Description
Title of Invention: CUTTING INSERT AND ROTARY CUTTING
TOOL INCLUDING SAME
Technical Field
[1] The present disclosure relates to a rotary cutting tool used for milling a workpiece. The present disclosure also pertains to a cutting insert mounted on such a rotary cutting tool.
Background Art
[2] An end mill (also referred to as an 'end milling cutter') is known as an example of a rotary cutting tool used for milling. Unlike a drill used only for perforation, the end mill has cutting edges on its periphery and tip, and may be used for groove cutting, side cutting and the like of a workpiece. Among end mills, the ball nose end mills having a round front end are divided into a solid ball nose end mill in which an end mill body and a ball nose are integrally formed and an indexable ball nose end mill in which a cutting insert is replaceably mounted on an end mill body (or a tool body), depending on w hether the cutting insert is mounted.
Disclosure of Invention Technical Problem
[3] In the indexable ball nose end mill, the cutting insert is usually coupled to the tool body by a screw. The screw provides only a fastening force in a direction perpendicular to the cutting insert (c.g., a direction in which the cutting insert is pressed against the tool body as the screw is tightened). As such, the screw docs not sufficiently support the reaction force generated by the cutting force. In particular, the cutting insert used in the ball nose end mill has an arc-shaped edge for curved surface cutting. Accordingly, if the cutting insert is fixed to the tool body only with a screw, then the cutting insert rotates around the screw due to the reaction force generated by the cutting force during machining. This leads to a problem wherein the cutting insert cannot be firmly fixed to the tool body. That is, there is a problem in that the deformation of the screw or the breakage of the cutting insert may be caused.
|4J To solve such conventional problems, there is disclosed a ball nose end mill in which
a cutting insert and a mounting structure of an insert pocket provided in a tool body are changed. According to such ball nose end mill, a concave groove is formed on the lower surface of the cutting insert, and a protrusion having a shape corresponding to the concave groove is formed on the bottom surface of the insert pocket on which the cutting insert is seated. The cutting insert is fixed in a direction perpendicular to the insert pocket by a screw, and is firmly fixed so that its rotation on the insert pocket is
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prevented by the engagement between the protrusion and the concave groove.
However, in the case of the ball nose end mill having such mounting structure, an additional manufacturing process is required to form the protrusion on the bottom surface of the insert pocket, and a grinding process is additionally required to precisely machine (he concave groove on the lower surface of the cutting insert. This may result in an increase in the manufacturing cost of the cutting insert. Moreover, the cutting vibration or cutting force is concentrated to these coupling portions in a state in which the protrusion is coupled to the concave groove. As such, there are drawbacks since the fatigue increases and the cutting insert is likely to be damaged.
Solution to Problem
[5] Various embodiments of the present disclosure provide a cutting insert having a ridge portion formed on a lower surface thereof so that the ridge portion can be stably fastened to a tool body of a rotary cutting tool. Furthermore, various embodiments of the present disclosure provide a cutting insert having both a center edge and a peripheral edge. In addition, various embodiments of the present disclosure provide a rotary cutting tool including such a cutting insert.
[6] One aspect of the present disclosure is directed to a cutting insert. The cutting insert according to an exemplary embodiment includes: an upper surface; a lower surface opposite to the upper surface; a first side surface and a second side surface configured to connect the upper surface and the lower surface; a mounting hole formed to penetrate the upper surface and the lower surface; a first cutting edge formed at an edge of the upper surface that meets the first side surface; a second cutting edge formed at an edge of the upper surface that meets the second side surface; and a first comer portion and a second comer portion provided at both ends of the upper surface where the first side surface and the second side surface meet. The lower surface includes a ridge portion, and a first inclined surface and a second inclined surface positioned on both sides of the ridge portion as a boundary, and when looking at the lower surface, the first inclined surface and the second inclined surface have asymmetric shapes with respect to the ridge portion.
