Patent Application
20190091772
The present invention relates to a cutting tool used in cutting.
A cutting tool for cutting may be provided with a honing surface in a cutting edge in order to strengthen the cutting edge. The size of the honing surface may be varied according to the cutting edge portion. For example, in the throwaway chip disclosed in Patent Document 1, a honing surface is machined in a cutting edge, and such honing surface is formed so as to involve different amounts of honing W (widths on the upper surface side) between a portion thereof near a corner R and a center portion thereof.
Patent Document 1: JPH09-019819 A
The fracture resistance and cutting resistance of a cutting tool can be improved simultaneously by, as in the throwaway chip of Patent Document 1, varying the dimensions of a honing surface according to the cutting edge portion. The present invention provides a cutting tool which allows the fracture resistance and cutting resistance to be further improved with good balance.
A cutting insert according to the present invention is a cutting tool comprising an end surface, first and second side surfaces which intersect with the end surface, a first cutting edge in an intersecting edge between the end surface and the first side surface, and a second cutting edge in an intersecting edge between the end surface and the second side surface, wherein: the first cutting edge has a first honing surface; and the second cutting edge has a second honing surface. A cross-sectional shape of the second honing surface is different from a cross-sectional shape of the first honing surface.
A cutting tool according to another aspect of the present invention can be used for grooving. The cutting tool comprises: a rake surface; a first flank; a front cutting edge which is formed in an intersecting edge between the rake surface and the first flank and which is capable of machining a bottom surface of a groove; a second flank; and a second cutting edge which is formed in an intersecting edge between the rake surface and the second flank and which is capable of machining a first wall surface of the groove, wherein: a first honing surface is formed in the front cutting edge; a second honing surface is formed in the second cutting edge; when, in a cross-section perpendicular to the front cutting edge, defining a width of an area where the first honing surface is formed which is viewed from a direction facing the rake surface as a first width, and defining a height of the area where the first honing surface is formed which is viewed from a direction facing the first flank as a first height, and when, in a cross-section perpendicular to the second cutting edge, defining a width of an area where the second honing surface is formed which is viewed from the direction facing the rake surface as a second width, and defining a height of the area where the second honing surface is formed which is viewed from a direction facing the second flank as a second height, a ratio of the second height to the second width is smaller than a ratio of the first height to the first width; and the second width is greater than the second height.
In this cutting tool, the first honing surface is formed in the front cutting edge which is capable of machining a bottom surface of a groove. Further, the second honing surface is formed in the second cutting edge which is capable of machining a wall surface of the groove. While, in general, honing surfaces having the same shape are typically formed regardless of the cutting edges, the first honing surface and the second honing surface are intentionally made to have different shapes. A special manufacturing process is required in order to form such honing surfaces, and the fracture resistance and the cutting resistance can be improved with good balance in accordance with the roles of the respective cutting edges. In particular, the second surface is formed such that the second width is greater than the second height. This makes it possible to increase the width on the rake surface side so as to ensure the fracture resistance of the second cutting edge and to suppress the height on the flank side so as to suppress degradation of the cutting ability.
Further, the ratio of the second height to the second width is smaller than the ratio of the first height to the first width, and this means that the first honing surface involves a height-to-width ratio at a value closer to 1 than the second honing surface. Thus, the fracture resistance of the front cutting edge can be further improved compared to that of the second cutting edge. Herein, the first width may be configured so as to be greater than the first height.
It should be noted that neither the first honing surface nor the second honing surface needs to be formed throughout each cutting edge, and for instance, a honing surface which satisfies the above-described conditions may be formed in at least half the area of each cutting edge.
An area where a honing surface is formed refers to an area defined by a boundary with respect to a surface which functions as a rake surface or a flank. In the case of chamfer honing in which a honing surface in a cross-section has a substantially linear shape, a boundary of a honing surface with a rake surface (or a flank) can be considered to appear more clearly. In the case of round honing, a honing surface involves variations in the curvature, and thus, a person skilled in the art will be able to recognize a boundary with a rake surface (or a flank). In a case where a honing surface is formed in an elliptical shape, the curvature varies at a boundary with a rake surface (or a flank), and thus, a person skilled in the art will also be able to recognize such boundary.
