JPS6234710A - Cemented carbide drill - Google Patents

Abstract

PURPOSE:To manufacture drills of long life an capable of high feed rate cutting by composing a drill of a central section made of cemented carbide alloy of high roughness and an external cylindrical section made of hard alloy in double structure and machining its end by way of thinning. CONSTITUTION:When a cylindrical body 11 made of hard WC or TiC is sintered with a tough bar 12 of which outer diameter is smaller by about 0.01mm to 0.5mm than the inner diameter of the cylinder body 11 inserted, the cylindrical body 11 is contracted enough to be united with the bar 12 in a boy. Then, chip discharge flutes 2 and 2 and cutting edges 4 and 4 are formed through proper machining processes forming a drill. The diameter (d) of a central section 1a is required to be C/15<=d<=D/5, and a central axis (l) and an axis O may either be aligned or arranged eccentrically with each other. The central section 1a is to be separated a distance from the chip discharge flutes 2 and 2, and although the external body 1b is deformed to a non cylindrical shape, the strength of the body should not be declined even if the body is devided into two parts. Being liable to be crushed due to the excessive thrust load acted on the drill, a chisel section 5 is formed on the central section 1a having toughness by way of web thinning preventing itself from crushes. The life of the drill is, therefore, prolonged, and a high speed and high feed rate cuttings become possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a carbide drill that can perform high-speed, high-feed drilling.

[Conventional technology and its problems] In general, carbide drills have cutting edges made of cemented carbide, which is harder than high-speed steel, so they can cut at higher speeds than high-speed steel drills. Therefore, drilling has the advantage of improving processing efficiency.

However, it was not possible to improve the feed rate. This is because while cemented carbide is hard, it is also brittle, so there is a risk that the part near the axis of the drill tip will be crushed by the thrust load acting on it.If you try to use a high feed rate, the thrust load will increase accordingly, making it even more difficult. This will further increase the risk of crushing. Therefore, in conventional carbide drills, there is a certain limit to the ability to drill holes in order to improve machining efficiency, and it is difficult to say that they are fully satisfactory in terms of service life.

In addition, in order to reduce the risk of crushing the area near the axis,
It is possible to use cemented carbide with higher toughness, but
Cemented carbide, which has high toughness, has low hardness, which necessitates a reduction in cutting speed, so this was not a fundamental solution.

[Purpose of the Invention] This invention was made in consideration of the above circumstances, and it is possible to perform not only high-speed cutting but also high-feed cutting, so that drilling improves the efficiency of machining. The purpose is to provide a carbide drill that can be significantly improved.

[Structure of the Invention] In order to achieve the above object, the present invention includes a part made of cemented carbide located between and apart from two chip evacuation ills, and including the axis of the drill. It consists of a central part and a cylindrical outer peripheral part provided outside the central part, and the central part is made of cemented carbide which has higher toughness than the outer peripheral part, while the outer peripheral part has higher hardness than the central part. It is constructed of cemented carbide, and is further thinned at least at the tip of the outer circumferential portion between the chip discharge groove and the center portion.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 7.

1 to 3 show an embodiment of the present invention. As shown in these figures, the present invention is characterized in that the drill body made of cemented carbide has a two-layer structure. That is,
The drill body 1 is composed of a center portion 1a including the axis 〇, and a cylindrical outer peripheral portion 1b provided outside the center portion 1a. The center portion 1a is made of a cemented carbide having higher toughness than the cemented carbide forming the outer peripheral portion 1b,
On the other hand, the outer peripheral portion 1b is made of cemented carbide, which is harder than the cemented carbide forming the central portion 1a. Center part 1a
As the cemented carbide constituting the outer peripheral portion 1b, it is desirable to use a cemented carbide whose main component is tungsten carbide (WC) or titanium carbide (TiC). In addition, when the outer diameter of the drill is D, the diameter d of the center portion 1a is D/15.
It is desirable that ≦d≦D15.

Further, as for the positional relationship of the center portion 1a with respect to the axis, as in the above embodiment, the center line l of the center portion 1a is set to the axis 0.
Alternatively, as shown in FIGS. 4 and 5, the center line 1 may be shifted from the axis 0, and the center portion la may be eccentrically formed.

However, the eccentric weight is such that the center portion 1a includes the axis of the drill, and the center portion 1a is separated from a chip discharge groove 2.2 which will be described later.

Further, the cross-sectional shape of the central portion 1a may be circular as in the above embodiment, but may also be oval as shown in FIGS. It may be a regular polygon or other shape.

