Machining tool for creating openings in multi-layer materials

Abstract

A machining tool for creating an opening in a multi-layer material is provided. The tool includes a body including a connector, 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 leading edge, a shroud inner diameter, and a shroud outer diameter, the shroud covering at least a portion of the area between the connector and the cutting edge and configured to direct contaminants away from the opening. The shroud inner diameter increases toward the proximal end such that, during use, the shroud tapers toward the cutting head. The cutting diameter is larger than the shroud outer diameter at the proximal end.

Description

[Technical Field]

[0001] The present invention relates to a machining tool for creating openings in multi-layer materials, a method for creating such openings, and the use of the machining tool in a one-way assembly process, for example in the manufacture of aircraft. [Background technology]

[0002] Hundreds of millions of fastener holes, or apertures, are created in aircraft each year during the assembly process. Because an aperture is an interference fit for its respective fastener, the apertures in the mating parts, or otherwise interchangeably called layers, must be extremely well aligned to allow for the interference fit. As such, apertures are typically created through assemblies made of multi-layer materials, with the parts held together as a stack. Typically, multiple parts are stacked together, and fastener holes are drilled through all of the layers simultaneously.

[0003] These material stacks increasingly consist of parts that mix metal and fiber-reinforced polymer (FRP) materials. This, along with gaps between parts due to fitment errors, difficult machining dynamics, and stringent quality requirements, pose significant challenges when creating openings in a stack of parts. Therefore, parts are typically disassembled, inspected, and, if necessary, reworked before fasteners can be installed. This extra work slows production while requiring expensive jigs, fixtures, and additional factory floor space.

[0004] Some methods of addressing these problems include separately machining the final holes through the parts precisely enough so that the holes will align when assembled. However, such methods inevitably lead to misalignment between the holes. These methods are sometimes called one-way assemblies because the parts are stacked only once after the holes are machined.

[0005] Another form of one-way assembly (OWA), also known as one-up assembly, eliminates the need for disassembly mid-process and involves machining holes through a stack of parts to ensure alignment and to ensure the machined holes are free of imperfections that would require remedial work requiring separation of the parts. After decades of research to attempt and achieve automated, reconfigurable, and flexible OWA solutions, this is still considered a high-priority research area by industry.

[0006] The gaps between layers in a multi-layer material (or between components in a stack of components) are known as interface areas, and in the OWA process, a gap filler, or otherwise interchangeably called a sealant, is typically applied before the components are assembled and the holes are machined. In the OWA process, it is preferred to machine the holes while the sealant is in its liquid state before it hardens. Contamination of the interface and damage to the sealant filling the interface are substantial technical barriers to the implementation of OWA.

[0007] Damage to the sealant typically takes the form of removal of the sealant from the faying surfaces. Chips and conventional cutting fluids are considered contaminants. Chips include, but are not limited to, material removed from metal and FRP materials (e.g., shavings and dust). Contaminants can remain between layers, at faying surfaces, or on the surface of openings after machining, thereby contaminating the openings. Gaps between parts are common, and conventional tool geometries allow contaminants to penetrate, potentially damaging the sealant. In this regard, little is known in the literature about contamination-free machining and sealant damage prevention for OWA applications. Other hole defects include contamination on the surface of the hole, hole geometry errors, burrs, metal caps, uncut FRP fibers, FRP abrasion (typically due to metal chips), FRP delamination and subsurface cracks, FRP surface defects (e.g., pitting, matrix smearing, matrix coating), surface gouging / scoring, poor surface finish (roughness and waviness), metal microstructure defects, and FRP heat-affected zone (HAZ).

[0008] Clamping of stacked parts is a current industry solution, including alternatives such as using adjacent final fasteners, disposable rivets, C-clamps, and electromagnetic clamping to hold layers together. Non-liquid sealants or adhesives have also been used to reduce joint surface contamination. All of these methods have drawbacks; they only protect the joint surface from contamination by minimizing gap thickness or preventing the flow of contaminants through liquid gap fillers, providing little protection from contamination to the walls of stacked fastener holes. Other efforts to achieve holes suitable for OWA include laser and waterjet cutting, vacuum extraction of chips, the use of non-contaminating cutting fluids, optimization of machining parameters, alternative tool paths, optimization of conventional cutting tool geometries, and optimization of material grades and coatings.

[0009] One known method for drilling holes in multilayer materials is disclosed in U.S. Patent No. 5,623,999. A drill bit for drilling holes in layer materials has a collar fixed to its outer surface to prevent chips from contacting the hole drilled in the first layer. However, there is a large axial gap between the collar and the outer corner of the cutting edge, and the collar lacks a shape to guide contaminants inside. The collar therefore does not provide complete protection against contamination of the opening and interference with the sealant at the mating surface. Furthermore, the outer diameter of the collar is equal to the diameter of the drill's cutting edge, and therefore the diameter of the opening, which causes undesirable friction between the collar and the opening, exacerbated by heat-driven contraction of the hole diameter caused by heat from the drilling process, mechanical deformation around the bore face (springback), and thermal expansion of the cutting tool. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 4,966,503 Summary of the Invention [Problem to be solved by the invention]

[0011] It is therefore an object of embodiments of the present invention to at least alleviate one or more of the problems associated with the prior art. [Means for solving the problem]

[0012] According to the present invention, there is provided a machining tool for creating openings in a multi-layer material, the tool comprising: a main body including a connecting portion; 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; a shroud having an average shroud wall thickness, a length, a distal end, a proximal end having a leading edge, a shroud inner diameter, and a shroud outer diameter, the shroud configured to cover at least a portion of the area between the coupling portion and the cutting edge and to direct contaminants away from the opening; Including, The cutting diameter is larger than the shroud outer diameter at the proximal end.

[0013] It will be appreciated that the cutting diameter of the cutting head is defined by at least one outer corner. In particular, the cutting diameter is defined by the position of the at least one outer corner relative to the axis of rotation of the tool. Accordingly, the outer diameter of the shroud at the proximal end is less than the diameter of the at least one outer corner. The outer diameter of the shroud at the proximal end is therefore less than the size of the opening created by the tool during use.

