WO2004037472A1

WO2004037472A1 - Improved drilling tools for composite materials

Info

Publication number: WO2004037472A1
Application number: PCT/EP2003/011640
Authority: WO
Inventors: Aldo Falchero; Franco Vacchiano
Original assignee: Alenia Aeronautica S.P.A
Priority date: 2002-10-22
Filing date: 2003-10-21
Publication date: 2004-05-06
Also published as: AU2003301642A1; ITTO20020919A1

Abstract

A drilling tool for making through-holes in composite materials comprises a hard metal body (10) having an elongate shape along a longitudinal axis (x), with a shank portion (11) and a helicoidal cutting portion (12) with a plurality of cutting lips. In the body (10) of the tool, there are compressed-air ducts (13, 14) which extend at least through the helicoidal cutting portion (12) and which open in the vicinity of the tip of the tool.

Description

Improved drilling tools for composite materials

The present invention relates to drilling tools for making through-holes in composite materials; more particularly, the invention relates to a drilling tool for making through- holes in laminated composite materials and to a tool for making through-holes in a composite material based on carbon fibre and known as CFC (carbon fibre composite) and/or based on glass fibre (fibreglass) .

The invention is intended for application particularly advantageously but not exclusively in the aircraft construction field in which the above-mentioned composite materials are widely used.

According to the prior art, in order to make a through-hole in a laminated composite material comprising a series of aluminium- lloy layers alternating with carbon-fibre layers, the operation was performed in two steps by first of all drilling with a thin drill, that is, a drill having a diameter considerably smaller than that of the hole to be produced and then enlarging the hole by means of a reamer to reach the desired diameter.

In drilling the laminated composite material combined with the metal it was necessary to use the so-called "back drilling" technique by advancing and retracting a helical tool cyclically after each of the metal-alloy layers had been drilled so as to remove the metal chippings from the tool in order not to damage the carbon-fibre layers. Otherwise, if the tool is advanced continuously to drill several successive metal layers, the metal chippings inevitably erode the carbon-fibre layers and the sealant layers; the sealant is usually a gummy resin that is applied to the carbon-fibre layers in the form of a liquid shim to improve the sealed joint with the adjacent metal-alloy layers. A series of forward drillings and retractions to discharge the chippings was therefore performed until a through-hole was produced.

As well as taking a long time, this technique produced insufficiently precise holes and had a further disadvantage owing to the fact that the metal chippings were inclined to adhere to and be deposited on the overheated tool. As well as damaging the carbon and sealant layers as stated, the deposits of chippings regularly caused jamming of the tool in the hole and breakage of the tool (by twisting) after the production of a small number of holes (at most 80 holes/drill) .

To make holes in a CFC composite material, it is known to use twist drill tools with two flutes and with a PCD (polycrystalline diamond) tip; these tools present overheating problems similar to those mentioned above with a propensity for the formation of deposits of chippings which, instead of being removed along the turns of the helix, accumulate, expanding transversely and inevitably causing breakage of the drill and damage to the material to be drilled. In this case also, holes outside the tolerances were obtained so that it was necessary to use a drill of small diameter and then to enlarge the hole in a second step by means of a reamer until the required nominal diameter was reached.

The present invention has the general object of providing drilling tools in which the above-mentioned disadvantages are radically eliminated.

A particular object of the invention is to propose drilling tools which can make very precise through-holes in a single step, that is, without the aid of a reamer and with a continuous forward movement.

Another object of the invention is to reduce the times and the costs connected with drilling operations, in particular by providing drilling tools which drastically reduce down times and the costs connected with the breakage of the tool and with its replacement with a new tool .

These and other objects and advantages which will be understood further from the following description are achieved, according to the invention, by a drilling tool having the characteristics defined in Claim 1. Preferred embodiments of the invention are defined in the dependent claims .

According to another aspect of the invention, the above- mentioned objects are achieved by drilling methods as defined in Claims 6 and 7.

Two preferred but non-limiting embodiments of drilling tools according to the invention will now be described with reference to the appended drawings, in which:

Figure 1 is a side elevational view of a first embodiment of a cutting tool according to the invention,

Figure 2 is a view of the tool of Figure 1 from above, taken in the direction of the arrow II,

Figure 3 is a cross-section taken on the line III of Figure 1,

Figure 4 is a side elevational view of a second embodiment of a drilling tool according to the invention, and Figure 5 is a plan view of the drilling tool of Figure 4 from above, taken in the direction of the arrow V.

With reference first of all to Figures 1 to 3 , a first embodiment of a cutting tool according to the invention is generally indicated 10; the tool 10 is particularly suitable for making holes in laminated composite materials comprising a plurality of light-alloy (for example, aluminium alloy) metal layers alternating with layers based on carbon fibre, optionally connected intimately to the metal layers by a sealant such as a gummy resin. Naturally, reference to this possible field of application should not be interpreted as in any way limiting of the scope of the patent.

The body of the tool 10 is made of hard metal (for example, Widia or tungsten carbide) and has a generally elongate shape in which a proximal portion or shank 11 and a helicoidal distal cutting lips 12 with two lips are distinguished .

According to the invention, two ducts 13, 14 are formed in the body of the tool 10; the ducts 13, 14 follow respective helical paths about the longitudinal axis x of the tool, allowing a through-flow of cooling compressed air.

