Patent Application
20120269591
The present invention relates to a drill suitable for boring of a composite material such as a fiber reinforced composite material represented by CFRP (Carbon-fiber Reinforced Plastics), and more particularly to a drill for a composite material capable of high-quality boring without causing burrs on a machined portion by one-time boring work or causing delamination on the bored surface.
In the boring of a fiber reinforced composite material and the like represented by CFRP, a method by using a straight cemented carbide drill coated with diamond is well-known.
However, when boring is performed at once with this method, cutting resistance at the time of the boring is large, and burrs are easily generated in the bored portion. As a method for suppressing generation of burrs, Patent Document 1 describes a drill for machining FPC (Flexible Printed Circuits) in which a flank is formed of a second flank and a third flank, and a relief angle of the third flank is set to 33° to 50° so that the length of a cutting edge on the outer periphery side is made smaller than that of the chisel edge. Since the width of a chip generated by a blade thereof is reduced, discharge performance of the chips is improved, and burrs caused by deterioration in discharge performance are suppressed.
In addition, Patent Documents 2 and 3 describe a drill which suppresses burrs on a through-hole by providing a small diameter portion on the tip side. Patent Document 4 describes a double-angle drill in which a primary blade having a tip angle of 118° and a secondary blade having a tip angle of approximately 30° are consecutively provided as a drill suitable for simultaneous boring of CFRP and an aluminum alloy plate. Patent Document 5 describes a double-stage drill having a prepared-hole boring portion for boring a prepared hole and a finishing portion, in which a diameter difference between the finishing portion and the prepared-hole boring portion is set to 0.1 mm or more and 2 mm or less as a drill suitable for boring of CFRP.
The fiber reinforced composite material or particularly, CFRP has high strength and rigidity despite its light weight and is frequently used as a structural material of an aircraft and the like. The CFRP used as the structural material of an aircraft is quite demanding in terms of quality, and it is required, for example, that no burrs protrude on an abutted surface with another member or the like and no delamination occurs on a bored surface of the CFRP.
However, since the CFRP contains a carbon fiber which cannot be cut easily and has a structure in which the carbon fiber and a resin material as a binder for binding it are formed in layers, burrs are easily generated on a machined portion rather than a member to be machined made of a single material of a resin material or a metal material in boring, and delamination is easily caused due to thrust resistance at the time of machining. Such a problem regarding boring of a fiber reinforced composite material cannot be effectively solved by the technologies described in Patent Documents 1 and 2 on practical side. Here, the “thrust resistance” is a resistance force applied in a direction opposite to the boring feed direction in drilling.
Patent Document 3 copes with the problem only by forming the small diameter portion on the tip side of the drill in the same manner as in Patent Document 2, and thus, when the member to be machined is CFRP, a satisfactory effect cannot be obtained for suppression of burrs even through the use of the technology described in Patent Document 3.
Therefore, when high-quality machining is required in boring of CFRP, a dedicated drill as described in Patent Document 4 is employed, but a double-angle drill described in Patent Document 4 has a problem in durability since burrs are generated in the machined portion in machining of 30 to 40 bores, and the drill is required to be replaced by a new one.
The drill described in Patent Document 4 is a drill having the double-stage structure with the prepared-hole boring portion and the finishing machining portion and has a machining form in which the burrs generated on the prepared-hole boring portion is removed by the finishing machining portion. However, in the case of a shape in which the diameter difference between the finishing machining portion and the prepared-hole boring portion is increased, the cutting mechanism is the same as in the case of usual drilling, and thus the suppression of tears or burrs is not fundamentally solved.
Therefore, in Patent Document 4, measures are taken to suppress generation of burrs due to chip clogging by improving chip discharging performance through reduction of a distortion angle. However, only the formation of the machining portion into a straight cutting edge structure cannot reduce the thrust resistance at the time of machining or does not lead to improvement of abrasion resistance of the blade tip of the tool, and thus the technology described in Patent Document 4 cannot realize a satisfactory effect, either.
In Patent Document 5, the prepared-hole boring portion has a plural-step structure, and thus the thrust resistance received by the drill at the time of diameter expansion is large, and improvement of abrasion resistance of the blade tip of the tool has a problem.
The present invention has been made in view of the above-described problems of the prior-art technologies and an object of the present invention is to realize high-quality boring in one step in which almost no burrs are generated or almost no delamination is caused in the member to be machined by performing composite machining by a drill provided with a tapered portion having a tapered shape and a straight portion.
