Abstract:
Method for making a form-fitting connection between a tool insert and a tool holder of a rotatingly driven tool, wherein the tool holder has bearing surfaces by which forces or torques are transmitted to the tool insert, wherein the tool insert is made from a material harder than that of the tool holder and by sintering a green compact of powder. A sintered green compact for the tool insert is used as a hob, by which the bearing surfaces in tool holders are manufactured by punching or press-forming.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   From DE 101 362 93 A1, the entire contents of which is hereby incorporated by reference in its entirety, a thread former or tap with a shaft and a separate profile element is provided as a forming or cutting profile section, which is centrically and splinedly attachable on the shaft by means of a fastening device. The profile element is plate-shaped and has a running-in or lead cone, respectively. High spots and/or pits are formed on the end surfaces of the shaft and on the side surface of the profile element facing it, which form-fittingly engage into each other. Through this, an automatic centering of the profile element on the shaft takes place when the profile element is put on the shaft. In addition, a torque transmission from the shaft to the plate-shaped profile element takes place by the form-fitting connection. The profile element is fixed on the shaft by means of a centrical screw in an axial threaded bore. The high spots can be formed by radial ribs and the pits by radial grooves. The profile element is made from a hard metal, ceramics or the like. The shaft is made from a suitable tool steel, for instance. In the known thread former or tap, the provision of a multiplicity of different profile elements with different diameter, different lead and so on is possible for the purpose of connection with a standardized shaft. As a consequence, only the profile element is required to be made from a suitable hard material. As a consequence, the expense of material is significantly reduced. 
   It is usual to manufacture tools and tool inserts from a green compact of a powder of a hard material by the sintering method. This is also invited in the profile element of the known tool. The high spots and the pits for a bearing surface around tool holders are made by cutting operation. Even the most accurate cutting operation can not avoid the occurrence of dimension variations. However, the dimension variations affect the precise arrangement of the profile elements on the tool shaft and they influence the torque transmission behaviour in the use. 
   The present invention is based on the objective to provide a method for making a form-fitting connection between a tool insert and a tool holder of a rotating tool which is free from float. 
   BRIEF SUMMARY OF THE INVENTION 
   In the method according to the invention, a sintered green compact for the tool insert is used as the hob by means of which the bearing surfaces in the tool holder are made by press-forming. 
   When pressing and sintering a tool insert, the bearing surfaces on the tool insert which co-operate with bearing surfaces of the tool holder can be formed at the same time through corresponding realisation of the pressing tool. The method according to the present invention makes use of this, as well as of the fact that the tool insert is harder than the tool holder. Thus, in the method according to the invention, one sintered green compact out of a multiplicity of equal green compacts for cutting inserts is used as a hob. With the aid of the hob, the bearing surfaces are punched into tool holders by the stamping method. 
   The method according to the present invention has the advantage that a float between the bearing surfaces of the tool insert at the one hand and the tool holder on the other hand does not occur, because both bearing surfaces originate from one original form, which is formed by the pressing tool for making the green compacts for the tool inserts. Conventionally, bearing surfaces are made by cutting form-giving, which naturally does not exclude a float. Deviations with respect to prescribed dimensions in this “original tool” are reproduced in the green compact and are in turn transmitted to the tool holder. The sintered green compacts from which tool inserts are made have also the deviations of the original tool, so that the bearing surfaces of tool insert and tool holder engage accurately into each other, i.e. without float. 
   It is to be understood that the described advantage is obtained essentially only in the case when the sintered green compact used as a hob as well as the tool inserts are produced with the same tools of the powder press. 
   The present invention can be used everywhere where tool inserts co-operate form-fittingly with a tool holder, in the cutting tips of a milling cutter which are held on bearing surfaces of the tool holder, for instance (e.g. as in DE 198 48 045 C2, the entire contents of which is hereby incorporated by reference in its entirety). 
   According to one embodiment of the present invention, it is provided that the method according to the invention is also used for tools with a shaft as the tool holder and with a thread former or a cutting tool as a tool insert, the tool insert being arranged axially and centrically to the shaft in this. The tool insert is preferably made from a solid hard material and the tool holder from a suitable tool steel. 