[0014] Advantageously, having a cutting diameter at the proximal end that is larger than the shroud outer diameter allows the shroud to pass through the aperture, reducing friction and interference between the shroud outer wall and the aperture wall. This is particularly advantageous when creating apertures in fiber-reinforced polymer (FRP) materials, because such friction can damage the FRP material, for example, by creating matrix smearing, heat-affected zones, or delamination. Additionally, when using the machining tool to create apertures through multi-layer materials (e.g., a stack of parts), the shroud acts to protect the interface between the parts, preventing the ingress of contaminants and preventing damage to any sealant (e.g., a curable sealant or tape at the interface). Thus, this machining tool is particularly well-suited for one-way assemblies because apertures can be created through multi-layer materials, including a stack of parts, without damaging or contaminating the aperture, eliminating the need to disassemble, clean, and / or rework the aperture.

[0015] Additionally, the shroud protects the bore of the aperture from chip damage. Specifically, the shroud prevents chips from passing between the tool and the aperture, thereby protecting against surface defects, gouging and scoring, and delamination caused by chip drag. This improves the geometry of the aperture.

[0016] In one example, the shroud inner diameter increases toward the proximal end. In particular, the shroud includes a taper that narrows toward the cutting head. Specifically, the cross-sectional area defined within the shroud increases toward the proximal end, particularly due to the tapering of the shroud wall thickness. This increases the internal size of the shroud at the proximal end to capture more contaminants generated at the cutting head.

[0017] In one example, the proximal end of the shroud can include a taper that extends partially or completely around the circumference. In one example, the taper can extend only partially around the circumference, and in such an example, the taper is preferably located adjacent the outer corner, particularly forward of the outer corner relative to the direction of rotation of the machining tool during use. Advantageously, the taper will thus be located where the cutting edge is forming contaminants (e.g., swarf or dust) as the workpiece material is cut, and the taper helps to direct the contaminants into the inner diameter of the shroud. If the machining tool includes multiple outer corners, the shroud can include a taper for each outer corner.

[0018] Advantageously, the taper directs contaminants into the shroud and away from the openings and mating surfaces, preventing contamination and damage to any sealant provided at the mating surfaces. In particular, the taper at the proximal end of the shroud forces contaminants inward, into the shroud, thus preventing them from passing between the outside of the shroud and the uncut workpiece material. This protects the opening surfaces from abrasion and contamination, and also protects the mating surfaces when machining tools are used on multilayer materials, such as stacks of parts. Additionally, the taper prevents accumulation of cutting material against the front face of the shroud, aiding in the evacuation of contaminants and reducing cutting forces. The taper also allows the leading edge of the shroud to fit snugly against the outer corner, reducing heat generation, tool wear, burr formation, and FRP delamination.

[0019] In another embodiment, the taper comprises a chamfer, bevel or fillet. Advantageously, this is a simple shape to manufacture while still providing the benefits associated with a typical tapered shape.

[0020] In another embodiment, the cutting head and shroud are integral with the body. Advantageously, this embodiment facilitates control of cutter head and shroud runout.

[0021] In another embodiment, the cutting head, shroud, and body are formed as a multi-piece structure. For example, the cutting head can be a replaceable cutting head, which can be attached to the shroud by, for example, threads, spline attachment, brazing, welding, adhesives, polygonal clamping, or an interference (shrink) fit. Advantageously, this can facilitate access to the internal structure during manufacturing and allow parts (particularly the replaceable cutting head) to be replaced as they wear. It also allows for the use of less expensive, more easily manufacturable materials, where possible, and harder materials in areas of the tool that are subject to wear.

[0022] In a preferred example, the leading edge of the shroud is positioned axially along the tool adjacent an outer corner of the cutting head, i.e., the leading edge of the shroud, optionally tapered, is close to the outer corner of the cutting head, so that cutting material passes directly through the shroud and not between the shroud and the uncut workpiece material, in the interface, or against the bore face, and does not damage any sealant that may be present.

[0023] In one embodiment, the shroud covers an area that is axially disposed less than 1 mm from at least one outer corner of the tool, and this area is circumferentially aligned with at least one outer corner of the tool. That is, the leading edge of the shroud is axially spaced distally from the at least one outer corner by less than 1 mm. In other examples, the leading edge of the shroud is axially spaced less than 0.6 mm, e.g., less than 0.3 mm, e.g., between about 0.3 mm and about 1 mm, e.g., between about 0.3 mm and about 0.6 mm, from the at least one outer corner. Advantageously, in these embodiments, contamination of the opening is best prevented because contaminants cannot enter the space between the outer diameter of the shroud and the opening, but are forced into the shroud.

[0024] In an embodiment, the axial offset between at least one outer corner of the tool and the leading edge of the shroud is less than 1 mm, preferably less than 0.6 mm, more preferably less than 0.3 mm, which advantageously best prevents contamination of the opening, as contaminants cannot pass between the shroud and the outer corner and in the interface or against the bore face.

[0025] In another embodiment, the outer diameter of the shroud at the proximal end is less than 0.16 mm less than the cutting diameter, preferably less than 0.08 mm less than the cutting diameter, more preferably less than 0.03 mm less than the cutting diameter, more preferably less than 0.02 mm less than the cutting diameter, and more preferably less than 0.01 mm less than the cutting diameter. In an example, the outer diameter of the shroud at the proximal end is less than 0.160 mm less than the cutting diameter, preferably less than 0.080 mm less than the cutting diameter, more preferably less than 0.030 mm less than the cutting diameter, more preferably less than 0.020 mm less than the cutting diameter, and more preferably less than 0.010 mm less than the cutting diameter. In examples, the outer diameter of the shroud at the proximal end is between 0.01 mm (0.010 mm) and 0.16 mm (0.160 mm) less than the cutting diameter, preferably between 0.08 mm (0.080 mm) and 0.16 mm (0.160 mm) less than the cutting diameter, more preferably between 0.03 mm (0.030 mm) and 0.08 mm (0.080 mm) less than the cutting diameter, more preferably between 0.02 mm (0.020 mm) and 0.08 mm (0.080 mm) less than the cutting diameter, and more preferably between 0.01 mm (0.010 mm) and 0.08 mm (0.080 mm) less than the cutting diameter.

