Cutting insert and cutting tool

A structure for cooling a rake face of a cutting insert in a region near a tip of a cutting edge. The cutting insert includes a rake face, a cutting edge formed on an outer periphery of the rake face, a base portion that supports the rake face, and an internal cooling path through which fluid for cooling the rake face flows. The internal cooling path includes an introduction flow path and a cooling flow path, and the cooling flow path is disposed behind a region in which a chip of a workpiece comes into contact with rake face. The cooling flow path is provided at a depth of less than or equal to 1.5 mm from the rake face.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2020/004701 filed on Feb. 7, 2020, which claims priority under U.S.C. § 119 (a) to Japanese Patent Application No. 2019-021386 filed on Feb. 8, 2019.

TECHNICAL FIELD

The present disclosure relates to a cutting insert and a cutting tool. This application is based on and claims the benefit of priority of Japanese Patent Application No. 2019-021386 filed on Feb. 8, 2019, the entire contents of which are incorporated by reference in this specification.

BACKGROUND ART

It has been known that frictional heat and shearing heat generated in a cutting process cause an increase in the temperature of a tip of a cutting edge of a tool and that thermal wear is caused as a result. During the cutting process, cutting oil is supplied to the tip of the cutting edge of the tool to absorb the frictional heat and shearing heat that are generated. However, since a chip is in contact with a rake face of the tool in a region near the tip of the cutting edge, where the temperature is highest, the cutting oil does not reach this region. Thus, the temperature cannot be easily sufficiently reduced in the contact region.

NPL 1 discloses a cooled cutting device in which a tip of a cutting edge of a tool is attached to a shank having a through hole and which includes a circulation circuit for causing coolant to flow from a cooling tank, pass through the through hole in the shank, and then return to the cooling tank.

CITATION LIST

Non Patent Literature

NPL 1: Sadaji Okamoto et al., “On Cutting with Internally Cooled Cutting Tool (1st Report)”, Journal of the Japan Society of Precision Engineering, May 1972, Vol. 38, No. 5

SUMMARY OF INVENTION

Technical Problem

NPL 1 discloses a structure in which a tip of a cutting edge of a tool is cooled through a cooled shank. However, a portion of a rake face in a region near the tip of the cutting edge, where the temperature is highest, is away from the through hole in the shank through which the coolant passes, and therefore cannot be efficiently cooled.

The present disclosure has been made in light of the above-described circumstances, and provides a structure for cooling a rake face in a region near a tip of a cutting edge.

Solution to Problem

To solve the above-described problem, a cutting insert according to an aspect of the present invention includes a rake face, a cutting edge formed on an outer periphery of the rake face, a base portion that supports the rake face, and an internal cooling path through which fluid for cooling the rake face flows.

A cutting tool according to another aspect of the present invention includes a tool body, a cutting insert including an internal cooling path, and a supply hole through which fluid is supplied to the internal cooling path.

Advantageous Effects of Invention

The present disclosure provides a structure for cooling a rake face in a region near a tip of a cutting edge.

DESCRIPTION OF EMBODIMENTS

As illustrated inFIG.1A, a chip comes into contact with a rake face in a region near the tip of the cutting edge immediately after being cut. As can be observed, frictional heat and shearing heat are transmitted from the chip to the rake face in the region near the tip of the cutting edge, and accordingly, the temperature in this region exceeds the temperature at the tip of the cutting edge. The analysis result shows that the highest temperature of the rake face is close to 1000 degrees. When the temperature is increased to around 1000 degrees, thermal wear may occur even in an insert made of a super-hard alloy having high strength at high temperatures.

Before describing an embodiment of the present disclosure, an increase in the temperature of a rake face in a region near a tip of a cutting edge will be described.

FIG.1Aillustrates the result of analysis of temperature distribution when a workpiece is being cut by a tool.FIG.1Bis an enlarged view of the result of analysis of the temperature distribution illustrating a region including a tip of a cutting edge.

