DE212010000118U1 - Coated tool - Google Patents

Abstract

End mill or drill made of solid carbide for machining or drilling fiber-reinforced materials or printed circuit boards provided with a CVD diamond layer, characterized in that this has an odd number of main cutting edges at least in one plane perpendicular to its axis of rotation.

Description

The invention relates to coated tools, in particular end mill for machining or drill for drilling fiber-reinforced materials such as circuit boards for electronics, which may also be constructed in several layers or are already laminated with printed conductors. For such boards has also come from the English term PCB ("Printed Circuit Board"). The corresponding end mills are sometimes referred to as routers. They are available, for example, in spiral-toothed or diamond-toothed form.

In particular, the invention deals with solid carbide end mills or drills with a CVD diamond coating.

The PCBs are often made of epoxy laminates. But the tool according to the invention is also suitable for other materials, especially for materials that include, for example, layers of glass or carbon fibers in a specific matrix.

The materials mentioned are extremely abrasive and quickly lead to uncoated tools failure of the tool and / or poor workpiece surfaces. Even conventional PVD and CVD layers fail early.

It is therefore known to provide such tools on the functional surfaces, in particular the cutting edges, with a diamond layer. A known method here is the application of a diamond layer by means of a CVD (chemical vapor deposition) process. Such a coating method is z. B. in the WO 98/35071 described.

The layer grows in the said method directly on the substrate. It is diamond, ie crystalline carbon in sp ₃ bond. In addition to unavoidable impurities, other carbon modifications can also be found along the crystallite boundaries. For the purposes of the invention, however, such layers are also understood as CVD diamond layer, which consist predominantly of diamond, especially to over 70 vol.%.

However, since even the diamond is subject to rapid wear in the applications considered, relatively high layer thicknesses must be applied in order to increase the service life of the tool.

However, a high layer thickness in turn causes a higher rounding of the cutting edge. Because the coating processes provide the substrate with a relatively uniform layer thickness, which causes the cutting edge radius to increase approximately by the thickness of the diamond coating.

However, higher cutting edge radii are particularly disadvantageous in the machining of fiber-reinforced materials, since here the fibers should be cut as smoothly as possible in order to avoid fraying on the machined workpiece surfaces and to avoid the stresses of the material composite by increased cutting forces. Otherwise, this leads to a low quality of the machined surfaces and increased roughness. Furthermore, fibers u. U. also be torn out of the composite and also lead at a greater distance to the machined surface to weaken the material.

To solve this dilemma, it has been proposed to postprocess the diamond layer on the sheaths. As a method laser ablation and plasma etching are known here. In addition to the high cost, it is particularly disadvantageous here that the diamond layer must first be deposited substantially thicker in order to create a corresponding processing reserve. This again requires a more intensive pretreatment and long coating times. The coating times are already comparatively long and a significant cost factor because of the peculiarities of the CVD diamond coatings on hard metals. The rework is particularly complex especially for small tools and / or tools with complex geometry. A post-processing by grinding method has comparable night parts and was, u. a. Because of the high hardness of diamond, on CVD diamond coated tools so far unsuccessful. Higher layer thicknesses also require more intensive pretreatment, ie a deeper etching away of the hard metal components on the surface, which further increases the cutting edge radius.

It is an object of the invention to propose an advantageous and cost-effective design of the tool and the diamond coating, wherein the tool has an increased load capacity and a long service life when machining the materials mentioned, without resulting in a reduced surface quality of the machined surfaces.

This object is achieved by a coated tool according to claim 1. Dependent claims relate to advantageous embodiments of the invention.

In the case of diamond-coated milling cutters or drills, it has surprisingly been found in the applications considered that an uneven number of cutting edges increases the service life.

The reason of the odd-numbered cutting advantage is not completely clear. Perhaps it is because in even-numbered cutting an elongated fiber strand usually has to be cut simultaneously by two opposing cutting and thus larger maxima occur in the cutting forces.

It has been found worthwhile that considerable service life can be achieved even with small layer thicknesses if the number of cutting edges is increased. This is especially apparent when the number of edges is five or more, especially seven or more, compared to the adjacent even number of edges. The number of cutting edges 7 showed particularly good results.

