CUTTING INSERT

Abstract: The present invention relates to a cutting insert (10; 10′; 10″; 10‴) adapted to be mounted in a holder (11), said insert (10; 10′; 10″; 10‴) being used for parting of details rotating about its longitudinal axis, e.g. rods and tubes, and that the insert has a leading cutting edge angle (χ). The characteristic for the invention is that the first face (15; 15′; 15″; 15‴) and/or the rake face (18; 18′; 18″; 18‴) are inclined in the transverse direction of the insert.

Description: The present invention relates to a cutting insert adapted to be mounted in a holder, said cutting insert and holder constituting a parting tool, said cutting insert having a cutting edge, a certain leading cutting edge angle, a first face located inside the cutting edge, and a rake face located farther inside the cutting edge than the first face. Parting tools are mainly used in order to cut off rods, tubes or other rotationally symmetrical details. It is often desirable that the cut-off details have such a surface finish that no further machining is necessary. To achieve such a surface finish parting tools are used that have a certain leading cutting edge angle. By such an arrangement none or just a minimal parting hub is created. The leading cutting edge angle, however, causes a certain deflection in axial direction of the cutting-off insert. Said deflection is caused by a component force in axial direction, said component force emanating from the radial force. This is explained more in detail below. The result of such a deflection is that unwanted chamfered end sufaces are achieved on the parted details. In "Werkstatt & Betrieb, Volume 118, No. 9, September 1985", pages 639-644, the working conditions in connection with parting are described, including the above-mentioned deflection in axial direction of the cutting insert. The aim of the present invention is to present a cutting insert of the type mentioned above, said insert when used for parting creating planar end surfaces having a good surface finish. The invention is realized through a cutting insert that has been given the characteristics of the appending claims. Below a number of embodiments of the invention will be described, reference being made to the accompanying drawings. In said drawings Fig. 1 discloses an end view of a cutting insert according to the present invention; Fig. 2 discloses a top view of a cutting insert according to Fig. 1; Fig. 3 discloses a portion of a section along III-III in Fig. 2; Fig. 4 discloses a side view of a cutting insert according to Fig. 1; Fig. 5 discloses a perspective view from above of a cutting insert according to Fig. 1; Fig. 6 discloses a perspective view having the cutting insert mounted in a holder; Fig. 7 discloses a front view of an alternative embodiment of the invention; Fig. 8 discloses a top view of the embodiment according to Fig. 7; Fig. 9 discloses a front view of a further alternative embodiment of the invention; Fig. 10 discloses a top view of the embodiment according to Fig. 9; Fig. 11 discloses still a further embodiment of the invention; and Fig. 12 discloses a top view of the embodiment according to Fig. 11. The indexable insert 10 comprises a chamfered cutting edge 12 that is most clearly disclosed in Fig. 2. Said cutting edge 12, that thus is not located in the plane of the paper in Fig. 2, forms an angle χ with a line 13 located in the plane of the paper in Fig. 2 and perpendicular to the side walls 14 of the cutting insert 10. To sum up one can say that the cutting edge 12 has a certain leading cutting edge angle. The radial cutting force F₁ that acts on the cutting insert 10 in the plane of the paper in Fig. 2 can due to the chamfered cutting edge 12 be divided into a component force F R in the radial direction and a component force F RA in the axial direction, the last-mentioned component force F RA tending to deflect the leading part of the insert 10 to the left in Fig. 2. As discussed above, this can imply unwanted chamfered end faces on the parted details. As is most apparent from Fig. 1 the first face 15 of the indexable insert has been inclined and thus a line 16 that abuts the first face 15 and is parallel to the cutting edge 12 forms an angle λ with a line 17, said line 17 in top view (see Fig. 2) of the insert 10 in its working position coinciding with the cutting edge 12 and being perpendicular to the tangential direction (T) (see Fig. 4) of the insert in its working position. The inclined first face 15 implies that the tangential cutting force F₂ can be divided into a component force F T in the tangential direction and a component force F TA in the axial direction, said last-mentioned component force F TA having a direction opposite to the component force F RA . From Fig. 1 it can be learnt that F TA = F T · tan λ . The angle λ is