Abstract:
A method of chamfering and deburring the teeth of a gear having first teeth, each of the first teeth having a first and a second side and respective end faces; the method providing for meshing the gear with at least one tool having a ring gear meshing with the first teeth at edges formed between the first and second sides and the end faces; exerting compression between the first teeth of the gear and the ring gear; effecting a first permanent deformation of the edges to form first chamfer faces; and effecting at least a second permanent deformation between the first and second sides and the respective end faces; the first and the second permanent deformation being effected by means of enbloc tools having a first number of teeth and a second number of teeth.

Description:
The present invention relates to a method of chamfering and deburring gear teeth. 
     In particular, the present invention relates to a method of chamfering and deburring helical gears, to which the following description refers purely by way of example. 
     BACKGROUND OF THE INVENTION 
     Gears normally comprise teeth defined by respective sides and end faces, which, with the sides, form sharp edges along which burrs are left after chip-forming machining, and which must therefore be chamfered for the gear to work and mesh properly. 
     One known deburring and chamfering method employs a tool featuring a ring gear comprising a number of teeth, which are brought into contact with and pressed against the sharp edges to deform them permanently and form bevels between the sides and end faces of the gear teeth. 
     A major drawback of the above known method, however, lies in the formation of curls projecting from the gear teeth and partly inside the gaps between the teeth, and which are formed by the permanently deformed material of the tooth, and seriously impair operation of the gear, particularly in the case of high-precision gears. The problem is further compounded in the case of gears which are ground after heat treatment, in which case, the hardened curls may indent the grinding tool. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a gear chamfering and deburring method designed to eliminate the above drawbacks. 
     According to the present invention, there is provided a method, as claimed in claim 1, designed to eliminate the aforementioned drawbacks. 
     The present invention also relates to a chamfering and deburring tool. 
     The present invention also relates to a chamfering and deburring device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows a small-scale section, with parts removed for clarity, of a device in accordance with the present invention; 
     FIG. 2 shows a section, with parts removed for clarity, of a tool of the FIG. 1 device; 
     FIG. 3 shows a view in perspective, with parts removed for clarity, of the FIG. 2 tool; 
     FIGS. 3 a  and  3   b  show sections of the FIG. 3 tool; 
     FIG. 4 shows a developed view of a gear engaged by the FIGS. 2 and 3 tool at two stages in the method according to the present invention; 
     FIGS. 4 a  and  4   b  show sections of the FIG. 4 tool; 
     FIG. 5 shows a view in perspective, with parts removed for clarity, of a variation of the FIG. 1 device tool; 
     FIG. 5 a  shows a section of the FIG. 5 tool; 
     FIG. 6 shows a developed view of a gear engaged by the FIG. 5 tool; 
     FIGS. 6 a  and  6   b  show sections of the FIG. 6 tool. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  1  in FIG. 1 indicates as a whole a device for chamfering and deburring the teeth of a gear  2  shown by the dash lines in FIG.  1 . Device  1  comprises a hub  3  and an axis  4  of rotation and symmetry. Hub  3  is fitted to a known shaft (not shown) and comprises a ring  5  integral with hub  3  and extending radially; an L-section ring  6  fitted to ring  5  by screws  7  (only one shown in FIG.  1 ); and two annular disks  8  and  9  fitted to ring  5  by screws  10  (only one shown in FIG.  1 ). 
     Rings  5  and  6  define an annular seat  11  housing two tools  12  and  13 , which are in the form of annular disks facing and parallel to each other, are fitted to respective rings  5  and  6  by means of screws  14 , and are located a given axial distance apart. 
     Disk  8  is located on the opposite side of rings  5  and  6  to disk  9 . Disks  8  and  9  are positioned facing and parallel to each other, and define a seat  15  housing two annular deburring disks  16  and  17  facing and parallel to each other and adjacent to respective tools  12  and  13 . Disks  16  and  17  rest on respective rings  5  and  6 , and are pushed towards each other by springs  18  located between disks  8 ,  9  and respective disks  16 ,  17 . 
     Disks  16  and  17  comprise screws  19  fitted to disks  16  and  17  and in turn comprising respective heads  20  projecting axially with respect to disks  16  and  17  and housed inside respective seats  21  formed in disks  8  and  9 . 