The analysis result shows that the highest temperature is approximately 1000 degrees and that the temperature drops to around 200 degrees at a location away from the tip of the cutting edge by about 5 times the cutting thickness of the workpiece (cutting depth in two-dimensional cutting). This is because the location is sufficiently away from the region in which the chip is in contact with the rake face. Therefore, it is clear from the analysis result that a region near the contact region needs to be cooled. Since the cutting thickness is in the range of about several tens of micrometers to about three hundred micrometers under many practical cutting conditions, a region in a range of less than or equal to 1.5 mm from the tip of the cutting edge needs to be cooled.

It is known that the contact length between the rake face and the chip correlates with the cutting thickness of the workpiece. The correlation also depends on the cutting speed, the shape of the tip of the cutting edge of the tool, etc. to be precise. However, under practical conditions, the contact length between the rake face and the chip is less than or equal to several times the cutting thickness, as in the example illustrated inFIGS.1A and1B. Since the cutting thickness is in the range of about several tens of micrometers to about three hundred micrometers under many practical cutting conditions, it can be assumed that the contact length falls within 1.5 mm. An embodiment of the present disclosure will now be described based on the above discussion.

FIG.2is a schematic diagram illustrating the structure of a cutting tool according to the embodiment. A cutting tool1includes a shank2made of a steel material. The shank2is a tool body, and includes a shank end portion2ato which a cutting insert10is attached and a held portion2bwhich is held by a machine tool in a cutting process. The shank end portion2ahas a top surface which is formed one step higher than a top surface of the held portion2b. An end portion of the top surface of the shank end portion2ahas a cutout portion to which the cutting insert10and a sheet member12are attached.

The cutting insert10and the sheet member12, which are made of a hard material, such as a super-hard alloy, are disposed in the cutout portion and fixed to the shank2by a clamp member14. The cutting insert10and the sheet member12may instead be fixed to the shank2by other means. For example, the cutting insert10and the sheet member12may have screw holes that extend therethrough, and be directly fixed to the shank2by a screw member. The cutting insert10may instead be directly fixed to the cutout portion of the shank end portion2awithout having the sheet member12disposed therebetween.

FIG.3is an enlarged view of a region including a cutting edge of the cutting insert10. The cutting insert10includes a rake face22, cutting edges20formed on the outer periphery of the rake face22, and a base portion24which supports the rake face22. The cutting insert10according to the embodiment includes two cutting edges20at diagonal corners of the rake face22, but may instead include the cutting edges20at all of the corners.

The base portion24, the sheet member12, and the shank end portion2aare provided with an internal cooling path40through which fluid for cooling the rake face22flows. The cooling fluid supplied to the internal cooling path40may be liquid, such as water-soluble cutting oil or water-insoluble cutting oil, but may instead be gas, such as cooling air. The cutting tool1is formed such that a supply hole32, which serves as an inlet of the internal cooling path40, is formed in a bottom surface of the shank end portion2a, and such that a plurality of flow-path openings30a,30b, and30c(hereinafter referred to also as “flow-path openings30” without distinction), which serve as outlets of the internal cooling path40, are formed in flank faces of the base portion24of the cutting insert10in a region near the cutting edge20. The internal cooling path40includes an introduction flow path and cooling flow paths. The introduction flow path extends from the supply hole32to a location immediately below the rake face22through the interior of the shank end portion2aand the sheet member12. The cooling flow paths extend behind the rake face22and parallel to the rake face22to the flow-path openings30. In the embodiment, the expression “parallel to the rake face22” may include any substantially parallel state that does not deviate from the intended purpose.

FIG.4is a sectional view of the cutting tool1taken along a diagonal of the rake face22on which the pair of cutting edges20are provided. The clamp member14is not illustrated. The internal cooling path40includes an introduction flow path44which extends from the supply hole32to the location immediately below the rake face22and cooling flow paths42which extend parallel to the rake face22from the end of the introduction flow path44to the flow-path openings30.

The introduction flow path44includes a first introduction flow path44aformed in the shank end portion2a, a second introduction flow path44bformed in the sheet member12, and a third introduction flow path44cformed in the base portion24of the cutting insert10. The introduction flow path44illustrated inFIG.4extends linearly in a direction perpendicular to the bottom surface of the shank end portion2a. However, the first introduction flow path44amay instead be bent so that the supply hole32is formed in a side surface of the shank end portion2a. The supply hole32is preferably formed at a location such that the cooling fluid can be easily supplied by a machine tool. To prevent leakage of the cooling fluid, abutting surfaces of the components may be sealed.

