The present invention relates to a cutting insert for threading, preferably of substantially triangular form.

The insert comprises a body having a flat upper surface, a plane parallel bottom surface and a number of edge surfaces therebetween. The edge surfaces meet at cutting corners each having a chamfered portion with a cutting tip. A recess is countersunk in the upper surface of the cutting corner portion, said recess being a chip breaker recess which extends from said tip and a distance inwards on said upper surface which is a chip face.

When threading with radial feed occurs a mainly V-shaped chip is obtained which is very stiff which makes it difficult to handle in a controllable manner. A non- triangular threading insert is known the nose portion of which is provided with a recess. The chip formation obtained with such insert, however, is not controllable because the degree of curvature of the chip becomes too large which results in chip jamming and an undesirable risky situation for the operator, the workpiece and the insert .

The objects of the present invention is to provide a thread cutting insert that solves the above mentioned problems. The shape of the insert will give a good controlled chip removal in threading of materials from which fairly long chips are obtained. As a result thereof one and same threading insert can be used in operations with limited human resources where a continuous watch of chip entanglement is not possible.

It is another object of the invention to provide a threading insert that is optimized for internal threading

whilst said insert being useful in standard type toolholders irrespective of the dimension of the cutting tip.

It is another object of the invention to provide a threading insert with such optimized form that a more efficient cooling of the cutting tip is possible.

It is yet another object of the invention to provide an insert with a chip face that is modified so that its form becomes favourable with regard to the cutting forces and the wear of such tool .

In accordance with another aspect of the invention such insert is provided with multiple cutting corners that can be indexed into several positions in the holder.

These and other objects of the invention will become apparent with reference to the following detailed description of a preferred embodiment of the invention made in conjunction with the drawings in which:

Fig. 1 is a top view of a threading insert for external threading according to the invention.

Fig. 2 is a side elevational view of the insert as shown in Fig. 1.

Fig. 3 is a top view of an enlarged cutting corner of the insert shown in Fig. 1.

Fig. 4 is a sectional view, taken along the line IV-IV in Fig. 3.

Fig. 5 is a sectional view taken along the line V-V in Fig. 1.

Fig. 6 is a top view of the insert in Fig. 1 after being located in an insert receiving pocket of a toolholder.

Fig. 7 is a top view of a threading insert for internal threading according to the invention.

Fig. 8 is a side view of the insert in Fig. 7.

Fig. 9 is a top view of an enlarged cutting corner of the insert in Fig. 7.

Fig. 10 is a sectional view taken along the line X-X in Fig. 9 and

Fig. 11 is a sectional view taken along the line XI-XI in Fig. 9.

Referring to Fig. 1-3 the thread cutting insert 10 is in the form of a wafer of triangular form preferably made of cemented carbide. Other cutting materials can also be used such as oxide based ceramic material or cermet . The insert 10 comprises an upper face 11 and a lower face 12 situated opposite and generally parallel to said upper face 11, and a plurality of side walls 13, 14, 15 extending substantially perpendicularly therebetween. The insert 10 is provided with three identical cutting corner portions 16, 17, 18, each of which carries a cutting tip 19, 20, 21 which shall engage with and cut threads of a metallic workpiece (not shown) . The insert 10 has a central aperture 22 for the receipt of a fastening screw for its mounting into an insert receiving pocket of a toolholder. The lower surface 12 of the insert has no cutting edges and is only intended for abutment against a supporting surface of said insert pocket.

In Fig. 3 is shown a cutting corner 16 having a cutting tip

19 arranged symmetrically to a line IV-IV. The cutting tip 19 which may also be unsymmetrically arranged has two main cutting edges 23, 24 extending in V-fashion and a corner cutting edge 25 located therebetween. The insert has primary phases 26, 27 inside said main cutting edges which come to a juncture at the cutting tip 19. The primary phases 26, 27 are located in a plane which slopes downwards towards the centre of the insert at an angle that preferably amounts to 5-15°. The primary phases 26, 27 serve as edge reinforcement surfaces.

