pinion, the speed of rotation in the region of the axis  17 ′ of the driven pinion  17  will varies during one rotation of the driving pinion  16 . 
     As is well illustrated in  FIG. 3 , in a first position P 1  the speed V 2  of the driven pinion  17  is greater than the speed V 1  of the driving pinion  16 . This speed V 2  of the pinion  17  decreases to become equal to the speed V 1  of the driving pinion  16  when the pinions  16 ,  17  are at the position P 2 , that is, when their point of meshing is at an equal distance of the axes of rotation  16 ′,  17 ′ of the pinions  16 ,  17 . 
     Then, in position P 3 , the speed V 2  of the driven pinion  17  is less than the speed V 1  of the driving pinion  16  until the two pinions are again at position P 2 . 
     Thus, when such a gear train is placed in the region of the transmission box  13  between the input pinion  15  and the tapped pinion  14 , the speed ratio between the driving pinion  15  connected to the threaded spindle  12  and the tapped pinion  14  is inverted at least once, and in this case twice, during the rotation of the input pinion  15 . 
     In practice, when the speeds V 1 , V 2  are identical, in position P 2  of the pinions  16 ,  17 , the rotational speed of the threaded spindle  12  and the tapped pinion  14  are identical, so that the translatory speed along axis A of the threaded spindle  12  and, consequently, of the cutting tool  10 , is zero. 
     Depending on the type of mounting of the tapped pinion  14  on the threaded spindle  12 , the direction of translation can be inverted during each rotation of the cutting tool  10 . 
     As a nonlimiting example, the cutting tool  10  can pull back by 0.10 mm and advance by 0.15 mm in each rotation. 
     By thus canceling at least once the speed of translation of the cutting tool  10  during one rotation of this cutting tool, it is possible to break up the resulting chips, which facilitates their removal. 
     Of course, the embodiment in the region of the gear train of the transmission box  13 , making it possible to modify the speed of translation of the cutting tool  10  during its rotation, is in no way limiting. 
     A second embodiment also making it possible to modify the speed of translation of the cutting tool  10  has been illustrated in  FIGS. 4A and 4B . 
     As is illustrated in  FIGS. 4A and 4B , the gear train comprises two pinions  18 ,  19  of identical diameter. One of the pinions, here the driven pinion  19 , has an evolutory modulus, that is, it has teeth arranged at irregular intervals on its periphery. 
     In this embodiment, the first pinion  18  has a predetermined number of teeth, here equal to twelve, distributed at a regular pitch on its periphery. The second pinion  19  has the same number of teeth, but distributed at an irregular pitch on its periphery. In this embodiment, five teeth are distributed along half the periphery of the second pinion  19  and seven teeth are distributed along the other half of the periphery of the second pinion  19 . 
     Of course, this irregular distribution of the teeth on this second pinion  19  could be different, as long as the driving of this second pinion  19  by the first pinion  18  remains possible. 
     Thus, in the position as illustrated in  FIG. 4A , when the first pinion  18  is driven in rotation, the speed in the region of the axis  19 ′ of the second pinion  19  is greater than the speed of rotation in the region of the axis  18 ′ of the first driving pinion  18 . 
     By the same token, in the position illustrated in  FIG. 4B , the output speed of rotation of the axis  19 ′ of the second pinion  19  is less than the speed of rotation in the region of the axis  18 ′ of the first pinion  18 . 
     This gear train arranged in the region of the transmission of a device as illustrated in  FIG. 1  also makes it possible to cancel the speed of translation of the cutting tool  10  at least once, in this case twice, during the rotation of the cutting tool  10 . 
     Of course, the present invention is in no way limited to the embodiments described above and many modifications can be made to these embodiment examples without departing from the context of the invention. 
     In particular, other types of gear train can be used, for example, pinions of complex shape, such as oval or potato-shaped. 
     Likewise, the embodiment illustrated in  FIG. 1  is not limiting: other types of means for driving the cutting tool in translation can be used, for example, a mounting on a carriage, mounted in translation, for the assemblage of the tool and these means of rotation. 
     It thus is possible by acting on the means for driving the carriage in translation to modify the speed of translation of the cutting tool during one rotation of this tool. 
     Furthermore, the speed of translation of the cutting tool can remain constant, only the speed of rotation varying during the rotation of the cutting tool.