JPH0531618A - Cutting tool and its manufacture - Google Patents

Abstract

PURPOSE:To provide a cutting tool whose surface hardness is high and whose durability is superior and which is of high precision and which is inexpensive. CONSTITUTION:A chip fitting groove 2a, a center hole 9, a boss surface 10 and the like are formed at a tool main body 1, and then, a hardened layer is formed by administering nitrification treatment over the whole surface of the tool main body 1. It is recommended that hardness at the hardened layer be made to be over Hv500 at a 0.1mm position from the tool surface. It is also recommended that the boss surface 10 and the inner periphery surface of the center hole 9 be made to be ground surfaces from which soft films produced by nitrification treatment are removed. It is desired that the chip fitting groove 2a be made to be a bare surface which has no finish processing after nitrification treatment, and it is also desired that the screw hole inside formed at the main body 1 be made to be a nitrification preventive portion. As a result, hardness necessary for the tool is given by means of the hardened layer due to nitrification treatment. As distortion is hard to occur at the time of nitrification treatment, precision can be maintained even if finish processing is not administered after treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a throw-away type cutting tool to which a throw-away tip is detachably attached.

[0002]

2. Description of the Related Art In recent years, in the field of cutting tools, a throw-away tip (hereinafter referred to as "tip") made of a hard material such as cemented carbide is detachably attached to a tool body made of steel such as tool steel. The so-called throw-away type that is installed is widely used. In such a throw-away tool, in order to prevent damage to the outer peripheral surface of the tool body due to rubbing with chips and to enhance the durability of the tool body, the tool body is subjected to a quenching treatment to reduce its surface hardness to H _R C
It is being raised to about 45.

[0003]

However, when the tool body is hardened, quenching distortion is inevitably generated.
Therefore, for example, the boss surface of the tool body for milling, the outer peripheral surface of the shank of the end mill, the mounting part to the machine tool, or the part where accuracy is required, such as the chip mounting groove, is polished to remove strain after quenching. Since it was necessary to perform processing and cutting with an end mill, an increase in cost due to an increase in processing man-hours was unavoidable. Moreover, depending on the size of the quenching strain, the processing time becomes extremely long and the processing cost may be further reduced.

Further, when cutting is performed after quenching, the surface hardness of the tool body is set to a high hardness of H _R C45 or more, so that the cutting edge of the end mill used for the machining is severely worn and the machining accuracy is high. Not a little was affected. Particularly, when a plurality of chip mounting grooves are continuously machined, the machining accuracy between the chip mounting groove formed immediately after the start of machining due to the wear of the cutting tool and the chip mounting groove formed just before the end of machining is high. There was a large change, and along with this, the runout accuracy of the chip mounted in the chip mounting groove was significantly deteriorated.

Further, a large residual stress is often generated inside the tool body due to the rapid cooling at the time of quenching, and the accuracy may be lost due to the subsequent release of such stress.

The present invention has been made under such a background, and the tool body has high surface hardness and excellent durability,
Moreover, it is an object of the present invention to provide a cutting tool which has good accuracy and is inexpensive, and a manufacturing method thereof.

[0007]

In order to solve the above problems, a cutting tool according to the present invention has a plurality of chip mounting grooves formed in a tool body having a mounting portion for a machine tool, and the chip mounting grooves are provided with chips. In a cutting tool detachably mounted, a hardened layer formed by nitriding treatment is formed on the surface layer portion of the tool body.

Here, when the tool body is formed with a screw hole for mounting a chip or a component such as a wedge member for mounting the chip, inside the screw hole, formation of a hardened layer by nitriding treatment is prevented. It is preferable to use the nitriding prevention part. In addition, a soft coating may be formed on the surface of the hardened layer in the process of forming the hardened layer by nitriding. In such a case, the surface of the mounting portion to the machine tool is polished to harden the mounting portion. The surface of the layer is preferably a polished surface from which the soft coating has been removed. Furthermore, in order to reduce the number of manufacturing steps of the tool body, the surface of the hardened layer in the chip mounting groove should be
It is better to leave it as it is on the bare surface that is not subjected to finishing after nitriding. Furthermore, in order to prevent the occurrence of cracks during the nitriding treatment, it is desirable to chamfer or round the corners of the chip mounting groove.

