Abstract:
Methods are disclosed for producing a hole in a work-piece having first and second layers of material. The first layer of material contains a full-sized hole through the first layer of material. The first layer of material is positioned adjacent the second layer of material. An orbital drill is secured to the first layer of material to position a cutting tool of the drill within the through-hole. During operation, when the cutting tool is used to cut a hole in the second layer of material, the alignment keeps the orbital drill stationary.

Description:
BACKGROUND  
       [0001]     In conventional drilling, a cutting tool rotates around its own axis while feeding forward into the material being drilled. The cutting edges perform best at the outside edges while the center of the drill essentially does not cut, but merely pushes its way through the material. This generates a lot of heat and thrust force which requires additional power from the drilling machine. When the drill reaches the other side of the material being drilled, the drill tip bursts through creating ragged edges that spread out to the final sized hole, leaving an exit burr around the hole. Exit burrs are unacceptable in aerospace assembly, and in many other industries, as they create stress risers and fatigue cracks in the structure.  
         [0002]     Orbital drilling has been used in an effort to avoid many of the problems often associated with conventional drilling. With orbital drilling, the cutter rotates around its own axis but the cutter spindle is offset from the centerline of the hole by the orbital axis of the machine. This dual rotating axis approach can be described as a spiral milling method of generating a hole. The cutting edges travel at very high speed and create very small chips that are vacuumed away. No lubrication is required and burrs are typically not generated as the cutter exits the material. Moreover, the same holes can be generated using much less thrust force and torque than would be needed from a conventional drilling machine.  
         [0003]     In the airline industry, amongst other industries, work-pieces comprised of multiple layers of material are often utilized. These layers of material often have varying hardness levels. When the outermost layer of material of the work-piece is extremely hard, such as Titanium, it is difficult to accurately and efficiently drill a hole through the multiple layers of material, even utilizing orbital hole drilling. During such an orbital drilling process, damage to the cutting tool may occur, the hole may end up misaligned, the drilling process may take an extended time, and the drilled hole may end up having sharp, undesired burrs.  
         [0004]     A method of orbital drilling a hole, in a work-piece having multiple layers, is needed to substantially avoid one or more of the problems associated with having to simultaneously drill through a hard outer layer while drilling the hole in the work-piece.  
       SUMMARY  
       [0005]     In one aspect of the invention, a method is disclosed for forming a hole in a multi-layer workpiece. A workpiece is provided which includes a first layer of material with a through-hole and a second layer of material positioned adjacent to the first layer of material. An orbital drill is secured to the first layer of material in order to position a cutting tool of the drill within the through-hole. The orbital drill remains stationary with respect to the workpiece when the cutting tool is cutting a hole in the second layer of material.  
         [0006]     In another aspect of the invention, a method is disclosed for manufacturing an aircraft component. An aircraft component is provided which includes a first aircraft element with a through-hole and a second aircraft element positioned adjacent to the first layer of material. An orbital drill is provided. The orbital drill includes a principal axis and a cutting tool with a tool axis. When in operation, the cutting tool rotates about the tool axis and orbits about the principal axis. The drill is secured to the first aircraft element such that the principal axis of the drill is substantially fixed with respect to the aircraft component when the cutting tool is in operation.  
         [0007]     In yet another aspect of the invention, an aircraft component is disclosed comprising a first aircraft element having a through-hole and a second aircraft element positioned adjacent to the first layer of material. The second aircraft element has a hole with a diameter that is substantially equal to that of the through-hole. The hole of the second aircraft element is formed using an orbital drill. The orbital drill contains a principal axis, and includes a cutting tool with a tool axis. The cutting tool is received in the through-hole and maintains the principal axis of the drill in a substantially fixed relationship with the aircraft component. When in operation, the cutting tool rotates about the tool axis and orbits about the principal axis to cut the hole.  
         [0008]     The present invention, together with further objects and advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0009]      FIG. 1  is a front elevational and partial sectional view of one embodiment of a prior art orbital hole drilling apparatus to which the methods of the present invention may be applied;  
         [0010]      FIG. 2  is a top plan schematic view of a cutting tool of a prior art orbital hole drilling apparatus positioned within a hole of a layer of material;  
         [0011]      FIG. 3  is a perspective view of another embodiment of a commercially available prior art orbital drilling unit to which the methods of the present invention may be applied;  
         [0012]      FIG. 4  is a perspective view of another embodiment of a commercially available prior art orbital drilling unit to which the methods of the present invention may be applied;  
         [0013]      FIG. 5  is a partial cross-sectional view of one embodiment of the employment of a method of the present invention;  
         [0014]      FIG. 6  is a partial cross-sectional view of another embodiment of the employment of a method of the present invention;  
         [0015]      FIG. 7  is a partial cross-sectional view of yet another embodiment of the employment of a method of the present invention; and  
         [0016]      FIG. 8  is a partial cross-sectional view of another embodiment of the employment of a method of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     The following description of preferred embodiments provides examples of the present invention. The embodiments discussed herein are merely exemplary in nature, and are not intended to limit the scope of the invention in any manner. Rather, the description of these preferred embodiments serves to enable a person of ordinary skill in the art to use the present invention.  