[0026] Advantageously, in these instances, contaminants cannot enter the space between the shroud outer diameter and the opening, but are forced into the shroud, preventing contamination of the opening. The smaller the difference between the shroud outer diameter and the cutting diameter, the fewer contaminants can pass between the shroud and the opening. However, this is balanced against the possibility that the shroud will contact the opening during use. The inventors have found that the above dimensions perform well for use on multi-layer materials, particularly when machining openings in a stack of parts for a one-way assembly.

[0027] In one embodiment, the shroud covers an area less than 0.6 mm, preferably less than 0.3 mm, in either direction from the cutting edge. In an example, the shroud covers an area less than 0.6 mm, preferably less than 0.3 mm, in either direction from at least one outer corner.

[0028] In other examples, the proximal end of the shroud is axially offset from at least one outer corner by less than 0.6 mm, preferably less than 0.3 mm, and the outer diameter of the shroud at the proximal end is less than 0.6 mm, preferably less than 0.3 mm, less than the cutting diameter (diameter of the outer corner).

[0029] This ensures that the proximal end of the shroud is as close as possible to at least one cutting edge (and at least one outer corner) and ensures that contaminants are forced into the shroud and do not get between the outer surface of the shroud and the opening where they could cause damage and / or contamination.

[0030] In one embodiment, the cutting diameter of the tool is less than 50 mm, which is advantageously sized to fit the majority of aerospace fastener holes.

[0031] In another embodiment, the average shroud wall thickness is less than 0.3 mm. Advantageously, such a thickness helps prevent clogging of the shroud by increasing the cross-sectional area through which chips can rise.

[0032] In another embodiment, the shroud inner diameter increases between the proximal and distal ends. That is, the shroud inner diameter at the distal end is larger than the shroud inner diameter at or near the proximal end (excluding any taper used to direct contaminants). The increase in the shroud inner diameter can be provided by a taper, such as a gradual taper extending over a substantial portion of the shroud's length, or by one or more steps. This increase in the shroud inner diameter creates a drafted passageway for extracting contaminants. The drafted passageway can facilitate extraction and prevent clogging by reducing frictional forces between the material being extracted and the passageway.

[0033] In examples, the shroud outer diameter at the proximal end is larger than the shroud outer diameter at the distal end. That is, the shroud outer diameter decreases distally. The decrease in outer diameter can be provided by a step, a taper, etc. The decrease in outer diameter can provide a (relatively) large shroud outer diameter near the cutting head to prevent contaminants from entering between the shroud and the opening, while preventing the distal portion of the shroud from contacting the opening.

[0034] In yet another embodiment, the shroud further comprises an outer wall (exterior surface), said outer wall comprising a rough, abrasive surface. Advantageously, the presence of the abrasive surface serves to collect contaminants during the drilling process and to remove uncut fibers if the fiber-reinforced polymer material is cut.

[0035] In one embodiment, the shroud includes an outer wall with a patterned surface, e.g., a roughened or polished surface. In an example, the patterned surface includes a plurality of recesses or grooves. Advantageously, this allows for an interference fit into the aperture while reducing friction. They also provide a location for recapture of lost contaminants. The grooves can have a wide width, essentially creating a margin similar to that commonly found in twist drills. The grooves and recesses can also be shaped to aid in the aerodynamic air bearing effect between the shroud and the bore surface of the aperture, helping to guide the tool straight for hole-making processes in which the tool is fed only axially. For example, the recesses or grooves can take the form of a spiral groove bearing.

[0036] In another embodiment, the leading edge of the shroud is a shroud cutting edge that acts to cut material, particularly chips. The shroud cutting edge can have a discontinuous profile that includes portions that are offset from one another, for example, by a step or notch. Advantageously, in such an embodiment, the shroud cutting edge can serve to remove FRP fibers.

[0037] In another embodiment, the cutting edges on the cutting head have a serrated, wavy, or zigzag profile. Advantageously, in such an embodiment, higher stresses are created in the chips, thereby assisting in chip breakage and extraction.

[0038] In one embodiment, the tool includes at least one fluid outlet disposed near the cutting edge, the at least one fluid outlet configured to deliver cutting fluid and face the distal end of the tool. In another embodiment, the cutting fluid is in a supercritical state during use. Advantageously, this directs the cutting fluid toward the interior of the shroud, allowing for cooling and lubrication at the cutting interface and assisting in the removal of swarf and chips. Further advantageously, having a fluid outlet configured to face the distal end of the tool minimizes contamination of the opening. Further advantageously, cutting fluid delivered in a supercritical state can change state to a gas under atmospheric conditions and is not considered a contaminant.

[0039] In examples, the tool further includes at least one extraction channel, e.g., a flute, extending from the proximal end of the tool at least partially through the inner diameter of the shroud. In examples, the extraction channel can be drafted such that the distal end is larger than the proximal end to facilitate removal of contaminants through the extraction channel.

[0040] In one embodiment, the tool further includes a web and at least one flute, the flute being at least partially surrounded by a shroud. The flute can be an extraction channel. Advantageously, the web adds rigidity to the tool and provides a convenient attachment point for the shroud. In examples, the flute can be straight or spiral. In examples, the flute can be drafted so that the distal end is larger than the proximal end, facilitating removal of contaminants through the flute.

[0041] In one embodiment, the cutting head has the shape of a drill, a reamer, a trepanning tool, or a boring tool. In particular, the machining tool can be a drill or a reamer. Advantageously, this allows for effective removal of material when creating an opening (hole) while feeding the tool only axially. In another example, the machining tool is a milling tool, which can be used to create openings within a substantial range of diameters by feeding the tool both axially and radially. In another example, the machining tool is not a milling tool.

[0042] In some examples, the tool further includes a countersink cutter disposed on the tool distal to the cutting head. The countersink cutter is positioned to cut a countersink into the workpiece material after the aperture is machined or during machining of the aperture. This is particularly advantageous when the tool is used to machine fastener holes in a part, since the hole can be machined and countersink in a single machining operation.

[0043] According to another aspect of the present invention, there is provided a method of creating an opening in a multi-layer material, comprising: providing a multi-layer material; providing a tool as described above; performing a machining operation using a tool to create the opening and directing contaminants away from the opening during the machining operation; The opening is provided substantially free of contaminants.

[0044] Advantageously, such methods direct contaminants away from the opening, thereby providing protection from contaminants at the opening, joint, and surface, thus improving contamination levels, sealant damage, FRP surface defects, surface gouging, delamination caused by chip drag, and opening geometry.

