The invention concerns a thread former according to the preamble of claim 1. Thread formers serve for non-cutting shaping of threads. The free end of the main body constitutes a working part that, distributed about the circumference, has moldings. The working part has a polygonal cross-section. In the area of the cross-sectional corners, the moldings in the form of cylindrical bars are provided that consist of hard and wear-resistant material. The moldings are soldered into grooves of the main body. In particular the common profile grinding for producing the thread-forming teeth in the main body and in the inserted moldings causes difficulties because the grinding wheels that are used for this purpose clog quickly. It is the object of the invention to develop the thread former of the aforementioned kind such that it can be produced in a simple and cost-effective way. This object is solved for the thread former ofthe aforementioned kind in accordance with the invention with the characterizing features of claim 1. In the thread former according to the invention, the moldings project radially past the main body to such an extent that with the profiling tool, preferably a grinding wheel, only the moldings for generating the thread-forming teeth are cut while the profiling tool no longer comes into contact with the main body. The profiling tool must only cut one kind of material so that the manufacturing process becomes simpler and faster. The profiling tool can therefore be selected optimally with respect to its profiling task. The moldings are advantageously fastened in receiving grooves of the main body. In the receiving grooves, the moldings can be fastened reliably, for example, by soldering or by an adhesive. The moldings advantageously can be formed to be symmetrical to their longitudinal center plane. However, it is also possible that the moldings are formed to be asymmetrical relative to their longitudinal center plane. The moldings can be arranged axis-parallel, i.e., the longitudinal axis of the thread former is positioned in the longitudinal center plane of the moldings. The bottom of the receiving grooves extends in this case parallel to the axial plane of the thread former. Depending on the type of use of the thread former, it is also possible that the moldings are positioned at an angle to a correlated axial plane. In this case, the bottom of the receiving grooves extends from the free end of thread former at a slant in the direction toward the exterior side of the thread former. The moldings, in a side view, can be positioned at an angle relative to the longitudinal axis of the thread former wherein the moldings may extends straight as well as in a spiral shape. In one embodiment, the moldings are advantageously arranged uniformly distributed about the circumference of the main body. In case of particularly long thread formers or in case of thread formers that operate at very high cutting speeds, it is advantageous when the moldings are arranged in non-uniform distribution about the circumference of the main body. Such non-uniform distribution leads to smoother running of the thread former. The moldings can be arranged symmetrically to the axial plane of the main body in such a way that their longitudinal plane is located in the corresponding axial plane of the moldings. It is however also possible that the moldings are arranged such that their longitudinal center plane is positioned at an acute angle relative to the correlated axial plane of the main body that extends through the moldings. The area between neighboring moldings can be used for supplying cooling lubricant to the processing site. However, it may also be advantageous to provide the thread former with an inner cooling medium supply. In this way, the cooling medium can be applied in a targeted fashion to the processing site of the thread former. Further features of the invention result from further claims, the description, and drawings.
The invention will be explained in more detail with the aid of some embodiments illustrated in the drawings. It is shown in: FIG. 1 in perspective illustration a first embodiment of a thread former according to the invention; FIG. 2 the thread former according to FIG. 1 in a side view; FIG. 3 in a detail view an end face of the thread former according to FIG. 1. FIG. 4 to FIG. 6 in an end view, respectively, further embodiments of thread formers according to the invention; FIG. 7 in perspective illustration a further embodiment of a thread former according to the invention whose moldings are illustrated only schematically; FIG. 8 in a side view the thread former according to FIG. 7; FIG. 9 in a detail view an end face of the thread former according to FIG. 7; FIG. 10 to FIG. 12 in illustrations according to FIGS. 7 to 9 a further embodiment of a thread former according to the invention; FIG. 13 and FIG. 14 in a side view, respectively, the thread former according to the invention with inner cooling action; FIG. 15 