JPH04217412A - Throw away drill - Google Patents

Abstract

PURPOSE:To enhance wear resistance, cohesion resistance or thermal crack resistance at the edge portion and enhance toughness at the shank portion by using silicon nitride as material for the cutting edge portion and steel as material for the shank portion. CONSTITUTION:The cutting edge portion 31 and the shank portion 32 are provided for cutting a workpiece and for mounting a cutting machine at preset position, respectively, and the cutting edge portion 31 and the shank portion 32 are mechanically joined together in a detachable manner. In this case, the cutting edge portion 31 is formed of silicon nitride sintered compact and the shank portion 32 is formed of steel.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a drill used mainly for drilling steel, and more particularly to the structure of a high-quality indexable drill with excellent wear resistance and toughness.

0002

2. Description of the Related Art A drill is one of the cutting tools used for drilling holes in steel materials. As an example, the structure of a twist drill is shown in FIG. twist drill is
It is composed of a cutting blade part 1 used for drilling, and a shank part 2 that does not participate in cutting but is mainly used to discharge chips and to be attached to a chuck part of a cutting machine such as a drilling machine.

Conventionally, drills have generally been made of high speed steel (high speed steel) and cemented carbide. High-speed steel has high toughness but low wear resistance, making it unsuitable for high-speed cutting. On the other hand, although cemented carbide has excellent wear resistance and precision characteristics as a tool, it is brittle, and may break when used in, for example, machine tools with low rigidity.

As improvements to these, a structure in which the cutting edge of high-speed steel is coated with hard TiN, or a structure in which the cutting edge is made of cemented carbide and brazed to the cutting edge have been considered.

Furthermore, in recent years, cemented carbide of different materials (P30
and D30) brazed structure (Utility Model Opening Show 58-1431)
15) or a metallurgically integrated and joined structure (Utility Model Publication No. 62-46489).Furthermore, we focused on the difference in required characteristics between the center and the outer periphery of the drill, and (Japanese Patent Application Laid-Open No. 62-218010), or a method of forming this double structure by injection molding (Japanese Patent Application Laid-Open No. 63-3).
8501, 38502), etc. have been devised. In addition, in order to improve the adhesion resistance of the drill, we have developed a structure in which the drill is made of cermet (Japanese Patent Laid-Open No. 62-292307
) etc.

[0006]

The cutting edge and shank of a drill are used under different load conditions. Therefore, the characteristics required for each part of the drill are different. For example, the cutting edge of the cutting edge requires wear resistance and adhesion resistance, and the shank requires toughness to maintain the strength of the tool. Further, since the cutting speed of the cutting edge portion of the cutting edge portion is greatly different between the center portion and the outer peripheral portion, the characteristics required are also different.

[0007] In order to meet these complex requirements for the characteristics that a drill should have, a coating has been applied to the cutting edge as a countermeasure. This has the drawback that the coating layer on the flank side is removed, and most of the coating effect is lost.

[0008] In addition, with the structure in which cemented carbide is brazed to the cutting edge, brazing itself is a method that inherently has poor thermal and mechanical strength, and is not suitable for deep hole machining of difficult-to-cut materials. It had the disadvantage that it could not be applied. Furthermore, if the shank part is made of steel, there is a large difference in coefficient of thermal expansion between it and the cemented carbide of the cutting edge, making it more likely that cracks will occur during brazing. Furthermore, in recent years, in order to improve the toughness of the shank of a drill, cemented carbide has been made coarser grained or has a higher bonding phase, but this has conversely reduced the strength of the material or caused strain to reach its elastic limit. There is a problem in that the shank part breaks during drilling due to vibration of the workpiece or unstable rotation of the cutting machine.

[0009] In addition, in the case of a drill in which the cutting edge and the shank are integrally joined inseparably, it is possible to continue using the drill by re-grinding the cutting edge every predetermined usage time; There is also a limit to the number of times grinding can be done, which increases costs. Additionally, there is a problem in that sharpness and tool life vary depending on whether the re-grinding process is good or bad. Furthermore, with the advancement of NC and automation of cutting machines that use drills, it is necessary to accurately grasp the length of the drill one after another. It needed work.

