JP2009039810A - Method for drilling hole in fiber-reinforced composite material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To drill a high-grade hole with reduced burrs and fuzz in a fiber-reinforced composite material represented by FRP, and maintaining excellent hole drilling quality for a long period of time by extending the service life of a tool while suppressing an increase in economic burden. <P>SOLUTION: The hole is drilled in the fiber-reinforced composite material comprising reinforced fiber and matrix resin by using a ball end mill 1 or a radius end mill. The feed of the tool per one blade, and a ratio of the radius of the inscribed circle of a cutting edge to the feed are appropriately selected, and hole drilling is performed while sucking chips. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  This invention is a fiber that makes it possible to drill so-called burrs, fluff, flaking, and high-quality holes with less chipping with a rotary cutting tool in a fiber-reinforced composite material reinforced with a matrix resin using a reinforcing fiber such as carbon fiber. The present invention relates to a method for drilling a reinforced composite material.

  Fiber reinforced composite materials represented by FRP (Fiber Reinforced Plastics), especially CFRP (Carbon Fiber Reinforced Plastics), because of their large specific strength and specific elastic modulus, have recently been widely used as outer panels for aircraft and vehicles. Tend to be. The member formed by this FRP is fixed to the structure using fastening elements such as bolts and rivets. For this reason, when using FRP material for structures, such as aircraft parts, it is necessary to make many holes for passing a fastening element in FRP material.

  The drilling of the FRP material is usually performed by using a drill. However, in the drilling by a general drill, fiber fluff as shown in FIG. 7 is likely to occur at the exit portion of the processed hole. Further, delamination of the laminated reinforcing fibers is likely to occur, and there is a high possibility that a problem in processing quality will occur. On the other hand, high-quality processing is particularly required in the manufacture of aircraft structures and the like, and it is extremely important to avoid the fuzz and delamination described above.

  The above-described fuzzing that deteriorates the processing quality is more likely to occur as the tool wear progresses and the processing resistance increases. On the other hand, in the processing of high-strength CFRP material, etc., the wear of the tool tends to be accelerated, and as a result, the tool change is accelerated in order to maintain the processing quality, and the ratio of the tool cost to the processing cost becomes high. It is the actual situation.

  In order to solve such a problem, several techniques have already been proposed (for example, see Patent Documents 1 to 3 below). Among these, in Patent Document 1, the twisted groove is a reversely twisted groove (a groove twisted in the drill rotation direction from the distal end side toward the proximal end side) and the cutting edge at the distal end is viewed from the rotation direction. We have proposed a twist drill formed in a V shape in which the inner periphery and the outer periphery intersect each other at the intermediate portion. The drill has an axial rake of the cutting edge by making the twist groove into a reverse twist groove. A negative angle cuts the fiber in the FRP so as to push it out, and the cutting edge has a V-shape to prevent vibration during processing and suppress burrs and whips at the hole edge. It is said.

In Patent Document 2, the cutting edge at the tip is constituted by a plurality of cutting edges that are radially divided, and the tip angle of the outer peripheral cutting edge is made smaller than the tip angle of the cutting edge on the rotation center side. ,further,
A drill is proposed in which a member having a higher hardness than the center of rotation is disposed on the outer peripheral side of the cutting edge. In the drill, the wear resistance of the outer peripheral portion of the cutting edge where the cutting speed is increased is enhanced by the high hardness member,
The wear of the cutting edge at the center of rotation proceeds while being guided by the high hardness member, so that the runout of the drill can be suppressed. Furthermore, since the tip angle of the outer peripheral side cutting edge portion is smaller than the tip angle of the cutting edge portion on the rotation center side, the action of expanding the hole by the outer peripheral portion of the cutting edge is reduced and the generation of burrs is suppressed.

