JPS60172403A - Coated cemented carbide chaser - Google Patents

Abstract

PURPOSE:To obtain a coated cemented carbide chaser which is long-life and free from damage with a good finish surface by making the coat thickness on a chaser edge and its neighborhood thinner or removing the coat. CONSTITUTION:A chaser tool, which is used in cutting comparatively large diameter and high-precision screw threads for oil well piping, etc., consists of a base 4 and a coated layer 5; (minimum thickness b of coated layer)/(average thickness a of coated layer 5)X100 is referred to as a coat thickness ratio (%). Therefore, the coat thickness on the chaser edge and its neighborhood is made thinner than that of the other area or the coat is removed. In addition, the chaser uses cemented carbide for the base 4, and the coated layer 5 is made by use of the CVD method. And the rake face and the relief face are wrapped at the same time. With this configuration, it is possible to obtain a chaser which is long-life and free from damage with a good finish surface.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a chaser tool used for machining screws having a relatively large diameter and high precision, such as those used for oil country tubular goods, etc. The base is made of cemented carbide, The present invention relates to a so-called coated cemented carbide chaser whose surface is coated with a material harder than the base material to a thickness of 1 to 20 μm by CVD.

[Prior art]

In the field of metal cutting, the processing conditions are becoming stricter year by year, and cutting tools used for cutting are desired to have improved wear resistance and heat resistance. The same is true for chaser tools made of cemented carbide; coated cemented carbide chasers are made of cemented carbide as a base and coated with a wear-resistant and heat-resistant material using the CVD method, which has excellent adhesion to the coating film. is used. FIG. 1 is an example of this, and FIG. 2 is a sectional view taken along line XX in FIG. 1. In these figures, code (1) is a chaser chip, (2
) indicates the base, and (3) indicates the vicinity of the cutting edge. FIG. 3 shows an enlarged cross section near the cutting edge (3).

By the way, it is generally known that the thicker the coating film formed by the CVD method, the better the wear resistance, but the lower the toughness and the more likely it is to chip. That is, in the conventional variously coated cemented carbide chaser shown in FIG. 3, the toughness of the cutting edge is reduced, resulting in a problem of deterioration of the finished surface due to irregular wear due to chipping of the cutting edge and microchipping. In particular, with chasers, the effective cutting feed speed is higher than in general cutting processing, and the contact length with chips, that is, the actual length of the cutting edge, is extremely long, so the load on the cutting edge is extremely large. , compared to tools used for general cutting, are extremely prone to breakage, and many conventional coated cemented carbide chasers have reached the end of their service life due to breakage. In addition, in thread cutting, importance is placed on the degree of finish of the thread surface, and the roughness of the finished surface also accounts for a large proportion of the service life.

Thread cutting with a chaser is generally performed by creating 3 to 9 multiple cutting edges, and the division of the machining allowance is complicated, and depending on the part of the cutting blade, the machining allowance may be extremely small or large. There are some spots. In areas where the machining allowance is large, the load is large and the above-mentioned chipping occurs, but in areas where the machining allowance is small, even if the absolute amount of the load is small, it is concentrated on the hard and brittle coating film, making microchipping more likely to occur. If the machining allowance is small, work hardening will result in cutting only 9 parts, which will further promote microchipping, and this chipping will deteriorate the finished surface. Moreover, it is the final cutting edge of the chaser that determines the finished surface of the thread, but since the machining allowance of this cutting edge is usually small, the microchipping mentioned above is particularly likely to occur, which easily deteriorates the finished surface. . Conventional coated cemented carbide chasers, which have a thick film near the cutting edge, have these problems conspicuously.

[Summary of the invention]

The present invention has been made in view of these circumstances, and it is an object of the present invention to provide a coated cemented carbide chaser that is stable against chipping, has a good finished surface, and has a long life.

In order to achieve the object of item 1, the coated cemented carbide chaser according to the present invention is a cemented carbide chaser coated by a CVD method, in which the film thickness at the cutting edge and its vicinity is set to be the same as the film thickness at other parts. It is constructed by making it thinner or by removing the coating film. By doing so, cutting performance is significantly improved.

