Throw away insert

Abstract: A throw away insert (1) having straight cutting edges (2), arcuately curved corner portions (3) formed between the adjacent cutting edges, and a rake facing having a center land. In the rake face, chip breaker grooves (4) are formed near the corner portions. Each breaker groove adjoins the center land (5) along line inclined with respect to one of the adjacent cutting edges and is inclined with respect to the direction of thickness of the insert. An ellipsoidal recess (6) is formed in the bottom surface of each breaker groove at the boundary between the center land and the breaker groove. The ellipsoidal recesses have a major axis extending parallel to borderline between the center land and the breaker groove.

Description: This invention relates to a throw away insert having according to the preamble of claim 1. With an increasing tendency to unmanned machining, the importance of chip disposal is increasing. Namely, because the depth of cut is small in finish cutting, the chips tend to be long. Such chips may make it difficult for a robot hand to attach and detach tools and works or may clog a conveyor, hampering unmanned operation. But it is not easy to eliminate such difficulties because in finish cutting, the requirements for the surface roughness and dimensional accuracy are very high. For example, if priority is given to breaking chips, there is known a method of cutting and breaking chips forcibly by providing the breaker wall as near to the tip of the cutting edge as possible. But in such a case, the material machined would develop so-called "plucking" and chattering, lowering the surface roughness. Also, because of increased cutting resistance, the dimensional accuracy as well as the tool life will be badly influenced. As will be apparent from the above discussion, in the unmanned finish cutting operation, it is necessary to solve the above-described two problems simultaneously. But this requirement cannot be met by any of the conventional chip breakers used in finish cutting such as small-diameter boring, e.g. ones as shown in Figs. 9a and 9b, ones as shown in Figs. 10a to 10c - being the basis for the preamble of claim 1 - and ones having a groove formed by use of a die so as to extend all the way around the insert. If it is impossible to break chips, the best way to dispose of chips is to curl them into as small pieces as possible and stably discharge them in such a direction as not to be tangled. In this respect, the conventional types shown in Figs. 9 and 11 are not desirable because they cannot forcibly discharge chips in a predetermined direction and thus the direction in which the chips flow after clearing the breaker tends to be unstable. With the breaker shown in Fig. 10, it has a chip guiding effect because it slopes downwardly toward its front at an angle of ϑ. But because the edge strength tends to drop with an increase in the angle ϑ, its maximum allowable value for ϑ is rather small. Thus it is difficult to reliably control the flow of chips. DE-A-22 41 176 dicloses a cutting insert, with a recess at the boundary between a center land and a chip breaker groove. The breaker groove breaks and curls the chips. This is not always desired, because the flow of broken and curled chips may be difficult to control. It is an object of this invention to provide an insert having a breaker which can dispose of chips in a desirable manner. According to this invention, there is provided a throw away insert having straight cutting edges, arcuately curved noses at corner portions formed between the adjacent cutting edges, and a rake face having a center land and having chip breaker grooves formed at the corner portions, each of the breaker grooves adjoining the center land along line intersecting one of the adjacent cutting edges at both sides of each groove at an angle α, each of the breaker grooves inclining downwardly toward the one of the adjacent cutting edges at an angle ϑ with respect to a horizontal plane, and ellipsoidal recesses formed in the rake face at the boundary between the center land an the breaker grooves, each of the recesses being a part of an ellipsoid having a major axis extending parallel, as viewed from top, to the borderline between the center land and the respective breaker groove. The ellipsoidal recesses may be formed in such a way as to cut out the cutting edge located in front thereof with respect to the direction in which chips flow. Also, they may have their major axis inclined at an angle equal to or larger than ϑ with respect to the direction of thickness of the inset. The chips pass over the bottom of the breaker groove and enter the ellipsoidal recess, where they are subjected to strain and curl. They curl reliably and smoothly because the recess has an arcuate surface and the chips are subjected to strain at a portion remoter from the cutting edge than the uprising portion of the breaker groove is. Thus, the surface roughness and dimensional accuracy are not badly affected, which is inevitable when the chips are forcibly broken. Further, because the breaker groove is inclined downwardly with respect to the direction in which chips flow, the flow of chips is forcibly directed obliquely downwardly of the inclined surface. According to this invention, by forming a chip breaker with a breaker groove and an ellipsoidal recess in the rake face at each corner, chips can be curled reliably and smoothly and discharged stably in a predetermined direction. Thus, the throw away insert according to this invention has a high cutting accuracy and free of such trouble as tangling of chips and is especially suited for use in finish cutting such as small-diameter boring. Other features and objects of embodiments of the present invention will become apparent from the following description taken with reference to the accompanying drawings, in which: Fig. 1 is a plan view of the first embodiment of this invention; Fig. 2 is a sectional view taken along line I-I of Fig. 1; Fig. 3 is a sectional view taken along line II-II of Fig. 1; Fig. 4 is a view showing how it operates; Figs. 5 and 6 are plan views of a portion of the other embodiments; Figs. 7 and 8 are schematic views showing how boring is done; Fig. 9a is a plan view of prior art throw away insert; Fig. 9b is a sectional view taken along line III-III of Fig. 9a: Fig. 10a is a plan view of another prior art insert; Fig. 10b is a sectional view taken along line IV-IV of Fig. 10a; Fig. 10c is a sectional view taken along line V-V of Fig. 10a; Fig. 11a is a plan view of a further prior art insert; and Fig. 11b is a sectional view taken along line VI-VI of Fig. 11b. Now the embodiments of this invention will be described with reference to the accompanying drawings. In Fig. 1, numeral 1 generally designates a throw away insert according to this invention. It has straight cutting edges 2 in the form of ridge lines between a rake face and side faces. The corner or nose portions 3 formed between the adjacent cutting edges 2 are curved arcuately. A chip breaker groove 4 is formed in the rake face at each corner portion of the insert. The braker grooves 4 adjoin a center land 5 along lines inclined at an angle of α with respect to the cutting edge 2 located rearwardly with respect to the feed direction as viewed from top in Fig. 1. The value α should be 10° or more. Also the grooves 4 are inclined downwardly toward the cutting edge 2 located rearwardly with respect to the feed direction at an angle of ϑ with respect to a horizontal plane (see Fig. 3). An ellipsoidal recess 6 is formed at the boundary between the center land 5 and each breaker groove 4 so as to intersect the bisector of the corner angle. Each ellipsoidal recess 6 is a part of an ellipsoid having a major axis extending parallel, as viewed from top, to the borderline between the center land and the respective breaker groove and inclined downwardly toward the cutting edge 2 located rearwardly with respect to the feed direction at an angle equal to or larger than the angle ϑ with respect to the horizontal plane. Next, the operation of the chip breaker will be described. Because the depth of cut is extremely small during finish cutting, as shown in Fig. 4, chips A produced near the nose 3 tend to move along the bisector of the insert corner angle. The chips then pass over the bottom of the breaker groove 4 and enter the ellipsoidal recess 6 located ahead of the groove 4. The chips are curled reliably by the arcuate surface of the recess 6. The chips thus curled are guided by the surface of the recess 6 so as to be discharged rearwardly with respect to the direction of feed (shown by arrow in Fig. 4), due to the fact that the major axis of the recess 6 is inclined at the angle ϑ₀. Fig. 5 shows the second embodiment of this invention. In this embodiment, the cutting edge 2 at the side where the bottom of the breaker groove 4 is lower is cut out by the ellipsoidal recess 6. This arrangement is effective particularly when the feed rate is high, i.e. when the chips produced are thick and thus require a large chip curling force. In the embodiment shown in Fig. 6, the inclinations α and ϑ of the breaker grooves 4 and the inclination ϑ₀ of the ellipsoidal recesses 6 are opposite in direction to those in the embodiment of Fig. 1. When boring a blind hole as shown in Fig. 7, chips are discharged through the entrance of the hole. In boring a through hole as shown in Fig. 8, chips should be discharged through the exit in order to prevent the finished surface from being damaged by the chips. The embodiment shown in Fig. 6 is intended specifically for this type of cutting operation. The value α in this case should be 100° or less. The value ϑ should be within such a range as not to impair the strength of the cutting edge. Even if the value is limited to a rather small value, chips can be discharged in a stable direction according to this invention, due to the effect of the surface of the recess 6 having an angle of inclination equal to or larger than ϑ. This invention is applicable not only to triangular inserts as shown but also to other types of insert.

