WO2018162321A1 - Cutting element for a machining tool and method for producing such a cutting element - Google Patents

Abstract

The invention relates to a cutting element for a machining tool, in particular a milling tool (1), which has at least one chip-removing cutting edge (13), wherein the cutting element (5) has a sintered base body (15), in which diamond grains (17) are embedded in a metallic binder (19), in particular made of cobalt or a cobalt alloy. According to the invention, the sintered base body (15) has a layered structure (20) with at least a cobalt-free or binder-free outer diamond layer (21) of diamond grains (25), which covers the base body (15) with a closed surface at least in the region of the cutting edge (13).

Description

 Cutting element for a chip processing tool and method for producing such a cutting element

The invention relates to a cutting element for a chip processing tool according to the preamble of claim 1 and to a method for producing such a cutting element according to claim 6.

Made of PCD (polycrystalline diamond) inserts or

Cutting elements are used in the milling of non-ferrous

Workpieces, in particular made of aluminum alloys used. Such PCD cutting elements have a sintered base body, in which a synthetically produced, extremely hard mass of diamond particles with random orientation in a metal matrix (hereinafter also called metallic binder) is embedded. As a metallic binder, cobalt or a cobalt alloy is exemplified. The grain size of the embedded in the metal matrix diamond grains can be exemplified in the μιτι- range, approximately between 2 μιτι to 100 μιτι, lie. In the sintering process, a metal-graphite mixture is subjected to a very high process pressure as well as a high process temperature, forming a porous diamond network in which the diamond grains are relative to their grain size

small-area sintered necks are chemically bound. The remaining pores are filled with the metallic binder. The diamond grains cause an increased hardness of the cutting element, while the cobalt-containing

Binder matrix gives the cutting element the required toughness.

The service life of a PCD cutting element depends on the material strength of the workpieces to be machined. With high material strength, the service life is correspondingly greatly reduced. From DE 10 2014 210 371 A1 discloses a cutting tool is known, the substrate surface not of PCD diamonds, but from

Carbide-based hard material particles, which are embedded in a cobalt-containing binder matrix. Immediately on the substrate surface, a diamond layer is applied. It has been shown that between the

Diamond layer and the carbide-based hard material particles one

Graphite layer can arise. In the machining process, this acts as a predetermined breaking point at which the diamond layer can chip off, which leads to a reduced service life.

The object of the invention is a cutting element for a

To provide chip machining tool, which is composed of a polycrystalline diamond (PCD) and its life, especially in the processing of non-ferrous metals, especially aluminum materials, increased in a simple manner.

The object is solved by the features of claim 1 or 6. Preferred embodiments of the invention are disclosed in the subclaims.

The invention is based on the finding that in the milling of an aluminum workpiece by means of PCD cutting elements, a chemical affinity of cobalt, which is contained in the metal matrix, to the aluminum is present. This means that at a correspondingly high cutting temperature, cobalt diffuses out of the PCD cutting element into the aluminum material. The chemical affinity increases with increasing cutting temperature. This reaction increases the friction between chip and cutting edge. The cutting edge is therefore exposed to increased mechanical stress, which requires increased cutting edge strength. The removal of the metallic binder phase, however, leads in addition to a Strength reduction of the cutting edge, due to the exposure of the porosity of the PCD structure. With increasing strength of the too

machined material thus increases the tendency for edge fractures on the tool.

Against this background, according to the characterizing part of

Claim 1, the sintered body to increase the Schneidelement- wear resistance on a layer structure with at least one cobalt-free or binder-free diamond layer of diamond grains, which covers the sintered body at least in the region of the cutting edge closed area. With the aid of the diamond layer, a direct contact of the metallic binder with a material to be processed is thus avoided in the cutting process. Diffusion of the metallic binder from the cutting element into the material to be processed (due to chemical affinity) is therefore prevented, whereby the service life of the tool is substantially increased compared to the prior art.

According to the invention, a completely new approach is thus taken in complete departure from the previous doctrine, in which "diamond on diamond" is applied directly, that is the diamond pore structure of the sintered cutting element main body in an additional

Application step is applied again with diamond grains.

