JP2020049587A - Diamond-coated cemented carbide cutting tool - Google Patents

Abstract

To provide a diamond-coated cutting tool that combines deposition resistance and wear resistance and has extended cutting life even when being used for high-speed drilling in a CFRP/Al alloy stack material, for example.SOLUTION: In a diamond-coated cutting tool, a diamond coating film with a film thickness of 7 to 25 μm is coated at a surface of a tool substrate that is made of a tungsten carbide-base cemented carbide alloy. The diamond coating film has an average crystal grain size of more than 3.0 μm, D/G of 10 or more and a surface roughness Ra of the coating film of 0.5 μm or less.SELECTED DRAWING: None

Description

  The present invention is particularly applicable to high-speed cutting of a difficult-to-cut composite material (hereinafter, referred to as a “CFRP / Al alloy stack material”) made of carbon fiber reinforced plastic (CFRP) and an Al alloy or the like. The present invention relates to a diamond-coated tungsten carbide (WC) -based cemented carbide cutting tool exhibiting wear properties and improving tool life.

  Conventionally, a diamond-coated cemented carbide cutting tool coated with a diamond film (hereinafter, referred to as a "diamond-coated tool") is used for a tool base made of a WC-based cemented carbide (hereinafter, referred to as a "hard metal"). When processing hard-to-cut materials such as Al alloys or CFRP, it has been proposed to reduce the surface roughness by reducing the crystal grain size of the diamond film in order to suppress abrasive wear.

  For example, Patent Document 1 discloses that a diamond film is formed by repeating a nucleus attachment process and a crystal growth process such that the crystal grain size of a surface and a cross section substantially perpendicular to the crystal growth direction of diamond is 2 μm or less. A diamond-coated tool characterized by having a multi-layer structure of crystals and having improved surface roughness of a processed surface on which an irregular surface of a diamond film is formed is described.

  Further, for example, in Patent Document 2, the base is a cemented carbide or a cermet, and the average grain size of diamond crystal grains constituting a growth surface of a diamond film having a thickness of 1 μm or more and 20 μm or less is 1.5 μm or less. The average surface roughness of the diamond film is not less than 0.01 μm and not more than 0.2 μm in Ra, and the diamond crystal particles are formed by assembling fine diamonds. A diamond film-coated tool, which is elongated in the direction of film growth, and where the minor axis of the fine diamond is 0.001 μm or more and 0.1 μm or less in a portion where the thickness of the diamond film is 1 μm or more from the substrate surface. Is described.

Japanese Patent No. 3377162 JP 2006-130578 A

  In recent years, there has been a strong demand for labor saving, energy saving, and further cost reduction in the technical field of cutting, and with this, cutting has tended to become faster. On the other hand, when a conventional diamond-coated tool is used, for example, for high-speed cutting of a CFRP / Al alloy stack material, a sharp edge is required, so that a high edge strength is required, and the abrasive wear is suppressed over a long period of use. In addition, it is not sufficient to exhibit the welding resistance and the chipping resistance, and it is difficult to maintain high processing accuracy. As a result, the service life is often shortened in a relatively short time.

The diamond coatings disclosed in Patent Literatures 1 and 2 have reduced surface roughness and smoothness by reducing crystal grains, and although improvement in welding resistance can be expected, the crystal grains of the diamond coating are reduced. By doing so, the ratio of the sp ³ bond to the sp ² bond is reduced, the hardness of the diamond film is not utilized, and the abrasion resistance may be reduced, which is sufficient for high-speed drilling of a CFRP / Al alloy stack material. It cannot be said that it has a service life.

  Therefore, a technical problem to be solved by the present invention, that is, an object of the present invention is to provide a diamond-coated tool having both welding resistance and abrasion resistance, for example, in high-speed drilling of a CFRP / Al alloy stack material. It is to provide a diamond coated tool having a long cutting life.

  In order to solve the above-mentioned problems of the conventional diamond-coated tool, the inventor diligently repeated research and experiments. As a result, in order to obtain a diamond film having both welding resistance and abrasion resistance, instead of reducing the crystal grain of the diamond film to reduce the surface roughness, the crystal grain of the diamond film is increased, A surprising new finding that the surface roughness should be reduced by appropriate post-treatment has been obtained. It has also been found that if the diamond film is oriented in the <110> direction, it is even more excellent in welding resistance and smoothness.