in an end view a further embodiment of a thread former according to the invention The thread formers disclosed in the following serve for non-cutting shaping of threads. In particular, with the thread formers internal threads are formed. The thread former according to FIGS. 1 to 3 has a main body 1′ with a preferably cylindrical clamping shaft 1 with which it is received in a tool receptacle. The clamping shaft 1 is provided at one end with a profiled section 2 with which positive fit of the thread former in the tool receptacle in rotational direction is achieved. The clamping shaft 1 passes with a short conical intermediate section 3 into a preferably cylindrical end section 4. It has a smaller cross-sectional surface area than the clamping shaft 1 in the area between the profiled section 2 and the intermediate section 3. The end section 4 is adjoined by a head section 5 to which moldings 6 are attached in a way to be described in the following. In deviation from the illustrated embodiment, the main body 1′ can have across its length any other suitable cross-sectional configuration. The clamping shaft 1 with the profiled section 2, the intermediate section 3, the end section 4, and the head section 5 is of a monolithic configuration and is comprised of a tough material, for example, a high-speed steel. The head section 5 has a conically tapering end. The head section 5 is provided with receiving grooves 7 for receiving the moldings 6 that extend axially away from the end face 8 of the head section 5. The receiving grooves 7 extend, for example, approximately about half the axial length of the head section 5. Depending on the design of the thread former, the receiving grooves 7 and thus also the moldings 6 disposed therein can also have different lengths. The receiving grooves 7 end at a minimal spacing from the end section 4 by tapering into the exterior side of the head section 5. The receiving grooves 7 can be introduced in a very simple and inexpensive way into the head section 5 by means of a grinding wheel. As can be seen in FIG. 3, the receiving grooves 7 have a planar bottom 9 that connects two parallel extending planar lateral surfaces 10, 11 with each other. The bottoms 9 of the receiving grooves 7 are positioned tangentially to an imaginary circle about the longitudinal axis 12 of the thread former. The moldings 6 are attached to the receiving grooves 7, for example, by soldering, by an adhesive, by welding or other conventional joining methods. An additional form-fitting action of the moldings 7 in the receiving grooves 7 is advantageous but not necessarily required. As is illustrated in FIG. 2, the moldings 6 project radially past the head section 5. This radial projection of the moldings 7 is so large that when forming the thread exclusively the moldings 6, but not the main body 1′, will contact the respective workpiece. The moldings 6 can be made of hard metal, cermet, CBN, diamond or other cutting materials of great hardness. The moldings 6 have at their exterior side thread-forming teeth 13, 14 (FIG. 2) positioned at a spacing behind each other which extend across the width of the moldings 6. The thread-forming teeth 13, 14 have across their length a constant pitch in order to generate the desired thread in the bore wall. The thread-forming teeth 13 that are neighboring the planar end face 8 have a smaller outer diameter than the subsequently arranged thread-forming teeth and serve for a stepwise forming of the thread during thread manufacture. In this way, it is achieved that the thread depth is not generated in a single pass but that first the thread is produced only over a portion of its profile depth in the bore wall and only the following thread-forming teeth 13 will complete the thread to the full profile depth. Also, depending on the configuration of the thread former, only one or several thread-forming teeth 13 may be provided in the initial thread-forming area of the thread former. In the embodiment, in the initial thread-forming area of each molding 6 there are three thread-forming teeth 13. The following thread-forming teeth 14 serve for guiding the thread former during the process of thread forming. The moldings 6 have advantageously a rectangular cross-section. The longer side 15 of the cross-section (FIG. 3) of the molding 6 is facing the bottom 9 of the receiving groove 7, preferably is connected to it. The moldings 6 of course can also have different cross-sectional shapes, for example, round or polygonal cross-section. As shown in FIG. 3, the thread-forming teeth 13, 14 are curved in circumferential direction of the thread former such that, in plan view according to FIG. 3, they have at half the length the greatest spacing from the longitudinal axis 12 of the thread former. The thread-forming teeth 13, 14 extend about a relatively great length in the circumferential direction of the head section 5. For example, the thread-forming teeth 13, 14 extend about an angle range between approximately 