Such a material order "diamond on diamond" has in comparison to the above prior art (that is, material deposition diamond on

Hard material particle substrate on a carbide basis) decisive advantages:

Thus, according to the invention, a graphite layer formation between the

Diamond layer and the substrate can be prevented. Rather, the material order "diamond on diamond" behaves like a consistent one material of the same material, whereby an extremely high adhesion of the diamond layer, without the risk of chipping, is achieved.

In addition, the diamond grains applied in the application step show a high tendency to completely fill in the remaining free spaces of the diamond pore structure, which further increases the layer adhesion strength. Furthermore, a substantially completely uniform layer thickness of

Diamond layer achieved, which reduces the extent of post-processing.

In addition, the material application "diamond on diamond" results in a - compared to the prior art - extremely low

Compressive residual stress of the diamond layer, which also has a positive effect on the layer adhesion. The low compressive residual stress enables a significantly increased layer thickness of the diamond layer compared to the prior art, without the risk of chipping. In addition, the penetration of the diamond layer into the pores between the PCD diamond grains leads to a multiplication of the diamond grain boundaries, which leads to a significant increase in strength.

Further aspects of the invention are described below: Thus, in a technical implementation, the diamond material of the diamond layer

material identical to the diamond material of the sintered body. In this way, layer adhesion of the diamond layer on the sintered base body is improved.

To further increase the layer adhesion and to form a coating which is as close as possible to the surface, it is preferred if the average grain size of the diamond bodies in the sintered base body is considerably larger than the grain size of the diamond grains in the sintered body Diamond layer. The diamond pore structure of the sintered body in this case is composed of diamond coarse grains, while in the

Application step diamond fine grains are applied. Accordingly, the diamond layer is composed of diamond fine grains whose

average grain size in the lower μηη range or especially even in the nm range can be. In contrast, the average grain size of the diamond coarse grains in the μηη range.

To further increase the adhesive strength, it is preferred if the

Layer structure of the sintered body additionally has a binder-free (that is, cobalt-free) intermediate layer which is disposed between the base body and the outer diamond layer.

The diamond bodies of the sintered base body form the already mentioned diamond pore structure whose interstices are filled with the metallic binder. In view of a simple formation of the above-mentioned intermediate layer, it is preferred if in the near-surface region of the diamond pore structure of the metallic binder is replaced by a filler material to achieve a further additional separation between the metallic binder and the material to be processed. With regard to a simple production of the intermediate layer, it is preferred if the

Filling material is formed directly by the diamond grains of the diamond layer. In this case, the method for producing a cutting element can be carried out as follows: For example, in a sintering process step known from the prior art, a sintered base body can be produced in which diamond grains are embedded in the metallic binder. It is important that a sufficient number of diamond-diamond grain boundaries are formed in the sintering process, so that after the Wegätzen the metallic binder (that is, the binder / filler phase) is still a certain strength of the remaining PCD composite exists.

Subsequently, an etching step can take place in which the metallic binder is removed from the near-surface region of the base body to form a near-surface open pore structure in the sintered base body.

Subsequently, an application step can take place in which the

Diamond layer is applied in particular by a chemical vapor deposition (CVD) on the sintered body. In this case, the applied diamond grains are first infiltrated as filler in the near-surface open pore structure of the sintered body, whereby the intermediate layer is formed. As the CVD application progresses, the applied diamond grains build up the outer diamond layer.

After the application of the intermediate layer and the diamond layer may optionally be carried out a post-processing step in which, for example, by a grinding process material is removed to a final dimension of the cutting element. The layer thickness of

Diamond layer is preferably dimensioned such that the in

Post-processing step taking material removal smaller than the

Layer thickness of the outer diamond layer is.

An exemplary embodiment of the invention is described below with reference to the attached figures:

Show it FIG. 1 shows a side view of a milling tool;

Figure 2 is a greatly enlarged sectional view through a

 Cutting element along the cutting plane A-A of Figure 1;

Figures 3 to 6 are views corresponding to the figure 2, the

 Process steps for producing a cutting element shown in Figure 2 illustrate.

In the figure 1 a milling tool 1 is shown by way of example, the

Tool axis W perpendicular to a machined

Workpiece surface 3 is aligned. The milling tool 1 has

circumferentially evenly distributed cutting elements 5 on. These are on the outer circumference with peripheral cutting 7 (Figure 2) and the front side on

Milling tool 1 formed with end cutting, which are facing the workpiece surface 3. In the illustrated milling operation, the milling tool 1 is driven with a rotational movement R about the tool axis W. In addition, the milling tool 1 is driven with a feed movement V (FIG. 1) transversely to the tool axis W and along the workpiece surface 3. In this way, the milling tool 1 cuts the material mainly with the peripheral blades 7, while the end cutting scrape only the machined workpiece surface 9.

