WO1997032682A1 - Thread-producing tool - Google Patents

Abstract

The invention concerns a rigid tapping tool which produces an internal thread and is either a screw tap or a thread former. The threaded head of the tool has a conventional chamfer (a) but not a conventional guide part. The disadvantages associated with this part, such as higher friction and the fact that the thread of the guide part occasionally has to cut through irregularly produced chips again, are thus avoided.

Description

THREADING TOOL

The invention relates to an internally threaded tool, which can either be a chip-cutting tap or a non-cutting thread former. The tool is usually made of either high-speed steel or hard metal. Furthermore, the invention provides a method for producing a thread by means of the tool according to the invention. A tap is an internal thread cutting tool with a shank for clamping in a tool holder and with a thread cutting portion, which is made up of screw threads and is interrupted at the free end and consists of screw threads. Following the gate, there is the so-called guide or guide part, which also consists of screw threads interrupted by flutes. However, this guide part does not perform any cutting work, but, as the name suggests, serves to guide and evenly advance the tap through the hole to be tapped. Due to the existence of the guide part, the tap is thus self-propelling forwards, the tool carrier being set up in such a way that it easily accommodates the axial movement of the drill. The tool holder is usually provided with a compensating chuck. In practice, however, the guide part has certain disadvantages. This creates considerable friction between the tool and the thread that has already been cut. This leads to increased thermal and mechanical stress. This friction has a particularly negative effect at high cutting speeds. Furthermore, the guide part hinders the coolant supply to the gate area, where the cutting takes place. Thereby arises at the cutting point increased temperature and thus increased wear. In the case of deep threads, there are additional welding problems. Furthermore, the thread teeth of the guide part have to cut through irregularly running chips again, especially when machining long-chipping materials. Therefore, breakouts in the guide part often occur during this processing; occasionally there is even a total breakage of the taps due to clamped chips. In principle, there are two basic types of taps, namely the blind hole taps (also called blind hole taps) and the through-hole taps. As the names already indicate, the first case involves holes with a bottom that are open on one side, while the second case involves holes that are bottomless and open on two sides. In the first case, the chips must be moved out of the hole, axially opposite to the thread cutting

Direction. For this reason, the flutes are helically shaped in the same direction as the direction of rotation of the drill, which means that they have a cutting effect.

Known blind hole taps are e.g. described in DE-U-86 23 509.5, DE-C-3 037 568 and EP-A-641 620.

In the second case (i.e. with through-hole taps) it is more favorable if the chips are pushed forward through the hole, in the same direction as d: e thread cutting. In this case, therefore, the flutes (or the so-called scarf cut-out grooves) are inclined against the direction of rotation of the drill and thus counteract the drill tip from cutting.

Examples of through taps are described, for example, in DE-A-3 419 850 and DΞ-U-83 24 835.8. Also known are taps ^e r with straight, axially extending flutes which, in principle, neither follow the chips forward, still backwards. These are particularly suitable for short-chipping materials and for shallow thread depths. When using this type of drill, three different types of straight-fluted drills are frequently used, namely a pre-cutter, a center cutter and a finish cutter.

As an example of this type of tap, see US-A-4,708,542.

In contrast to the tap, the thread former does not produce chips; it only deforms the material. Thread formers are also referred to as a "gate" and a guide part, although the term gate is strictly incorrect, since thread formers do not cut. For the sake of simplicity, however, this expression is also used here for the tapering front part, in which, just as with taps, the deformation work for the thread production is carried out. Furthermore, the guide part in thread formers has the same disadvantages as mentioned above with regard to taps. For example, In DE-A-2 414 635, a thread turret according to the

State of the art described.

It is an object of the invention to avoid the above-mentioned disadvantages associated with a guide part. Furthermore, it is an object of the invention to propose a male thread-forming tool which, even without the advantages associated with a guide part, succeeds in creating a standardized thread in a single operation.

These and other tasks which are obvious to the person skilled in the art are solved by the present invention, in which a thread-producing tool is produced with the features specified in the characterizing part of claim 1. The invention will now be described in more detail with reference to embodiments shown in the drawings. It shows

1 shows a spirally grooved tap according to the prior art;

2 shows a blind hole tap according to the invention; 3 shows a second embodiment of a blind hole tap according to the invention;

4 shows a third embodiment of a blind hole tap according to the invention;

5 shows a through-hole tap according to the invention; and

Fig. 6 shows a thread former according to the invention. As shown in Fig. 1, a used blind hole tap comprises a shank 1 and a square 2, which is arranged on the shank 1 for the transmission of a torque in a chuck. The shaft carries a tapered neck 3 with a threaded head 4. The head 4 and the neck 3 are provided with, for example, three equidistant, helical flutes 5. At the operative end, the tool is usually with a conical tip 6, which has no function, but is only there for manufacturing reasons.

As already mentioned above, the used tap (and also the used thread former) comprises a chamfer a and a guide part b. As can be seen from all the figures, the bleed a tapers evenly towards the front. While the entire machining takes place in the gate area a, the guide part b only serves for the axial guidance of the tool in the thread that has already been produced. All taps and turrets are available. therefore after the State of the art on both the gate and the guide part. The length of the guide part is usually about 7 to 14 threads, with blind hole taps in the lower area and through taps in the upper area. The gate length is 1.5 to 6 threads. The well-known taps (and also thread formers) are used for both tapping in normal

