Drill reamer

Abstract

A drill reamer (20) comprises an elongate body (21) disposed about a longitudinal axis. The elongate body comprises flutes (22a-22d) having separate hard cutting sections (27a, 28a, 28a, 28b, 28b) and a soft cutting section (24a, 24b). The soft cutting section is formed of a material such as carbide having a hardness that is less than that of the hard cutting sections, which may be formed of polycrystalline diamond. At least one first hard cutting section (27a) is axially displaced relative to at least one second hard cutting section (28a, 28a). The reamer has a tip cutting edge (23a, 23c) and tapered cutting edge portions (24a-24d) disposed at an acute angle relative to the longitudinal axis.

Claims

1. A drill reamer, comprising: an elongate body disposed about a longitudinal axis, the elongate body comprising a plurality of separate hard cutting sections and a soft cutting section, wherein said soft cutting section is formed of a material having a hardness that is less than said hard cutting sections and at least one first hard cutting section is axially displaced relative to at least one second hard cutting section; and a tip at a leading end of the drill reamer, the tip having a tip cutting edge that defines a drilling angle: and a plurality of flutes each having a tapered cutting edge portion disposed at an acute angle relative to the longitudinal axis, the tapered cutting edge portions being operative for drilling a tapered hole during a machining process: wherein the drilling angle relative to the longitudinal axis is greater than said acute angle, wherein said first hard cutting section is disposed at the tip and defines all of said tip cutting edge and defines part of said tapered cutting edge portion of at least one of said flutes.

2. A drill reamer according to claim 1, wherein said at least one of said flutes comprises said second hard cutting section axially spaced apart from said first hard cutting section, defining another part of said tapered cutting edge portion of said at least one of said flutes.

3. A drill reamer according to claim 2, comprising two pairs of flutes each having said second hard cutting section axially spaced apart from said first hard cutting section.

4. A drill reamer according to claim 2, wherein said first hard cutting section of said at least one flute overlaps the second hard cutting section of an opposite flute in an axial direction.

5. A drill reamer according to claim 1, wherein said second hard cutting section is disposed on alternate flutes and defines a part of said tapered cutting edge portion of a different flute from said at least one of said flutes.

6. A drill reamer according to claim 1, wherein the plurality of flutes each have a reaming edge disposed parallel to the longitudinal axis.

7. A drill reamer according to claim 6, wherein said second hard cutting section also comprises part of said reaming edge.

8. A drill reamer according to claim 1, wherein the acute angle is between 11 and 23.

9. A drill reamer according to claim 1, wherein said plurality of hard cutting sections are inserts attached, fused or brazed onto or into said elongate body, and the elongate body of the drill reamer is formed of the material of the soft cutting section.

10. A drill reamer according to claim 1, wherein the material of the soft cutting section is carbide or tungsten carbide.

11. A drill reamer according to claim 1, wherein the material of the hard cutting section is diamond or polycrystalline diamond.

Description

(1) The invention will now be further described by way of example with reference to the accompanying drawings in which like reference numeral designate like elements:

(2) FIG. 1a illustrates a conventional twist drill;

(3) FIG. 1b illustrates a cutting direction D and a thrust direction F of the drill of FIG. 1a;

(4) FIG. 1c illustrates a conventional dagger drill;

(5) FIG. 1d illustrates a cutting direction D and a thrust direction F of the drill of FIG. 1d;

(6) FIG. 2a is a side elevation of a drill reamer according to a first embodiment of the present invention;

(7) FIG. 2b is a view of the drill of FIG. 2a rotates through 90 about its longitudinal axis;

(8) FIG. 2c is an end-on view of the drill reamer of FIGS. 2a and 2b;

(9) FIG. 2d is an isometric view of the drill reamer of FIGS. 2a to 2c;

(10) FIGS. 3a to 3c show views of a drill reamer according to a second embodiment; and

(11) FIGS. 4a to 4c show views of a drill reamer according to a third embodiment.

(12) FIG. 1a shows a conventional twist drill 10 having a drilling tip point angle 12 of =120 and FIG. 1b shows a drilling direction D and direction F of thrust generated by the tip 12. FIG. 1c illustrates a dagger drill 14 having a drilling point/cutting edge angle 16 of =30. The drill 14 has a pair of cutting edges 18 disposed at this acute angle relative to the longitudinal axis of the drill, the cutting edges 18 being provided with respective diamond inserts 19 (one being shown in hidden detail in FIG. 1c). The drill 14 exerts a cutting force dispersion F away from cutting direction, into the part as illustrated.