Further, Patent Document 3 discloses that a back taper portion whose outer diameter decreases at a predetermined rate as it goes from the tip toward the shank portion is a tip portion of the drill over an axial length range of 0.5 to 1.0 times the drill diameter. In addition, the diameter of the portion following the back taper portion is made constant. Further, similarly to Patent Document 2, the cutting edge is divided into a cutting edge portion having a large tip angle and an outer cutting edge portion having a small tip angle. A structure in which a plurality of nicks for cutting chips are provided in each of the two cutting edges is proposed. In this drill, the cutting resistance is reduced by the installation of the back taper portion or the cutting of chips by nicking, so that it is possible to reduce the tool wear and increase the time during which a good machining quality can be maintained.
Japanese Patent No. 2699527 Japanese Patent No. 2984446 Japanese Patent No. 3534839

  The drills disclosed in the above-mentioned Patent Documents 1 to 3 cannot be said to sufficiently meet the demand for maintaining good processing quality for a longer time in processing of fiber-reinforced composite materials. For example, in the drill of Patent Document 1, the load during processing is concentrated on the outer peripheral portion having a sharp cutting edge, and wear and chipping are likely to occur in the same portion. In addition, burrs and fluffing inevitably occur if machining is performed with the blade edge damaged, but the entire outer periphery of the cutting edge cuts through the work piece at the same time, and the axial rake has a negative angle. Therefore, the generated burrs and fluff remain without being removed, and it is difficult to maintain good processing quality.

  In addition, since the drills of Patent Documents 2 and 3 gradually enlarge the processing hole with the outer peripheral cutting edge, burrs once generated, and recutting with subsequent blades of fluffing are repeated, and by the recutting, burrs, It is possible to scrape fluff. However, when the joints (parts where the tip angle is changed) of the cutting blades cut through the work material, large burrs are likely to occur, and when the number of holes is increased and the joints are damaged, the outer peripheral cutting blades As a result, the removal of burrs becomes insufficient and the processing quality deteriorates. In addition, disposing a high-hardness member such as diamond on the outer peripheral portion is effective in suppressing wear, but increases the cost of the tool, so the wear amount is suppressed by a substrate made of cemented carbide or the like. It should be limited to just handling and coating the hard film on the base material.

  Although attempts have been made to improve the FRP material itself so that burrs and fluff are less likely to occur, in order to eliminate the above problems in drilling existing materials that have been used as aircraft materials, etc. It is necessary to cope with improvement of the drilling method.

  This invention can drill high-quality holes with few burrs, fluffs, flaking and chipping in fiber reinforced composite materials, and also prolongs the tool life while suppressing an increase in economic burden, resulting in excellent machining quality for a long time. The challenge is to be able to maintain it.

  As a result of repeating drilling tests with various tool shapes, the inventors have found a drilling method that can solve the above problems. In this method, a fiber reinforced composite material containing reinforcing fibers and a matrix resin is drilled using a ball end mill or a radius end mill. The present invention provides a method for drilling such a fiber reinforced composite.

  The end mill is usually used for die-cutting, step machining, and the like, but has a cutting edge on the tip side from the center of rotation to the outer periphery, so in principle, drilling is also possible. Usually, the cutting resistance is high and the chip disposability is poor, so it is not suitable for drilling and is not used as a drilling tool. However, in the processing of FRP material reinforced with carbon fiber, chips are not generated. Since it is produced in the form of powder, there is no problem with chip disposal. In addition, the end mill is used for drilling because the cutting mechanism is significantly different from normal metal processing, and processing is performed by cutting reinforcing fibers, and low feed conditions are generally applied to maintain the processing quality. However, as will be described later, the cutting force does not increase, but it is possible to suppress the increase of the cutting force over a long period of time.

In the drilling method of the present invention, it is preferable that the feed amount per blade of a tool (ball end mill or radius end mill) at the time of drilling is set to 0.03 mm or less for processing. In addition to setting the feed amount f per blade of the tool to 0.03 mm or less, the inscribed circle radius of the cutting edge forming the arc shape of the ball end mill or the radius end mill is defined as R, and R and the It is more preferable to perform processing with the ratio f / R of the feed amount f per tooth being 0.03 or less.
Furthermore, it is also preferable to use a ball end mill or a radius end mill having a back taper whose outer diameter decreases toward the shank side, and it is possible to perform drilling while suctioning chips generated at the time of drilling using a chip suction means. preferable.

  This invention can of course be used for drilling GFRP (glass fiber reinforced plastics), KFRP (polyester fiber reinforced plastics), etc., but the tool is more easily worn than other FRP processing, and the quality of the processing is high. A particularly large effect can be expected when used for through-hole processing of a CFRP material that is difficult to maintain for a long time.

  In the processing of fiber reinforced composite materials, it is necessary to cut the fibers as described above, and in order to cut the fibers well, the cutting edge should be as close to the vertical as possible with respect to the fiber direction (longitudinal direction). Is desired. When drilling is performed with a ball end mill or a radius end mill, it becomes possible to meet the demand.