This effect is large when the minimum value of the film thickness near the edge of the cutting edge is 90% or less of the other average film thickness, and is particularly remarkable when it is 60% or less.

In order to obtain the chaser tip of the present invention, it is possible to coat the surface of the cemented carbide with an appropriate method and then perform barrel treatment, but it is difficult to treat the valleys of the chaser blade, and
Since there is a decrease in yield due to chipped cutting edges and an increase in cost due to inefficiency, a large number of coated chasers are placed on a rotary plate with the scooping side facing up, and the cutting edge of the chaser is placed on the scooping side. Rotate and press against a resilient puff whetstone containing abrasive grains such as silicon carbide.
Lapping the scooping surface and the flank at the same time to make the film on the edge of the cutting edge and its vicinity smooth and thin is most suitable because it can follow the complex shape of the chaser and can be processed efficiently.

[Embodiments of the invention]

4 and 5 are enlarged sectional views of the vicinity of the cutting edge of a coated cemented carbide chaser according to an embodiment of the present invention, respectively, and FIG. 6 shows the dimensional relationship of the chaser according to the embodiment. FIG. In these figures, symbol (4) is the base, (5) is the coating layer, (mu) in FIG. 6 is the average thickness of the coating layer (5), (b) is the minimum thickness, and b/ a
xioo is called the film thickness ratio (4).

Therefore, the chaser in FIG. 4 shows a state where kl/a>O, and the chaser in FIG. 5 shows a state where t)/a=O.

In this example, a round chaser for thread cutting equipment manufactured by Pipe Machinery Co., Ltd., that is, a chaser with one set of three pieces (3 threads/piece, 9 threads/set) was used, and a seamless steel pipe for oil wells (material: AI8 STO-N material) was used. , diameter 194 m). The chaser is made of cemented carbide (
The base material is ISO standard M20), and the coating shown in Table 1 (A
, B, and C) using the CVD method.

In addition, the blade edge treatment before coating and the blade edge treatment after coating are performed by pressing an elastic grindstone while rotating.
The processing amount before coating is 0.0 in Figure 6 for a straight cutting edge.
Make a round so that it is 6 mm.

The results of the performance evaluation are shown in Table 2.

In addition, in Table 2, AI, 2.6, 7, 11°12
The chaser has a conventional structure! 1>, 43°4.5
, 8, 9, 10, 13, 14, 15, and 16 are related to this embodiment. The cause of the lifespan of chasers with a conventional structure is microchipping or chipping, but the cause of lifespan of chasers according to this embodiment is wear.

Therefore, as can be seen from the results in Table 2, it can be said that the chaser according to this example exhibits superior performance compared to the conventional chaser.

Table 1 Table 2 [Effects of the Invention] As is clear from the above explanation, according to the coated cemented carbide chaser of the present invention, the film thickness at the cutting edge and its vicinity can be reduced or removed. Because of this structure, a chaser that is stable against chipping, has a good surface finish, and has a long life has been realized.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a conventional coated cemented carbide chaser, Fig. 2 is a sectional view taken along line XX in Fig. 1, Fig. 6 is an enlarged sectional view near the cutting edge in Fig. 2, Fig. 4, and FIG. 5 is an enlarged sectional view of the vicinity of the cutting edge of a coated cemented carbide chaser according to an embodiment of the present invention;
FIG. 6 is an explanatory diagram showing the dimensional relationship of the chaser of the embodiment. (1)... Chaser chip, (2)... Base, (3
)...near the cutting edge ridge, (4)...substrate, (5)...
Covering layer. Agent Patent Attorney Sanro Kimura (9)r Figure 1, Figure 3, Figure 5, Figure 2, Figure 4, Figure 6 (

Claims (2)

[Claims] (1) A coated carbide chaser coated by a CVD method, characterized in that the film thickness at the cutting edge and its vicinity is made thinner than other parts or removed. Alloy chaser. (2) The coated cemented carbide chaser according to claim 1, wherein the thickness ratio of the cutting edge and its vicinity is 90(4) or less.