         [0018]     The methods of the present invention may be applied to any type of orbital hole drilling apparatus. A better understanding of the methods of the present invention will be obtained by first describing conventional orbital hole drilling apparatus, as shown in  FIGS. 1-4 , to which the methods of the present invention may be applied. After this description, the methods of the present invention will be described using  FIGS. 5-8 .  
         [0019]      FIG. 1  depicts one embodiment of a conventional orbital hole drilling apparatus  110 . Generally, there is shown a spindle motor  112 , a radial offset mechanism  114 , an axial feed mechanism  116 , and an eccentric rotation mechanism  118 . Radial offset needle  120  is movable in an axial feed direction indicated by double arrow  122 .  
         [0020]     The spindle motor  112  causes a rotation of tool holder  124  and a corresponding rotation of cutting tool  126 . Radial offset mechanism  114  allows a user to create a radial offset  128  between the tool axis  130  which is defined by the cutting tool  126 , and the principal axis  132  which is defined by axle  134  and radial offset needle  120 . In  FIG. 1 , the radial offset mechanism  114  has been utilized to create a radial offset  128 . The axial feed mechanism  116  allows the rotating cutting tool  126  to be advanced into a work-piece (not shown) in order to machine a hole (not shown) in the work-piece. Eccentric rotation mechanism  118  includes an eccentric rotation motor  140  which drives an eccentric rotation belt  144  engaged with axle  134 . Belt  144  rotates axle  134  around principal axis  132 , and due to the offset of tool axis  130  from principal axis  132  created by radial offset mechanism  114 , provides a corresponding eccentric rotation of cutting tool  126  around principal axis  132 .  
         [0021]     The operation of eccentric rotation mechanism  118  causes cutting tool  126  to oscillate or orbit around principal axis  132  while tool  126  simultaneously rotates about its own axis  130 . The radius of the circular oscillation is substantially equal to the radial offset between tool axis  130  and principal axis  132 . Using the orbital tool drilling apparatus  110 , cutting tool  126  can be simultaneously fed in an axial direction, rotated about its own axis  130 , and eccentrically oscillated about a principal axis  132  in order to produce a hole (not shown) having a diameter greater than the diameter of cutting tool  126 . In addition, by using radial offset mechanism  114  to adjust the radial offset of cutting tool  126  during the machining process, it is possible to produce conical holes or other types of axis-symmetrical complex-shaped holes.  
         [0022]      FIG. 2  shows a schematic view of a cutting tool  226  of a conventional orbital hole drilling apparatus producing a hole  250  in a layer of material  205 . The diameter  252  of the cutting tool  226  is substantially smaller than the diameter  254  of the hole  250  being produced. This is accomplished due to the rotation of the offset cutting tool  226  around a principal axis (not shown).  
         [0023]      FIGS. 3 and 4  show two additional embodiments of conventional orbital drilling units to which the methods of the present invention may be applied. The machine mounted orbital drill unit  310  shown in  FIG. 3  is programmed with a numerical control. The orbital drill unit  410  shown in  FIG. 4  is portable and may be carried to the assembly area by a mechanic and locked into a drill template attached to the structure being assembled.  
         [0024]      FIG. 5  depicts an orbital hole drilling apparatus  510  utilizing one embodiment of a method of the present invention to orbital drill a hole  550  in a multiple-layered work-piece  560 . A shoulder bushing  562  substantially stabilizes the orbital drill  510 . As shown, a full-sized through hole  564  has been pre-formed in a Titanium outer (first) layer  566  of the multiple-layered work-piece  560 . The multiple-layered work-piece  560  comprises a portion of an airplane such as a portion of a wing, or a portion of an airplane&#39;s main body. In other embodiments, the work-piece  560  may comprise a non-aeronautical apparatus such as a vehicle assembly or other type of apparatus. In still other embodiments, the outer layer  566  may comprise any material known in the art, such as Steel, Aluminum, Graphite, or a composite material. The full-sized through hole  564  in the outer layer  566  may be formed using any process known in the art, such as drilling or molding, and is preferably chamfered. At least one additional layer  568  of the work-piece  560 , preferably comprised of a material softer than the Titanium outer layer  566 , is positioned substantially parallel to the Titanium outer layer  566  adjacent the full-sized hole  564 .  
         [0025]     The additional layer  568  comprises any material known in the art softer than the material of the outer layer  566 , such as Aluminum, Graphite, or a composite material. In other embodiments, the additional layer  568  and subsequent layers in the workpiece  560 , may comprise any material known in the art, such as Titanium, which is as hard or harder than the material of the outer layer  566 . In still other embodiments, the additional layer  568  may be positioned in non-parallel configurations near the outer layer  566 .  