  Holes in the fiber reinforced composite are perpendicular to the fiber orientation. On the other hand, ball end mills and radius end mills have an arc shape in which the outer periphery of the cutting edge rises gradually, and the direction of the cutting edge is almost parallel to the tool axis at the outer end connected to the outer cutting edge (the influence of the twist angle etc.). The one received is not perfectly parallel). This means that the cutting edge is infinitely perpendicular to the fiber when machining the edge of the hole. Therefore, it is ideal that the outer peripheral side of the cutting edge has an arc shape, and since the hole expanding process is performed gradually by the arc-shaped cutting edge, burrs and fluffing that occurred at an early stage after the start of processing are generated. It is effectively scraped off by the subsequent blade until the hole expansion is completed. In addition, as the cutting edge gets closer to the outer cutting edge, the rising angle (crossing angle to the fiber) becomes steeper, so that the generation of new burrs when the outer peripheral work area is machined can be suppressed, and the hole surface can be wiped off. And the surface roughness of the hole is improved. In addition, when machining with arc-shaped cutting edges, the cutting thickness at the outer periphery is small, so the cutting resistance (thrust force) per unit cutting edge length is reduced, and the work material consists of several prepreg layers. It can be expected to improve the processing quality of the hole, such as suppressing delamination that is likely to occur when it is configured.

Further, unlike the drills disclosed in Patent Documents 1 to 3, the ball end mill and the radius end mill do not have a specific step shape in the cutting edge portion. Therefore, the generation of burrs is most likely to occur when the center of rotation starts machining a hole in the initial stage, and thereafter the workability is monotonously improved. For this reason,
It is less likely to leave burrs and is effective in suppressing delamination as described above. In addition, since there is no unique step shape in the cutting edge, the possibility of abnormal damage occurring at a specific location is small.

  When drilling with a ball end mill or a radius end mill, the entire cutting edge is involved in the cutting. For this reason, there is little difference in the damage status of each part of the cutting edge, and even if a part of the cutting edge is damaged, the subsequent cutting edge is struck (finished), and the adverse effect on the machining quality is suppressed to a small level.

  In addition, in the processing of the plate material, a plurality of sheets may be stacked to make a hole at a time, but even in such processing, if an end mill having an arc cutting edge is used, the upper plate material is penetrated to the lower plate material. Since the change (increase) in the cutting force at the time of processing is moderated, the lift of the stacked plate materials is suppressed, and the deterioration of the processing quality and hole accuracy due to the lift is also suppressed.

  Also, unlike a drill, the ball end mill and radius end mill have no margin on the outer periphery. For example, powdered chips generated when machining CFRP are less likely to clog between the land and the hole wall surface. Good results for improving the quality of the wall.

  Furthermore, in the processing of fiber reinforced composite materials, processing such as cutting and trimming of cut edges is often performed, and the processing is performed using an end mill, but when drilling is performed using a ball end mill or a radius end mill, The end mill can also be used for cutting and trimming. In cases where drilling, cutting, and trimming are required, there is an advantage in terms of tool integration and tool change.

  In addition, in addition to setting the feed amount f per blade of the end mill at the time of drilling to 0.03 mm or less, preferably the feed amount f per blade is 0.03 mm or less, the ball end mill or the radius is further reduced. When the inscribed circle radius of the cutting edge forming the arc shape of the end mill is R, and the ratio f / R between the R and the feed amount f per blade is 0.03 or less, high machining quality can be obtained.

Further, the end mill generally does not have a back taper unlike a drill or the like, and the tool outer peripheral diameter is uniform. For this reason, when the hole to be processed is deep, the outer peripheral blade interferes with the inner wall of the hole due to the influence of the minute deflection of the tool, etc., causing vibration during processing and increasing the diameter of the hole at the hole entrance. A processing method performed using an end mill having a back taper can avoid such a problem. In principle, this effect starts to appear when the hole depth exceeds the inscribed circle radius (R radius) of the arc-shaped cutting edge of the ball end mill or the radius end mill. It becomes.
In addition, if drilling is performed while suctioning chips generated during drilling using the chip suction means, clogging of powdered chips between the land part of the end mill and the hole wall surface is more reliably prevented, and chip clogging occurs. This eliminates the degradation of the processing quality caused by