Herein, the first width may be greater than the second width.
With such configuration, the fracture resistance of the front cutting edge is improved while the cutting ability of the second cutting edge can be enhanced.
Further, in the cross-section perpendicular to the front cutting edge, the first honing surface may have a circular-arc shape.
With such configuration, the fracture resistance of the front cutting edge can be further improved.
Further, in the cross-section perpendicular to the second cutting edge, the second honing surface may have an elliptical shape.
With such configuration, the second height is suppressed, thereby making it possible to suppress degradation of the cutting ability.
Herein, an elliptical shape encompasses not only an elliptic circular arc but also multiple arcs with different curvatures, as well as a curve close to an ellipse, i.e., a curve wherein the sums comprising the distances between the two focuses and any point on the curve are substantially equal to one another. Such multiple circular arcs with different curvatures allow for the exertion of the effect of being manufactured more easily than an ellipse.
Further, the first rake angle of the rake surface connected to the front cutting edge may be greater than the second rake angle of the rake surface connected to the second cutting edge.
A greater rake angle further improves cutting ability, and thus, degradation of the cutting ability of the front cutting edge which is accompanied by honing can be further suppressed by employing a greater rake angle. The front cutting edge is used for the machining of a bottom surface, etc., of a groove and is therefore applied with more resistance, and thus, fracture resistance needs to be secured for the front cutting edge, whereas the front cutting edge is required to avoid degradation of the cutting ability. Therefore, it is possible to prevent a situation in which the employment of a greater rake angle causes excessive degradation of the cutting ability. Meanwhile, with regard to the second cutting edge whose cutting ability is less likely to be degraded by honing, such second cutting edge is given a rake angle smaller than that of the front cutting edge. Thus, as to the front cutting edge which can be used for the machining of a bottom surface, etc., of a groove and the second cutting edge which can be used for the machining of a side surface, etc., of a groove, the honing surfaces and the flanks are set with good balance, thereby making it possible to provide a more practical cutting tool.
Further, the cutting tool may further comprise: a third flank; and a third cutting edge (20c) which is formed in an intersecting edge between the rake surface and the third flank and which is capable of machining a second wall surface opposing the first wall surface of the groove, wherein: the front cutting edge and the second cutting edge may be connected so as to form an acute angle as viewed from the direction facing the rake surface; and the front cutting edge and the third cutting edge may be connected so as to form an acute angle as viewed from the direction facing the rake surface.
With such configuration, chips, etc., are restrained from being caught in between the second (or third) cutting edge and the wall surface, and the wall surface of a groove can be preferably machined using a portion near a connecting part with the front cutting edge.
Further, a third honing surface is formed in the third cutting edge, and, when, in a cross-section perpendicular to the third cutting edge, defining a width of an area where the third honing surface is formed which is viewed from the direction facing the rake surface as a third width, and defining a height of the area where the third honing surface is formed which is viewed from a direction facing the third flank as a third height, a ratio of the third height to the third width may be smaller than a ratio of the first height to the first width.
With such configuration, in the third cutting edge as well, the fracture resistance on the rake surface side is ensured while the third height is suppressed, thereby making it possible to suppress degradation of the cutting ability.
Furthermore, the cutting tool may be used for parting.
Preferred embodiments of the present invention will hereinafter be described with reference to the drawings. It should be noted that the same elements are denoted by the same symbols and will not be further explained. Unless otherwise specified, positional relationships, such as vertical and horizontal relationships, are based on the positional relationships shown in the drawings. Further, the dimensional ratios of the drawings are not limited to those shown therein. Furthermore, the embodiments set forth below are illustrative in order to describe the present invention, and the present invention is not limited to the above embodiments.