In order to solve the above-mentioned problems, the present invention has the cutting edge of a drill having excellent wear resistance and adhesion resistance, and the shank having sufficient breakage resistance. It is an object of the present invention to provide an indexable drill that has toughness and does not require re-grinding for continued use.

[0011]

[Means for Solving the Problems] In order to solve the above problems, the indexable drill of the present invention has a cutting blade part for cutting a workpiece, and a shank part for attaching to a predetermined position of a cutting machine. An indexable drill with a cutting edge and a shank part mechanically connected to the shank part in a separable manner,
The cutting edge portion is made of silicon nitride sintered body, and the shank portion is made of steel.

[0012] The silicon nitride sintered body of the cutting edge is made of Si3 N4
Or Sialon (Si 0~Z AlZ OZ
N8-Z: The crystal phase of z=0~4.2) is 8 in the sintered body.
It is preferable that it accounts for 0% by weight or more. In addition, this silicon nitride sintered body contains Al2O3, Y2O
3. It is more preferable to contain MgO and rare earth metal oxides in an amount of 5 to 20% by weight. If it is less than 5% by weight, the density will decrease and the strength will decrease, and if it is more than 20% by weight, the heat resistance will be improved. Heat cracking resistance and wear resistance decrease.

Furthermore, the surface of the cutting edge is coated with TiC, TiN,
A coating of TiCN, TiAlN, Al2O3, etc. may be applied in one layer or in multiple layers.

The method of joining the cutting edge and shank of the indexable drill of the present invention is mainly shown in FIG. 5(a).
- What is shown in (c), what is shown in Fig. 6, Fig. 1 and Fig. 2
There are three types shown in (a) and (b). Among these, those shown in FIGS. 5(a) to 5(c) are two-blade indexable drills. In this drill, the shank part 1
The tip 11a is on the outer periphery of the tip of 2 and the tip 11 is on the inner periphery.
b are each fixed with screws. Further, the drill shown in FIG. 6 is a typical example of a single-blade indexable drill. In this drill, a cutting edge part 21 is fitted into a shank part 22 as shown by the arrow, and is fixed in a screw hole 24 with a screw 23. Coolant is directly supplied to the cutting edge of the cutting edge portion 21 from the coolant supply hole 25 . Further, a chip breaker 26 for cutting chips is formed at the cutting edge of the cutting edge portion 11.

The method of joining the cutting blade and shank shown in FIGS. 1 and 2(a) and 2(b) is to attach the cutting blade 31 to the shank 32 in the direction of the arrow in FIG. A so-called self-grip method is adopted in which the cutting edge portion 31 and the shank portion 32 are joined together without using a tool or the like. The state in which the cutting edge portion 31 and the shank portion 32 are joined in this joining method is as shown in FIGS. 2(a) and 2(b). In this joined state, the clamped portion 31 of the cutting blade 31
The cutting edge part 31 is fixed to the shank part 32 by the frictional force generated when the side part a comes into contact with the inner end surfaces of the clamping parts 33a and 33b of the shank part 32. The manner in which the cutting edge portion 31 and the shank portion 32 are fitted together in this embodiment will be explained as follows with reference to FIGS. 3(a) and 3(b). In the state before the cutting edge part 31 and the shank part 32 are fitted together, as shown in FIG. It is slightly larger than the angle θ2 between the end faces of . When the cutting edge part 31 is press-fitted into the shank part 32, a wedge effect is produced by the tapered left and right sides of the clamped part 31a, and a slit 34 is formed on the clamping part 33a side. Angle θ2
is gradually being expanded. While the relationship θ1 > θ2 exists, the held part 31a and the display part 33b are connected to the held part 33.
They are in contact only at the upper end of the inner end surface of a. θ2
At the point when θ1 coincides with θ1, the contact area between both sides of the clamped part 31a and the inner end surface of the clamped part 33a becomes maximum, as shown in FIG. 3(b). In this state, the press-fitting is stopped, and the elastic force caused by the elastic deformation of the clamping part 33a generates a pressing force on the contact surface with the clamped part 31a, and the frictional force between the contact surfaces causes the cutting blade part 31 to move toward the shank part 32. It will be bonded and fixed to.

