GB2623578A

GB2623578A - A machining tool for creating openings in a multi-layered material

Info

Publication number: GB2623578A
Application number: GB2215616.0A
Authority: GB
Inventors: Edward Bramley Robert; Lawrence Crawforth Peter
Original assignee: University of Sheffield
Current assignee: University of Sheffield
Priority date: 2022-10-21
Filing date: 2022-10-21
Publication date: 2024-04-24
Also published as: GB202215616D0; WO2024084185A1

Abstract

The machining tool 100 is for creating openings in a multi-layered material. The tool includes a main body 101 comprising a coupling 102, and a cutting head (103, Figure 1a) at one end. The cutting head has a cutting diameter 104, at least one cutting edge 105, and at least one outer corner 111. A shroud 106 has an average shroud wall thickness (107, Figure 3a), a length (L, Figure 2), a distal end 106a, a proximal end 106b having a front edge, an internal shroud diameter 120, and an external shroud diameter 121. The shroud covers at least part of the region between the coupling and cutting edge and is configured to direct contaminants away from the opening. The cutting diameter is greater than the external shroud diameter at the proximal end. The tool may also include an internal shroud diameter that increases towards the proximal end such that, in use, the shroud is tapered 109 in the direction of the cutting head. The cutting head and shroud may be integral with the main body, or they may all be part of a multipiece arrangement. The cutting head may have the geometry of a drill or a reamer.

Description

A machining tool for creating openings in a multi-layered material [0001] This invention relates to a machining tool for creating openings in a multi-layered material, to a method of creating such openings and to a use of the machining tool in a one-way assembly process, for example in the manufacture of an aircraft.

BACKGROUND

[0002] Hundreds of millions of fastener holes, or openings, are made in aircraft each year during the assembly process. As openings are a tight fit to their respective fasteners, openings in mating components, or otherwise interchangeably referred to as layers, must align extremely well to allow fit. This leads to openings typically being made through assemblies made of multi-layered material while the components are held together as a stack.

[0003] However, such material stacks increasingly consist of mixed metallic and fibre reinforced polymer (FRP) materials; this along with gaps between components due to poor fit up, challenging machining dynamics and stringent quality requirements, presents a significant challenge when creating openings in a multi-layered material. Components are therefore normally disassembled; inspected, and where necessary reworked before a fastener can be fitted. This extra work slows production rate while expensive jigs, fixtures and additional factory floorspace are occupied.

[0004] Assembly without this need to disassemble part-way through the process is known as one-way assembly (OWA), also known as one-up assembly. After decades of research to try and achieve an automated, reconfigurable, and flexible OWA solution, it is still considered a very high priority research area by the industry.

[0005] The gap between the layers in a multi-layered material is known as the interfey and for OWA processes, a sealant is generally applied prior to assembly and drilling of components. Contamination of the interfey with lubricant and FRP dust, along with damage to the sealant that fills the interfey are substantial technical barriers to implementing OWA.

[0006] Metallic swarf, FRP dust and conventional cutting fluids are considered contaminants. They can remain between the layers, in the interfey, or on the surface of the opening after machining, thereby contaminating the opening. Gaps between components are the norm and if there is a gap, contaminants can enter with conventional tool geometry. In view of this, little coverage of contaminant-free machining for OWA applications has been seen in literature.

[0007] Clamping of the stack of the components is a solution currently used in industry that includes such alternatives as using adjacent final fasteners, disposable rivets, C-clamps, electromagnetic clamping to hold the layers together. Non-liquid sealants or adhesives have also been used to reduce interfey contamination. All these methods have drawbacks and provide little protection from the contaminants to the walls of the stacked fastener holes as they only protect the interfey from contamination by minimising the gap thickness or preventing flow of contaminants through a liquid gap filler.