Claims: A throw away insert (1) having straight cutting edges (2), arcuately curved noses at corner portions (3) formed between the adjacent cutting edges, and a rake face having a center land and having chip breaker grooves (4) formed at said corner portions (3), said each breaker groove (4) adjoining said center land (5) along line intersecting one of the adjacent cutting edges (2) at both sides of said each groove (4) at an angle α, said each breaker groove (4) inclining downwardly toward said one of said adjacent cutting edges (2) at an angle ϑ with respect to a horizontal plane, characterised by ellipsoidal recesses (6) formed in said rake face at the boundary between said center land (5) and said breaker grooves (4), each recess (6) being a part of an ellipsoid having a major axis extending parallel, as viewed from top, to said borderline between said center land (5) and said respective breaker groove (4). A throw away insert as claimed in claim 1, wherein each of said ellipsoidal recesses (6) terminates at said one of said adjacent cutting edges (2) to cut out part of said cutting edge. A throw away insert as claimed in claim 1 or 2, wherein said major axis of said each ellipsoid (6) inclines downwardly toward said one of said adjacent cutting edges (2) at an angle equal to or larger than the angle ϑ with respect to the horizontal plane.

Inventors: TAKASHASHI NOBUHIRO C O ITAMI, TAKASHASHI, NOBUHIRO, C/O ITAMI WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1990
Main classification: B23B27
IPC codes: B23B27, F41H5, A41D1, F41H1, A41D13