     Device  1  also comprises two disks  22  located between deburring disks  16 ,  17  and respective tools  12 ,  13 . That is, whereas tools  12  and  13  are fitted rigidly to hub  3 , deburring disks  16  and  17  are allowed to slide axially by a limited amount with respect to hub  3 . 
     Deburring disks  16  and  17  have respective outer peripheral edges  23  bent towards each other at the outer peripheries of respective tools  12  and  13 , and having cutting edges for deburring the sides of gear  2 . 
     Gear  2  is connected to device  1  and mounted for rotation about a respective axis  24  parallel to axis  4 . 
     The following description with reference to FIGS. 2,  3 ,  4   a  and  4   b  refers for the sake of simplicity to tool  12 , it being understood, however, that the same also applies to tool  13 . 
     With reference to FIG. 2, tool  12  comprises an axis  25  coincident, in use, with axis  4  of device  1 ; an annular disk  26  having a central hole  27 ; and a ring gear  28  integral with disk  26 . Annular disk  26  has a number of threaded holes  29  equally spaced about axis  25  and which are engaged, in use, by screws  14  (FIG.  1 ). 
     With reference to FIGS. 3 a  and  4   a , each tooth  31  comprises sides  34  and  35  forming an acute angle A ranging between 0° and 90°. With reference to FIGS. 3 b  and  4   b , each tooth  33  comprises sides  36  and  37  forming an acute angle B that is preferably considerably smaller than angle A and ranging between 0° and 15°. 
     With reference to FIGS. 3 a  and  4   a , each tooth  31  comprises sides  34  and  35  forming an acute angle A ranging between 0° and 90°. With reference to FIGS. 3 b  and  4   b , each tooth  33  comprises sides  36  and  37  forming an acute angle B considerably smaller than angle A and ranging between 0° and 15°. 
     With reference to FIGS. 4 a  and  4   b , gear  2  comprises a succession of helical teeth  38 , each of which has a respective axis  39  inclined at an angle C with respect to a direction parallel to axis  24 . Each tooth  38  comprises two sides  40  and  41  parallel to axis  39 ; and two end faces  42  parallel to each other and perpendicular to axis  24  of gear  2 . 
     With reference to FIG. 1, in actual use, gear  2  is aligned with tools  12  and  13 , with axis  24  parallel to axis  4  of device  1 , so as to mesh with tools  12  and  13 ; a known device (not shown) applies pressure between gear  2  and device  1  in direction  44  to push tools  12  and  13  against gear  2 ; deburring disks  16  and  17  push respective edges  23  into contact with the sides of gear; and springs  18  press edges  23  against the sides of gear  2 . 
     With reference to FIG. 4 a , portion  30  of ring gear  28  of tool  12 , viewed in section, engages gear  2  on one side of gear  2 , with teeth  31  located successively between respective teeth  38  of gear  2 . More specifically, side  35  of each tooth  31  is positioned contacting an edge between side  41  and respective end face  42  of one tooth  38 , while side  34  of tooth  31  is positioned contacting an edge between side  40  and the respective end face of an adjacent tooth  38 . Gradual forced insertion of teeth  31  between teeth  38  of gear  2  and the pressure exerted in direction  44  between gear  2  and device  1  produce considerable pressure between faces  34  and  35  of each tooth  31  and the edges of two successive, adjacent teeth  38 , so as to permanently deform the edges as shown in the enlarged detail of FIG. 4 a . Permanent deformation of the edges is such as to flatten the edges and form respective chamfer faces  45  between respective sides  40  and  41  and respective end faces  42 , and to also form a curl  46   a  on the side of tooth  38 , and a curl  46   b  on face  42  (FIG. 4 a ). 
     That is, each tooth  31  forms, by permanent deformation, chamfer faces  45  on sides  40  and  41  of two adjacent teeth  38  of gear  2 . Chamfer faces  45  are inclined, with respect to respective sides  40  and  41 , at an angle D, which is a complement of 180° with the inclination E of faces  34  and  35  with respect to the axes  39  of teeth  38 . Tests have shown gears  2  to operate best with an inclination E ranging between 5° and 45°. 