[0008] One known way to provide an opening in a multi-layered material is disclosed in US4966503. The drill bit for drilling holes in a layered material is provided with a collar fixed to the outer surface to prevent chips from contacting the bore drilled in the first layer. There is however a large gap between the collar and outer corner of the cutting edge in the axial direction and a lack of geometry for guiding contaminants inside the collar. The collar therefore does not provide full protection against contamination of the opening and interference with sealant at the interfey. Furthermore, the outer diameter of the collar is of equal diameter to the cutting teeth of the drill, and therefore the diameter of the opening, this would cause undesirable rubbing between the collar and opening.

[0009] It is therefore an object of embodiments of the invention to at least mitigate one or more of the problems associated with the prior art.

BRIEF SUMMARY OF THE DISCLOSURE

[0010] In accordance with the present invention there is provided a machining tool for creating openings in a multi-layered material, the tool comprising: -a main body comprising a coupling, and - a cutting head at one end thereof, the cutting head having a cutting diameter, at least one cutting edge and at least one outer corner; and - a shroud having an average shroud wall thickness, a length, a distal end, a proximal end having a front edge, an internal shroud diameter and an external shroud diameter, said shroud covering at least part of the region between the coupling and cutting edge and configured to direct contaminants away from the opening, wherein the cutting diameter is greater than the external shroud diameter at the proximal end.

[0011] Advantageously, having cutting diameter that is greater than the external shroud diameter at the proximal end provides clearance between the shroud outer wall and wall of the opening.

[0012] In another aspect of the present invention, there is provided a machining tool for creating openings in a multi-layered material, the tool comprising: -a main body comprising a coupling, and -a cutting head at one end thereof, the cutting head having a cutting diameter, at least one cutting edge and at least one outer corner; and -a shroud having an average shroud wall thickness, a length, a distal end, a proximal end having a front edge, an internal shroud diameter and an external shroud diameter, said shroud covering at least part of the region between the coupling and cutting edge and configured to direct contaminants away from the opening, wherein the internal shroud diameter increases towards the proximal end such that, in use, the shroud is tapered in the direction of the cutting head, and wherein the cutting diameter is greater than the external shroud diameter at the proximal end. Advantageously, the presence of the taper allows to guide contaminants into the shroud and away from the opening and interfey, preventing contamination.

[0013] In yet another embodiment, the cutting head and the shroud are integral with the main body. Advantageously, this embodiment makes it easier to control runout of the cutting head and shroud.

[0014] In yet another embodiment, the cutting head, the shroud and the main body are formed as a multipiece arrangement. Advantageously, this makes internal features easier to access during manufacture and can allow for components to be replaced if worn.

[0015] In another embodiment, the shroud covers the region located less than 1 mm axially from the at least one outer corner of the tool and wherein the region is circumferentially aligned with the at least one outer corner of the tool. Advantageously, this embodiment best prevents contamination of the opening.

[0016] In another embodiment, axial offset between the at least one outer corner of the tool and the front edge of the shroud is less than 0.6 mm, preferably less than 0.3 mm. Advantageously, this embodiment best prevents contamination of the opening.

[0017] In another embodiment, the outer diameter of the shroud at the proximal end is less than 0.16 mm smaller than the cutting diameter, preferably less than 0.08 mm. Advantageously, this embodiment allows to prevent contamination of the opening.

[0018] In an embodiment, the shroud covers the region less than 0.6 mm from the cutting edge in any direction, preferably less than 0.3 mm.

[0019] In another embodiment, the taper has a chamfer, bevel or fillet. Advantageously, this is a simple form to manufacture, guides contamination inside the shroud and, for embodiments where the cutting head and shroud are separate pieces, improves the strength of the outer corner of the cutting head.

[0020] In an embodiment, the cutting diameter of the tool is less than 50 mm. Advantageously, this is an appropriate size for the majority of aerospace fastener holes.

[0021] In another embodiment, the average shroud wall thickness is less than 0.3 mm. Advantageously, such thickness helps prevent clogging of the shroud by providing a bigger cross sectional area for swarf to travel up.