Example 1
Examples of the present invention will be described below. FIG. 1 shows a tool used for drilling in Invention Example 1. The tool is a ball end mill (SSB2060 manufactured by Sumitomo Electric Hardmetal Co., Ltd.). The ball end mill 1 includes a main body 2 and a shank 3 held by a holder of a machine tool, and has a semicircular ball blade (cutting edge) 4 having a radius R = 3 mm at the tip of the main body 2. Further, an outer peripheral edge (cutting edge) 5 and a twisted groove 6 are provided on the outer periphery of the main body 2. A land portion 7 is provided between the two twisted grooves 6 and 6, and a flank 8 is formed between the land portion 7 and the outer peripheral blade 5. The material of the tool is JIS Z20 type cemented carbide (the same is true for the comparative example).
For the processing of the comparative example, a general twist drill having a tip angle of 140 ° (MDS060MG manufactured by Sumitomo Electric Hardmetal Co., Ltd.) and a square end mill having a flat tip (JSM2060 manufactured by Sumitomo Electric Hardmetal Co., Ltd.) were used. . In either case, the outer diameter is 6 mm and has two blades.
On the other hand, the material to be processed (work material) is a CFRP plate material, and eight layers of prepregs reinforced with carbon fibers are stacked in the in-plane direction of the plate material and joined to a total thickness of 2.78 mm. . When this CFRP material was observed in a cross section in the plate thickness direction, each prepreg layer contained a fiber bundle layer having a thickness of 50 to 700 μm.
The CFRP material was drilled using the above tools. The machining conditions at this time were a cutting speed of 100 m / min, a feed rate per tooth (f) of 0.025 mm / tooth, and through-hole machining by a dry method.

  Table 1 summarizes the outer diameter of the tool used, the thrust force at the time of processing the first hole and the 100th hole, the maximum length of burr (fluff) at the hole exit, and the wear amount of the tool flank. The thrust force is data for evaluating the cutting resistance.

  Inventive Example 1 in which drilling was performed with a ball end mill, both the thrust force (cutting resistance) and the wear amount were smaller than those in Comparative Example 1 using a twist drill. Further, Comparative Example 2 using a square end mill also has a smaller thrust force and wear amount than Comparative Example 1, but there is an extreme difference when comparing the size of burrs, particularly the size at the 100th hole. The superiority of the present invention is remarkable in terms of processing quality. The properties of the machined hole H by the method of Invention Example 1 are shown in FIG. 2, the properties of the machined hole H by the method of Comparative Example 1 are shown in FIG. 3, and the properties of the machined hole H by the method of Comparative Example 2 are shown in FIG. Each is shown. Both are the properties of the first and 100th holes.

  In addition, since the entire bottom blade is involved in cutting at the same time, the square end mill has a strong effect of peeling the upper and lower layers from each other in the processing of a CFRP material having a laminated structure. Chipping (peeling) around the hole outlet is likely to occur (see FIG. 4). On the other hand, in the invention example 1 which drilled with the ball end mill, the chip | tip has hardly generate | occur | produced (FIG. 2), and this invention is excellent also in this point.

  As for the wear of the tool, in Comparative Examples 1 and 2, the wear of the margin portion where the chips are easily clogged with the hole wall surface and the outer edge of the cutting edge having a high working speed tends to be large. In this case, the wear situation of the ball blade and the flank is uniform, which is considered to be effective in suppressing abnormal damage and local damage when the number of holes processed further increases.

  In addition, when the state of the hole wall surface of the hole processed into the 1st hole was also confirmed, the surface in which the hole in invention example 1 was almost peeled was not confirmed. On the other hand, peeling of a length of about 2 to 3 mm was observed in the processed hole H according to Comparative Example 1. The hole surface of the processed hole H according to Comparative Example 2 was also normal. Since the end mill has a clearance angle on the outer peripheral blade (no margin), it is difficult for chips to be clogged between the outer peripheral surface and the hole wall surface, which is considered to have contributed to improving the properties of the hole wall surface.