The hardness of the hardened layer of the tool body mentioned above is H _V at a position of 0.1 mm from the surface of the tool body.
It is preferably 500 or more.

As a method of manufacturing a cutting tool in which the inside of the screw hole serves as a nitriding prevention portion, a recess is attached to the screw hole, the tool body is subjected to nitriding treatment, and the surface layer portion of the tool body is hardened. A manufacturing method is preferred in which the layers are formed and then the recess is removed. In this case, in order to reduce the manufacturing cost, it is desirable to use a non-nitriding material for the burying, or to mount the nitriding prevention layer on the surface of the burying and then mount the burying into the screw hole. In order to prevent unnecessary enlargement of the nitriding prevention part of the peripheral part, a taper surface that expands toward the opening end of the screw hole is formed at the mouth of the screw hole of the tool body, and It is preferable to use a flat head screw having a taper surface that can be in close contact with the taper surface. In addition, various screw members such as a hexagon bolt and a set screw are used for the burying.

[0011]

In the cutting tool having the above structure, the hardened layer formed by the nitriding process provides the surface layer of the tool body with the required hardness. Moreover, since the heating temperature of the nitriding treatment is sufficiently lower than the quenching temperature of the steel material, there is no risk of distortion. Therefore, it is not necessary to perform strain relief processing after the nitriding treatment. Further, since no large residual stress is generated during the nitriding treatment, the stress is not released later and the accuracy is not deteriorated.
Further, particularly when the inside of the screw hole is a nitriding prevention portion in a tool body having a screw hole, there is no fear that the thread hardness of the screw hole unnecessarily increases and cracks or chips occur,
The other bolt will not be damaged.

Further, by making the mounting portion of the tool body a polished surface from which the soft coating is removed, the mounting portion is prevented from being deformed when the cutting tool is mounted on the machine tool, and the reproducibility of mounting accuracy is improved. be able to. On the other hand, if the hardened layer surface in the chip mounting groove is a bare surface that is not subjected to finishing processing after nitriding treatment, the work after nitriding processing is saved, especially in the case of a cutting tool with many chip mounting grooves. In addition, processing man-hours are greatly reduced. Further, when chamfering or rounded surface processing is applied to the corners of the chip mounting groove, stress concentration on the corners is alleviated and cracking of the hardened layer is prevented.

Further, according to the method of manufacturing a cutting tool having the above structure, the inside of the screw hole is sealed by the burial mounted in the screw hole, so that ammonia gas or nitriding gas supplied to the periphery of the tool body at the time of nitriding treatment is performed. Invasion of a nitriding agent such as a solution into the screw hole is prevented, so that the nitriding prevention portion can be easily obtained only by removing the bur after the nitriding treatment. Moreover, in the case of burying, it is inconvenient that the desired hardened layer cannot be obtained because the anti-nitriding agent adheres to unnecessary portions as in the case of applying the anti-nitriding agent in the screw hole to prevent nitriding. Since there is no unevenness in the nitriding prevention effect due to uneven coating of the nitriding inhibitor, a uniform nitriding prevention portion can be obtained.

Further, in the above manufacturing method, when the hard-nitriding material is used for the burying or the nitriding treatment is performed by forming the nitriding prevention layer on the surface of the burying, the burying does not change before and after the nitriding treatment. The cost required for the nitriding treatment can be reduced by repeatedly using the burying.