The upper limit for the number of cutting edges is not limited in principle. However, the chip spaces become flatter with increasing number of cutting edges. It is u. U. attached that the chip space has sufficient space for a fiber bundle or at least one fiber. Ie. the depth of the chip space should preferably be greater than or equal to the diameter of a fiber bundle or the fiber.

Since the chip space must remain free between two cutting edges, the cross section of a multi-bladed tool with the same functional diameter has more tool material. This constitutes a further advantage of the invention since it reduces the sensitivity to breakage, especially in the case of thin, diamond-coated solid carbide tools.

In a 2-flute tool with a layer thickness of 30 microns, it has a wear volume of about 60 microns. But a cutting edge rounding of more than 30 μm has to be accepted. With a 7-edged tool of 9 μm, the same wear volume is easily obtained, but only an edge rounding of approx. 9 μm must be accepted. A more general rule for the number of blades and associated layer thicknesses can be found in the claims.

Above all, end mills in the range of 1 to 2 mm were tested positive. But an improvement was also noticeable in other diameter ranges.

Particularly preferred are helical cutters. These have spiral-shaped rake surfaces, are ground into the additional notches for chip breaking.

As the substrate material, hard metals and cermets are considered within the scope of the present invention, i. H. Sintered materials of hard material particles and binder material, in particular with WC grains in a Co-containing matrix. Preferably, WC-Co hard metals containing less than 2% by weight, more preferably less than 1% by weight of other ingredients are used. The cobalt content of the hard metal is preferably from 6 to 12% by weight, more preferably up to 9% by weight. The average WC grain size is preferably less than or equal to 1 .mu.m, more preferably less than or equal to 0.5 .mu.m.

In order to achieve a good adhesion of the diamond coating on the substrate, various pretreatment methods are known. It is common that the binder of the substrate, especially cobalt, is removed from the surface. During the long process times and high temperatures in the CVD diamond coating, harmful interactions occur between the carbon that is to form the diamond layer and the cobalt. This prevents diamond formation, and instead leads to graphitic phases. The removal of the cobalt can be carried out, for example, with the aid of acids. Thin interlayers that prevent the direct contact of cobalt and diamond can also be used.

It was found that the removal of the cobalt can be inventively lower than in the conventional art. In particular, the cobalt needed to be removed only to a depth of 1.8 to 3.2 microns. This further contributes to a reduction of the cutting edge rounding and preserves the ductility of the substrate. The reason is likely that the cutting forces and layer thicknesses turn out lower in the above-mentioned inventive measures.

The diamond layer according to the invention preferably contains fine-crystalline or nanocrystalline diamond. Such layers are smoother and cut the fibers more effectively and with lower cutting forces. Layers of several individual layers, which contain different crystallite sizes and / or different proportions of carbon in non-diamond configuration, have particular advantages, since stress resulting from stress is deflected at the boundaries of the individual layers and does not reach the critical substrate-layer interface. The thickness of the entire diamond layer can be 1 to 15 μm at the cutting edges. Particularly good results could be achieved with layer thicknesses of 8 to 10 μm.

The coating is necessary especially on the cutting edges. But it can also include the entire function of the tool.

Ground tools have, after coating, a cutting edge radius at least equal to the diamond layer thickness. However, the ratio of edge radius to layer thickness should remain low. Numerous figures can be found in the claims.

A milling cutter may be formed at its tip as a drill preferably with fishtail geometry, so that a pre-drilling for internal milling paths can be omitted or to allow easier dipping.

The advantages of the invention mentioned apply analogously to drills. However, particularly in the case of holes for PCBs or printed circuit boards, even very small diameters are technically desirable, for example, from below 1 mm or 0.5 mm, or even with a diameter of less than or equal to 0.2 mm. The smaller diameter compared to milling cutters are possible because during drilling, there are hardly any forces transverse to the longitudinal direction of the tool which could cause a breakage.

Embodiments of the invention will be described in more detail with reference to drawings.

1 shows the cross section through a cutter with 5 cutting edges;

2 shows the longitudinal view of a 5-edged cutter with fishtail bevel;

3 shows the cross section through a cutter with 7 cutting edges and

4 shows the longitudinal view of a 5-edged spiral-toothed fishtooth bevel.

