JP3223843B2 - Throwaway small diameter boring bar - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boring cutting tool in which the entire part from a shank to a tip mounting seat is made of cemented carbide, and a plug member of a sintered alloy different from the shank body is partially provided in the tip mounting seat. This is related to a throw-away small-diameter boring tool buried and brazed.

[0002]

2. Description of the Related Art It is well known in the art that a boring cutting tool, particularly a small-diameter boring tool, employs a cemented carbide having high rigidity in order to suppress deflection of a shank and improve vibration isolation. Japanese Utility Model Application Laid-Open No. 5-161010 proposes a throw-away type cutting tool using a cemented carbide from the shank portion to the lower surface of the tip mounting seat.

FIG. 9 is a cross-sectional view of a tool tip portion of the above publication. In FIG. 9, reference numeral 112 denotes a shank portion made of cemented carbide, and reference numeral 113 denotes a chip mounting member such as a machinable sintered alloy. The throw away tip 115
The chip mounting member 113 is fixed to the tip mounting member 113 by a clamp screw 116, and the tip mounting member 113 is inserted into the through hole of the shank portion and fastened to the shank member by the mounting screw.

According to the above-described configuration, the tip mounting member is fixed in the direction in which the cutting force is applied.
Since the cutting force is formed so as to extend in a direction intersecting the cutting force, the cutting force does not act to shear the joint surface between the tip mounting member and the shank portion, and high strength against the cutting force is secured, and Even when a cutting load is applied, it is possible to prevent the chip mounting member from being separated or the like.

[0005] Further, since the shank portion made of cemented carbide extends to the vicinity of the cutting edge at the tool tip, rigidity at the tool tip is increased, vibration damping is improved, and generation of cracks and the like is effective. It is said that it has the effect that it can be suppressed to.

However, since it is difficult to form a threaded hole in the cemented carbide in the shank portion, a separate machineable sintered alloy chip mounting member 113 and a stopper 117 for mounting a throw-away chip, which are to be machined, are required. We have prepared. Further, the tip mounting member 113 is
In addition, since a space (not shown in FIG. 9) for attaching the screw is required, there is a limit in reducing the diameter while using a screw-on type suitable for boring with a small angle.

[0007]

In a cutting tool to which a throw-away tip is mounted, a screw-on method is generally employed as a fixing means of the throw-away tip in order to bore a small-diameter hole. Therefore, the tip mounting seat needs a screw hole for fixing the throwaway tip. On the other hand, it is necessary to make the shank as rigid as possible in order to bore a small hole with a deep hole. Therefore, it is desirable that the entire tool is made of a cemented carbide. However, providing a fine pitch screw hole in the chip mounting seat requires advanced technology and expensive steps.

The present invention is to solve the above-mentioned technical problem by brazing a plug-shaped sintered alloy having a thermal expansion coefficient close to that of a cemented carbide and having good workability to a chip mounting seat. It is.

[0009]

SUMMARY OF THE INVENTION In a boring cutting tool entirely made of cemented carbide from a shank portion to a tip mounting seat, a stepped hole having a body portion is provided below the tip mounting seat, and the tip mounting is provided at the center. A Bragg member having a screw hole is buried in the stepped hole and fixed by brazing, so that a flat throw-away chip is fastened to the chip mounting seat in the chip mounting screw hole.

Further, since a sintered member having a coefficient of thermal expansion similar to that of the cemented carbide in the shank portion is employed for the plug member having a chip mounting screw hole in the center, the plug member is brazed to the chip mounting seat. It is possible to minimize the damage of heat cracks and residual stress caused by thermal distortion between materials caused by heat history during the process. As such a material , Cu- W
Alloys are suitable.

The end surface of the plug member having a chip mounting screw hole at the center is positioned at the body of the stepped hole. Therefore, if the stop width is set to 0.5 mm or more, the end surface of the plug member becomes larger than the chip mounting seat. It automatically sinks by 0.5 mm or more and is brazed, so that the brazing material does not impair the flatness of the chip mounting seat.