Further, while a tapered surface is formed at the base of the screw hole of the tool body, when a countersunk screw is used for the burying, the tapered surface of the countersunk head and the tapered surface of the screw hole are in close contact with each other. By doing so, the airtightness inside the screw hole is further improved and the quality of the nitriding prevention part is improved, while the nitriding inhibitor surely reaches the periphery of the screw hole mouth and the hardened layer by nitriding treatment is applied to the periphery of the screw hole. It can be formed up to the limit and the nitriding prevention part does not unnecessarily expand.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 to 4 show a throw-away type face milling machine according to this embodiment. In these drawings, reference numeral 1 is a tool body. The tool body 1 has a tip pocket 2 that is recessed toward the center side in the tool radial direction on the outer peripheral portion thereof.
A plurality of chip mounting grooves 2a connected to the rear end side of the chip pocket 2 in the circumferential direction are formed at equal intervals in the circumferential direction, and the chip mounting seat 3 provided at the end of the chip mounting groove 2a. A square flat sheet 4 is placed and fixed with a set screw 5. On the upper surface of the sheet 4, a chip 6 formed by molding a cemented carbide into a substantially square flat plate is placed, and the chip 6 is inserted into the chip mounting groove 2a and tightened by a clamp screw 7. It is pressed in the tool circumferential direction by the member 8 and firmly fixed to the tool body 1. Further, a center hole 9 is formed in the center of the tool body 1, and a boss surface 10 orthogonal to the tool axis is formed around the opening on the tool rear end side of the center hole 9. The center hole 9 and the boss surface 10 form a mounting portion for mounting the tool body 1 on a spindle (not shown) of a machine tool.

The tool body 1 includes SCM440 and SNCM4.
It is made of steel such as 39 as a raw material and is formed into a substantially annular shape.
The chip mounting groove 2a, the center hole 9, and the boss surface 10 are formed by cutting this. Then, the entire surface of the tool body 1 is subjected to a nitriding treatment, whereby a hardened layer (not shown) having a higher hardness than the inside is formed on the surface layer of the tool body 1. The hardness of the hardened layer is appropriately determined according to the usage conditions of the tool body 1, the internal hardness, and the like.
It is preferable that H _{V of} 500 or more is secured at a position of a depth of 1 mm. This is because if the hardness is less than H _V 500, the difference from the internal hardness of the tool body 1 is too small and the effect of improving the tool life may not be sufficiently exerted.

A well-known nitriding method is used as a nitriding method for the tool body 1. For example, nitrogen atoms are removed by heating the tool body 1 in an atmosphere containing ammonia gas (NH ₃ ) or other nitrogen. Gas nitriding, which is permeated from the tool surface to form a nitride layer, is preferably used. In addition, cyanide (KCN, NaCN) and cyanate (KC)
Various methods such as salt bath nitriding treatment in which the tool body 1 is immersed in a mixed solution of NO and NaCNO) and heating, and ion nitriding can be used.

The heating temperature of the tool body 1 at the time of nitriding treatment is 500 to 550 ° C. in the case of gas nitriding and less than 600 ° C. in the case of salt bath nitriding. It is much lower than the heating temperature of 850 ° C or higher. Further, the nitriding treatment time is 2 in the case of gas nitriding.
It is 0 to 100 hours, and in the case of salt bath nitriding, it is about 2 to 3 hours. The depth of the hardened layer to be formed is preferably 0.1 mm or more and 0.4 mm or less. When the thickness is 0.1 mm or less, the hardness is too thin and the hardness is likely to be easily lost. On the other hand, when the thickness is 0.4 mm or more, the hardness on the surface side is too high and cracks are likely to occur. . Incidentally, in order to achieve the above-mentioned hardened layer thickness by gas nitriding, it is advisable to set the treatment time to 20 to 40 hours.

The chip mounting groove 2a, the center hole 9 and the boss surface 10 are cut or ground before the nitriding treatment to be formed with a predetermined accuracy. However, since the carbon content of the tool body 1 is combined with the nitride during the nitriding treatment, a soft coating may be formed on the surface layer portion of the tool body 1. Only the tool attachment portion (portion indicated by the one-dot chain line T in FIG. 1) through the hole 9 is subjected to polishing so that the surface of the hardened layer formed in these attachment portions becomes the polished surface with the soft coating removed. There is. If you leave the soft coating on the mounting surface,
This is because when the tool body 1 is attached to a machine tool, the soft coating may be deformed to cause an attachment error such as misalignment, and the reproducibility of the attachment accuracy of the tool body 1 may not be ensured. The thickness of this soft coating is about 0.01 mm at the maximum, and the removal allowance for polishing for removing the coating is 0.0
About 5 mm is enough.

