Film cutting tools

Abstract

This invention provides a ball end mill that extends tool life by maintaining the sharpness of the cutting edge where the diamond film is formed for an extended period. [Solution] In the cutting edge, an inhibitory region (a region containing a cobalt-containing metallic phase) that inhibits particle growth of the diamond film 17 or bonding with the constituent elements of the diamond film 17 exists only on the rake face 11', while a deinhibition region (a region treated with decobalt removal) 14 exists on the surface of the cutting edge and flank face. As a result, only the diamond film 17 on the rake face 11' peels off, and the sharpness of the cutting edge can be maintained for a longer period.

Description

Technical Field

[0001] The present invention relates to a coated cutting tool in which a carbon film is coated on the surface of the cutting edge portion of a cutting tool.

Background Art

[0002] In cutting applications that require high durability and accuracy, a coated cutting tool in which a diamond film having a much higher hardness and friction characteristics than a titanium-based metal film is coated on a tool substrate is often used. However, the diamond film does not have sufficient affinity with metal elements contained in cemented carbide or the like, for example, cobalt or a cobalt alloy. Therefore, when a diamond film is grown on the surface of a tool substrate containing these metal elements, the adhesion at the interface is poor, and the diamond film is likely to peel off from the tool body.

[0003] As a means for improving such a problem, a technique is disclosed in Patent Document 1 in which a depression is provided on the surface of the tool substrate facing the diamond film, so that a large number of diamond crystal nuclei are easily generated in the depth direction of the tool substrate during film formation, thereby enhancing the adhesion between the diamond film and the tool substrate.

[0004] Also, a technique for improving the adhesion between a diamond film and a tool substrate is disclosed in Patent Document 2 by forming a partial metal bond phase removal region in which a part of a metal bond phase mainly composed of cobalt is removed from the interface (the outermost surface) of the tool substrate on which the diamond film is formed toward the inside (depth) of the tool substrate before forming the diamond layer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The thickness of the diamond film, which is a crystalline film, ranges from several micrometers to tens of micrometers. Therefore, in small-diameter end mills, such as those with a tip radius of R1 (1 mm) or less, the curvature of the diamond film at the cutting edge (the ridge between the rake face and the flank face) becomes excessive, making it prone to peeling. When the diamond film at the cutting edge peels off, the cutting edge deforms rapidly due to wear, and then the diamond films on the rake face and flank face also peel off rapidly in a chain reaction, eventually causing the entire cutting edge to deform and rendering the tool unusable.

[0007] The technologies disclosed in Patent Documents 1 and 2 both contribute to improving the adhesion of the diamond film to the cutting edge, thereby extending tool life, but the diamond film at the cutting edge is still the first to peel off. Therefore, they cannot maintain the sharpness of the cutting edge for an extended period.

[0008] One of the objectives of the present invention is to provide a coating cutting tool that can maintain the sharpness of the cutting edge portion on which the crystalline film is formed for a long period of time while ensuring adhesion to the crystalline film. Other issues of the present invention will become clear from this disclosure. [Means for solving the problem]

[0009] One aspect of the present invention is a coating cutting tool in which a crystalline film is formed on the surface of the cutting edge, wherein inhibiting regions that inhibit particle growth of the crystalline film or bonding with constituent elements of the crystalline film are present only on the rake face of the cutting edge. However, there may be a configuration in which a deinhibition region exists on the surface of the cutting edge portion other than the rake face that maintains or promotes particle growth or bonding. [Effects of the Invention]

[0010] According to the above embodiment, only the crystalline film formed on the rake face peels off during cutting, and as a result, the cutting edge formed on the ridge between the rake face and the flank becomes sharper and relatively harder than the tool substrate due to the remaining crystalline film, and the adhesion of the crystalline film to parts other than the rake face can also be ensured. [Brief explanation of the drawing]

[0011] [Figure 1] A procedure diagram illustrating the general method for manufacturing coated end mills. [Figure 2] (a) to (c) are schematic diagrams showing the surface state of the tool substrate before coating of the coated end mill. [Figure 3] A schematic diagram showing the surface state of the tool substrate after film deposition. [Figure 4] A schematic diagram showing the surface condition of the tool base of a comparative end mill. [Figure 5] (a) and (b) are micrographs showing the peeling state of the diamond film in the comparative end mill, and (c) is a schematic cross-sectional view of (a) along A-A'. [Figure 6] (a) and (b) are micrographs showing the peeling state of the diamond film in the coated end mill according to this embodiment, and (c) is a schematic cross-sectional view of (a) along A-A'. [Modes for carrying out the invention]

[0012] The following describes an example of an embodiment in which the present invention is applied to a ball end mill coated with a diamond film. However, it can be similarly applied not only to ball end mills but also to other types of end mills and drills. In this embodiment, an example of a manufacturing method for a coated end mill in which a diamond layer is formed on the surface of a ball end mill will be described. First, an overview of the overall process according to this embodiment will be described with reference to Figure 1.

