Patent Description:
<CIT> (Patent Document <NUM>) discloses a method of machining a workpiece. According to the method, a cutting edge is positioned askew with respect to a feed direction and fed in a transverse direction to a rotational axis of a rotating workpiece. The machining method enables the surface of the workpiece to be machined into a smooth surface and also enables high-productivity machining. <CIT> relates to an indexable cutting tool according to the preamble of independent claim <NUM>.

A cutting tool according to the present invention is a cutting tool according to claim <NUM>.

<CIT> does not specifically disclose cutting tools suitable for cutting as described above.

An object of the present disclosure is to provide a cutting tool suitable for cutting a rotationally symmetrical surface of a rotating workpiece.

Initially, manners of carrying out the present invention are described one by one.

A cutting tool according to the invention is presented in claim <NUM>.

Thus, a cutting tool suitable for cutting a rotationally symmetrical surface of a rotating workpiece can be provided. In the step of feeding the cutting tool, the point of the cutting tool that is in contact with the rotationally symmetrical surface shifts as the cutting tool is fed. Namely, the whole of the cutting edge is used for cutting the rotationally symmetrical surface. Accordingly, the surface roughness of the rotationally symmetrical surface can be reduced. The shape of the cutting edge as seen from above the flank face includes an arc, and thus the cutting resistance can be reduced. Meanwhile, the radius of curvature of the arc is not less than <NUM> and not more than <NUM>, and thus the wear amount of the flank face can be reduced. In this way, the cutting tool life can be extended.

Preferably, the cutting edge has a length of not less than <NUM> and not more than <NUM>.

Thus, with the whole of the cutting edge, a rotationally symmetrical surface can be cut. Accordingly, the wear amount of the flank face can be reduced. In this way, the cutting tool life can be extended. If the cutting edge is short, the point of the cutting tool that is in contact with the rotationally symmetrical surface hardly shifts during cutting. In the case of such cutting (point cutting), the wear amount of the flank face is likely to increase. On the contrary, if the cutting edge is long, the point of the cutting tool that is in contact with the rotationally symmetrical surface can be shifted along the cutting edge during cutting. The cutting tool, however, is likely to have a portion which is not used for cutting. The above-described features thus enable the cutting edge to be used efficiently.

Preferably, the rake face and the flank face form a wedge angle of the cutting tool of not less than <NUM>° and not more than <NUM>°.

Thus, the cutting resistance can be reduced. In the case of cutting of a workpiece made of a high-hardness material, a greater force is applied to the cutting edge so as to cause the cutting edge to bite into the workpiece. The wedge angle falling in the above-defined range enables further reduction of the possibility that the cutting edge is damaged (fracture occurs to a part of the cutting edge, for example).

Preferably, the cutting edge is a part of a sintered material containing cubic boron nitride.

Thus, the cutting edge is formed of a material having a sufficient hardness for stable machining. Accordingly, a workpiece made of a high-hardness material can be cut and the cutting tool life can be extended.

The cutting edge as seen from above the flank face has a shape tapering toward a back surface opposite to the rake face.

Thus, flank angles are also formed laterally with respect to the cutting edge. Accordingly, the whole of the cutting edge from one end of the cutting edge to the other end thereof can be used for cutting a rotationally symmetrical surface.

The cutting edge includes a first end and a second end opposite to the first end. The first end and the second end each have a radius of curvature smaller than the radius of curvature of the cutting edge.

Thus, the possibility that fracture occurs to the first end or the second end of the cutting tool during cutting of a rotationally symmetrical surface can be reduced.

Preferably, the cutting edge has a rounded honed portion. A honing amount of the honed portion with respect to the rake face is not less than <NUM> and not more than <NUM>.

Thus, the strength of the cutting edge can be maintained while the cutting resistance is prevented from increasing.

Preferably, the cutting edge has a negative land portion. The negative land portion forms an angle of not less <NUM>° and not more than <NUM>° with the flank face.

