JP2008093800A - Surface coated cemented carbide end mill for rapid feed cutting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more surely restrain chipping of a cutting blade even when the blade is used for rapid-feed cutting. <P>SOLUTION: This surface coated cemented carbide end mill has a cutting blade part made of a tungsten carbide base cemented carbide whose main binder phase is Co, and a hard coating is coated on the surface of the cutting blade. Coercive force Hc(kA/m) of the tungsten carbide base cemented carbide is made to 16.0≤Hc≤34.0, and heat conductivity λ(W/mK) is made to 120-2Hc≤λ≤120. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface-coated cemented carbide end mill for high-feed cutting that is particularly suitable for high-feed machining.

An end mill made of a tungsten carbide (WC) -based cemented carbide having Co as a main binder phase is used for cutting of a mold or the like. As such an end mill, the end portion of an end mill body having an outer shape that is rotated around an axis is a cutting edge portion, and a wall surface that faces the rotation direction of a chip discharge groove formed on the outer periphery of the cutting edge portion. Many so-called solid end mills in which cutting edges are formed at the side ridges have been proposed, for example, starting from Patent Document 1. Also, Ti carbide, nitride, carbonitride, composite carbide of Ti and Al, composite nitride, composite carbonitride, composite of Ti, Al and Si on the surface of the end mill body made of such a cemented carbide A number of surface-coated cemented carbide end mills coated with a hard film such as nitride have been proposed, for example, starting from Patent Document 2.
JP 2005-246492 A JP 2004-174616 A

  By the way, in recent years, there has been a strong demand for high-efficiency machining in the above-described cutting of molds, and so-called high-feed cutting, in which high-efficiency cutting is performed by increasing the feed rate of the end mill, is often used. It has become. However, such a high-feed cutting end mill naturally has a large burden on the end mill body, and there is a problem that the cutting edge is particularly likely to be damaged.

  Here, in the end mill described in Patent Document 1, a radius end mill in which a corner blade of which the outer peripheral blade and the bottom blade intersect among the cutting blades is curved so as to protrude toward the outer peripheral end of the end mill body is used. By gradually reducing the clearance angle of the blade from the tip of the outer peripheral blade toward the outer peripheral end of the bottom blade, the cutting blade strength is ensured so that the cutting blade will not be chipped or chipped even in high feed cutting. . On the other hand, in the end mill described in Patent Document 2, the cemented carbide forming the end mill body has toughness so that Co, which is a binder phase, becomes a fine Co grain dispersed structure, and is a strong mechanical component that is generated under high feed cutting conditions. Chipping is also prevented from occurring on the cutting edge due to impact.

  However, even with an end mill in which the shape of the cutting edge is improved as in Patent Document 1 or the structure of the cemented carbide forming the end mill body is controlled as in Patent Document 2, a high-hardness work material can be obtained. In the case of high feed cutting at a higher feed rate, it has been difficult to sufficiently suppress chipping of the cutting edge. Accordingly, an object of the present invention is to provide a surface coated cemented carbide end mill for high feed cutting that can more reliably suppress chipping of the cutting edge even when used in such high feed cutting. Yes.

  Here, in order to increase the fracture resistance of the cemented carbide end mill, it is generally considered that the toughness is increased by increasing the amount of Co. However, if the amount of Co is increased, the hardness of the cemented carbide decreases and the wear resistance also decreases. Therefore, it is conceivable to increase the hardness by atomizing the WC grain size in the cemented carbide.

  On the other hand, when the inventors of the present invention repeated high-feed cutting tests under various conditions using various cemented carbide end mills with increased Co content and WC grain size in this way, considerable heat was generated at the cutting edge. It was observed that it occurred. Therefore, the inventors of the present invention do not cause a cutting edge defect in high-feed cutting due to thermal damage to the base material of the cemented carbide in relation to these Co amount and WC grain size. As a result of conducting various experiments on the cemented carbide forming the end mill body, the WC grain size, the amount of Co as the main binder phase, and the type and amount of the grain growth inhibitor, When the coercive force related to the WC grain size and Co content and the thermal conductivity related to thermal damage have a specific relationship within a predetermined range in a hard alloy, even under conditions of high feed cutting with a higher feed rate It came to the knowledge that the outstanding defect resistance could be exhibited.

