Electrolysis: processes – compositions used therein – and methods – Electrolytic erosion of a workpiece for shape or surface...
Patent
1997-10-21
1999-03-09
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic erosion of a workpiece for shape or surface...
205641, B23H 1100
Patent
active
058795332
DESCRIPTION:
BRIEF SUMMARY
This application is a national phase filing of international application Ser. No. PCT/NL 96/00003, filed Jan. 2, 1996.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of electrochemically machining a metal piece, wherein by applying a voltage, a current is passed across a narrow gap (6) formed by said metal piece and an adjustable electrode means (2) to locally remove material from the metal piece, electrolyte (A) being supplied to the gap (6) in a direction substantially tangential to the surface of the metal piece, and the metal piece being rotated around its axis, the amount of current being under the control of a sensing means capable of sensing the surface of the metal piece.
2. Description of the Related Art
Such a method is known from U.S. Pat. No. 4,456,516. Here, the general roundness of a cylindrical shaft is improved by electrochemical machining. A bracket is shaped to be slidably associated with the shaft in a two point contact. The bracket comprises a contact sensor which controls the current passed across a gap formed by the shaft and an electrode.
DETAILED DESCRIPTION OF THE INVENTION
It is an object of the present invention to provide a method of electrochemical machining in which a fast and precise control of the machined surface is obtained.
To the end, the method according to the invention is characterized in that the metal piece is a bearing ring, and wherein the electrochemical local removal of material from the bearing ring is enhanced by controlling a parameter chosen from the group of
i) changing the speed with which the bearing ring is rotated around its axis to change the time during which a local elevation is subjected to electrochemical machining; and
ii) increasing the voltage when the gap is narrow due to a local elevation on the bearing ring, comprising the bearing ring, the adjustable electrode means and a Volt-Ampere meter, and using the voltage and current being measured as data to control the parameter.
The width of the gap will vary with the angular position of the bearing ring as it rotates around its axis, in accordance with irregularities on the surface of the bearing ring as well as any out-of-roundness. The change in gap width corresponds to a change in the resistance and consequently in the current, thus removing more material when the gap is narrow and less when the gap is wide. In this way, elevations are removed and the surface of the bearing ring is smoothed.
Now, according to the invention, the material is removed in a controlled way to speed up this process using the voltage and current being measured as data to control the parameter, i.e. when the gap is narrow, the electrochemical removal of material from the bearing ring is enhanced by adjusting relevant process parameters. With this active control, it is possible to have more control over the final form of the bearing ring and obtain this form faster. For example, it is possible to increase the voltage when the gap is narrow due to an elevation on the metal piece, resulting in additionally increase current, which in turn enhances the removal rate. It is also possible to stop or slow down the rotation of the bearing ring around its axis, which causes in, particular, the elevation to be subjected to the electrochemical treatment. Thus, with the active control according to the invention, there is more control over the final form of the bearing ring and this form can be achieved faster. Thus, it is possible to obtain bearing rings with improved circular form or with more complex forms.
According to a preferred embodiment, the method according to the invention is characterized in that the bearing ring is a cylindrical roller bearing inner ring and material is removed from the raceway of the outer ring while sa harmonic variation is superimposed on the current at three times the frequency of the rings rotational speed, resulting in a trilobed raceway.
In this way it is possible to obtain trilobed rings cheaply, which allows a more widespread use of the super
REFERENCES:
patent: 0143014 (1985-05-01), EPX
patent: 1235339 (1971-06-01), GBX
patent: 2005780 (1969-12-01), FRX
patent: 2032162 (1971-04-01), DEX
Gorgos Kathryn
Parsons Thomas H.
SKF Industrial Trading & Development Company B. V.
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