Work holders – Solidification of work contacting medium
Reexamination Certificate
1999-07-19
2001-02-06
Watson, Robert C. (Department: 3723)
Work holders
Solidification of work contacting medium
Reexamination Certificate
active
06182954
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
The present invention refers to a fixture apparatus that uses a combination of magnetorheological fluids and a special fixture to hold irregular shaped as well as regular shaped work pieces for precision machinery and measurements or other applications that require such apparatus.
It is an applied apparatus making use of a magnetorheological fluid or magneto-viscous fluids. The viscosity of the fluids changes upon application of a magnetic field produced either by a permanent magnet or an electromagnet. A specially designed mechanical fixture is used to hold any regular or irregular shaped work pieces.
In this apparatus, the magnetorheological fluid supplies the average pressure to the work piece that is fastened into it. The special fixture absorbs the extra force, preventing movement or climbing of the work pieces inside the apparatus during machining process.
Previously, a work piece to be machined with an irregular shape was fixed by clamps or some fixtures. Because they solely rely on the force from the clamps or fixtures, the process can cause permanent damage to the work piece. Another way was using a low-melting point metal alloy to hold a work piece by melting the alloy to liquid form, then dipping the work piece into the melted alloy, and then cooling the alloy to hold the work piece. This heating and cooling process will introduce strains in the work piece. Most of the low-melting point alloys have a harmful high vapor pressure, which will damage to the health of the personnel involved and will pollute the environment in the long run.
This invention has solved the long unsolved problem in industry—to firmly hold an irregular shaped work piece in a fixture to perform precision machining and/or measurements without introducing permanent deformation in the work piece or other damages, especially when the work piece is made of heat sensitive or non-magnetic materials. The invented apparatus, naturally, works even better for conventional work pieces with regular shape.
This invention has made magnetorheological fluids enter practical industrial fixture applications. Besides using the applied conventional magnetorheological fluid, a pressure in one or more directions, especially in the magnetic field direction is applied. This will greatly increase the strength of the fluid (i.e., the hold force of the fluid). Most importantly, a special fixture is used to accurately position and hold a work piece inside magnetorheological fluids to prevent the work piece from climbing which is a fatal drawback to the practical applications of magnetorheological fluids. Therefore, this invention overcomes the drawback of conventional fixture apparatus. This makes practical application of magnetorheological fluids in industry or research institutes possible. The obvious advantages of the apparatus compared with other apparatus available are:
i. The phase of a magnetorheological fluid is reversible with the field on or off, which is convenient to use. It can hold any irregular as well as regular shaped work piece firmly for precision machining and/or measurements.
ii. Since no heating or cooling cycle is introduced into the system during the process, the least amount of damage to the work piece is introduced.
iii. The work piece can be any material: metals or non-metals and magnetic materials or non-magnetic materials.
iv. Because magnetorheological fluid is a very good shock absorbing material, the apparatus will reduce the vibration in the work piece due to the processes (i.e., cutting, milling or grinding process).
v. It is environmentally safe.
SUMMARY OF THE INVENTION
The primary objective of the invention is to provide an apparatus, which can hold irregular shaped as well as regular shaped work pieces firmly, and accurately to do machining, measurements, and other purposes. In this invention, a work piece holding apparatus with a combination of a magnetorheological fluid and a special fixture is applied. In some special situations, it may even work with only the magnetorheological fluid or the special fixture alone. The apparatus is comprised of a cell that contains a magnetorheological fluid, a special fixture that will hold the work piece, and a magnet with either a permanent magnet or an electromagnet to supply the magnetic field. The cell is placed in the gap of the magnet. The gap can be adjusted to compress the fluids inside cell. The cell has two walls and a centerpiece. Each wall is made of two pieces, one part is made of non-magnetic material which holds the other part made of magnetic material in contact with one of the poles of the magnet. The center frame is used to form a hollow center for the cell and holds a special fixture at a fixed position inside the cell. The special fixture holds a work piece inside the center frame. The center frame is made of non-magnetic material. The special fixture can be made of either magnetic or non-magnetic material. On each side of the center frame is a “U” shaped O-ring groove or flexible sealing material. The special fixture has a hollow center and a wall or walls surrounding the hollow center, depending on different geometries.
It can be cylindrical, triangular or rectangular, depending on the geometries of the work piece to be processed. It can be fastened to the hollow center of the center frame of the cell. On the surrounding wall or walls of the fixture, there are several uniformly distributed threaded holes. The special fixture holds the work piece inside the fixture by several screws through the threaded holes. The cell walls holding the center frame are pressed together to form a cell that is sealed by an O-ring or other flexible material. The magnetorheological fluid is placed inside the cell. The cell is placed into the gap of the magnet. After turning on the magnetic field, a pressure is applied through a clamp or other means to reduce the gap of the magnet by compressing the cell walls toward each other, which in turn compressing the O-rings or the flexible sealing material. The magnetorheological fluids are squeezed inside the cell by this process. This will change the structure of the fluid and increase the pressure applied to the work piece inside the special fixture. Therefore, the pressurized magnetorheological fluids supply an average holding force to a work piece and the special fixture absorbs extra peak force that will prevent displacement of the work piece. With this combination, any work piece placed inside the cell will be held firmly in place and ready to be used for precision cutting, grinding, or accurate measurement.
REFERENCES:
patent: 3953013 (1976-04-01), Griffith et al.
patent: 5971835 (1999-10-01), Kordonski et al.
Polster Lieder Woodruff & Lucchesi L.C.
Watson Robert C.
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