Turning – Process of turning
Reexamination Certificate
2000-03-23
2001-11-20
Tsai, Henry (Department: 3722)
Turning
Process of turning
C082S001200, C082S001500, C082S131000
Reexamination Certificate
active
06318220
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the machining of materials and, more particularly, to the machining of inner contours in work piece cavities accessible only through small openings.
DISCUSSION OF THE BACKGROUND ART
Frequently, it is necessary to surface machine precise contours within cavities that are formed in a work piece but accessible only through very small openings. For example, in the machining of a work piece such as an automotive differential housing, it is necessary to machine two or more coaxial bores of different diameters with at least one bore having a shoulder at one end so that a shaft can be journalled in the housing. Machining of differential housings requires very close tolerances, accurate coaxial alignment of the two bores and precise location of bearing faces. This generally requires that the bores be machined while the work remains chucked at the same station and preferably by the same boring tool. Moreover, multiple shafts are typically journalled in the differential housing so that close tolerances must also be met as between these shaft journals.
In U.S. Pat. No. 3,884,590, there is disclosed an adjustable dual tool boring bar that is mounted for rotational adjustment with its axis offset from the axis of the machine spindle. Cutting tools are mounted diametrically opposite on the boring bar. Because the boring bar axis is offset from the spindle axis, rotation of the boring bar on its adjustment axis through 180 degrees reverses the tools, one being retracted inwardly and the other being advanced radially outwardly of the spindle axis. Other types of eccentric quills have also been used to machine differential housings. Generating heads, also known as facing heads, can also be used to carry a boring bar and move the boring bar radially, transversely of the spindle axis, to perform the multiple machining operations required for differential housings. However, during machining the boring bar is still eccentric to the spindle axis. Such facing heads may be of the general type shown in U.S. Pat. No. 4,004,332.
Prior art techniques for machining differential housings using eccentric tooling operated satisfactorily at relatively low speeds of say 250 to 750 rpm with housings made of steel or cast iron. However, they cannot be used effectively at higher cutting speeds required for cast aluminum housings, for example, 1,000 to 4,000 rpm. With prior art eccentric tools, it is difficult, if not impossible, to maintain the tool balanced and hence maintain the close tolerances and accuracies required for precise machining of the differential housing. The larger internal diameter of the back bore further contributes to the difficulties in maintaining the tool balanced. The tool must have a diameter small enough to allow it to be inserted through the bore with sufficient clearance to allow it to be moved radially to its eccentric position for the back boring operation. With tools extending any substantial distance from the spindle bearings, commonly referred to as overhang, any unbalance in the tooling is further accentuated at the unsupported end of the tool. Even with generating heads where the overhang of the head has been minimized, for example, of the type disclosed in U.S. Pat. No. 4,004,332, the overhang of the generating head and the boring bar contribute further to unbalance and wobble at high cutting speeds.
Accordingly, a need exists for a machine tool and method to perform precise high-speed finish machining, of internal cavities accessible through small bores, that may be easily adapted to machining bores of different diameters.
SUMMARY OF THE INVENTION
The aforementioned need is addressed, and an advance is made in the art, by employing a rotating tool having a pivotable cutting insert that is configured to open up upon insertion through a bore of given diameter. This extension of the tool permits machining of a cavity having arcuate shoulders and a larger interior diameter region. In accordance with an illustrative embodiment of the present invention, arcuate positioning of the cutting insert is achieved and maintained by the camming action of a draw bar that is moved axially within the tool bore. Alternatively, however, the tool may be readily adapted for use with a wider range of machining center devices (i.e., those not equipped with a drawbar) by including a push rod which extends, upon the application of a fluid such as the coolant oil, to provide the requisite camming action.
According to the method of the present invention, the tool is inserted within an access opening previously bored in the workpiece. Guide pads disposed within the access opening, at either end of the workpiece, maintain the tool in a precise alignment so as to ensure dimensional accuracy. During this time, the cutting insert is maintained in a retracted orientation within the tool by, for example, a biasing spring disposed near the distal end of the tool. Once the tool is properly positioned, the cutting insert is advanced out of the retracted position. In machine centers not equipped with a draw bar, this is achieved by applying an amount of coolant pressure to the push rod sufficient to achieve the desired camming action. Illustratively, to obtain a spherical cavity having a diameter of 104 mm, the tool may be inserted into a 20.3 mm hole, rotated at a speed of 3000 rpm with a feed rate of 0.1 mm per revolution and a depth of cut of 0.3 mm per surface. Under such conditions, a coolant pressure of about 20 bar is sufficient to provide the necessary camming action.
Once the appropriate cavity has been machined, the coolant pressure is bled off to allow the cutting insert to return to the retracted position, whereupon the tool is withdrawn from the workpiece.
REFERENCES:
patent: 3315549 (1967-04-01), Malschner
patent: 4945792 (1990-08-01), Gardner
patent: 5086676 (1992-02-01), Gifford et al.
patent: 5159862 (1992-11-01), Byrnes
patent: 5209145 (1993-05-01), Baudermann
patent: 5967007 (1999-10-01), Scheer
Dinicola Brian D.
Malpal, Inc.
Tsai Henry
LandOfFree
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