Cutting tool

Abstract: The present invention relates to cutting tool (10) for chip removing machining, said cutting tool (10) including a holder body (11) with a cutting insert receiving site including a base surface (13) and side supporting means (14,15), a cutting insert (12) located in said cutting insert receiving site and supported by said base surface (13) and said side supporting means (14,15), a locking pin (22), means (16,18,25,26) for detachably connecting the locking pin to the holder body (11) in the area of the cutting insert receiving site, said means (16,18,25,26) allowing axial displacement of the locking pin (22) relative to the holder body (11), said locking pin (22) having a longitudinal centre axis (27) diverging away from said side supporting means (14,15) as it progresses upwardly, said cutting insert (12) having a fixing hole (19) extending through the insert (12), said locking pin (22) having a head (23), a lower contact portion of said head (23) engaging the inner portion of the fixing hole (19) and an upper contact portion of said head (23) engaging the outer portion of the fixing hole (19), said contact portions being located on opposite sides of the head (23) of the locking pin (22). When locking cutting inserts having a hole designed in accordance with ISO 6987 to a holder body the locking screw must be removed when exchanging the cutting insert. The aim of the present invention is to present a cutting tool having a locking mechanism that is extremely easy to handle yet completely reliable. The cutting tool according to the present invention has a locking screw (22) that is inclined relative to a line perpendicular to the base plane of the cutting insert receiving site of the holder body (11). The head (23) of the locking screw (23) is in its simpliest functional form cylindrical.

Description: The present invention refers to a cutting tool for chip removing machining, said cutting tool including a holder body with a cutting insert receiving site including a base surface and side supporting means, a cutting insert located in said cutting insert receiving site and supported by said base surface and said side supporting means, a locking pin, means for detachably connecting the locking pin to the holder body in the area of the cutting insert receiving site, said means allowing axial displacement of the locking pin relative to the holder body, said locking pin having a longitudinal centre axis diverging away from said side supporting means as it progresses upwardly, said cutting insert having a fixing hole extending through the insert, said locking pin having a head, the design of said head and said fixing hole and the inclination of the longitudinal centre axis being so mutually adapted to each other that, in an active position of the locking pin, a lower contact portion of said head engaging the inner portion of the fixing hole and an upper contact portion of said head engaging the outer portion of the fixing hole, said contact portions being located on opposite sides of the head of the locking pin, and that in an inactive position of the locking pin, i.e. the locking pin being displaced axially away from the base surface a limited distance, the cutting insert can be mounted in/removed from the cutting insert receiving site, the fixing hole having at least in the areas of contact between the locking pin and the cutting insert, a decreasing cross-sectional area in direction towards the base surface in mounted position of the cutting insert in the cutting insert receiving site. Cutting tools of the above-mentioned type are previously known, see US-A-3,913,197. In the arrangement shown in US-A-3,740,807 the cutting insert has a cylindrical hole and the portions of the locking screw that engage said hole are frusto-conical with a decreasing cross-section in direction towards the free end of the head of the locking screw. By studying e.g. Fig.2 of US-A-3,740,807 one easily realizes that a lifting force upon the cutting insert is counter-acted only by friction forces between the locking screw and the hole of the cutting insert. In the arrangement shown in US-A-3,913,197 the cutting insert has a hole including two frusto-conical sections converging at the centre of the insert. The locking screw is generally of the same design as the locking screw of US-A-3,740,807. However, when the locking screw engages the upper frusto-conical section of the hole of the cutting insert a locking against lifting forces will be present. The present invention is primarily related to a cutting tool including a cutting insert having a fixing hole according to ISO 6987 or a similar design. However, a locking screw according to US-A-3,740,807 or US-A-3,913,197 will not work in combination with a hole according to ISO 6987 due to the fact that the upper contact portion of the locking screw is frusto-conical with a decreasing cross-section towards the free end of the head of the locking screw. The aim of the present invention is to present a cutting tool having a simple but reliable locking arrangement for a cutting insert having a hole according to ISO 6987 or a similar design. This aim is realized by a cutting tool that is given the characteristics of the appending claims. Below embodiments of the cutting tool according to the present invention will be described, reference being made to the accompanying drawings where Fig.1 shows a top view of a cutting tool according to the present invention; Fig.2a shows a section