JP2008110437A - Ball end mill made from cubic boron nitride - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a long-lived cubic boron nitride ball end mill suppressing chipping of the whole ball blade caused by impact when a cutting edge is bitten in a high hardness material machining of ≥55 in HRC. <P>SOLUTION: In this ball end mill made from a cubic boron nitride sintered body, a neck portion with diameter contracted from a shank is provided at the end of the shank, the sintered body containing cubic boron nitride is joined to the end of the neck portion, and the ball blade and a peripheral cutting edge are provided at the end of the neck portion. The rake angle in a normal direction of the ball blade is set from -5 to -15 degrees at R 10 degrees, set from -5 to +3 degrees at R 50 to 70 degrees to have a peak, set from -10 to 0 degrees at R 90 degrees, set to be gradually increased from the R 10 degrees toward the R 50 to 70 degrees, and set to be gradually decreased from the peak toward the R 90 degrees. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sintered ball end mill containing cubic boron nitride (hereinafter referred to as CBN).

Patent Document 1 describes a joint between a CBN sintered body and a shank portion using a CBN ball end mill. Patent Document 2 describes an example of extending the tool life in a ball end mill made of cemented carbide by changing the normal rake angle of the ball blade from -20 degrees to 0 degrees from the outer peripheral side to the tip side. Yes.
JP 2002-144132 A Japanese Patent Laid-Open No. 10-113809

  CBN is a brittle material and is brittle. For small diameters, turning tools and blade-end-type end mills, which usually use CBN sintered bodies, can adjust cutting speed, enable relatively high-speed cutting, and reduce specific cutting resistance. On the other hand, relatively low-speed cutting tends to cause chipping, and chipping due to impact at the time of biting of the cutting edge becomes a problem particularly in high-hardness material processing of HRC 55 or higher. An object of the present invention is to provide a long-life CBN ball end mill that suppresses chipping of the entire ball blade.

  The present invention relates to a ball end mill made of a sintered body containing cubic boron nitride, wherein the ball end mill is provided with a neck portion having a diameter reduced from the shank at the tip of the shank, and sintered containing cubic boron nitride at the tip. The body is joined, and a ball blade and an outer peripheral blade are provided, and the normal rake angle of the ball blade is −5 degrees to −15 degrees at R10 degrees, −5 degrees to +3 degrees at R50 degrees to R70 degrees, and A ball made of CBN characterized by having a peak, R90 degrees -10 degrees to 0 degrees, gradually increasing from R10 degrees to R50 degrees to R70 degrees, and gradually increasing from the peak to R90 degrees It is an end mill. By applying the present invention, it is possible to reduce the chipping by reducing the impact when the cutting edge bites even in the processing of a hard material.

  The present invention can provide a CBN ball end mill capable of suppressing chipping by suppressing vibration of the end mill and processing stable for a long time in processing of a hard material having HRC 55 or higher.

In the present invention, as shown in FIG. 1, a neck portion having a diameter smaller than that of the shank 1 is provided at the tip of the shank 1, and an outer peripheral blade 2 and a ball blade 3 made of a CBN sintered body are provided at the tip.
First, the normal direction rake angle 4 is set at -5 degrees to -15 degrees at R10 degrees. Thereby, the strength of the ball blade 3 is increased, and even when the cutting resistance in the direction of the rotation center axis acts on the ball blade 3, it can withstand chipping and chipping. If the normal direction rake angle 4 is larger than -5 degrees to the plus side, the strength of the ball blade 3 is weak and causes chipping. If it is less than −20 degrees, the biting property of the ball blade 3 on the work material is deteriorated, and the cutting resistance increases. R10 degrees is a left side view of the end mill from FIG. 2, and a straight line passing through the center 6 of the hemisphere formed by the ball blade rotation locus 5 and having an angle of 10 degrees with the end mill rotation center axis is the ball blade 3. It is a position where it intersects.
Next, the normal direction rake angle 4 is gradually increased in the positive direction from R10 degrees to R50 degrees or R70 degrees, and has a peak that increases most in the positive direction at a position of R50 degrees to R70 degrees from the tip of the ball blade. Provide to have. At R50 to R70 degrees, the machinability of the ball blade 3 is improved, the cutting resistance is reduced, the chipping of the entire ball blade is suppressed, and stable machining becomes possible. If the peak is at a position of less than R50 degrees, the peak has the lowest ball blade strength, and therefore the cutting resistance in the direction of the center axis of the end mill acts and chipping is likely to occur. On the other hand, if the peak is at a position exceeding R70 degrees, the outer peripheral side of the ball blade 3 bites into the work material and the end mill is easily bent. The peak at the rake angle 4 in the normal direction is provided in the range of -5 degrees to +3 degrees. If the peak of the rake angle 4 in the normal direction is larger than -5 degrees on the minus side, the cutting resistance increases and chipping is likely to occur. If it exceeds +3 degrees, it becomes too sharp and bites into the work material. Chipping cannot be suppressed by impact.
Further, in the present invention, by providing the rake angle 4 in the normal direction gradually in the minus direction from the peak position toward R90 degrees, the ball blade 3 on the outer peripheral side that has the highest cutting speed and is most affected by the vibration of the end mill. Can increase the strength and suppress chipping. Hereinafter, the present invention will be described based on examples.

