The invention concerns an end mill for chip removal of metallic materials, especially steel and titanium.
An end mill having a fastening section and a cutting area, is known from DE 37 06 282 A1. The cutting area is formed by a rotationally symmetric core and four cutting edges, which are arranged helically around the core and joined in one piece to the core. The four cutting edges each have a peripheral main cutting edge and a secondary cutting edge on a free face of the cutting area in order to make possible chip removal in both peripheral and face milling. A situation is thereby achieved in which, in addition to peripheral milling with the face of the solid carbide end mill, surface milling operations can also be conducted. However, there is the drawback that such end mills are not suitable for drilling, i.e., chip removal with the secondary cutting edges at an advance direction along the axis of rotation of the end mill, since the secondary cutting edges often do not have the desired stability and service life. In addition, the geometry of both the secondary cutting edges and the chip grooves on the face of the milling cutter are not suitable for drilling, since the cutting function is not guaranteed in the center area and the chips cannot be ejected laterally during drilling. Commercial milling cutters are not suitable or only marginally suitable for axial chip removal during drilling, i.e., along the chip grooves, since the chip spaces clog too quickly.
At least some of the embodiments of the invention relate to an end mill that is easy to produce and optimized for drilling.
Advantageous embodiments of the invention are also disclosed.
It is first clarified that a fastening section of the end mill need not necessarily be designed as a cylindrical holding section. Other types of fastening section or coupling sites are contemplated by the present invention. Any type of coupling site can be understood under the term “shank” with which the cutting section is joined to a separate toolholder. The coupling site, for example, can also be conical, carry threads or include clamping surfaces. The holding section can even be designed as a hole in the cutting area, which is accommodated on a complementary pin of the toolholder.
Solid carbide milling cutters are understood to mean milling cutters in which the chip-removing cutting edges are a fixed component of the tool body. All cutting materials suitable for machining of high-strength materials are to be understood as base material of this cutter, i.e., ceramic materials, PCD and powder mixtures, in addition to steels.
Preferably, end mills according to the invention have at least one cutting edge on the face of the cutting area has a single, flat or continuously curved front surface (or relief angle), which delimits the cutting edge in the longitudinal direction of the end mill on the face. Through this precisely one front surface on each cutting edge on the face of the cutting area, a single free surface is formed, which is particularly stable relative to multiple free surfaces with different relief angles and permits stability in heat removal suitable for special requirements of drilling and also milling with the end mill. Due to the one front surface, such an embodiment is also easy to manufacture and subsequently grind as required, since only one surface need be machined with an angle.
In addition, the end mill, despite “drilling-optimized” geometry, is characterized by excellent milling performance with quiet running. The special geometry also proves to be very robust for milling. Intensive research and studies with milling experiments have shown that the milling cutters from the prior art do not function universally enough in different materials. The end mill according to the invention is characterized by high universal applicability and milling performance in a wide variety of materials and applications, for example, roughening and finishing, ramping, plunge milling and grooving.
In an advantageous embodiment the front surface of each cutting edge on the secondary cutting edge has a relief angle between 5° and 7°, especially equal to 6°, relative to a plane perpendicular to the axis of rotation of the end mill. A particularly stable secondary cutting edge with high removal performance and long service life can thereby be achieved, especially together with the described precisely one front surface of the cutting edges on the face.
In considering the front face of the cutting area of the end mill, each at least one secondary cutting edge can also have at least one curved, especially concave, trend at least in sections, so that particularly advantageous chip removal is achieved in conjunction with the aforementioned features.
At least one secondary cutting edge can preferably have a protruding center distance in the radially outer area. A protruding center distance is characterized by the fact that the at least one secondary cutting edge is designed so that it extends beyond an imaginary connection of the end point lying closest to the face of the main cutting edge, i.e., the transition from the main to the secondary cutting edge, with the center in the direction of rotation. Simply put, this means that both cutting edges are in front of the axis of rotation and their cutting edges do not meet at the tips in the direction of the center but partially overlap.