along IIa-IIa in Fig.1; Fig.2b shows a section of an alternative embodiment along IIb-IIb in Fig.1; Fig.3 shows in section a detail of the cutting tool according to Fig.2a in an initial state of clamping the cutting insert to the holder body; Fig.4 shows in section a detail of the cutting tool according to Fig.2a in a final state of clamping the cutting insert to the holder body; and Fig.5 shows in exemplifying purpose a number of alternative embodiments of the head of the locking screw. The cutting tool 10 in Fig.1 includes a holder body 11 that at one end part is provided with a cutting insert receiving site. In the cutting insert receiving site a cutting insert 12 is located. In the embodiment according to Figs.2a, 3 and 4 the cutting insert receiving site includes a base surface 13 supporting the cutting insert 12. The cutting insert receiving site has also side support means for the cutting insert, and as is shown in Fig.1 said side support means includes two side surfaces 14 and 15 extending in a transverse direction relative to the base surface 13. The side surfaces 14 and 15 also between them include an angle α, said angle mating with the cutting insert 12 located in the cutting insert receiving site. Normally the angle α is in the interval of 35° - 160°. In the holder body 11 a hole 16 is provided, said hole 16 emerging in the base surface 13 of the cutting insert receiving site. In the disclosed embodiment the hole 16 has a circular cross-section and the longitudinal centre axis 17 of the hole 16 is inclined relative to the base surface 13 of the cutting insert receiving site. The inclination of the longitudinal centre axis 17 of the hole 16 is such that said axis 17 diverges outwardly away from the side surfaces 14, 15 as said axis 17 progresses upwardly. An angle β is included between the axis 17 and an intersecting line L extending perpendicular to the base surface 13. The angle β is in the interval of 5° - 30°, preferably in the magnitude of 20°. The hole 16 is provided with an internal thread 18. The cutting insert 12 has a fixing hole 19 that at least partly in axial direction, i.e. at the areas of contact between the locking screw 22 and the cutting insert 12, has a decreasing cross-sectional area towards the base surface 13 in mounted position of the cutting insert 12. Preferably the fixing hole 19 is designed in accordance with ISO 6987, i.e. the design shown in the attached Figs.2a, 2b, 3 and 4 of the present application. A fixing hole 19 in accordance with ISO 6987 has a cylindrical portion 20 located closest to the base surface 13 in mounted position of the cutting insert 12. Above said cylindrical portion 20 the fixing hole 19 has portion 21 decreasing in cross-sectional area towards said cylindrical portion 20 of the fixing hole 19. In the shown embodiment the profile of the wall of the portion 21 is smoothly curved. A locking screw 22 is adapted to clamp the cutting insert 12 in the cutting insert receiving site of the holder body 11 of the cutting tool 10 according to the present invention. In the shown embodiment the locking screw 22 includes a cylindrical head 23, an intermediate portion 24 and a cylindrical shaft 25 that is provided with an external thread 26. The longitudinal centre axis of the locking screw 22 is designated 27. The thread 26 is dimensioned so as to cooperate with the internal thread 18 of the hole 16. Preferably there is a limited transverse clearance between the respective tips and roots of the threads 18 and 26. This means that until tightened the locking screw 22 may float laterally a limited distance. In the shown embodiment the intermediate portion 24 has a smaller diameter than both the head 23 and the shaft 25. A first transition portion 28 extends between the head 23 and the intermediate portion 24 and a second transition portion 29 extends between the shaft 25 and the intermediate portion 24. Said transition portions 28, 29 are smoothly curved in the shown embodiment. However, within the scope of the invention other designs are also possible, said transition portions 28, 29 may e.g. be frusto-conical. An intersecting portion between the cylindrical head 23 and the first transition portion 28 is of a relatively sharp design, said intersecting portion will be active in the clamping of the cutting insert 12. Below, said intersecting portion will be called a lower contact portion 30 of the head 23. In Fig.4 a distance in a plane through the centre axis 27 of the locking screw 22 and the lower contact portion 30 is designated e. Said distance e is defined by two lines parallel with the centre axis 27, one line extending through the lower contact portion 30 and the other line extending through the intersection between the inner part of the lower end of the hole 19 and the base surface 13. It is at once understood that the distance e > 0 since otherwise the head 23 of the locking screw 22 will slide through the hole 19 when displaced axially downwards. With reference to Figs.3 and 4 the clamping function of the cutting tool 10 according to the present invention will be described below. A basic idea of the present invention is that the cutting insert can be mounted/removed without removing the locking screw 22 from the holder body 11. In fact only a limited axial displacement of the locking screw 22 is needed to allow the cutting insert 12 to be mounted/removed. When a cutting insert 12 is mounted/removed the locking screw 22 is displaced further axially upwards