FIG. 2 shows the material structure of one of the cutting elements 5, specifically along the sectional plane A-A from FIG. 1. Accordingly, the cutting element 5 a leading in the direction of rotation R of the milling tool 1 rake face 9 and a trailing in the tool rotation R free space 1 1, which at a cutting edge 13 of

Peripheral cutting 7 converge. In the figure 2 is the cutting element 5 formed of a sintered base body 15, are embedded in the diamond coarse grains 17 in a metallic, cobalt-containing binder 19. The diamond coarse grains 17 are in point contact with each other, thereby forming a porous diamond network (hereinafter also diamond pore structure) in which the diamond grains are chemically bonded by sintering necks small in area relative to their grain size. The

remaining pores (or spaces) are filled with the metallic binder 19. On the sintered base body 15, a double layer structure 20 (Figure 2) is applied, which consists of a cobalt-free or binder-free outer

Diamond layer 21 and an intermediate layer 23 which is disposed between the outer diamond layer 21 and the sintered base body 15. The diamond layer 21 has a layer thickness S3 in FIG. 2, which includes the sintered base body 15 and the intermediate layer 23

Covered closed. In this way, a direct contact of the cobalt contained in the metallic binder 19 is avoided with the machined aluminum material of the workpiece 3 in the machining process. The diamond layer 21 is formed of fine diamond grains 25 whose average grain size is much smaller than the average grain size of the diamond coarse grains 17 in the sintered base body 15.

The binder-free (that is cobalt-free) intermediate layer 23 is in view of an increased adhesive strength of the diamond layer 21 and for a

Increasing the strength of the PCD composite (that is, the base body 15) provided. In the intermediate layer 23, the diamond pore structure in the near-surface region of the sintered base body 15 is no longer filled with the metallic binder 19, but rather is replaced by the diamond fine grains 25 of the diamond layer 21. The diamond Fine grains 25 of the diamond layer 21 are therefore infiltrated as Füllmate al in the near-surface diamond pore structure of the sintered body 15.

Hereinafter, with reference to the figures 3 to 6, the process steps for

2 illustrates the sintered base body 15 in a sintering process. The starting component for the

Sintering process forms a metal-graphite mixture, which is exposed to a very high process pressure and a very high process temperature. In this way, the diamond pore structure is formed with the diamond coarse grains 17, which are completely embedded in the metallic binder 19.

Subsequently, in FIG. 4, an etching step takes place. In the etching step, a near-surface open diamond pore structure 27 in the sintered

Base 15 formed by the metallic binder 19 is etched away from a near-surface region of the sintered body 15. The open diamond pore structure 27 has a layer thickness s1 in FIG.

By way of example, WO 2004/031437 A1 discloses such an etching step (in order to produce a sufficient layer adhesion of the diamond layer to hard metal). From DE 195 22 371 A1 it is likewise known to provide a cobalt-selective etching step with subsequent cleaning of the etched substrate surface prior to the application of a diamond layer. In the same way, a method for diamond coating of a cemented carbide substrate is known from US 6 096 377 A1, in which a

Cobalt selective etching step is used. From WO 2004/031437 A1, moreover, a chemical etching step is known in which the metallic binder, in particular the cobalt contained therein, is removed. This is followed by an application step (Figure 5), in which the sintered

Base body 15 with the binder-free, that is cobalt-free diamond layer 21 is coated. The application step is carried out by depositing a polycrystalline diamond film by chemical vapor deposition (CVD). Such a method is known, for example, from US Pat. No. 5,082,359 A. WO 98/35071 A1 likewise discloses depositing a polycrystalline diamond film on a cemented carbide substrate made of a tungsten carbide embedded in a cobalt matrix (WO 2004/031437 A1).

The application step according to FIG. 5 is carried out in two stages: First, the diamond fine grains 25 are infiltrated as filling material into the open pore structure 27 of the sintered base body 15, whereby the intermediate layer 23 is formed. In the further course of the CVD application, the diamond layer 21 is then built up with a layer thickness S2 by the diamond fine grains 25.