On the other hand, the tip mounting groove 2a of the tool body 1
The surface of the hardened layer formed inside is made a bare surface that is not subjected to finishing after nitriding. This is because the number of chip mounting grooves 2a is large in a milling tool, and if the finishing machining is performed for each of these after the nitriding treatment, the number of manufacturing steps is significantly increased.

Further, as shown in more detail in FIGS. 2 to 4, the corners where the wall surfaces of the chip mounting groove 2a intersect are rounded to form minute curved surfaces 11 and 12. These minute curved surfaces 11 and 12 are for protecting the hardened layer by preventing the generation of cracks during the nitriding treatment. Instead of forming the minute curved surfaces 11 and 12, chamfering may be performed on the corners in the chip mounting groove 2a to form minute inclined surfaces that obliquely intersect each wall surface.

In the face mill having the above structure, however, the tool body 1 is subjected to the nitriding treatment so that the surface of the tool body 1 has a necessary hardness. Moreover, since the nitriding temperature is much lower than the quenching temperature, a large strain such as during quenching is applied to the center hole 9, the boss surface 10, the chip mounting groove 2a, or the like where precision is required. Does not occur. Therefore, it is not necessary to carry out finishing work after the nitriding treatment, and the number of man-hours and working time of the tool body 1 are greatly reduced, whereby the manufacturing cost is significantly reduced. Even if it is necessary to process the boss surface 10 and the like after the nitriding treatment in order to remove the soft coating due to the nitriding treatment, the machining allowance is much smaller than the strain removal at the time of quenching. There is no cost pressure. Incidentally, the stock removal in this embodiment is 0.05.
mm, which is far shorter than the conventional machining allowance of 0.2 mm or more after hardening. Furthermore, since the nitriding temperature is low, no large residual stress is generated inside the tool body 1, and the accuracy is not affected by the subsequent release of stress. Further, since it is not necessary to finish the chip mounting groove 2a after the nitriding treatment, the runout accuracy is not deteriorated due to the wear of the tool during the finishing.

In the present embodiment, the general face milling machine in which the chips are mounted so that the upper and lower surfaces thereof face the circumferential direction of the tool has been described as an example, but the present invention is not limited to this. For example, as shown in FIGS.
Even with a vertical blade type milling cutter in which the side surface of the chip 22 is mounted in the chip mounting groove 21 of 0, the boss surface 23, the center hole 24, and the chip mounting groove 21 can be accurately positioned. After processing, a similar effect can be obtained by forming a hardened layer by nitriding. Even in such a vertical blade type milling machine, the corners of the wall surface of the chip mounting groove 21 are rounded to form the minute curved surface 25, or the corners are chamfered to prevent the growth of cracks. Of course you can.

In each of the above examples, the present invention is used in a face mill, but in addition, as shown in FIGS. 9 and 10, for example, as shown in FIGS. Of course, it can be applied to a ball end mill equipped with chips 33 and 34 having blades 31 and 32. In this case, the surface of the shank portion 35 (the range shown by the one-dot chain line T in FIG. 9) mounted on the spindle of the machine tool was generated by the nitriding treatment, like the boss surface and the center hole in the case of the milling machine. It is preferable to use a polished surface from which the soft coating has been removed. In addition to these examples, the present invention is applied to various throw-away type cutting tools.