than the state shown in Fig.3. However, it is only needed to displace the locking screw 22 axially upwards so much that the cutting insert 12 can pass between the side supporting means, i.e. the side walls 14, 15, and the lower contact portion 30 of the head 23 of the locking screw 22. When a cutting insert 12 is clamped in the cutting insert receiving site the locking screw 22 is rotated in a given direction. By cooperation of the internal and external threads 18 and 26 resp. a displacement axially downwards of the locking screw 22 will take place. In Fig.3 the locking screw 22 is shown in a state where the lower contact portion 30 just has entered into contact with the decreasing portion 21 of the fixing hole 19. In this state the longitudinal centre axis 27 of the locking screw 22 coincides with the longitudinal centre axis 17 of the hole 16. Fig.3 shows the forces F₁, F₂ that the first contact portion 30 excerts upon the cutting insert 12 thus forcing the inner (left in Fig.3) portion of the cutting insert 12 towards the side supporting means by the force F₁ and towards the base surface 13 by the force F₂. Between the outer portion of the fixing hole 19 and the head 23 there is, in this state, a small gap d, said gap d being in the interval of 0 - 1.0 mm, preferably in the interval of 0 - 0.5 mm. According to a preferred embodiment of the invention the gap d is in the magnitude of 0.2 mm. A further displacement axially downwards of the locking screw 22, said displacement being effected by rotation of the locking screw 22 in a given direction, will bring the cutting tool 10 to the state shown in Fig.4. Said further displacement axially downwards will cause the locking screw 22 to tilt outwards, i.e. from the intersection between the side walls 14, 15. Normally said tilting is due to the transverse clearance between the threads 18 and 26 but within the scope of the present invention said tilting can also include an elastic deformation of the locking screw 22. When said tilting has taken place, see Fig.4, the longitudinal centre axis 27 of the locking screw 22 will no longer coincide with the longitudinal centre axis 17 of the hole 16. This also means that the angle β′ included between the intersecting line L and the longitudinal centre axis 27 of the locking screw 22 in Fig.4 is bigger than the angle β in Fig.3. Normally said angle increase is in the magnitude of 2°. The clamping effect of said tilting of the locking screw 22 is that an upper contact portion 31 of the cylindrical head 23 of the locking screw 22 contacts the decreasing portion 21 of the fixing hole 19 of the cutting insert 12, said contact portion 31 being on an opposite side of the head 23 of the locking screw 22 compared to the lower contact portion 30. As is shown in Fig.4 the cylindrical head 23 excerts a force F₃ upon the cutting insert 12 in an outward direction and a force F₄ upon the cutting insert in a downward direction. It is easily understood that the force F₃ must be smaller than the force F₁. The presence of the force F₄ is very important in that said force prevents a raising of the outer cutting corner of the cutting insert 12 from the base surface 13. In the shown embodiment the head 23 of the locking screw 22 is cylindrical, i.e. said head 23 has a constant radial extension relative to its longitudinal centre axis 27. However, within the scope of the present invention it is also possible that the head of the locking screw at the area of its upper contact portion 31 has a widening cross-section in direction upwards, i.e. towards the free end of the head of the locking screw. In exemplifying but not limiting purpose reference is made to Fig.5. From said figure it is at once realized that the shape of the head can be varied in many different ways within the scope of the present invention. However, in the area of the upper contact portion 31 the head must either be cylindrical or have a widening cross-section in direction towards the free end of the head 23 of the locking screw 22. In this connection it should also be pointed out that said lower contact portion 30 does not need to be of a sharp design. As exemplified in Fig.5 other designs are possible within the scope of the present invention as long as a good contact surface is established between the lower contact portion 30 and the hole 19 of the cutting insert 12. The embodiment shown in Fig.2b corresponds to the embodiment described in Figs.1, 2a, 3 and 4 with the following differences. A shim 32 is located between the cutting insert 12 and the cutting insert receiving site. Said shim 32 is fixed to the holder body 11 by means of an externally and internally threaded sleeve 33 that is mounted in an internally threaded hole 16′. The internal thread 18′ of the sleeve 33 functions in a way corresponding to the upper portion of the internal thread 18 of the hole 16. In the described embodiments the locking pin is in the shape of a locking screw. However, within the scope of the present invention it is also possible that the locking pin is of a non-rotating type, i.e. the locking pin is displaceable in an axial direction without being rotated. The present invention is primarily intended to be used in connection with cutting inserts having positive basic shape. However, the principles of the invention can also be used in connection with cutting inserts having negative basic shape. Also in other respects the invention can be varied freely within the scope of the appending claims.