  The present invention has been made based on such knowledge, and has a cutting edge portion made of a tungsten carbide-based cemented carbide containing Co as a main binder phase, and the surface of the cutting edge portion is covered with a hard film. A surface-coated cemented carbide end mill, wherein the coercive force Hc (kA / m) in the tungsten carbide-based cemented carbide is in the range of 16.0 ≦ Hc ≦ 34.0, and the thermal conductivity λ ( W / m · K) is in the range of 120−2Hc ≦ λ ≦ 120.

  Here, the coercive force in the tungsten carbide-based cemented carbide is based on the magnetic properties of Co, which is the binder phase, and the smaller the WC grain size, that is, the higher the hardness of the cemented carbide, if the amount of Co is the same. As the individual Co magnetic domains are finely divided, the number thereof increases and the coercive force also increases. Therefore, when the coercive force of the cemented carbide forming the end mill body is increased, the hardness is also increased and the fracture resistance of the cutting edge is improved. However, if this coercive force is increased too much, the WC particle size is reduced. In other words, the coercive force Hc (kA / m) is set to 16. In the present invention, the coercive force Hc (kA / m) is reduced to 16. The range is 0 ≦ Hc ≦ 34.0. Incidentally, if the coercive force Hc (kA / m) is less than 16.0, the hardness is insufficient and the wear resistance is insufficient, and high-feed cutting cannot be performed.

  On the other hand, according to the above experiment by the inventor of the present invention, the thermal conductivity of the cemented carbide has a tendency to decrease in proportion to the higher the coercive force. On the other hand, if the thermal conductivity is not within a specific range, the cutting heat generated in the cutting edge is not dissipated under high feed cutting conditions, and the cutting edge resistance of the cutting edge is increased by improving the hardness of the cemented carbide. It was found that the damage was excessive and the defect could not be suppressed sufficiently. Therefore, in the present invention, the thermal conductivity λ (W / m · K) with respect to the coercive force Hc (kA / m) is in the range of 120−2Hc ≦ λ, whereby the hardness, strength and thermal conductivity of the cutting edge are set. In addition, it is possible to effectively suppress the occurrence of defects by harmonizing with the heat dissipating property. However, if the thermal conductivity is too high, the amount of Co is too small and the toughness is insufficient. Therefore, in the present invention, the upper limit of the thermal conductivity λ (W / m · K) is set to 120.

  The end mill main body only needs to be formed of at least the tungsten carbide base cemented carbide on the tip side where the cutting edge is formed, and therefore includes the shank portion on the rear end side. Of course, the entire body may be formed of such a tungsten carbide base cemented carbide. Moreover, as high feed cutting by such a surface-coated cemented carbide end mill, for example, when a steel material having a hardness of about 35 to 55 HRC is used as a work material, the outer diameter (diameter) D of the cutting edge is When it is 3 mm or more, the feed rate per cutting edge is 0.3 mm / feed rate or more, and when the outer diameter (diameter) D of the cutting edge is less than 3 mm, the feed amount per cutting edge is also this outer diameter. The cutting conditions are such that the feed rate is 0.05 × D / tooth or more with respect to D (mm).

  On the other hand, the hard coating coated on the surface of the cutting edge of the cemented carbide end mill increases the wear resistance of the cutting edge and improves heat resistance and oxidation resistance, thereby suppressing damage to the cutting edge and improving resistance. As such a hard film, a film made of a nitride or carbonitride of one or more elements of Al, Si, Ti, V, and Cr is used as such a hard film. In order to further improve the chipping resistance of the cutting blade, it is desirable that the layer is coated with a plurality of layers or a plurality of layers. Furthermore, the fracturing resistance can be further improved by applying a honing treatment with a honing width of 5 to 30 μm to the cutting edge of the above-mentioned cutting edge portion coated with the hard coating.

  As described above, according to the present invention, the cutting edge portion of the end mill body is formed of a tungsten carbide base cemented carbide having a predetermined range of coercive force and a specific range of thermal conductivity. By doing so, it is possible to balance the hardness and strength of the cutting edge with the thermal conductivity of the cutting edge, that is, the radiating property of the cutting heat, and to improve the chipping resistance of the cutting edge reliably and effectively. Therefore, even if the work material is high hardness, it is possible to perform cutting at a higher feed rate, and for high-feed cutting that can fully satisfy the demands for high-efficiency machining in cutting such as dies in recent years. It becomes possible to provide a surface-coated cemented carbide end mill.

  Hereinafter, embodiments of the present invention will be described based on specific examples.