[7] In one embodiment, the first cutting edge may include a peripheral edge extending in a curved shape from the first comer portion and a long edge connected to the peripheral edge and extending to the second corner portion, the second cutting edge may include a center edge extending in a curved shape from the second corner portion and a short edge connected to the center edge and extending to the first corner portion, and a straight-line distance between both ends of the long edge may be longer than a straight line distance between both ends of the short edge.
[8] In one embodiment, each of the long edge and the short edge may have a straight line
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shape.
[9] In one embodiment, when looking at the lower surface, the ridge portion may be
spaced apart from the second corner portion and may be formed so as to be inclined with respect to a virtual line that connects a point where the peripheral edge and the long edge meet and the second comer portion, the ridge portion extending across the mounting hole.
[ 10] In one embodiment, when looking at the lower surface, the ridge portion may be formed to extend from an edge of the lower surface adjacent to the long edge to an edge of the lower surface adjacent to the short edge.
[11] In one embodiment, the ridge portion may be formed in a planar shape to have a set width between the first inclined surface and the second inclined surface.
[12] In one embodiment, the ridge portion may be formed in a shape of a line where the first inclined surface and the second inclined surface meet.
[13] In one embodiment, each of the first inclined surface and the second inclined surface may be formed to be inclined upward as a distance from the ridge portion increases.
[ 14] In one embodiment, each of the first inclined surface and the second inclined surface may be inclined at an inclination angle within a range of 5 degrees to 30 degrees with respect to a reference line perpendicular to a centre axis line passing through a centre of the mounting hole and extending in an extension direction of the mounting hole.
[15] In one embodiment, the upper surface may include a centre surface on which the mounting hole is formed, a land surface formed along the first cutting edge and the second cutting edge, and a rake surface formed between the centre surface and the land surface, and when the cutting insert is viewed from a lateral side, each of the first comer portion and the second comer portion may be raised more than the centre surface.
[16] Another aspect of the present disclosure is directed to a rotary cutting tool for milling a workpiece. The rotary cutting tool according to an exemplary embodiment includes: a cylindrical tool body having two rows of helical flutes formed at a longitudinal front end portion thereof; a pair of cutting inserts replaceable mounted on the tool body; and a pair of screws configured to respectively fix the pair of cutting inserts to the tool body. Each of the pair of cutting inserts includes: an upper surface; a lower surface opposite to the upper surface and including a ridge portion, and a first inclined surface and a second inclined surface positioned on both sides of the ridge portion as a boundary and having asymmetric shapes with respect to the ridge portion; a first side surface and a second side surface configured to connect the upper surface and the lower surface; a mounting hole formed to penetrate the upper surface and the lower surface so that each of the pair of screws is fitted to the mounting hole; a first comer portion and a second comer portion provided at both ends of the upper surface where
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the first side surface and the second side surface meet; a first cutting edge formed between the first side surface and the upper surface and including a peripheral edge extending in a curved shape from the first corner portion; and a second cutting edge formed between the second side surface and the upper surface and including a centre edge extending in a curved shape from the second comer portion, a first insert pocket and a second insert pocket for accommodating the pair of cutting inserts arc formed in the two rows of helical flutes, respectively. The pair of cutting inserts includes a first cutting insert mounted on the first insert pocket such that the first corner portion is positioned in a forward axial direction in which a front end of the tool body is oriented, whereby the peripheral edge of the first cutting insert is positioned in a radially outward direction and the forward axial direction of the tool body with respect to the centre edge, and the pair of cutting inserts includes a second cutting insert mounted on the second insert pocket such that the second corner portion is positioned in the forward axial direction, whereby the centre edge of the second cutting insert is positioned in the radially outward direction and the forward axial direction of the tool body with respect to the peripheral edge.
[17] In one embodiment, the lower surface of the first cutting insert may have a V-shape when the first cutting insert is viewed from a lateral side. The first insert pocket may include a first bottom surface configured to support the V-shaped lower surface of the first cutting insert and a first side wall extending in the radially outward direction of the tool body from the inside of the first bottom surface and configured to support (he second side surface of the first cutting insert. Further, the lower of the second cutting insert may have a V-shape when the second cutting insert is viewed from a lateral side. The second insert pocket may include a second bottom surface configured to support the V-shaped lower surface of the second cutting insert and a second side wall extending in the radially out rad direction of the tool body from the inside of the second bottom surface and configured to support the first side surface of the second cutting insert.
