Conveyors: power-driven – With means to facilitate working – treating – or inspecting... – Means engaging conveyor or load on a conveyor to align load...
Reexamination Certificate
1999-08-25
2002-04-16
Valenza, Joseph E. (Department: 3651)
Conveyors: power-driven
With means to facilitate working, treating, or inspecting...
Means engaging conveyor or load on a conveyor to align load...
Reexamination Certificate
active
06371274
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to workpiece machining systems and, more particularly, to a system and method for clamping of a pallet carrying a workpiece to a support stand for aligning the workpiece and giving it the necessary stiffness for accurate machining thereof.
BACKGROUND OF THE INVENTION
For machining of workpieces, special requirements or unique workpieces often govern the selection of a specific type of machine and fixturing. For instance, the size and configuration of the workpiece may affect the stiffness or rigidity with which a part can be held while being machined. In machining of large parts, a major consideration is the rigidity of the fixturing of the large part. An effective fixture for machining some large parts such as aircraft parts is a problem because of their great size in relation to wall thickness. Nevertheless, rigidity of the machine and setup is essential for optimum results. Lack of sufficient rigidity in the tooling and workpiece setup can result in tool deflection and chatter causing excessive tool wear and breakage, damage to workpieces, dimensional inaccuracy, and unacceptable surface finish.
Large and/or extremely heavy parts are usually cut by machines designed specifically for these parts. The present invention will be described in connection with one use thereof which is the profile machining of large aircraft parts; but the invention is not limited to this particular use of the invention. Large aircraft parts can be machined by profilers which are high and very long machines having horizontal spindles for advancing the cutting tool transversely relative to high and long vertical surfaces on the large parts for machining thereof. Because these large, heavy parts are not lying flat and are upstanding when being machined, there generally is greater instability introduced into the fixturing, making it very difficult to mount the part so that it is held with sufficient rigidity and has the necessary stiffness to provide for accurate machining results.
The profilers are machine tools that can generally include support structure and carriages, e.g., columns and rams, driven as by linear motors for carrying spindles along three axes of movement for high speed and high force machining along the entire extent of the large aircraft component and which can also include a nutating head for machining at various angles into the workpiece transversely to the vertical. These types of machines represent a major capital investment so that their use is generally restricted to removing large amounts of metal from massive workpieces like aircraft components. In machining large aircraft components, skin milling, which involves deep cuts, i.e., on the order half an inch or more, is commonplace. In rugged machining operations such as these where there are deep, heavy cuts, the workpiece will commonly be subjected to such great force, e.g. on the order of approximately 500 lbs. of cutting force, that it will bend and shift if not firmly secured which, as previously discussed, can be especially difficult with large, heavy workpieces that are arranged vertically. In this regard, stiffness of the part being machined is critical so as to avoid damage to the workpiece by miscuts, and damage to the tools and machine.
Accordingly, with the above-described profiler machines, the aircraft parts are mounted and clamped to a fixture plate that has, in turn, been clamped to a large thick and stiff pallet which gives the part the stiffness or rigidity necessary for accurate machining. In other words, it is the large thick pallet that provides the heavy fixture to add sufficient rigidity to the setup for the large part. Once the part is properly mounted to the pallet, it is then transported to the profiler machine for machining. This rigid setup minimizes or eliminates the previously discussed adverse conditions that can occur when machining large, relatively thin cross-section aircraft components in terms of obtaining proper fixturing, thereby increasing production and lowering production cost, and also allowing for increased feed rates and spindle speeds to be utilized which further increases production rates.
A shortcoming of the use of the pallet to provide the part the required stiffness is that the pallet itself has to be sufficiently massive for this purpose. Before setup, the pallets have to be transported from storage to the setup location. Once the part is mounted to the pallet, the massive pallet and attached part have to be moved to the profiler machine for machining. Where the pallet'storage is removed from where the part setup is to occur, and also where the setup of the part to the pallet is at some distance from the machine tool, the sheer size of the pallet and attached part can create problems in terms of time, equipment and manpower in transporting this assembly to the machine. Thus, there is a need for a machining system for workpieces, such as large, heavy thin-walled aircraft components, which provides sufficient stiffness to the part while being machined without the drawbacks afforded by the use of large, thick and heavy pallet fixtures.
SUMMARY OF THE INVENTION
In accordance with the present invention, a new and improved machining system is provided for machining large, heavy workpieces that are oriented vertically, such as large aircraft components. The machining system includes a workpiece support and a transportable thin pallet for being selectively magnetically clamped to the support. The pallet is large enough to support the large workpiece but is still relatively thin and light so that it can be easily transported to the machining station where the workpiece support is located. Due to the very large pallet surface area for mounting of the large workpiece, and because it is not very thick, e.g., approximately 8 inches, and has an open frame construction, the pallet on its own cannot impart the stiffness to the part necessary for accurate machining. The much thicker upstanding support is utilized to provide the pallet and affixed part the necessary stiffness when the pallet is clamped thereto, by a magnetic clamping arrangement that will be described hereinafter. In this manner, it is the larger workpiece support with its greater mass and stiffness vis-a-vis the transportable pallet that provides the workpiece mounted to the pallet the necessary stiffness so that it can be accurately machined. And because the pallet is relatively thin and flexible, it can more easily be maneuvered and transported than if it were the pallet that had to provide the stiffness for machining which would require it to be much more massive akin to the pallets previously utilized and thus making it much more difficult to transport. Thus, the present invention keeps workpieces held in a fixed and stationary position when they are being machined but not when they are being transported so that the weight of a large, heavy and massive pallet need not be transported.
In accordance with an important aspect of the invention, the use of magnetic attraction forces to clamp the pallet to the support results in quick assembly and disassembly of the pallets to the support. This reduces machining cycle time and increases production rates. Additionally, the magnetic forces provide a strong uniform clamping force across the entire area of the pallet that makes it strong and rigid like the stand support during the machining operation.
In one form of the invention, a machining system is provided for machining heavy workpieces by a cutting machine located at a predetermined machining position. A workpiece support upstanding at the machining position receives and holds a pallet in a vertical position during a machining operation on a vertical surface of the workpiece. A transportable pallet is provided having a vertical side and a workpiece affixed to the vertical side at a precise position thereon for being machined by the cutting machine while the pallet is on edge and being vertically positioned. Electromagnets and magnetizable areas are provided on the work support a
Ditter Norman J.
Rindels Christopher C.
Fitch Even Tabin & Flannery
The Ingersoll Milling Machine Company
Valenza Joseph E.
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