A drill for a composite material according to the present invention is a drill for a composite material for boring a member to be machined containing a fiber reinforced composite material at least partially, having a tip portion on which a tip cutting edge is formed and a tapered portion formed so as to be connected to the rear end side of the tip portion and formed so as to have a tapered shape with a diameter difference between a diameter on the tip side and a diameter on the rear end side larger than the diameter on the tip side, in which a helically twisted outer peripheral cutting edge is formed on an outer periphery of the tapered portion and set so that a boring diameter becomes continuously larger, and a straight portion formed so as to be connected to the rear end side of the tapered portion and formed entirely so as to have the same diameter such that a finishing machining diameter larger than the diameter on the rear end side of the tapered portion can be formed is provided. Moreover, the tapered portion has a helically twisted chip discharge flute formed along the outer peripheral cutting edge. Moreover, the tapered portion has a taper angle set to 45° or less between an outer diameter line tangential to the outer diameter of the tip side as well as the outer diameter of the rear end side thereof and a center line of a drill axis. Moreover, the tip cutting edge of the tip portion has a tip angle of 60° to 140°, the outer peripheral cutting edge of the tapered portion is formed continuing to the tip cutting edge, and a rake angle is formed, or a rake angle and a relief angle are formed with respect to a conical face tangential to a land outer periphery of the tapered portion. Moreover, the tip portion, the tapered portion, and the straight portion are integrated coaxially. Moreover, the straight portion is formed into a shape of a circular land drill or a reamer. Moreover, an axis of the tip portion, an axis of the tapered portion, and an axis of the straight portion are matched with a rotation axis. Moreover, a connection portion between the tapered portion and the straight portion is connected by reducing, in a tapered shape, the outer diameter on the tip side of the straight portion toward the outer diameter on the rear end side of the tapered portion.
A machining method according to the present invention is a machining method for boring a member to be machined containing a fiber reinforced composite material at least partially by using the above drill, in which boring is performed by boring a prepared hole in the member to be machined by the tip cutting edge of the tip portion and the outer peripheral cutting edge of the tapered portion and by finishing the formed prepared hole by the straight portion.
A machining apparatus according to the present invention is provided with driving means for holding the drill and also for rotating and driving the drill around the drill axis, supporting means for supporting a member to be machined containing a fiber reinforced composite material at least partially, and moving means for relatively moving the driving means and/or the supporting means so that the drill performs boring on the member to be machined.
The drill for a composite material according to the present invention is capable of boring a prepared hole while expanding the diameter while cutting resistance is kept low by the tapered portion, burrs cannot occur easily on the machined portion, and moreover, the thrust resistance applied to the member to be machined in the boring direction is reduced, and a delamination force acting on the boundary surface in the composite material decreases and thus, delamination cannot easily occur. Moreover, since the straight portion for performing the finishing machining and the tapered portion are set coaxially and configured continuously and integrally and thus, highly accurate boring can be performed.
Moreover, since the drill is provided with the tip cutting edge, the outer peripheral cutting edge on which the rake angle or the rake angle and the relief angle are formed with respect to the conical face tangential to the land outer periphery of the tapered portion, and the straight portion connected to it, cutting resistance is reduced, and highly accurate boring can be realized hardly causing burrs or delamination.
Embodiments of the present invention applied to a double-bladed drill having two twist flutes will be described by referring to a first embodiment in which a straight portion is formed so as to have a reamer shape and a second embodiment in which the straight portion is formed so as to have a circular land drill shape.
The first embodiment according to the present invention will be described on the basis of
The drill 1 according to the present embodiment is a double-bladed drill, in which a straight portion 3 forming a reamer is connected to the tip of a shank 2, and a tapered portion 4 is integrally connected to the tip of the straight portion 3. At the tip of the tapered portion 4, a tip cutting edge 5 which is a tip portion is formed.
The tip cutting edge 5 is a cutting edge which first cuts into a member to be machined and performs cutting and induces diameter-expanding machining by means of an outer peripheral cutting edge 7 formed on the tapered portion 4. By forming its tip angle within a range of 60° to 140°, cutting performance and centripetal characteristic of the drill are improved, and wobbling of the drill is reduced.
As illustrated in
The tapered portion 4 has a tapered shape formed with a diameter difference between an outer diameter D1 on the tip side and an outer diameter D2 on the rear end side, and the straight portion 3 is integrally connected to the rear end side. The straight portion 3 is formed so as to have a diameter larger than that of the tapered portion 4. Here, the term “taper” means a shape in which a predetermined angle is set between a straight line tangential to the outer diameter on the tip side and the outer diameter on the rear end side and the drill center axis.