[0045] In a preferred example, the multilayer material includes a stack of parts. Each part can include a fiber-reinforced polymer (FRP) material (e.g., carbon fiber reinforced polymer) and / or a metal material such as aluminum, titanium, or steel. In an example, the stack of parts can include a mixture of FRP and metal materials. In an example, the method is a method for one-way assembly (OWA) of a stack of parts in which apertures are created through multiple parts arranged in a stacked manner. The apertures can be fastener holes. Advantageously, the machining tool pushes contaminants through the shroud, preventing them from migrating into the faying surfaces and between the shroud and the apertures, thereby preventing contamination and / or damage to the apertures and / or faying surfaces as the apertures are machined. This helps prevent the need to disassemble the stack of parts to finish the apertures and remove contaminants from the faying surfaces, allowing for one-way assembly.

[0046] In one embodiment, the step of providing the multi-layer material may comprise stacking a plurality of components, at least one of which may comprise a fiber reinforced polymer material, in particular a carbon fiber reinforced polymer material.

[0047] In one embodiment, the tool is a drill, reamer, trepanning tool, or boring tool, and the step of performing the machining operation includes creating a hole by rotating the tool about its axis and moving the tool axially, and in particular moving the tool only axially and not laterally to create a circular hole.

[0048] In one embodiment, the method may further include cutting a countersink during or after machining the aperture. The countersink may be cut by a countersink cutter located on the machining tool, spaced from the cutting head.

[0049] In one embodiment, the method may further include inserting the fastener through the opening without disassembling the stack of parts, i.e., the method may be a one-way assembly method.

[0050] In one embodiment, controlled vibrations, such as those provided in vibration-assisted machining, are applied to the machining tool. Advantageously, vibrating the tool during drilling further assists in chip breakage. Also advantageously, cutting temperatures are reduced, thereby reducing abrasive tool wear. Also advantageously, it helps impart preferential compressive residual stresses to the metal part.

[0051] In another embodiment, the method further includes a step of localized clamping to compress layers of multi-layer material together, for example, to compress components of a stack of components together. Advantageously, the use of additional clamping reduces the size of gaps between layers (components) and helps prevent contamination, flash, and FRP delamination at the joining interfaces.

[0052] In yet another embodiment, the method further comprises the step of vacuum extraction of contaminants, advantageously, particularly when cutting fluids are used, to efficiently remove contaminants under controlled conditions.

[0053] In one embodiment, the step of performing a machining operation is performed to enlarge an existing opening, such as a pilot hole or a defective hole. Advantageously, this method allows for the provision of a contaminant-free final-size opening where a temporary fastener has been placed to provide clamping, where an undersized opening already exists to minimize the amount of machining that must be performed during the assembly stage, or where an attempt to create a final-size opening has already been made but resulted in a defective opening. In such instances, the machining tool may be a trepanning tool or a boring tool.

[0054] According to the present invention there is provided the use of such a tool or method in a one-way assembly process. Advantageously, the use of the above-described machining tool and method allows for the provision of clean openings even when gaps exist at the joining surfaces when one-way assembly methods are used.

[0055] Embodiments of the present invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0056] [Figure 1] 1 is a perspective view of a machining tool according to an embodiment of the present invention; FIG. [Figure 1a] FIG. 2 is an end view of the machining tool shown in FIG. 1. [Figure 1b] FIG. 2 is an enlarged view of an outer corner of the machining tool shown in FIG. 1. [Figure 2] FIG. 2 is a cross-sectional view of the machining tool shown in FIG. [Figure 3a] FIG. 1 is a close-up view of the machining tool showing the chamfer. [Figure 3b] FIG. 10 is a close-up view of the machining tool showing the change in outer diameter achieved by a step in the outer diameter of the shroud. [Figure 4] FIG. 10 is a plan view of a machining tool according to an alternative embodiment of the present invention including a groove. [Figure 5] FIG. 1 is a plan view of one embodiment of the present invention including at least one fluid outlet facing the distal end of the tool. [Figure 5a] FIG. 10 is an enlarged view of an embodiment of the present invention including at least one fluid outlet facing the distal end of the tool. [Figure 6a] 1 is a perspective view of an example of a machining tool having a multi-piece construction. FIG. [Figure 6b] FIG. 6b shows a cross section of the machining tool of FIG. 6a. [Figure 6c] FIG. 6c is an enlarged view of the machining tool of FIGS. 6a and 6b. DETAILED DESCRIPTION OF THE INVENTION

[0057] Figure 1 shows a machining tool 100 according to one embodiment of the present invention, and Figures 1a, 1b, and 2 are an end view, an enlarged view, and a cross-sectional view, respectively, of the same embodiment. The tool has an elongated body 101 having a connector 102 at its distal end and a cutting head 103 at its proximal end. In this example, the tool 100 is a drill, and the cutting head 103 includes a drill tip. However, in other examples, the tool 100 can be a reamer, and the cutting head 103 can include the cutting features of a reamer, or the tool 100 can be a trepanning or boring tool.

[0058] The tool 100 can be made from a variety of materials (e.g., cemented carbide, tool steel, high-speed steel), with hard materials being more suitable for the cutting head 103. Various wear-resistant coatings (e.g., diamond coatings) can also be applied to reduce wear during use. Similarly, various low-friction coatings can be applied to reduce friction. The cutting head 103 has a cutting diameter 104 and at least one cutting edge 105. The cutting diameter 104 can be less than 50 mm. It is understood that the periphery of the cutting edge can take various shapes known in the art, such as various rake and clearance angles, various cutting edge profiles, and that for drills, various chisel designs are possible.

[0059] It will be understood by those skilled in the art that the term "distal" defines the location of any portion of the tool that is located away from the drilling area, and the term "proximal" defines the location of any portion of the tool that is located towards or adjacent to the drilling area.