(13) As noted above, the twist drill 10 is ineffective in composite machining due to high forces generated due to the obtuse tip point angle 12. As the forces are in the same direction as the drilling direction, the drill pushes through the material and can cause premature burst out and delamination on exit of hole. The high forces generated also results in heating which affects the cured state of the matrix in FRC materials. This can lead to structural degradation and alteration of the FRC properties thereby deterioration of the final part quality, or final part ruin. This also compromises dimensional accuracy.

(14) The dagger drill 14 represents an improvement over the conventional twist drill 10 as the acute angle of the cutting edges 18 allows for a hole to be drilled gradually which helps to prevent de-lamination. The two flute dagger drill of FIGS. 1c and 1d is provided with diamond inserts to help increase tool life and hole quality. However this type of drill exerts very high cutting forces into the part, which causes rapid edge quality deterioration on the drill increasing the rate of tool failure. This compromises productivity and increases the cost per hole. Furthermore, the load on each of the cutting edges 18 is notably high as it can only be distributed over the two cutting edges 18, which limits further development of this type of drill.

(15) FIG. 2a is side elevation view of a drill reamer 20 embodying the present invention and FIG. 2b is another side elevation view in the direction of arrow A of the drill reamer 20. FIG. 2c is an end-on view and FIG. 2d is an isometric view. The drill reamer has a cylindrical body 21 of a high hardness sintered material, such as tungsten carbide, and has four flutes 22a to 22d disposed at approximately 90 with respect to one another. The drill reamer 20 is intended for, but not limited to, the drilling of any non-ferrous materials, such as Carbon Fibre Composite (CFC). The geometry of the drill reamer is twofold. The drill reamer 20 has a tip defined by cutting edges 23a and 23c which are provided at the leading end of corresponding ones of the flutes 22a and 22c. The tip has standard drill point geometry, with an angle (see FIG. 2a). The tip cutting edges 23a and 23c are formed from or provided with diamond or polycrystalline diamond inserts on respective flutes 22a and 22c. The polycrystalline diamond tip on the flute 22a is opposite facing relative to the polycrystalline diamond tip on the flute 22c so that the cutting edges 23a and 23c of the tip are defined by the polycrystalline diamond inserts as the drill reamer rotates in the direction of arrow shown in FIG. 2d.

(16) Each flute 22a to 22d has a tapered cutting edge portion 24a to 24d disposed at an angle /2 relative to the longitudinal axis of the drill reamer 20. The tapered cutting edge portions 24a to 24d extend between the tip of the drill and reaming edges 25a to 25d provided on respective flutes 22a to 22d. The tapered cutting edge portions are operative to drill a tapered hole during a machining process, the hole having a finished diameter of d when the reaming edges 25a to 25d enter the hole (not shown). The polycrystalline diamond inserts of the cutting edges 23a and 23c define leading parts 27a and 27c of the tapered cutting edge portions 24a and 24c that are provided on respective flutes 22a and 22c. These leading parts 27a and 27c establish an initial drill cut as the drilling action is performed by the tapered cutting edge portions 24a and 24c. This embodiment adopts a combination cutting edge concept in which the drilling is performed by a combination of cutting edges that are formed from hard and relatively soft materials.

(17) For example, in this embodiment, the tapered cutting edge portions 24a and 24c of the flutes 22a and 22c have the leading parts 27a and 27c formed from polycrystalline diamond inserts and the corresponding portions of the tapered cutting edge portions 24b and 24d of the flutes 22b and 22d are formed from the relatively soft carbide material. Consequently, in the cutting direction of the arrow R, the initial cut of the tapered cutting edge portions 24a to 24d is performed by alternate hard and soft cutting edges. The flutes 22a to 22d of the drill reamer 20 are each further provided with a second hard cutting section 28a, 28a to 28d, 28d respectively. Each of the second hard cutting sections is formed of a harder material, such as a polycrystalline diamond, than the material of the cylindrical body 21 and has one cutting edge 28a to 28d which forms part of the corresponding reaming edge 25a to 25d, and another cutting edge 28a to 28d that forms a part of the corresponding tapered cutting edge 24a to 24d. The cutting edges 28a and 28c are separated from the leading drill tip 27a and 27c respectively so that the tapered cutting edges 24a and 24c each have a cutting section 29a and 29c of relatively soft material, which may be of the same material as the cylindrical body 21, disposed substantially along their mid-region (see FIG. 2b). This provides a further combination cutting edge structure which utilizes a hard cutting section as the drill reamer 20 transitions its cut from a tapered hole to a cylindrical one that corresponds to the reaming edge diameter d.

(18) The polycrystalline diamond inserts can be secured on to the drill reamer 20 by fusing or brazing the inserts into a machined slot or pocket.