   According to one embodiment of the present invention, the bearing surfaces are formed with prismatic high spots and pits. Alternatively, the bearing spots are formed by gear teeth on the ends of tool insert and tool holder, wherein the crowns and bottoms of the teeth are arranged radially in equal distances from each other in the perimeter direction. 
   In the known tool described above, the bearing surfaces are such that tool holder on the one hand and profile element on the other hand can occupy different turning positions with respect to each other. However, as there can be dimensional differences when seen in the perimeter direction, it is advantageous according to a further embodiment of the present invention when the bearing surfaces have an indexing such that the bearing surfaces of tool insert and tool holder can be brought into form-fitting engagement in only one turning position with respect to each other. 
   For instance, the indexing may be obtained in that one high spot or pit is dimensioned differently with respect to the others, so that in this manner the form fit can be obtained only by bringing the prismatic high spot and pit in engagement with each other. 
   The method according to the invention does not only lead to greater precision in the match of tool insert and tool holder, but it makes also possible a very economic production method. Further, a higher stability on the bearing surfaces is also attained by the method according to the present invention. In each case it is greater than in the production of the bearing surfaces by a cutting operation. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The present invention will be explained in more detail below by means of drawings of shown examples of its realisation. 
       FIG. 1  shows a sintered green compact for the execution of the method according to the present invention. 
       FIG. 2  shows a section through the green compact according to  FIG. 1   
       FIG. 3  shows a section through the representation according to  FIG. 2  along the line  3 - 3 . 
       FIG. 4  shows a perspective view of another embodiment of a green compact as a hob for the execution of the method according to the present invention. 
       FIG. 5  shows the final view of the green compact according to  FIG. 4   
       FIG. 6  shows a perspective view of another embodiment of a green compact, usable as a hob for the execution of the method according to the present invention. 
       FIG. 7  shows the final view of the green compact according to  FIG. 6 . 
       FIG. 8  shows a cutting tool with cutting tips, in a perspective view. 
       FIG. 9  shows a thread forming tool in a perspective view. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   While this invention may be embodied in many different forms, there are described in detail herein a specific preferred embodiment of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated 
   In  FIG. 1 , a sintered green compact  10  can be recognised, which has a cylindrical body  12 , the one end surface of which is provided with gear teeth  14 . The green compact  10  is formed from a hard metal or tool ceramics and serves as a profile element for a thread former according to DE 101 36 293 A1 described above, for instance. For this purpose, a green compact body corresponding to the green compact according to  FIG. 1  is cutting processed, in order to provide it with a suitable tool profile (cutting edges, grooves and the like). However, in the method described below such processing is not undertaken with the green compact  10 , instead it remains unprocessed and is taken as a hob for a stamping operation. 
   As is known, the green compact  10  is produced in a powder press by means of an upper and a lower stamp, which co-operate with a die. The gear teeth  14  are usually formed by the suitably formed lower stamp. The upper stamp acts on the opposite side and has a flat front surface, for instance. In addition, an axial circular bore  16  is formed. 
   It is not obligatory that the cylindrical body  12  has the same height as have the green compacts which are subsequently subjected to a form-giving cutting operation to yield profile elements or cutting inserts, respectively. How high or long, respectively, the cylindrical body  12  is, depends only from the powder amount and the path length of the upper stamp. 
   In the case of the  FIGS. 1 to 3 , special gearing teeth  14  are formed in the green compact  10 . Individual teeth  18  are arranged in uniform perimeter distances from each other with their radial crowns. The bottom in the tooth gaps is also formed by only one line, as results from the overall view of the  FIGS. 1 to 3 . The gearing teeth  14  are formed in a somewhat elevated portion  20  of the body  12 , wherein the crown lines  22  lay in a plane perpendicular to the axis of the cylindrical body  12 , whereas the bottom lines  24  are inclined about a small angle thereto, as results from  FIG. 2 . Thus, there are front gearing teeth  14 . 