As shown in
As shown in
The cutting tool 1 according to the present embodiment has a shape of 180-degree rotational symmetry around a central axis C of the hole 24. At the same time, the cutting tool 1 has a shape of 180-degree rotational symmetry around a central axis (not shown) of the upper surface 10 which is orthogonal to the central axis C. Thus, the cutting tool 1 has four sets of cutting edges 20 and a shape in which the sets of cutting edges 20 constitute 180-degree rotational symmetries. Therefore, the description below will be made, centering on one set of a cutting edge 20, and, since the same applies to the other three sets of cutting edges 20, the description thereof will be omitted here. The same also applies to the peripheral shapes other than the cutting edges 20. It should be noted, however, that, as shown in
As shown in
The dimension from the second side surface 14 of the cutting tool 1 to the fourth side surface 16 thereof is, for example, approximately 4 mm when being represented based on the distance (not shown) between two parallel planes which circumscribe the cutting tool 1. The dimension from the first side surface 13 of the cutting tool 1 to the third side surface 15 thereof is, for example, approximately 13 mm when being represented based on the distance (not shown) between two parallel planes which circumscribe the cutting tool 1. The dimension from the upper surface 10 of the cutting tool 1 to the lower surface 11 thereof is, for example, approximately 13 mm when being represented based on the distance (not shown) between two parallel planes which circumscribe the cutting tool 1. The diameter of the hole 24 is, for example, approximately 5 mm.
As shown in
As shown in
As shown in
A portion of the peripheral side surface 12 which is connected to the cutting edge 20 functions as a flank. As shown in
The cutting tool 1 has a chip breaker in the upper surface 10. A portion of the upper surface 10 which is connected to the cutting edge 20 functions as a rake surface. As shown in
As shown in
Materials used for the cutting edges 20 of the cutting tool 1 and their peripheral areas are not particularly limited, but may be selected, for example, from among: hard materials, such as cemented carbide, cermet, ceramic and a sintered body containing cubic boron nitride; materials obtained by applying a PVD or CVD coating to the surface of such hard materials; and mono-crystalline diamond and a sintered body containing diamond.
The present embodiment describes a cutting tool suited for grooving or parting. The experiments conducted by the inventor, etc., of the present application and the accompanying consideration have found that the fracture resistance of a cutting edge is greatly affected by a honing width on the rake surface side and that the cutting ability thereof is greatly affected by a honing height on the flank side. It has also been found that fracture resistance can be maintained while the degradation of the cutting ability can be suppressed by achieving a large honing width on the rake surface side and a small honing height on the flank side. More specifically, it has been made clear that the balance between the cutting ability and the degree of resistance to chipping is suitably improved by using, for grooving, the combination of the following two types of employment: the configuration shown in
As shown in
In the case of grooving, the cutting resistance applied on the second cutting edge 20b and the third cutting edge 20c for inner-wall machining is smaller than the cutting resistance applied on the front cutting edge 20a for the machining of a bottom surface of a groove. This allows for honing surfaces to be formed with greater importance being placed on the cutting ability than that involved in the honing surface provided in the front cutting edge 20a, thereby making it possible to avoid circumstances where, although the front cutting edge 20a is still sufficiently usable, the second cutting edge 20b and the third cutting edge 20c fracture and become unusable.
It should be noted, however, that, since a sharp edge leads to the frequent occurrence of chipping, chipping can be suppressed while the cutting ability can be preferably improved by making W3 (a honing width provided on the rake surface 10 side) be greater than H3 (a honing height provided on the flank 12 side).
The ratio between W3 and H3 should be determined in accordance with, for example, the material of a workpiece, the depth of a groove, and the length of the front cutting edge 20a. However, in general, the cutting ability can be further improved by forming the honing surfaces 21b and 21c in order for W3 to be greater than three times H3.
Herein, contours of the honing surfaces 21b and 21c in a cross-section are each formed in an elliptical shape, as shown in
Meanwhile, if the honing surface provided in the front cutting edge 20a does not involve greater importance being placed on fracture resistance, this may invite circumstances where, when performing grooving, although the second cutting edge 20b and the third cutting edge 20c are still sufficiently usable, the front cutting edge 20a fractures and becomes unusable.
In order to prevent the above problem, as shown in
The ratio between W1 and H1 should be determined in accordance with, for example, the material of a workpiece, the depth of a groove, and the length of the front cutting edge 20a. However, in general, fracture resistance can be further improved by forming the honing surface 21 in order for W1 to be smaller than three times H1.