-Example 2-
Next, the effect of the tool feed amount per blade on the machining quality was investigated. The tool used here is a ball end mill (SSB2060 manufactured by Sumitomo Electric Hardmetal Co., Ltd.) having an outer diameter of φ6 mm (ball blade radius R = 3 mm), and the tool feed amount f per blade is 0.025 mm to 0.00. The cutting force (thrust force) at that time was evaluated up to 35 mm / tooth. Processing conditions other than feeding are the same as those in the first embodiment. The result is shown in FIG. As can be seen, the thrust force increases as the tool feed amount f per tooth increases. In particular, when the tool feed amount f per blade exceeds 0.025 mm / tooth, the thrust force exceeds 200 N. As for the burr at the hole exit, the size is 0.05 mm when f = 0.025 mm / tooth, and 0.43 mm when f = 0.05 mm / tooth, when a higher processing quality is required. The tool feed per blade is desirably suppressed to 0.03 mm / tooth or less.

Example 3
Next, the outer periphery of the ball end mill and the cutting edge is arcuate like the ball end mill (
For the radius end mill having the R shape, the influence of the radius of curvature of the arc-shaped cutting edge on the machining quality was investigated.
Here, as a tool, a ball end mill (SSB2080ZX manufactured by Sumitomo Electric Hardmetal Co., Ltd.) with an outer diameter of φ8 mm (ball blade radius R = 4 mm) and a radius of curvature of the cutting edge corner portion with an outer diameter of φ8 mm (cutting blade outer peripheral portion) Two types of radius end mills (SSM2080ZX-R0.5, R1.0 manufactured by Sumitomo Electric Hardmetal Co., Ltd.) having a corner R) of 0.5 mm and 1.0 mm were used. For comparison, a twist drill having an outer diameter of φ8 mm (MDS080MK manufactured by Sumitomo Electric Hardmetal Co., Ltd.) was also used. Both are coated tools having a (Ti, Al) N-based coating on the surface.
The machining conditions were a cutting speed of 133 m / min, a feed amount per tooth (f) of 0.025 mm / tooth, and through-hole machining by a dry method. The same work material as in Example 1 was used.
Table 2 shows the radius of curvature R of the edge corner of the end mill used in this machining, the ratio of the feed rate f per tooth to the radius of curvature R of the edge of the cutting edge, and the maximum burr length after drilling the first hole. Shown in

  In comparison with Comparative Example 3, Invention Example 2 using a ball end mill in Example 2 shows that good processing quality can be obtained in drilling a fiber-reinforced composite material. In addition, it can be confirmed that the invention example 3 and the invention example 4 using the radius end mill also reduce the generated burr compared to the comparative example 3. It was confirmed by this test that not only burrs but also chips were suppressed, and the processing quality is clearly superior to that of Comparative Example 3. Inventive Example 4 in which the radius of curvature R of the cutting edge corner portion is small is slightly inferior in machining quality compared to Inventive Examples 2 and 3, and it is advantageous that the curvature radius R of the cutting edge corner portion is larger. ing.

Example 4
The influence of the shape of the tip center part (rotation center part) of the cutting edge when the fiber reinforced composite material was processed in a stacked state was evaluated. The tools used in this test are two products, the ball end mill adopted in Invention Example 1 of Example 1 and the twist drill adopted in Comparative Example 1.
The work material is a CFRP plate similar to that of Examples 1-3. Five CFRP materials were stacked without being bonded and clamped on a processing table, and a through hole was processed with a sample tool. Then, the cutting resistance (thrust force) during machining was measured, and the fluctuation range (its maximum value) of the thrust force from when the tool outer peripheral portion started to participate in machining until the tool tip began to penetrate was examined. In addition, the state of processing was photographed with a video camera, and the presence or absence of the phenomenon that the plate material floats during processing was verified. The results are shown in Table 3.

  From this test result, it can be seen that in the machining using the ball end mill, the fluctuation range of the cutting resistance is small and the lifting of the plate material is suppressed.

-Example 5
The test which evaluates the effectiveness of the method of processing while sucking chips using a chip suction means was conducted. Here, as shown in FIG. 6, the ball end mill 1 is mounted on the spindle 11 of the machining center 10 through the tool holder 12 in the same manner as is normally performed, and then a cover 15 that covers the processing portion is attached. The cover 15 is a component of the chip suction means 13. The chip suction means 13 includes a suction device 14, a cover 15, and a hose 16 that connects both of them. A commercial vacuum cleaner was used for the suction device 14. The cover 15 has a cylindrical movable cover 15b capable of axial relative sliding at a lower portion of a fixed cover 15a attached to the machining center 10, and the movable cover 15b is placed on the upper surface of the work material W prior to the tool. In this state, the main shaft 11 is further lowered and drilling is performed by the ball end mill 1. Therefore, the machining portion is always surrounded by the cover 15 during machining, and the generated chips are forcibly removed by suction.

