Sintered cubic boron nitride compact tool

Abstract

A tool includes, at least on its edge, a sintered cBN compact which includes cBN particles and a bonding phase, a plurality of flutes is formed on a rake face, each of the flutes having a starting end on the edge ridgeline and causing the edge ridgeline to be wavy, and the terminal end of the flute is disposed inwardly of the edge ridgeline. It is preferable that the flute width of the flute decreases with distance from the edge ridgeline, the flute depth of the flute decreases with distance from the edge ridgeline, and the rake face has a positive rake angle.

Claims

1. A sintered cubic boron nitride compact tool having a polygonal shape with a corner such that the corner defines an arc, the compact tool comprising: a sintered cBN compact at least on an edge of the corner of the polygonal shape, the sintered cBN compact including a cubic boron nitride particle and a bonding phase, wherein a plurality of flutes is formed on a rake face of the arc of the corner such that the plurality of flutes are formed over the entire arc of the corner, each of the flutes has a starting end on an edge ridgeline such that the edge ridgeline is wavy, and a terminal end of each of the flutes is located inwardly of the edge ridgeline.

2. The sintered cubic boron nitride compact tool according to claim 1, wherein each of the flutes has a flute width of 10 to 100 m and a flute depth of 10 to 50 m, the flute width of the flutes decreases with distance from the edge ridgeline, the flute depth of the flutes decreases with distance from the edge ridgeline, and the rake face has a positive rake angle.

3. The sintered cubic boron nitride compact tool according to claim 1, wherein an average particle diameter of the cBN particle included in the sintered cBN compact is 2 m or less, and a thermal conductivity of the sintered cBN compact is 70 W/m.Math.K or lower.

4. The sintered cubic boron nitride compact tool according to claim 2, wherein an average particle diameter of the cBN particle included in the sintered cBN compact is 2 m or less, and a thermal conductivity of the sintered cBN compact is 70 W/m.Math.K or lower.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a perspective view illustrating an example of a sintered cBN compact tool of the present invention.

(2) FIG. 2 is an enlarged plan view of an edge side of the sintered cBN compact tool of FIG. 1.

(3) FIG. 3 is an enlarged perspective view of the edge side of the sintered cBN compact tool of FIG. 1.

(4) FIG. 4 is an enlarged cross-sectional view at a position along line X-X of FIG. 2.

DESCRIPTION OF EMBODIMENTS

(5) Hereinafter, a sintered cBN compact tool which is an example of the present invention will be described. As described above, the sintered cBN compact tool as an example of the present invention features to have, at least on its edge, a sintered cBN compact which includes cBN particles and a bonding phase, a plurality of flutes is formed on the rake face, each of the flutes having a starting end on the edge ridgeline, and the terminal end of the flute is disposed inwardly of the edge ridgeline.

(6) An example of the sintered cBN compact tool having the above feature is illustrated in FIGS. 1 to 4. A sintered cBN compact tool 1 illustrated as an example is a rhombus negative cBN edge exchange type insert that uses an acute angle corner portion as an edge. In the sintered cBN compact tool 1, the acute angle corner portion of a base metal 2 is provided with a down layered support seat 3, the support seat 3 is bonded to a sintered cBN compact 4, and a rake face 5 of the sintered cBN compact 4 is provided with a plurality of flutes 6. A ridge (projecting portion) 7 is formed between adjacent flutes 6, 6.

(7) In each of the flutes 6, the starting end is on an edge ridgeline (cutting edge at the acute angle corner portion) 8. Also, the flute 6 extends from the edge ridgeline 8 in a direction nearly perpendicular to the tangent at a corresponding point of the edge ridgeline 8, and the terminal end is located inwardly of the edge ridgeline 8. Furthermore, a flute width W (see FIG. 2 and FIG. 3) decreases with distance from the edge ridgeline 8. Moreover, a flute depth d (see FIG. 4) decreases with distance from the edge ridgeline 8, and the flutes are radially disposed in an area with a certain width along the edge ridgeline 8 in a plan view of the insert.

(8) Also, the rake face 5 is a face that has a positive rake angle (see FIG. 4) of approximately 15.

(9) In the sintered cBN compact tool 1 of the present invention, configured in this manner, the flutes 6 formed on the rake face 5 cause the edge ridgeline 8 to be wavy, and thus the contact area of generated chip is decreased and adhesion is inhibited.