In this example, WC powder having an average particle size of 0.3 to 1.5 μm, 1.1 μm VC powder, 1.3 μm Cr ₃ C ₂ powder, 0.9 μm TaC powder, and 1 as raw material powders, respectively These were appropriately blended with the blending composition shown in Table 1 below using .3 μm Co powder. However, the balance in the blend composition of Table 1 is WC.

  Each raw material powder thus blended is mixed with an attritor using alcohol as a solvent and 1% by weight of paraffin wax with respect to the raw material powder for 8 hours. After mixing, the resulting powder is filled into a mold. After press-molding into a round bar molded body of a predetermined size at a pressure of 100 MPa, dewaxing treatment, the temperature is raised to 1350-1450 ° C. in a vacuum of 1.3 Pa and sintered for 1 hour. Further, Ar was introduced at this sintering temperature, and the atmosphere pressure was increased to 6 MPa and held for 1 hour to perform HIP treatment. A round bar-shaped cemented carbide material was obtained. The results of measuring the coercive force and thermal conductivity of these materials are shown in Table 1 and the relationship is shown in FIG. In Table 1, the value of 120-2Hc with respect to the measured coercive force Hc (kA / m) is also shown. Further, the straight line S in FIG. 1 indicates a case where the thermal conductivity λ (W / m · K) is 120−2Hc = λ with respect to the coercive force Hc (kA / m).

  The round bar-shaped cemented carbide materials of the base symbols A to L thus obtained were each ground to form a chip discharge groove at the tip and sharpen the cutting edge. 12 types of two-blade ball end mills of the same shape and size indicated by 12 were produced. In these ball end mills, the outer diameter (diameter) D of the cutting edge was 6 mm, the radius of the bottom edge R was 3 mm, and the honing treatment was performed on the cutting edge with a honing width of 5 μm. Further, the surface of the cutting edge portion of these ball end mills was coated with a hard coating composed of each hard coating layer having the composition and layer thickness shown in Table 2 by the arc ion plating method. A cemented carbide end mill (tool numbers 1 to 6) and a comparative surface-coated cemented carbide end mill (tool numbers 7 to 12) were manufactured.

And by the surface-coated cemented carbide end mill of these examples and comparative examples,
Work material: SKD61 (hardness 52HRC),
End mill rotational speed: 16000 min ⁻¹
Feed rate: 9600 mm / min (feed amount per blade 0.3 mm),
Cutting depth: axial direction 0.3 mm, pick feed 1.8 mm,
Cutting method: down cut,
Cooling method: air blow,
End mill protrusion length: 21mm,
Cutting length: 200m,
The first cutting test was performed under the above cutting conditions, and the cutting edge was observed for every 50 m of cutting length, and flank wear with a wear width exceeding 0.2 mm was confirmed, or the size exceeding 0.2 mm The life of the end mill was determined by assuming the case where a defect in thickness occurred in the cutting edge as the life. The cutting test results are shown in Table 2.

  Accordingly, from the results of the cutting test shown in Table 2, the ball end mills having the tool numbers 1 to 6 according to the embodiments of the present invention do not reach the end of their life even when the cutting length is 200 m, that is, exceeds 0.2 mm. While flank wear and cutting edge defects were not observed, the ball end mills of comparative tool numbers 7 to 12 coated with the same hard coating were all damaged and worn before reaching the cutting length of 200 mm. It has become a lifetime. Among these, the ball end mill of the tool number 7 manufactured from the cemented carbide material made of the base symbol G having a coercive force Hc (kA / m) exceeding 34.0 has a shortage due to a lack of toughness of the cutting edge. On the contrary, the ball end mill of the tool number 9 manufactured from the cemented carbide material of the base symbol I whose coercive force Hc (kA / m) is less than 16.0 has flank wear due to insufficient wear resistance. Life has been reached due to the increase. On the other hand, even if the coercive force Hc (kA / m) is in the range of 16.0 ≦ Hc ≦ 34.0, the base symbols H, J, and B having a thermal conductivity λ (W / m · K) lower than 120-2Hc. In the ball end mills of tool numbers 8, 10, 11, and 12 formed of K and L cemented carbide materials, the life was expedited earlier than the ball end mills of tool numbers 7 and 9 due to the missing cutting edge. .

