JPH08243820A - Cemented-carbide-made drill excellent in chipping resistance - Google Patents

Abstract

PURPOSE: To provide a cemented-carbide-made drill excellent in its chipping resistance together with its capability of improving the service life of a drill as well as suppressing a chipping quantity during its use. CONSTITUTION: A cemented-carbide-made drill excellent in its chipping resistance includes a total amount 0.2 to 30wt.% of one kind or two kinds including more kinds of substances selected out of a group consisting of carbide of Cr, Ta or V or carbonitride and an amount 4.0 to 10.0wt.% of Co, and includes the rest in which the cemented carbide alloy consisting of WC and inevitable impurities is considered a raw material and the value of its coercive force is within a range from 430 to 580 (Oe). Preferable value to that is within a range from 490 to 550 (Oe).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cemented carbide drill having excellent chipping resistance, which is suitable for drilling small diameter holes in resin products or metal products used for electronic parts, machine parts, dies and the like.

[0002]

2. Description of the Related Art In a small diameter drill such as a miniature drill using a cemented carbide, it is chipping resistance that determines the life of the drill. In order to improve the chipping resistance, the structure, hardness and toughness of the material have been improved. For example, by optimizing the amount of Co, atomizing WC, or adding a trace amount of carbide such as TaC or Cr ₃ C ₂ , the mechanical properties of the material have been improved.

[0003]

However, for example, atomizing WC can generally improve the wear resistance and the bending strength, but it is necessary to reduce the toughness. There are many contradictory properties that are different from each other, and it is difficult to clarify quantitative material design guidelines.

Further, when using cemented carbide as a tool for a drill or the like, it is known from experience that improving the material as described above does not always directly lead to the improvement of the tool life. . Moreover, the parameters of the material that govern the life of the tool are not accurately understood.

Further, the cemented carbide drill is not only different in material from the high speed steel which has been widely used in the past, but also in terms of dimensions, it is much smaller than a general drill as compared with a general drill. Required to be present.
Therefore, it is not possible to design a tool that fully utilizes the characteristics of cemented carbide with the shape of the tool based on the conventional method for designing a medium or large diameter drill.

The present invention has been made in view of the above problems, and by clarifying the characteristics of the material and shape of the cemented carbide drill, it is possible to suppress the amount of chipping during use and improve the life of the drill. An object of the present invention is to provide a carbide drill having excellent chipping resistance that can be obtained.

[0007]

A cemented carbide drill having excellent chipping resistance according to the present invention comprises at least one selected from the group consisting of carbides or carbonitrides of Cr, Ta or V. 0.2 to 3.0% by weight of total material, Co
Of WC and unavoidable impurities, the coercive force of which is 430 to 580.
It is characterized by using a cemented carbide of (Oe) as a raw material. The cemented carbide preferably has a volume of Co pool in the structure of 0.02% or less. Further, in the relationship between the twist angle δ (°) and the diameter d (mm), 0.
It is preferable that 8d + 19 ° ≦ δ ≦ 0.8d + 29 ° is satisfied, and the relation between δ and d is 0.8d + 2.
It is preferable to satisfy 1 ° ≦ δ ≦ 0.8d + 23 °. Furthermore, the diameter of the drill is preferably 3 mm or less.

[0008]

The present inventors have found that the alloy components are WC, TaC,
The following tests were carried out on each of the cemented carbide drills made of an alloy made of Cr ₃ C ₂ , VC and Co and having a systematically changed value of the coercive force Hc.

That is, starting from resin-based materials used for printed circuit boards, to various metal materials such as carbon steel or alloy steel used as molds, the cemented carbide drills can be used for several thousand times. A drilling test was performed 10,000 times. Then, every time one hole was drilled, a high resolution electron microscope was used to carefully observe the damage condition of the cutting edge.
As a result, it was found that the drill leads to chipping through the following damage process.

First, immediately after the start of cutting, initial wear occurs on the rake face side, the width of which is about several times the size of the carbide in the material. The width of this initial wear will be referred to as D below.

Second, in particular, the portion where the texture of the material is nonuniform, for example, the portion where the carbide is nonuniformly distributed or coarse C
o Large wear locally occurs in the pool (Co phase) part. In the following, the width of local wear is a ₀ .

Thirdly, as the number of drilling times increases, the carbides are lost and the wear width gradually increases. As a result, the fluctuation range of the cutting resistance value acting on the cutting edge increases, so that a crack is generated in the above-mentioned locally worn portion, and this crack gradually progresses due to fatigue. In the following, the number of drilling times is N and the fluctuation range of the cutting resistance value is ΔT.

