JP2003159611A - Ball end mill and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball end mill which has excellent wear resistance together with excellent chipping resistance and a long life by optimizing the composition of hard layers formed on the respective portions of the cutting edges of the ball end mill. <P>SOLUTION: In the ball end mill 1 having an approximately circular cutting edge 8 attached to the tip end of the tool body of a holder 4, the turning locus of the cutting edge 8 being an approximate hemisphere, at least a hard film 10 is formed by deposition on the cutting edge 8, and further the friction coefficient of the hard film 10a at the most outside surface of the cutting edge 8 positioned on the rotational center (a) of the approximate hemisphere is set to be smaller than the friction coefficient of the hard film 10b at the most outside surface of the cutting edge 8 positioned on the side surface of the approximate hemisphere. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball end mill for processing a free-form surface while rotating at high speed, such as die processing, and more particularly to a throw-away type ball end mill having both wear resistance and fracture resistance.

[0002]

2. Description of the Related Art Among the ball end mills frequently used for die machining, the throw away type ball end mill is
One or a plurality of throw-away tips are attached to a predetermined position of a holder having a rotating shaft, and a work piece is processed into a complicated shape while the cutting edge of the tip presents a substantially hemisphere with the rotation of the holder. Is.

In such a ball end mill, during cutting, the cutting speed is small near the center of rotation, and the cutting speed is large near the outer peripheral edge. Therefore, friction resistance is large at the center of rotation where low speed machining occurs, and conversely at the outer peripheral part. However, there is a problem that the wear progresses quickly.

Therefore, in Japanese Utility Model Laid-Open No. 5-88822, a hard film of TiCN, TiN or the like is formed on the surface of the chip base material at the center of rotation to reduce the frictional resistance with the work material and to provide chipping resistance. A method of increasing the value is described.

[0005]

However, in the ball end mill in which the above-mentioned hard film is adhered to the center of rotation, the friction resistance near the center of rotation can be reduced in the initial stage of cutting, but the cutting time can be extended. If the hard film is peeled off, it will be damaged more than the one without the hard film, and the performance of the end mill as a whole will be deteriorated because the wear resistance at the outer peripheral part cannot be improved. .

The present invention has been made to solve the above problems, and an object thereof is to provide a long-life ball end mill having excellent fracture resistance and wear resistance.

[0007]

The present inventor has studied the structure of a hard film to be adhered and formed on a ball end mill tip, and as a result, wear resistance is emphasized on the outer peripheral portion where the cutting speed is high. In addition to selecting a hard film composition with high resistance, by focusing on chipping resistance near the center of rotation and selecting a composition with a higher friction coefficient than the peripheral surface, long-term wear resistance and fracture resistance are achieved. The present invention has been accomplished by finding that a long-life chip can be obtained.

That is, the ball end mill of the present invention is
In a ball end mill having a substantially arcuate cutting edge exhibiting a substantially hemispherical rotation locus at the tip of a tool body, at least the cutting edge portion is coated with a hard film and is located at the rotation center of the substantially hemisphere. The coefficient of friction of the outermost surface of the hard film in the cutting edge portion is smaller than the coefficient of friction of the outermost surface of the hard film in the cutting edge portion located on the circumferential surface of the substantially hemisphere.

Another ball end mill of the present invention is
The hard film outermost surface of the cutting edge portion located at the rotation center of the substantially hemisphere is titanium carbide, titanium carbonitride, aluminum oxide,
It consists of one kind selected from the group of chromium nitride, manganese sulfide, diamond-like carbon (DLC) and diamond, and the outermost surface of the hard film of the cutting edge portion located on the circumferential surface of the above-mentioned hemisphere consists of titanium nitride and aluminum titanium nitride. It is characterized by consisting of one kind selected from the group.

Here, the surface roughness (Ra) of the outermost surface of the hard film at the cutting edge portion located at the rotation center of the substantially hemisphere is the surface roughness of the outermost surface of the hard film located at the peripheral surface of the substantially hemisphere. (R
It is preferably smaller than a).