Herein, the honing surface 21a is formed such that, as shown in
It should be noted that the magnitude relationship between a width and a height covers such magnitude relationship which is intentionally established and thus does not encompass circumstances where such magnitude relationship is incidentally achieved, in part of a side-surface cutting edge, due to manufacturing variations, etc., in the manufacturing process. The ratio between a width and a height also covers such ratio which is intentionally established and does not encompass circumstances where an area involving such ratio locally exists without intention.
The cutting tool (cutting insert) 1 configured as described above can be manufactured as set forth below. Firstly, an outer shape of the cutting tool 1 is molded by press-molding a material and sintering the resulting product. Thereafter, the resulting product is subjected to grinding, etc., if necessary. At this time, the honing surfaces 21 are formed. The honing surfaces 21 can be formed by a machining method with a grinding stone and various known methods, such as a machining method with a brush, a machining method with free grains, a machining method with a rubber grinding stone and a machining method with laser beams. The shape of each of the honing surfaces 21 can be adjusted by adjusting the machining conditions in accordance with the machined portion of the cutting edge 20. For example, in the case of a machining method with free grains, the cross-sectional shape and dimensions of the honing surface 21 can be adjusted by varying the angle of a nozzle which ejects free grains and the ejection pressure thereof. When free grains are caused to hit substantially uniformly on an end surface and a side surface from a direction orthogonal to a cutting edge portion, a honing surface 21 having a substantially circular-arc cross-sectional shape can be obtained, by way of example. Here, when the angle of the nozzle is changed such that free grains hit strongly on the end surface 10 side and hit weakly on the peripheral side surface 12 side, a honing surface 21 having a combined (substantially elliptical) cross-sectional shape of multiple circular arcs can be obtained, by way of example. A direction in which the angle of the nozzle is changed is not limited to the vertical direction, and the cross-sectional shape can be adjusted also by adjusting the in-plane angle in a front direction of the cutting edge portion. It should be noted that the cutting tool 1 of the present embodiment can be obtained by the machining process set forth below. Firstly, the second cutting edge 20b is machined by, for example, a machining method with a grinding stone, so as to be provided with a honing surface having a substantially linear cross-sectional shape. Next, using, for example, a machining method with free grains, the first honing surface 21a is machined in a direction orthogonal to the first cutting edge 20a, and a portion of the second honing surface 21b which has a substantially circular-arc cross-sectional shape is machined in an oblique direction in a plane with respect to the second cutting edge 20b. The first honing surface 21a and the second honing surface 21b may be machined simultaneously. Alternatively, the first honing surface 21a and the second honing surface 21b may be machined separately. It should be noted that a CVD or PVD coating may be additionally provided, if necessary.
For instance, when forming the honing surface 21a, free grains are ejected in a direction which is orthogonal to the front cutting edge 20a and which forms a bisector between the rake surface 10 and the flank 13 in a cross-section orthogonal to the front cutting edge 20a, thereby making it possible to form the honing surface 21a having a circular-arc cross-sectional shape of the front cutting edge 20a.
With regard to the honing surfaces 21b and 21c, free grains are ejected in directions closer to normals of the flanks 14 and 16 so as to form parts of the honing surfaces 21b and 21c each having a cross-section with a predetermined curvature, and the ejection angle is then shifted such that free grains are ejected in a direction close to a normal of the rake surface 10, thereby making it possible to form the honing surfaces 21b and 21c each involving a large amount of honing on the rake surface 10 side and also having a high curvature.
The cutting tool 1 is attached to the holder 2 by, for example, as shown in
Next, the operation and effects of the cutting tool 1 according to the present embodiment will be described. Further, preferred embodiments of the present invention will be described below.