In particular, in order to increase the cutting performance of the secondary cutting edge during drilling, it can be prescribed that a point thinning of the core be provided between two adjacent cutting edges on the face of the cutting area, which has an angle from 30° to 40° relative to the axis of rotation of the end mill. Through this sharp point thinning of the core between two adjacent cutting edges, particularly good chip removal is made possible, in which case the cutting edges in the area of the face of the cutting area have high stability despite point thinning of the core.
Point thinning according to the invention embraces any embodiment with which the material of the core and possibly also the cutting edges in the area of the face of the cutting area is locally reduced in the peripheral direction between the cutting edges. The rotationally symmetrical core area of an end mill in the cutting area is to be understood as core. The cutting edges are arranged around this core and made in one piece with the core. The bottom of each chip removal groove, which is formed in the peripheral direction between the cutting edges, is then bounded by the core.
With particular preference, the point thinning can be designed as a recess in the area of the face of the cutting area approaching the axis of rotation of the end mill in the direction from the fastening section to the face of the cutting area. Such a recess can be achieved particularly simply by grinding.
In order to permit chip removal on the entire face during drilling by at least one secondary cutting edge, the recess can also extend in the radial direction of the cutting area essentially up to the axis of rotation of the end mill and delimit the secondary cutting edge in the area of the axis of rotation of the end mill.
The cutting edges in a particularly advantageous embodiment are unevenly distributed at least on the face of the cutting area. The stability of the cutting edges can thereby be increased, since cutting edges with a small intermediate angle can have a mutually stabilizing effect. In order to reduce the tendency toward vibration, the cutting edges can also have different helix angles so that the cutting edges can also be arranged equally distributed at least in sections in the cutting area outside of the face.
It can be particularly advantageous that the cutting area have a total of four cutting edges, of which a first cutting edge and a third cutting edge are diametrically opposite each other, as are a second cutting edge and a fourth cutting edge, in which case point thinning is provided between the second cutting edge and the third cutting edge, as well as between the first cutting edge and the fourth cutting edge, and in the peripheral direction of the cutting area the angle between the first cutting edge and the fourth cutting edge and between the second cutting edge and the third cutting edge is greater than 90° and less than 110°, especially equal to 100°. This ensures that, despite the sharp point thinning between the second cutting edge and the third cutting edge, as well as the first cutting edge and the fourth cutting edge, the cutting edges are mutually supported by the smaller angular distance between the first cutting edge and the second cutting edge and between the third cutting edge and the fourth cutting edge, so that high stability is thereby achieved. The end mill is therefore particularly suited for drilling even in materials that are difficult to machine. This permits a particularly stable secondary cutting edge to be created with high removal performance and long service life and to ensure chip removal, especially together with the described point thinning and the precisely one front surface of the cutting edge on the face.
In order to further increase the drilling performance of the end mill and facilitate chip removal, an additional point thinning can be provided between the first cutting edge and the second cutting edge and between the third cutting edge and the fourth cutting edge, which has an angle from 20 to 40° relative to the axis of rotation of the end mill.
It can also be particularly advantageous for drilling performance if the cutting edges have a hollow grinding on the face of the cutting area, i.e., the secondary cutting edges on the face protrude radially outwards in the direction from the axis of rotation in the longitudinal direction of the cutting area so that the front surface has a concave configuration.
In order additionally to improve the chip removal performance, it can be prescribed that the core of the cutting area have two conical sections with different conicity. Starting from the face of the cutting area, a first conical part can be provided, which widens from a diameter corresponding to 35-45% of the cutting area diameter to a diameter corresponding to 45-60%, preferably 50-55% of the cutting area diameter. This first conical part can extend in the longitudinal direction of the cutting area over a length of 0.25 times to the entire length of the area diameter. A second conical area can follow this first conical part, which widens along the useful cutting area to 50-70%, preferably 55% of the cutting area diameter. The first conical area is always designed so that it has a greater slope than the second conical area and the diameter of the first conical area does not become greater than the diameter of the second conical area.
The milling cutter according to the invention can additionally be provided in the fastening section with protrusions for a limit stop, for example, in the form of a Weldon or Whistle-notch surface or also in the form of a blocking groove starting on the shank side, as described in WO 2007118626 A1, or in the form of a blocking element protruding from the fastening section.