The tapered portion 4 has a candle-grinding shape as illustrated in
The chip discharge flute 6 provided on the outer periphery of the tapered portion 4 is formed as a flute having a twist angle α3. The twist angle α3 of the chip discharge flute 6 is preferably set to 60° or less in order to prevent the cutting edge from becoming too sharp and being chipped easily, though it depends on the size of the tip angle and the material of the member to be machined, and by setting the angle to 60° or less, chips containing a fiber material made of a composite material can be quickly discharged.
As illustrated in
As illustrated in
As illustrated in
As illustrated in
The straight portion 3 is formed into a reamer shape in order to shape and machine the portion remaining after being cut out by the tapered portion 4 which performs prepared-hole boring and is formed to have a finishing machining diameter D3 larger than the rear end side outer diameter D2 of the tapered portion 4 by 0.01 to 0.1 mm. The axis of the tip cutting edge 5, the axis of the tapered portion 4, and the axis of the straight portion 3 are matched with the rotation axis, and the connection portion between the tapered portion 4 and the straight portion 3 is connected for machining with a tolerance of coaxiality of 0.01 while the outer diameter on the tip side of the straight portion 3 is reduced in a tapered shape toward the outer diameter on the rear end side of the tapered portion 4, and boring with good machining quality can be realized without causing burrs. Moreover, the tip cutting edge 5, the tapered portion 4, the straight portion 3, and the shank 2 are also connected with tolerance of coaxiality of 0.01
As the material of the drill, cemented carbide, high-speed steel, tool steel and the like can be included, and the use of the cemented carbide is preferable for the tapered portion 4 and the tip cutting edge 5 performing prepared-hole boring. The tapered portion 4 and the straight portion 3 may be formed of different materials, respectively.
In boring of a fiber reinforced composite material, the drill tip is severely chipped or worn, and thus the drill surface is preferably coated by a diamond thin film or a DLC film.
The drill 1 is attached to a known machining apparatus and used for boring of a composite material as a member to be machined. As the composite material, the drill is suitable for boring of a fiber reinforced composite material and particularly suitable for a composite material in which fibers are laminated in a layered state. The fiber reinforced composite materials include carbon-fiber reinforced plastic (CFRP), glass fiber reinforced plastic (GFRP), glass-mat reinforced thermoplastics (GMT), boron fiber reinforced plastic (BFRP), aramid fiber reinforced plastic (AFRP, KFRP), polyethylene fiber reinforced plastic (DFRP) and the like. The member to be machined may partially contain the fiber reinforced composite materials and is not particularly limited.
Subsequently, a second embodiment according to the present invention will be described on the basis of
A drill 10 according to the present embodiment includes a tip cutting edge 14 which is a tip portion, a tapered portion 13 having an outer peripheral cutting edge 16, a straight portion 12 formed so as to have a circular land drill shape, and a shank 11 as illustrated in
The drill 10 is a double-bladed drill, in which the straight portion 12 is connected to the tip of the shank 11, and the tapered portion 13 is integrally connected to the tip of the straight portion 12. The tapered portion 13, the straight portion 12, and the shank 11 are connected with a tolerance of coaxiality of 0.01.
The tapered portion 13 has a tapered shape formed with a diameter difference between an outer diameter D4 on the tip side and an outer diameter D5 on the rear end side, and the straight portion 12 is integrally connected to the rear end side thereof. The straight portion 12 is formed so as to have a diameter larger than the tapered portion 13. To the tip side of the tapered portion 13, the tip cutting edge 14 having a tip angle β1 is connected.
On the tapered outer periphery formed from the outer diameter D4 on the tip side and the outer diameter D5 on the rear end side of the tapered portion 13, the helically twisted outer peripheral cutting edge 16 is formed and set so that a boring diameter continuously increases, and two helically twisted streaks of chip discharge flutes 15 are formed along the outer peripheral cutting edge 16. The straight portion 12 is formed so as to have a circular land drill shape for shaping and machining a portion remaining after cutting out by the tapered portion 13 which is a prepared-hole boring portion.
