MILLING TOOL

Abstract

The invention relates to a milling tool made of cemented carbide having a cylindrical shank (16) and a cutting head (18) for the face milling of workpieces made of a hard-brittle material. The cutting head (18) is configured as an end mill with corner radius or a ball nose end mill having a cutting length (L 2.2). The shank (16) has, up to its chucking end (26), at least one clearance segment (28) having a smaller diameter (d3) than the cutting head (18). The tip of the cutting head (18) is coated or tipped with hard mineral along a length (L2) having a diameter (d1) used for finishing, to which is connected a segment (24), which is used for roughing, having the cutting length (L2.2−L2=L2.1) and a reduced diameter (d4), which is smaller than the diameter (d1) of the cutting length (L2) on the cutting head (18) used for finishing and is greater than the diameter (d3) of the clearance segment (28).

Description

The invention relates to a milling tool made of carbide having a cylindrical shank and a cutting head for the face milling of workpieces made of a hard-brittle material according to the preamble of claim 1.

In the milling processing of workpieces made of very hard material, the milling tools used for this purpose are subject to great wear. This problem also occurs, in particular, in the profile machining of workpieces made of graphite, in order to produce from it, for example, electrodes for spark eroding, which are used for CNC machines. The graphite block used as the starting material is normally machined using an end mill made of cemented carbide, the cutting head of which can be coated or tipped with diamond.

A milling tool having the features of the preamble of claim 1 is known from EP 2 540 427 of the applicant. There, the cutting head is suitable only for finishing due to its small coated length, which permits only a short feed, but not for roughing. The adjoining length of the shaft is configured as a clearance segment and thus is not cutting, so that it is available neither for roughing milling nor for finishing.

Another milling tool, which has the features of the preamble of claim 1, is described and illustrated in DE 10 2006 026 851. However, also in this, a non-cutting clearance segment directly adjoins the head segment, which is used for finishing, so that two differently-configured milling tools have to be kept available and used for roughing and finishing.

The same also applies to a milling tool according to WO 2018/163148, the cutting region of which is also suitable either only for roughing or only for finishing.

The object underlying the invention is to configure a milling tool so that it can be used both for roughing and for subsequent finishing of a workpiece.

The solution to this problem results from the characterizing features of claim 1, according to which a segment, which enables a roughing, is connected to the short cutting length of the cutting head that is suited for finishing. Due to its set-back diameter, the clearance segment prevents the undesired pressing in the radial direction during the finishing after the roughing.

In an advantageous development of the invention, both the finishing segment and the roughing segment of the cutting head are coated or tipped with hard mineral, in particular diamond.

The invention is explained below with exemplary embodiments, which are illustrated in the drawings.

FIG. 1 shows the schematic illustration of a workpiece to be machined, for example, an electrode for spark eroding, using an end mill or a ball nose end mill,

FIG. 2 shows the view of an end mill with corner radius having a coated cutting head according to the prior art,

FIG. 3 shows, in a variant of FIG. 2, a known end mill with corner radius having a non-cutting clearance,

FIG. 4 shows the view of a milling tool according to the invention and

FIG. 5 shows a cutout enlargement of the cutting head in the region V of FIG. 4.

FIG. 1 schematically shows the view of a workpiece 10 made of a hard-brittle material, for example graphite, the conical upper part 12 of which is to be machined in order, for example, to produce an electrode for spark eroding. In order to produce the desired profile of the upper part 12, a milling tool, designated overall by 14, is used, which has a cylindrical shank 16 and a ball nose-shaped cutting head 18 here. During the machining, the milling tool 14 rotates around its longitudinal axis 22 and simultaneously moves along the profile of the workpiece 10 around its longitudinal axis 20. For the machining of the conical upper part 12, the milling tool 14 is moved both in the x-direction and in the z-direction, optionally also in all three axes x, y and z.

FIG. 2 shows a schematic view of a conventional milling tool 14, which is configured here as an end mill with corner radius. As is known from EP 2 540 427 B1 of the applicant, the cutting head 18, which is provided at the tip of the shank 16 having the diameter d1, has a length s that consists of the radius r of the edge rounding and a short additional length a. The cutting head 18 has, in the height s, i.e. at the transition to the shank 16, the same diameter d1 as the shank 16. This has the consequence that, with progressive feeding of the milling tool 14 in the axial direction z (see FIG. 1) during roughing and finishing, the non-cutting shaft 16 is subjected to radial compressive loads and thus deformations, which not only affects the milling accuracy but can also lead to a fracture of the shank 16.

The improved configuration of the milling tool 14 according to EP 2 540 427, which is shown in FIG. 3, brings about a certain remediation here, because there the shank 16 has a smaller diameter d3 than the cutting head 18, which projects radially beyond the shank 16, in height s. In this way, a non-cutting clearance 28 is formed up to the chucking end 26 of the milling tool 14, so that no radial compressive forces are generated during roughing or finishing. These occur only when the blade diameter d1 gradually decreases when the milling tool 14 is axially fed until it reaches the dimension d3, so that the non-cutting longitudinal region of the clearance 28 causes a radial pressing.

The design of the cutting head 18 of the milling tool 14 according to the invention results from FIGS. 4 and 5. In particular, FIG. 5 shows that the cutting head 18 has, at its tip, a cutting region having the length L2 and the diameter d1, which is used for finishing a previously roughened upper part 12 of a workpiece 10 (cf. FIG. 1). The length L2 corresponds to the maximum feeding of the milling tool 14 during the finishing.

At point W1, the cutting head 18 transitions into the segment 24 having the length L2.2−L2=L2.1, the diameter d4 of which is somewhat (for example, approximately 0.05 mm) smaller than the diameter d1 of the cutting region L2. According to the invention, the segment L2.2−L2=L2.1 is configured in a cutting manner and is used for roughing milling of the workpiece.

Only at the circumference W2, a vacant, non-cutting clearance segment 28 having the once more reduced diameter d3 extends over the length L3−L2.2 of the shaft 16 up to the beginning of the chucking end 26. The chucking end 26 then has an identical or somewhat larger diameter d2.

Both the cutting head 18 and the roughing segment 24 can be coated with hard mineral, for example diamond, over their length L2 or L2.2−L2=L2.1.

Claims

1. Milling tool made of cemented carbide, having a cylindrical shaft (16) and a cutting head (18) for the face milling of workpieces made of hard-brittle material, wherein the cutting head (18) is configured as an end mill with corner radius or a ball nose end mill having a cutting length, and the shank (16) has, up to its chucking end (26), at least one clearance segment (28) having a smaller diameter (d3) than the cutting head (18), characterized in that the tip of the cutting head (18) is coated or tipped with a hard mineral along a length (L2) having a diameter (d1) that is used for finishing, to which is connected a segment (24), which is used for roughing, having the cutting length (L2.2−L2=L2.1) and a reduced diameter (d4), which is smaller than the diameter (d1) of the cutting length (L2) on the cutting head (18) used for finishing and is greater than the diameter (d3) of the clearance segment (28).

2. Milling tool made of cemented carbide according to claim 1, characterized in that the cutting length (L2.1) used for roughing is also coated or tip with hard mineral.