[0022] In yet another embodiment, the shroud further comprises an outer wall, wherein said outer wall comprises a rough, abrasive, surface. Advantageously, the presence of the abrasive surface helps to collect contaminants during the drilling process and remove uncut fibres.

[0023] In another embodiment, the outer wall comprises a plurality of depressions or grooves. Advantageously, this enables a tight fit to the opening while reducing friction. They also provide a place for any lost contamination to be recaptured.

[0024] In an embodiment, the tool comprises at least one fluid outlet located by the cutting edge, said at least one fluid outlet is configured to deliver a cutting fluid and to point towards the distal end of the tool. In another embodiment, the cutting fluid is in a supercritical state. Advantageously, this enables cooling and lubrication at the cutting interface whilst also assisting in chip and swarf removal. Further advantageously, having the fluid outlet configured to point towards a distal end of the cutting tool minimises contamination of the opening. Further advantageously, cutting fluids delivered in the supercritical state can change state into a gas under atmospheric conditions where they would not be considered a contaminant.

[0025] In an embodiment, the tool further comprises a web and at least one flute, said flute being at least partly enclosed by the shroud. Advantageously, this adds stiffness to the tool and provides a convenient mounting point for the shroud.

[0026] In an embodiment, the cutting head has the geometry of a drill or a reamer. Advantageously, this allows for effective removal of material when forming the opening while feeding the tool in the axial direction only.

[0027] In accordance with another aspect of the present invention there is provided a method of creating an opening in a multi-layered material comprising the steps of Providing the multi-layered material; Providing a tool as described above; Performing a machining operation using the tool to create the opening, such that contaminants are directed away from the opening during the machining operation, wherein the opening is provided substantially free from contaminants. Advantageously, such method guides contaminants away from the opening, thus providing protection of the opening from dust and swarf and, in turn, improving FRP surface defects, surface gouging, delamination caused by swarf dragging, and the geometry of the opening.

[0028] In an embodiment, controlled vibration, such as that provided in vibration assisted machining, is applied to the machining tool. Advantageously, vibrating the tool during drilling further assists swarf breaking. Further advantageously, it reduces cutting temperatures thus reducing tool wear. Even further advantageously, it helps impart preferential compressive residual stresses in metallic components.

[0029] In another embodiment, the method further comprises a step of localised clamping to compress the layers of the multi-layered material. Advantageously, using additional clamping reduces the size of gaps between layers, assisting with preventing contamination, burrs and FRP delamination at the interfey.

[0030] In yet another embodiment, the method further comprises the step of vacuum extraction of the contaminants. Advantageously, it provides efficient removal of contaminants under controlled conditions, especially when cutting fluid is used.

[0031] In an embodiment, the step of performing a machining operation is performed to widen a pre-existing opening such as a pre-hole or a defective hole. Advantageously, the method allows to provide contaminant-free, final-size, openings where temporary fasteners have been positioned to provide clamping, where there is already an undersized opening to minimise the amount of machining to be carried out in the assembly stage, or in areas where creation of a final-size opening has already been attempted but produced an opening with defects.

[0032] In accordance with the present invention there is provided a use of the tool or the method as described above in a one-way assembly process. Advantageously, the use of the machining tool and the method described above allows to provide clean openings when a one-way assembly method is used, even if gaps are present at the interfey.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Embodiments of the invention are further described hereinafter by way of example only with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a machining tool according to an embodiment of the present invention; Figure la is an end view of the machining tool depicted in Figure 1; Figure lb is a close up view of the machining tool depicted in Figure 1 showing the outer corner; Figure 2 is a cross-sectional view of the machining tool depicted in Figure 1; Figure 3a is a close up view of the machining tool showing the chamfer; Figure 3b is a close up view of the machining tool showing a change in the external diameter of the shroud, achieved by a step in the diameter; Figure 4 is a plain view of the machining tool according to an alternative embodiment of the present invention comprising grooves; Figure 5 and 5a are plain and close up views of an embodiment of the present invention comprising at least one fluid outlet that points towards the distal end of the tool.

