DE9303053U1 - End mill - Google Patents

Description

PATENT ATTORNEYS D-J830 OOtcnloh, Vennstraßc

Telephone: (05241)13054

Dipi.-ing. Gustav Meldau I Zl". , II *. . Dettfa: '.5.03.93

DipLPhys. Dr. Hans-Jochen Strauß ** ** * ** &ugr;&eeacgr;&kgr;&Ggr; Reference: P 802

Mister

Franz Josef Pokolm

Starenweg 3

4834 Harsewinkel

End mills

The invention relates to an end mill with corner radius - also referred to as a toric milling cutter - in particular with diameters of less than 16 mm, in which at least the cutting area is hardened for very high cutting speeds.

Such cutters are often made of high-speed steel, tungsten-based hard metal or titanium-based hard metal and are formed and ground in one piece, including the cutting edges; in addition, the cutting edge area can be covered with hard metal cutting plates or, in a very shallow groove provided in this area, can be provided with a soldered coating of "cubic boron nitride" (CBN) or of "polycrystalline diamond" (PKD). Finally,

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Ceramic materials can also be used as cutting material. Milling cutters of this type are designed for very high cutting speeds and are used in particular for finishing work with up to about 0.3 mm material removal. The diameters of such end mills are preferably less than 16 mm, because for larger diameters, milling cutters with screwed-on or otherwise attached cutting or indexable inserts can be used; they are therefore comparable to end mills.

Such milling cutters are used to machine workpieces that already have a pre-machined contour, and they must be operated at very high cutting speeds. When working with such milling cutters, it is often necessary for the milling cutter to plunge into the layer to be machined on the workpiece to the depth of the layer in order to then work in lateral feed, for example to finish. The cutting speed must not drop to zero on the cutting edge, as is the case with a ball milling cutter. Dropping the cutting speed to zero would result in problems, such as the cutting edges breaking or becoming coated.

On flat contours, the cutting center of ball milling cutters is generally stressed, which mills without any cutting speed. In contrast, the cutting speed on the cutting edge of such end mills must not drop to zero, as is the case with a ball milling cutter. A drop in cutting speed to zero would result in malfunctions, such as the hard coatings, such as the CBN or PCD coating, breaking.

Toric end mills are a tool that can reliably handle the cutting speeds required for CBN-PCD milling cutters when milling contours and form with a line offset below the center offset of the milling cutter. Only this possibility guarantees the reliable use of milling tools with CBN-PCD coating when milling contours and free-form surfaces.

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The invention has set itself the task of avoiding these difficulties and of creating an end mill that is suitable for working in the direction of the Z-axis, i.e. drilling, even if only for a short time or at low immersion depths.

To solve this problem, an end mill of the generic type is characterized in that when designed with two cutting edges opposite one another in a plane, these are drawn in in the middle area down to the axis of rotation and the coating is only arranged up to the apex.

In practice, it has been shown that it is possible to drill with an end mill designed in this way at the small immersion depths required here, so that the entire processing can be programmed and controlled without manual intervention. During drilling, the material is apparently partially displaced due to the slot arranged in the area of the axis of rotation, while it initially remains in a conical shape in the center. Since the speeds in the area of the axis of rotation are very low, the particularly high-stress coating soldered onto the cutting edges has also been omitted in this area, since otherwise it would be subjected to undue stress due to the low speeds here, which tend towards zero, and would, for example, chip off. Apparently, when the milling cutter is fed sideways, the cone that has remained in the center of rotation is also milled off, namely from cutting areas that lie outside the axis of rotation and therefore have a sufficient cutting speed. Advantageously, the recess from the apex to the axis of rotation is in the range of approximately 1 to 5 based on the total diameter of the milling cutter.

To give a practical example, with a cutter diameter of 12 mm, the total width of the recess from vertex to vertex is about 2 mm, while the adjacent

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the rounded cutting edges now have a radius of 5 each.

The recess may have rounded flanks, it may also have straight flanks, so that it is formed as a notch, for example.

The recess is designed to be in the form of a groove or notch transverse to the plane of the cutting edges. This means that it is also open to the outside and material machined within the recess can flow outwards.

The invention is explained in more detail using exemplary embodiments with reference to the drawings. In the drawings:

Fig. 1 - a toric milling cutter in side view;

Fig. 2 - a toric milling cutter in side view rotated by 90° compared to Fig. 1;

Fig. 3 - a toric milling cutter according to Figs. 1 and 2 in plan view;

Fig. 4 - a toric milling cutter in side view in a slightly different embodiment;

Fig. 5 - a toroidal milling cutter according to Fig. 3 in plan view.