Further, it is desirable that the hard film is formed by physical vapor deposition, and the hard film of the cutting edge portion located on the peripheral surface of the substantially hemisphere is located at the rotation center of the substantially hemisphere. It is desirable that the cutting edge portion is coated with more layers than the hard film.

Further, in the method for manufacturing a ball end mill which is attached to the tip of the tool main body according to the present invention so that the rotation locus of the cutting edge exhibits a substantially hemispherical shape, a hard coating is formed on the substantially arc-shaped cutting edge in the first step. It is desirable to form a hard film on the cutting edge portion located on the peripheral surface by using a mask on the cutting edge portion located on the rotation center of the hemisphere in the subsequent second step.

[0013]

1 is a schematic front view of an example of a throw away type ball end mill in which a throw away tip is attached to a holder, which is a preferred example of the ball end mill of the present invention, and the throw away tip is enlarged. 2 will be described.

According to FIG. 1, the throw-away type ball end mill 1 has a throw-away tip 6 and a set screw 7 in the holding portion 3 of a holder (tool body) 4 in which a holding portion 3 is provided at the tip of a cylindrical shank 2. It is fixed in. The cutting edge 8 of the tip 6 has an arc shape so that the cutting edge 8 of the throw-away tip 6 has a substantially hemispherical shape by rotating around the center a of the shank 2.

According to the present invention, as shown in FIG. 2, the outermost surface of the hard film 10a of the portion of the cutting edge 8 located at the center of rotation of the substantially hemisphere is located on the outermost surface of the hard film 10a. A major feature is that the coefficient of friction is smaller than the coefficient of friction of the outermost surface of the hard film 10b at the cutting edge portion located on the peripheral surface of the approximately hemisphere, which improves both the fracture resistance and wear resistance of the ball end mill. Can be made.

That is, the hard film 10 of the cutting edge 8 is made of the same material over the entire region, or the thickness of the hard film 10a of the cutting edge located at the rotation center of the substantially hemisphere is located on the peripheral surface of the substantially hemisphere. If the thickness of the hard film 10b at the cutting edge portion is thicker, a load is applied to the cutting edge 8 near the center blade having a slow cutting speed due to the difference in cutting speed at the cutting edge position, resulting in peeling of the hard film 10 and damage to the cutting edge. And it cannot be used as a cutting tool.

According to the present invention, in order to achieve both fracture resistance and wear resistance, the surface roughness (Ra) of the outermost surface of the hard film 10a at the cutting edge portion located at the rotation center of the substantially hemisphere is the above. It is desirable that it is smaller than the surface roughness (Ra) of the outermost surface of the hard film 10b located on the peripheral surface of the substantially hemispherical portion.

According to another end mill of the present invention,
In order to achieve both fracture resistance and abrasion resistance, the outermost surface of the hard film 10a of the cutting edge portion located at the rotation center of the approximately hemisphere is titanium carbide, titanium carbonitride, aluminum oxide, chromium nitride, manganese sulfide, diamond-like. Carbon (DL
C), one selected from the group of diamonds, and the outermost surface of the hard film 10b of the cutting edge portion located on the peripheral surface of the approximately hemisphere is composed of one selected from the group consisting of titanium nitride and titanium aluminum nitride. Is a major feature.

Further, it is located at the center of rotation of the substantially hemisphere.
Thickness d of the hard film 10a at the cutting edge ₁And the hard film 1
Maximum thickness d of 0₂Ratio with₁/ D₂Is 0.7 or less, especially
It is preferably 0.3 to 0.6.

Further, from the viewpoint of improving fracture resistance, wear resistance, and finished surface roughness, the thickness of the hard film 10 ranges from the cutting edge portion located at the rotation center of the substantially hemisphere to the peripheral surface of the substantially hemisphere. It is desirable to increase gradually toward, ie, continuously or stepwise, particularly continuously.

The base material of the throw-away tip 6 is preferably made of, for example, cemented carbide or cermet.

According to the present invention, it is desirable to form the hard film 10 on the plane portion other than the cutting edge 8 of the chip 6 in order to prevent damage and heat generation due to the collision of the chips, but it is preferable that the hard film 10 is formed. It is desirable from the viewpoint of wear resistance that the film thickness of the hard film 10 on the surface is larger than that of the hard film 10 on the rake face.

