JP2015091627A - Cbn cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong a life of a cBN cutting tool used for cutting heat resistant alloys including a Ni-based one.SOLUTION: A cBN cutting tool comprises: a cutting-edge tip made of a cBN sintered body with heat conductivity of 20 to 70 W/mK using cBN particles with an average diameter between 0.5 μm and 2 μm; and an alloy holding the cutting-edge tip at a corner portion. The cutting-edge tip is provided with a cutting edge having a positive rake angle between 2° and 20°.

Description

  The present invention relates to a cBN cutting tool having a cutting edge made of a cBN (cubic boron nitride) sintered body, and more specifically, to improve the life in high-speed cutting applications of heat-resistant alloys represented by Ni-base heat-resistant alloys. It relates to a cutting tool.

  One of difficult-to-cut materials in cutting is Ni-base heat-resistant alloy. When using a cemented carbide tool that has been widely used in the cutting work using this Ni-based heat-resistant alloy as a work material, the cutting speed is limited to 80 m / min or less at the earliest in terms of strength, and the machining efficiency does not increase.

  For this reason, performing high-speed cutting of 200 m / min or more using a cBN cutting tool having a cutting edge made of a cBN sintered body excellent in high-temperature hardness has been studied.

  However, cBN has higher hardness than cemented carbide, but its toughness is low. Therefore, when a heat-resistant alloy is cut with the cBN cutting tool, a defect occurs in the side cutting edge, and the reliability for maintaining the life is lacking. Although cBN has higher toughness than ceramics, cutting to a heat-resistant alloy cannot deny the lack of toughness.

  As a countermeasure, as described in Patent Document 1 below, the thermal conductivity of the cBN sintered body constituting the cutting edge is lowered, thereby softening the work material with the heat (cutting heat) generated at the cutting edge. There is an attempt to cut while.

  Further, as a measure for strengthening the cutting edge, there is a method of making the rake angle of the cutting edge negative by applying a negative land or the like, and this method is effective for preventing the cutting edge made of a brittle material from being broken.

JP2011-189421A

  For cutting edges made of a brittle material with low toughness, the cutting edge is usually reinforced. The cutting edge that has been subjected to the strengthening process (such as application of negative land) is dull due to the blunting of the cutting edge due to the strengthening process, thereby increasing the amount of cutting heat generated.

  Therefore, when cBN sintered body is used as the material of the cutting edge and cutting is advanced while softening the work material with cutting heat, it was considered effective to improve the tool life by blunting the cutting edge.

  However, with this method, the life of the cBN cutting tool was not sufficiently increased.

  Therefore, an object of the present invention is to improve the life of a cBN cutting tool used for cutting a heat-resistant alloy by applying a conventionally avoided technique.

  In order to solve the above problems, in the present invention, a cutting edge tip comprising a cBN sintered body having a thermal conductivity of 20 to 70 W / m · K using cBN particles having an average particle diameter of 0.5 μm or more and 2 μm or less. Then, a cBN cutting tool was provided with a base metal holding the cutting edge tip at the corner, and a positive rake angle was given to the cutting edge provided on the cutting edge tip of the tool.

  In the cBN cutting tool of the present invention, the cutting edge tip is formed of a cBN sintered body having a low thermal conductivity, and a positive rake angle is imparted to the cutting edge provided on the cutting edge tip.

  As a result of experiments, cBN cutting tools with a positive rake angle applied to the cutting edge have a side cutting edge boundary wear (hereinafter referred to as VN) compared to conventional cBN cutting tools for cutting heat-resistant alloys that have been reinforced. And flank wear (flank wear: hereinafter referred to as VB) were suppressed, and it was confirmed that the life was improved as compared with conventional tools.

It is a perspective view which shows an example of the cBN cutting tool of this invention. It is a perspective view which shows the other example of the cBN cutting tool of this invention. FIG. 2 is an enlarged plan view of a corner portion provided with a cutting edge tip of the cBN cutting tool of FIG. 1. FIG. 4 is a sectional view taken along a bisector CL of a corner angle in FIG. 3. It is an expansion perspective view of a blade edge | tip part. It is a top view which shows the principal part of an example of the grinding machine utilized for manufacture of the tool of this invention. It is a front view which shows the motion of the chuck | zipper of a grinding machine. It is a top view which shows the motion of the chuck | zipper of a grinding machine. It is a figure which shows the grinding state of a rake face.

  Embodiments of a cBN cutting tool according to the present invention will be described below with reference to FIGS.