[0013] [Tool base manufacturing] In this embodiment, first, a ball end mill before film formation is manufactured (S101). For convenience, the substrate of the ball end mill before film formation is referred to as a "tool substrate". The tool substrate is a cemented carbide substrate containing an alloy mainly composed of tungsten carbide (WC) as a hard phase component and cobalt (Co) as a metal bonding phase component, and a predetermined number of cutting edge portions that contact the workpiece are formed at its tip portion. Each cutting edge portion has a cutting edge (edge) that is the intersection ridge line between the rake face and the flank face. The size of the tool substrate is R0.5, that is, a so-called small diameter with a tip radius of 0.5 mm in one cutting edge portion.

[0014] [Inhibition Region Removal] As described in Patent Documents 1 and 2, in a tool substrate made of cemented carbide, it is known that a metal bonding phase component mainly composed of cobalt (Co) inhibits the bonding with the constituent elements of the diamond film, and sufficient adhesion cannot be ensured. In this specification, the region where such a metal bonding phase component exists is called an "inhibition region". In this embodiment, a process for removing the metal bonding phase component from such an inhibition region is performed on the entire cutting edge portion (S102).

[0015] The region formed by such a process is called a "deinhibition region". In the examples described in Patent Documents 1 and 2, the region formed by the "decobaltization process" corresponds to the "deinhibition region". The deinhibition region is formed at a depth exceeding 3 μm and not exceeding about 30 μm from the surface in a tool substrate with a small diameter of R0.5. If it is less than 3 μm, it is easily affected by the inhibition region, and the formation of the diamond phase film is inhibited. If it exceeds 3 μm, the influence by the inhibition region becomes small, but the toughness of the tool substrate decreases. Therefore, in a tool substrate with a small diameter of R0.5, about 30 μm is the upper limit value for a practical coated ball end mill. In this embodiment, a deinhibition region was formed on the entire cutting edge portion at a depth exceeding 3 μm and less than 30 μm.

[0016] [Partial Removal of Deinhibition Region] After forming a de-inhibition region on the entire cutting edge portion, the de-inhibition region on the rake face surface is removed (S103). Such partial removal of the de-inhibition region can be carried out, for example, using a commercially available CNC (Computerized Numerical Control) device. The depth of the de-inhibition region to be removed on the rake face may be the depth formed in S102, or may be less than that. For example, it may be less than 5 μm. As a result, on the rake face, the metal bond phase component that inhibits the bonding with the constituent elements of the diamond film becomes relatively more than that on the cutting edge and flank face of the cutting edge portion.

[0017] [Crystal film deposition] A diamond film is deposited on the tool body manufactured in the procedure of S103 (S104). The deposition of the diamond film can be carried out using known technical means such as a CVD device. The film thickness is 10 μm to 15 μm on average. Through the above steps, the coated end mill according to the present embodiment is completed.

[0018] [Surface state of cutting edge portion] Figs. 2(a) to 2(c) are schematic views showing the surface state of the tool substrate before film deposition of the coated end mill 10 according to the present embodiment, and Fig. 3 is a schematic view showing the surface state of the tool substrate after film deposition. Fig. 2(a) corresponds to the step of S101. The tool substrate has a rake face 11, a cutting edge (edge) 13, and a flank face 12 formed at its tip portion. In each of the schematic views, for the sake of convenience of explanation, both the rake face 11 and the flank face 12 are represented as planes, but they may be curved surfaces.

[0019] Fig. 2(b) corresponds to the step of S102. That is, a de-inhibition region 14 is formed at a substantially uniform depth starting from the surfaces of the rake face 11, the cutting edge 13, and the flank face 12 respectively. As a result, the metal phase component mainly composed of cobalt that inhibits the deposition of the diamond film 17 in Fig. 4 is removed, and the adhesion between the surfaces of the rake face 11, the cutting edge 13, the flank face 12 and the diamond film can be ensured.