The cooling flow paths42are formed as groove-shaped flow paths that extend parallel to the rake face22. The cooling flow paths42are provided at least behind the region in which the chip of the workpiece comes into contact with the rake face22. The cooling flow paths42have a function of causing the cooling fluid supplied from the supply hole32through the introduction flow path44to flow along the rake face22toward the flow-path openings30formed immediately below the cutting edges20, thereby cooling the rake face22in the regions near the cutting edges20.

The cutting insert10of the embodiment includes a thin plate member52having a top surface that serves as the rake face22and a base body50which supports the thin plate member52and constitutes the base portion24. The cooling flow paths42are formed by bringing a bottom surface (back surface) of the thin plate member52into contact with a top surface of the base body50.

FIG.5Aillustrates the top surface of the base body50, andFIG.5Bis a partial sectional view of the top surface. The top surface of the base body50has a plurality of cooling flow paths42a,42b, and42c(hereinafter referred to also as “cooling flow paths42” without distinction) which extend parallel to each other and along which the cooling fluid flows. The cooling flow paths42extend at least over a range from the position of the cutting edge20on the rake face22to a region in which the chip comes into contact with the rake face22. As described above, under practical conditions, the contact length between the chip and the rake face22falls within 1.5 mm from the tip of the cutting edge. Therefore, the cooling flow paths42may be provided over a range of about 1.5 mm from the tip of the cutting edge20. In the embodiment, the cooling flow paths42are formed to extend from the upper end of the third introduction flow path44ctoward the corners corresponding to the positions of the cutting edges20on the rake face22.

FIG.6Aillustrates a top surface of the thin plate member52, andFIG.6Billustrates the bottom surface of the thin plate member52. The top surface of the thin plate member52serves as the rake face22, and the cutting edges20are formed on the outer periphery of the rake face22. The bottom surface of the thin plate member52is placed on the top surface of the base body50, so that the cooling flow paths42are formed between the base body50and the bottom surface of the thin plate member52.

To increase the cooling efficiency, the cooling flow paths42are preferably provided at a depth that is less than or equal to 1.5 mm from the rake face22. In the embodiment, the depth of the cooling flow paths42from the rake face22is defined as the distance between the top surface of each cooling flow path42and the rake face22, and is therefore equal to the thickness of the thin plate member52. To ensure sufficient strength of the thin plate member52and increase the efficiency in cooling the thin plate member52, the depth of the cooling flow paths42from the rake face22, that is, the thickness of the thin plate member52, is preferably set in the range of 0.2 mm or more and 1.5 mm or less, more preferably in the range of 0.2 mm or more and 1 mm or less, and still more preferably in the range of 0.2 mm or more and 0.5 mm or less.

The thin plate member52is made of a super-hard alloy having a low toughness. Therefore, when the cooling flow paths42have a width Wa greater than the above-described depth, there is a possibility that the thin plate member52will break. Therefore, the flow-path width Wa is set to be less than or equal to a predetermined length. More specifically, the flow-path width Wa is preferably less than or equal to the depth. To prevent breakage of the thin plate member52, the ratio of the flow-path width Wa to a distance Wb between the flow paths (Wa/Wb) is preferably set to be less than or equal to 1.

Since the cutting insert10is composed of two members, which are the base body50and the thin plate member52, the cutting insert10can be easily manufactured. In addition, when the flow-path openings30are clogged with chips, the chips can be easily removed by separating the thin plate member52from the base body50. In addition, when the cutting edges20are worn, only the thin plate member52needs to be replaced, and the base body50can be reused.

The present disclosure has been described based on the embodiment. It is to be understood by a person skilled in the art that the embodiment is illustrative, that various modifications are possible with regard to combinations of the components and processes in the embodiment, and that such modifications are also included in the scope of the present disclosure.