By the way, the above-mentioned tool bodies 1, 20, 3
0, chips 6 and 2, as shown in FIGS. 4 and 8, for example.
Screw holes 40, 41, 42 for attaching parts such as 2, 33, 34 and the sheet 4 are formed, and the inside of these screw holes 40 to 42 is a nitriding prevention portion in which formation of a hardened layer is prevented. Preferably. When the nitriding treatment is performed to the inside of the screw holes 40 to 42, the hardness of the screw thread is significantly increased and the toughness is lost, and the set screw 5 and the clamp screws 7 and 26 are lost.
This is because the screw thread may be cracked or chipped at an early stage by repeating the attachment and detachment of the screw, and the hardness of the screw thread may damage the other clamp screw 7, 26 or the like.

Here, as a method of forming the nitriding prevention portion of the screw holes 40 to 42, for example, a method of applying a known nitriding inhibitor into the screw holes can be considered. However, since the nitriding inhibitor is liquid, it is difficult to apply it accurately only to the necessary parts, and the nitriding prevention part unnecessarily spreads due to the expansion of the application area, or the nitriding prevention effect is uneven due to uneven coating. There is a risk that In addition, the nitriding inhibitor may adhere to extra portions of the tool bodies 1, 20, 30 and a desired hardened layer may not be obtained. Furthermore, the nitriding inhibitor may remain inside the screw holes 40 to 42, which may make it difficult to smoothly rotate the clamp screw 7 and the like.

Therefore, in order to form the nitriding preventive portion,
For example, as shown in FIG. 11, screw holes 40 to
42 (Only the screw hole 42 is shown in the figure) Set screw (buried)
50 is screwed in to seal the screw holes 40 to 42, and in this state, a nitriding treatment is performed to form a hardened layer on the surface of the chip mounting groove 21 and the like, and thereafter, as shown in FIG.
It is desirable to follow the method of removing the set screw 50 from 2. According to this method, the inside of the screw holes 40 to 42 is reliably sealed by the set screw 50, so that the nitriding agent such as ammonia gas is prevented from entering the screw holes 40 to 42, and the nitriding prevention portion is reliably obtained. In addition, since it is not necessary to apply the nitriding preventive agent, there is no possibility that the nitriding preventive portion is erroneously formed at a position other than the inside of the screw holes 40 to 42, and further, the nitriding preventive effect due to the uneven application of the nitriding preventive agent is not sufficient. This is because evenness cannot occur.

Although the material of the set screw 50 is not specified in the examples shown in FIGS. 11 to 12, for example, copper,
When the set screw 50 is formed of a hard-nitriding material such as brass, the set screw 50 is not nitrided during the nitriding process, and therefore the set screw 50 does not deteriorate before and after the nitriding process. Therefore, the set screw 50 is repeatedly used. The cost required for the nitriding treatment can be reduced. In this case, the material of the set screw 50 is 500 ° C. which is the heating temperature during the nitriding treatment.
Of course, it is necessary to select a refractory material that can withstand a high temperature of 600 ° C. Even when the set screw 50 is made of a material that is easily nitrided, such as steel, it can be stopped by forming a nitriding prevention layer in advance by plating the surface with nickel or applying a nitriding inhibitor. It is possible to prevent nitriding of the screw 50 and realize reuse of the set screw 50.

Further, in the example shown in FIGS. 11 and 12, the set screw 50 is used as the pad, but the present invention is not limited to this. For example, as shown in FIG. 13, a normal hexagon socket head bolt 51,
Other head bolts such as hexagon bolts may be used. In this case, since the end surface 51a of the head of the bolt 51 is in close contact with the bottom surface 21a of the chip mounting groove 21, the hermeticity in the screw hole is further improved and the nitriding prevention effect can be further enhanced. However, in FIG.
In the example shown in FIG. 3, since the nitriding agent does not come into contact with the portion of the bottom surface 21a of the chip mounting groove 21 that is in close contact with the bolt head end surface 51a, the nitriding prevention portion is not only inside the screw holes 40 to 42, but also at the mouths thereof. There is the inconvenience of slightly expanding around the part.