An in 1 and 2 illustrated 5-edged cutter 10 has five cutting edges 12 on.

In a second embodiment of a 5-edged milling cutter 20 ( 4 ), the cutting edges are spiral-toothed, namely with notches 22 provided for chip breaking.

Only notches are drawn near the router tip. Preferably, the entire function has notches.

Finally shows 3 a third embodiment of a cutter with 7 cutting edges 12 ,

As from the comparison of 1 and 3 recognizable, the cross section of a multi-bladed tool with the same functional diameter more tool material.

All tools are first chemically pretreated and then subjected to a CVD diamond coating with nanocrystalline diamond. At the cutting edges, the layer thickness is 12 or 9 μm.

When processing printed circuit boards, a 5-flute milling cutter with a 12 μm thick CVD diamond layer shows better service life than a 6-flute with the same thickness. The best service life was achieved with a 7-flute tool with 9 μm layer thickness.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 98/35071 [0005]

Claims (20)

Solid carbide end mill or drill bit for machining or drilling fiber-reinforced materials or printed circuit boards provided with a CVD diamond layer, characterized in that it has an odd number of main cutting edges at least in a plane perpendicular to its axis of rotation. End mill or drill according to claim 1, characterized in that the number of main cutting edges is 5 and more, preferably 7 and more, more preferably 7. End mill or drill according to one of the preceding claims, characterized in that the thickness of the diamond layer is 1 to 15 microns, preferably 6 to 12 microns, more preferably 8 to 10 microns. End mill according to one of the preceding claims, characterized in that the functional diameter without the coating is 0.5 to 6 mm, preferably 1 to 2.5 mm. End mill or drill according to one of the preceding claims, characterized in that the product of the number of cutting edges multiplied by the layer thickness at the cutting edge at least 28 microns, preferably at least 42 microns, more preferably at least 56 microns to at most 98 microns, preferably at most 84 microns, most preferably highest 70 microns. End mill according to one of the preceding claims, characterized in that the tip of the end mill is designed as a drill, preferably as a fishtail drill. End mill or drill according to one of the preceding claims, characterized in that the quotient of edge radius by layer thickness in the coated tool is less than 1.5, preferably less than 1.2, particularly preferably 1 to 1.1. End mill or drill according to one of the preceding claims, characterized in that the fiber-reinforced materials consist of epoxy laminates. End mill or drill according to one of the preceding claims, characterized in that the materials include glass fibers and / or carbon fibers. End mill or drill according to one of the preceding claims, characterized in that the hard metal consists of WC and Co with a maximum of 2 wt.% Of further admixtures, preferably with a maximum of 1 wt.%. End mill or drill according to one of the preceding claims, characterized in that the hard metal has a mean WC grain size of less than or equal to 1 .mu.m, preferably of less than or equal to 0.5 microns. End mill or drill according to one of the preceding claims, characterized in that the diamond layer has at least one layer of fine crystalline diamond having an average particle size of less than or equal to 3 μm, preferably less than or equal to 1.5 μm. End mill or drill according to one of the preceding claims, characterized in that the diamond layer has at least one layer of nanocrystalline diamond having an average particle size of less than or equal to 100 nm, more preferably less than or equal to 50 nm. End mill or drill according to one of the preceding claims, characterized in that the diamond layer is multi-layered. End mill or drill according to one of the preceding claims, characterized in that the cobalt content of the hard metal is reduced before the diamond coating in the surface region, preferably to a depth of up to 5 microns, more preferably to a depth of 1.8 to 3.2 microns. End mill or drill according to one of the preceding claims, characterized in that between carbide substrate and diamond layer is a metal-containing intermediate layer to improve the adhesion of the diamond layer. End mill or drill according to one of the preceding claims, characterized in that the number of main cutting edges is more than 9, preferably more than 11, particularly preferably more than 13. End mill according to one of the preceding claims, characterized in that the end mill is spiral-toothed. Drill according to one of the preceding claims, characterized in that the functional diameter without the coating is less than 1 mm, preferably less than 0.5 mm, particularly preferably less than or equal to 0.2 mm. Use of a milling cutter or drill according to one of the preceding claims in the machining or drilling of PCBs or printed circuit boards.

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