     With reference to FIG. 4 b , portion  32  of ring gear  28  of tool  12 , viewed in section, engages one side of gear  2 , with teeth  33  located successively between respective teeth  38  of gear  2 . More specifically, side  37  of each tooth  33  is positioned contacting curl  46   a  between side  41  and respective chamfer face  45 , while side  36  of tooth  33  is positioned contacting curl  46   a  between side  40  and respective chamfer face  45  of an adjacent tooth  38 . Like teeth  31 , the pressure exerted in direction  44  produces considerable pressure between faces  36  and  37  and curls  46   a , so as to deform curls  46   a  as shown in the enlarged detail of FIG. 4 b . Deformation of curls  46   a  is a permanent deformation by which curls  46   a  are flattened and “ironed out” so to speak on to sides  41 , while curls  46   b  projecting from end faces  42  of tooth  38  are removed by cutting edges  23  of deburring disks  16 ,  17 . 
     In the variation shown in FIGS. 5,  5   a  and  6 , tool  12  comprises a ring gear  48  in turn comprising teeth  49  and teeth  50  equally spaced and alternating with each other about ring gear  48 . 
     Each tooth  49  comprises a side  51  inclined at a given angle with respect to a direction parallel to axis  25 , and a side  52  inclined with respect to axis  25  at a smaller angle than side  51 ; and sides  51  and  52  of each tooth  49  form an angle H comparable to angle B in the FIG. 3 embodiment. Each tooth  50  comprises a side  53  inclined at a given angle with respect to axis  25 , and a side  54  inclined with respect to axis  25  at a given angle considerably smaller than that of side  53 ; and sides  53  and  54  of each tooth  50  form an angle I comparable to angle A in the FIG. 3 embodiment. Teeth  49  and  50  are so arranged that side  51  of each tooth  49  faces side  53  of the adjacent tooth  50  on one side, and side  52  faces side  54  of the adjacent tooth  50  on the opposite side, and so that flared gaps  55   a  of a given size between sides  51  and  53  of adjacent teeth  49  and  50  alternate about ring gear  48  with flared gaps  55   b  formed between sides  52  and  54  of respective teeth  49  and  50  and considerably smaller than gaps  55   a.    
     With reference to FIG. 6, in actual use, ring gear  48  of tool  12 , viewed in section, engages gear  2  on one side, with teeth  49  and  50  located successively between respective teeth  38  of gear  2 . More specifically, sides  51 ,  52  and  53 ,  54  of respective teeth  49  and  50  are brought into contact with the edges between sides  40  and  41  and end faces  42  of gear  2 . In particular, the edge between side  41  and end face  42  of each tooth  38  contacts side  53 ; and, as in the FIG. 3 embodiment, side  53  of tooth  50  forms, by permanent deformation, chamfer face  45  between side  41  and face  42 . 
     The edge between side  40  and end face  42  contacts side  51 ; tooth  49 , by means of a respective side  51 , forms, by permanent deformation, chamfer face  45  between side  40  and respective end face  42 ; and the formation of chamfer face  45  produces a respective curl  46   a , which is eliminated by further permanent deformation by the pressure exerted by faces  52  and  54  of respective teeth  49  and  50 . In other words, each side  41  is brought into contact with a respective side  52  of a tooth  49 , which provides for further permanent deformation by exerting pressure on curl  46   a . Similarly, each side  40  is brought into contact with a respective side  54  of a respective tooth  50 , which provides for further permanent deformation by exerting pressure on curl  46   a . As in the FIG. 3 embodiment, the outer curl  46   b  is removed by cutting edges  23  of disks  16 ,  17 . 
     The main characteristics of the present invention may be summed up as follows: 
     (a) double permanent deformation to form the edge between the side and one face, and to flatten the inside curl on the side of the gear tooth; 
     (b) highly compact tools  12 ,  13 , the ring gears  28 ,  48  of which are formed in one piece with respective disks  26 , thus reducing production and storage cost of tools  12 ,  13 ; 
     (c) highly straightforward timing of the chamfer-face-forming and curl-flattening teeth; 
     (d) the axial distance between tools  12  and  13  of the same device may be varied extremely easily to work gears  2  of different axial widths, while at the same time maintaining the same angle C of inclination of the spiral of the teeth of gear  2 ; and 
     (e) within certain limits, a device comprising two tools  12 ,  13  may be used to work gears  2  with slightly differing angles C of inclination of the teeth, by simply rotating one tool  12 ,  13  with respect to the other  13 ,  12  depending on the difference in the angle C of inclination of the teeth of gear  2 .