  FIG. 1 shows the present invention applied to a triangular cBN cutting insert, and FIG. 2 shows the present invention applied to a square cBN cutting insert.

  These cBN cutting tools (cBN cutting inserts) 1 are small pieces of a cBN sintered body at a corner of a base metal (a polygon including a rhombus) 2 made of cemented carbide, ceramics, cermet, sintered alloy, or the like. The cutting edge tip 4 constituted by the above is provided by bonding or the like, and the cutting edge 4 is constituted by the cBN sintered body. Reference numeral 5 denotes a rake face formed on the cutting edge tip 3, and reference numeral 6 denotes a flank face.

The cutting edge tip 3 uses cBN particles having an average particle size of 0.5 μm or more and 2 μm or less, and the thermal conductivity is set to 20 to 70 W / m · K by adjusting the content of the cBN particles. Made of union.

  The average particle diameter of the cBN powder used as the raw material for the cBN sintered body is 0.5 μm or more and 2 μm or less, and the thermal conductivity of the cBN sintered body using the cBN powder is 20 to 70 W / m · K. Thus, it is possible to achieve both the provision of a positive rake angle, which will be described later, and the suppression of wear and tear on the side cutting edge portion.

  In the tool of FIG. 2, the cutting edge tip 3 is provided at all corners. The cutting edge tip 3 does not have to be at all corners. As in the tool of FIG. 1, it may be provided at one corner portion, or may be provided at two acute angle corner portions in the rhombus cutting insert.

  The cutting edge tip of the cBN sintered body can be manufactured by the method described below. Since this method is described in detail in the above-mentioned Patent Document 1, only a brief description will be given here.

  In the manufacturing method described in Patent Document 1, first, WC powder, Co powder, and Al powder having a fine particle diameter are mixed at a mass ratio of WC: Co: Al = 25: 68: 7. The compound heat-treated at 1000 ° C. for 30 minutes in a vacuum is pulverized to obtain a raw material powder constituting the binder phase.

  Next, a first compound is obtained by heat-treating a mixture of Al powder and Zr powder having a fine particle diameter at 1000 ° C. for 30 minutes in a nitrogen atmosphere. Thereafter, the compound is coarsely pulverized, and further, the medium and the coarsely pulverized first compound are pulverized in an ethanol solvent using a zirconia medium having a diameter of less than 1 mm, and the medium is removed to form an adiabatic phase. The raw material powder to be obtained is obtained.

  Next, the cBN content after sintering the obtained raw material powder constituting the binder phase, the raw material powder constituting the heat insulating phase, and the cBN powder having an average particle diameter of 0.5 μm or more and 2 μm or less becomes a desired volume%. Blend and mix and dry. Further, the mixed powder is laminated on a metal support plate and filled into Mo capsules, and then sintered with, for example, 7 GPa and a temperature of 1750 ° C. for 30 minutes by an ultrahigh pressure apparatus.

Then, the cBN sintered body thus obtained is cut into a predetermined shape and joined to a base metal to obtain a tool blank. Then, grinding of a required part is performed and it finishes in the tool of a predetermined shape.

  Grinding is performed on at least the rake face 5 and the flank face 6 provided on the cutting edge tip 3, and when the rake face 5 is ground, a positive rake angle is given to the cutting edge 4. The rake angle θ shown in FIG. 4 is a positive value of 2 ° or more and 20 ° or less, more preferably 5 ° or more and 15 ° or less.

  The rake angle θ is a value at the cutting edge tip (cutting edge). 4 shows a cross section along the bisector CL of the corner angle in the plan view of FIG. 3, and the position where the bisector CL of the corner angle intersects the cutting edge 4 in FIG. The tip of the cutting edge.

  The reason for setting the rake angle θ in the above range is that, as a result of the evaluation test, the effect of suppressing wear was confirmed even when the rake angle θ was 2 ° to 5 ° or 15 ° to 20 °, but θ was 5 °. As described above, the effect of suppressing wear is particularly high at 15 ° or less.

  An NC grinder is used to grind the necessary parts during tool manufacture. The grinder to be used has a chuck 11 as shown in FIG. 6 in which numerical control of the position and orientation is performed, and a grindstone (in the figure, a cup grindstone) 12 that rotates at a fixed position.

  The work (cBN cutting tool) is carried into and out of the grinding machine, and the work is delivered to the chuck 11 using a robot hand (not shown) whose position is controlled.

  The grinding machine used for grinding the tool of the present invention has four-axis control shown in FIGS. 7 and 8, that is, chuck movement in the X-axis and Y-axis directions, rotation around the axis O of the chuck 11 and FIG. 8 has each function of b-axis direction rotation (does not move in the Z-axis direction), and can be ground with a so-called one-chuck without changing the flank, rake face and cut-off face described later. .