Further, the position of the substantially pentagonal indexable insert mounting hole in plan view is such that the ratio of the distance L ₁ from the mounting wall on the opposite side of the cutting blade to the distance L ₂ from the cutting blade is L ₂ / L. ₁ ≧
If it is set to be 1.5, it is possible to sufficiently secure the excess thickness around the stepped hole provided in the cemented carbide chip mounting seat.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view of a shank portion 2 and a tip mounting seat 3 of a small diameter boring tool according to the present invention.
FIG. 3 is a plan view of the tool holder 1 which leads to FIG. Shank part 2
Is obtained by shaving a part of a round bar flat to form a clamp surface 2a, and is made of a cemented carbide in order to suppress bending during cutting. Since the applicable range of the effective bore diameter of the present invention is 5 to 20 mm, the diameter of the round bar also conforms to this.

The tip mounting seat 3 according to the present invention is not formed by joining tool steel which is easy to machine a screw hole to the shank part 2 by screwing or brazing as in the conventional example. The part 2 is made of the same cemented carbide. However, the screw-on type requires a screw hole for mounting the throw-away tip 5 on the tip mounting seat 3 side.
Therefore, in the present invention, a plug member 4 made of a sintered alloy which is easy to machine is filled in a stepped hole 3d having a body portion 3f at the center of a chip mounting seat 3 provided in advance and fixed by brazing. In this way, the pulling force for fastening the throw-away tip 5 to the brazed portion is borne by the body portion 3f, and the component force of the cutting resistance acts on the mounting walls 3a, 3b and the inner wall of the stepped hole 3d. No burden is placed on the brazing part.

FIG. 2 shows a cross section taken along the line AA of FIG. 1 in which the plug member 4 is brazed to the chip mounting seat 3. The upper end surface of the plug member 4 in which the screw hole 4a can be easily processed is automatically set to 0.5 mm from the mounting surface of the throw-away tip 5 if the stop width of the body portion 3f is set to 0.5 mm or more.
Thus, the flatness of the mounting surface 3e is not impaired by the brazing material.

In addition, due to the difference in thermal expansion coefficient and contraction rate between the plug member 4 and the chip mounting seat 3 due to the heat history during the brazing step, heat cracks and residual stress are generated on both, and the brazing strength is reduced. In order to prevent this, it is desirable that the sintered alloy of the plug member 4 and the cemented carbide of the tip mounting seat 3 have similar thermal expansion coefficients. The component of the cemented carbide of the chip mounting seat of the present invention is, for example, WC-Co (5 to 20%), and the coefficient of thermal expansion is 5 to 6 × 1 in the range of 400 to 800 ° C.
0 ^-6 / ° C. The component of the sintered alloy used as the plug member is, for example, heavy metal (registered trademark No. 2289920) of w-Cr.Ni (3 to 5%), and has a coefficient of thermal expansion of 5.1 to 5.6 × 10 ^−6. / ° C., which is almost equivalent. In addition, the plug member has excellent workability, and has a coefficient of thermal expansion of 7.4% × 10 ⁻⁶ / ° C.
W (copper tungsten) is also suitable.

Further, since the entire tool from the shank portion to the tip mounting seat is made of a cutting tool made of cemented carbide, the bending when receiving a cutting resistance is suppressed and the Young's modulus contributing to vibration isolation is as follows. 2.1 × 10 ⁴ k of tool steel
g / mm ² , the cemented carbide is 5.5 × 10 ⁴ kg / mm ²
About twice as high and anti-vibration effect can be expected. Therefore, boring can be performed even if the machining of a deep hole increases the cutting speed.

FIG. 3 is a plan view showing the tool holder 1 of the present invention with the indexable insert 5 mounted thereon. FIG.
3 shows details of a BB cross section of FIG. The chip mounting seat 3 has mounting wall surfaces 3a and 3b which engage with two sides perpendicular to the ridge line of the flat-shaped insert chip 5 having a substantially pentagonal shape in plan view.
Are arranged and bear a part of the cutting force. Symbol 3c is
This is a slipper for accurately seating the throw-away tip 5. The mounting screw 6 is screwed into the screw hole 4 a of the plug member 4 to fix the throw-away tip 5.

It is possible to mount a well-known polygonal throw-away tip to the cutting tool holder of the present invention, but it is preferable to mount a generally pentagonal throw-away tip 5 shown in FIG. .

FIG. 5 is a plan view showing a state in which a well-known polygonal throw-away tip 9 is mounted on a cutting tool holder, and FIG. 6 is a view taken in the direction of arrow C in FIG. As shown in FIG. 5, a conventionally known bite holder has a shank portion 7 made of cemented carbide and a tip mounting member 8 joined by tool steel by brazing or the like. In the well-known form of a throw-away insert having a cutting edge at each corner, the center of the insert mounting seat is away from the axis of the shank as shown in FIG. 6 to secure a margin for burying the plug member 4 of the present invention. Not done.