[0060] The machining tool 100 further includes a shroud 106 located at the proximal end of the tool 100 and configured to at least partially cover an area along the tool axis 116 distal to the cutting edge 105. The axial offset between the shroud leading edge 115 and the outer corner 111 of the tool is minimized to best contain contaminants, yet large enough to prevent the shroud leading edge 115 from contacting uncut material. To avoid contact between the shroud leading edge 115 and uncut material during use, the magnitude 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 the workpiece. This axial offset allows chips a distance they can travel radially inward before contacting the shroud leading edge 115. The shroud 106 covers a circumferentially aligned area within 1 mm, preferably within 0.6 mm, or 0.3 mm of the outer corner 111 of the tool 100. That is, shroud leading edge 115 is adjacent to the outer corner 111 of cutting head 103. In conventional tools, the shroud does not cover this area because it may prevent chip formation at cutting edge 105. However, by covering this area in tool 100 with shroud 106, contaminants that slide along the rake face of the tool near cutting edge 105 are advantageously trapped and directed into shroud 106.

[0061] The proximity of the shroud leading edge 115 to the cutting edge 105, particularly the outer corner 111, prevents contaminants created during machining from passing between the shroud 106 and the uncut workpiece material, thus preventing damage to openings and contamination of faying surfaces when multi-layer materials are being machined.

[0062] The outer diameter 121 of the shroud 106 is maximized to best capture contaminants and prevent chips from catching on the shroud leading edge 115, yet remains far enough below the tool's cutting diameter 104 to prevent interference with the aperture wall. To prevent interference between the shroud's outer diameter and the aperture wall, the offset between the cutting diameter and the shroud outer wall is greater than the amount of shrinkage seen in the aperture as the FRP and metal layers shrink during the hole creation process due to thermal effects and mechanical springback. The effects of thermal expansion of the tool should also be considered, for example, when the cutting head 103 and shroud 106 are made from different materials. During the axial hole creation process, margins are often used on the tool to guide it straight and help achieve the desired hole tolerance. With the shroud 106 in place, it's not possible to have substantial margins along the flute edges. Instead, the tight fit between the shroud 106 and the cutting diameter 104 is used to guide the tool straight. The tight contact can create an aerodynamic air bearing effect.

[0063] As the cutting edge 105 wears, the offset will decrease, and regrinding and sharpening the tool will also reduce the axial offset. Additional axial offset can be provided between the shroud leading edge 115 and the cutting edge 105 to accommodate wear and regrinding. Without proper offset between the shroud and the outer corner, friction, forces, and heat will increase, which negatively impacts tool life and hole quality.

[0064] The shroud 106 has a shroud wall thickness 107 and a length L. The wall thickness can range from, but is not limited to, 0.1 to 0.3 mm. The shroud length can be long enough to extend beyond the depth of the opening to protect it from contaminants. In this case, dust does not accumulate on the top surface of the workpiece, as is common when drilling an opening, because air circulates underneath the shroud and a vacuum can remove the cutting material as it exits the shroud. The thin wall thickness 107 increases the cross-sectional area over which chips can travel. Additionally, the thin wall thickness 107 reduces the area over which chips can trap on the front of the shroud 106, thereby reducing cutting forces and heat generation, which can have a negative impact on tool life and hole quality.

[0065] The shroud 106 has a shroud inner diameter 120 and an outer diameter 121, a distal end 106a, and a proximal end 106b. It will be appreciated that the shroud inner diameter 120 increases toward the proximal end (shroud leading edge 115), resulting in a tapered shroud wall thickness. The chamfer 109 shown in FIG. 3a is a preferred embodiment of the taper. The chamfer 109 guides contaminants from the cutting edge 105 into the shroud 106, thereby also helping to prevent contaminants created during machining from passing between the shroud 106 and the uncut workpiece material. The chamfer 109 helps prevent chips from being trapped and pushed into the front surface of the shroud 106, thereby reducing heat generation, tool wear, burr formation, and CFRP delamination. In instances where the shroud 106 is a separate component from the cutting head 103, this increases the strength of the cutting head 103 at the outer corner 111.

[0066] It will also be appreciated that the difference between the distal and proximal shroud outer diameters shown in Figure 3b may be the result of having different wall thicknesses 107 at the distal and proximal ends 106a, 106b of the shroud 106. However, it is also possible for the wall thickness 107 to be constant and for the outer diameter of the shroud 106 at its distal end to be smaller than the outer diameter at its proximal end. In other words, the former describes an embodiment in which the shroud inner diameter is constant, while the latter describes a shroud in which the wall thickness is constant and the shroud inner diameter varies.

[0067] Optionally, the body 101 and the cutting head 103 may have a web 117 and at least one flute 108. The at least one flute 108 may be spiral or straight. The shroud 106 may at least partially cover the at least one flute 108. The distal end of the at least one flute 108 is open (not covered by the shroud 106) to allow extraction of contaminants from the flute 108. In some examples, the at least one flute 108 may be drafted, having a smaller size at the proximal end and a larger size at the distal end. Such draft can assist in the extraction of contaminants, for example, when a vacuum is applied to the distal end of the at least one flute 108. However, it is understood that the web 117 and the at least one flute 108 may be absent or may not be present along a substantial length of the shroud. In such an example, the shroud 106 may include a hollow portion, and there may be a space within the shroud 106 between the cutting head 103 and the body 101 that defines an extraction channel for extracting contaminants. In such an example, the extraction channel may be drafted.

[0068] FIG. 3a shows an enlarged cross-sectional view of the proximal end of a shroud 106 according to the present invention. The shroud 106 covers at least a portion of the area along the tool axis distally from the cutting edge 105, as described above. The shroud outer diameter at its proximal end 106b is smaller than the cutting diameter 104 of the cutting head 103 so that friction between the shroud 106 and the bore surface of the opening is reduced during use. As shown, the distal side of the cutting head 103 may optionally be tapered where the chamfer 109 abuts. The chamfer 109 (and an optional corresponding taper on the cutting head 103) allows the shroud leading edge 115 to approach the outer corner 111 of the cutting edge 105, as described above. When the chamfer 109 aligns with the flutes 108, the chamfer 109 also acts to guide contaminants into the shroud 106, increasing the strength of the outer corner of the cutting head 103.

[0069] It will be understood by those skilled in the art that the chamfered interface between the shroud 106 and the cutting head 103 is only present for configurations in which the cutting head 103 and the shroud 106 are separate pieces. In some instances, the shroud 106 and the cutting head 103 are formed from a single piece, and in such instances, the chamfer 109 is only present if there are extraction channels, e.g., if at least one flute 108 is provided. It will also be understood that a chamfer-like shape that performs the same function can instead be formed. Such a structure can be, without limitation, a bevel, a fillet, or a freeform profile.