The drill body l formed as described above has chip evacuation grooves 2.2 formed on its outer periphery, as in conventional drills, and the wall surface facing the rotational direction of each chip evacuation groove 2.2 and the tip relief. Cutting edges 4.4 are formed on the edges formed by the 3. A chisel portion 5 is formed between these cutting edges 4.4. This chisel portion 5 is formed only in the center portion 1a by thinning 6. The reason for applying this thinning 6 is as follows.

That is, in a general drill, an excessive thrust load is applied to the chisel part, which is at risk of being crushed. Therefore, if crushing of the chisel part is simply to be prevented, it is better to make the diameter of the center part equal to or slightly larger than the length of the chisel part (the chisel part in a state where no thinning is applied). However, if you do this,
Inevitably, the outer periphery cannot be cylindrical, and the outer periphery is divided into two parts sandwiching the center. For this reason, the strength of the outer circumferential portion against torsional moments is reduced, and the outer circumferential portion may break due to the cutting load during drilling. In addition, when the outer periphery is divided into two parts, they are joined metallically to firmly connect them to the center, but since the diameter of the center is small and the joint area is narrow, the center and outer periphery are separated. There is a risk that the parts may peel off from the joints. Note that peeling can be prevented by increasing the diameter of the center part and widening the joint area, but in this case, even the parts of the cutting edge other than the chisel part are made of soft cemented carbide. As a result, the cutting speed cannot be increased.

In this regard, in the carbide drill of the present invention, the outer peripheral portion 1b
Since the whole is integrally formed into a cylindrical shape, the outer peripheral part 1
The strength of b can be improved. Moreover, the outer peripheral part 1
When b is formed into a cylindrical shape, the center part 1a in the outer peripheral part 1b
A chisel part is formed in the part between the chip discharge groove 2 and the chip discharge groove 2, and there is a risk that this part will be crushed, but in this drill,
Since the thinning 6 is applied to the portion between the center portion 1a of the outer peripheral portion 1b and the chip discharge groove 2, an excessive thrust load is not applied thereto, and therefore, crushing can be prevented.

In this case, the entire drill body l is made of cemented carbide, but only the tip thereof may be made of cemented carbide. For example, the drill body is made up of a blade part and a nyank part, and the blade part has a two-layer structure as described above, while the shank part is made of steel, and the blade part is fixed to this nyank part by brazing. Good too.

When drilling is performed using the M3 drill configured as described above, since the center portion 1a of the drill body 1 is made of a cemented carbide having higher toughness than the outer circumferential portion 1b, the hole is drilled near the axis O. It is possible to prevent parts from being crushed. Therefore, high feed drilling can be performed. On the other hand, since the outer peripheral portion 1b is made of cemented carbide, which has a harder hardness than the central portion 1a, the cutting speed can be increased. In this way, since drilling can be performed at high speed and with high feed, drilling efficiency can be greatly improved. Furthermore, since crushing of the portion near the zero axis can be prevented, the life of the drill can be improved.

Further, in the cemented carbide drill of the present invention, since the part made of cemented carbide is composed of the cylindrical body 11 and the rod-shaped body 12, breakage of the part made of cemented carbide can be prevented.

That is, if the part made of cemented carbide is to have a two-layer structure, instead of the cylindrical body 12, an insertion hole having the same diameter as the cylindrical body 12 and slightly longer than the re-grinding length on the tip surface may be formed. It is conceivable to mold an outer circumferential part structure having the above-mentioned structure and insert a rod-shaped body into this outer circumferential part molded body. However, when this is done, the wall thickness of the outer circumferential component changes greatly at the bottom of the insertion hole, so there is a difference in shrinkage rate between the tip and rear ends of the bottom, which causes a difference in the shrinkage rate of the insertion hole. There is a risk that sintering cracks will occur in the portion corresponding to the bottom, and there is a risk that the drill manufactured in this way will break at the sintering crack portion during drilling. In addition, stress concentration due to changes in wall thickness acts on the portion of the outer peripheral structure corresponding to the insertion hole, which further increases the risk of drill breakage.

In this regard, in the carbide drill of the present invention, since the cylindrical body 11 is used as the outer circumference component, there is no change in wall thickness, and therefore cracking during sintering or stress concentration can be prevented. can. Therefore, the risk of drill breakage can be significantly reduced.

Next, the above-mentioned effects will be clarified by showing experimental data obtained when drilling holes using a high-speed steel drill, a conventional carbide drill, and a carbide drill according to the present invention. In addition, in the experiment, the diameter and other specifications of the drill were of course the same. The work material is cast iron, and the hole has a diameter of 8 mm and a depth of 30 mm.

The experimental data are as follows.

