CZ308342B6 - Ball cutter - Google Patents

Abstract

A ball end mill with a cutting diameter of D6 to D32 has an even number of cutting edges with different shapes of odd and even cutting edges (3), the odd cutting edges (3) being provided with engaging segments (2) and reliefs (1) and the following even cutting edges (3) being provided with engaging segments (2) at the relief point (1) of the previous odd cutting edges (3) to form full cutting edge profiles over the entire surface of the ball end mill.

Description

Ball cutter

Field of technology

The invention relates to machining tools, and more particularly to line milling on constant depth levels. Ball end mills or high-speed milling cutters are most often used for this operation.

Prior art

At present, ball milling cutters and high-speed milling cutters are used for milling operations, so-called Z-constant constants, which means line milling by levels, of constant depth. The milling operation of Z constants is one of the most widespread roughing operations with subsequent 3D milling according to the model.

In addition to corner cutters, ball end mills are among the most common shapes of end mills. They are most often produced in 2, 3 and 4-edged versions. The aim of these operations is to remove as much material as possible in the form of chips. For these cutters, the basic parameter is the chip power limit, which can be determined from the working area, which is defined by the depth of the level and the width of the row. The definition of acceptability is determined by the moment of vibration that occurs at certain values. In order for the vibrations to occur as late as possible and thus speed up the entire operation, so-called high-speed milling cutters were introduced. Their main advantage is smooth running, without vibrations in the area of smaller depths. The chip power was thus increased, but at the cost of lower tool economy, as this power is taken only by a small part of the cutter on the face, where the wear of the cutting edge is concentrated. Higher feed rates, in turn, are greatly eliminated by reducing the cut size.

The generation of vibrations is initiated by the magnitude of the cutting force during chip separation. The curvature of the blade is extremely important for its size. The cause is based on the analysis of chip formation in the area of the so-called primary plastic deformation of shaped cutting edges, where the deformation work during chip formation is significantly increased. In contrast to the chips taken by the straight edge at the circumference with the same engagement area, it is necessary to add the energy necessary to transform the chip body in the shape of a radius into the collapsed or undevelopable shape of its surface. This change costs a large amount of energy and is reflected in an increase in the resultant cutting force and thus an increase in tool deflection and vibration.

KR 101629586 B describes a ball end mill in which the angle of the cutting edge formed in the ball part differs from the angle of the cutting edge formed on the outer circumference of the ball end mill. This solution makes it possible to distribute the cutting load during machining and to prevent damage and chipping of the cutting edge, but does not make it possible to reduce the chip width.

Modifications of cylindrical cutters are also known. For example, DE 202006016531 U and US 2016089728 describe the alternation of "smooth" and "rough" cutting edges on a cylindrical cutter. U.S. Pat. No. 2008206003, U.S. Pat. No. 3,775,819 and others also describe modifications to cylindrical cutters, in particular various corrugations of the cutting edge. Such adjustments cannot be applied directly to ball end mills due to different cutting speeds at different points on the same cutting edge.

The essence of the invention

The above-mentioned drawbacks are largely eliminated by a ball end mill with segment cutting edges according to this technical solution. Cutting edges, based on the hypothesis of a comparison of the size of deformation work during chip formation on a straight and indirect cutting edge, eg a cutting edge in the shape of a cutter radius. Here, in contrast to cylindrical milling cutters with straight cutting edges, there is no chipping into rolls with parallel vectors perpendicular to the cutting edge. In the case of shaped cutting edges, these vectors have a different direction,

- 1 CZ 308342 B6 which are also perpendicular to the cutting edge, but thus point approximately to the center of the radius of curvature of the cutting edge. There is an additional, transverse compaction of the chip into a collapsed shape, which places considerable resistance. This type of resistance depends on the angular size of the segment, which defines the chip width. By introducing the segmental cutting edges, the invention reduces the size of the circular segment and thus the chip width, whereby the chip formation is closer to the proportions of the straight cutting edges and thus a minimum transverse compaction is achieved.