[0070] In an alternative embodiment, as shown in FIG. 3b, the outer diameter of the shroud 106 varies. This variation is shown in FIG. 3b as a step 119. Thus, the outer diameter of the shroud 106 at its distal end 106a is smaller than the outer diameter at its proximal end 106b. In this embodiment, the cutting diameter 104 remains larger than either of the diameters of the shroud 106. As discussed above, a chamfer 109 is formed at the interface of the shroud 106 and the cutting head 103. Having the cutting diameter 104 larger than the maximum outer diameter of the shroud 106 can reduce contact between the shroud 106 and the walls of the aperture during use. The step 119 in the outer diameter of the shroud 106 provides additional clearance between the shroud 106 and the wall of the hole in the material being machined. It is further understood that other features, such as a fillet or gradual taper, can be used in place of the step contour 119 to perform substantially the same function.

[0071] In prior art machining tools such as those mentioned above (e.g., U.S. Pat. No. 4,966,503), when the cutting tool is rotated by a powered rotating device to create an opening in a multi-layer material, contaminants are formed during the drilling process, which not only contaminate the opening and the surface of the joining interface, but can also cause defects such as scratching and / or gouging.

[0072] In the machining tool 100 of Figures 1-5, the shroud 106 creates a barrier between the contaminants and the aperture, directing chips and other contaminants away from the inner wall of the aperture. Having a chamfer 109 at the shroud leading edge, rather than a flat edge as in the prior art, is advantageous because it directs contaminants toward the inside of the shroud. In embodiments where the cutting tip is a separate component from the shroud, this allows the leading edge of the shroud to be closer to the outer corner of the cutting tip while maintaining strength at the outer corner. Directing contaminants toward the inside of the shroud provides a clean interface between the laminations. This result is particularly beneficial in one-way assemblies when all layers of material are stacked together and drilled simultaneously, without the need for intermediate disassembly to evaluate and improve aperture quality before installing the final fastener. Furthermore, having the shroud 106 in place adds additional rigidity to the tool 100, thereby allowing for the use of thinner webs than standard for cutting tools, or even the elimination of web 117. Reducing the web increases the cross-sectional area for chip removal.

[0073] In the above-described embodiment, the body 101, cutting head 103, and shroud 106 are separate components. In alternative embodiments, these components can be integrated in various combinations. For example, in an alternative embodiment, the shroud 106 can be integral with the body 101, and they can be machined or 3D printed as a single unit. As a further example, this can be manufactured using a mold, e.g., carbide powder formed into the desired shape in a "green state" and then sintered. In alternative embodiments, these components can be further subdivided. For example, the cutting head can include inserts with additional interfaces that are connected to the cutting head.

[0074] It is understood that when the shroud 106 is not integral with the body 101 and cutting head, the shroud can be retrofitted to an existing tool by grinding the shape that interfaces with the shroud and fitting the shroud in place. The fitting procedure can be, for example, as follows: The shroud is preheated and fitted onto the body 101 from the end of the coupling 102. The shroud 106 is then advanced further towards the distal end of the tool 100 until it contacts the chamfer 109. As a final step, the shroud is allowed to cool and shrink before being fitted to the tool 100. It is understood that other alternative fitting methods are also contemplated.

[0075] 6a-6c illustrate an example tool 200 having a multi-piece construction. In this example, a substantial portion of the chip passage is free of webs or flutes. In this example, a two-piece construction is shown. FIG. 6a illustrates a perspective view of tool 200, FIG. 6b illustrates a longitudinal cross-section through tool 200, and FIG. 6c illustrates an enlarged cross-sectional view of the proximal end of the shroud. Tool 200 includes a removable cutting head 201 and a shroud 206. In this example, removable cutting head 201 is attached to the proximal end of shroud 206. In this example, removable cutting head 201 is a drill cutting head, but in other examples, it may be a reamer cutting head, a trepanning tool cutting head, a boring tool cutting head, or a milling cutter cutting head.

[0076] As shown, the removable cutting head 201 includes a cutting head 203 with a cutting edge 205 having an outer corner 211. The cutting head 203 is substantially as described above with respect to the previous example. A shroud 206 is attachable to the removable cutting head 201 and at least partially covers an area along the tool axis distally from the cutting edge 205. As shown, the shroud 206 is attached to the removable cutting head 201 by screws 212. Alignment surfaces are also used for precise positioning. The screws 212 are preferably positioned toward the proximal end of the shroud 206 to reduce the distance between the screws 212 and the proximal end of the shroud 206, thereby increasing the rigidity of the proximal end of the shroud 206. Alternative methods of attaching the removable cutting head 201 to the shroud 206 are possible, such as the use of splines, brazing, welding, adhesives, shrink-fit connections, and polygonal clamping. It will also be understood by those skilled in the art that some combination of these attachment methods may also be used.

[0077] Having the connection between the removable cutting head 201 and the shroud 206 near the proximal end of the shroud 206 allows the removable cutting head 201 to be short, and therefore allows for a longer chip passage without being restricted by the web.

[0078] In this example, the removable cutting head 201 extends only partially into the shroud 206 and has a distal end 214 disposed within the shroud 206, as shown in FIG. 6b. The shroud 206 provides a connection when the tool 200 is in use. Thus, the tool 200 can be assembled by threading the removable cutting head 201 onto the shroud 206, and the removable cutting head 201 can be removed in the same manner and replaced, for example, with a new removable cutting head 201.

[0079] As shown, the removable cutting head 201 includes extraction passages, in this example flutes 208, that extend from the cutting head 203 to the distal end 214 of the removable cutting head 201 and allow chips and other contaminants to pass from the cutting head 203 into the shroud 206 and exit the tool at openings 213. The flutes 208 may be straight (axially), spiral, or drafted (tapered). The flutes 208 are axially shorter in this example than in the examples of FIGS. 1 through 5, which can help prevent clogging and improve contaminant extraction. Notably, the flutes 208 extend only the axial length of the removable cutting head 201, defining extraction channels beyond the removable cutting head 201 and into the shroud 206 at openings 213. Thus, in this example, the flutes 208 extend only a short axial distance from the cutting edge 205, making them less susceptible to clogging. In this example, a bleed passage is defined through the longitudinal grooves 208 through the shroud 206 to the opening 213 .