Fourth, when the stress intensity factor K determined by the crack length during development and the variation width ΔT of the cutting resistance reaches the fatigue fracture toughness Kfc peculiar to the material, macro chipping occurs.

From the above, it was found that the number of drilling operations, that is, the drill service life N, is controlled by the following factors. That is, the drill life is the initial wear width D related to the size of the carbide, the local friction width a ₀ due to the unevenness of the carbide or the Co pool,
Fatigue crack growth resistance da / dN, fatigue fracture toughness Kfc,
It is governed by the variation width ΔT of the cutting resistance. Therefore,
In order to improve the life of the carbide drill, it is effective to reduce D and a ₀ , improve da / dN and Kfc, and reduce ΔT.

However, as a result of repeated experiments on various cemented carbides, the inventors of the present invention have found that the factors of the above-mentioned and the drill life are alloy structure, carbide grain size,
It was also found that the drill life cannot be improved only by, for example, reducing the grain size of the carbide or increasing the amount of the carbide, because the dispersed state of the carbide and the amount of Co are involved in a complicated manner. Therefore, a parameter that comprehensively reflects the elements of the material that improves the drill life is necessary, and the inventors of the present application have found that the coercive force Hc is the most appropriate parameter.

FIG. 1 is a graph showing the relationship between the coercive force and the life of the drill, with the coercive force Hc on the horizontal axis and the number of times the drill can withstand the use of drilling on the vertical axis. In addition, the composition of the material of the drill used to acquire the data in FIG. 1 is TaC 0.05 wt%, Cr
_It contains 1.2% by weight of ₃ C ₂ and 8.0% by weight of Co, and the balance is WC and inevitable impurities. As shown in FIG. 1, it is understood that by optimizing the coercive force to 430 to 580 (Oe), the drill life can be significantly improved.

FIG. 2 is a graph showing the relationship between the Co pool amount and the drill life by plotting the Co pool amount (volume%) on the abscissa and the number of drilling times on the ordinate. This figure 2
It was also found that by limiting the amount of Co pool that causes local wear to 0.02% or less, a more stable drill life can be obtained, as shown in FIG. In addition, this FIG.
The component composition of the material of the drill used to acquire the data is similar to that of the drill used to acquire the data in the graph of FIG.

Next, based on these data, the component composition, coercive force, Co of the material of the carbide drill according to the present invention will be described below.
The reasons for limiting the pool amount, the helix angle, and the drill diameter will be described.

Cr (chromium), Ta (tantalum) and V
Carbide or carbonitride of (vanadium): 1 or 2 or more
The basic hardness as a drill having a total amount of 0.2 to 3.0% by weight can be secured by adding WC described later, but with WC alone,
The coercive force required to grow the WC grains during sintering cannot be obtained. Therefore, by adding carbides or carbonitrides of Cr, Ta, and V, it is possible to suppress the growth of WC crystal grains and reduce the coercive force necessary for the growth of WC crystal grains, and at the same time, to improve the coercive force. Can be improved. Thus, in order to improve the coercive force, it is necessary to add the above-mentioned carbides or carbonitrides in a total amount of 0.2% by weight or more. On the other hand, if it exceeds 3.0% by weight, the fatigue fracture toughness Kfc is Along with the decrease, the characteristics of fatigue crack growth resistance da / dN deteriorate. Therefore, one or more carbides or carbonitrides of Cr, Ta and V are added to the material of the cemented carbide, and the content thereof is 0.2 to 3.
0% by weight.

Co (cobalt): 4.0 to 10.0 weight
Amount% Co is an element that improves the fatigue fracture toughness Kfc of the cemented carbide drill. If the amount of Co added is less than 4.0% by weight,
The fatigue fracture toughness of the drill cannot be improved,
On the other hand, if the amount of Co added exceeds 10.0% by weight, the necessary coercive force cannot be secured. Moreover, the hardness of the drill becomes insufficient, and the amount of Co pool further increases. Therefore, the addition amount of Co is set to 4.0 to 10.0% by weight.

WC (Tungsten Carbide): The balance WC is a compound capable of suppressing the increase of the wear width D of the drill and the fluctuation width ΔT of the cutting resistance and obtaining the necessary coercive force. Therefore, in order to maximize such an effect, the rest is WC as much as possible.

Next, the reasons for limiting the coercive force and the amount of Co pool will be described.