As illustrated in
As illustrated in
In the outer peripheral cutting edge 16 of the tapered portion 13 which is a prepared-hole boring portion, the margin 8 as illustrated in
As illustrated in
The surface of the drill 10 main body is covered with a coat 19 made of diamond as illustrated in
An XY-axis movement mechanism 102 moves an installation table along the X-axis or the Y-axis or an XY-composite axis. As the moving means, a ball screw mechanism or a linear motor mechanism is used. On the installation table, a supporting tool 106 such as a vise or a restricting jig or the like is arranged, and a member to be machined 105 made of a fiber reinforced composite material or the like is placed and fixed to the supporting tool 106. The XY-axis movement mechanism 102 is driven by a ball screw mechanism or a linear motor mechanism.
Then, by controlling the Z-axis movement mechanism 101 and the XY-axis movement mechanism 102, boring is performed for the member to be machined 105 while the drill 104 is rotated and driven.
As the supporting tool 106, those having a function of sandwiching the member to be machined 105 in the thickness direction or the planar direction may be used. Alternatively, the spindle shaft may be arranged on the X-axis or the Y-axis.
As illustrated in
In the cutting test, four types of drills illustrated in
As the drill illustrated in
As a drill for a comparative example, a drill without a taper angle in the outer peripheral cutting edge on the drill outer peripheral edge (β2=0°) was used as a comparative target, and three types of drills, one of which uses cemented carbide as the drill base material, diamond coating, the drill tip angle β1=118°, the twist angle β3 of the outer peripheral cutting edge=30°, and the drill outer diameter D4=D5=D6=5.0 mm (drill E), another of which uses cemented carbide as the drill base material, TiC coating, the drill tip angle β1=140°, the twist angle β3 of the outer peripheral cutting edge=30°, and the drill outer diameter D4=D5=D6=5.0 mm (drill F), and the rest of which uses high-speed steel as the drill base material, the tip shape as special grinding (candle shape), the twist angle β3 of the outer peripheral cutting edge=30°, and the drill outer diameter D4=D5=D6=5.0 mm (drill G) were used.
The cutting test was conducted under the following conditions, and carbon-fiber reinforced plastic was cut with the purpose of measurement of thrust resistance (a force applied in the drill axial direction) in the boring.
<Cutting Speed>
when the drill base material is cemented carbide: 100 m/min
when the drill base material is high-speed steel: 24 m/min
<Drill Feeding Speed>
when the drill base material is cemented carbide: 200 m/min
when the drill base material is high-speed steel: 150 m/min
<Member to be Machined>
plate-like body having plate thickness of 5 mm made of carbon-fiber reinforced plastic (by Toray: model T700)
<Cutting Oil>
not used
<Drilling Machine>
vertical MC manufactured by Matsuura Machinery Corporation (model: MC-510VF-Gr; model number: BT40)
<Cutting Resistance Measuring Instrument>
cutting dynamometer manufactured by Kistler Corporation (model: 9123C)
Examining the values of the thrust resistance, they are 50N or less in all the examples and are lower than those in the comparative examples. Moreover, even in the case of cutting with the drill D having the base material made of high-speed steel that is considered to be unsuitable for cutting of carbon-fiber reinforced plastic in general, the thrust resistance is lower than that of the drill E made of cemented carbide in the comparative example, and favorable cutting characteristics are exhibited.
From the above result, it was found that the drill provided with the tapered portion on which the tip portion having the tip cutting edge and the outer peripheral cutting edge are formed and the straight portion, as illustrated in
Subsequently, the similar cutting test was conducted by using the seven types of drills similar to those in the example 1, and presence or absence of burrs near a through-hole in the member to be machined (carbon-fiber reinforced plastic) was visually observed.
Examining the observation result, there was no generation of burrs in the drills A and B of the example even in machining of 120 bores. The drill C was broken on the 92nd bore. The drill C is considered to have been broken due to a synergetic effect of reduction in the drill core thickness and deterioration of chip discharging performance since the twist angle which is an angle of the chip discharge flute was increased. In contrast, the effect substantially equal to that of the drill E can be obtained for the drill D although the drill is made of high-speed steel, and it was found that the drills in the example had a large effect of suppressing generation of burrs.
As known from the photos, when the drill of the comparative example was used, favorable machining was not possible because of the generation of burrs from the first bore.
From the above results, by providing a structure in which the tip portion having the tip cutting edge, the tapered portion having the outer peripheral cutting edge, and the straight portion for performing finishing machining are connected and integrated, stable cutting without causing burrs or delamination was able to be performed on the composite material, and boring with high quality and high accuracy was able to be realized by a single drill with a simple structure and a low cost.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-241971 | Oct 2009 | JP | national |
| 2010-234838 | Oct 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/068401 | 10/19/2010 | WO | 00 | 7/6/2012 |
