THREAD CUTTING THROW-AWAY TIP

Abstract: A throw-away thread cutting insert (1) having a cutting tip (5) at a corner part thereof corresponding to a shape of a thread groove, a lead groove (8) formed in an upper surface of the insert and disposed adjacent to and inwardly of said cutting tip (5), and a curl recess (9) formed in an upper wall of the insert in continuous relation to one side wall of the insert and disposed inwardly of said lead groove (8).

Description: The present invention relates generally to a throw-away thread cutting insert for use in a cutting tool, and more particularly to such a throw-away thread cutting insert which is suitable for chasing threads and improved in removal of chips at chasing of threads. BACKGROUND OF THE INVENTION At chasing of threads, just as in other cutting operations, it is desirable to break each chip into small pieces so that the chip will not be wound around the cutting tool or workpiece. However, under conditions in which a depth of cut is extremely small and that a feed rate is high, a chip would hardly be broken, and if it is tried to forcibly break the chip by a chip breaker or the like, an undesirable cutting resistance would increase. As a result, if the cutting tool or thread cutting insert is made of a material having an inferior rigidity, the cutting tool may be subjected to abnormal vibration, which lowers the machining accuracy. For this reason, a conventional throw-away thread cutting insert 51, as shown in Fig. 1, either have no chip breaker or have a groove 53 provided in the vicinity of each cutting tip 52 in a manner to separate the cutting edge 52 from the insert body. However, in such a throw-away insert 51, it has been impossible to break a chip into small pieces, to control the direction of guide and removal of the chip or to stabilize the curling of the chip, which would cause a problem that the elongated chip winds around the cutting tool, the workpiece or the like. In view of the above difficulty and problems accompanying the conventional thread cutting insert, the present inventor has proposed a throw-away thread cutting insert in which a recess is formed in a rake surface so as to smoothly remove chips as disclosed in Laid-open Japanese Utility Model Application Nos. 63-113502 and 64-12705. However, in the throw-away insert disclosed in JUMA No. 63-113502, the recess is disposed rearwardly of the cutting tip spaced apart therefrom and, therefore, the leading of chips from the cutting edge to the recess would not satisfactorily be controlled. In the case of the throw-away insert disclosed in JUMA No. 64-12705, the recess is disposed near the cutting tip and, accordingly, although chips can be smoothly guided and led to the recess, the chips cannot satisfactorily be curled into a helical shape (i.e., a regular curl-shape) at the recess. Thus, the proposed thread cutting inserts having a recess would still raise a problem. From EP-A1-0119175, there is known a thread cutting insert of the type as reflected in the pre-characterizing portion of claim 1. A chip produced by a cutting edge of said conventional cutting insert is led through a groove and comes into abutment against an up-standing area such that the chip is curled. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to eliminate the above-described difficulty accompanying a conventional and proposed thread cutting insert. More particularly, an object of the invention is to provide a throw-away thread cutting insert capable of smooth guiding and leading chips produced during a thread cutting operation to a recess, and of stably removing each chip in a helical form. The above and other objects have been achieved by the subject-matter of claim 1. A throw-away thread cutting insert is provided with a cutting tip at a corner part thereof corresponding to a shape of a thread groove, a lead groove formed in an upper surface of the insert and disposed adjacent to and inwardly of said cutting tip, the lead groove being recessed to a level below the cutting tip, and a curl recess formed in an upper wall of the insert in continuous relation to one side wall of the insert and disposed inwardly of said lead groove, the curl recess being deeper than the lead groove and being continuous with the lead groove, and the curl recess having a side wall opening formed by removing part of an upper portion of the one side wall of the insert. It is preferable that the side wall opening is provided at a thread leading side of the insert. In the throw-away thread cutting insert according to the present invention, chips produced by the cutting tip are guided by the lead groove and led to the curl recess, so that the chips are continuously curled by the curl recess. Since the curl recess opens to one side wall of the insert, a chip is curled into a helical shape and is removed from this side wall opening. The chip can effectively be removed to the thread leading side of the tip. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of the conventional thread cutting insert; Fig. 2 is a perspective view of a preferred embodiment of a throw-away thread cutting insert; Fig. 3 is a partially enlarged plan view of the insert, showing a cutting edge portion; Fig. 4 is a side-elevational view of Fig. 3; Fig. 5 is a schematic plan view showing the flow of a chip during the cutting operation; and DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of a throw-away thread cutting insert of the present invention will now be described with reference to accompanying drawings. Figs. 2 to 5 show a preferred embodiment of a throw-away thread cutting insert of the present invention. Fig. 2 is a perspective view of the thread cutting insert. Fig. 3 is a partially enlarged plan view of the insert, showing its cutting portion. Fig. 4 is a side-elevational view of Fig. 3, and Fig. 5 is a schematic plan view, showing the flow of a chip during a chasing operation. The throw-away thread cutting insert 1 (hereinafter referred to as "insert") comprises a thick plate of a substantially triangular shape in plan formed from a cemented carbide, cermet, ceramics or the like. Both the upper and lower surfaces of the insert 1 have insert-supporting surfaces 2, respectively, and a central aperture 3 for mounting the insert 1 on a tool holder of a cutting tool is formed through the insert 1 at its center portion. A cutting tip 5, having a shape corresponding to a shape of a thread groove of a workpiece, is defined by an outer peripheral wall of each corner portion 4 of the insert 1. A side wall of the corner portion 4 defines a relief surface 6 having substantially the same cross-section as the cutting tip 5. A lead groove 8 for guiding chips is formed in an upper surface of the insert 1 disposed adjacent to the cutting tip 5, the lead groove 8 being slanting inwardly and downwardly toward a curl recess 9 (described later). A narrow land 7 extending along the first cutting tip 5 is formed between the first cutting tip 5 and the lead groove 8. An upper wall of the insert 1 adjacent to the cutting tip 5 is inclined inwardly downwardly. The lead groove 8 has a small depth, for example, of 0.05 to 0.5 mm. The curl recess 9 for curling chips is formed in the upper surface of the insert 1 at the thread leading side of the insert, the curl recess 9 being continuous with the lead groove 8 and being of a conical concave shape defined by an upwardly-diverging curved surface. The curl recess 9 is greater in depth than the lead groove 8. The curl recess 9 is so formed that an upper portion of the side wall of the insert 1 disposed at the thread leading side is partially notched or removed, and this notch defines a side wall opening 10. The insert 1 is fixedly secured to a tool holder of a cutting tool by passing a bolt or the like through the central aperture 3. Then, the cutting tool is attached to a cutter device, and the cutting tip 5 is abutted against a suitable workpiece 20, such as a round bar, and the workpiece 20 is fed at a predetermined speed in a thread chasing direction, so that a thread groove is formed by the cutting tip 5 in the workpiece 20. During the formation of the thread groove, chip 21 is produced by the cutting tip 5, respectively. The chip 21 produced by the cutting tip 5 passes over the land 7 into the lead groove 8, and then the chip is guided by the lead groove 8 while being pushed by a subsequently-produced chip 21 into the curl recess 9. Then, the chip 21 impinges on an inclined surface of the curl recess 9. After that, the chip 21 is continuously curled upwardly into a helical shape, and finally discharged from the side wall opening 10 (provided in the side wall of the insert 1) in the thread leading direction. Further, the present invention is not limited to the substantially triangular plate mentioned above, and can be applied to plates of various polygonal shapes, and also the cutting tips can be of any suitable shape corresponding to desired shapes of thread grooves. A wall part 11 may selectively perform as a cutting wall. That is, during the thread cutting operation, a crest of the thread may selectively be cut by the wall part 11 in accordance with rates of accuracy or surface roughness of the thread. In case that the wall part 11 performs as a cutting wall, the wall part 11 should, as shown by dotted line in Fig. 3, preferably be formed perpendicularly to a bisector (one-dotted line in Fig. 3) of the cutting tip 5 cutting a trough of the thread. As shown in Figs. 3 and 4, the curl recess 9 has a bottom portion 9a. The bottom portion 9a of the curl recess 9 may preferably be positioned at the thread leading side relative to the bisector of the thread cutting tip, so that the chip 21 can be smoothly guided and led constantly to the thread leading side. Although the above-described embodiment shows the thread cutting insert having a central aperture 3, the present invention is not limited thereto or thereby. That is, the invention can also be applied to a throw-away thread cutting insert of a clamp type having no central aperture. As described above, in the throw-away thread cutting insert according to the present invention, the chip produced during the thread cutting or chasing operation is led into the curl recess through the lead groove, thus leading the chip in the predetermined direction, so that the chip can be smoothly removed. At the same time, the chip is continuously curled upwardly by the curl recess and is discharged in a helical shape from the side wall opening. Therefore, the chip would not wind around the cutting tool or the workpiece, and this enhances the chip-removal efficiency and hence the productivity. In the case where the opening of the curl recess is formed in the side wall of the insert disposed at the thread leading side of the insert, the chip is curled into a helical shape toward the leading side of the insert and is discharged from this opening. Therefore, the chip is not brought into contact with the thread-cut portion of the workpiece and hence does not damage this thread-cut portion. Therefore, high- quality products having threads, such as a screw or a bolt, can be produced efficiently, and the manufacturing cost of such product can be reduced.