Further, according to the present invention, it is desirable that the hard film 10 is formed by physical vapor deposition so that the film thickness can be easily controlled. Further, according to the present invention, the hard film 10 is not limited to a single layer, and may be formed in multiple layers. In this case, the number of layers of the hard film 10 is changed, that is, the hard film 10 is formed by multilayering. 10 It is also possible to change the film quality of the outermost surface.

Further, in the throw-away type ball end mill 1 of FIG. 1, one throw-away tip is mounted, but the present invention is not limited to this, and the tip is separately provided on the bottom surface and the side surface. May be attached. Even in this case, the chipping resistance described above can be obtained by making the film thickness of the hard film of the bottom edge blade including the center of rotation thinner than that of the side edge blade, or gradually decreasing toward the center of rotation, that is, continuously or stepwise. The wear resistance can be improved.

Further, the present invention is particularly effective for a ball end mill which often moves the holder 4 in the plane direction such as engraving processing and contouring processing.

(Manufacturing Method) Next, a method for manufacturing the above-described throw-away ball end mill will be described. First, a base material such as cemented carbide or cermet is prepared by conventionally known molding and firing, and if necessary, is ground into a predetermined shape by using a processing device such as a diamond wheel, a grinder, or a grinding center. Wash with acid, alkali, organic solvent, and pure water, and dry thoroughly. If necessary, blasting, brushing, barreling, etc. are performed.

Next, as a method for forming a hard film on the surface of the chip base material, there are a CVD method (chemical vapor deposition method) and a PVD method (physical vapor deposition method). Particularly, an arc method and a hollow cathode method are used. A PVD method using an ion plating device such as the above, a magnetron sputtering device, or the like is preferable in terms of film thickness control.

According to the present invention, in order to locally vary the material of the hard film on the outermost surface as described above, the surface of the cutting edge portion located at the rotation center as shown in FIG. The mask 17 is formed on the hard film of the cutting edge portion located on the peripheral surface of the hemisphere. When forming a multilayer hard film, the composition and film thickness were adjusted according to the film quality such as hardness and toughness, with emphasis on fracture resistance at the center of rotation and wear resistance on the side surface. The configuration.

[0029]

EXAMPLE 89% (weight ratio) of tungsten carbide (WC) powder having an average particle size of 0.7 μm and metallic cobalt (C)
o) 10% (weight ratio) of powder, and 1% (weight ratio) of vanadium carbide (VC) and chromium carbide (Cr ₃ C ₂ ) combined, crushed and granulated, and molded into end mill tip shape. After that, it was fired at 1400 ° C. for 1 hour to produce a cemented carbide for chip base material. This cemented carbide was ground by a grinder and a grinding center, washed, and dried.

The obtained base material is set in an arc type ion plating, the hard film shown in Table 1 is formed on the entire chip, and a stainless steel mask is installed directly above the cutting edge portion located at the center of rotation. The hard film shown in Table 1 was produced in this state (see FIG. 3). After film formation, the cross section of the chip produced in the same manner was observed by SEM, and the results of measuring the film thickness are shown in Table 1.

Then, the throw-away tip thus obtained was used to cut an injection molding die under the following cutting conditions, and the wear amount and damage state of the three-way tip were measured. The maximum wear amount during the cutting test was 0.2 m
m or the surface quality of the machined part was deteriorated or the machined size was measured, the tool life was defined at that time.

(Cutting evaluation conditions) Processed parts: plastic mold Material: Carbon steel (S55C) Tool used: diameter 16 mm Cutting speed: 100m / min Feed rate: 400 mm / min Notch: 0.2 mm Processing time: 5 hours per part Other conditions: Dry cutting

[0033]

[Table 1]

From the results shown in Table 1, the hard film structure manufactured by the conventional method has the same No. 1 in the rotation center part and the peripheral surface part. No. 1 different from the proper coating composition in the rotation center part and the peripheral surface part. 2 is
During cutting, peeling of the hard film due to welding of the work material occurred near the center of the rotation axis, the work piece was welded to the exposed portion of the cemented carbide base material, and the machined surface deteriorated.