preferably given such a value that the size of F TA is the same as the size of F RA that has a direction opposite to F TA . This means that F TA and F RA will counterbalance each other and thus the unwanted deflection of the leading part of the insert 10 is avoided. Empirically it has been found that the component F R and the component F T have the following relationship: F R ≈ 0.6 F T . Provided that F RA = F TA the angle λ can be calculated in the following way: F RA = F TA = F R · tan χ = F T · tan λ ; If is inserted the following relation is received: 0.6 · tan χ = tan λ λ = arc tan (0.6 tan χ) . When chosing a suitable value for χ practical tests have shown that χ = 6 o gives acceptable effect when trying to avoid cutting off hubs and also that this value for the leading setting angle of the cutting insert 12 is possible to counterbalance. If χ is chosen equal to 6 o λ = 3.6 o , and this means that the edges of the first face 15 are located at different height levels. It has turned out that the difference in height created by λ = 3.6 o in an insert of the present type and of ordinary size causes machining problems. According to the embodiment of Figs. 1 to 6 a smaller inclination is chosen for the first face 15 and λ = 2 o has been found to be a suitable value. For a cutting width of 3 mm the difference in heigt is: 3 · arc tan 2 o ≈ 0.10 mm. This is an acceptable value. However, in order to provide a complete counterbalancing of the axial component forces F RA and F TA the rake face 18 must be inclined to a greater extent than the first face 15, the inclination of the rake face 18 being symbolized by the angle γ in Fig. 3 between a line 19 that abuts the rake face 18 and in top view according to Fig. 2 is parallel to the cutting edge 12 and a line 20 that in top view also is parallel to the cutting edge 12 and perpendicular to the tangential direction (T) of the insert 10 (see Fig. 4) in its working position. To what extent the inclination of the rake face 18 will exceed the inclination of the first face 15 is preferably determined by practical tests. For the embodiment discussed above it has turned out that an inclination of about 5 o for the rake face 18 is convenient if the first face 15 has an inclination of about 2 o and the leading cutting edge angle χ is about 6 o . The values of the different parameters discussed above in connection with the description of the embodiment only constitute a preferred embodiment within the scope of the invention. Thus the different angles can be varied due to different influencing factors, e.g. the dimension of the insert, material, field of application and so on. Without in any way limiting the principle idea of the present invention the following preferred intervals for the different angles can be mentioned. The leading setting angle χ is preferably in the magnitude of 4 to 8 o . The angle of inclination γ for the first face 15 is preferably in the magnitude of 1 to 4 o . The angle of inclination γ for the rake face 18 is preferably in the magnitude of 4 to 7 o . Within the scope of the invention a number of further embodiments are possible. A few of these embodiments will be described below with reference to Figs. 7 - 12. All of these embodiments have a cutting edge angle χ. The embodiment of Figs. 7 and 8 has a first face 15' having an inclination angle λ between the lines 16' and 17' in accordance with the embodiment of Figs. 1 to 5. However, the rake face 18' of the cutting insert 10' has no inclination. The embodiment of Figs. 7 and 8 does not provide any complete counterbalancing of the forces in the radial and axial direction due to the problems discussed above. In the embodiment of Figs. 9 and 10 the cutting insert 10'' has a rake face 18'' having an inclination angle γ between the lines 19'' and 20'' in accordance with the embodiment of Figs. 1 to 5. However, the first face 15'' of the cutting insert 10'' has no inclination. In the embodiment of Figs. 11 and 12 the first face 15''' has an inclination angle λ between the lines 16''' and 17''' for only a part of the first face 15'''. From Fig. 12 it can be learnt that the inclined part of the first face 15''' corresponds to the distance "a" along the cutting edge 12'''. In this embodiment the rake face 18''' can either be inclined or not. The principle idea of the present invention is to design the geometry of the cutting insert 10; 10'; 10''; 10''' in such a way that the apparent forces in the radial and tangential directions are counterbalanced at least to a certain extent in the axial direction of the parted detail. The embodiments described above refer to an indexable insert. However, the invention is also applicable to parting tools having fixed inserts. Also the holder 11 and its structure for clamping the insert do not constitute any part of the present invention.

