Abstract:
A machining method for machining a superficial portion of a laminate using machine tool having a depth limiter which restricts a maximum depth of the machine tool. A guide frame having an inner guide contour restricts a maximum dimension of the superficial portion, and is secured over the superficial portion. The superficial portion is machined while the machine tool is guided by the guide contour. From another point of view, a machining apparatus for machining a superficial portion of a material is provided. The machining apparatus comprises a guide frame, an inner guide contour for guiding a machine tool, an attachment member for securing the guide frame to an attachment member, adjacent to the superficial portion, of the material.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/134,180, filed Jun. 5, 2008, which claims priority from U.S. provisional application No. 60/942,014, filed Jun. 5, 2007, both of which are incorporated by reference herein. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a method and apparatus for machining a laminate, and in particular a fiber-metal laminate. 
       BACKGROUND OF THE INVENTION 
       [0003]    Although applicable to any laminates, the present invention and the problem on which this invention is based will be described in detail with respect to fiber glass-aluminum laminates in aircraft construction. 
         [0004]    Aluminum which is traditionally used as a standard material in aircraft construction is increasingly being replaced by novel materials, such as fiber-reinforced plastics materials or fiber-metal laminates, in which layers of fiber-reinforced plastics materials and metals are joined to form a laminate. 
         [0005]    For example, large areas of the outer shell of the commercial aircraft Airbus A380 are produced from a fiber-metal laminate known under the name of GLARE (glass-fiber reinforced aluminum). This material consists of alternating layers, in each case only a few tenths of a millimeter thick, of aluminum and a glass fiber-reinforced epoxy resin plastics material which are bonded together under pressure during production. Important advantages of such laminates over aluminum are, for example favorable burn through and impact behavior as well as increased tear strength. 
         [0006]    During regular flight operation of an aircraft, during loading and unloading, maneuvering on the ground, during lightning strike, maintenance and in other situations, the outer shell frequently suffers relatively slight damage, for example scratches. To be able to remedy damage of this type quickly and reliably, various standardized repair methods are used on conventional aircraft outer shells made of aluminum. 
         [0007]    For example, according to one such repair method, scratches in the outer shell are ground out and polished with hand-held tools driven by compressed air. Another repair method comprises drilling or rubbing holes to seat repair bushes. 
         [0008]    If repair methods of this type are applied analogously to the case of damage to outer shells consisting of a laminate, for example outer shells made from GLARE, the problem arises when a scratch is ground out for example, that the top layer of the laminate which, in the case of GLARE consists of aluminum, is penetrated and the underlying fiber layer is damaged, which impairs the stability of the fiber layer. 
         [0009]    When holes are drilled and rubbed using hand-held tools, the precision required for seating the repair bushes is not achieved, because the fibers in penetrated fiber layers of the laminate exert a laterally deflecting force on the tool. An alternative method of guiding the repair bushes through a structure located behind the outer shell weakens this structure and is not always possible, or is only possible at great expense. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides a machining method and a machining apparatus for use in conjunction with a machine tool that makes it possible to carry out repairs in particular on laminates at a low cost, with a high degree of precision and in a high quality manner. 
         [0011]    The machining apparatus includes a guide frame, having a guide contour, that is secured over a superficial portion of a laminate to be machined. The guide frame makes it possible to guide the machine tool, such as a milling cutter, by means of the guide contour, so that even if fiber layers are penetrated, forces which arise and act laterally on the tool do not deflect the tool in a direction parallel to the superficial portion, which means that a high degree of machining precision is achieved, in particular in directions parallel to the superficial portion. 
         [0012]    Since, for guidance, a guide frame with a guide contour is used which delimits a maximum dimension of the superficial portion, it is also possible to guide the machine tool along the entire guide contour, such that the entire circumferential edge of the machined region is machined in a high-quality manner and with a high degree of precision. The delimitation to the maximum dimension of the superficial portion also ensures that, for example when an aircraft fuselage is being repaired, the maximum size of machined or penetrated regions which is established by the manufacturer&#39;s technical specifications is not exceeded, which makes the repairs safer and more reliable. 
         [0013]    Finally, where the machine tool has a machining depth limiter, the machined region is also precisely defined in the direction vertical to the superficial portion, thus in all three spatial directions. 
         [0014]    According to an embodiment of the invention, the guide frame is secured to by an attachment member, adjacent to the superficial portion, of the laminate. This has the advantage that additional attachment devices, for example scaffolds are unnecessary, such that the method can be implemented rapidly with simple equipment, for example by maintenance technicians at an airport. Since the guide frame is positioned on a portion of the surface on which the superficial portion to be machined is also located, hooks, counter bearings or the like are not required for support on further surfaces which makes it possible for the method to be carried out at practically any point of an aircraft outer shell. 