Coercive force Hc: 430 to 580 (Oe ) FIG. 1 is a graph showing the relationship between coercive force and drill life as described above. As shown in FIG.
Drill life increases monotonically with increasing c. As described above, the drill life is improved by reducing the initial wear width D by refining the carbide, homogenizing the two-phase structure of the carbide and Co, or reducing the local friction width a ₀ due to the uniform dispersion of the carbide. This is because the overall contribution is to improve the fatigue crack growth resistance da / dN characteristics. In order for these combined effects to work effectively, it is necessary that the coercive force Hc is 430 (Oe) or more, as shown in FIG. On the other hand, the coercive force Hc is 580 (O
e), the initial wear width D and the local friction width a
_The negative effect due to the decrease in fatigue fracture toughness Kfc is greater than the effect of improving the drill life due to the reduction of ₀ , and the drill life is reduced. Therefore, the coercive force of the cemented carbide material of the cemented carbide drill is 4
It is set to 30 to 580 (Oe). Further, as shown in FIG. 1, a more preferable coercive force for improving the drill life is 490 to 550 (Oe).

Co Pool Amount: Volume Ratio 0.02% or Less The volume ratio of Co pool can be measured by observing with a microscope, for example, by the method specified in ASTM A02. FIG. 2 is a graph showing the relationship between the Co pool amount and the drill life. As shown in FIG. 2, Co
The larger the pool amount, the larger the difference between the upper limit value and the lower limit value of the drill life, and the shorter the drill life. Therefore,
By setting the Co pool amount to 0.02% or less in volume ratio, it is possible to prevent a large variation in drill life and improve the drill life.

Next, the reasons for limiting the helix angle and the drill diameter will be described.

The relationship between the twist angle δ (°) and the diameter d (mm)
Relation: 0.8d + 19 ° ≦ δ ≦ 0.8d + 29 ° Fatigue crack growth rate is proportional to the power of the variation width ΔT of the cutting resistance, which is the driving force, so reducing ΔT has an extremely large effect on the improvement of drill life. give. The value of ΔT varies depending on the material composition such as the amount of WC, but the value is greatly influenced by the shape of the drill. In particular, ΔT changes depending on the twist angle δ of the drill, so an attempt was made to optimize the twist angle according to the drill diameter.

First, a drill was manufactured by giving various helix angles to each solid rod of cemented carbide having a diameter of 1 to 12 mm. Next, drilling was performed with each drill, and the cutting resistance at that time was measured with a dynamometer. The composition of the material of the drill is TaC: 0.05% by weight, Cr ₃ C ₂ : 1.
The one containing 2% by weight and 8% by weight of Co and the balance being WC was used.

A part of the analysis result is shown in FIG. FIG. 3 is a graph showing the relationship between the twist angle and the cutting resistance for each drill diameter, with the horizontal axis representing the helix angle and the vertical axis representing the cutting resistance. In the upper graph of Figure 3, the diameter is 7mm and 11m.
In the lower graph of FIG.
The relationship between the helix angle and the cutting resistance is shown for a 2 mm drill.

As shown in FIG. 3, like the drills shown in these graphs, the drills each having a diameter of 1 to 12 mm have a helix angle with which the cutting resistance is minimized. FIG. 4 is a graph showing the relationship between the drill diameter and the helix angle when the cutting resistance is reduced, including the optimum helix angle. In FIG. 4, the horizontal axis represents the drill diameter, and the vertical axis represents the helix angle. In the graph as shown in FIG. 3, the minimum value, the maximum value and the optimum value in a good helix angle range are plotted. It is a straight line connecting these points. As shown in FIG. 4, the straight line connecting the points can be represented by a single straight line.

Therefore, the relation between the diameter of the drill and the helix angle can be expressed as a linear function, and as shown in FIG.
The helix angle δ at which the cutting is good is straight line δ = 0.8d + 19 and δ = 0.8d + 29 in relation to the drill diameter d.
It only needs to be in between. That is, the twist angle δ is 0.8d + 1
Good cutting becomes possible if the relationship of 9 ° ≦ δ ≦ 0.8d + 29 ° is satisfied. Also, the twist angle δ is 0.8d + 21 °
Optimal cutting can be performed by satisfying the relationship of ≦ δ ≦ 0.8d + 23 °.

[0031]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples that depart from the claims of the present invention. First, ten types of drills having different alloy material composition, coercive force, Co pool amount, drill diameter and helix angle were manufactured. The composition of the alloy material is shown in Table 1 below.
There are three types of A, B, and C shown in Table 1. The material A has a composition within the scope of the claims of the present invention, while the materials B and C have a composition outside the scope of the claims of the invention.

[0032]

[Table 1]

A drilling test was carried out on the glass / epoxy type printed circuit board using each of the drills made of the above materials. The holes were punched in the substrate 3000 times, and then the performance was evaluated by the chipping amount of the blade edge. In other words, it can be said that a drill with a small amount of chipping has a long life. The results are shown in Table 2 below.

[0034]

[Table 2]

As shown in Table 2 above, Nos. 1, 2, 3,
4, 5, 9 and 10 drills belong to the claims of the present invention.