   With the aid of the green compact  10 , a hob is obtained, with the aid of which complementary teeth are formed in a tool holder, the end of a tool shaft for instance. Such a tool shaft with a complementary punching is not shown here. As a consequence, a tool insert, for instance a profile element according to the thread former described above, can come into form-fitting engagement with the gearing teeth of the tool holder, the tool shaft in particular, with its own gearing teeth, which are similar to the gearing teeth  14 . As the gearing teeth of the hob are made by the same powder press as the gearing teeth of the tool inserts, a high coincidence of dimension and form exists between the gearing teeth of tool insert and tool holder. As a consequence, a great torque can be transmitted, in particular also by means of the form of the gearing teeth shown in  FIGS. 1 to 3 . 
   As can be recognised from  FIG. 3 , one tooth  18   a  is formed in a flattened manner. Thus, a complementary pit is formed when the counter profile is formed in the tool holder. As a consequence, it is possible to bring the profiles of tool insert and tool holder form-fittingly together only when the tooth  18   a  is aligned to the complementary pit  18   a . Thus, the indexing provides that tool insert and tool holder are always form-fittingly connected in the proper turning position with respect to each other. 
   In the  FIGS. 4 to 7 , two different embodiments for the realisation of bearing surfaces for form-fitting connection of tool insert and tool holder are represented. In the  FIGS. 4 and 5 , a green compact  10   a  with a cylindrical body  12   a  and a bore  16  a can be recognised. One recognises that a series of prismatic high spots  30  is formed on an elevated portion  20   a  on one end of the cylindrical body  12   a . The prismatic high spots  30  are arranged radially and are set in a series at equal distances from each other. They have slant side surfaces  32 , through which the high spots  30  taper towards the free end. 
   In the embodiment according to  FIGS. 6 and 7 , a series of round naps  36 , flattened on their upper ends, are formed on an elevation  20   b  of the cylindrical body  12   b . The naps  36  are arranged on a circle coaxial to the axis of the cylindrical body  12   b  and are set in a series at equal distances from each other. When used as a hob, a complementary profile is formed in the tool holder, so that upon connection of the tool inserts with the tool holder, a form-fitting engagement of the profiles is then ensured. Even in the embodiments according to the  FIGS. 4 to 7 , an indexing as described above is functional, i.e. a connection of tool insert and tool holder is possible only in a predetermined relative turning position of the two parts with respect to each other. For instance, a prismatic higher spot  30  or a nap  36  which has less or greater height than all the others can be formed. 
   In  FIG. 8 , a cutting tool is shown, with a shaft-like cutting body  40 , which has chambers in perimeter spacings on one end, which have bearing surfaces  42 ,  44 ,  46  for cutting tips  48 . The cutting tips have a bore  50  and a rectangular frame  52  on the rear side, which co-operates with the cutting tips  42  to  46 . At the bottom of the chambers, a threaded bore  54  is formed, into which an attachment screw  56  is screwed in when the cutting tips  48  of the chambers are fixed with the aid thereof. 
   It will not be dealt in more detail with the realisation of the cutting tips  48 . They are made of a very hard material, of hard metal for instance, and the bearing surfaces  42  to  46  are formed in the holder  40  with the aid of a sintered cutting tip  48 . Thus, any cutting operating is avoided. An accurate form fitting connection is achieved between the cutting tips  48  and the bearing surfaces. 
   In  FIG. 9 , a tool holder in the form of a shaft  60  can be recognised, which has a prismatic higher spot  62  of pentagonal contour with slant surfaces  64  on its face. A profile element  66  with thread forming profile  68  has a profile  70  complementary to the prismatic higher spot  62  at a front end, through which profile element  66  and shaft  60  engage form-fittingly into each other. The profile element  66  has a centrical bore  72 , which is aligned to an axial bore  74  of the shaft  60 . With the aid of a not shown screw, the profile element  66  can be screwed down against the shaft  60 . 
   In turn, the profile on the face of the shaft  60  can be produced with the profile of the profile element  66  in the already described manner by punching or press-forming. 
   The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims. 
   Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim  1  should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below. 
   This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.