Optionally, a shown in the figure 6 below

Post-processing step carried out, in which a material removal Δχ takes place in a grinding process in order to produce the cutting element 5 to a final dimension. The material removal Δχ is smaller in FIG. 6 than the layer thickness S3 of the diamond layer 21. In this way, it is ensured that a residual layer thickness S3 of the diamond layer 21 remains even after the finishing, in order to reliably prevent a diffusion of cobalt into the aluminum material of the workpiece 3.

In summary, according to the invention, an adhesive, preferably sub-μηη crystalline diamond layer 21 on the PCD cutting element

deposited to the strength of the cutting element to the Increase cutting edges. The layer thickness of the diamond layer 21 can be, for example, 7 μm, a perfect layer connection being achieved without the risk of spalling. Due to the material identity between the diamond layer 21 and the diamond pore structure in the intermediate layer 23 and in the sintered base body 15 results in the diamond layer 21 an extremely low compressive residual stress, whereby the diamond layer 21 can be applied significantly thicker than in a comparable sintered body made of hard metal without this being critical for the stability of the cutting edge.

Claims

claims Cutting element for a chip processing tool, in particular a milling tool (1) having at least one cutting edge (13), wherein the cutting element (5) has a sintered Base body (15), wherein the diamond coarse grains (17) in a metallic binder (19), in particular of cobalt or a Cobalt alloy, embedded, characterized in that to increase the wear resistance of the sintered base body (15) has a layer structure (20) with at least one cobalt-free or binder-free outer diamond layer (21) of diamond fine grains (25), at least in the region of the cutting edge (13) covering the base body (15) closed area, and that by means of the diamond layer (21) in the chip machining direct contact of the metallic binder (19) is avoided with a material to be machined that the average grain size of the diamond coarse grains (17) in the sintered base body (15) is larger than the average grain size of the diamond fine grains (25) in the diamond layer (21), and that the layer structure (20) of the Base body (15) has a binder-free or cobalt-free intermediate layer (23) between the base body (15) and the Diamond layer (21) is arranged, and that the binder-free or cobalt-free intermediate layer (23) consists of both the diamond coarse grains (17) of the sintered base body (15) and from the diamond coarse grains (25) of the diamond layer (21). Cutting element according to claim 1, characterized in that the diamond material of the diamond layer (21) is material identical to the diamond material of the sintered base body (15), and in particular that the diamond material is PCD. Cutting element according to claim 1 or 2, characterized in that the diamond coarse grains (17) of the sintered base body (15) form a diamond pore structure, whose interstices are filled with the metallic binder (19), and that for forming the intermediate layer (23 ) in the near-surface region of the diamond pore structure, the metallic binder (19) is replaced by a filler material, and that the filler material is the diamond fine grains (25) of the diamond layer (21). Method for producing a cutting element (5) according to one of the preceding claims, comprising a sintering process step in which a base body (15) is sintered in the diamond coarse body (17) in a metallic binder (19), in particular of cobalt or cobalt alloy , are embedded, and with a subsequent application step, in which the sintered base body (15) is coated with a cobalt-free or binder-free diamond layer (21) of diamond fine grains (25), wherein before carrying out the application step, a pretreatment step, in particular Etching step, takes place, in which, forming a near-surface open pore structure (27) of the metallic binder (19) from a near-surface region of the base body (15) is removed, wherein after the pretreatment step, a filling step takes place in which the open pore structure (27) of Basic body (15) with a Filling material is filled, with the formation of a Intermediate layer (23), and wherein the filling step and the Application step are carried out together, the Diamond fine grains (25) of the diamond layer (21) first as Filling material are infiltrated into the open pore structure (27) of the main body (15), to form the intermediate layer (23), and then in the further course of the application of the diamond fine grains (25) build up the outer diamond layer (21). A method according to claim 4, characterized in that in the application step diamond grains, in particular diamond fine grains (25), to form the diamond layer (21) by a chemical vapor deposition (CVD) on the sintered base body (15) is applied. Method according to one of claims 4 or 5, characterized characterized in that in a post-processing step, a post-processing of the cutting element (5), in particular a Grinding, with a material removal (Δχ) takes place to a final dimension of the cutting element (5), and that in particular the Material removal (Δχ) smaller than the layer thickness (S3) of Diamond layer (21) is.