Abrading – Work holder – Clamp
Reexamination Certificate
1999-04-08
2001-09-11
Eley, Timothy V. (Department: 3723)
Abrading
Work holder
Clamp
C269S296000, C451S387000, C451S405000
Reexamination Certificate
active
06287182
ABSTRACT:
TECHNICAL FIELD
The present invention relates to precisely shaped parts, and more particularly to a fixture for manufacturing precisely shaped parts.
BACKGROUND OF THE INVENTION
Many industries use precisely shaped parts. For example, conventional blades for use in gas turbine engines must be precisely shaped. Typically, precision investment casting or die-forging forms a metal starting blank into a blank having a blade shape. Generally, the blank includes a tip, a root region longitudinally spaced therefrom, and a midspan region extending between the tip and the root region. The tip may include an attached or integral shroud. A number of details must be machined into these portions of the blank. For example, a plurality of dove tails must be machined into the root region. These dove tails allow the blade to be secured to the rotor disk in the engine. In order to achieve acceptable engine performance, these dove tails must be formed within small tolerances. To accomplish this, there must be references from which to measure the configuration of the dove tails, and a fixture for holding the blank during machining.
Reference is made to U.S. Pat. No. 2,577,747 issued to Gibian and U.S. Pat. No. 3,818,646 issued to Peterson. However, the method taught in Gibian is not sufficiently accurate and the method taught in Peterson requires complex fixturing which is expensive to design, manufacture and maintain. Furthermore, a different fixture is needed for different sized and shaped blades.
Reference is also made to a method of providing references that entails encapsulating the blank in a block of material, such as a low melt alloy. The block of material is formed around the blank, so that the root region extends from the block. The sides of the block provide reference planes from which the configuration of the dove tails or other details can be determined with the necessary accuracy. However, encapsulating the blank requires a complex encapsulation tool. Furthermore, after machining the dove tails, the material must be melted off the blank and must be disposed of without causing environmental problems.
To overcome the problems above, it is known to use a blank having a sacrificial region and three locators. The sacrificial region extends longitudinally from the root region. The three locators are shaped and positioned to mate with corresponding features on a fixture. One of the locators is a conical shaped projection disposed at the tip. The other two locators are machined notches in the sacrificial region, one rectangular shaped notch and one wedge shaped notch. The conical shaped projection and the rectangular shaped notch both lie within a plane containing a stacking axis. The wedge shaped notch has a corner aligned with the root centerline, perpendicular to the stacking axis.
The fixture has a U-shaped base with spaced apart end walls to accommodate the blank. One of the end walls supports a clamping mechanism having a conical bore. The other end wall supports an abutment having rectangular and wedge shaped projections. Actuating the clamping mechanism moves the conical bore into contact with the conical projection on the blank. This forces the notched locators into contact with the corresponding projections on the abutment to thereby position the blank within the fixture. The surfaces of the wedge shaped projection make substantial contact with corresponding surfaces of the wedge shaped notch. Such contact helps to prevent the blank from rotating during machining and enables the blank to be secured within the fixture using only a minimal amount of clamping force in the longitudinal direction. Details, such as dove tails in the root region, can then be accurately machined into the blank to form a precisely shaped part.
The blank and fixture described above are disclosed in related copending application Ser. No. 08/641,251, “A Blank for Manufacturing Precisely Shaped Parts”; and Ser. No. 08/640,045, “A Fixture for Manufacturing Precisely Shaped Parts”. This approach enables the part to be machined with improved accuracy. It also eliminates the need for fixtures with complex clamping mechanisms and does not require encapsulation with low melt alloy. The fixture is relatively simple to manufacture and can be easily modified to accommodate different size or shaped blades.
However, better fixtures are always being sought. For example, with the blank and fixture above, a significantly greater amount of longitudinal clamping force must sometimes be applied in order to prevent the blank from rotating during machining. However, greater clamping forces can distort the blank while it is secured within the fixture. This can result in misalignment of the subsequently machined features. Large clamping forces also present a risk of permanently distorting the blank. Thus, a fixture that does not require significantly greater than desired clamping forces in order to secure the blank is sought.
SUMMARY
An object of the present invention is to provide an improved fixture.
Another object of the present invention is to provide a fixture that uses less clamping force to secure a blank having a plurality of locators.
Another object of the present invention is to provide a fixture that enables more accurate machining of a blank.
According to a first aspect of the present invention, a fixture for securing a blank having at least two spaced apart locators, includes a fixture having a U-shaped base with two spaced apart end walls, one supporting a clamping mechanism and the other supporting an abutment where at least one of the clamping mechanism and the abutment is free to pivot in relation to the end wall that supports it, wherein upon securing the blank into the fixture the clamping mechanism mates with one of the locators and forces another of the locators into contact with the abutment.
According to a second aspect of the present invention, a method includes providing a blank having at least two spaced apart locators, providing a fixture having a U-shaped base with two spaced apart end walls, one supporting a clamping mechanism and the other supporting an abutment where at least one of the clamping mechanism and the abutment is free to pivot in relation to the end wall that supports it, and securing the blank into the fixture wherein the clamping mechanism mates with one of the locators and forces another of the locators into contact with the abutment, and subsequently machining the blank.
It has been determined that due to limitations in manufacturing technology, there is inevitable imprecision in the machining process that forms the notch locators on the blanks. Thus, the wedge shaped notch may not be perfectly positioned on the blank, e.g., the corner of the wedge shaped notch may not be perfectly aligned with the root centerline, i.e., not perfectly perpendicular to the stacking axis. In such event, the previous fixture requires a greater amount of longitudinal clamping force to attain substantial contact between the surfaces of the wedge projection and the wedge shaped notch. In the absence of such contact, the surfaces may make contact in only a limited area and may not secure the blank.
By employing a pivotal attachment, the present invention enables better mating between a locator on the blank and a corresponding feature on the fixture. As a result, the fixture is able to secure the blank while imparting less clamping force on the blank that imparted by the previous fixture. The use of less clamping force reduces the likelihood that the blank will be distorted when it is secured in the fixture, and thereby reduces the likelihood of misalignment of subsequently machined features. It also reduces the risk of permanently distorting the blank. In the best mode embodiment, this is accomplished without disturbing the positioning or mating of the other locators, thereby ensuring that the blank is positioned as desired within the fixture.
REFERENCES:
patent: 2088359 (1937-07-01), Albertson
patent: 2577747 (1951-12-01), Gibian
patent: 2854875 (1958-10-01), Patrick
patent: 3145512 (1964-08-01), Hircher
Eley Timothy V.
United Technologies Corporation
LandOfFree
Fixture for manufacturing precisely shaped parts does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fixture for manufacturing precisely shaped parts, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fixture for manufacturing precisely shaped parts will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2500967