Work holders – With fluid means – Vacuum-type holding means
Reexamination Certificate
1999-06-29
2001-04-17
Smith, James G. (Department: 3723)
Work holders
With fluid means
Vacuum-type holding means
Reexamination Certificate
active
06217013
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to milling machines for machining metallic workpieces. The invention relates more particularly to milling machines for machining wing skins of an aircraft, in which both surfaces of the wing skin must be machined in sequence.
BACKGROUND OF THE INVENTION
Wing skins for aircraft are typically machined from metal plate stock that is essentially flat on both sides. In accordance with one known technique for machining a wing skin, a plate is held down on a mill bed by the use of vacuum exerted on an under surface of the plate. The upper surface of the plate is then machined to the desired contour. The first side machined is generally the aerodynamic surface, also known as the “outside mold line” or OML. The majority of the OML surface is smooth, but at the inboard end of the wing skin there typically are protruding features such as padups, steps, or taper planes serving to enable the wing skin to be attached to the fuselage or other structure.
After the OML surface is machined, the wing skin is turned over on the mill bed so that the other surface of the plate can be machined to form the “inside mold line” or IML. The protruding features at the inboard end of the wing skin are accommodated in pockets or depressed regions of a plate-shaped metallic adapter tool that fits into a well area defined in the mill bed. This adapter tool enables the wing skin to fit snugly against the seal that engages the wing skin for vacuuming the wing skin down onto the mill bed so that the IML can be machined.
Each aircraft model has unique wing skin configurations with unique protruding features, and hence, whenever it is desired to machine a new wing skin configuration, the existing adapter tool must be removed from the well area of the mill bed and a new adapter tool having the appropriate configuration for the new wing skin must be installed in the well area. Each such adapter tool typically can be 60 inches wide, 80 inches long, and 1.125 inches thick, and can weigh 600 pounds. Accordingly, it will be appreciated that the adapter tools cannot be handled manually, but must be moved through the use of heavy equipment such as cranes. It can take two hours for removing an adapter tool and installing a new adapter tool in the mill bed. Every time a new wing skin configuration is to be machined, the adapter tool must be removed and replaced with a different one. Thus, the significant time required for changing the heavy adapter tools introduces considerable inefficiencies in the manufacturing process. Furthermore, a significant capital expenditure is required where a substantial number of different wing skin configurations must be machined, because each wing skin configuration requires its own adapter tool, and each tool can be quite expensive.
SUMMARY OF THE INVENTION
The present invention enables the time required for changing the tooling to be substantially reduced, for example, from about two hours to about 15 minutes. The invention also enables a substantial reduction in the capital expenditure required for tooling where a substantial number of different wing skin configurations are to be machined. Additionally, the invention facilitates improved safety conditions for workers involved in changing the tooling.
The invention can achieve the above and other advantages by eliminating the requirement of changing a large and heavy metallic tool every time a new wing skin configuration is to be machined. To this end, the invention provides a workpiece holder assembly comprising a base plate adapted to be received in the well area of a mill bed, and an insert tool that is received in a recess defined in the upper surface of the base plate. The insert tool's upper surface includes one or more depressed regions configured to accommodate one or more protruding features on a previously machined contour of a wing skin or other workpiece. The base plate and insert tool have vacuum passages adapted to communicate with the vacuum system of the mill bed such that a vacuum can be exerted on the workpiece. A seal is provided on the upper surface of the insert tool for sealingly engaging the workpiece so that the workpiece can be vacuumed down to permit the other surface of the workpiece to be machined. When a new workpiece configuration is to be machined, the insert tool is removed and replaced with a new insert tool configured to match the contour of the new workpiece configuration. Each insert tool advantageously is configured so that it can be received in the recess in the base plate, such that any of a plurality of insert tools can be installed in the recess. Accordingly, the base plate need not be changed when changing to a new workpiece configuration.
The base plate preferably is metallic. The insert tool, however, advantageously is made of a lightweight material such as a polymer material preferably having good resistance to oils and lubricants commonly used in milling operations. Thus, the insert tool can be made light enough in weight to enable workers to manually remove the insert tool and replace it with a different insert tool. The time required for a tooling change consequently can be substantially reduced. Moreover, tooling changes can be made safer by the elimination of the need to move heavy metallic plates with cranes or the like.
In accordance with a preferred embodiment of the invention, the insert tool includes vacuum holes formed through the thickness of the tool for providing a vacuum at the upper surface of the tool. The vacuum holes act in cooperation with one or more elongate seal strips extending along the upper surface of the insert tool so as to sealingly engage a workpiece and suction it against the tool and the mill bed. Advantageously, the insert tool also includes a series of vacuum slots formed in its upper surface in communication with the vacuum holes so that vacuum is more uniformly distributed over the surface of the insert tool.
Where the mill bed includes two separate vacuum systems independently feeding two dedicated sets of vacuum passages through the well area in the mill bed, the base plate and the insert tool each advantageously includes two separate sets of vacuum holes respectively communicating with the two sets of vacuum passages in the mill bed. The insert tool further includes two seals disposed with one seal spaced along the upper surface of the insert tool interior of the other seal such that an outer peripheral waste portion of a workpiece can be cut from the remainder of the workpiece along a path located between the outer and inner seals. One set of vacuum holes in the insert tool is located interior of the inner seal, and the other set of vacuum holes is located between the inner seal and the outer seal, so that vacuum can be independently exerted on the waste portion and the remainder of the workpiece.
The invention thus facilitates the milling of thin plate-shaped workpieces such as wing skins on both surfaces, and enables a plurality of different machined configurations to be produced with greatly reduced time required for tooling changes relative to the conventional method employing large metallic adapter plates. The insert tools can be manually interchanged, thus improving the safety of the tool change procedure. A single metallic base plate can receive a plurality of different insert tools, which are substantially less costly to manufacture than conventional metallic adapter tools, and thus the invention facilitates a substantial reduction in the capital expenditures required for tooling.
REFERENCES:
patent: 2573087 (1951-10-01), Youngblood et al.
patent: 3967816 (1976-07-01), Ramsperger et al.
patent: 4468854 (1998-07-01), Chou et al.
patent: 4729804 (1988-03-01), Dillner
patent: 5253454 (1993-10-01), Carlson et al.
patent: 5316255 (1994-05-01), Marcusen
patent: 5667128 (1998-07-01), Rohde et al.
patent: 5730431 (1998-03-01), Cattini
patent: 5775395 (1998-07-01), Wilkins
patent: 5853169 (1998-12-01), Hern et al.
Alston & Bird LLP
Smith James G.
The Boeing Company
Wilson Lee
LandOfFree
Workpiece holder assembly for vacuum-holding a workpiece for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Workpiece holder assembly for vacuum-holding a workpiece for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Workpiece holder assembly for vacuum-holding a workpiece for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2492317