Claims: Cutting tool (10) for chip removing machining, said cutting tool (10) including a holder body (11) with a cutting insert receiving site including a base surface (13) and side supporting means (14,15), a cutting insert (12) located in said cutting insert receiving site and supported by said base surface (13) and said side supporting means (14,15), a locking pin (22), means (16,18,25,26;33,18',25,26) for detachably connecting the locking pin to the holder body (11) in the area of the cutting insert receiving site, said means (16,18,25,26;33,18',25,26) allowing axial displacement of the locking pin (22) relative to the holder body (11), said locking pin (22) having a longitudinal centre axis (27) diverging away from said side supporting means (14,15) as it progresses upwardly, said cutting insert (12) having a fixing hole (19) extending through the insert (12), said locking pin (22) having a head (23), the design of said head (23) and said fixing hole (19) and the inclination of the longitudinal centre axis (27) being so mutually adapted to each other that, in an active position of the locking pin (22), a lower contact portion (30) of said head (23) engages the inner portion of the fixing hole (19) and an upper contact portion (31) of said head (23) engages the outer portion of the fixing hole (19), said contact portions being located on opposite sides of the head (23) of the locking pin (22), and that in an inactive position of the locking pin (22), i.e. the locking pin (22) being displaced axially away from the base surface (13) a limited distance, the cutting insert (12) can be mounted in/removed from the cutting insert receiving site, the fixing hole (19) having, at least in the areas of contact between the locking pin (22) and the cutting insert (12), a decreasing cross-sectional area in direction towards the base surface (13) in mounted position of the cutting insert (12) in the cutting insert receiving site, characterized in that the portion of the fixing hole (19) having a decreasing cross-sectional area is provided with a smothly curved wall profile, and that the head (23) of the locking pin (22) in the area of its upper contact portion (31) has a substantially constant radial extension relative to its longitudinal centre axis (27) or a radial extension relative to its longitudinal centre axis (27), said radial extension increasing towards the free end of the head (23). Cutting tool (10) according to claim 1, wherein the locking pin is in the shape of a locking screw (22) having a symmetrical design relative to its longitudinal centre axis (27), said locking screw (22) including a shaft (25) having an external thread (26), and the means for detachably anchoring the locking pin to the holder body (11) and allow axial displacement of said locking pin relative to said holder body (11) being in the shape of a hole (16) having a circular cross-section and an internal thread (18) adapted to engage said external thread (26) of the locking screw (22), said hole (16) having a longitudinal centre axis (17) deverging away from the side supporting means (14,15) as it progresses upwards, characterized in that the head (23) of the locking screw (22) is cylindrical or that the head (23) has a cross-section increasing towards the free end of the head (23). Cutting tool (10) according to claim 2, characterized in that there is a transverse clearance between the internal thread (18) of the hole (16) and the external thread (26) of the locking screw (22). Cutting tool according to any of the preceding claims, characterized in that the locking pin (22) has an intermediate portion (24) having a smaller cross-sectional area than the head (23), that a first transition portion (28) is located between the intermediate portion (24) and the head (23), that the intersection between the first transition portion (28) and the head (23) constitutes the lower contact portion (30) of the head (23). Cutting tool according to any of the preceding claims, characterized in that in its clamping state the locking pin (22) is in a bent state due to an elastic deformation of said locking pin (22). Cutting tool according to any of the preceding claims, wherein an angle (β) is included between a longitudinal centre axis (17) of the fixing hole (16) and a line (L) extending perpendicular to the base surface (13), characterized in that the angle (β) is in the interval of 5° - 30°. Cutting tool according to claim 6, characterized in that the angle (β) preferably is in the order of 20°.

Inventors: FORSBERG KARL-ERIK, JANSSON MIKAEL, FORSBERG, KARL-ERIK, JANSSON, MIKAEL
Applicants: SECO TOOLS AB
Application year: 1991
Main classification: B23B27
IPC codes: B23B27