         [0015]    According to one embodiment, the guide frame is secured by a suction attachment of at least one suction cup in the attachment member. This is an advantage, as the frame can be attached without leaving behind imprints in the attachment member. Moreover, suction cups are simple and cheap to construct, do not require an energy supply and only slightly increase the weight of the guide frame. The considerable suction force of the suction cups allows the frame to be attached to a surface of any orientation, for example even on the lower side of the fuselage or on the lower side of a wing. 
         [0016]    Furthermore, in another embodiment, the maximum machining depth is set corresponding to an overall thickness of at least one upper layer of the laminate. This makes it possible to remove the top layer or a plurality of adjacent layers including the top layer in a precise and complete manner, without damaging underlying layers. 
         [0017]    In this respect, a step for detaching the at least one upper layer in the superficial portion is preferably also provided. In this way, the at least one upper layer is intentionally removed in a precise manner not only in superficial regions machined by the machine tool, for example along a delimiting line around the superficial portion, but in the entire superficial portion. 
         [0018]    Furthermore, a step of replacing the detached at least one upper layer by a substitute material is preferably also provided. In this way, the original surface is re-closed, for example by a substitute material which is identical to the original top layer. Aluminum or an aluminum alloy is particularly advantageous, as this provides a resistive replacement surface. 
         [0019]    According to one embodiment wherein the machine tool is a milling cutter, a maximum cutting depth is set according to a total thickness of the laminate. In this way, it is possible to cut through the entire laminar structure, without damaging structures which may be located underneath, for example reinforcing elements. 
         [0020]    Furthermore, an embodiment provides after fixing the guide frame a step of adjusting the guide contour over a recess in the laminate. This makes it possible for the machine tool to be positioned precisely over the recess, for example to widen an existing hole or to mill off damaged areas around a rivet. 
         [0021]    The adjustment step preferably comprises a plurality of partial steps. First of all, a probe tool which is shaped corresponding to the recess and can be moved inside the guide contour in a vertical direction to the superficial portion is inserted into the guide contour, i.e. is guided through the guide contour such that it does not move relative to the guide contour in directions horizontal to the superficial portion. In a further partial step, the guide contour and the probe tool are moved relative to the guide frame in at least one direction parallel to the superficial portion. Since the probe tool is shaped exactly according to the recess, it can be introduced into said recess, but cannot be moved inside the recess in a direction horizontal to the superficial portion. After a suitable searching movement, the probe tool is locked into the recess. Finally, in this state, the guide contour is fixed relative to the guide frame. Since the probe tool is held at a lower end fitting exactly in the recess and is held at an upper end in the guide contour, the guide contour is positioned exactly over the recess. 
         [0022]    According to another embodiment of the machining apparatus according to the invention, the attachment member is configured to secure the guide frame over the superficial portion while leaving a predetermined distance to the superficial portion. This makes it possible to reliably position the guide frame over differently shaped, in particular over curved, superficial portions. Moreover, the surface of the laminate is treated as carefully as possible. 
         [0023]    Furthermore, according to an embodiment, a first slide block is provided which slides along opposite, parallel first and second sides of the guide frame in a lockable manner. In this respect, the guide contour is configured to be displaceable with the first slide block. This makes it possible to adjust the guide contour by moving the first slide block in a parallel direction to the first and second frame sides and to fix the adjustment by locking the first slide block such that, in the adjusted state, the guide contour can be loaded by a tool. 
         [0024]    In this arrangement, a second slide block is also preferably provided which slides in a lockable manner along the first slide block, the guide contour being configured to be displaceable with the second slide block. This makes it possible, by moving the first and second slide blocks, to adjust the guide contour in any parallel direction to the superficial portion and for the adjustment to be loaded by tools by locking the first slide block. The second slide block can be configured, for example such that it slides on the upper side or lower side of the first slide block or in grooves formed in the first slide block. 
         [0025]    According to an embodiment, the guide contour is substantially rectangular and in particular square. This is advantageous because it thus allows a maximum possible surface to be machined without adversely affecting the reliability of the laminate. For example, a 7×7 cm surface maximally permitted by safety regulations for aircraft shells consisting of GLARE can be freed from its top layer by following a square contour. 
         [0026]    According to an alternative embodiment, the guide contour is circular. This provides the advantage that a correspondingly cylindrically shaped milling cutter or other machine tool can be positioned exactly over a circular superficial portion to be machined, and this also allows the machine tool to be rotated about its axis for specific machining procedures. 
         [0027]    The features and advantages described in this summary and the following detailed description are not all-inclusive. Many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims presented herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The invention will be described in detail in the following on the basis of embodiments with reference to the accompanying figures of the drawings. 
