JPH0453616A - End mill - Google Patents

Abstract

PURPOSE:To secure an end mill suitable for finish-cutting of high hardness materials in addition to ease of manufacture by curving each of polygonal sides of the end mill, whose axial perpendicular section is formed into a polygon of more than a triangle, and a ridge, made by each of the apexes in the axial direction, forming a cutting edge being inscribed to a virtual cylinder, into a recess form. CONSTITUTION:A cutting edge twisted by a ridge 12 being produced in the axial direction by each apex of a polygon of more than a triangle in an axial perpendicular section, for example, a regular hexagon, is formed in the peripheral surface of a tool body 11, and each side is curved into a recess or projection form. Then, a land, forming a circular form concentric with the center of the polygon or a flank slightly in the rotational direction, is installed in the cutting edge part that each ridge of the section polygons produces, and a sintered hard alloy that applied coating to a tool material is used. Thus, wear of the cutting edge and reduction in chipping both are lessened and, what is more, even in case of a high hardness workpiece, cutting is made possible at a feed rate of several times over the conventional end mill, thus an excellent finished surface can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an end mill for cutting high-hardness materials having a plurality of twisted cutting edges formed on the outer periphery.

[Conventional technology]

An end mill shown in FIG. 2 is an example of this type of cutting tool for cutting general materials such as steel using a conventional machine tool such as a milling machine. These generally have a sharp cutting edge with a helix angle and a positive rake angle arranged on a virtual cylinder, followed by a large cutting groove 14, which makes it easy to cut into the rigid material and to reduce the amount of chips. It has good discharge properties and is extremely easy to work with. Here, the rectangular shape of the cutting edge can be used in an optimal shape by appropriately setting the angle according to the properties of the material to be stiffened. For example, for materials with high hardness and poor machinability, a sharp cutting edge will cause severe wear and tear and will likely cause chipping during cutting. Therefore, we have improved the cutting edge specifications by reducing the rake angle and clearance angle to increase the strength of the cutting edge, and by making the cutting groove leaky to increase tool rigidity, reducing wear and tear on the cutting edge and preventing chipping. I was using it.

In end mills, it is known that the greater the number of teeth, the longer the tool life, especially when cutting high-hardness materials. Therefore, increasing the number of blades was one of the improvement measures. Furthermore, when the hardness of the workpiece material increases and the sharpness deteriorates, methods have been used to improve the number of teeth and cutting edge specifications while simultaneously lowering the depth of cut and other cutting conditions.

When cutting high-hardness materials, tool materials are required to have sufficient hardness and strength for the workpiece material. High speed steel and cemented carbide are commonly used as tool materials for end mills, but cemented carbide coated with a hard substance such as TiN is often used for high-hardness materials. However, even in this case, when applied to a conventional rectangular end mill, the work material hardness H
There was a limit to what RC55 could cut.

[Problem that the invention seeks to solve]

Expectations for cutting high-hardness materials are increasing in a wide variety of fields. However, when it comes to high-hardness materials that reach HRC60, such as hardened tool steel, even if we try to improve cutting edge specifications such as rake angle, relief angle, or number of teeth, end mills with conventional shapes are not suitable for practical use. value, and it is no longer possible to respond even if the cutting conditions are changed.

For this reason, grinding or electric discharge machining is often used, but these have slow machining speeds and problems with machining efficiency.

Regarding tool materials used in cutting, there are ceramics, CBN, diamond, etc. for ultra-hard materials, but although these have extremely high hardness, they are relatively brittle, and are not suitable for end milling, which requires interrupted cutting. In addition to being prone to chipping during cutting, the processability is poor and the tool shape cannot be obtained freely, so there is a problem that it can only be used for limited applications such as micro-cutting.

[Object of the present invention]

The present invention aims to eliminate the above-mentioned drawbacks and provide an end mill that is easy to manufacture and suitable for finishing cutting of high hardness materials such as hardened materials.

[Means to solve the problem]

In order to achieve the above object, the present invention forms a cutting edge in which the cross-sectional shape perpendicular to the axis of the cutting edge part is a polygon of trigon or more, and the edges formed by each vertex in the axial direction are twisted.

The cutting edge angle made by each school is 90° to 1 in the cross section perpendicular to the axis.
A setting of 30° is suitable for this purpose, and for this purpose each side of the cross-sectional polygon is curved concavely.

Further, the cutting edge may have a land forming a relief angle, which also achieves this purpose.

In addition, technical measures have been taken to use a super hard alloy coated with a hard substance such as TiN as the tool material to enable the cutting of highly hard materials due to the synergistic effect with the above-mentioned rectangular shape.

[For production]

There are U.S. Pat. To explain with a diagram, the case where the bottom blade is rotated clockwise as is self-evident is illustrated here, but the cross-sectional shape perpendicular to the axis is octagonal and has a rightward twist angle. . In the case of an octagonal cross section, the number of peripheral cutting edges corresponds to 8 teeth, and as shown in the cross-sectional view in Fig. 4, the rake angle θr and clearance angle θC in the direction perpendicular to the axis are -60 and 30'', respectively. Therefore, the cutting edge angle θt is 120°.In other words, it is possible to obtain cutting edge strength and tool rigidity suitable for cutting high-hardness materials as high as HRC 60.Furthermore, compared to conventional end mills, even when the diameter is small, the cutting edge is relatively small. This has the effect of increasing the number of chip pockets.The chip pocket, which is essential for end mills, is represented by the part surrounded by the cylinder circumscribing the edge that forms the cutting edge and the faces formed by each side of the polygon. By curving it into a concave shape, it is possible to improve sharpness and chip disposal.

