JPH0351057Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Field of Industrial Application] The present invention relates to an improvement in the shape of the bottom blade of end mills such as ball end mills, which have a bottom blade near the rotation center axis. [Problems to be Solved by Prior Art and Ideas] FIG. 1 shows what is generally called a square end mill as a conventional example of an end mill having a bottom cutter near the center axis of rotation. Figure 1a is a side view,
Fig. b is a front view, and Fig. 1c is an enlarged sectional view of the cutting blade portion at the - portion of Fig. 1a. This conventional square end mill is mainly used for shoulder milling and groove milling using the peripheral cutting edge A, but like the keyway cutting of a shaft shaft, it first makes a hole with the bottom cutting edge RO, similar to a drill, and then performs lateral feed. It is also used for cutting. As described above, in the drilling cutting performed in the axial direction, peel-like defects are likely to occur on the rake face as schematically shown in FIG. 1d in the vicinity of the rotation center axis of the bottom cutter B. This is because the cutting speed decreases the closer you get to the rotation center axis of the bottom cutter, and the specific cutting force increases in inverse proportion to the cutting speed, and rotational runout (deflection) caused by machine holders and end mill tools, etc. ), the inside of the flank often becomes the center of rotation, and for this reason, excessive thrust force from the flank is generated especially near the center of rotation, which leads to breakage. In general, when working conditions are poor for chip evacuation, such as during drilling, the first e
Peel-like defects also occur on the flank surface as shown in the figure. Furthermore, FIG. 2 shows an example of a conventional ball end mill, and FIG. 2a is a side view, FIG. 2b is a front view, and FIG. 2c is an enlarged sectional view of the cutting blade portion at the - part of FIG. 2b. Figure 2d is the − of Figure 2b.
FIG. In a ball end mill like this conventional example, the central axis of rotation is in the form of a chisel, as shown in Figure 2c, and initial breakage in this part is rare, but in Figure 2d, which connects to this chisel blade. In the arcuate cutting edge shown, peel-like defects are likely to occur on the rake surface similar to those described above. This is particularly noticeable when cutting work materials with strong work hardening properties. The present invention improves the problems of the prior art described above, and provides an end mill that prevents cutting edge breakage near the center of rotation and increases and stabilizes tool life. [Means for Solving the Problems] The present invention provides an end mill having a bottom cutter near the rotational center axis, in which the honing amount of the cutting edge located on the rotational center axis side of the bottom cutter is reduced to the cutting edge located on the outer peripheral side. The honing amount is larger than the honing amount of the blade, and more preferably, the cutting edge portion located on the central axis side within a diameter range of approximately 1/2 of the outer diameter of the end mill is 25° to 70°. This end mill has negative land honing at an angle of , and curved honing on the cutting edge on the outer circumferential side of the bottom blade. [Function] The end mill of the present invention is located on the rotation center axis side of the bottom cutter in order to prevent the bottom cutter from breaking especially near the rotation center due to excessive thrust force from the flank side or chip bite. The honing amount of the cutting edge is greater than the honing amount of the cutting edge located on the outer peripheral side of the bottom blade. In addition, whether or not to hone the outer peripheral cutting edge on the cylindrical or conical surface of the end mill is determined depending on the type, size, workpiece material, and usage conditions of the end mill, but in the case of steel cutting, For square end mills, ball end mills, etc. used for drilling and counterbore processing, it is desirable to hone the entire cutting edge of the bottom edge, but in this case, the cutting mechanism near the center of rotation will deteriorate further. Even if honing is applied to the bottom blade, as in the present invention, greater honing is required near the center of rotation. In addition, the honing of the cutting edge located on the rotation center axis side of the bottom blade is provided in the form of negative land honing at an angle of 25° to 70° within a diameter range of approximately 1/2 of the outer diameter dimension. The reason for this is that the cutting edge strength is greatly improved by honing the center cutting edge at a strong angle, where the cutting speed at the outer periphery is less than 1/2 to 1/5 of the cutting speed. If the angle of the negative land is less than 25 degrees, initial defects will occur sporadically, and if it is more than 70 degrees, abnormal wear or defects due to fatigue will easily occur, so a range of 25 degrees to 70 degrees is preferable. It should be noted that the honing shape of the cutting edge on the rotation center axis side is basically a negative land shape, but for the purpose of this invention, it is possible to prevent initial chipping by using other curved shapes or shapes with a curved surface added to the negative land. be. [Example] Hereinafter, an example of the present invention will be described with reference to the drawings. Example 1 In the conventional ball end mill shown in FIG. 2, which has two blades with an outer diameter of φ20 mm and a solid spiral end mill made of JIS P25 cemented carbide, an SiC-containing brush grinding wheel (Japanese Patent Publication No. 1983-1983), which was previously proposed by the applicant, was used. −
No. 54619), the cross section is approximately elliptical (now Similarly, honed specimens with curved surfaces (hereinafter referred to as curved surfaces) were prepared as shown in Table 1. Note that the bottom edge here refers to an R-shaped circular arc edge cutting edge, and the cutting conditions are as follows. SKD 61 (H _R C = 40), rotation speed = 1500 rpm, table feed = 500 mm/min, axial depth of cut = 8
mm, pick feed = 10 mm, dry cutting, and down cutting results are shown in Table 1. As is clear from this, the honed product has a lifespan of at least twice as long, and the product of the present invention is much better.