Although the cooling flow paths42are formed in the top surface of the base body50in the embodiment, the cooling flow paths42may instead be formed in the bottom surface of the thin plate member52. Alternatively, the cooling flow paths42may be formed in both the top surface of the base body50and the bottom surface of the thin plate member52. In addition, although the introduction flow path44is formed also in the sheet member12and the shank end portion2ain the embodiment, the third introduction flow path44cmay be omitted, and the cooling fluid may be supplied from the flow-path openings30near the other cutting edge20.

FIG.7a schematic diagram illustrating the structure of a cutting tool according to a modification.FIG.8is a top surface of a base body50according to the modification. The cooling structure illustrated inFIG.4discharges the cooling fluid from the flow-path openings30disposed immediately below the cutting edges20. In contrast, the cooling structure illustrated inFIG.7, which is applicable to dry processing, discharges the cooling fluid from a flow-path opening30formed in the bottom surface of the shank end portion2a.

According to the modification, an internal cooling path includes an introduction flow path44which extends from a supply hole32to a location immediately below a rake face22; cooling flow paths48d,48e,48f,48g,48h, and48i(hereinafter referred to as “cooling flow paths48”) which extend parallel to the rake face22from the end of the introduction flow path44; and a discharge flow path46which extends from a location immediately below the rake face22to the flow-path opening30. As illustrated inFIG.7, the supply hole32which serves as an inlet of the internal cooling path40and the flow-path opening30which serves as an outlet of the internal cooling path40are formed in the bottom surface of the shank end portion2a.

The cooling flow paths48are formed as groove-shaped flow paths that extend parallel to the rake face22, and the cooling flow paths48are provided at least behind a region in which the chip of the workpiece comes into contact with the rake face22. The cooling flow paths48have a function of causing the cooling fluid supplied from the supply hole32through the introduction flow path44to flow along the rake face22toward the discharge flow path46so as to pass through regions near the cutting edges20, thereby cooling the rake face22in the regions near the cutting edges20. In this modification, the cutting edges20may be formed at four corners of the rake face22.

Based on the assumption that the contact length between the chip and the rake face22falls within 1.5 mm from the tip of the cutting edge, the cooling flow paths48which extend parallel to each other are preferably provided to cover a range of within 1.5 mm from the tip of the cutting edge20.

In the examples illustrated inFIGS.4and7, the cutting insert10is composed of two members, which are the base body50and the thin plate member52. However, the cutting insert10may instead have an integral structure. For example, when the cutting insert is manufactured by sintering, super-hard alloy powder may be compression-molded while a low-melting-point material having the shape of an internal cooling path is embedded therein. Then, the super-hard alloy powder may be sintered at a high temperature so that the low-melting-point material is eluted and the internal cooling path is formed.

Although the shank2is described as a tool body of the cutting tool1in the embodiment, the cutting tool1is not limited to a turning tool, and may instead be a milling tool having a cutter body.

Aspects of the present disclosure will now be described. A cutting insert according to an aspect of the present disclosure includes a rake face, a cutting edge formed on an outer periphery of the rake face, a base portion that supports the rake face, and an internal cooling path through which fluid for cooling the rake face flows.

According to this aspect, since the cooling path is formed in the cutting insert, the cutting insert can be efficiently cooled.

The internal cooling path may be disposed behind a region in which a chip of a workpiece comes into contact with the rake face. When the internal cooling path is disposed behind the contact region, the cooling efficiency can be increased. At least a portion of the internal cooling path may be disposed to extend parallel to the rake face behind the region.

The internal cooling path is preferably provided at a depth of less than or equal to 1.5 mm from the rake face. When the internal cooling path is provided at a depth of less than or equal to 1.5 mm from the rake face, the cooling efficiency can be increased. The cutting insert may include a thin plate member having a top surface that serves as the rake face, and the internal cooling path may be provided between the base portion and a bottom surface of the thin plate member.

A cutting tool according to another aspect of the present disclosure includes a tool body, such as a shank, a cutting insert including an internal cooling path, and a supply hole through which fluid is supplied to the internal cooling path.

REFERENCE SIGNS LIST