  Grinding of the rake face 5 is performed by rotating the chuck 11 holding the cBN cutting tool 1 in a required direction and pressing the rake face of the cutting edge tip 3 parallel to the end face of the grindstone 12 as shown in FIG. .

  At this time, the rake face 5 having a positive rake angle can be generated by slightly inclining the cutting edge tip 3 with respect to the end face of the grindstone 12 for grinding.

  In the present invention, a positive rake angle is given to the heat-resistant alloy cutting tool.

  Giving a positive rake angle to the cutting edge is common for cutting tools made of cemented carbide or high speed steel with high toughness.

  However, setting a rake angle positive in a cBN cutting tool used for cutting heat-resistant alloys has not been conventionally performed.

  One of the reasons is that it was thought that it was important for the cutting edge formed of the cBN sintered body to improve the fracture resistance in the cutting application of the heat-resistant alloy.

  The second reason is that when the rake angle is made positive, the cutting edge temperature is lowered due to improved sharpness. This is done by selecting a cBN sintered body having a low thermal conductivity as the cutting tool material for the purpose of cutting a heat-resistant alloy, and increasing the cutting speed to increase the cutting edge temperature while softening the work material with the cutting heat. This is contrary to the intention in the cutting method, and is thought to reduce the effect of preventing the cutting edge from being broken.

  The present inventors have not found any knowledge that can improve the life of a cutting tool by imparting a positive rake angle to a cBN cutting tool for cutting the heat-resistant alloy. I found the effect by chance while repeating various explorations and tests.

  The rake face 5 is preferably a flat face because of its excellent workability. When the rake face 5 with the positive rake angle is formed, a step is generated between the ground surface that is depressed and the unground surface.

A portion where the step is generated is a curved cut-up surface 7 and the cut-up surface 7 is raked surface 5.
It is good to make it continue to the terminal (end part on the side away from the cutting edge).

  The curved cut-up surface 7 can be processed on the side surface of the grindstone 12. The grindstone 12 may have a radius of about 50 mm to 200 mm, and the rounded surface 7 ground with the side surface of such a grindstone has a corner portion with a radius r of an inscribed circle of about 5 μm to 50 μm. Improve the curl of chips.

  By grinding the rake face 5, as shown in FIG. 4, in the cross section along the bisector CL of the corner angle, the tip (cutting edge) of the cutting edge 4 is an extension of the flat upper face 2a of the base metal 2 (upper face). 2a) and slightly lower toward the bottom surface of the base metal. It is preferable that the core descent amount (amount of decrease from the extension of the upper surface 2a) d is in the range of 10 μm to 100 μm.

  By setting the lower limit of the descent amount d to 10 μm, a sharp edge can be generated during grinding of the rake face.

  On the other hand, the amount of useless grinding of the rake face increases as the descent amount d increases. Further, the cutting resistance increases as the core descent amount d increases. In consideration of these, the upper limit of the center-down amount d is about 100 μm.

  In addition, the amount of reduction of the cutting edge 4 from the extension of the upper surface of the base metal increases as the distance from the tip (cutting edge) increases. As a result, the rake angle of each part of the cutting edge at the position retracted from the tip (the rake angle appearing in the cross section along the line perpendicular to each part of the cutting edge in the plan view) is, for example, the rake angle at the tip shown in FIG. For example, when the angle is 10 °, the value is 7 ° or 8 ° smaller than the tip at the rear.

  It is desirable that the cutting edge 4 has a higher strength than the cutting edge at a position away from the central portion (cutting edge), and the demand can be met by making it a rake face constituted by a flat surface.

  By grinding the rake face 5 by the method of FIG. 9, as shown in FIG. 3, an abrasive bar 8 substantially perpendicular to the bisector CL of the corner angle is formed on the rake face 5 in plan view of the tool. . The abrasive bar 8 extending in that direction is effective in preventing chip welding. Strictly speaking, the polishing bar 8 is curved with a radius of curvature close to the outer diameter of the grindstone 12, and for this reason, it is expressed here as being substantially vertical.

  In addition, the cBN cutting tool of this invention sharpens a cutting edge by provision of a positive rake angle. Since the sharp cutting edge is easily chipped, it is preferable to subject the cutting edge to a minute R honing treatment for strengthening the cutting edge as necessary.

  The R honing ensures that the effect of setting the rake angle positive (that is, enhancing the sharpness) is not impaired. If it is R honing whose curvature radius is 0.005 mm or more and 0.02 mm or less, the demand can be met.