Therefore, in order to prevent the nitriding prevention portion from expanding while improving the airtightness inside the screw holes 40 to 42, for example, as shown in FIG.
(Only shown), a flat head screw 52 having a taper surface 53 that has a diameter increasing toward the open ends of the screw holes 40 to 42 and is provided with a taper surface 53 that can be in close contact with the taper surface 52. Is preferred. According to this example,
The taper surface 53 of the flat head screw 54 and the taper surface 52 of the screw holes 40 to 42 are in close contact with each other to improve the hermeticity of the inside of the screw holes 40 to 42 and to obtain a high nitriding prevention effect, while the chip mounting groove is provided. Since the bottom surface 21a of 21 does not come into close contact with the countersunk screw 54 and the peripheries of the screw holes 40 to 42 are opened, the nitriding agent such as ammonia gas reaches the limit around the peripheries of the screw holes 40 to 42 to prevent nitriding. This has the effect of preventing unnecessary expansion of the.

(Experimental example) Here, the tool body of the face milling cutter shown in FIGS. 1 to 4 was actually manufactured and the hardness thereof was measured. The results are shown in FIG. As the nitriding method at this time, a gas nitriding method using ammonia gas was used, and SCM440 was selected as the material of the tool body. Further, the nitriding treatment time was changed in three stages of 20 hours, 30 hours, and 40 hours. As is clear from FIG. 15, after the maximum hardness was obtained in the range of 0.05 mm from the tool surface regardless of the length of the nitriding treatment time, the hardness decreased as it proceeded to the inside of the tool, and 0.4 mm from the tool surface. At the position, there is no difference in hardness from the inside of the tool. Therefore, to ensure a hardened layer on the surface layer of the tool, the thickness is preferably 0.1 mm or more, and even if the nitriding treatment time is extended, it is 0.4 mm.
It has been found that it is preferable to set the hardened layer to 0.4 mm or less because it is difficult to obtain the above hardened layer and there is a risk that only the hardness of the surface layer increases and cracks may occur.

[0033]

As described above, according to the cutting tool of the first aspect, the nitriding treatment secures the hardness required for the tool body, while the nitriding treatment causes a large strain as in the quenching treatment. Since it does not occur, there is no need to perform finishing processing later, and the number of manufacturing steps of the tool body is greatly reduced. Moreover, since a large residual stress does not occur during the nitriding treatment, there is no fear that accuracy will be lost due to the subsequent release of stress. Further, since the accuracy of the tip mounting groove is maintained, the runout accuracy is not impaired, and as a result, an excellent effect that a highly accurate and inexpensive cutting tool can be provided can be obtained.

According to the cutting tool of claim 2,
Since an unnecessary increase in the internal hardness of the screw hole is prevented, cracking or chipping of the thread of the screw hole is prevented, and damage to the mating bolt is also prevented. Further, according to the cutting tool of claim 3, since the soft coating is removed from the mounting portion that serves as the mounting reference of the tool body, the mounting portion is prevented from being deformed when the tool body is mounted on the machine tool, and the mounting accuracy is improved. Reproducibility can be secured. Further, according to the cutting tool of the fourth aspect, the manufacturing cost is drastically reduced particularly in the case of a tool body such as a milling tool having a large number of chip mounting grooves.
Furthermore, according to the cutting tool of claim 5, stress concentration at the corners of the chip mounting groove during nitriding is alleviated, cracking of the hardened layer is prevented, and a hardened layer of high quality is provided. . In addition, according to the cutting tool of claim 6, the hardness of the hardened layer can be sufficiently ensured and cracking of the hardened layer can be prevented, so that the quality of the hardened layer can be further improved.

Further, according to the method of manufacturing a cutting tool of claim 7, the inside of the screw hole is surely sealed by the burying so that a uniform nitriding prevention portion can be easily obtained, while the inside of the screw hole is not mistaken. Therefore, there is no possibility that the nitriding prevention portion is formed. Further, according to the method for manufacturing a cutting tool according to claims 8 and 9, since the burying can be repeatedly used, it is possible to greatly reduce the cost required for the nitriding treatment.
According to the cutting tool described above, it is possible to further improve the airtightness in the screw hole and obtain a more uniform nitriding preventive portion, and to make sure that the nitriding inhibitor reaches the periphery of the screw hole mouth portion to prevent nitriding prevention portion. It can prevent unnecessary expansion.