The cutting tool 1 is suited for grooving with the use of a lathe. When being used for grooving, the cutting tool 1 may be arranged such that the first cutting edge 20a of one set of a cutting edge 20, from among the four sets of cutting edges 20, acts as a front cutting edge. That is, the cutting tool 1 may be arranged such that the first cutting edge 20a is parallel to a bottom of a groove machined in a workpiece. With such arrangement, the first cutting edge 20a, the first corner cutting edge 20d and the second corner cutting edge 20e determine the width of the groove initially formed. The second and third cutting edges 20b, 20c can be made to act as wiper edges (cutting edges for finishing) for inner wall surfaces of a groove. It should be noted that the second and third cutting edges 20b, 20c can also be made to act as side surface cutting edges for extending the width of a groove. That is, after a groove is formed, the cutting tool 1 is fed in a lateral direction, whereby the width of the groove can be extended. Since the cutting tool 1 has the four sets of cutting edges 20, even when one set of a cutting edge 20 is damaged, the cutting tool 1 can be used at least four times by replacing such set with each of the other three sets of cutting edges 20 and then remounting the cutting tool 1 on the holder 2.
As described above, the first honing surface 21a of the first cutting edge 20a and the second honing surface 21b of the second cutting edge 20b differ from each other in terms of their cross-sectional shapes. Therefore, it is possible to provide individual shapes of the honing surfaces 21 which are suitable for the cutting characteristics of the respective cutting edge portions. For instance, in grooving, when the first cutting edge 20a serves as a front cutting edge, the first cutting edge 20a is preferably resistant to chipping, since the entire width affects cutting. That is, the first honing surface 21a preferably has a substantially circular-arc cross-sectional shape, which is resistant to chipping. Meanwhile, the second cutting edge 20b, which acts as a wiper edge or a side-surface cutting edge, is required to have cutting ability when, in particular, the quality of a machined surface is enhanced. The cutting ability of the cutting tool 1 can be evaluated according to, for example, the extent to which the cutting resistance is low. Alternatively, the cutting ability may be evaluated in terms of wear resistance. The second honing surface 21b preferably has a substantially linear cross-sectional shape, which provides high cutting ability.
However, the balance between cutting ability and the degree of resistance to chipping is important from a practical viewpoint, and a shape for each of the first and second honing surfaces 21a, 21b may be selected from among intermediate shapes between a substantially circular-arc shape and a substantially linear shape, i.e., a substantially elliptical shape, a combined shape of a plurality of circular arcs, and a combined shape of at least one line and at least one circular arc. It should be noted that the combined shape of a plurality of circular arcs may refer to, for example, the shape shown in
Basically, an intermediate shape, such as a substantially elliptical shape, refers to a shape which is more resistant to chipping when such intermediate shape is more similar to a substantially circular-arc shape while referring to a shape with higher cutting ability when such intermediate shape is more similar to a substantially linear shape. It should be noted that, when the cutting ability and the resistance to chipping have good balance and also when the cutting conditions are applied successfully, it may be possible to obtain a shape with resistance to chipping and good cutting ability. That is, basically, the first honing surface 21a of the front cutting edge preferably has a substantially circular-arc cross-sectional shape or a cross-sectional shape which is similar to a substantially circular-arc shape. More specifically, the cross-sectional shape of the first honing surface 21a is preferably selected from among a substantially circular-arc shape, a substantially elliptical shape, a combined shape of a plurality of circular arcs, and a combined shape of at least one line and at least one circular arc. The cross-sectional shape of the second honing surface 21b is preferably comprised of a shape which is more similar to a substantially linear shape than the cross-sectional shape of the first honing surface 21a. More specifically, the cross-sectional shape of the second honing surface 21b is preferably selected from among a substantially linear shape, a combined shape of at least one line and at least one circular arc, a substantially elliptical shape, and a combined shape of a plurality of circular arcs.