Speeds, used for high-speed tapping as well as for rigid tapping. So even in such cases where the tool is taken over by the machine (the so-called rigid thread cutting or thread forming), taps or thread formers with a guide part are used. Of course, this entails the disadvantages discussed above. The present invention has found a remedy for precisely these disadvantages. As can be seen from FIGS. 2 to 6, the geometry and the design of the tools according to the invention differ considerably from the prior art in that a guide part is practically missing. With rigid tapping, as already mentioned, the axial guidance is taken over by the machine; also with reversion. This eliminates the actual purpose of the guide part. As can be seen from FIG. 2, a blind hole tap according to the invention has a chamfer a but practically no guide part b. Although three threads 7 are formed behind the chamfer a in FIG. 2, they do not serve to guide the tool but merely form a reserve for possible regrinding. A possibly ⁰ Nachschleifbarkeit ensure the tool, the tools can bevorzugsweise a grout to three such threads underway. 7 By reducing the length of the guide part to a minimum (if no regrinding is provided, can the guide part can be completely dispensed with), the service life of the tool improves on average by a factor of 2. In addition, chip evacuation is significantly improved with deep threads. The length of the threaded part after the gate (the 5 "regrinding reserve") never needs to be longer than 5 threads, preferably at most 3 (the ground teeth 8 and 10 in FIGS. 3 and 4 are not paid for). 3 shows a further embodiment according to the invention. Here, too, three full threads 7 are provided for regrinding. In order to achieve a longer chip guidance, a number of increasingly ground thread turns 8a, 8b, 8c, etc. are arranged axially behind the thread turns 7. In order not to unnecessarily increase the low friction achieved by the invention, a recess 9 is formed in the 5 direction of rotation in front of this row of increasingly truncated teeth 8, the diameter of which, like the neck 3, allows a certain amount of play with the thread already created. The thread core diameter is mainly the same along the entire thread head, including the cores between the ground 0 teeth 8.

According to FIG. 4, after the regrinding reserve (tooth 7), a number (for example 3 to 7) of heavily ground thread turns 10a, 10b, 10c, etc. is provided. The thread cores of these threads describe the same cylinder as the other 5 thread cores of the thread head. This thread core diameter is somewhat larger than the diameter of the neck 3. The thread tips of the thread already generated protrude bevorzugsweise somewhat in the grooves 11a, 11b, ll ^r, wirα between the abraded teeth 10 into which a secure '/) Soanfuhrung ensured. In addition, a chip clamping safely avoided between the thread already created and the tool.

5 shows a through tap according to the invention. The inclination of the cutting edges and flutes drives the chips forward, in the opposite direction to the shank. A tap of this type comprises a form-cutting groove 12 and a so-called dirt groove 13. Like the tools shown previously, this drill also comprises a threaded head with a mainly uniform core diameter and with a chamfer a. As can be seen from the figure, the regrinding reserve or "extra thread part" in this case comprises only one thread 7.

In contrast to the previous figures, FIG. 6 shows a thread former, which therefore produces threads in the workpiece without cutting. As with the taps, it is

Thread core diameter slightly larger than the diameter of the neck 3 '. The tool can be formed with or without lubrication grooves 14. The tool shown has five full threads. A thread former according to the state of the art, which therefore also includes a guide part, has more than twice as many threads.

drastisch erhont werden. Somit kann der erfindungsgemasse Gewindebohrer einen Freiwinkel im Gewinde von über 0,5° haben, vorzugsweise ungefähr 0,8 bis 2°, d.h. mindestens etwa das fünffache des üblichen Wertes. Dadurch wurde die Standzeit dieses Werkzeuges beim Hochgeschwindigkeitsgewindeschneiden (Schnittgeschwindigkeit V_c = ungefähr 100 m/min) nach dem Verfahren "rigid tapping" (d.h. ohne Ausgleichsfutter) um den Faktor 4 erhöht.According to the prior art, the radial clearance angle in the thread flanks 15 is relatively small because of the axial guidance and to avoid radial fluctuations. As an example, it can be mentioned that when machining tempered steel, the internal clearance angle in the thread of the M8 tap is approximately 0.15 °. A higher clearance angle leads to axial intersection of the tap (lack of guidance). Due to the rigid guidance of the tool according to a preferred embodiment of the invention, the clearance angle ir

be drastically raised. Thus, the tap according to the invention can Have clearance angles in the thread of over 0.5 °, preferably about 0.8 to 2 °, ie at least about five times the usual value. As a result, the service life of this tool in high-speed thread cutting (cutting speed V _c = approximately 100 m / min) was increased by a factor of 4 using the rigid tapping method (ie without compensating chuck).

The embodiments described above all relate to tools that produce a right-hand thread, since these are the most common without comparison. Of course, the invention also applies accordingly to tools that produce a left-hand thread.

Claims

PATENT CLAIMS 1. Internal thread-producing tool, which is either a tap or em thread former, for rigid thread cutting with a shank (1) for clamping in a tool holder and a threaded head (4), characterized in that the threaded head (4) has a chamfer (a) but does not include a conventional guide part (b). 2. Tool according to claim 1, characterized gekennzei chet that after the gate (a) an extra thread part (7) is provided, the length of which corresponds to a maximum of five threads. 3. Tool according to claim 2, characterized in that the length of the extra thread part after the gate at most (a) corresponds to three threads. 4. Tool according to one of claims 1 to 3, characterized gekennzei chnet that after the extra thread part, a number of ground teeth (8, 10) are provided, which serve to chip removal. 5. Tool according to claim 4, characterized in that a recess or thread removal (9) is provided in front of the ground teeth (8) in the direction of rotation, for further reducing αer friction. 6. Tool according to one of the preceding claims, characterized in that the radial clearance angle in the lead thread is above 0, X. 7. Method for internal threading in a metallic work piece by means of a threading tool, which is either a tap or a thread former, the tool being clamped in a rigid tool holder without a compensating chuck, characterized in that the thread is produced with a tool that does not Usual guide part includes.