Abstract:
A grinding wheel and a method for grinding bar blade for the production of spiral gear teeth are described. For economical grinding of such bar blades the grinding wheel has a conical grinding surface (Pp) widening from a small diameter (d 1 ) to a large diameter (d 2 ), a cylindrical grinding surface (Ps) adjoining the conical grinding surface (Pp), and a toroidal grinding surface (G) adjoining the cylindrical grinding surface (Ps). The grinding wheel embodied in this manner enables profile grinding (rough grinding) and subsequent generating grinding (finish grinding) of the surfaces of the bar blade without the necessity of remounting the blade. For practical purposes the grinding wheel rotates about a stationary axis (S), and the bar blade to be ground is guided along the grinding wheel [( 12 )] at appropriately set angles.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Patent Application PCT/EP02/00600 filed on Jan. 22, 2002 and German Patent Application No. 101 03 755.4 filed on Jan. 27, 2001.  
         FIELD OF THE INVENTION  
         [0002]    This invention refers to a grinding wheel and to a method of grinding bar blades, particularly carbide blades for the production of bevel and hypoid gears having arcuate teeth.  
         BACKGROUND OF THE INVENTION  
         [0003]    A known blade for the production of arcuate teeth is designed as a cuboid bar with a shaft having a trapezoidal end. The trapezoidal end comprises a relief flank, a minor flank, a head surface connecting the relief flank with the minor flank, and a rake flank.  
           [0004]    A method and a grinding wheel for grinding carbide inserts affixed to the teeth of a grinding tool are known from EP 0 343 983 A2. The design of the grinding wheel is such that its working regions are capable of grinding not only flat surfaces on the carbide inserts, but also adjacent curved surfaces of the tooth.  
           [0005]    It is the object of the present invention to provide a grinding wheel and a method for rapid, efficient and precise grinding of bar blades.  
         SUMMARY OF THE INVENTION  
         [0006]    The grinding wheel according to the invention has a conical grinding surface smoothly adjoined by a cylindrical grinding surface smoothly adjoined in turn by a toroidal grinding surface. Therefore, the relief flank, the minor flank and-the rake flank can be rough ground by profile grinding with the method according to the invention using the conical grinding surface and its area of transition to the cylindrical grinding surface. The relief flank and the minor flank can be subsequently finish ground by generating grinding at the toroidal grinding surface. In this manner it is possible with one single grinding wheel not only to rough grind all three essential surfaces, namely the relief flank, the minor flank and the rake flank, but also to finish grind the relief flank and the minor flank without resetting the blade. This permits performance of a rapid, complete and precise grinding of the blade.  
           [0007]    In one advantageous embodiment of the invention the conical and the cylindrical grinding surfaces have a coarser grain than the toroidal grinding surface. For this reason, the minor flank and the relief flank can be rough ground and the rake flank can be ground, all at high stock removal rates.  
           [0008]    In another advantageous embodiment of the invention, the cylindrical grinding surface merges tangentially into the toroidal grinding surface. For this reason it is advantageously possible in one translational movement first of all to rough grind the head surface of the blade with the cylindrical grinding surface, and to finish grind it with the adjacent toroidal grinding surface. This combination of rough grinding and finish grinding of the head surface in one operation reduces the amount of time required for the entire blade grinding process.  
           [0009]    In yet another advantageous embodiment of the invention a first radius is formed between the conical grinding surface and the cylindrical grinding surface. The toroidal grinding surface here has a circular arcuate cross section with a second radius. The first radius here is larger than the second radius. During the roughing, i.e. in profile grinding of the blade, the relief flank or the minor flank or the rake flank of the blade is brought into contact with the conical grinding surface in such a manner that a respective shoulder surface is ground at the transition of the relief flank or the rake flank to the blade shaft by the first radius and the transition between the conical and the cylindrical grinding surface, or in addition by a portion of the cylindrical grinding surface. Following the profile grinding, the relief flanks or the rake flank is finished by generating grinding with an overlapping relative translational movement between the blade and the grinding wheel relative to the toroidal grinding surface. Since the radius of the toroidal grinding surface is smaller that the first radius in the transitional area between the conical grinding surface and the cylindrical grinding surface, the respective associated shoulder surface does not have to be ground along with the relief flank or the minor flank during their finishing. This means that the toroidal grinding surface is spared and therefore has a longer working life. Furthermore, the grinding process is abbreviated, since the shoulder surfaces between the relief flank or minor flank and the shaft do not have to be finish ground.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    An embodiment of the invention is explained in greater detail below on the basis of the drawings.  