           [0029]    The figures are as follows: 
           [0030]      FIG. 1  is a perspective view of a machining apparatus according to a first embodiment of the invention; 
           [0031]      FIG. 2A-E  are schematic cross-sectional views of five machining steps of a laminate according to a method of a second embodiment; 
           [0032]      FIG. 3  is a perspective view of a machining apparatus according to a third embodiment of the invention; and 
           [0033]      FIG. 4A-E  are schematic cross-sectional views of five machining steps of a laminate according to a method of a fourth embodiment. 
       
    
    
       [0034]    The figures depict various embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0035]      FIG. 1  is a perspective view of a machining apparatus for machining a superficial portion  102  of a laminate  100 . The laminate  100  is shown with an open border and can be, for example a part of an outer shell of an aircraft or spacecraft. The machining apparatus comprises a guide frame  106  with four frame sides  304 ,  305 ,  306 ,  307  which are joined together such that their insides have a square inner contour  108 . Two opposite sides  305 ,  307  are each extended at both ends beyond the connection points with the two other sides  304 ,  306  and each support a suction cup  112  on each of their extended ends. The guide frame  106  guides a machine tool as it operates on the laminate. The machine tool can be any type of machine tool, including but not limited to a milling cutter, grinder, sander, welding gun, drill, finisher, rotary tool, shaper, planar, and the like. 
         [0036]    Each of the suction cups  112  is fitted with a mechanical actuating lever  114  by which, when the suction cup is positioned on a surface, the suction effect can be activated and deactivated. In the illustrated drawing, all the suction cups  112  are directed in a common vertical spatial direction relative to the plane spanned by the frame  106 . This makes it possible to secure the frame  106  in the illustrated manner to the surface of the laminate  100  in that the suction openings of the suction cups  112  are positioned on the surface and the suction cups  112  are activated by actuation of their levers  114 . However, the suction cups  112  are appropriately configured to be rotatable with respect to the frame in one or more spatial directions to thus allow the machining apparatus to be secured to surfaces of a different shape and curvature. 
         [0037]    When the machining apparatus is used, it is positioned over a superficial portion  102  on which the laminate  100  is to be machined such that the superficial portion is located inside the frame  106 . The suction cups are firmly attached by suction in attachment members  110  of the surface which are located outside the superficial portion  102 . The suction cups  112  are joined to the frame  106  such that when the suction cups  112  are firmly attached by suction to a surface, the frame  106  is positioned at a distance a parallel to the surface. 
         [0038]    The inner contour  108  of the positioned frame  106  forms a guide contour  108  for guiding a machine tool. When the machine tool is suitably fitted with a spacer disc  116 , which is shown in outline form, for guidance along the guide contour  108 , the centre of the machine tool is guided on a square trajectory  102  located in the centre of the frame  106 , by which trajectory the guide contour  108  fixes the boundary of the machined superficial portion  102  by means of the spacer disc  116 . 
         [0039]      FIG. 2A-E  are five schematic cross-sectional views showing steps in which a five-layered laminate  100  is machined, with a thickness D and consisting of three aluminum layers  204  and two layers  205  of glass-fiber reinforced plastics material. 
         [0040]      FIG. 2A  shows the laminate  100  in a starting position. Before the start of the method, an upper aluminum top layer  204  was damaged, for example by impact of a stone, in a superficial portion  102  which is now to be repaired. The illustrated laminate has under the upper aluminum layer  204  a glass fiber layer  205  which was not damaged by the impact of the stone. 
         [0041]    In  FIG. 2B , secured to the laminate  100  is a machining apparatus  106  with a guide frame  106  and suction cups  112  such that the superficial portion  102  to be machined is located in the centre of the frame  106 . The frame  106  is located at a distance from the top layer  204 . A machine tool  200  is fitted with a spacer disc  116  and with a depth limiter  202  and is then simultaneously guided with the spacer disc  116  along the guide contour  108  of the frame  106  and with the depth limiter  202  along the surface of the top layer  204  around the superficial portion  102 . In so doing, on the one hand the depth limiter  202  restricts the machining depth to a value d which was previously set in accordance with the thickness d 1  of the damaged top layer  204 . On the other hand, the guide contour  108  restricts the lateral dimensions of the machined superficial portion  102 . 
         [0042]      FIG. 2C  shows the result of the milling procedure shown in  FIG. 2B . Produced around the superficial portion  102  is a circumferential milled groove  210  which precisely cuts through the top layer  204  but does not extend into the underlying layer  205 . Thus, located in the centre of the superficial portion  102  is an isolated layer  212  consisting of the material of the top layer  204  (aluminum) which still only adheres to the laminate  100  by its bond with the underlying layer  205 . The bond is now detached using a plastics material wedge  208 , made for example of nylon and the isolated layer is removed. 