Additional details and advantages of the invention are apparent from the following description of a preferred embodiment example with reference to the drawings. In the drawings:
A solid carbide end mill 1 is shown in a side view in
Each cutting edge 4, 5, 6 and 7 has a peripheral main cutting edge 10 and a secondary cutting edge 11 on a face 12 of the cutting area 3, which are designed to cooperate with the workpiece being machined during rotation of the solid carbide end mill 1 around axis of rotation 9. For better clarity the reference numbers for the main cutting edge 10 and the secondary cutting edge 11 in the depiction in the figures are not entered for all cutting edges 4, 5, 6 and 7, but each cutting edge 4, 5, 6 and 7 has both a main cutting edge 10 and a secondary cutting edge 11.
Point thinning 13 of core 8 is also provided at least in the area of face 12 of cutting area 3.
The core 8 in the peripheral direction of the solid carbide end mill 1 is reduced in cross section by this point thinning 13 locally delimited between the cutting edges 5 and 6.
The solid carbide end mill 1 from
The cutting edge 5 depicted in
As can also be seen, the cutting edges 4, 5, 6 and 7 have a hollow grinding on face 12 of the cutting area 3, which means that the cutting edges 4, 5, 6 and 7 and therefore especially the secondary cutting edges 11 on face 12 protrude radially outward in the longitudinal direction of the cutting area 3 in the direction from axis of rotation 9 so that the front surface 15 has a concave configuration.
A cross section of the solid carbide end mill 1 is shown in
The cutting edges 4, 5, 6 and 7 extend in the peripheral direction on their outside roughly over a length corresponding to 0.1 to 0.2 times the diameter of the cutting area 2 (cutting area diameter).
The point thinning 13 is provided between the second cutting edge 5 and the third cutting edge 6, as well as between the fourth cutting edge 7 and the first cutting edge 4. The cross section of the cutting area 3 and especially the first cutting edge 4 is reduced by the point thinning 13 in the chip removal groove 14 between the fourth cutting edge 7 and the first cutting edge 4, and of the third cutting edge 6 in the chip removal groove 14 between the second cutting edge 5 and the third cutting edge 6. Because of the reduced angle described above between the first cutting edge 4 and the second cutting edge 5, as well as between the third cutting edge 6 and the fourth cutting edge 7, a situation is achieved in which the stability of the first cutting edge 4 and the third cutting edge 6 is not reduced due to the spatial proximity to the second cutting edge 5 and the fourth cutting edge 7. In the area close to the face 12 of the cutting area 3 the cross section of the circular core 8 depicted in cross section by means of the dotted line in
A front view of the free face 12 of the cutting area 3 of the solid carbide end mill 1 is shown in
As can be deduced from
As already indicated, the described unequal division of cutting edges 4, 5, 6 and 7 in the area of face 12 of cutting area 3 is of special significance for the stability of the cutting edges 4, 5, 6 and 7 in conjunction with the design of the point thinning 13 and the additional point thinning 16. Differently than described with reference to
As can also be deduced from
A cross-sectional view through the solid carbide end mill 1 in the area of face 12 of the cutting area 3 is shown in
A cross-sectional view through the solid carbide end mill 1 is shown in
A detail view of area X of
The center line of the secondary cutting edge 11 that runs through the axis of rotation 9 is indicated by the dash-dot line in
As can be further deduced from the detail view in
A side view of the solid carbide end mill 1 with a schematic depiction of the core 8 of the cutting area 3 is shown in
The technical features described in this embodiment example can be combined individually or in their entirety in order to advantageously solve the problem posed.
1 Solid carbide end mill
2 Fastening section
3 Cutting area
4 First cutting edge
5 Second cutting edge
6 Third cutting edge
7 Fourth cutting edge
8 Core
9 Axis of rotation
10 Main cutting edge
11 Secondary cutting edge
12 Face of cutting area
13 Point thinning
14 Chip removal grooves
15 Front surface
16 Additional point thinning
17 Bulge
18 Corner chamfer
19 First conical section of core
20 Second conical section of core
21 Blocking groove
22 Threads
23 Additional support area
24 Relief angle
25 Front rake angle
26 Key surface
Number | Date | Country | Kind |
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10 2015 116 624.0 | Sep 2015 | DE | national |