[18] In one embodiment, the first bottom surface may include a first outer bottom surface making contact with the first inclined surface adjacent to the peripheral edge of the first cutting insert, a fust inner bottom surface making contact with (he second inclined surface adjacent to the centre edge of the first cutting insert, and a first ridge receiving groove formed between the first outer bottom surface and the first inner bottom surface and configured to receive the ridge portion of the first cutting insert. Further, the second bottom surface may include a second inner bottom surface making contact w ith the first inclined surface adjacent to the peripheral edge of the second cutting insert, a second outer bottom surface making contact with the second inclined surface adjacent to the centre edge of the second cutting insert, and a second ridge receiving groove
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formed between the second inner bottom surface and the second outer bottom surface and configured to receive the ridge portion of the second cutting insert.
[ 19] In one embodiment, the rotary cutting tool may be a ball nose end mill.
Advantageous Effects of Invention
[20] According to embodiments of the present disclosure, due to the role of the protruding V-shaped bottom surface of the cutting insert, the rotary cutting tool has stable fastening capability even in the three-dimensional cutting performed in the rotational direction, the radial direction and the axial direction. The lower surface of the cutting insert has the pair of inclined surfaces formed in asymmetrical shapes. This makes it possible to prevent cross mounting of the cutting insert (that is, it is possible to prevent the second cutting insert from being mounted on the first insert pocket, and to prevent the first cutting insert from being mounted on the second insert pocket). Moreover, the lower surface of the cutting insert is divided by the ridge portion so that the pair of inclined surfaces have as much a uniform pocket contact surface as possible. Accordingly, it is possible to expect a stable tool lifespan, which makes it possible to improve the productivity of the cutting process.

claims:
A cutting insert, comprising: an upper surface;
a lower surface opposite to the upper surface;
a first side surface and a second side surface configured to connect the upper surface and the lower surface;
a mounting hole formed to penetrate the upper surface and the lower surface;
a first cutting edge formed at an edge of the upper surface that meets the first side surface;
a second cutting edge formed at an edge of the upper surface that meets the second side surface; and
a first corner portion and a second corner portion provided at both ends of the upper surface where the first side surface and the second side surface meet,
wherein the lower surface includes a ridge portion, and a first inclined surface and a second inclined surface positioned on both sides of the ridge portion as a boundary, and
when looking at the lower surface, the first inclined surface and the second inclined surface have asymmetric shapes with respect to the ridge portion.
The cutting insert of Claim 1, wherein the first cutting edge includes a peripheral edge extending in a curved shape from the first comer portion and a long edge connected to the peripheral edge and extending to the second comer portion,
the second cutting edge includes a centre edge extending in a curved shape from the second corner portion and a short edge connected to the centre edge and extending to the first comer portion, and a straight-line distance between both ends of the long edge is longer than a straight-line distance between both ends of the short edge.
The cutting insert of Claim 2, wherein each of the long edge and the short edge has a straight line shape.
The cutting insert of Claim 2, wherein when looking at the lower surface, the ridge portion is spaced apart from the second comer portion and is formed so as to be inclined with respect to a virtual line that connects a point where the peripheral edge and the long edge meet and the second corner portion, the ridge portion extending across the mounting hole.
The cutting insert of Claim 2, wherein when looking at the lower surface, the ridge portion is formed to extend from an edge of the lower surface adjacent to the long edge to an edge of the lower surface adjacent to the short edge.
The cutting insert of Claim 1, wherein the ridge portion is formed in a planar shape to have a set width between the first inclined surface and the second inclined surface.
The cutting insert of Claim 1, wherein the ridge portion is formed in a shape of a line w here the first inclined surface and the second inclined surface meet.
The cutting insert of Claim 1, wherein each of the first inclined surface and the second inclined surface is formed to be inclined upward as a distance from the ridge portion increases.