Claims: A throw-away thread cutting insert (1) having upper and lower insert-supporting surfaces (2) as well as a side wall connecting said upper and lower insert-supporting surfaces comprising: a cutting tip (5) provided at a corner portion of said insert, said cutting tip defining the shape of a thread groove to be manufactured, and a groove (8) formed in the surface of a land portion (7) adjacent to said cutting tip (5) characterized in that a recess (9) is formed which intersects the surface of said land portion (7) as well as the insert-supporting surface (2) of said insert (1), wherein the surface of said groove (8) intersects the surface of said recess (9) in a line situated under the surface of said land portion (7), and wherein the surface of said recess (9) intersects with the surface of a side wall of the cutting tip (5). A throw-away thread cutting insert according to claim 1, wherein said intersection of the surface of said recess (9) with the surface of said side wall is provided at a thread leading side of said insert (1). A throw-away thread cutting insert according to claim 1, wherein said intersection of the surface of said recess (9) with the surface of a side wall is provided at the opposite of a thread leading side of said insert (1). A throw-away thread cutting insert (1) according to claim 1, wherein said groove (8) is slanting inwardly downwardly toward said recess (9). A throw-away thread cutting insert (1) according to claim 1, wherein the surface of said land portion (7) adjacent to said cutting tip (5) is inclined inwardly downwardly. A throw-away thread cutting insert (1) according to claim 1, wherein said recess (9) is deeper in said groove (8). A throw-away thread cutting insert (1) according to claim 1, wherein the depth of said groove (8) is within a range of 0.05 mm to 0.5 mm. A throw-away thread cutting insert (1) according to claim 1, wherein said upper and lower insert supporting surfaces (2) are parallel. A throw-away thread cutting insert (1) according to claim 8, wherein said insert is of polygonal shape. A throw-away thread cutting insert (1) according to claim 9, wherein said insert is of substantially triangular shape. A throw-away thread cutting insert (1) according to claim 1, whreein said insert is formed from a cemented carbide. A throw-away thread cutting insert (1) according to Claim 1, wherein said insert is formed from cermet. A throw-away thread cutting insert (1) according to Claim 1, wherein said insert is formed from ceramics. A throw-away thread cutting insert (1) according to one of the preceding Claims, wherein said groove (8) is provided at a thread leading side of said insert and serves as a chip guiding means. A throw-away thread cutting insert according to Claim 1, further comprising a cutting wall (11) cutting a crest of the thread groove of the workpiece. A throw-away thread cutting insert according to Claim 15, wherein said cutting wall (11) rises perpendicular to the bisector of said cutting tip (5). A throw-away thread cutting insert (1) according to Claim 16, wherein a bottom (9a) of said recess (9) is positioned at a thread leading side relative to said bisector of said cutting tip (5) so that a chip (21) can be smoothly guided and led constantly to the thread leading side.

Inventors: TAKAHASHI, NOBUHIRO ITAMI WORKS SUMITOMO ELECTRIC
Applicants: SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1989
Main classification: B23B27
IPC codes: B23B27