On the other hand, sample No. 1 according to the present invention was used. Three
In Nos. 10 to 10, even the cutting edge near the center of the rotation axis was in a normal wear state, and it was possible to machine two or more machined parts (total machining time of 10 hours or more), and it was stable without causing abnormalities such as damage to the cutting edge. Processing became possible.

[0036]

As described above in detail, in the ball end mill according to the first and second aspects, by optimizing the hard film material of the outermost surface according to the required performance,
Wear resistance and chipping resistance are combined by focusing on wear resistance to lower the friction coefficient in the outer peripheral area where the cutting speed is high, and increasing the friction coefficient near the center of rotation by focusing on chipping resistance. Long-life chips can be obtained.

Further, in the method for manufacturing a ball end mill according to the present invention, since a hard film is formed on the cutting edge portion using a mask on the cutting edge portion located at the center of rotation of the hemisphere, the rotation of the substantially hemisphere is performed. It is possible to easily form a ball end mill in which the coefficient of friction of the outermost surface of the hard film in the cutting edge portion located at the center is smaller than the coefficient of friction of the outermost surface of the hard film in the cutting edge portion located on the peripheral surface.

[Brief description of drawings]

FIG. 1 is a front view of a ball end mill according to the present invention.

FIG. 2 is a view for explaining a throw-away tip in the ball end mill of FIG.

FIG. 3 is a diagram for explaining an example of a method for manufacturing a throw-away tip in the ball end mill of the present invention.

[Explanation of symbols]

1 ball end mill 2 shank 3 clamping part 4 Holder (tool body) 6 Throw-away tip 7 Set screw 8 cutting edges 9 Base material 10 Hard film 11 mounting holes 17 mask

Claims (6)

[Claims] 1. A ball end mill having a substantially arcuate cutting edge exhibiting a substantially hemispherical rotation locus at its tip, wherein at least the cutting edge portion is coated with a hard film and at the center of rotation of the substantially hemisphere. A ball end mill, wherein the coefficient of friction of the outermost surface of the hard film of the cutting edge portion located is smaller than the coefficient of friction of the outermost surface of the hard film portion of the cutting edge portion located on the peripheral surface of the substantially hemisphere. 2. A ball end mill having a substantially arcuate cutting edge exhibiting a substantially hemispherical rotation locus at its tip, wherein a hard film is adhered and formed on at least the cutting edge portion, and at the center of rotation of the substantially hemisphere. The hard film outermost surface of the cutting edge portion located is made of one kind selected from the group of titanium carbide, titanium carbonitride, aluminum oxide, chromium nitride, manganese sulfide, diamond-like carbon (DLC) and diamond, and the circumference of the above-mentioned approximately hemisphere A ball end mill characterized in that the outermost surface of the hard film of the cutting edge portion located on the surface is made of one kind selected from the group consisting of titanium nitride and aluminum titanium nitride. 3. The surface roughness (Ra) of the outermost surface of the hard film at the cutting edge portion located at the rotation center of the substantially hemisphere is the surface roughness (Ra) of the outermost surface of the hard film located at the peripheral surface of the substantially hemisphere ( It is smaller than Ra), The ball end mill according to claim 1 or 2. 4. The ball end mill according to claim 1, wherein the hard film comprises at least one layer deposited and formed by a physical vapor deposition method. 5. The hard film of the cutting edge portion located on the peripheral surface of the substantially hemisphere is coated more in a multilayer than the hard film of the cutting edge portion located at the rotation center of the substantially hemisphere. Item 5. The ball end mill according to any one of items 1 to 4. 6. A method of manufacturing a ball end mill, in which a throw-away tip having a hard film adhered to at least a cutting edge portion on a surface of a base material is attached to a tip of a tool body such that a rotation locus of the cutting edge exhibits a substantially hemispherical shape. 2. The method for manufacturing a ball end mill according to, wherein a hard film is formed on the cutting edge portion located on the peripheral surface by using a mask on the cutting edge portion located on the rotation center of the hemisphere.