Thus, the cutting resistance can be prevented from increasing.

Embodiments of the present invention will be described hereinafter based on the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and a description thereof will not be repeated. For the sake of easy understanding of description, only a part of components of the invention may be shown in the drawings.

<FIG> is a perspective view of a cutting tool according to an embodiment of the present invention. <FIG> is a top view of the cutting tool according to an embodiment of the present invention. <FIG> is a front view of the cutting tool according to an embodiment of the present invention. <FIG> is a right side view of the cutting tool according to an embodiment of the present invention.

Referring to <FIG>, a cutting tool <NUM> according to an embodiment of the present invention includes a rake face <NUM>, a flank face <NUM>, and a cutting edge <NUM>.

Cutting edge <NUM> corresponds to an intersection of rake face <NUM> and flank face <NUM>. In other words, cutting edge <NUM> corresponds to a portion formed by connecting rake face <NUM> and flank face <NUM> together.

Cutting edge <NUM> may be a ridgeline connecting rake face <NUM> and flank face <NUM> together. Such a cutting edge may be called "sharp edge. " Alternatively, one or more parts selected from the group consisting of a honed portion, or a negative land portion, or a combination of a honed portion and a negative land portion produced by machining cutting edge <NUM> may be formed in the surface (cutting edge <NUM>) connecting rake face <NUM> and flank face <NUM> together. Specific examples of the honed portion and the negative land portion are described later herein.

Cutting tool <NUM> includes a base material <NUM>, a hard sintered material <NUM>, and a joint member <NUM>. Base material <NUM> includes at least a part of rake face <NUM> and at least a part of flank face <NUM>. Further, base material <NUM> includes a back surface <NUM> located opposite to rake face <NUM>.

Hard sintered material <NUM> is a sintered material containing cubic boron nitride (hereinafter also referred to as "cBN"). The cutting edge is formed of the material having a hardness sufficient for stable machining. Accordingly, a workpiece made of a high-hardness material can be cut, and the life of the cutting tool can be extended. Hard sintered material <NUM> may be a sintered material containing cBN, Al<NUM>O<NUM>, and a Zr compound, for example. Hard sintered material <NUM> forms cutting edge <NUM>, at least a part of rake face <NUM>, and at least a part of flank face <NUM>. Joint member <NUM> is a member joining hard sintered material <NUM> to base material <NUM>.

As shown typically in <FIG>, the shape of cutting edge <NUM> as seen from above flank face <NUM> is an arc. The arc has a radius of curvature R of not less than <NUM> and not more than <NUM>. In an embodiment, radius of curvature R is <NUM>.

In an embodiment shown in <FIG>, the shape of cutting edge <NUM> as seen from above flank face <NUM> is a single arc. Cutting edge <NUM>, however, may have a shape made up of a combination of multiple arcs.

Cutting edge <NUM> has a length L. In an embodiment, length L is not less than <NUM> and not more than <NUM>. In an embodiment, length L falls in a range of <NUM> to <NUM>.

Cutting edge <NUM> has a corner <NUM> at each of a first end and a second end opposite to the first end. Corner <NUM> is rounded. Corner <NUM> has a radius of curvature Rc smaller than radius of curvature R of cutting edge <NUM> (Rc < R). Accordingly, cutting edge <NUM> has a lateral flank angle θa. In other words, the shape of the cutting edge as seen from above flank face <NUM> is tapered from rake face <NUM> toward back surface <NUM>. In an embodiment, flank angle θa is <NUM>°.

<FIG> is a schematic diagram showing cutting with the cutting tool according to an embodiment of the present invention. Referring to <FIG>, a workpiece <NUM> rotates about a rotational axis <NUM>. Cutting tool <NUM> is attached to a holder (not shown) and pressed against a rotationally symmetrical surface <NUM> of workpiece <NUM>. Cutting tool <NUM> moves on rotationally symmetrical surface <NUM> along a path <NUM>. Accordingly, cutting edge <NUM> machines rotationally symmetrical surface <NUM>.