The cutting insert of Claim 8, wherein each of the first inclined surface and the second inclined surface is inclined at an inclination angle within a range of 5 degrees to 30 degrees with respect to a reference line perpendicular to a centre axis line passing through a centre of the mounting hole and extending in an extension direction of the mounting hole.
The cutting insert of Claim 1, wherein (he upper surface includes a centre surface on which the mounting hole is formed, a land surface formed along the first cutting edge and the second cutting edge, and a rake surface formed between the centre surface and the land surface, and
when the cutting insert is viewed from a lateral side, each of the first comer portion and the second comer portion is raised more than the centre surface.
A rotary cutting tool for milling a work piece, comprising: a cylindrical tool body having two rows of helical flutes formed at a longitudinal front end portion thereof;
a pair of cutting inserts replaceable mounted on the tool body; and a pair of screws configured to respectively fix the pair of cutting instils to the tool body,
wherein each of the pair of cutting inserts includes: an upper surface; a lower surface opposite to the upper surface and including a ridge portion, and a fust inclined surface and a second inclined surface positioned on both sides of the ridge portion as a boundary and having
asymmetric shapes with respect to the ridge portion; a first side surface and a second side surface configured to connect the upper surface and the lower surface; a mounting hole formed to penetrate the upper surface and the lower surface so that each of the pair of screws is fitted to the mounting hole; a first corner portion and a second comer portion provided at both ends of the upper surface where the first side surface and the second side surface meet; a first cutting edge formed between the first side surface and the upper surface and including a peripheral edge extending in a curved shape from the first corner portion; and a second cutting edge formed between the second side surface and the upper surface and including a centre edge extending in a curved shape from the second comer portion,
a first insert pocket and a second insert pocket for accommodating the pan- of cutting inserts are formed in the two rows of helical flutes, respectively,
the pair of cutting inserts includes a first cutting insert mounted on the first insert pocket such that the first comer portion is positioned in a forward axial direction in which a front end of the tool body is oriented, whereby the peripheral edge of the first cutting insert is positioned in a radially outward direction and the forward axial direction of the tool body with respect to the center edge, and
the pair of cutting inserts includes a second cutting insert mounted on the second insert pocket such that the second comer portion is positioned in the forward axial direction, whereby the centre edge of the second cutting insert is positioned in the radially outward direction and the forward axial direction of the tool body with respect to the peripheral edge.
The rotary cutting tool of Claim 11, wherein the lower surface of the first cutting insert has a V-shape when the first cutting insert is viewed from a lateral side,
the first insert pocket includes a first bottom surface configured to support the lower surface of the first cutting insert and a first side wall extending in the radially outward direction of the tool body from tire inside of the first bottom surface and configured to support the second side surface of the first cutting insert,
the lower surface of the second cutting insert has a V-shape when the
second cutting insert is viewed from a lateral side, and
the second insert pocket includes a second bottom surface configured to
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support the lower surface of the second cutting insert and a second side w all extending in the radially outward direction of the tool body from the inside of the second bottom surface and configured to support the first side surface of the second cutting insert.
[Claim 13] The rotary cutting tool of Claim 12, wherein the first bottom surface
includes a first outer bottom surface making contact with the first inclined surface adjacent to the peripheral edge of the first cutting insert, a first inner bottom surface making contact with the second inclined surface adjacent to the centre edge of the first cutting insert, and a first ridge receiving groove formed between the first outer bottom surface and the first inner bottom surface and configured to receive the ridge portion of the first cutting insert, and the second bottom surface includes a second inner bottom surface making contact with the first inclined surface adjacent to the peripheral edge of the second cutting insert, a second outer bottom surface making contact with the second inclined surface adjacent to the centre edge of the second cutting insert, and a second ridge receiving groove formed between the second inner bottom surface and the second outer bottom surface and configured to receive the ridge portion of the second cutting insert.
[Claim 14] The rotary cutting tool of Claim 11, wherein the rotary cutting tool is a
ball nose end mill.