DETAILED DESCRIPTION

[0034] Figure 1 shows a machining tool 100 according to an embodiment of the present invention, Figure la, Figure lb and Figure 2 are an end view, close up view and cross-sectional view, respectively, of the same embodiment. The tool has an elongated main body 101 that has a coupling 102 at its distal end and a cutting head 103 at its proximal end. The tool 100 could be made from a variety of materials (for example, carbide, tool steel, high speed steel), with hard materials being more suitable for the cutting head 103. Various wear resistant coatings (for example, diamond coatings) could also be applied to decrease wear in use. The cutting head 103 has a cutting diameter 104 and at least one cutting edge 105. The cutting diameter 104 may be less than 50 mm. It is understood that the geometry around the cutting edges can take a variety of forms known in the art, for example, various rake and clearance angles, various profiles of the cutting edge and, for drills, various chisel designs are possible.

[0035] It will be understood by the skilled person that the term "distal" defines location of any part of the tool that is situated away from the drilling area, and the term "proximal" defines the location of any part of the tool that is situated towards or adjacent to the drilling area.

[0036] The machining tool 100 further has a shroud 106 that is located at the proximal end of the tool 100 and is configured to at least partly cover the region along the tool axis 116 in the distal direction from the cutting edge 105. The axial offset between the shroud front edge 115 and the outer corner 111 of the tool is minimised to best contain contamination however, remains big enough such that the shroud front edge 115 does not contact uncut material. To avoid contact, the size of the axial offset should be at least the axial feed per tooth of the tool plus the amplitude of any axial vibration between the tool and workpiece. The external diameter 121 of the shroud 106 is maximised in order to best capture contamination; however, it remains far enough under the cutter diameter 104 of the tool to prevent interference with the wall of the opening. To prevent interference between the external diameter of the shroud and the wall of the opening, the offset between the cutting diameter and shroud outer wall should be greater than the amount of contraction seen in openings as FRP layers contract during the hole generation process. As the tool wears, the offset would be reduced, the axial offset would also be reduced if the cutting tool underwent regrinds to sharpen it. Additional offset can be provided to accommodate for wear and regrinds. The shroud 106 covers the region circumferentially aligned and within 1 mm axially of the outer corners of the tool. The shroud 106 has a shroud wall thickness 107 and a length L. The wall thickness can be in the range of, but is not limited to, 0.1 -0.3 mm. The length of the shroud can be such that it is long enough to extend beyond the depth of the opening to protect the opening from contaminants. In this case it allows air to circulate underneath cut material as it exits the shroud, and clear it by a vacuum, so that the dust does not settle on the top surface of the workpiece as is normal when drilling openings.

[0037] The shroud 106 has internal 120 and external 121 shroud diameters, a distal end 106a and a proximal end 106b. It will be understood that the internal shroud diameter 120 increases towards the proximal end such that, in use, the shroud wall thickness tapers. A chamfer 109, shown in Figure 3a is the preferred embodiment of the taper.

[0038] It is also understood that the difference in the external distal and proximal shroud diameters, shown in Figure 3b, can be a result of having different wall thickness 107 at the distal end 106a and the proximal end 106b. However, it is also possible that the wall thickness 107 remains constant and the external diameter of the shroud 106 at its distal end is smaller than the external diameter at its proximal end. In other words, the former describes an embodiment wherein an inner diameter of the shroud remains constant, whereas the latter describes the shroud with constant wall thickness and changing inner shroud diameter.

[0039] Optionally, the main body 101 and cutting head 103 can have a web 117 and at least one flute 108. The at least one flute 108 can be helical or straight. The shroud 106 may at least partially cover the at least one flute 108. However, it is also understood that the web 117 and at least one flute 108 may not be present.