         [0026]     A cutting tool  526  of an orbital hole drilling apparatus  510  is placed into the full-sized hole  564 , so that the bottom  570  of the cutting tool  526  is substantially parallel to an outer surface  572  of the additional layer  568 . In other embodiments, the cutting tool  526  may be configured in different alignments. The cutting tool&#39;s axis  530  is offset from the principal axis  532 . In other embodiments, the cutting tool&#39;s axis  530  may be aligned with the principal axis  532 . The cutting tool  526  is stabilized by a connected shoulder bushing  562  which has a flange  574  abutting against an outer surface  576  of the outer layer  566  and a substantially cylindrical surface  578  abutting against an inner surface  580  of the full-sized hole  564  in the outer layer  566 . The diameter d of the cutting tool&#39;s head  527  is larger than the diameter d 1  of the cutting tool&#39;s shaft  529 . The flange  574  may abut against the outer surface  576  of the outer layer  566  in a parallel or non-parallel configuration. Similarly, the substantially cylindrical surface  578  may abut against the inner surface  580  of the full-sized hole  564  in the outer layer  566  in a parallel or non-parallel configuration.  
         [0027]     The shoulder bushing  562  helps to stabilize the cutting tool  526  in the Z direction. The orbital hole drilling apparatus  510  is used to drill a hole  550  in the additional layer  568 , which is a continuation of the hole  564 . The hole  550  may be drilled to match the size of the full-sized, pre-formed hole  564 . In other embodiments, the hole  550  may be drilled in any configuration, shape, or size. Moreover, the hole  550  may be drilled through the entire additional layer  568  and subsequent layers in the workpiece  560 . A fastening device (not shown), such as a bolt or other fastening device known in the art, may be inserted from the full-sized through hole  564  into the hole  550  to attach the outer layer  566  to the additional layer  568  and subsequent layers in the workpiece  560 .  
         [0028]      FIG. 6  depicts an orbital hole drilling apparatus  610  utilizing another embodiment of a method of the present invention to orbital drill a hole  650  in a multiple-layered work-piece  660  utilizing a shoulder bushing  662  and a stabilizing arm  682  to substantially stabilize the orbital drill  610 . One end  684  of the stabilizing arm  682  is attached to the shoulder bushing  662  while the other end  686  of the stabilizing arm  682  is attached to an outer surface  676  of the outer layer  666 . The end  686  of the stabilizing arm  682  may be attached to the outer surface  676  of the outer layer  666  using one of a suction cup, a magnet, a mechanical clamp, or by any other attachment mechanism known in the art. Due to the stabilizing arm  682 , the orbital drill&#39;s  610  motion in the ±Z direction is substantially blocked when positive F z  forces are less than negative F z  forces. In addition, unwanted rotational movement of the orbital drill  610  is substantially restricted. Moreover, undesired deviation of the orbital drill  610  from a perpendicular position, which is sometimes caused by applying bending moment M b  to the orbital drill  610 , is substantially avoided.  
         [0029]      FIG. 7  shows an orbital hole drilling apparatus  710  utilizing another embodiment of a method of the present invention to orbital drill a hole  750  in a multiple-layered work-piece  760 . In this embodiment, an expandable, substantially cylindrical bushing  762  provides a substantially tight fit of the bushing  762  within the full-sized, pre-formed hole  764  in the outer layer  766 . The substantially cylindrical surface  778  of the bushing  762  is expanded so that it abuts against an inner surface  780  of the full-sized hole  764  in the outer layer  766 , while the flange  774  abuts against an outer surface  776  of the outer layer  766 . The bushing  762  expansion may be achieved using any type of expansion mechanism known in the art including mechanical, and hydraulic devices. Use of the expansion mechanism substantially avoids displacement of the orbital drill  710  in the X-Y plane caused by F x  and F y  process forces. Movement of the orbital drill  710 , caused by drilling thrust forces F z  and rotational torque forces, is also substantially restrained.  
         [0030]      FIG. 8  depicts an orbital hole drilling apparatus  810  utilizing another embodiment of a method of the present invention to orbital drill a hole  850  in a multiple-layered work-piece  860  having a sloped outer layer  866 . An expandable, substantially cylindrical bushing  862  is utilized to substantially lock the orbital drill  810  in place within a full-sized, pre-formed hole  864  in the sloped outer layer  866  without the use of a flange. The substantially cylindrical surface  878  is expanded so that it abuts against an inner surface  880  of the full-sized hole  864  in the outer layer  866 . Use of the bushing expansion mechanism improves the stability of the orbital drill  810  and aids in substantially resisting bending moments M b .  
         [0031]     The methods of the present invention may allow for a hole to be drilled in additional layers of a multiple-layered work-piece utilizing a full-sized, pre-formed hole in a Titanium or other material outer layer of the work-piece. These methods may substantially avoid one or more of the problems associated with having to simultaneously drill through a Titanium or other material outer layer, such as time-inefficiency, damage to the cutting tool, and inaccurateness. Additionally, these methods may allow for burr-less, dry-drilling, with chips evacuated during the drilling process.  
         [0032]     Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. As such, it is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that the appended claims, including all equivalents thereof, are intended to define the scope of the invention.