(10) The terminal ends of the flutes 6 are disposed inwardly of the edge ridgeline 8, the ridge 7 between flutes 6, 6, with directly facing a flank face 9 of the side cutting edge, extends in the directly-facing direction, and thus the cross-sectional shape of the generated chip is what is transferred from the wavy shape of the edge ridgeline 8 (cutting edge). Because the chip having a wavy cross-section is narrowed as the flute width W is more apart from the edge ridgeline 8, the outflow speeds at the bottom of the flutes 6 and the ridgeline side of the ridge 7 vary, whereby a shearing force is applied and the chip is bent, and also a contact pressure with the rake face 5 reduces, a contact area decreases due to promoted shearing, and thus a tensile stress generated at the side cutting edge also reduces. It is estimated that a synergistic effect from these causes chipping to be inhibited.

(11) Because the flute depth d is made to decrease with distance from the edge ridgeline 8, a shearing force applied to the chip is increased. In addition, the rake face 5 having a positive rake angle with a low outflow resistance of the chip and a guidance effect of the flutes 6 cause smooth discharge of the chip, thereby achieving reduction in adhesion and further reduction in chipping of the side cutting edge.

(12) When the flute width W, the flute depth d of the flutes 6 provided on the rake face 5 are less than 10 m, a difference hardly occurs between the outflow speeds at the flute bottom and the ridgeline side of the ridge 7, and thus the reducing effect on chipping of the side cutting edge is low. When the flute width W exceeds 100 m, it is difficult to form one pitch in a wavy shape at the position of the side cutting edge. When the flute depth d exceeds 50 m, the strength of a projecting portion is reduced and chipping is likely to occur. Consequently, it is preferable that the flute width W is 10 to 100 m and the flute depth d is 10 to 50 m.

(13) It is preferable that the average particle diameter of the cBN particles included in the sintered cBN compact 4 is 2 m or less and the thermal conductivity of the sintered cBN compact 4 is 70 W/m.Math.K or lower. When the average particle diameter of the cBN particles included in the sintered cBN compact 4 exceeds 2 m, the thermal conductivity of the sintered cBN compact tends to increase. In order to regulate the thermal conductivity to be lower than or equal to 70 W/m.Math.K, it is necessary to reduce the content rate of the cBN particles, and as a consequence, the strength of the sintered cBN compact is reduced, which is not preferable.

(14) The above-described flutes 6 can be formed by adjusting parameters such as a beam diameter, a pulse width, an output, and a pitch width using a YAG laser or a picosecond laser.

(15) The present invention is also applicable to a sintered cBN compact tool to which coating such as TiAlN, TiCN, AlCrN, TiAlCrN, TiAlSiN is applied for increasing wear resistance.

EXAMPLES

Example 1

(16) A sintered cBN compact tool was produced as follows. First, WC powder having an average particle diameter of 1.2 m, Co powder having an average particle diameter of 1.5 m, and Al powder having an average particle diameter of 2 m were mixed with a mass ratio of WC:Co:Al=40:50:10 and heat treated for 30 minutes at 1100 C. in a vacuum, and a resultant compound was pulverized using a cemented carbide ball having 4 mm so as to obtain a bonding material.

(17) Subsequently, powder of the bonding material and cBN particles having an average particle diameter of 0.5 m were prepared, mixed, and dried so that the cBN rate after sintering is 75 volume %.

(18) Furthermore, the powder is stacked on a cemented carbide support plate, and was filled into an Mo capsule, then was sintered for 30 minutes at a temperature of 1350 C. at a pressure of 6.5 GPa by an ultra-high pressure device.

(19) The thermal conductivity of the obtained sintered cBN compact was then measured by a laser flash method, and as a result of calculation based on the specific heat and density of the sintered cBN compact which were calculated by another method, the thermal conductivity was found to be 50.5 W/m.Math.K.

(20) Next, using the sintered cBN compact of this trial product, a rhombus negative cBN edge exchange type insert (sintered cBN compact tool) with ISO model number CNGA120408 (side length of 12.7 mm, corner angle of 80 at the edge corner, entire thickness of 4.76 mm) was produced with the sintered CBN compact bonded to the acute angle corner portion of the base metal. The edge was formed in a shape using a YAG laser such that a flute width is 50 m and a flute depth is 30 m, the flute depth decreases with distance from the edge ridgeline, and the rake face has a positive rake angle of 15. The conditions of the YAG laser were as follows: a machining speed of 500 mm/s, a frequency of 50 kHz, an output of 6.0 W, a beam diameter of 80 m, and a pitch width of 0.01 mm.