30 degrees and 60 degrees, preferably approximately about 45 degrees. In the embodiment according to FIGS. 1 to 3, the moldings 6 are embodied and arranged symmetrical to the respective axial plane 16 of the thread former. The moldings 6 have about the circumference of the head section 5 an angular spacing of 90 degrees relative to each other. Between neighboring moldings 6 intermediate spaces 17 are formed by means of which during the thread forming process a cooling lubricant can be supplied to the processing site. Since the thread-forming teeth 13, 14 are provided exclusively on the moldings 6, during manufacture of the thread-forming teeth 13, 14 or when they are re-ground the grinding wheel must cut only one type of material so that the manufacturing process becomes simpler and faster. The bottom 9 of the receiving groove 7 may extend parallel to an axial plane 16 of the thread former. The moldings 6 are formed such that their cross-sectional thickness, beginning at the end face 8 of the thread former, increases in axial direction continuously. The moldings 6 are arranged axis-parallel on the head section 5. The moldings 6 may also be attached conically in relation to the longitudinal axis 12 of the head section 5. In this case, the moldings 6 extend from the end face 8 of the head section 5 at a slant outwardly. With the aid of FIGS. 4 to 6 it will be explained in an exemplary fashion that the moldings 6 can also be arranged non-uniformity about the circumference of the head section 5 as well as angled relative to the corresponding axial planes. FIG. 4 shows the situation that oppositely positioned moldings 6a, 6c and 6b, 6d are displaced at a minimal angle relative to each other. All of the moldings 6a to 6d are symmetrical to their correlated axial plane 16 or their longitudinal center plane 24. The axial planes 16 of the oppositely positioned moldings 6a, 6c and 6b, 6d are positioned at an angle that deviates slightly from 180 degrees relative to each other, respectively. The arrangement of the moldings 6a to 6d along the circumference of the head section 5 is selected such that the moldings 6a and 6b as well as 6d and 6c have a smaller spacing relative to each other than the moldings 6a and 6d or 6d and 6d. With this non-uniform distribution of the moldings about the circumference of the head section 5 a smoother running of the thread former during thread forming is achieved. In particular, this non-uniform distribution of the moldings 6a to 6d is advantageous for especially long thread forms. Also, in case of thread formers that operate at very high cutting speeds the moldings 6a to 6d that are non-uniformly distributed about the circumference of the head section 5 calm the running of the threat former. The thread former according to FIG. 4 can also be designed such that, for example, the moldings 6a, 6c are positioned diagonally opposite each other while the moldings 6b, 6d are displaced in circumferential direction relative to each other. In this way, a non-uniform distribution of the moldings is achieved also. FIG. 5 shows the possibility to distribute the moldings 6 uniformly about the circumference of the head section 5. In contrast to the preceding embodiments the moldings 6 are however fastened to the thread former in such a way that the longitudinal axes 24 of the moldings 6 are positioned at an angle relative to the axial planes 16 that extend at the radial external side of the moldings through their center 18. Moreover, the moldings 6 are not arranged to be axis-parallel on the head section 5 but extend in longitudinal direction of the head section 5 at a slant. Oppositely positioned moldings are arranged such that the aforementioned center 18 is positioned in the outer radial area of the moldings on a common axial plane 16, respectively. The two axial planes 16 of the moldings 6 that are formed in this way are positioned at a right angle to each other. The moldings 6 are of identical design and arranged on the head section 5 slantedly in the same direction. In other respects, the moldings 6 are of the same configuration as in the preceding embodiments. FIG. 6 shows in an exemplary fashion that the moldings 6 in deviation from the preceding embodiments may also have an asymmetrical cross-section. The moldings 6 themselves are positioned diametrically opposed to each other on the head section 5 in the way described. Moreover, the moldings 6 are uniformly distributed about the circumference of the head section 5. As a result of the asymmetric cross-sectional configuration, the part 18 of each molding 6 that is positioned farthest outwardly in radial direction is no longer positioned at half the width of the molding. The axial planes 16 of the thread former that extend through this outer point 18 of the moldings are positioned at an angle deviating from 90 degrees relative to the bottom 9 of the receiving groove 7 or to the cross-sectional side 15 of the moldings 6. The moldings 6 themselves are