The present invention is based on the above findings and includes the following embodiments.
"(1) In a diamond coated tool in which a diamond coating having a film thickness of 7 to 25 μm is coated on the surface of a tool substrate made of a tungsten carbide-based cemented carbide, the diamond coating has an average crystal grain size exceeding 3.0 μm. And Raman spectroscopy using a visible laser with a wavelength of 532 nm, and the peak intensity (D) of diamond confirmed at 1332 to 1337 cm ^-1 and the peak intensity (G) of graphite having a peak between 1560 and 1600 cm ^-1. A diamond-coated cutting tool having a D / G ratio of 10 or more and a surface roughness Ra of the coating of 0.5 μm or less.
(2) A diamond-coated cutting tool, wherein the orientation ratio of the columnar crystal constituting the diamond film of (1) in the <110> direction is 40% or more. "

  Since the diamond-coated cutting tool has both welding resistance and wear resistance, even when used for high-speed drilling of difficult-to-cut materials such as CFRP / Al alloy stack materials, for example, by drilling. In addition, there is an excellent effect that machining accuracy can be maintained over a long period of time, life is long, sudden chipping is suppressed, and cutting tool performance is stably exhibited.

  Next, the diamond film of the diamond-coated cutting tool of the present invention will be described in more detail. In the present specification and claims, when a numerical range is expressed by using “to”, the range includes upper and lower numerical values.

1. Average thickness of diamond film:
The average thickness of the diamond film in the diamond-coated cutting tool of the present invention is 7 to 25 μm. The reason for this range is that if it is less than 7 μm, a sufficient tool life cannot be obtained when cutting a CFRP / Al alloy stack material which emphasizes wear resistance, and if it exceeds 25 μm, a sharp edge is obtained. This is because it becomes difficult to produce burrs and delamination on the work material when cutting the CFRP / Al alloy stack material.
Here, the average film thickness of the diamond film was measured by processing a cross section in a direction perpendicular to the tool base (a vertical cross section that is a cross section in the film thickness direction) with a Cross-section Polisher (hereinafter, referred to as CP). The film thickness of the cross section is measured using a scanning electron microscope at an appropriate magnification (for example, 5000 times), and for example, the film thickness is measured and averaged at five points in the observation visual field.

2. Average grain size of diamond film:
The average crystal grain size of the diamond film in the diamond-coated cutting tool of the present invention exceeds 3.0 μm. The reason is that if the thickness is 3.0 μm or less, the volume occupied by the crystal grain boundaries in the diamond film increases, the ratio of sp ² bonds increases, and the wear resistance decreases.
Here, the average crystal grain size of the diamond film is determined by observing the surface of the diamond film on the flank of the cutting edge of the diamond-coated cutting tool with a scanning electron microscope and arbitrarily drawing a 10 μm line segment in three visual fields of 50 μm square. The number of diamond crystal grains contained in the sample is measured, and the average value of the value obtained by dividing the line length (10 μm) by the number of crystals is calculated.

3. D / G values:
Measured by Raman spectroscopy using a visible laser of wavelength 532 nm, the peak intensity of graphite (G) with a peak between 1560～1600Cm ^-1 and the peak intensity of the diamond (D) to be checked 1332～1337Cm ^-1 The ratio (D / G) is 10 or more. The reason is that if it is less than 10, the ratio of sp ³ bonds in the diamond film is low, the film cannot obtain the original hardness of diamond, and the wear resistance is not sufficient.

4. Surface roughness (Ra):
The surface roughness (Ra) is 0.5 μm or less. The reason is that if the thickness exceeds 0.5 μm, welding occurs on the cutting edge, peeling easily occurs, the shape of the cutting edge cannot be maintained, and the processing quality deteriorates.

5. Orientation ratio of columnar crystal constituting diamond film in <110> direction:
In the diamond-coated cutting tool of the present invention, the orientation ratio of the diamond film in the <110> direction is preferably 40% or more in order to improve wear resistance and welding resistance.
Here, the orientation ratio of the columnar crystal constituting the diamond film in the <110> direction can be determined by polishing the cross section of the cutting edge with a CP, and making a 30 μm square region of the film cross section perpendicular to three film surfaces by EBSD. An electron beam is irradiated to each of the crystal grains existing within the measurement range of the polished surface of the film cross section, and the angle formed by the normal of the (110) plane of each of the crystal grains of the film and the inclination angle between the film thickness direction are measured. Of the measured inclination angles, the inclination angles within the range of 0 to 45 degrees are divided for each pitch of 0.25 degrees, and the frequencies existing in each division are totaled, whereby the angles of 0 to 45 degrees are counted. The <110> orientation ratio is defined as the ratio of the sum of the frequencies in which the tilt angle is in the range of 0 to 20 ° with respect to the frequencies existing in the range (entire frequencies in the tilt angle number distribution).

6. Manufacturing method (film formation conditions)
The diamond film in the diamond-coated cutting tool of the present invention is manufactured by, for example, forming a film under the following conditions using a CVD apparatus used for a hot filament method, and performing a post-process including a plasma process and a blast process. be able to.
(1) Film formation conditions Filament temperature: 2300 to 2500 ° C
Ratio of CH ₄ gas to H ₂ gas: 0.8 to 2.0% by volume
Reaction pressure: 600 to 1000 Pa
Film formation time: 10 to 25 hours (2) Post-treatment (2-1) Plasma treatment The surface of the diamond film is modified by oxygen plasma to reduce the surface roughness.
Oxygen gas: 300 ml / min
Discharge method: RF (high frequency)
Output: 100-300W
Treatment time: 2.5 to 3.5 hours Bias: DC pulse (2-2) Blast treatment Removal of the brittle layer formed on the film surface by plasma treatment and reduction of surface roughness.
Medium: Mixed media of SiC powder and diamond powder (diamond mixing ratio: 2 to 4%)
Projection pressure: 0.10 to 0.20 MPa
Processing time: 4-6 minutes

  Next, examples will be described. In the embodiment, a drill will be described as an example, but the diamond-coated cutting tool according to the present invention is not limited to this.