The cutting edge of a ball end mill is characterized in that the overall shape of the cutting edge on the ball part - 90 ° - is not solid, but is divided by sections between several other, successive cutting edges. In the case of a four-edged cutter, the overall solid shape is formed by two consecutive cutting edges. This implies the need for an even number of cutting edges. The individual parts reduce the width of the segment of the future chip, which has a smaller transverse deformation against the solid edge, resulting in less harmful force of a transient nature, which initiates the vibration. In the tests with the milling cutters according to the invention, it was possible to increase all measurable values without causing vibrations.

The increase can be attributed to the smaller deformation work of sectionally divided cutting edges with a smaller coefficient of specific cutting resistance. This fact will also allow an increase in the feed per tooth, which affects the resulting volume of chips removed.

A milling cutter in the range of diameters D6 to D32 according to the invention with a spherical face with a radius D / 2 and an even number of teeth is able to take a depth and a working width Ap, Ae equal to at least D / 2 at the same time during lateral as well as grooving milling.

Explanation of drawings

A ball end mill with sectional edges according to the invention will be described in more detail on the basis of a specific exemplary embodiment with the aid of the accompanying drawings, in which FIG. 1a and FIG. 1b show a four-edge ball end mill. Fig. 1a shows segmented cutting edges 1 and 3 and Fig. 1b shows segmented cutting edges 2 and 4. Figs. 2a and Fig. 2b show a ball end mill with four cutting edges and a marked chip width and chip movement vectors. Fig. 2a shows the edges 1 and 3 and Fig. 2b shows the edges 2 and 4. Figs. 3 shows the amount of material removed by a ball end mill with sectional edges compared to the prior art.

Examples of embodiments of the invention

The ball end mill with segment cutting edge 3 in Fig. 3 according to the invention is used in the interlacing technology in the surface machining of Z constants, in roughing operations, where the decisive criterion of the material removed per minute is "V" in cm ³ . To facilitate the calculation, it is sufficient to use the programmed quantities from the NC program and these are the area of engagement of one line Ap, Ae in cm ² multiplied by the feed rate per minute in cm. Geometric differences in the engagement areas of complex shapes against the pattern of the area of the rectangle axb between the compared technologies are always taken in the next level or the next line.

The performance achieved with the milling cutters according to the invention in the verification tests exceeds the existing milling parameters by levels by more than 100%.

Exemplary embodiment of the invention ball end mills with segment cutting edges 3 with a cutting diameter D10 with a spherical face of radius D / 2 and an even number of cutting edges, with different shapes of odd and even cutting edges, and relieving 1 on two successively rotating cutting edges 3 and thus forming two solid profiles composed of cutting edge segments 3 with a radius D / 2 over the entire 90 ° quadrant.

-2 CZ 308342 B6

The ball cutter with cutting edges 3 solved in this way is able to take a depth equal to at least D / 2 and a width D / 2 at the same time during grooving.

The following calculations compare the machining productivity of three milling cutter variants with a diameter of D10 and different cutter face designs, based on catalog cutting conditions. Formula for chip volume per minute for the second and next level:

V = Ap * Ae * Fz * z * n [cm ³ ], where Ap is the depth of field; Ae is the working width; Fz is the feed per tooth; z is the number of teeth; A = Ap * Ae

High-speed milling cutter (21):

Ball end mill (22):

V = 0.05 * 0.6 * 0.03 * 4 * 3200 = 11.52 cm ³ / min

V = 0.2 * 0.4 * 0.01 * 4 * 3200 = 10.24 cm ³ / min

Ball end mill with sectional cutting edges (3): H = 0.5 * 0.5 * 0.007 * 4 * 3200 = 22.4 cm ³ / min

Industrial applicability

The preferred application of the milling cutter according to the invention can be recommended in the production of all kinds of molds for casting, forging dies and blocks of pressed sheet metal products.

Claims (1)

PATENT CLAIMS A ball end mill with a cutting diameter D6 to D32, characterized in that it has an even number of cutting edges with different shapes of odd and even cutting edges (3), the odd cutting edges (3) being provided with engaging segments (2) and reliefs (1) and the following even cutting edges (3) are provided with engaging segments (2) at the relief point (1) of the previous odd cutting edges (3), to form full cutting edge profiles on the entire surface of the ball end mill.