Coolant is directly supplied to the cutting edge of the cutting edge portion 31 from the coolant supply hole 35 . Further, a chip breaker 36 for cutting chips is formed at the cutting edge of the cutting edge portion 31.

As another example of the shank portion 32, as shown in FIG. 4, the slit 33 may be formed not only on the side of the clamping portion 33a but also on the side of the clamping portion 33b. In this case, the cutting edge part 31 is press-fitted into the shank part 32 and the clamping part 3
Both 3a and 33b are pushed apart, and the held portion 31a is pinched by their elastic force.

[0018]

[Operation] The properties required of a drill can be broadly divided into wear resistance and adhesion resistance of the cutting edge, and breakage resistance represented by toughness of the shank. In the present invention, by using silicon nitride sintered body as the material for the cutting edge, heat resistance and wear resistance are significantly higher than when conventional high speed steel (high speed steel) or cemented carbide is used. . Therefore, adhesion resistance is also improved.

Furthermore, since steel is used as the material for the shank portion, it has excellent toughness and good breakage resistance. Moreover, material costs can also be reduced.

Furthermore, in the present invention, since the cutting edge part and the shank part are separably mechanically joined,
The cutting edge, which is relatively prone to damage and has a short lifespan, can be easily attached and detached, making it disposable.

[0021]

[Embodiment] An embodiment of the present invention will be described below.

First Embodiment The indexable drill according to the first embodiment of the present invention uses a silicon nitride sintered body for the cutting edge and steel for the shank, both of which are constructed as shown in FIG. and are formed by mechanically joining them so that they can be separated.

The silicon nitride sintered body constituting the cutting edge in this example is prepared by mixing various powders so that the composition has the values shown in Table 1 after sintering. The steel used for forming the shank portion is shown in Table 1. In the products of the present invention and comparative products in this example shown in Table 1, the cutting edge portion and the shank portion were both joined in the manner shown in FIG. Among the products A to C of the present invention, sample C is within the scope of the present invention, but is an example in which the weight percent of Si3 N4 marked with ** is considerably lower than the preferred value. Comparative product D has a cutting edge portion made of silicon nitride sintered body, but differs from the product of the present invention in that the material of the shank portion marked with * is not steel but P30 grade carbide.

[0024]

[Table 1]

The drill performance evaluation test was conducted using a drill with a diameter of 8 mm under the conditions shown below.

[0026] Work material: S50C (HB = 230) Cutting speed: 150 m/min, wet type (water-soluble cutting oil) Feed: 0.10 mm/rev. Depth: 15mm Judgment criteria: After machining to the end of its life, observe the condition of the cutting edge.

[0027] Life: Normally, the amount of wear on the outer circumferential flank surface is 0.
It is defined as when it becomes 2mm or more. The results of the above drill performance evaluation test are shown in Table 2. From this result, good results were obtained for the products A and B of the present invention. As shown in Table 1 with **, the reason why the number of holes machined for the same amount of wear is smaller for product C of the present invention than for products A and B is because of the Si3N4 silicon nitride sintered body of the cutting edge. This is due to the fact that the weight % of the carbon does not satisfy the preferable value of 80% or more. For reference, similar experiments were also conducted on conventional drills whose cutting edges were made of coated carbide or coated high speed steel (Table 2, lower row), and these results also showed that the products A to C of the present invention were superior. I understand.

[0028]

[Table 2]

Second Embodiment Next, a second embodiment of the present invention will be described. In this example, three types of joining methods were used for an indexable drill according to the present invention, in which the cutting edge portion and the shank portion are respectively made of the same material as Sample A in the first example.
The self-gripping type (sample G) shown in Fig. 5 (a) to (
2-flute screw-fixed drill (sample H) shown in c) and Fig. 6
A single-flute screw-fixed drill shown in (Sample I) and a brazed drill with a carbide cutting edge that is outside the scope of the present invention (Sample J)
This is a comparison of their cutting characteristics. The cutting conditions are as follows.