[0020] Figure 2(c) corresponds to step S103. Specifically, it shows the state in which only the de-inhibition region 14 formed on the rake face 11 has been removed from the rake face 11, 13, and flank face 12 of the tool body. Note that it is not necessary for all of the de-inhibition region 14 formed on the rake face 11 to be removed, but from the viewpoint of enhancing the effects (advantages) described later, it is desirable for all of the de-inhibition region 14 to be removed.

[0021] Figure 3 corresponds to step S104. Specifically, it shows the state in which the diamond film 17 has been deposited on the entire surface of the cutting edge portion, after the deinhibition region 14 of the rake face 11 has been removed.

[0022] [Comparative example: End mill] The inventors created a comparative end mill for tool performance comparison in which step S103, i.e., partial removal of the de-inhibition region, was omitted from steps S101 to S104. The size and material of the tool base, the shape and structure of the cutting edge, the depth of the de-inhibition region, and the conditions for forming the diamond film are the same as those of the coated end mill 10 according to this embodiment.

[0023] Figure 4 is a schematic diagram showing the state of the cutting edge surface of comparative example end mill 20 with a diamond film deposited on it. Compared with the coated end mill 10 according to this embodiment, the difference is that the diamond film 17 was deposited on the cutting edge surface with a de-inhibition region 14 formed, as shown in Figure 2(b).

[0024] [Tool performance comparison] Next, we will explain an example of how the wear state of the cutting edge changes when the coated end mill 10 according to this embodiment and the comparative example end mill 20 are used to machine a common workpiece, for example, a plate-shaped ultra-fine-grained material AF312 (carbide alloy for molds), under the following common cutting conditions. <Cutting conditions> • Machining shape: Concave cylinder with a diameter of φ6.0 and a depth of 0.75 [mm] ·Processing method: Contour roughing Tool rotation speed: 30,000 [min] -1 ] Feed rate: 300 [mm / min] • Cutout: ap×ae: 0.02 [mm] × 0.1 [mm] • Coolant: Oil mist

[0025] <Changes in wear and tear> Figure 5(a) is a magnified view of the cutting edge surface of the comparative example end mill 20 when delamination occurs in the diamond film, Figure 5(b) is a view of the cutting edge surface at the tip, and Figure 5(c) is a schematic cross-sectional view (A-A') of the same (a).

[0026] As is clear from these figures, in the comparative example end mill 20, the diamond film peels off mainly around the cutting edge 13 as the cutting process progresses. This is partly because the thickness of the diamond film is relatively large compared to the cutting edge 13, and the diamond film on the surface of the cutting edge 13, the diamond film on the surface of the rake face 11, and the diamond film on the surface of the flank face 12 are integrated. As a result, the diamond film on the surfaces of the rake face 11 and the flank face near the cutting edge 13 peels off in a disorderly manner almost simultaneously with the diamond film on the surface of the cutting edge 13 in the early stages of cutting.

[0027] In Figures 5(a) to (c), reference numeral 111 represents the remaining portion of the diamond film deposited on the surface of the rake face 11 at the start of peeling, and reference numeral 121 represents the remaining portion of the diamond film deposited on the surface of the flank face 12. As shown in Figure 5(a), the remaining portions of the diamond film 111 and 121 are not caused by wear resulting from contact with the workpiece, and therefore a step difference is created between the rake face 11 and the flank face 12. If cutting continues in this state, the peeling of the diamond film 17 will progress rapidly and in a chain reaction, causing the entire cutting edge to lose its shape and immediately ending the tool's lifespan. Furthermore, the amount and rate of reduction of each remaining portion 111 and 121 vary greatly from one individual to another. As a result, the machining accuracy of the workpiece and the tool performance are not stable, making it difficult to predict when to change tools.

[0028] In contrast, the coated end mill 10 of this embodiment converts the peeling of the diamond film, which is harder than the tool body, into an advantageous effect. Figure 6(a) is a magnified view of the cutting edge surface of the coated end mill 10 of this embodiment when peeling occurs in the diamond film, Figure 6(b) is a view of the cutting edge surface at the tip, and Figure 6(c) is a schematic cross-sectional view (A-A') of the same (a).