<FIG> is schematic diagram schematically showing the cutting shown in <FIG>. Referring to <FIG>, at the start of cutting, the position of one end 3a of cutting edge <NUM> is in contact with rotationally symmetrical surface <NUM>. As cutting tool <NUM> is fed, the position (point P) of cutting edge <NUM> that is in contact with rotationally symmetrical surface <NUM> shifts from end 3a along cutting edge <NUM>. At the end of the cutting, point P of cutting edge <NUM> is located at the other end 3b of cutting edge <NUM>.

Regions of cutting edge <NUM> from end 3a to end 3b are successively brought into contact with the surface to be machined (rotationally symmetrical surface <NUM>). This manner of machining enables the surface of workpiece <NUM> to be machined into a smooth surface of workpiece <NUM>, and also enables high-productivity machining. Further, the whole of the cutting edge is used for cutting, and therefore the amount of wear of the flank face can be reduced. Accordingly, the life of the cutting tool can be extended.

Regarding the manner of cutting as described above, the contact resistance of cutting edge <NUM> and the surface roughness of machined workpiece <NUM> are related to each other. The closer the shape of cutting edge <NUM> to a linear shape, the smaller the surface roughness of machined workpiece <NUM>. Meanwhile, the cutting resistance of cutting edge <NUM> against contact with workpiece <NUM> is larger. In an embodiment of the present invention, cutting edge <NUM> has a radius of curvature falling within a range of not less than <NUM> and not more than <NUM>. Accordingly, the surface of workpiece <NUM> can be machined into a smooth surface while the contact resistance of cutting edge <NUM> is prevented from increasing.

Regarding the manner of cutting as described above, the whole of cutting edge <NUM> is used to cut the surface of workpiece <NUM>. If cutting edge <NUM> is short, substantially the same region of cutting edge <NUM> is used to cut the surface of workpiece <NUM>. In this case, there is a possibility that the surface roughness is larger. In an example, a threaded groove is formed in rotationally symmetrical surface <NUM>. Further, the amount of wear of the flank face is likely to increase. In contrast, if cutting edge <NUM> is too long, some regions of cutting edge <NUM> may not be involved in cutting, depending on the size of workpiece <NUM>. In this case, effective use of the whole cutting edge <NUM> cannot be accomplished.

In an embodiment of the present invention, cutting edge <NUM> has a length of not less than <NUM> and not more than <NUM>. Accordingly, cutting with effective use of the whole of cutting edge <NUM> can be achieved.

<FIG> is a partially enlarged view of a cutting edge during cutting of a workpiece. Referring to <FIG>, a wedge angle θb is an angle formed by rake face <NUM> and flank face <NUM>. The smaller the wedge angle θb, the smaller the cutting edge resistance.

If workpiece <NUM> is made of a high-hardness material such as hardened steel, for example, cutting tool <NUM> is required to be pressed strongly in a direction <NUM>, in order for cutting edge <NUM> to bite into workpiece <NUM>. If wedge angle θb is small, fracture of the cutting edge is likely to occur. In an embodiment of the present invention, wedge angle θb falls in a range of not less than <NUM>° and not more than <NUM>°. Accordingly, the possibility that fracture of the cutting edge occurs can be lowered while the cutting resistance is reduced.

<FIG> is a schematic diagram showing a first example of machining of cutting edge <NUM>. As shown in <FIG>, cutting edge <NUM> may be honed. Specifically, cutting edge <NUM> has a rounded portion (honed portion 3c). H represents a honing amount of honed portion 3c with respect to rake face <NUM>. In the present embodiment, honing amount H is not less than <NUM> and not more than <NUM>.

<FIG> is a schematic diagram showing a second example of machining of cutting edge <NUM>. As shown in <FIG>, cutting edge <NUM> may be machined to have a negative land. Specifically, cutting edge <NUM> has a negative land portion 3d. A negative land angle θn is an angle formed by negative land portion 3d with respect to flank face <NUM>. In the present embodiment, negative land angle θn is not less than <NUM>° and not more than <NUM>°.