         [0011]    [0011]FIG. 1 shows a plan view of a hard-material bar blade;  
         [0012]    [0012]FIG. 2 shows a lateral inclined view of the bar blade;  
         [0013]    [0013]FIG. 3 shows an enlarged plan view of the rake flank of the bar blade;  
         [0014]    [0014]FIG. 4 shows a cut through the grinding wheel;  
         [0015]    [0015]FIG. 5 shows a perspective view of a grinding machine; and  
         [0016]    [0016]FIGS. 6 a, b, c  show the process of grinding a bar blade using the grinding wheel according to FIG. 4. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    FIGS.  1  to  3  show an example of a bar blade. There is a great variety of blade types. However, all are similar in shape to the one described below (for example, the flank  40  could be located instead on the left-hand side in FIGS.  1  to  3 ).  
         [0018]    According to FIGS.  1  to  3  a cuboid or bar-shaped blade  1  has a shaft  2  with a rectangular cross section, and a trapezoidal tip  3 . A rake flank C is provided on the trapezoidal tip  3 ; a minor flank B extending back from the rake flank C is provided on the left-hand side in FIG. 1 on a flank  5  of the tip; a relief flank A extending back from the rake flank C is provided on the right-hand side in FIG. 1 on a flank  6  of the tip; and a head surface K extending back from the rake flank C is formed on a top face of the tip. A continuous cutting edge  4  runs along the minor flank B, the head area K, the relief flank A and the rake flank C. As shown here, shoulder areas As or Bs, respectively, can be provided in the area of transition from the relief flank A and the minor flank B to the shaft  2 . Also, as shown here, a curved shoulder area Cs can be provided in the area of transition of the rake flank C to the shaft  2 . The head, flank, and shoulder are shown on the right in FIG. 2 as  30 ,  40 , and  50 , respectively.  
         [0019]    The shape of the right-hand and the left-hand flanks of the trapezoidal tip  3  is described below on the basis of FIG. 3. However, due to the largely similar shape of the three flanks, only that of the right-hand flank  6  will be described in detail. The shoulder area As on the right-hand flank  6  has a straight segment  7  and a curved segment  8  with a radius Rs. The straight segment  7  of the shoulder area As merges at a tangent into the curved segment  8 , which in turn merges at a tangent into the relief flank A at point F. The relief flank A merges tangentially at point L into a curved segment with radius R 2  on the top face of the trapezoidal tip  3 . The curved segment in turn merges tangentially into the head surface K, and the head surface K merges tangentially into a curved area  10  with a radius R 1 , which in turn connects tangentially to the minor flank B. The right flank  6  and the left flank  5  each has a length PL, and the straight segment of the shoulder area As or Bs, respectively, has a length SL. The profile shapes of the flank  6  (length PL) and of the flank  5  depend on the tooth-cutting process. In any event they are not straight.  
         [0020]    [0020]FIG. 4 shows a grinding wheel  12  with which the blade according to FIGS.  1  to  3  can be ground. The grinding wheel  12  has an axis of rotation S, in relation to which the grinding wheel is mounted in rotational symmetry. The grinding wheel  12  has on one end face a circular clamping surface  13  perpendicular to the axis of rotation S. A conical grinding surface Pp with a small diameter d 1  and a large diameter d 2  extends from the outer periphery of the clamping surface  13 . The small diameter d 1  here is located at the clamping surface  13 . A curved grinding surface  14  with the radius Rs follows tangentially at the side with the large diameter d 2  of the conical grinding surface Pp. This grinding surface  14  in turn merges into a cylindrical grinding surface Ps. A toroidal grinding surface G having a circular arcuate cross section with a radius Rg tangentially adjoins the cylindrical grinding surface Ps. The toroidal grinding surface G extends radially inwardly and merges tangentially into a second conical surface  15  undercutting the toroidal grinding surface G.  