[0029] As shown in these figures, in the coated end mill 10 of this embodiment, the only area where peeling of the diamond film 17 begins is the portion of the rake face 11' closest to the cutting edge 13. Even if the diamond film 17 on the rake face 11' peels off, it does not significantly affect the machining accuracy of the workpiece, and the diamond film 17 remains on the cutting edge 13 while maintaining approximately the designed rake angle. This remaining diamond film 171 is much harder than the tool base and maintains a highly sharp shape. Therefore, even if the rake face 11' is exposed, stable cutting can be continued for a long period of time. Furthermore, the time it takes for the diamond film 17 to peel off from both the relief surface 12 and the cutting edge 13 is almost constant regardless of the individual piece, provided that the thickness of the diamond film 17 is constant. As a result, the machining accuracy of the workpiece and the tool performance are also stable.

[0030] Thus, with the coated end mill 10 of this embodiment, although only the diamond film 17 formed on the rake face 11' peels off in the initial stages of cutting, the remaining diamond film 17 not only makes the cutting edge 13 sharper but also allows it to maintain its sharpness for a long time, and also ensures good adhesion between the diamond film 17 and the parts other than the rake face 11'.

[0031] The above advantages of this embodiment can also be achieved by forming a de-inhibition region only in the portion other than the rake face 11 before the diamond film 17 is deposited. In short, it is sufficient for the inhibition region to exist only on the rake face of the cutting edge before the diamond film 17 is deposited. However, as in this embodiment, removing only the rake face 11 portion after forming a de-inhibition region across the entire cutting edge has the advantage of shortening the time required for the manufacturing process, suppressing individual variations in tool performance, and facilitating mass production. These advantages are even more pronounced in the case of small-diameter end mills.

[0032] [Differentiation] In this embodiment, the deinhibition region 14 formed in S102 was described as a region from which metal phase components that inhibit bonding with the constituent elements of the diamond film 17 have been removed. However, it may also be a process to remove metal phase components that inhibit particle growth of the diamond film 17.

[0033] In this embodiment, an example was described in which the tool substrate is made of cemented carbide, the crystal film is a diamond film, and the deinhibition region is a region from which the metal phase component mainly composed of cobalt has been removed. However, the present invention is generally applicable to combinations of materials that satisfy the relationship that the crystal film is made of a material harder than the material of the tool substrate, and that there is a component at the interface of the tool body (the surface of the tool body that is in contact with the crystal film) that inhibits adhesion with the crystal film.

[0034] In this embodiment, a step of forming a de-inhibition region, i.e., a de-cobalt treatment (S102), after manufacturing the ball end mill before film deposition (S101) has been described. However, a treatment step may be added prior to step S102. For example, the entire surface of the cutting edge may be subjected to mechanical etching, chemical etching, ultrasonic cleaning, oxide removal, or a combination thereof, i.e., a surface treatment. This removes impurities and oxides from areas other than the rake face, which will be removed later, allowing the cobalt removal process to proceed evenly and suppressing wear of the diamond film on the cutting edge and flank.

[0035] Mechanical etching can be performed, for example, by blasting (such as shot blasting) or surface polishing using abrasives. Chemical etching can be performed by alkaline cleaning or acid pickling. Ultrasonic cleaning can be performed by removing fine dirt and oil using an ultrasonic cleaner. Oxide removal can be performed using specialized acid cleaning.

[0036] Furthermore, although this embodiment describes an example of a small-diameter ball end mill with a tool base size of R0.5, the same method can be applied to end mills and drills of other sizes. [Explanation of Symbols]

[0037] 1 Coated cutting tools 11, 11' Scoop face 12 Escape 13. Cutting edge 14. Deinhibition region 17 Diamond film

Claims

1. A coated cutting tool in which a crystalline film is formed on the surface of the cutting edge, A coating cutting tool wherein inhibiting regions that inhibit particle growth of the crystalline film or bonding with constituent elements of the crystalline film exist only on the rake face of the cutting edge.

2. On the surface of the cutting edge portion other than the scooping surface, there exists a deinhibition region that maintains or promotes particle growth or bonding. The coating cutting tool according to claim 1.

3. The cutting edge portion is formed at the tip of the tool base made of cemented carbide, The coating cutting tool according to claim 2, wherein the inhibiting region is a region on the surface of the tool substrate from which the deinhibiting region has been removed.

4. The aforementioned crystalline film is a diamond film, The aforementioned inhibitory region is a region containing cobalt or a cobalt alloy. A coating cutting tool according to claim 1, 2, or 3.

5. The depth of the inhibition region is greater than 3 μm and less than 30 μm. The coating cutting tool according to claim 4.

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