As raw material powders, WC powder having an average particle size of 1 μm or less, TaC powder, NbC powder, Cr ₃ C ₂ powder, and Co powder each having an average particle size of 1 to ₃ μm were prepared. The mixture was wet-mixed in a ball mill for 96 hours, dried, and then pressed into a green compact at a pressure of 100 MPa, and the green compact was vacuumed at 6 Pa at a temperature of 1350 to 1400 ° C. Sintering under the condition of holding for 1 hour to form a round bar sintered body for forming a tool base having a diameter of 10 mm. Tool bases A and B made of hard alloy were produced.

  Subsequently, the surfaces of the cemented carbide substrates A and B were subjected to ultrasonic cleaning in ethanol, dried, and then subjected to an etching treatment, followed by 10 minutes in an isopropyl alcohol solution containing diamond powder having a particle size of 1 to 2 μm. Was subjected to ultrasonic treatment.

  Thereafter, the cemented carbide substrates A and B are charged into a CVD apparatus used for a hot filament method, a crystalline diamond layer having a predetermined average film thickness and an average particle diameter is formed and blasted, and the present invention is coated. Tools 1 to 13 were manufactured. The film forming conditions are as shown in Table 2. A thermocouple was introduced into the CVD apparatus, a thermocouple was inserted through a φ1 mm hole on the shank side of the substrate, and the substrate temperature was measured. In addition, an increase in the graphite component from the surface layer to a thickness of 0.5 μm was observed in the diamond film, and up to this thickness was removed by blasting.

  With respect to the diamond film thus obtained, the average thickness, average crystal grain size, D / G, surface roughness (Ra), and orientation ratio in the <110> direction of the diamond film were determined by the methods described above. . Table 3 shows the respective values.

For the purpose of comparison, the cemented carbide substrates A and B were charged into a hot filament CVD apparatus, a diamond film was formed, and comparative coating tools 1 to 9 were manufactured. The film forming conditions are as shown in Table 2.
The average thickness, average crystal grain size, D / G, surface roughness (Ra), and orientation ratio in the <110> direction of the diamond film were determined by the above-described methods. Table 4 shows the respective values.

Subsequently, the coated tools 1 to 13 of the present invention and the comparative coated tools 1 to 9 were subjected to an evaluation test of the number of perforations under the following conditions, and the tool life was examined.
Work material: thickness 27mm
Composite material consisting of CFRP (thickness 20 mm) and Al alloy (A7075: thickness 7 mm) Cutting speed: VC = 100 m / min Feeding amount: fr = 0.15 mm / rev penetration * Tool life judgment method: Number of machining holes 50 Each time, the edge of the drill and the workpiece were observed, and the life of the drill was defined as the point at which the base was exposed, chipped, or chipped. In addition, as a criterion for maintaining the processing accuracy, a processing state in which burrs did not occur on the processed surface of the work material and delamination was suppressed within 1 mm from the processed surface was determined to be acceptable.
Table 5 shows the test results.

From the results shown in Table 5, the coated tools 1 to 13 of the present invention were able to obtain stable machined holes for a long period of time.
In contrast, all of the comparative coated tools 1 to 9 that do not satisfy the requirements of the present invention not only cause chipping and chipping, but also have a short cutting length or a short service life.

  As described above, the diamond coated tool of the present invention exhibits excellent welding resistance and wear resistance over a long period of use in cutting a CFRP / Al alloy stack material which is a difficult-to-cut material. This makes it possible to fully satisfy the requirements for FA of the apparatus, labor saving and energy saving of the cutting process, and furthermore, cost reduction.

Claims (2)

In a diamond coated tool in which a diamond film having a film thickness of 7 to 25 μm is coated on a tool substrate surface made of a tungsten carbide based cemented carbide, the diamond film has an average crystal grain size exceeding 3.0 μm and a wavelength of 532 nm. It is measured by Raman spectroscopy using a visible laser, and is the ratio of the peak intensity (D) of diamond confirmed at 1332 to 1337 cm ^-1 to the peak intensity (G) of graphite having a peak between 1560 and 1600 cm ^-1. A diamond-coated cutting tool having a D / G of 10 or more and a surface roughness Ra of 0.5 μm or less.   2. A diamond-coated cutting tool, wherein the columnar crystal constituting the diamond film according to claim 1 has an orientation ratio in a <110> direction of 40% or more.