Comparing Example No. 1 with Comparative Example No. 6, it was found that both were drills made of the material A, and the elements other than the coercive force were exactly the same. However, the drill of Example No. 1 having a coercive force within the scope of the claims was superior in performance to the drill of Comparative Example No. 6 outside the range. Therefore, it can be said that the drill having the coercive force within the scope of claims is superior in performance when the other elements except the coercive force are the same. Example No.
From the comparison of 1 and 2, it can be said that if the coercive force is in the optimum range, it has more excellent performance.

Comparing Example No. 2 and Comparative Example No. 7, all the elements except the composition were the same, but the chipping amount of Example No. 2 was superior. Therefore, the material A within the scope of the claims is
It can be said that it is superior to the material B which is out of the scope of claims.

When Example No. 1 and Comparative Example No. 8 are compared, in this case as well, all the elements other than the composition are the same drill, and the amount of Co contained in the material C of Comparative Example No. 8 is patented. Although within the scope of the claims, the material C does not include carbides such as Cr, Ta, and V. Therefore, the performance was inferior to the material A of Example No. 1 containing them. Therefore, it can be said that the drill made of the material A is the best among the drills having the same elements other than the composition.

When Example No. 1 and Example No. 3 are compared, the Co pool amount of the drill of Example No. 3 is a more preferable amount, so that Example No. 1 is not such a value.
The drill of Example No. 3 showed higher performance than the drill of No. Therefore, by setting the Co pool amount to an appropriate value, it is possible to suppress an increase in the chipping amount and manufacture an excellent drill.

Comparing Example No. 1 and Example No. 4, since the helix angle of the drill of Example No. 4 is a value within a more preferable range, the drill of Example No. 4 has a twist angle outside that range. It showed higher performance than the drill. Therefore, by setting the twist angle of the drill to an appropriate value, it is possible to suppress an increase in the amount of chipping and obtain an excellent drill.

Further, comparing Examples Nos. 1, 3, 4 and 5, Example N satisfying all the claims of the present invention.
The o5 drill now has the best performance.

[0042]

As described above, according to the present invention,
The material of the drill has a predetermined component composition, and by setting the coercive force, the helix angle and the drill diameter to the predetermined values, it is possible to suppress the amount of chipping during use,
The life of the drill can be improved. Further, since an extremely small drill such as a miniature drill can be manufactured and the drill can be used for a long period of time, the cost of using the drill can be reduced.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between coercive force and drill life.

FIG. 2 is a graph showing the relationship between Co pool amount and drill life.

FIG. 3 is a graph showing the relationship between cutting resistance and twist angle of a drill.

FIG. 4 is a graph showing a relationship between a drill diameter and a helix angle at which cutting resistance is reduced.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaru Ishii 179-1 Kanegasaki Nishi-Oike, Uozumi-cho, Akashi-shi, Hyogo Inside the Akashi Plant, Kobe Steel, Ltd. (72) Minoru Fukunaga Kaneizaki Nishi-Oike, Uozumi-cho, Akashi-shi, Hyogo Prefecture 179-1 Kobe Steel Co., Ltd. Akashi Plant (72) Inventor Akira Egami Kanegasaki Nishioike, Uozumi-cho, Akashi City, Hyogo Prefecture 179-1 Kobe Steel Co., Ltd. Akashi Plant (72) Inventor Masaya Akashi, Hyogo Prefecture 179-1, Kanegasaki Nishioike, Uozumi Town Inside the Akashi Plant, Kobe Steel, Ltd.

Claims (5)

[Claims] 1. A total amount of one or two or more substances selected from the group consisting of Cr, Ta or V carbides or carbonitrides of 0.2 to 3.0% by weight, and Co of 4.0 to 4.0% by weight. 1
Ultra-high chipping resistance characterized by using a cemented carbide containing 0.0% by weight, the balance being WC and unavoidable impurities, and having a coercive force of 430 to 580 (Oe). Hard drill. 2. The cemented carbide drill with excellent chipping resistance according to claim 1, wherein the amount of Co pool in the structure of the cemented carbide is 0.02% or less in volume ratio. 3. In the relationship between the twist angle δ (°) and the diameter d (mm), 0.8d + 19 ° ≦ δ ≦ 0.8d + 29
3. The carbide drill having excellent chipping resistance according to claim 1 or 2, which satisfies the condition. 4. The relationship between δ and d is 0.8d + 2.
The carbide drill having excellent chipping resistance according to claim 3, wherein 1 ° ≦ δ ≦ 0.8d + 23 ° is satisfied. 5. The cemented carbide drill having excellent chipping resistance according to claim 3, wherein the diameter d is 3 mm or less.