         [0021]    The grinding wheel  12  can be designed as a one-piece grinding wheel in which the conical grinding surface Pp, the cylindrical grinding surface Ps and also the toroidal grinding surface G can have the same grain size and the same bonding agent.  
         [0022]    However, the grinding wheel  12  can also be provided with varying abrasive grain sizes. In this case, the conical grinding surface Pp and the cylindrical grinding surface Ps have a coarser abrasive grain than the toroidal grinding surface G. It is advantageous to apply the different abrasive grain sizes with the same bonding. A small indentation (not shown) can be provided between the toroidal grinding surface G and the cylindrical grinding surface Ps to distinguish the areas with different abrasive grain sizes. Either a galvanic bonding or synthetic resin can be provided as the bonding agent for the abrasive. Either CBN (for HSS) or diamond (for HM) can be used as the abrasive.  
         [0023]    In addition, it is possible to design the wheel  12  in two parts, with the toroidal grinding surface G provided on a ring (not shown) that would be mounted by a flange connection to the cylindrical grinding surface Ps. In this case it would be possible to provide the respective region with the abrasive and bonding agent that are best suited to perform the task at hand. It is also possible to replace the two regions at different times independently of one another as a function of the respective wear.  
         [0024]    [0024]FIG. 5 shows a grinding machine which is equipped with the grinding wheel  12  according to FIG. 4 and which can be used to grind the blade  1 . The machine has a table  17  on which a slide  18  is capable of reciprocating movement along an x-axis. A column  19  is capable of reciprocating movement along a z-axis at right angles to the x-axis. A second slide  20  can be moved on the column  19  along a y-axis perpendicular to the x-axis and to the z-axis. The x-axis, the y-axis, and the z-axis form a rectangular coordinate system. The grinding wheel  12  is mounted so as to rotate on the second slide  20 . A clamping device  21  for holding the blade  1  is mounted on the slide  18 . The clamping device is bearing mounted relative to the slide  18  by a swivel axis C-C and an axis of rotation A-A perpendicular to the swivel axis C-C. The x-axis, the y-axis, the z-axis, the A-A-axis, and the C-C-axis can be used not only for positioning, but also to traverse CNC-controlled paths.  
         [0025]    A chronological description of the operation of grinding the blade  1  with the grinding wheel  12  is given below.  
         [0026]    Grinding the Rake Flank C  
         [0027]    The rake flank C is oriented parallel to the conical grinding surface Pp such that the shoulder surface Cs of the rake flank C is positioned at the curved grinding surface  14  with the radius Rs. The rake flank C and the associated shoulder surface Cs are ground using reciprocating grinding with relatively successive feed of the blade  1  in relation to the grinding wheel  12 .  
         [0028]    Grinding the Minor Flank B  
         [0029]    The left-hand flank  5  is oriented with the minor flank B parallel to the conical grinding surface Pp, with the shoulder surface Bs being positioned at the curved grinding surface  14  with the radius Rs. The minor flank B is then ground together with the associated shoulder surface Bs by reciprocating grinding with successive feed until the desired amount has been removed.  
         [0030]    Grinding the Relief Flank A  
         [0031]    The relief flank A is oriented parallel to the conical grinding surface Pp, with the shoulder surface As being positioned at the curved grinding surface  14  with the radius Rs. The relief flank A is ground together with the associated shoulder surface As by reciprocating grinding with successive feed until the desired amount has been removed.  
         [0032]    Subsequent to the grinding of the relief flanks A and B, the blade has been transformed from the shape represented by a dot-dash line in FIG. 6 a  to that shown as a thin line in FIG. 6 b . A large overmeasure  24  has been left over here, especially at the head end of the blade  1 . An additional comma or sickle-shaped overmeasure  60 —depending on the profile shape—is also left on the relief flanks A and B.  