For high-hardness materials, it is appropriate to increase the number of blades, that is, the number of corners of the polygon, but it is necessary to increase the number of teeth, especially when the diameter of the end mill becomes large. However, when the polygon exceeds an octagon, the apex angle formed by each side becomes too large to act as a knife angle, so it is effective to curve each side concavely, as shown in Figure 4. If the polygon is less than a hexagon, each side will be curved and the blade angle will become too small. Therefore, by providing a land 15 that forms a relief angle as shown in Fig. 5, the required blade angle of 90° can be achieved.
~130° can be obtained, and further, by having a land, repolishing is easy.

Note that the grinding method for forming a curved shape can be easily achieved by making the grinding wheel have a curved surface, and it is also possible to make the concave surface on each side into a shape like a trochoidal curve.

As for the tool material, a coated carbide base metal was used, and the synergistic effect with the square shape made it possible to cut high-hardness materials. Due to its rectangular shape with a large negative rake angle, it has the effect of preventing peeling, which is the most undesirable phenomenon for coatings that occurs during cutting.

〔Example〕

FIG. 1 shows an embodiment of the present invention in which each side of a regular octagon is concave. Here, the case where it is used with clockwise rotation is shown,
On the outer periphery of the tool body 11, a ridge 12 formed in the axial direction by each vertex of a regular octagon with a cross section perpendicular to the axis forms a cutting edge with a right-handed helix angle of 30''.

The two bottom blades 13 disposed on the end face of the tool body have a rake angle of -20° in the radial direction and -5° in the axial direction. Tool dimensions: diameter 8, blade length 20m, total length 6
The tool material is cemented carbide and TiN coated cemented carbide. This product of the present invention was compared with solid end mills made of cemented carbide and coated cemented carbide shown in FIG. 2 having the same dimensions, by cutting alloy steel for cold work molds tempered to a hardness of HRC62. Here, the depth of cut was 0.1 m in the radial direction, and dry cutting was performed. The result is the 6th
As shown in Figures 7 to 7, the end mill of the present invention clearly shows superior results in terms of durability, which is more than three times that of the conventional end mill, and also in terms of finished cut surface roughness. In other words, with conventional cemented carbide solid end mills, only 0.2
The chipping of the cutting edge became severe after 5 m of cutting, and cutting had to be stopped after 1 m. The product of this invention can cut 6 m without chipping even at three times the feed speed of conventional end mills and is still in use. It was possible.

In addition, regarding the roughness of the cutting surface, the cemented carbide solid end mill has a roughness of approximately 20μ■Rm due to chipping.
ax, the product of the present invention using coated carbide had a good value of around 3 μmRsax. That is, this square shape is shown to be well compatible with the coating. Furthermore, when a highly finished surface is required, it is preferable to use cermet, ceramics, etc. depending on the hardness of the workpiece material.

〔Effect of the invention〕

As described above, according to the present invention, since the cross-sectional shape perpendicular to the axis is polygonal, the number of cutting edges is increased, and the cutting edge strength and tool rigidity are excellent, thereby reducing wear and chipping of the cutting edges. Furthermore, by providing a helix angle that is the same as the tool rotation direction, the impact during cutting is alleviated, and as a result, it is not only possible to cut high-hardness workpieces at several times the feed rate of conventional end mills. It is now possible to obtain an excellent finished surface.

In this way, cutting using coated carbide, a conventional tool material, has become comparable to grinding and electrical discharge machining, which are common machining methods for high-hardness workpieces.

This effect can be achieved by curving each side when the polygon has many angles, and by providing a land that forms a clearance angle even when the polygon has a small number of angles, the blade angle becomes appropriate.

[Brief explanation of drawings]

Figures 1A and B show an embodiment of the present invention, Figure A is a front view thereof, Figure B is a side view, Figure 2A and B are an example of a conventional end mill, and Figure A is a front view thereof. , B is a side view. FIGS. 3A and 3B show another embodiment of the present invention, with FIG. 3A being a front view and FIG. 3B being a side view. Fig. 4 is an explanatory diagram of the rake angle and relief angle of the peripheral cutting edge when the cross-sectional shape perpendicular to the axis of the present invention is a regular octagon with concavely curved sides, and Fig. 5 is an explanatory diagram of each side of the regular hexagon. FIGS. 6 and 7 are explanatory diagrams showing a comparison result between the end mill of the present invention and a conventional end mill. 11... Body 12... Cutting edge ridge 13... Bottom blade 14... Blade groove 15
... Land θa ... Helix angle θr ... Rake angle θ
C... Relief angle θt... Blade angle (A
) (A) (A)

Claims (4)

[Claims] (1) A plurality of twisted cutting edges are formed on the outer periphery of the tool body, the cross-sectional shape perpendicular to the axis of the cutting edge portion is a polygon of triangle or more, and the ridge formed by each vertex in the axial direction forms a virtual cylinder. An end mill for cutting high-hardness materials forming an inscribed cutting edge, characterized in that each side of the polygon in the cross section is curved in a concave shape. (2) The end mill according to claim 1, wherein each side of the cross-sectional polygon is curved in a convex shape. (3) The cutting edge portion formed by each edge of the polygon in cross section is provided with a land having an arc shape concentric with the center of the polygon or having a slight relief angle with respect to the rotation direction. The end mill according to Items 1 and 2. (4) Claims 1 to 3, characterized in that the tool material is a coated cemented carbide.
End mill described in section.