A toric milling cutter according to Fig. 1 to 3 has an essentially circular cross-section, with only the opposing cutting edges 1 and the free surfaces 2 behind them projecting beyond this circular cross-section. At its end, the milling cutter has a rounding 3 with a large radius that adapts to the running edge 2. In the middle area between the two dash-dotted lines 4 on either side of the axis of rotation 5, in which a straight or flat surface is usually arranged in toric milling cutters, there is a recess or notch 6 with two opposing straight flanks of equal size 7 in this milling cutter. All of this is in the area of the cutting edges 3, which continue into the flanks 7 towards the axis of rotation 5, as well as in the area of the

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Free surfaces 2. At the outer end 8 of the flanks 7, due to the rounding of the shape of the milling cutter, there is no longer any material towards the outside, so that the notch or groove 6 runs out into the open here.

The surface 10 running inwards in a radial plane from the cutting edge 1 is coated with a cubic boron nitride or with a polycrystalline diamond 10. This coating can be applied over the entire surface 10, but it is advisable to only apply the coating up to the lines 4 running parallel to the axis of rotation 5 at a distance, so that there is no coating within these lines and thus in the area of the notch 6.

In Fig. 1 and 3, the design and position of the recess or notch 6 can be clearly seen, with its deepest point in the area of the axis of rotation 5 or its valley apex running through the axis of rotation. The flanks 7 of the recess or notch run flat and straight up to their end 8 in the areas in which the outer curve of the cutter has sunk down to the valley apex of the notch. The flanks rise laterally up to the apex points 9, at which the cutting edges 1 of the cutter from both sides, facing each other, meet at the closest point and at the same time reach the outermost point of the cutter in the axial direction. This can be seen particularly well in Fig. 2. This also makes it clear that these outermost points of the cutting edges machine the area around the recess or notch 6 at a relatively close distance around the axis of rotation 5, or machine it away during milling, so that only a relatively small core of material remains in the area of the rotating notch 6 during the feed in the axis of rotation, i.e. in the Z direction, which is then also machined away when the milling cutter is moved sideways.

In the embodiment according to Fig. 4 and 5, the milling cutter is essentially the same shape with the same reference numerals for the same parts. However, in this case, a very flat groove 11 is arranged in the area of the cutting edge on the side of the chip discharge surface. On this flat

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The CBN or PCD coating is applied or secured to the groove 11. This flat groove extends to the apex 9 of the rounding 3. This apex coincides with the intersection of the cutting edges 1 in the rounded area 3 with the distance lines 4 running at a distance from the axis of rotation 5. Within these distance lines 4 there is a recess or flat notch 12, the deepest or valley line 13 of which intersects the axis of rotation 5 and runs diagonally to the cutting edges 1, as can be seen in the top view of Fig. 5. Due to the rounding 3 of the milling cutter, this recess or depression 12 runs out approximately in the area of the lines that delimit the free surfaces 2 opposite the cutting edge 1. The rounding radius of the roundings 3 is marked with the arrow A. The center of the roundings is at the intersection of the distance lines 4 with the plane that limits the straight section of the cutting edges 1 parallel to the axis of rotation. The length of the arrow A is related to the distance B of the distance line 4 from the axis of rotation 5 as approximately 5:1. Accordingly, the width of the recess 12 or notch 6 in relation to the total diameter is also approximately 5:1. ·

Claims (1)

PATENT ATTORNEYS D-4830 OOtenloh, Vcnnstraße 9 Dipl.-Ing. Gustav Meldau &iacgr;&idgr;&iacgr; J * &iacgr;&idgr;. Date: V3 .»03193 Dipl.Phys. Dr. Hans-Jochen Strauß Our reference: P 802 Protection claims 01. End mill with corner radius - also referred to as toric mill - in particular with diameters of less than 16 mm, in which at least the cutting area is designed to be hard for very high cutting speeds, characterized in that when designed with two cutting edges (1) lying opposite one another in one plane, these are drawn in in a sloping manner in the middle area up to the axis of rotation (5) and the coating (10 or 11) is only arranged up to the apex (9). 02. End mill according to claim 1, characterized in that the width of the recess (6 or 12) from vertex (9) to vertex (9) is in the range of approximately 5:1, based on the total diameter. 03. End mill according to one of the preceding claims, characterized in that the recess (6 or 12) has rounded flanks. - 2 - P802 04. End mill according to one of the preceding claims, characterized in that the recess has straight flanks (7). 05. End mill according to one of the preceding claims, characterized in that the recess (6 or 12) in the form of a groove or notch runs transversely to the plane of the cutting edges (1).