Compressed air is blown through one or more inlet holes 15 formed at the base of the shank portion 11 and emerges in the region of the tip of the tool. The air serves both for cooling the cutting tool as a whole and, in particular, its cutting surfaces, and for promoting the removal of the chippings which rise along the cutting edges; the chippings are pushed upwards by the flow of pressurized air which emerges from the ducts 13, 14 and flows towards the shank through the helicoidal flutes that are defined between the helical surfaces of the tool and the wall of the hole being formed.

The reduction in temperature and the absence of metallic deposits on the cutting surfaces of the tool, as discussed in the introductory portion of the present description, enable very precise through-holes to be produced in extremely short times and enable the same cutting tool to be used for the production of a large number of holes. Experimental tests have shown that, with a drilling tool such as that shown in Figures 1-3, the average time required to produce a hole in a laminated composite material is reduced from the conventional 105 seconds to about 25 seconds .

Since no final reaming step is required, a reaming machine becomes superfluous .

An important advantage is that, by virtue of the cooling effect and the elimination of the deposits by the effect of the compressed air, the holes can be produced continuously, that is, with a constant forward movement, without the need for the conventional repetitions in accordance with the so- called "back drilling" method.

Experimental tests have shown that the same tool can produce more than 300 holes without undergoing appreciable wear or degradation. A further saving in time is therefore achieved by the reduction in down times for changing the tool . With the drilling tool according to the invention, it is possible to change from the conventional cycles with drill replacement after 80 holes (at most) to replacement every 300 holes or more. The results of the tests also showed that the drilling tools according to the invention can produce holes which satisfy the tolerance requirements prescribed by the norms relating to the radial clearance for the connection members that are used to assemble an aircraft structure.

Although the Applicant does not wish to be bound by any specific theory in this connection, tests which he has carried out show that excellent results are achieved in terms of the precision of the hole and of tool life with a rake angle α of about 140° and that optimal evacuation of the chippings is achieved with a helix angle β of about 30- 40° with admission of compressed air at a pressure of about 5-6 bar.

A second embodiment of a drilling tool according to the invention which is particularly suitable for making through- holes in carbon-fibre-based composite materials (CFCs) will now be described with reference to Figures 4 and 5 and with the use of the same reference numerals to indicate parts identical or corresponding to those of Figures 1 to 3.

The tip of the hard metal body 10 carries a sintered PCD (polycrystalline diamond) insert 16, fixed by braze welding in a suitable seat (not shown) formed at the distal end of the body 10.

As described above with reference to Figures 1 to 3 , the tool 10 also has two ducts 13, 14 which follow respective helical paths about the longitudinal axis x of the tool, permitting the flow of cooling compressed air. The compressed-air ducts 13, 14 extend through the body 10 from one or more inlet holes 15 formed in the end of the shank portion 11 and open in the vicinity of the diamond tip 16, as shown in Figure 5. The drilling tool shown in Figures 4 and 5 affords substantially the same advantages as discussed above with reference to the embodiment of Figures 1-3. Experimental tests have shown that the drilling tool 10 with a PCD tip enables the average time required to produce a hole in a CFC composite material to be reduced from the conventional 25 seconds to about 7 seconds. The tips have been found not to be subject to breakages and to require cleaning of the diamond tip only after they have produced about 2000 holes.

The invention is not intended to be limited to the embodiments described and illustrated herein, which should be considered as examples of the drilling tool; rather, the invention may be modified with respect to shape, dimensions, and materials used.

Claims

1. A drilling tool for making through-holes in composite materials, comprising a hard metal body (10) having an elongate shape along a longitudinal axis (x) , with a shank portion (11) and a helicoidal cutting portion (12) with a plurality of cutting lips, characterized in that, in the body (10) of the tool, there is at least one compressed- air duct (13, 14) which extends through at least the helicoidal cutting portion (12) and which opens in the vicinity of the tip of the tool.

2. A drilling tool according to Claim 1, characterized in that the helicoidal cutting portion (12) has cwo cutting lips, and in that two of the said compressed-air ducts (13, 14) are formed in the body (10) of the tool and follow respective helical paths about the longitudinal axis (x) .

3. A drilling tool according to Claim 1 or 2, characterized in that it also has the following combination of characteristics:

- a rake angle (α) of about 140°, and

- a helix angle (β) of about 30-40°.

4. A drilling tool according to any one of the preceding claims, characterized in that the compressed-air duct or ducts (13, 14) extend through the body (10) from one or more inlet holes (15) formed in the end of the shank portion 11.

5. A drilling tool according to any one of the preceding claims, characterized in that the tip of the body (10) carries a PCD polycrystalline diamond insert (16) .

6. A method of making a through-hole in a laminated composite material comprising a series of light metal or light-metal alloy layers alternating with layers based on carbon-fibre and/or glass-fibre, comprising the following steps:

- providing a cutting tool according to any one of Claims 1 to 4, advancing the cutting tool (10) continuously in a direction parallel to its own longitudinal axis (x) , causing it to rotate about the said axis, and simultaneously blowing in compressed air through the at least one duct (13, 14) until a through-hole is produced in the laminated composite material .

7. A method of making a through-hole in a composite material based on carbon fibre and/or glass fibre, comprising the steps of:

- providing a cutting tool according to Claim 5, advancing the cutting tool (10) continuously in a direction parallel to its own longitudinal axis (x) , causing it to rotate about the said axis, and simultaneously blowing in compressed air through the at least one duct (13, 14) until a through-hole is produced in the composite material.

8. A method according to Claim 6 or Claim 7, characterized in that the compressed air is blown in at a pressure of about 5-6 bar.