As is clear from the table above, the carbide drill of the present invention can improve drilling efficiency compared to both high-speed steel drills and conventional carbide drills. While hard drills had shorter lifespans than high-speed steel drills, we were able to make the lifespan longer than high-speed steel drills.

Next, three examples of manufacturing methods suitable for manufacturing the cemented carbide drill having the above configuration will be introduced.

[First Manufacturing Method] In this manufacturing method, as shown in FIG. 8, a cylindrical body II made of a green compact of cemented carbide is first manufactured. In this case, the columnar body may be compression-molded in advance and the center portion of the columnar body may be hollowed out to form the cylindrical body 11, or the cylindrical body 11 may be obtained by compression molding.

Next, the rod-shaped body 12 is inserted into the cylindrical body 11.

This rod-shaped body 12 is made by compression molding a cemented carbide that has higher toughness than the cemented carbide forming the cylindrical body 11 and has a smaller shrinkage rate during sintering. The outer diameter is determined by taking into account the difference in shrinkage between the cylindrical body 11 and the rod-shaped body I2 after sintering, but is generally 0.0 mm smaller than the inner diameter of the cylindrical body 11. It is better to make the OI smaller by about 0.5 mm.

Thereafter, with the rod-shaped body 12 assembled inside the cylindrical body 11, they are sintered. Then, the cylindrical body 11 becomes the rod-shaped body 12
As they contract more, they become unified.

Next, as shown in FIG.
+3, perform shape processing such as cutting edge 14. This shape processing may be performed before sintering and then sintered.

In the above case, the cylindrical body 11 is made into a simple cylindrical shape, but for example, a groove may be formed in advance in the portion where the chip discharge groove 13 is to be formed.

[Second Manufacturing Method] This second manufacturing method differs from the first manufacturing method in that the rod-shaped body is sintered in advance, and the other steps are the same as the first manufacturing method. Therefore, in this case, there is no need to consider the difference in shrinkage rate between the cemented carbide forming the rod-shaped body and the cemented carbide forming the cylindrical body.

[Third manufacturing method] In this third manufacturing method, a cemented carbide having higher toughness and a smaller shrinkage rate during sintering than the cemented carbide constituting the outer peripheral portion is arranged in the center, and A rod-shaped green compact is manufactured by simultaneously compression molding the powder body and the outer peripheral portion, and then this green compact is sintered and then shaped. Note that, of course, the shape processing step and the sintering step may be reversed.

[Effects of the Invention] As explained above, according to the carbide drill of the present invention,
The drill body has a two-layer structure consisting of a rod-shaped center and a cylindrical outer periphery.The center is made of cemented carbide, which has higher toughness than the outer periphery, while the outer periphery is harder than the center. Since it is made of cemented carbide, high-speed, high-feed drilling can be performed, and therefore, the drilling efficiency can be greatly improved, and the life of the hole can be extended. Moreover, effects such as being able to prevent occurrence of breakage accidents of parts made of cemented carbide can be obtained.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the carbide drill according to the present invention, FIG. 1 is a front view thereof, FIG. 2 is a partially omitted side view, and FIG. 3 is a ■A sectional view taken along the line, FIGS. 4 and 5 show other embodiments of the carbide drill according to the present invention, FIG. 4 is a front view thereof, FIG. 5 is a partially omitted side view,
6 and 7 show still another embodiment of the carbide drill according to the present invention, FIG. 6 is a front view thereof, FIG. 7 is a partially omitted side view, and FIGS. 8 and 9 are FIG. 8 is a perspective view showing an assembly process, and FIG. 9 is a partially omitted side view showing the carbide drill after shape processing. It is a diagram. l...Drill body, 1a...Center, I
b...Outer peripheral part, 11...Cylindrical body, 12...
Rod-shaped body, O...axis line, l...center line.

Claims (4)

[Claims] (1) In a cemented carbide drill in which at least the tip of the drill body is made of cemented carbide and two chip discharge grooves are formed on the outer periphery of the drill body, the portion made of cemented carbide is It consists of a center part that is located between and apart from the two chip discharge grooves and includes the axis of the drill, and a cylindrical outer peripheral part provided outside the center part, and the center part is located between the two chip discharge grooves and includes the axis of the drill. the outer peripheral part is made of a cemented carbide that has a higher hardness than the central part; A carbide drill characterized by being thinned. (2) The cemented carbide drill according to claim 1, wherein the center portion and the outer peripheral portion are each made of a cemented carbide whose main component is tungsten carbide or titanium carbide. (3) The center line of the center portion is offset from the axis of the drill, as claimed in claim 1.
The carbide drill according to item 1 or 2. (4) The carbide drill according to any one of claims 1 to 3, wherein the central portion has a circular, elliptical, or regular polygonal cross-sectional shape.