  Next, the tool numbers of the cutting edge outer diameter D (diameter), bottom cutting edge R radius, and cutting edge honing amount shown in the following table 3 are obtained by grinding from the cemented carbide materials of the base symbols A to L shown in Table 1. 13 to 22 2-blade ball end mills were produced. In these ball end mills, a hard film made of a single (Al, Ti) N hard coating layer having a layer thickness of 3 μm was coated on the surface of the cutting edge portion by an arc ion plating method. Accordingly, of these ball end mills, tool numbers 13, 15-17, 19, and 21 are the surface-coated cemented carbide end mills of the examples according to the present invention, and the remaining tool numbers 14, 18, and 20 are compared with this. An example. However, among the examples, the end mill with the tool number 13 has a honing amount of 32 μm exceeding 30 μm, and the end mill with the tool number 16 has a honing amount of 2 μm less than 5 μm.

  The surface-coated cemented carbide end mill thus obtained is based on the cutting conditions in Table 4 for tools Nos. 13 and 14, and the cutting in Table 4 for tools Nos. 15 to 18. Based on the condition (a), the tool lengths 19 and 20 are based on the cutting conditions in Table 4, and the tool numbers 21 and 22 are based on the cutting conditions in Table 4 and the cutting length is 5 m. A second cutting test was performed, and the tool life at that time was determined by the same evaluation as in the first cutting test. The cutting test results are shown in Table 5 for tool numbers 13 and 14, Table 6 for tool numbers 15 to 18, Table 7 for tool numbers 19 and 20, and tool numbers 21 and 22. Are shown together with the feed rate (feed amount per tooth) in Table 8.

  However, in this second cutting test, three surface-coated cemented carbide end mills with tool numbers 13 to 22 were prepared and tested three times under the same conditions, and the cutting length was 5 m. If the life is not determined at the time when the cutting test is completed, the cutting test with the cutting length of 5 m is performed by successively increasing the feed amount per blade as shown in Tables 5 to 8. Thus, cutting tests were conducted until all end mills reached the end of their lives. In Tables 5 to 8, a circle indicates that the life has not been reached, and a cross indicates that the life has been reached at the feed speed (feed amount per tooth) at that time, and is marked with-. Indicates that the previous cutting has reached the end of its life.

  From the cutting test results in Tables 5 to 8, first, according to Table 5, the end mill of the tool number 13 of the example according to the present invention has a longer life than the end mill of the tool number 14 of the comparative example, Moreover, it can be seen that high chipping resistance and wear resistance are exhibited even with high feed cutting with a large feed amount per tooth. Also, from the results in Table 6, it is apparent that the end mills of the tool numbers 15 to 17 of the examples according to the present invention have a longer life than the end mill of the tool number 18 of the comparative example. In these examples, the end mills with tool numbers 15 and 17 in which the honing amount (honing width) is in the range of 5 to 30 μm are more than the end mills in tool number 16 in which the honing amount is smaller than this range. Long life. Further, the end mill of the embodiment according to the present invention has a longer life as described above, and is common to end mills having a small outer diameter (diameter) of 4 mm or 1 mm as shown in Tables 7 and 8. It was a thing.

It is a figure which shows the relationship between the coercive force and thermal conductivity of the cemented carbide material concerning the Example and comparative example in embodiment of this invention.

Explanation of symbols

  S A straight line showing a case where the thermal conductivity λ (W / m · K) is 120−2Hc = λ with respect to the coercive force Hc (kA / m).

Claims (3)

A surface-coated cemented carbide end mill for high-feed cutting, having a cutting edge portion made of a tungsten carbide-based cemented carbide with Co as the main binder phase, and having a hard coating coated on the surface of the cutting edge portion. ,
The coercive force Hc (kA / m) in the tungsten carbide-based cemented carbide is
16.0 ≦ Hc ≦ 34.0
And the thermal conductivity λ (W / m · K) is
120-2Hc ≦ λ ≦ 120
A surface-coated cemented carbide end mill for high-feed cutting, characterized in that   The hard coating is a coating made of a nitride or carbonitride of one or more elements of Al, Si, Ti, V, and Cr, which is a single layer or a laminate of multiple layers. The surface-coated cemented carbide end mill for high-feed cutting according to claim 1, wherein the end mill is made of high-feed cutting.   3. The surface coated cemented carbide end mill for high feed cutting according to claim 1 or 2, wherein a honing treatment having a honing width of 5 to 30 [mu] m is applied to the cutting edge of the cutting edge portion.

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