  This test was carried out using a ball end mill with an outer diameter of φ6 mm under the same conditions as in Example 1, and the properties of the hole wall surface when the obtained hole chips were sucked and when not obtained Compared. As a result, the hole processed without sucking chips was observed to be 1 mm or less, but peeling was observed on the wall surface. On the other hand, the holes processed while sucking the chips were reduced to a level at which peeling was not visually confirmed. Chip clogging between the tool periphery and the hole wall surface is considered to be a factor in the hole wall peeling, and the chip clogging is suppressed to some extent by using an end mill with no margin on the outer peripheral edge and a clearance angle. However, it is considered that the adverse effect of the chips is more reliably eliminated by sucking the generated chips and the properties of the hole wall surface are improved.

-Example 6
Next, the effect of back taper in deep hole machining was examined. The work material used in this example is a CFRP material having a thickness of 14 mm. This material was drilled using a ball end mill having a diameter of 5 mm, and the hole diameters at the inlet and outlet of the hole were measured. The used ball end mill has a normal outer diameter with no back taper (SSB2050 manufactured by Sumitomo Electric Hardmetal Co., Ltd.) and the same equivalent, with an outer peripheral portion of 0.3 mm per axial length of 100 mm. There are two types with back taper. The results of this experiment are shown in Table 4. As can be seen from Table 4, when a normal ball end mill is used, in deep hole machining, the hole diameter tends to expand at the inlet portion of the hole. In this embodiment, the inlet diameter is about 0.04 mm larger than the outlet diameter. It has become. In contrast, the hole diameter difference at the entrance and exit when using a ball end mill with a back taper is as small as 0.006 mm, indicating that the back taper is effective for deep hole machining.

  In addition, this invention is not limited to said Example. For example, although the example about a radius end mill is only Example 3, since the subject of this invention is solved by drilling with the tool which has an arc-shaped cutting edge, when drilling with a radius end mill, The object of the invention is also achieved.

The figure which shows an example (ball end mill) of the tool used for implementation of the method of this invention The figure which shows the processing hole {(a): 1st hole, (b): 100th hole} in invention example 1. The figure which shows the processing hole {(a): 1st hole, (b): 100th hole} in the comparative example 1. The figure which shows the processing hole {(a): 1st hole, (b): 100th hole} in the comparative example 2. Diagram showing the relationship between feed per blade and thrust force Outline explanatory diagram of drilling method using chip suction means The figure which shows the fluff of the fiber of the exit part of the drilling processed into FRP material

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ball end mill 2 Main body part 3 Shank 4 Ball blade 5 Outer peripheral blade 6 Torsion groove 7 Land part 8 Flank 10 Machining center 11 Spindle 12 Tool holder 13 Chip suction means 14 Suction device 15 Cover 15a Fixed cover 15b Movable cover 16 Hose R Arc shape Cutting edge radius of curvature W Workpiece material H Drilling hole

Claims (6)

  A method for drilling a fiber reinforced composite material, wherein a fiber reinforced composite material including a reinforcing fiber and a matrix resin is subjected to drilling using a ball end mill or a radius end mill.   The method for drilling a fiber-reinforced composite material according to claim 1, wherein the processing is performed with a feed amount f per blade of the tool at the time of drilling being 0.03 mm or less.   In addition to setting the feed amount f per blade of the tool to 0.03 mm or less, the inscribed circle radius of the cutting edge forming the arc shape of the ball end mill or the radius end mill is defined as R, and R and the tool The method for drilling a fiber-reinforced composite material according to claim 2, wherein the processing is performed with the ratio f / R of the feed amount f per blade being 0.03 or less.   The method for drilling a fiber-reinforced composite material according to any one of claims 1 to 3, wherein an end mill having a back taper whose outer diameter decreases toward the shank side is used as the ball end mill or the radius end mill. .   The drilling method of the fiber reinforced composite material according to any one of claims 1 to 4, wherein drilling is performed while suctioning chips generated during drilling using a chip suction means.   The said fiber reinforced composite material is carbon fiber reinforced plastics, The drilling method of the fiber reinforced composite material in any one of Claims 1-5 which opens a through-hole in this carbon fiber reinforced plastics.