[0080] As shown in Figure 6c, the proximal end of the shroud 206 includes a chamfer 209 that engages a corresponding taper on the cutting head 203, as described with reference to other examples. As in the above examples, the proximal end of the shroud 206 is axially adjacent to the outer corner 211 of the cutting edge 205 and is axially spaced apart by less than 1 mm, as described above for the examples of Figures 1-5. Additionally, as described above, the outer diameter of the shroud 206 is less than the cutting diameter, as described above for the examples of Figures 1-5.

[0081] In another alternative embodiment, the shroud 106, 206 can have a rough, abrasive outer surface. Advantageously, this can aid in the collection of contaminants and remove uncut fibers in the FRP material. In yet another embodiment, such as that shown in FIG. 4, the outer wall of the shroud 106 can have a plurality of grooves 110 or recesses configured to maintain a tight seal while minimizing rubbing against the aperture. The purpose is to reduce friction while maintaining a tight fit in the aperture. The grooves 110 can have a variety of shapes, e.g., axial, spiral, or circumferential. The recesses can also have a variety of shapes. The grooves or recesses can be configured to act like margins on a drill or to help create an aerodynamic air bearing effect (e.g., configured as a spiral groove bearing with a journal shape).

[0082] In yet another embodiment, at least one cutting edge 105, 205 can have a chip breaker to improve chip breaking and consequently chip evacuation. Many shapes of chip breakers are already used on cutting tools. In examples, the cutting edge 105, 205 can include a step or notch to reduce the width of the chip. In examples, a chip breaking fixture can be located on the rake face of the tool, or the cutting edge 105, 205 can include a step or notch to reduce the width of the chip.

[0083] In Figures 1-6, the machining tools 100, 200 are configured to deliver cutting fluid through at least one fluid outlet 113 in the region of the cutting edges 105, 205. In the example of Figures 6a-6c, a fluid path can be formed in the shroud 206 and connected to a fluid outlet in the cutting head 203. The cutting fluid can be, for example, cutting oil, cryogenic cutting fluid, or a fluid maintained in a supercritical state upstream of the fluid outlet 113. When using a fluid in a supercritical state, the outlet diameter is smaller than the upstream pipe diameter, between 0.1 mm and 0.3 mm, to create a restriction to maintain upstream pressure and allow for a rapid pressure drop. When other fluids are used, the outlet diameter can be larger because a rapid pressure drop is not required. It is understood that the larger the hole, the less restriction there is to the flow and the higher the flow rate. Optionally, at least one fluid outlet 113 passes through the coupling portion 102, the cutting head 103, and exits near the cutting edge 105, 205 to discharge fluid in a proximal direction, as shown in FIGS. 1-4. In an alternative embodiment, as shown in FIG. 5, the at least one fluid outlet faces away from the drilling area toward the distal end. This is achieved by a U-turn 114 in the fluid outlet 113. Directing the at least one fluid outlet away from the drilling area (rearward) aids in chip removal and cooling and minimizes disruption of the interface. In another example, the fluid outlet 113 and U-turn 114 can be formed in a removable cutting head 201, as shown in FIGS. 6a-6c. In another example, the fluid outlet 113 and U-turn 114 can be formed partially by the tool body 101 and partially by the removable cutting head. Forming the fluid outlets 113 and U-turns 114 at least partially in the removable cutting head rather than in the tool body 101 can make manufacturing easier. By directing the at least one fluid outlet 113 at least partially towards the distal end, the risk of contamination is reduced as the fluid flow is directed away from the mating surfaces, which has the added benefit of reducing pressure at the opening and assisting in closing the gap between the parts.

[0084] The following method can be used to create openings in the multi-layer material.

[0085] As a first step, a multilayer material is provided. The term "multilayer" includes at least two layers of material, and it is understood that these layers can share or possess different chemical and mechanical properties. By way of example, these layers can be, but are not limited to, carbon fiber reinforced polymer, aluminum alloy, stainless steel, titanium, and titanium alloy. It is also understood that layers can be repeated; for example, a material can include two or more layers of carbon fiber separated by an aluminum alloy, or vice versa. It is also understood that a sealant can be present between layers.

[0086] In the next step, a machining tool 100 is provided and the tool is rotated about its axis and advanced towards the workpiece to create the opening.

[0087] In the next step, tool 100 creates an aperture through the layers of the multi-layer material. A shroud, at least partially covering the area between connecting portion 102 and cutting edge 105, acts as a protector for the aperture, thus creating a clean, contaminant-free aperture free of surface imperfections typically caused by chips passing through the aperture.

[0088] As a final step, once the opening is created, the tool is extracted from the opening.

[0089] In this way, the need to minimize gaps between components to limit interface contamination is reduced.

[0090] Optionally, the machining tool can be vibrated. Vibration-assisted drilling typically uses axially controlled vibrations to promote chipping in the metal. This can be ultrasonic vibration as well as low-frequency vibration-assisted drilling (Mitis systems, https: / / www.mitis.fr / ).

[0091] Further optionally, localized clamping can be used to minimize gaps between layers during drilling, which can be provided, for example, by a pressure foot, adjacent final fasteners, disposable rivets, C-clamps, or electromagnetic clamping.

[0092] In an alternative embodiment, vacuum extraction can be applied during the process of creating the openings. Vacuum extraction is particularly advantageous when cutting fluid is used to facilitate the evacuation of swarf and chips.

[0093] It is understood that the above-described methods can also be used for pilot holes and defective holes, thus allowing for rework to correct substandard openings without the need to discard the machined part. It will be apparent to those skilled in the art that some prefabricated parts can be supplied with pilot holes as standard, which may subsequently require further machining to achieve the correct size. Pilot holes can exist if temporary fasteners are utilized in the assembly process. Once the temporary fasteners are removed from the pilot holes, the pilot holes will be machined to size and permanent fasteners will be applied. Pilot holes can exist as a result of a defect during the primary machining step, resulting in the hole being re-machined, usually oversized.

[0094] Although the methods and machining tools described above may be particularly advantageous for use in one-way assemblies, many different cutting tool technologies can be applied to the methods and machining tools described.