At a location inside the primary phases 26, 27 and the cutting tip 19 there is provided a raised portion 28 that is intended to serve as a chipbreaker. The raised portion 28 has a forwardly extending wedge shaped portion whereas its rear portion is terminated by a circularly formed rear edge 30. The wedged forward portion of said raised portion 28 is confined to the extension of the downwardly sloping plane that contains said primary phases 26, 27 whereas the rear portion 29 of raised portion 28 is convexly curved and terminated by the curved rear edge 30 that lies in the plane of the upper surface 11. More specifically, the wedged portion of said raised portion 28 extends to said curved rear portion 29 along a section line 31 which defines the transition between the plane of the primary phases 26, 27 and the upper chip face 11.

The upper surface 32 of said raised portion 28 is plane and extends downwards via surface 33 to a surface portion 34 that is convexly rounded and serves as a top surface of an essentially C-shaped upper surface portion 35, the forward portion of which is convex and directed towards the cutting tip 19. It is also a distinguishing feature that the side surfaces of said wedge formed portion 28 are provided with concave recesses 36 and 37.

Fig. 6 illustrates the insert after being secured into a pocket of a toolholder 40, the bottom surface 12 of said insert being in abutment with a corresponding bottom support surface of said pocket. One cutting tip 19 of the insert is exposed from said pocket in order to engageable with a workpiece for cutting of threads.

The width of each of said primary phases 26, 27 is essentially smaller at the positions adjacent to said C- formed portion 35 compared with the width of said primary phases at locations closer located to the central portions of said insert. These primary phases 26, 27 extend forwardly in a corner phase 41 the width of which is somewhat larger than the width of said primary phases. The acute angle β between said main cutting edges 23, 24 amounts to 25-80°, preferably 50-70°.

At chasing of threads with radial feeding with a thread cutting insert according to the present invention, the chip will be cut by either of the cutting edges 23, 24 or along parts thereof and therefore the chip will be preformed while it follows an upward path towards the C-shaped portion 35 after which it is additionally formed by the recess 36 or 37 of the raised portion 28. The chip is then finally shaped and controlled by the inclined surface 33 so that it obtains a small radius of curvature like a spiral at the same time as the chip is guided away from the workpiece and the tool . Thanks to this form of the chip face at the V-shaped cutting corner 16 a satisfactory working result is achieved when using the same insert when machining different materials and at varying machining data. By limiting the chipbreaker 28 only to the corner region whilst providing the insert's central area as a recessed portion in relation to said chipbreaker it is possible to provide a more efficient supply of a cooling medium towards the active cutting tip.

In Fig. 7-11 there is shown an alternative embodiment intended for internal thread cutting of a workpiece. In similarity with Fig. 1-3 each cutting corner has two main cutting edges 23, 24 and a curved cutting edge 25 therebetween. Each said corner is provided with a raised portion 28 the extension of which is confined to the corner area. The forward portion of said raised portion 28 located next to the corner edge 25 is essentially wedge-shaped whereas the rear portion 29 is convexly formed.

The limiting side surfaces of said portion 28 which are located adjacent the primary phases 26, 27 are partially in the form of concave recesses 36, 37 the cross section of which is composed by a circular portion 36a, 37a and a portion 36b, 37b with straight contour which join a plan top portion 43 which is essentially flat and intersects with the top surface of the insert at an angle δ of 5-20°. There is a difference in design with this insert in comparison with Fig. 1-3 to the extent that the insert of Fig. 7-11 lacks the provision of a convexly raised portion 34 as shown in Fig. 4. The insert has a bevelled phase 41 next to the corner edge 25 which extends, via a concave recess 42, into the upwardly inclined plane surface 43. Thanks to this embodiment a more efficient chipbreaking and chip removal can be achieved during internal thread cutting thereby avoiding problematic chip entanglement that would otherwise occur.