[Brief description of drawings]

FIG. 1 is a sectional view in a tool axis direction according to an embodiment of the present invention.

FIG. 2 is a view from the direction of the arrow II in FIG.

FIG. 3 is a view from the direction of the arrow III in FIG.

FIG. 4 is an arrow view from the IV direction of FIG.

FIG. 5 is a sectional view in the axial direction of the tool according to another embodiment of the present invention.

FIG. 6 is a view from the direction of arrow VI in FIG.

FIG. 7 is a view from the direction of the arrow VII in FIG.

8 is a view from the direction of the arrow VIII in FIG.

FIG. 9 is a side view of a tool according to still another embodiment of the present invention.

FIG. 10 is a view taken in the direction of the arrow X in FIG.

FIG. 11 is a cross-sectional view of a chip mounting groove in an example of a method for manufacturing a cutting tool according to the present invention.

FIG. 12 is a view showing a state in which a buried state is removed from the state shown in FIG.

FIG. 13 is a diagram showing a modification of the example shown in FIG. 11.

FIG. 14 is a diagram showing still another modified example of the example shown in FIG. 11.

FIG. 15 is a diagram showing a relationship between a nitriding depth and hardness.

[Explanation of symbols]

1,20,30 Tool body 2a, 21, 31 Chip mounting groove 6,22,33,34 chips 9,24 Center hole (mounting part) 10,23 Boss surface (mounting part) 35 Shank part (mounting part) 40, 41, 42 screw holes 50 setscrew (buried) 51 Hexagon socket head cap screw (buried) 52 Tapered surface of screw hole 53 Flat head taper surface 54 Flat head screw (buried)

Claims (10)

[Claims] 1. A cutting tool in which a plurality of tip mounting grooves are formed in a tool body having a mounting portion for a machine tool, and a throw-away tip is removably mounted in these tip mounting grooves. A cutting tool having a hardened layer formed by a nitriding treatment on a portion thereof. 2. A screw hole for attaching the throw-away tip and other parts is formed in the tool body,
The cutting tool according to claim 1, wherein the inside of the screw hole is a nitriding prevention portion in which formation of a hardened layer by nitriding treatment is prevented. 3. The surface of the hardened layer formed on the mounting portion of the tool body is a polished surface from which the soft coating generated by the nitriding treatment has been removed. The cutting tool according to claim 2. 4. The surface of the hardened layer formed in the chip mounting groove is a bare surface that is not subjected to a finishing process after nitriding treatment. Cutting tool described in. 5. The cutting tool according to claim 1, wherein chamfering processing or rounded surface processing is applied to a corner of the chip mounting groove. 6. The hardness of the hardened layer of the tool body is set to H _V 500 or more at a position of 0.1 mm from the surface of the tool body, according to any one of claims 1 to 5. The cutting tool described in 1. 7. The tool body is fitted with a recess into a screw hole, and then the tool body is subjected to a nitriding treatment to form a hardened layer on a surface layer portion of the tool body, and then the recess is removed. The method for manufacturing a cutting tool according to claim 2, wherein: 8. The method for manufacturing a cutting tool according to claim 7, wherein a refractory nitriding material is used for the burying. 9. The manufacturing of a cutting tool according to claim 7, wherein after the nitriding prevention layer is formed on the surface of the recess, the recess is attached to the screw hole of the tool body to perform the nitriding treatment. Method. 10. A tool body is provided with a taper surface at the base of the threaded hole, the diameter of which increases toward the open end of the threaded hole, and the recess has a taper surface that can be in close contact with the taper surface. A method for manufacturing a cutting tool according to any one of claims 7 to 9, wherein a flat head screw is used.