(Example 1)
As Example 1 of the present invention, a CBN sintered body was inserted and fixed in a cemented carbide shank 1, one end having a diameter of 4 mm, a neck having a straight shape, and a diameter of 0.94 mm. Since the CBN sintered body has a blade diameter of 1 mm, the number of blades is 2, and the ball blade has a chisel blade, the normal direction rake angle 4 is −10 degrees at R10 degrees, 0 degrees at R60 degrees, and a peak. R90 is set to -5 degrees, provided in a gradually positive direction from R10 degrees to R60 degrees, gradually in a negative direction from R60 degrees to R90 degrees, an outer peripheral blade, a twist angle of 20 degrees, and an effective blade length of 1.8 mm Provided. An AlCrSiN film of HV30 GPa was coated on the ball blade and the outer peripheral blade. The gradual plus direction was changed by a constant angle every 10 degrees on the rotation trajectory of the ball, and about half of the change before and after the peak. In Example 1 of the present invention, in the gradual plus direction from R10 degrees to R50 degrees, 2 degrees every 10 degrees on the rotation trajectory of the ball, in the gradual plus direction from R50 degrees to R60 degrees, 1 degree, gradually from R60 degrees to R70 degrees. In the minus direction, it is 1 degree, and in the gradually minus direction from R70 degrees to R90 degrees, it is provided every 2 degrees every 10 degrees on the rotation trajectory of the ball.
The workpiece used for the cutting test is SKD11 (HRC60) on the work material, and the corner is finished to a curved surface with the same radius of R0.5 mm as the diameter of the ball blade, then expanded to R1.0 mm, and finally the finish processing Went. The curved surface machining of R0.5 mm from the corner is cut at R90 degrees only at the start, and the finishing process is completed with one ball blade of R0 to R90 degrees in contact with each other to complete one machining.
Next, curved surface machining from R0.5 mm to R1.0 mm was performed while following the above conditions, but the curved surface of R0.5 mm was expanded while repeating pick feed in the horizontal direction and the vertical direction, and curved surface machining of R1.0 mm was performed. Carried out. When expanding in the horizontal direction of the work material, the ball blade of R60 to R90 degrees is mainly cut, and when expanding in the vertical direction of the work material, the ball blade of R40 degrees or less is mainly cut. Yes. However, when an uncut portion was generated in the program, the uncut portion was complementarily cut.
Cutting conditions are as follows: curved surface machining with a radius of 0.5 mm from the corner, the rotational speed is 40,000 min ⁻¹ , the feed rate is 1 m / min, the axial cutting depth is 0.5 mm, and the radial cutting depth is 0.01 mm. Mist was used. As an evaluation method, the tool wear and the finished surface state were observed after completion of one process. The tool wear was observed with an optical microscope at a magnification of 100, and the tool life was determined when the maximum wear width of the flank face of the ball blade exceeded 0.1 mm, or when chipping or breakage occurred. Moreover, the finished surface state was observed and evaluated with an optical microscope at a magnification of 100 times. Next, curved surface machining from R0.5mm to R1.0mm is basically done with an axial depth of cut of 0.5mm and a radial depth of cut of 0.01mm. The test was conducted while cutting regularly.