[0040] Figure 3a shows the close up, cross sectioned, view of the proximal end of the shroud 106 according to the present invention. The shroud 106, as described above, covers at least part of the region along the tool axis in the distal direction from the cutting edge 105. The shroud outer diameter at its proximal end 106a is smaller than the cutting diameter 104 of the cutting head 103, such that a chamfer 109 is formed at an interface of the shroud 106 and the cutting head 103. It will be understood by a skilled person that the interface between the shroud and the cutting head only exists for arrangements where the cutting head and shroud are separate pieces. It will also be understood that chamfer-like geometries fulfilling the same function can be formed instead. Such structures can be, without limitation, a bevel, a fillet or a freeform profile.

[0041] In an alternative embodiment, as shown in Figure 3b, the external diameter of the shroud 106 changes. The change is shown as a step 119 in Figure 3b. Thus, the external diameter at the distal end 106a of the shroud 106 is smaller than the external diameter at the proximal end 106b. In this embodiment the cutting diameter 104 is still greater than any of the diameters of the shroud 106, such that the chamfer 109 is formed at the interface of the shroud 106 and the cutting head 103. Having the cutting diameter 104 bigger than the maximum external diameter of the shroud prevents the shroud from contacting the wall of the opening. The step in the outer diameter of the shroud provides additional clearance to the hole wall. It is further understood that other features, such as a fillet or gradual taper for example, can be used instead of stepped profile, fulfilling substantially the same function.

[0042] In the prior art machining tools such as those described above (for example, US4966503), when the cutting tool is rotated by a powered rotary device to create an opening in a multi-layered material, the contaminants are formed during drilling.

These contaminants can contaminate the surfaces of the opening and the interfey, as well as create such defects as scouring and/or gouging.

[0043] In the machining tool of Figures 1-5, the swarf and other contaminants are guided away from the inner walls of the opening as the barrier is created between the contaminants and the outer wall of the opening. It is advantageous to have the chamfer 109 rather than a flat edge as seen in prior art, as this guides contaminants inside the shroud, and for embodiments where the cutting tip is a separate piece to the shroud, it allows the front edge of the shroud to be in close proximity to the outer corner of the cutting tip while maintaining the strength at the outer corner. Guiding contaminants inside the shroud will provide a clean interface between stack layers. Such a result is particularly beneficial in one-way assembly when all the layers of the material are stacked together and drilled simultaneously when stacked, without the need for intermediate disassembly to evaluate and improve quality of the openings before fitting a final fastener. Furthermore, having the shroud 106 in place adds extra stiffness to the tool 100 and, in turn, enables the use of thinner than standard webs of the cutting tool, or no web 117. Reduction of the web provides a greater cross sectional area for swan f removal.

[0044] In the embodiment described above, the main body 101, cutting head 103 and shroud 106 are separate pieces. In alternative embodiments, these pieces can be united into one in various combinations. For example, in an alternative embodiment, the shroud 106 can be integral with the main body 101, they can be machined or 3D-printed as one piece. As a further example, it can be produced using a mould, e.g. carbide powder is formed to the desired shape in the "green state" and then sintered. In alternative embodiments, these pieces can be broken down into further subcomponents. For example, the cutting head can include inserts with an additional interface to connect them to the cutting head.

[0045] It is understood, that when the shroud 106 is not integral with the main body and cutting head, the shroud can be retrofitted to existing tools by grinding the geometry that interfaces with the shroud and fitting the shroud in place. The fitting process can be, for example as follows: the shroud is pre-heated and fitted onto the main body 101 from the coupling end 102. The shroud 106 is then progressed further towards the distal end of the tool 100 until the shroud touches the chamfer 109. As the final stage, the shroud cools and shrinks to fit the tool 100. It is understood that other alternative fitting methods are also contemplated.

[0046] In another alternative embodiment, the shroud 106 can have a rough, abrasive, outer surface. Advantageously, this may help with collecting contaminants and remove uncut fibres in FRP material. In yet another alternative embodiment, such as one shown on figure 4, the outer wall of the shroud 106 can have a plurality of grooves 110 or depressions, configured to minimise rubbing against the opening while maintaining a close fit. The purpose is to keep a fight fit to the opening while reducing friction. The grooves 110 could have a variety of forms, e.g. axial, helical, circumferential. Depressions could also have variation in geometry. The grooves or depressions work in a similar way to a margin on a drill.