Claims: Cutting insert (10) adapted to be mounted in a holder (11), said cutting insert and holder constituting a parting tool, said cutting insert (10) having a cutting edge (12), a certain leading cutting edge angle (χ), a first face (15) located inside the cutting edge (12), and a rake face (18) located farther inside the cutting edge (12) than the first face (15), characterized in that a first line (16), abutting the first face (15) and being parallel to the cutting edge (12) of the insert (10) forms an angle (λ) with a second line (17) that in top view of the insert (10) in its designed working position coincides with the cutting edge (12), said second line also being perpendicular to the tangential direction (T) of the insert (10) in its designed working position, and that a third line (19) abutting the rake face (18) is parallel to the cutting edge (12) in top view of the insert (10) in its designed working position, said third line (19) forming an angle (γ) with a fourth line (20) that is parallel to the cutting edge (12) in top view of the cutting insert (10) in its designed working position, said fourth line (20) also being perpendicular to the tangential direction (T) of the insert (10) in its designed working position, the first face (15) and the rake face (18) having their highest located areas on the same side of the insert (10) where the cutting edge (12) is retracted. Cutting insert (10';10''') adapted to be mounted in a holder (11), said cutting insert and holder constituting a parting tool, said cutting insert (10';10''') having a cutting edge (12), a certain leading cutting edge angle (χ), a first face (15'; 15''') located inside the cutting edge (12), and a rake face (18';18''') located farther inside the cutting edge (12) than the first face (15';15'''), characterized in that a first line (16';16'''), abutting the first face (15';15''') and being parallel to the cutting edge (12';12''') of the insert (10';10''') forms an angle (λ) with a second line (17';17''') that in top view of the insert (10';10''') in its designed working position coincides with the cutting edge (12';12'''), said second line also being perpendicular to the tangential direction (T) of the insert (10';10''') in its designed working position, the first face (15';15''') having its highest located area on the same side of the insert (10';10''') where the cutting edge (12) is retracted. Cutting insert (10'') adapted to be mounted in a holder (11), said cutting insert and holder constituting a parting tool, said cutting insert (10'') having a cutting edge (12), a certain leading cutting edge angle (χ), a first face (15'') located inside the cutting edge (12), and a rake face (18'') located farther inside the cutting edge (12) than the first face (15''), characterized in that a third line (19'') abutting the rake face (18'') is parallel to the cutting edge (12) in top view of the insert (10'') in its designed working position, said third line (19'') forming an angle (γ) with a fourth line (20'') that is parallel to the cutting edge (12) in top view of the cutting insert (10'') in its designed working position, said fourth line (20'') also being perpendicular to the tangential direction (T) of the insert (10'') in its designed working position, the rake face (18'') having its highest located area on the same side of the insert (10'') where the cutting edge (12) is retracted. Insert according to claim 1 or 3, characterized in that the angle (γ) of the rake face (18;18'') is greater than the angle (λ) of the first face (15;15''). Insert according to claim 1, characterized in that the first face (15) has an inclination angle (λ) in the magnitude of 1 - 3°, preferably 2°, and that the rake face (18) has an inclination angle (γ) in the magnitude of 4 - 7°, preferably 5°. Insert according to claim 1 or 2, characterized in that the inclination angle (λ) for the first face (15;15';15''') is in the magnitude of 1 - 4°, preferably 2°. Insert according to any of the previous claims, characterized in that the leading cutting angle (χ) is in the magnitude of 4 - 8°, preferably 6°.

Inventors: NIEMI, MATTI
Applicants: SECO TOOLS AB
Application year: 1987
Main classification: B23B27
IPC codes: B23B27