positioned axis-parallel and, as in the embodiment according to FIGS. 1 to 3, can be positioned with their cross-sectional side 15 parallel to the respective axial plane 16 but may also be positioned an acute angle relative thereto. In the described embodiments the thread-forming teeth 13, 14 each have pressing edges 19 that, in the embodiments according to FIGS. 1 to 5, are ground centrally relative to the molding. In this way, the part 18 that is positioned farthest outwardly in radial direction of each molding 6; 6a to 6d is positioned of half the length of these pressing edges 19. In the embodiment according to FIG. 6 the pressing edges 19 are ground off-center relative to the molding 6 so that the part 18 of the pressing edges 19 that in radial direction projects farthest outwardly no longer is positioned at half the length of the pressing edges. FIGS. 7 to 9 show a thread former where the moldings 6 are arranged with the same pitch, respectively, along the circumference of the head section 5 of the thread former. The receiving grooves 7 extend from the planar end face 8 of the thread former into the end section 4. The moldings 6 are each of same configuration and, relative to their longitudinal center plane 24, of a symmetrical cross-section. The moldings 6 have the thread-forming teeth 13, 14 with which the thread is produced in the workpiece and with which the thread former is guided. Each molding 6 has a planar end face 20 that is positioned in the planar end face 8 of the head section 5. A slanted surface 21 adjoins the end face 20 at an obtuse angle. The moldings 6 can be arranged axis-parallel. In the embodiment, the moldings 6 have also a rectangular cross-section. With their cross-sectional side 15 the moldings 6 rests against the bottom 9 of the receiving grooves 7. The receiving grooves 7 can be designed such that their bottom 9 extends parallel to an axial plane of the head section 5. However, it is also possible that the bottom 9 extends at an acute angle to the corresponding axial plane of the head section 5. FIGS. 10 to 12 show a thread former in which the receiving grooves 7 for the moldings 6 extends also into the end section 4. The moldings 6 themselves extend in accordance with the preceding embodiment only across a portion of the length of the head section 5. In contrast to the preceding embodiment the receiving grooves 7 have only a minimal pitch so that accordingly also the moldings 6 have only a minimal pitch. The pressing edges 19 of the moldings 6 are ground, as in the preceding embodiment, centrally relative to the molding 6. As illustrated in FIG. 12, the moldings 6 are positioned at an angular spacing of 90 degrees relative to each other. In other respects, the thread former is of the same configuration as the embodiments according to FIGS. 1 to 4. The thread formers can also be provided with an inner cooling medium supply in order to convey the cooling medium into the processing area. FIG. 13 shows in an exemplary fashion a central axial cooling bore 22 that extends from the clamping end 2 into the head section 5. Cooling medium bores 23 extend at a slant outwardly away from the cooling medium bore 22 and open into the area between neighboring moldings 6 at the head section 5. The cooling medium is thus directly transported during thread-forming action through these cooling medium bores 22, 23 into the processing area of the thread former so that an optimal cooling action is ensured. In the exemplary illustrated embodiment according to FIG. 14 only the central cooling medium bore 22 is provided that opens at the end face 8 of the thread former. FIG. 15 shows in an exemplary fashion the possibility to configure the moldings also with a different cross-sectional shape. In the preceding embodiments the moldings 6 have an angled cross-section. In this embodiment, the outer side 15 of the molding 6 facing the bottom 9 of the receiving grooves 7 is in cross-section of partcircular shape. The bottom 9 of the receiving grooves 7 has also a matching cross-sectional shape. The moldings 6 are positions with their curved outer side 15 in flat contact on the curved bottom 9 of the receiving grooves 7. The area radially projecting past the head section 5 of the moldings 6 is provided with the thread-forming teeth 13, 14 with the pressing edges 19. When the moldings 6 and the head section 5 of the thread former in a preferred way are connected by soldering or adhesive connection detachably with each other, a simple refurnishing of the thread former by reusing the main body 1′ is ensured. It is only necessary to exchange the moldings 6. The thread former with the moldings 6 can be provided with wear protection layers or friction-reducing layers. In this way, a long service life of the thread former is achieved. In the described and illustrated embodiments the thread former has four moldings. Depending on the application and/or size, the thread former can also have fewer than or more than four moldings. |