However, as to a substantially linear shape, the resistance to chipping and the cutting ability can be adjusted by also adjusting an inclination angle with respect to the upper surface 10. That is, when the inclination angle is increased so as to increase the ratio of the height to the width of the honing surface 21, the honing surface 21 has a shape resistant to chipping; conversely, when the inclination angle is decreased so as to decrease the ratio of the height to width of the honing surface 21, the honing surface 21 has a shape with good cutting ability. Further, as to intermediate shapes, such as a substantially elliptical shape, various shapes under the same category can be achieved through adjustment, ranging from a shape similar to a substantially circular-arc shape to a shape similar to a substantially linear shape. Therefore, in the present invention, the first honing surface 21a and the second honing surface 21b can be made to have different cross-sectional shapes under the same category. In other words, intermediate shapes, such as a substantially elliptical shape, can be considered to be different from one another unless they are similar shapes. That is, it is important in the present invention that the cross-sectional shape of the first honing surface 21a and the cross-sectional shape of the second honing surface 21b are not similar shapes. To put it another way, in terms of the width and height of the honing surface 21, the ratio of the height and width H2/W2 of the second honing surface 21b is preferably smaller than the ratio of the height and width H1/W1 of the first honing surface 21a.
The cross-sectional shape of each of the honing surfaces 21 has been described above, centering on the issue of whether it is close to a substantially circular-arc shape or a substantially linear shape. However, in practice, the magnitudes, etc., of the dimensions, such as the width and height, of the honing surface 21 can be changed, and thus, the applicable combinations involve a higher degree of freedom. For instance, even in the case where: the cross-sectional shape of the first honing surface 21a of the front cutting edge is a combined shape of a line and a circular arc; and the cross-sectional shape of the second honing surface 21b is a substantially circular-arc shape, when the width W2 of the second honing surface 21b is made to be sufficiently smaller than the width W1 of the first honing surface 21a, it is possible to obtain shapes which respectively result in the first cutting edge 20a with resistance to chipping and the second cutting edge 20b with good cutting ability.
In the cutting tool 1 according to the present embodiment, the peripheral area of the first cutting edge 20a and the peripheral area of the second cutting edge 20b involve different clearance angles and rake angles. That is, the first clearance angle A1 is a negative angle with respect to the second clearance angle A2, and the first rake angle B1 is greater than the second rake angle B2. Damage to the cutting edge 20 and the cutting ability thereof are closely related to the clearance angles and rake angles. When a true clearance angle is appropriately set with respect to a workpiece, the cutting ability is improved by increasing the actual rake angle. Further, various chip breakers may be provided in the upper surface 10. Various chip breakers allow for the adjustment of a rake angle of a portion connected to each cutting edge 20. In the present invention, in addition to the above-described adjustments of clearance angles and rake angles, the honing surfaces can be set independently in accordance with the characteristics required for each cutting edge, and thus, the cutting ability, fracture resistance, etc., can be adjusted appropriately, whereby the cutting performance of the cutting tool 1 can be enhanced. For instance, although the cutting tool 1 according to the present embodiment involves a small angle as the second rake angle B2 of the second cutting edge 20b, the cutting ability can be improved by decreasing the second honing surface 21b.
Although the embodiments of the present invention have been described above, various changes may be made to the cutting tool of the present invention. For instance, in the above-described embodiments, the cross-sectional shape of the first honing surface 21a is a substantially circular-arc shape, and the cross-sectional shape of the second honing surface 21b is a combined shape of one line and one circular arc; however, such cross-sectional shapes are not limited thereto, as described above. The cutting tool 1 according to the present embodiment is suitable for grooving, but the application is not limited thereto. For instance, the cutting tool 1 is applicable to various cutting tools each having a major cutting edge and a wiper edge. Further, the second cutting edge 20b is not limited to a cutting edge for finishing, such as a wiper cutting edge. The cutting tool 1 is applicable to various cutting edges each having two different cutting edges, i.e., the first cutting edge 20a and the second cutting edge 20b.
The cutting tool of the present invention is not limited to cutting tools in the form of using cutting inserts and is also applicable to cutting tools in the form of brazing chips. Further, the cutting tool of the present invention is not limited to turning tools and is also applicable to other forms of cutting tools, such as rotating tools and hole machining tools.
In the above-described embodiments, the present invention has been described specifically in a given way, but the present invention is not limited thereto. It should be appreciated that various alterations and changes can be made to the present invention without departing from the spirit and scope of the invention defined in the scope of the claims. That is, the present invention covers all kinds of modifications, applications and equivalents which are encompassed by the idea of the present invention defined by the scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-188012 | Sep 2017 | JP | national |