(19) The combination cutting edge adopted in the embodiment of FIGS. 2a to 2d is advantageous in that the ability of the drill reamer to ream holes in abrasive materials, such as CFCs while achieving a tool life of over 1200 holes without undue burring/de-lamination is enhanced. This reduces the cost of manufacturing as the cost of the drill is spread over more holes. Embodiments of the present invention utilize the high axial forces created by a drill tip with traditional geometry (obtuse angle) to initially break through the material. Due to the diamond insert, the tool wear is greatly reduced, resulting in a much higher tool life. The elongate, tapered cutting edge then removes the regions of material that has been damaged by the high forces generated by the drilling operation and drills a clean hole.

(20) As noted above, the cutting sections 29a and 29c of the tapered cutting edges 24a and 24c are made from exposed body, typically carbide. This is advantageous as the carbide wears quicker than the diamond and stabilises the drill reamer in the hole, preventing vibration.

(21) The hard cutting sections 28a, 28a to 28d, 28d ensure a sharp cutting edge is retained for longer than common drill materials such as tungsten carbide or high speed steel. When this section of the cutting edge is engaged, there is little material left to remove. Therefore these diamond inserts require lower cutting forces to finish the hole resulting in a clean surface finish. This embodiment utilizes four flutes 22a to 22d thereby reducing the load per cutting edge. This improves tool life and reduces vibration. It also reduces chip size and helps with swarf evacuation from cutting surfaces due to evacuation channels, or flutes, created when using coolant. By incorporating four flutes, the tool is stabilised and therefore the highest feed rate at which the drill can perform is increased.

(22) In addition, the high wear resistance characteristics of diamond ensure the sharp cutting edges remain sharp, allowing for a clean cut and reamed surface on the interior of the hole. As the cutting edges retain a clean sharp edge any vibration is scarce and surface finish quality is retained. Extensive structural testing in a variety of materials has shown that the structural integrity is not compromised in or around the hole for the entire tool life. Some embodiments of the present invention may provide for drilling of three times the number of holes than achievable through use of the dagger drill of FIGS. 1c and d. Some embodiments may achieve an increase in speeds and feeds of around 40% relative to the conventional dagger drill. This increases productivity, decreases machine downtime a result of multiple tool changes and therefore reduces the cost per hole.

(23) Although embodiments are described as having 4 flutes, the number of flutes may be varied to include, for example, two, three or more than 4. Embodiments may preferably have a flute length of between 5 to 70% of the overall length of the cylindrical body. For example, the drill reamer may have a diameter in the range of 2 mm to 50 mm and a length in the range of 20 mm to 330 mm. Each flute preferably contains at least one section of diamond, but in the case of the 4 flute drill reamer at least two of the flutes must contain two portions of diamond as illustrated in FIGS. 2a to 2d. In this case, the drill tip provides at two cutting surfaces. Embodiments may be provided with channels through which coolant may be applied through the body of the tool, either exiting at the tip of the tool or on one or more of the flutes.

(24) Other variants to the embodiment described with reference to FIGS. 2a to 2d are envisaged. For example, FIGS. 3a-3c and 4a-4c show drill reamers which are similar to the drill reamer of FIGS. 2a to 2d but have different arrangements of combination cutting edges. FIGS. 3a-3c and FIGS. 4a-4c correspond to the views presented in FIGS. 2a, 2b and 2d respectively,

(25) FIGS. 3a-3c show a drill reamer 30 having the four flutes 22a to 22d but as seen from FIG. 3c, the flutes 22a and its opposite flute 22c, are not provided with second hard cutting sections that correspond to sections 28a, 28a and 28c, 28c of FIG. 2b. In addition, the axial lengths of the tapered cutting sections 24a to 24d are shorter than the corresponding tapered cutting sections of FIGS. 2a to 2d. Consequently, as shown in FIG. 3a, the second hard cutting sections 28b, 28b and 28d, 28d overlap in region in an axial direction with the leading parts 27a and 27c.

(26) FIGS. 4a-4c show a drill reamer 40 also having the four flutes 22a to 22d but as seen from FIG. 4c, the flutes 22a and its opposite flute 22c, are also not provided with second hard cutting sections that correspond to the sections 28a, 28a and 28c, 28c of FIG. 2b. In contrast to the embodiment shown in FIGS. 3a-3c, the axial lengths of the tapered cutting sections 24a to 24d are longer than the corresponding tapered cutting sections of FIGS. 3a to 3c. Consequently, as shown in FIG. 4a, the second hard cutting sections 28b, 28b and 28d, 28d are axially displaced in an axial direction relative to the leading parts 27a and 27c.