[0047] In yet another embodiment, the at least one cutting edge 105 can have a chip breaker to improve swarf breaking and resultantly, swarf evacuation. Many geometries of chip breaker are already used on cutting tools.

[0048] In Figures 1-5 the machining tool 100 is configured to deliver cutting fluid in the region of the cutting edge 105 via at least one fluid outlet 113. The cutting fluid can be, for example, a cutting oil or a fluid that is held in the supercritical state upstream of the fluid outlet 113. The diameter of the outlet when using fluid in a supercritical state is between 0.1 and 0.3 mm, smaller than upstream pipe diameters, to create a restriction to maintain upstream pressure and utilise the Bernoulli effect to create a rapid pressure drop. When other fluids are used, the diameter of the outlet can be larger as the rapid pressure drop is not needed. It is understood that larger holes provide less restriction to flow and a higher flow rate. Optionally, the at least one fluid outlet 113 runs through the coupling 102, the cutting head 103 and exits near the cutting edge 105, ejecting the fluid in the proximal direction as shown in Figures 1-4. In an alternative embodiment, as shown in Figure 5, the at least one fluid outlet is facing away from the drilling area, towards the distal end. This is achieved by means of a u-turn 114 in the fluid outlet 113. Facing the at least one fluid outlet away from the drilling area (rearward) assists with swarf removal and cooling, with minimal disturbance of the interfey.

[0049] The following method can be used for creating an opening in a multi-layered material.

[0050] As a first step, a multi-layered material is provided. It is understood that the term "multi-layered" comprises at least two layers of materials, the layers may share or have differing chemical and mechanical properties. By way of example, the layers can be without limitation carbon fibre reinforced polymer, aluminium alloys, stainless steel, titanium and titanium alloys etc. It is also understood that layers can be repeated, for example, the material can comprise two or more layers of carbon fibre separated by the aluminium alloy, or vice versa.

[0051] At the next step the machining tool 100 is provided, said tool being rotated about its axis and advanced towards the drilling area to create the opening.

[0052] At the next step the tool 100 creates the opening through the layers of multi-layered material. The shroud that at least partially covers the region between the coupling and cutting edge, forms a chamfer with the cutting head and acts as a protector for the opening, thus creating clean and contaminant free opening without the surface defects normally caused by the swarf passing through the opening.

[0053] As the final step, when the opening is created the tool is extracted from the opening.

[0054] In this way the need for a minimised gap between components to restrict interfey contamination is reduced.

[0055] Optionally, the machining tool can be vibrated. Vibration assisted drilling uses controlled vibration, typically in the axial direction, to aid swarf breaking in metallic. This could be ultrasonic vibration as well as low frequency vibration assisted drilling (Mitis systems, https://www.mitis.fr/).

[0056] Further optionally, it is possible to use localised clamping to minimise gaps between the layers during drilling.

[0057] In an alternative embodiment, vacuum extraction can be applied during the process of creating the opening. Vacuum extraction is particularly advantageous when using the cutting fluid to assist chip and swarf evacuation.

[0058] It is understood that the method described above can also be used on the pre-holes and defective holes, thus allowing to use re-working to correct the sub-standard openings without the need to discard the machined part. It will be clear to the skilled person that some prefabricated components may be supplied with pre-holes as standard which subsequently require further machining to get them to the correct size. A pre-hole may be present as the assembly process utilises temporary fasteners. Once the temporary fastener is removed it will be machined to size and a permanent fastener applied. A pre-hole may be present as a result of a malfunction during the primary machining step resulting in the hole being revisited and usually oversized.

[0059] The method and the machining tools described above can be particularly advantageous for use in one-way assembly, however many different cutting tool technologies could be applied to the method and machining tool described.