Work material: S50C, HB = 220 Cutting speed V: 50 m/min, 150 m/min (water-soluble cutting oil) Feed: 0.2 mm/rev. Depth: 40 mm Processed hole diameter: 20 mm Table 3 shows the characteristics evaluation results in this example. In addition, the cutting characteristics represented by definiteness are shown in Table 3. The smaller the horizontal component force and thrust of the cutting balance acting on the drill due to cutting resistance are, and the smaller the dependence on speed, the better the cutting. It can be said that it shows the characteristics.

From the results of this example, it can be seen that, as a joining method for the indexable drill to which the present invention is applied, the self-grip method of sample G exhibits the best cutting characteristics compared to other methods.

Note that the self-grip indexable drill shown in FIG. 1, which was applied as the joining method for Material G in this example, connects the cutting edge and the shank.
It is fixed by utilizing the elastic force of the steel, which is more likely to occur due to the slits formed in the shank. Therefore, there is no need for a separate fastening means such as screws. therefore,
It becomes possible to manufacture small indexable drills with a diameter of 10 mm or less, which was not possible with the conventional screw fastening method due to the lack of fastening strength and crushing of the screws. In addition, there is no need to screw the cutting edge and shank in the process of joining them at the processing site, and the drill can be assembled by simply press-fitting, improving work efficiency.

[0033]

[Table 3]

[0034]

As described above, according to the present invention, by using silicon nitride sintered body as the material of the cutting edge part and steel as the material of the shank part, the cutting edge part has wear resistance and adhesion resistance. It has excellent toughness and heat cracking resistance (chipping resistance), the shank portion has high toughness, and the cost can be kept relatively low. Therefore, it is possible to provide an indexable drill at low cost that has high reliability, long life, and high quality without chipping of the cutting edge or sudden breakage of the shank.

[0035] Furthermore, since the cutting edge part and the shank part are separably mechanically joined, it is easy to attach and detach them.
The cutting edge, which is relatively prone to damage and has a short lifespan, can be easily removed and disposed of. Therefore, the cutting edge part does not have to be continuously used by re-grinding, and the cost can be further reduced compared to a conventional drill in which the cutting edge part and the shank part are integrated in an inseparable manner. Furthermore, since there is no need to re-grind the cutting edge, not only is there less variation in sharpness and tool life, but the overall length of the drill is kept constant, and there is no need to measure the length of the drill. In addition, since the base material of the cutting edge can be molded with high precision by injection molding,
It also becomes easier to form chip breakers and the like, further reducing processing costs.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing an enlarged joint of a so-called self-grip drill among indexable drills to which the present invention is applied.

2(a) is a front view of the self-gripping indexable drill shown in FIG. 1, and FIG. 2(b) is a right side view thereof.

FIG. 3(a) is a cross-sectional view taken along line A-A in second (a), showing the state at the time when the cutting blade 31 starts to be press-fitted into the shank in the indexable drill shown in FIG. 1; (b)
2 is a cross-sectional view showing a state in which the cutting edge portion 31 is joined and fixed to the shank portion 32. FIG.

4 is a cross-sectional view of another example of the joint portion of the indexable drill shown in FIG. 1, in which slits are provided on both sides of the clamping portions 33a and 33b.

[Fig. 5] (a) is a front view of a two-flute screw-fastened indexable drill among indexable drills to which the present invention is applied, (b) is a right side view of the same, and (c) is a cutting edge tip. 1
It is a perspective view which expands and shows 1a.

[Figure 6] One of the indexable drills to which the present invention is applied
FIG. 2 is an exploded perspective view showing a single-blade screw-fastened indexable drill.

FIG. 7 is a structural diagram showing Zilla's general twist drill.

[Explanation of symbols]

1, 21, 31 Cutting blade part 2, 12, 22, 32 Shank part

Claims (2)

[Claims] [Claim 1] A cutting blade part for cutting a workpiece, and a shank part for attaching to a predetermined position of a cutting machine, the cutting blade part being mechanically connected to the shank part so as to be separable. 1. A throw-away drill, characterized in that the cutting edge portion is made of silicon nitride sintered body, and the shank portion is made of steel. 2. The silicon nitride sintered body is made of Si3 N4
Or Sialon (Si0 ~Z AlZ OZ
N8-Z: The crystal phase of z=0~4.2) is 8 in the sintered body.
The indexable drill according to claim 1, characterized in that the amount is 0% by weight or more.