Example 2

(21) Rhombus negative cBN edge exchange type inserts (Inventions 2 to 6 illustrated in Table I) were produced by the same method as in EXAMPLE 1 where the flute width, the flute depth, and the rake angle of the rake face were changed but other specifications were the same as in EXAMPLE 1. Invention 1 of Table I is the tool which was produced in EXAMPLE 1.

(22) Furthermore, using each cutting tool which was prepared by mounting one of the rhombus negative cBN edge exchange type inserts of Inventions 1 to 6 and Comparative Example 1 on a holder, outer peripheral cutting was performed on Inconel (trademark of INCO, Ni-based alloy) 718 as a workpiece with cutting speed of 300 m/min, depth of cut of 0.2 mm, and feed rate of 0.1 mm/rev. Table I illustrates the shapes and results of the cutting for Inventions 1 to 6 and Comparative Example 1. Comparative Example 1 is a sintered cBN compact tool in which the rake face is not provided with flutes.

(23) TABLE-US-00001 TABLE I Cutting distance when Chipping size at side the chipping size of Rake angle (+sign cutting edge in a chip side cutting edge in a indicates a positive outflow direction at a chip outflow direction Flute width(m) Flute depth(m) rake angle) point of 0.2 km (mm) exceeds 0.2 mm (km) Invention 1 50 30 +15 0 1.5 Invention 2 10 30 +15 0.01 1.38 Invention 3 100 30 +15 0.02 1.34 Invention 4 50 10 +15 0.05 1.15 Invention 5 50 50 +15 0 1.43 Invention 6 50 30 0 0.03 1.36 Comparative 0 0.13 0.35 example 1

(24) As seen from the test result, in contrast to Comparative Example 1, chipping at the side cutting edge is inhibited in Inventions 1 to 6, and the tool life in the case where life evaluation criterion is set with respect to a chipping size of 0.2 mm is extended 3 times or more the tool life in Comparative Example 1.

Example 3

(25) A rhombus negative cBN edge exchange type insert (Invention 7 illustrated in Table II) with cBN particles having an average particle diameter of 2 m and a cBN rate of 80 volume %, and a rhombus negative cBN edge exchange type insert (Invention 8 illustrated in Table II) with cBN particles having an average particle diameter of 4 m and a cBN rate of 90 volume % were produced by the same method as in EXAMPLE 1. Other specifications for these tools were the same as in Invention 1. The thermal conductivity of Invention 7 was 70 W/m.Math.K and the thermal conductivity of Invention 8 was 120 W/m.Math.K.

(26) Next, using each cutting tool which was prepared by mounting one of the sintered cBN compact tools of Inventions 1, 7, 8 on a holder and the cutting tool of Comparative Example 2, outer peripheral cutting was performed on the above-mentioned Inconel 718 with cutting speed of 100 m/min, depth of cut ap of 0.2 mm, and feed rate f of 0.1 mm/rev. Table II illustrates the result of the cutting. Comparative Example 2 is a commercial sintered cBN compact tool (cBN rate of 60 volume %, bonding phase of TiN) in which the rake face is not provided with flute shapes.

(27) TABLE-US-00002 TABLE II Chipping size at Cutting distance when the side cutting edge in a chipping size of side cutting chip outflow direction at edge in a chip outflow direction a point of 0.2 km (mm) exceeds 0.2 mm (km) Invention 1 0 2.25 Invention 7 0 1.98 Invention 8 0.06 1.65 Comparative 0.45 0.2 example 2

(28) From this test result, it can be seen that a tool having a lower thermal conductivity has a longer tool life. This is because when a sintered cBN compact has a lower thermal conductivity, it is estimated that shearing heat generated at the edge is distributed to the workpiece side and the chip side at a higher rate, thereby softening the workpiece and the chip and causing smooth discharge of the chip, and occurrence of chipping at the side cutting edge is inhibited.

(29) It is to be noted that the sintered cBN compact tool of the present invention is not limited to the tools shown in EXAMPLES. It is cost-effective to provide a tool in which only the edge of the tool is configured of a sintered cBN compact, but the entire tool may be configured of a sintered cBN compact.

(30) Also, the width and depth of the flutes 6, the average particle diameter of the cBN particles included in the sintered cBN compact, and the thermal conductivity of the sintered cBN compact may be changed as appropriate to have different combinations from those in EXAMPLES.

REFERENCE SIGNS LIST

(31) 1 sintered cBN compact tool 2 base metal 3 support seat 4 sintered cBN compact 5 rake face 6 flute 7 ridge 8 edge ridgeline 9 flank face W flute width d flute depth