<FIG> is a schematic diagram showing a third example of machining of cutting edge <NUM>. As shown in <FIG>, cutting edge <NUM> may be honed and additionally machined to have a negative land. In other words, cutting edge <NUM> may have both honed portion 3c and negative land portion 3d.

Influences of the radius of curvature of the cutting edge on the cutting performance were examined. With cutting tools of Examples and Comparative Example shown in Table <NUM> below, cutting was performed under the following cutting conditions, and the finished surface roughness, the cutting resistance, and the tool wear were evaluated. The results of the evaluation are shown in Table <NUM>. The evaluation was made based on the criterion that a cutting tool exhibiting a finished surface roughness Rz (ten-point mean roughness) of <NUM> or less, a cutting resistance of <NUM> N or less, and a wear amount of the flank face that did not lead to fracture was identified as acceptable.

As to the cutting tool of Sample No. 1A (comparative example), while the cutting resistance was low, finished surface roughness Rz was more than <NUM>. As to the cutting tools of Sample Nos. 1F and <NUM> (comparative examples), while finished surface roughness Rz was <NUM> or less, the cutting resistance was <NUM> N or more. As to the cutting tool of Sample No. <NUM>, cutting edge fracture occurred.

As to the cutting tools of Sample Nos. 1B to 1E (examples according to the present invention), both the finished surface roughness and the cutting resistance were acceptable. Further, no cutting edge fracture occurred.

It is seen from the above-described results that the arc shape of the cutting edge can reduce the cutting resistance. When radius of curvature R of the cutting edge is excessively small, the finished surface roughness is large. As shown in Table <NUM>, it was confirmed the radius of curvature of the cutting edge is preferably not less than <NUM> and not more than <NUM>.

Influences of the length of the cutting edge on the cutting resistance and the tool wear during cutting were examined. With cutting tools of Examples and Comparative Examples shown in Table <NUM> below, cutting was performed under the following cutting conditions, and the cutting resistance was evaluated. The results of the evaluation are shown in Table <NUM>. The evaluation was made based on the criterion that a cutting tool exhibiting a cutting resistance of <NUM> N or less and a wear amount of the flank face of <NUM> or less was identified as acceptable.

The cutting tool of each of Sample Nos. 2A and 2B had a low cutting resistance. The cutting tool of Sample No. 2A had a flank face wear amount of <NUM> or more. The cutting tool of Sample No. 2B had a flank face wear amount of <NUM> or more.

The cutting tool of Sample No. <NUM> had a smaller flank face wear amount as compared with the cutting tools of Sample Nos. The cutting tool of Sample No. <NUM> had a cutting resistance of more than <NUM> N. As to the cutting tools of Sample Nos. 2C to <NUM>, both the cutting resistance and the flank face wear amount were acceptable.

It is seen from the above-described results that the cutting tools having a cutting edge length of <NUM> or less exhibit a low cutting resistance. It is further seen from the above-described results that the cutting tools having a cutting edge length of <NUM> or more exhibit a smaller flank face wear amount as compared with the cutting tool having a cutting edge length of <NUM> or <NUM>.

It is seen that the smaller the flank face wear amount, the longer the life of the cutting tool. As shown in Table <NUM>, it has been confirmed that the length of the cutting edge is preferably not less than <NUM> and not more than <NUM>.

Influences of the wedge angle on the cutting performance were examined. With cutting tools of Examples and Comparative Example shown in Table <NUM> below, cutting was performed under the following cutting conditions, and evaluation was made for the cutting resistance and whether or not fracture occurred. The evaluation was made based on the criterion that a cutting tool having a cutting resistance of <NUM> N or less and experiencing no fracture was identified as acceptable.

As to the cutting tool of Sample No. <NUM>, while it had the lowest cutting resistance, fracture occurred. As to the cutting tools of Sample Nos. 3A to 3F, the cutting resistance was <NUM> N or less, and occurrence of fracture was suppressed.