         [0043]      FIG. 2D  shows the result of the detachment procedure shown in  FIG. 2C . The top layer  204  has been precisely removed from the laminate  100  in the surface region  102 , without thereby damaging the underlying layer  205 . 
         [0044]      FIG. 2E  shows the result of a further step in which the removed region of the top layer  204  has been filled with a substitute material  206 . This substitute material  206  can be, for example aluminum and thus is identical to the material of the top layer  204 . For example for this step, an aluminum sheet  206  of thickness d 1  of the top layer  204  can be cut to size according to the shape of the superficial portion  206  and bonded therein. Since the illustrated method allows superficial portions  206  to be machined with ever constant dimensions, aluminum sheets  206  which are ready cut to size can be prepared in advance to save time. 
         [0045]      FIG. 3  is a perspective view of a machining apparatus according to a third embodiment. As in the first embodiment shown in  FIG. 1 , the machining apparatus comprises a frame  106  which is supported by four suction cups  112  and which, when the machining apparatus is in use, is secured over a superficial portion  102  of the laminate  100  by the firm suction of the suction cups  112  in attachment members  110 , located outside the frame  106 , of a laminate  100 . 
         [0046]    Unlike the first embodiment, the superficial portion  102  to be machined is centered circularly around a rivet  310  and is considerably smaller than the dimensions of the frame  106 . In order to be able to position a machine tool precisely over the rivet  310 , the machining apparatus has a first slide block  302  and a second slide block  308  which make it possible to position precisely over the superficial portion surrounding the rivet  310  a guide contour  108  formed on the second slide block inside the frame initially positioned roughly over the portion to be machined using the suction cups  112 , by a fine adjustment. 
         [0047]    In this arrangement, the first slide block  302  is configured in the form of a bridge which joins two opposite frame sides  304 ,  306 , can be moved along the frame sides  304 ,  306  and can be locked with respect to the frame sides  304 ,  306  by locking screws  303 . The second slide block  308  is configured as a carriage which slides on the lower side of the first slide block  302  as if it were on a rail and can be locked with respect to the first slide block by locking screws  309 . The guide contour  108  can thus be adjusted and locked over any point inside the frame  106  by the cooperation of the slide blocks. 
         [0048]      FIG. 4A-E  are five schematic cross-sectional views of five machining steps of a laminate according to a method of a fourth embodiment.  FIG. 4A  shows the starting position of the laminate  100  in which, for reasons of clarity, no individual layers are shown inside the thickness D. Introduced into the laminate  100  is a rivet  310  on which milling is to be carried out in a superficial portion  102  which is precisely centered on the rivet  310 . 
         [0049]    In  FIG. 4B , secured to the laminate  100  is a machining apparatus  106 ,  112  with a guide frame  106  and suction cups  112  such that the superficial portion  102  to be machined is located inside the frame  106 . The guide contour  108  which can be adjusted in two directions with the first slide block  302  displaceable on the guide frame  106  and the second slide block  308  displaceable on the first slide block is, however, not centered precisely over the rivet  310  in the centre of the superficial portion  102 . 
         [0050]    In  FIG. 4C , a probe tool  300  is inserted into the second slide block  308 . The diameter of the upper end of the probe tool  300  fills the guide contour  108 . Configured at the lower end of the probe tool  300  is a probe rod  400  having a diameter which corresponds to an internal diameter of the rivet  310  with a looser fit. To probe the position of the rivet  310 , the probe tool  300  is then guided over the surface of the laminate  100  by means of the slide blocks  302 ,  308 . 
         [0051]      FIG. 4D  shows a stage in which the position of the rivet  310  has been successfully probed such that the probe rod  400  is locked into the rivet  310 . The positions of the slide blocks  303 ,  308  are then locked with the associated locking screws  303 ,  309  and the probe tool  310  is then removed. 
         [0052]    In  FIG. 4E , a machine tool  200  has been introduced into the guide contour  108  instead of the removed probe tool  300 . As a result of the previous adjustment, the machine tool  200  is centered precisely over the rivet  310 , such that the superficial portion  102  is accurately machined. In so doing, the machining depth (e.g., cutting depth) of the machine tool is restricted by a depth limiter  202 . 
         [0053]    Although the present invention has been described here on the basis of preferred embodiments, it is not restricted thereto, but can be modified in many different ways, and it will be understood by persons skilled in the relevant art that various changes in form and details can be made therein without departing from the spirit and scope of the invention. 
         [0054]    For example, a superficial portion to be machined can also be located on the edge of a material surface or can extend beyond said edge, in which case it is possible for the frame to be secured using only two of the suction cups. During machining, it is possible for more than one top layer to be removed and replaced by a substitute material. The machining apparatus can be used for machining other materials, such as aluminum or carbon fiber-reinforced plastics materials. 
         [0055]    Reference in the specification to “one embodiment” or to “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
         [0056]    Finally, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.