[Table] Embodiment 2 Fig. 4 is a diagram showing the main parts of a square end mill that is a second embodiment of the present invention, in which Fig. 4a is a side view, Fig. 4b is a front view, and Fig. 4c is a diagram showing the main parts of a square end mill. It is a partial enlarged sectional view of the cutting blade at the negative part in the figure. In step 4c, negative land honing of lengths l and m was performed at an angle θ with respect to the line AA representing the center axis of rotation. Note that m is the honing amount at the rotation center. In an end mill made of ultra-fine cemented carbide with an outer diameter of 10 mm and 2 flutes, after changing θ, l, and m variously as shown in Table 2, all cutting edges, including the outer peripheral edge, were curved by a brush method with 0.02 curved honing. A drilling test with a depth of 10 mm was conducted under the following cutting conditions. Cutting conditions Work material: S50C (H _S = 30) Cutting speed (outer circumference) = 30 m/min Feed = 0.12 mm/blade Oil-based cutting oil

[Table] The maximum amount of damage including chipping, chipping, etc.
When it reached 0.2mm, it was stopped midway. The results are listed in Table 2, and compared to the conventional shape that was not honed, the honed one had several steps fewer initial defects. In Example 2 of the present invention, it was possible to drill more than 1000 holes when the feed rate was set to 0.07 mm/blade. In addition,
At this time, both the conventional product without negative honing and the product of Comparative Example 2 had less than 50 defects. Embodiment 3 Fig. 5 shows the main parts of a ball end mill which is the third embodiment of the present invention. Fig. 5a is a side view of the ball tip, Fig. 5b is a front view, and Fig. 5c is a front view. FIG. 5 is an enlarged cross-sectional view of the cutting edge portion of the - portion of 5a. The ball end mill of this example is an improvement over the conventional ball end mill shown in Fig. 2, which has a chisel-like shape at the center, so the rotation locus tends to be flat at the tip of the ball. This is what I did. In this type of ball end mill, the ball tip is not negatively honed, and θ=
Comparative Example 1 with 15°, m=0.2, l=5, and θ=
45°, m = 0.2, l = 5, and both Comparative Example 1 and the invention example have R0.02 curved honing added to all cutting edges other than negative land honing. Cutting blade (up to 20mm in axial direction)
Four types of comparative example 2 were manufactured in which uniform negative honing was performed at θ=45° and m=0.2 (in the above, the unit of honing amount is mm). End mill: φ20, JIS P25 cemented carbide cutting blade with brazing Test machine: Vertical machining center (AC11kW) Work material: SKD61 (H _R C = 40) Cutting conditions: Peripheral cutting speed = 80m/min Feed = 0.15mm/ Blade Axial depth of cut = 10mm Radial depth of cut (buck feed) = 10mm Dry type, down cut No negative honing when cutting with four types of end mills under the above conditions, and Comparative example 1 with θ = 15°
However, when the cutting distance was 200 to 400 mm, a peeling-like defect occurred on the rake face near the center of the bottom edge.
= 45° had no abnormalities even after cutting 4000 mm, and further cutting was possible. In Comparative Example 2, in which the entire cutting edge was uniformly negatively honed, cutting was stopped due to severe chatter due to poor sharpness. [Effects of the invention] As described above, the present invention makes it possible to improve the honing of the cutting edge located on the rotation center side of the bottom blade of the end mill by making it larger than the honing amount of the cutting blade located on the outer peripheral side. In drilling, counterbore machining, ball end milling, etc., the bottom edge of the end mill, especially near the rotation center axis, can be almost completely free of damage, increasing the degree of freedom in the shape of the bottom edge of the end mill, and making it easier to adjust the machining conditions. A suitable shape can be obtained, and at the same time, a stable and long-life end mill, especially for steel cutting, can be obtained.

[Brief explanation of the drawing]

Figure 1 shows a conventional square end mill; Figure 1a is a side view, Figure 1b is a front view, and Figure 1c is a front view.
The figure is a partial enlarged view of the cutting edge in part 1a-, and part 1d.
Figures 1 and 1c are schematic diagrams showing defects, Figure 2 is a diagram showing the main parts of a conventional ball end mill, Figure 3 is an enlarged view of a cutting blade part of a ball end mill showing an embodiment of the present invention, and Figure 4 The figure shows the main parts of a square end mill showing another embodiment of the present invention, and FIG. 5 shows the main parts of a ball end mill showing a third embodiment of the invention. A...Peripheral blade, A-A...Rotation center axis, B...
Bottom edge, m...Amount of honing in the rake face direction.

Claims (1)

[Claims for Utility Model Registration] (1) In an end mill having a bottom blade near the rotation center axis, the honing amount of the cutting blade located on the rotation center axis side of the bottom blade is honing of the cutting blade located on the outer peripheral side. A reinforced end mill with a cutting edge that is larger than its weight. (2) In claim 1 of the utility model registration, the cutting edge portion located on the central axis side within a diameter range of approximately 1/2 of the outer diameter of the end mill is cut with a negative land at an angle of 25° to 70°. An end mill with a reinforced cutting edge, characterized in that the cutting edge is honed and the cutting edge on the outer peripheral side connected to the honing is honed in a curved shape.