[0095] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations thereof mean "including but not limited to" and are not intended to exclude (exclude) other moieties, additives, ingredients, whole bodies or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context requires otherwise. In particular, where the indefinite article is used, the specification should be understood as contemplating the plural as well as the singular, unless the context requires otherwise.

[0096] It should be understood that any feature, integer, property, compound, chemical moiety, or group described in connection with a particular aspect, embodiment, or example of the invention is applicable to any other aspect, embodiment, or example described herein, unless inconsistent therewith. All features disclosed in this specification (including any accompanying claims, abstract, and drawings), and / or all steps of any method or process so disclosed, may be combined in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive. The invention is not limited to the details of any of the foregoing embodiments. The invention extends to any novel, or any novel combination of, features disclosed in this specification (including any accompanying claims, abstract, and drawings), or to any novel, or any novel combination of any method or process so disclosed.

[0097] The reader's attention is drawn to all articles and documents related to this application that have been filed contemporaneously or previously hereto and that are open to public inspection herewith, and the contents of all such articles and documents are incorporated herein by reference. [Explanation of symbols]

[0098] 100 tools 101 Main Unit 102 Connection part 103 Cutting head 104 Cutting diameter 105 Cutting Edge 106 Shroud 106a distal end 106b proximal end 107 Wall thickness 108 Vertical grooves 109 Chamfering 110 Groove 111 Outside Corner 113 Fluid outlet 114 U-turn 115 Shroud leading edge 116 Tool axis 117 Web 119 steps 120 Inner diameter 121 outer diameter 200 Tools 201 Removable Cutting Head 203 Cutting Head 205 Cutting Edge 206 Shroud 208 Vertical grooves 209 Chamfering 211 Outside Corner 212 Screw 213 Aperture 214 Distal end

Claims

1. 1. A machining tool for creating an opening in a multi-layer material, comprising: a main body including a connecting portion; a cutting head at one end of the body, the cutting head having a cutting diameter, at least one cutting edge, and at least one outside corner; a shroud having an average shroud wall thickness, a length, a distal end, a proximal end having a leading edge, an inner shroud diameter, and an outer shroud diameter, the shroud covering at least a portion of an area between the coupling portion and the cutting edge and configured to direct contaminants away from the opening; Including, the cutting diameter is greater than the shroud outer diameter at the proximal end; machining tools.

2. The machining tool of claim 1 , wherein the shroud inner diameter increases toward the proximal end such that the shroud includes a taper that converges toward the cutting head.

3. The tool of claim 2 , wherein the taper comprises a chamfer, a bevel, or a fillet.

4. The tool of claim 1 , wherein the cutting head and the shroud are integral with the body.

5. The tool of claim 1 , wherein the cutting head, the shroud, and the body are formed as a multi-piece structure.

6. The tool of claim 5 , wherein the cutting head is an interchangeable cutting head, the interchangeable cutting head being attachable to the shroud.

7. The tool of claim 1 , wherein the leading edge of the shroud is positioned axially along the tool adjacent the outer corner of the cutting head.

8. 8. The tool of claim 1, wherein the shroud covers an area disposed axially less than 1 mm from the at least one outer corner of the tool, the area being circumferentially aligned with the at least one outer corner of the tool.

9. 9. A tool according to any one of claims 1 to 8, wherein the axial offset between the at least one outer corner of the tool and the leading edge of the shroud is less than 1 mm, preferably less than 0.6 mm, more preferably less than 0.3 mm.

10. 10. A tool according to any one of claims 1 to 9, wherein the outer diameter of the shroud at the proximal end is less than 0.16 mm, preferably less than 0.08 mm, more preferably less than 0.03 mm less than the cutting diameter.

11. A tool according to any one of claims 1 to 10, wherein the shroud covers an area less than 0.6 mm, preferably less than 0.3 mm in any direction from the cutting edge.

12. The tool of claim 1 , wherein the shroud inner diameter increases toward the distal end.

13. The tool of claim 1 , wherein the shroud outer diameter at the proximal end is greater than the shroud outer diameter at the distal end.

14. 14. A tool according to any one of claims 1 to 13, wherein the cutting diameter of the tool is less than 50 mm.

15. The tool of claim 1 , wherein the average shroud wall thickness is less than 0.3 mm.

16. The tool of claim 1 , wherein the shroud further comprises an outer wall including a patterned surface, e.g., a rough, abrasive surface.

17. The tool of claim 16 , wherein the patterned surface of the outer wall comprises a plurality of recesses or grooves.

18. 18. The tool of claim 1, further comprising at least one fluid outlet disposed near the cutting edge, the at least one fluid outlet configured to deliver cutting fluid and facing the distal end of the tool.

19. 19. The tool of any one of claims 1 to 18, wherein the cutting fluid is in a supercritical state.

20. The tool of claim 1 , further comprising at least one extraction channel extending from the proximal end of the tool at least partially through the inner diameter of the shroud.

21. 21. The tool of any one of claims 1 to 20, further comprising a web and at least one flute, said flute being at least partially surrounded by said shroud.

22. 22. A tool according to any one of claims 1 to 21, wherein the cutting head has the shape of a drill or a reamer.

23. 23. The tool of claim 1, further comprising a countersink cutter spaced from the cutting head distally of the tool.

24. 1. A method of creating an opening in a multi-layer material, comprising: providing the multi-layer material; Providing a tool according to any one of claims 1 to 23; performing a machining operation using the tool to create the opening, and directing contaminants away from the opening during the machining operation; Including, the opening is provided substantially free of contaminants; method.

25. The method of claim 24 , wherein the multi-layer material comprises a plurality of components in a stacked arrangement.

26. The method of claim 25 , wherein at least one of the plurality of parts comprises a fiber-reinforced polymer material.

27. 27. A method according to any one of claims 24 to 26, wherein controlled vibrations, such as those provided in vibration assisted machining, are applied to the machining tool.

28. 28. The method of any one of claims 24 to 27, further comprising the step of localized clamping to compress the layers of the multi-layer material.

29. 29. The method of any one of claims 24 to 28, further comprising the step of vacuum extraction of the contaminants.

30. 30. A method according to any one of claims 24 to 29, wherein the step of performing a machining operation is performed to enlarge an existing opening, such as a pilot hole or a defective hole.

31. Use of a tool according to any one of claims 1 to 23 or a method according to any one of claims 24 to 30 in a one-way assembly process.

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