[0060] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0061] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0062] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

CLAIMS1 A machining tool for creating openings in a multi-layered material, the tool comprising: - a main body comprising a coupling, and - a cutting head at one end thereof, the cutting head having a cutting diameter, at least one cutting edge and at least one outer corner; and a shroud haying an average shroud wall thickness, a length, a distal end, a proximal end having a front edge, an internal shroud diameter and an external shroud diameter, said shroud covering at least part of the region between the coupling and cutting edge and configured to direct contaminants away from the opening, wherein the cutting diameter is greater than the external shroud diameter at the proximal end.
2 A machining tool for creating openings in a multi-layered material, the tool comprising: - a main body comprising a coupling, and a cutting head at one end thereof, the cutting head having a cutting diameter, at least one cutting edge and at least one outer corner; and a shroud having an average shroud wall thickness, a length, a distal end, a proximal end having a front edge, an internal shroud diameter and an external shroud diameter, said shroud covering at least part of the region between the coupling and cutting edge and configured to direct contaminants away from the opening, wherein the internal shroud diameter increases towards the proximal end such that, in use, the shroud is tapered in the direction of the cutting head, and wherein the cutting diameter is greater than the external shroud diameter at the proximal end.
3. The tool of claim 1 or 2, wherein the cutting head and the shroud are integral with the main body.
4. The tool of claim 1 or 2, wherein the cutting head, the shroud and the main body are formed as a mulfipiece arrangement.
The tool of any of the preceding claims, wherein the shroud covers the region located less than 1 mm axially from the at least one outer corner of the tool and wherein the region is circumferentially aligned with the at least one outer corner of the tool.
6 The tool of any of the preceding claims, wherein an axial offset between the at least one outer corner of the tool and the front edge of the shroud is less than 0.6 mm, preferably less than 0.3 mm.
7. The tool of any of the preceding claims, wherein the outer diameter of the shroud at the proximal end is less than 0.16 mm smaller than the cutting diameter, preferably less than 0.08 mm.
8. The tool of any of the preceding claims, wherein the shroud covers the region less than 0.6 mm from the cutting edge in any direction, preferably less than 0.3 mm.
9. The tool of any of the preceding claims, wherein the taper has a chamfer, a bevel or a fillet.
10. The tool of any of the preceding claims wherein the cutting diameter of the tool is less than 50 mm.
11. The tool of any of the preceding claims, wherein the average shroud wall thickness is less than 0.3 mm.
12. The tool of any of the preceding claims, wherein the shroud further comprises an outer wall, wherein said outer wall comprises a rough, abrasive, surface.
13. The tool of claim 12, wherein the outer wall comprises a plurality of depressions or grooves.
14. The tool of any of the preceding claims, further comprising at least one fluid outlet located by the cutting edge, wherein said at least one fluid outlet is configured to deliver a cutting fluid and to point towards the distal end of the tool.
15. The tool of any of the preceding claims, wherein the cutting fluid is in a supercritical state.
16. The tool of any of the preceding claims further comprising a web and at least one flute, said flute being at least partly enclosed by the shroud.
17. The tool of any of the preceding claims where the cutting head has the geometry of a drill or a reamer.
18 A method of creating an opening in a multi-layered material comprising the steps of Providing the multi-layered material; Providing a tool according to any of the preceding claims; Performing a machining operation using the tool to create the opening, such that contaminants are directed away from the opening during the machining operation, wherein the opening is provided substantially free from contaminants.
19. The method of claim 18, wherein controlled vibration, such as that provided in vibration assisted machining, is applied to the machining tool.
20. The method of claim 18 or 19 further comprising a step of localised clamping to compress the layers of the multi-layered material.
21. The method of any of claims 18-20 further comprising the step of vacuum extraction of the contaminants.
22. The method of any of claims 18-21, wherein the step of performing a machining operation is performed to widen a pre-existing opening such as a pre-hole or a defective hole.
23. Use of the tool of any of claims 1-17 or the method of any of claims 18-22 in a one-way assembly process.