         [0033]    Grinding the Head Surface K  
         [0034]    After the grinding of the relief flank A the blade  1  is retracted substantially longitudinally of its shaft relative to the conical grinding surface Pp. It is oriented at an angle_ in relation to the cylindrical grinding surface Ps and the toroidal grinding surface G such that first of all the overmeasure  24  on the head  30  of the blade  1  is removed by the cylindrical grinding surface Ps with a movement in the direction of an arrow  22 , then, toward the end of the movement along the arrow,  22  it is moved past the toroidal grinding surface G, and a head surface K is produced.  
         [0035]    Finish Grinding the Minor Flank B  
         [0036]    Following the grinding of the head surface K as described above, the blade  1  is guided by an overlapping movement along the toroidal grinding surface G, so that both the radius R 1  and the remaining comma-shaped overmeasure are ground. Since the radius Rg of the toroidal grinding surface G is smaller than the radius Rs of the curved grinding surface  14 , the process of finishing the minor flank B is completed upon reaching the point Fb, so that the shoulder surface Bs is no longer ground by the toroidal grinding surface G  
         [0037]    Finishing the Relief Flank A  
         [0038]    The blade  1  is reoriented such that the relief flank A at point Fa is positioned at a point on the periphery of the toroidal grinding surface G. Through an overlapping movement of the blade  1  and of the grinding wheel  12 , the comma-shaped overmeasure on the relief flank A is ground down to the final form of the blade  1 . With the blade  1  oriented in the same direction, the radius R 2  and the head surface K are finish ground in a continued overlapping movement. As was the case in the finishing of the minor flank B, the shoulder surface As of the relief flank A is not also ground when the relief flank A is ground by the toroidal grinding surface G. The transition from reciprocating grinding to generating grinding takes place precisely at base point F, so that the shoulder is not finish ground unnecessarily.  
         [0039]    In the process of grinding the blade  1  using the grinding wheel  12  described above, it is not always necessary to grind the rake flank C as well. Instead, the rake flank C is only ground as needed.  
         [0040]    According to FIG. 3 a shoulder angle Sw is formed between the right-hand flank  6  and the shoulder surface As, and also between the left-hand flank  5  and the shoulder surface Bs. Furthermore, according to FIG. 4 a swing angle Pw is formed at the grinding wheel  12  between the conical grinding surface Pp and the cylindrical grinding surface Ps. In the rough grinding of the relief flank A and the associated shoulder surface As, and of the minor flank B and the associated shoulder surface Bs, the respective shoulder angle Sw is determined by the swing angle Pw and the spatial orientation between the blade  1  and the grinding wheel  12 . An interrelationship Rs&gt;Rg exists between the shoulder radius Rs and the generating radius Rg. The shoulder angle or the swing angle has both a geometric and a technological definition.  
         [0041]    [0041]FIG. 6 c  shows the selection of a setting angle AW, which can be selected on either side of a position with a setting angle AW of zero degrees. The overmeasure for the subsequent finishing is optimized by way of the setting angle AW, which can differ from the shoulder angle (30° or 45°). The comma-shaped overmeasure resulting from this is optimally designed in this way. When a certain number of blades has been ground at a certain setting angle AW, a change to another setting angle is made before a significant amount of wear occurs. Each setting angle will result in a removal area or a flattened area in the working region of the grinding wheel  12 . The next setting angle AW is selected such that the next flattened area adjoins the preceding flattened area. The result of this is that at the end, the cross section of the working region is delimited by a polygon. The sides of the polygon here are formed by the flattened areas. The maximum width of the permissible flattened areas, for example, lies within a magnitude of 1 μm.  
         [0042]    To be able to determine the point at which a significant amount of wear has occurred, the removal areas or flattened areas of the grinding wheel working regions produced by the grinding are continuously measured and compared with a value of the maximum permissible removals or flattened areas that corresponds to a significant amount of wear in the working region G of the grinding wheel  12 . A change to another setting angle is made in time before the point at which a significant amount of wear occurs. This process permits optimal exploitation of the toroidal grinding surface G, thereby maximizing the tool life.