  A cBN cutting tool having the specifications shown in Table 1 was prototyped and its performance was evaluated. The prototype tool has the shape shown in FIG. Table 1 also shows the thermal conductivity of the cutting edge tip used in Sample Nos. 1 to 10 in Table 1 and the positive rake angle given to the cutting edge of the cutting edge tip. Table 2 shows the composition of the cutting edge tip of each sample in Table 1.

  As the cBN sintered body constituting the cutting edge tip, cBN particles having an average particle diameter of 1 μm were used. However, when the average particle diameter is 0.5 μm or more and 2 μm or less, the performance without much difference is obtained.

  Samples No. 1 to No. 3 and No. 7 to No. 10 satisfy the conditions of the present invention for both the thermal conductivity of the cutting edge tip made of the cBN sintered body and the size of the positive rake angle. In Sample Nos. 4 to 6, the thermal conductivity of the blade tip is outside the conditions of the present invention.

  The thermal conductivity of the cutting edge tips of Sample Nos. 1 to 4 and Nos. 7 to 10 was varied by adjusting the content of cBN. Sample No. 5 used a commercially available borazon (trade name of Diamond Innovation) as a cutting edge tip, and Sample No. 6 used a commercially available β-SiAlON ceramic tool.

  Using this prototype tool, a rod of Inconel 718 (trade name: Special Metals Inc., Inconel: registered trademark) of work material: HRC46 hardness diameter: 120 mm and length: 250 mm was cut under the following conditions. .

Cutting conditions Cutting speed V: 200 m / min
Feed f: 0.1mm / rev
Incision ap: 0.3 mm
Coolant: 20 times diluted emulsion

  In this evaluation test, when one of VN and VB reached 0.2 mm, the tool life was determined, and the cutting length up to that life was examined. The results are also shown in Table 1.

  As can be seen from the test results, the cutting tool in which the thermal conductivity of the cutting edge tip made of the cBN sintered body is in the range of 20 to 70 W / m · K is Sample No. 4 having a thermal conductivity of 10 W / m · K. As compared with Sample No. 5 having a thermal conductivity of 100 W / m · K, the service life is greatly extended. The effect of improving the life is particularly remarkable when the positive rake angle is 5 ° to 15 °.

  The shape of the cutting tool to which the present invention is applied is not particularly limited, such as a rhombus, a triangle, a square, or a polygon having 5 or more corners. In addition, all of those having a cBN sintered body cutting edge tip at least at one corner of the base metal are applicable to this invention.

DESCRIPTION OF SYMBOLS 1 cBN cutting tool 2 Base metal 2a Flat top surface 3 Cutting edge tip 4 Cutting edge 5 Rake face 6 Relief face 7 Ramp surface 8 Abrasive muscle θ Rake angle CL Corner angle bisecting line d Cutting edge top metal base surface Decrease from extension 11 Chuck 12 Grinding wheel O Chuck axis

Claims (6)

  A cutting edge tip made of a cBN sintered body having a thermal conductivity of 20 to 70 W / m · K using cBN particles having an average particle diameter of 0.5 μm or more and 2 μm or less, and a base metal holding the cutting edge tip in a corner portion A cBN cutting tool for heat-resistant alloy cutting, in which a positive rake angle is imparted to the cutting edge provided on the cutting edge tip of the tool, and the size of the rake angle is 2 ° or more and 20 ° or less.   The cBN cutting tool for heat-resistant alloy cutting according to claim 1, wherein the size of the positive rake angle is not less than 5 ° and not more than 15 °.   In the cross section along the bisector of the corner angle of the corner portion, the tip of the cutting edge is lowered by 10 μm to 100 μm from the extension of the flat upper surface of the base metal toward the base metal lower surface side. The cBN cutting tool for heat-resistant alloy cutting according to claim 1 or 2, wherein the amount of decrease in the cutting edge position increases with increasing distance.   The cBN cutting tool for heat-resistant alloy cutting according to claim 3, wherein the rake face attached to the cutting edge tip is a flat surface.   5. The curved cutting surface having a radius of curvature of R50 mm to R200 mm is connected to the end of the rake face to which a positive rake angle is imparted, of the cutting edge tip, according to any one of claims 1 to 4. CBN cutting tool for cutting heat-resistant alloys.   The portion of the rake face having a positive rake angle has a polishing bar substantially perpendicular to the bisector of the corner angle of the corner portion in plan view of the tool. The cBN cutting tool for heat-resistant alloy cutting of description.

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