It is seen from the above-described results that a wedge angle of the cutting tool falling in a range of not less than <NUM>° and not more than <NUM>° is preferred for achieving acceptable cutting performance.

Influences of the honing amount of the cutting tool on the cutting resistance during cutting were examined. With the cutting tools of Examples and Comparative Examples shown in Table <NUM> below, cutting was performed under the following cutting conditions, and the cutting resistance and the fracture resistance were evaluated. The evaluation was made based on the criterion that a cutting tool having a cutting resistance of <NUM> N or less and experiencing no fracture was acceptable.

The cutting tool of Sample No. 4A was a cutting tool having a non-honed cutting edge profile, namely a cutting tool having a sharp edge. As to the cutting tool of Sample No. 4A, while the cutting resistance was lower as compared with the cutting tools of other sample numbers, fracture occurred. As to the cutting tool of Sample No. <NUM>, while no facture occurred, the cutting resistance was <NUM> N or more. As to the cutting tools of Sample Nos. 4B to 4F, both the cutting resistance and the fracture resistance were acceptable.

It has been confirmed from the above-described results that the honing amount achieving both reduction of the cutting resistance and high fracture resistance falls within a range of not less than <NUM> and not more than <NUM>.

Influences of the negative land angle of the cutting tool on the cutting resistance during cutting were examined. With the cutting tools of Examples and Comparative Example shown in Table <NUM> below, cutting was performed under the following cutting conditions, and the cutting resistance was evaluated. The evaluation was based on the criterion that a cutting tool having a cutting resistance of <NUM> N or less was acceptable.

The cutting tool of Sample No. 5E had a cutting resistance of more than <NUM> N. As to the cutting tools of Sample Nos. 5A to 5E, the negative land angle was <NUM>° or less. As to the cutting tools of Sample Nos. 5A to 5E, the larger the negative land angle, the higher the cutting resistance. As to the cutting tool of any of Sample Nos. 5A to 5E, the cutting resistance was less than <NUM> N.

It has been confirmed from the above-described results that a negative land angle of not less than <NUM>° and not more than <NUM>° is preferable for reducing the cutting resistance.

Claim 1:
A cutting tool (<NUM>) for cutting a rotationally symmetrical surface (<NUM>) of a rotating workpiece (<NUM>), the cutting including the step of feeding the cutting tool in a direction inclined with respect to a rotational axis (<NUM>) of the rotationally symmetrical surface (<NUM>) while holding the cutting tool (<NUM>) in contact with the rotationally symmetrical surface (<NUM>),
in the step of feeding the cutting tool (<NUM>), the cutting tool (<NUM>) having a point (P) being in contact with the rotationally symmetrical surface (<NUM>), the point shifting as the cutting tool (<NUM>) is fed,
the cutting tool (<NUM>) comprising:
a rake face (<NUM>);
a flank face (<NUM>); and
a cutting edge (<NUM>) connecting the rake face (<NUM>) and the flank face (<NUM>),
the cutting edge (<NUM>) as seen from above the flank face (<NUM>) having a shape including at least one arc,
the arc having a radius of curvature of not less than <NUM> and not more than <NUM>, characterized in that the cutting edge (<NUM>) as seen from above the flank face (<NUM>) further includes:
a first end having a convex shape, the first end corresponding to an end which contacts to
the rotationally symmetrical surface (<NUM>) at a start of cutting the rotating workpiece (<NUM>); and
a second end opposite the first end and having a convex shape, the second end corresponding to an end which contacts to the rotationally symmetrical surface (<NUM>) at an end of cutting the rotating workpiece (<NUM>), and
the first end and the second end each having a radius of curvature smaller than the radius of curvature of the arc, and
the flank face (<NUM>), as seen from above the flank face, having a shape tapering from the first and second ends toward a back surface opposite to the rake face (<NUM>).