Example 1 of the present invention was a curved surface machining with a radius of 0.5 mm from the corner, and was cut about 10 m as a cutting length with 50 tool passes, but after one machining, there was no chipping and showed a normal wear state. Subsequently, in the curved surface machining from R0.5 mm to R1.0 mm, the cutting length was cut by about 40 m, but after one machining, there was no chipping and a normal wear state was shown.
Furthermore, as a result of repeating the curved surface processing of R0.5 mm and the curved surface processing of R0.5 mm to R1.0 mm from the corner portion 10 times, Example 1 of the present invention showed a normal wear state without chipping.

  As present invention examples 2 to 10, as shown in Table 1, the normal direction rake angle is -5 degrees to -15 degrees for R10 degrees, -5 degrees to +3 degrees for R50 degrees to R70 degrees, and shows a peak. , R90 degrees was set to −10 degrees to 0 degrees, and an example in which R10 degrees was gradually increased in a positive direction from R50 degrees to R70 degrees and a peak was gradually increased in a negative direction from R90 degrees to R90 degrees was manufactured. For comparison, as Comparative Example 11, an example in which R10 degrees is −20 degrees, as Comparative Example 11 is provided with an incremental positive direction of 3 degrees every 10 degrees, and as Comparative Example 12, an example in which R10 degrees is 0 degrees is manufactured. A similar test was conducted.

Examples of the present invention examples 2 and 3 where the peak positions are set at R50 degrees and R70 degrees are the same as in the present invention example 1, in the curved surface machining of R0.5 mm from the corner and the curved surface machining of R0.5 mm to R1.0 mm. There was no chipping and the finished surface was free of chattering and stable cutting. In the inventive examples 4 to 6, the rake angle in the normal direction is set to -15 degrees at R10 degrees, and the positive direction is gradually changed slightly abruptly to 2.5 degrees, so that the work material is expanded in the horizontal direction. In some cases, good cutting performance was shown. In Invention Examples 7 to 9, the rake angle in the normal direction was set to -5 degrees at R10 degrees, and further, the positive direction was gradually changed slightly more gently, so there was no chipping and the finished surface state showed traces of chatter. Stable cutting was possible.
In Comparative Example 10, R0.5 mm curved surface processing resulted in chipping and a lifespan. In Comparative Example 11, when processing a curved surface from R 0.5 mm to R 1.0 mm, particularly when expanding in the vertical direction of the work material, chatter occurred from vibration, and chatter marks were generated in the finished surface state. The test was stopped. In Comparative Example 12, since the chipping was performed at around R20 degrees, the test was similarly stopped.

FIG. 1 shows a front view of an example of the present invention. FIG. 2 shows a left side view of FIG. FIG. 3 shows a cross-sectional view perpendicular to the straight line L of FIG.

Explanation of symbols

1: Shank 2: Peripheral blade 3: Ball blade 4: Rake angle in normal direction 5: Ball blade rotation locus 6: Center of ball blade rotation locus 7: Ball blade rake face 8: Neck length L: Ball A straight line connecting the center of the blade's rotation trajectory and the ball blade

Claims (1)

In a ball end mill made of a sintered body containing cubic boron nitride, the ball end mill is provided with a neck portion having a diameter reduced from the shank at the tip of the shank, and a sintered body containing cubic boron nitride is joined to the tip. The ball blade and the outer peripheral blade are provided, and the normal rake angle of the ball blade is -5 degrees to -15 degrees for R10 degrees, -5 degrees to +3 degrees for R50 degrees to R70 degrees, and exhibits a peak. A ball end mill made of CBN, characterized in that it is provided in the range of -10 degrees to 0 degrees at R90 degrees, gradually in the positive direction from R10 degrees to R50 degrees to R70 degrees, and gradually in the negative direction from Rpeak to R90 degrees.

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