On the other hand, as shown in FIG. 3, the indexable insert 5 of the present invention has a mounting wall 3a on the opposite side of the cutting blade 5a.
The distance of the mounting screw holes 5b and L ₁ and, if the distance from the cutting edge 5a to the mounting screw hole 5b was _{L 2, L 2 / L 1} ≧
If it is set to 1.5, the screw hole 4a is relatively close to the shank axis, and the excess thickness of the stepped hole 3d can be appropriately secured.

However, the life is assumed to be apparently shorter than the conventional example in which the cutting edge exists at each corner of a polygon.
The cutting blade 5a of the indexable insert 5 of the present invention preferably has a multiplex structure as shown in FIG. 7 which is a plan view and FIG. 8 which is a cross-sectional view of the side surface of FIG. In other words, the base metal 5c of tool steel or cemented carbide, and the back metal 5d of a separately prepared cemented carbide equivalent to polycrystalline C having higher wear resistance than cemented carbide
It is obtained by brazing a blank in which the BN sintered body 5e is integrally sintered, and it is possible to extend the life even if only one cutting edge 5a is provided.

[0024]

According to the present invention, there is provided a boring cutting tool in which the entire tool holder from the shank to the tip mounting seat is made of a cemented carbide, wherein a stepped hole is provided in the tip mounting seat and a tip mounting screw hole is provided at the center. It has a thermal expansion coefficient similar to that of the holder body and is buried with a plug-shaped sintered alloy with good workability and brazed, so even if it receives heat history during the brazing process, the brazing strength does not decrease, rigidity It is an object of the present invention to provide a throw-away small-diameter boring tool having a high and deep hole and capable of preventing chatter during cutting even when the cutting speed is increased.

[Brief description of the drawings]

FIG. 1 is a plan view of a tool holder according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a plan view in which a throw-away tip is mounted on the cutting tool holder of the present invention.

FIG. 4 is a sectional view taken along line BB of FIG. 3;

FIG. 5 is a plan view in which a throw-away tip is mounted on a known bite holder.

FIG. 6 is a view as viewed in the direction of arrow C in FIG. 5;

FIG. 7 is a plan view of the throw-away tip of the present invention alone.

FIG. 8 is a sectional view of a side surface of the throw-away tip of the present invention alone.

FIG. 9 is a sectional view of a conventional tool tip.

[Explanation of symbols]

 1: Tool holder 2: Shank part 3: Tip mounting seat 3d: Stepped hole 3f: Body part 3e: Mounting surface of throw-away tip 4: Plug member 4a: Screw hole 5: Throw-away tip 5a: Cutting blade 5b: Mounting screw hole 5c: base metal 5d: back metal 5e: polycrystalline CBN sintered body 6: mounting screw 7: shank portion of well-known tool holder 8: chip mounting member 9: well-known throw-away chip

Continuation of the front page (56) References Japanese Utility Model Hei 5-12004 (JP, U) Japanese Utility Model Hei 4-115503 (JP, U)

Claims (3)

(57) [Claims] 1. A boring cutting tool entirely made of a cemented carbide from a shank portion to a tip mounting seat, wherein a stepped hole having a body portion is provided below the tip mounting seat, and a tip mounting screw hole is provided in the center. The plug member is embedded in the stepped hole and fixed by brazing, and the plug member is
A throw-away small-diameter boring tool comprising a W alloy, wherein a flat-shaped throw-away tip is fastened to the tip mounting seat with respect to the tip mounting screw hole. 2. An end face below a tip mounting seat of the plug member having a tip mounting screw at a center thereof is lowered by 0.5 mm or more from a tip mounting seat positioned at a body part of a stepped hole. The throw-away small-diameter boring tool according to claim 1. 3. The form of a flat throw-away tip has a cutting edge at one end of a substantially pentagonal shape in plan view,
Two perpendicular sides of the adjacent ridge line including the opposite side become the mounting wall surface, and the position of the throw-away tip mounting hole is such that the ratio of the distance L1 from the mounting wall on the opposite side of the cutting blade to the distance L2 from the cutting blade is L2 /. The throw-away small-diameter boring tool according to claim 1, wherein L1 ≧ 1.5.