Apparatus for working electrically conductive materials by elect

Details Apparatus for working electrically conductive materials by elect Apparatus for working electrically conductive materials by elect

1987-07-13

1988-12-06

Valentine, Donald R.

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204225, 219 69G, B23H 718, B23H 732

Patent

active

047894474

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

Field of the Invention
The present invention relates to an apparatus and method for working electrically conductive materials by electric erosion, particularly but not exclusively to apparatus for applying a surface finish to a workpiece.
Related Art
The surface texture of some materials, for example sheet metal, can sometimes be of great importance. In the automobile industry, for example, it is important that sheet metal used for the bodywork of cars has a surface texture which produces good results under press and which gives a good appearance to the final paint finish.
Surface texture is usually applied to sheet metal by rolling with steel rolls, the surface texture of the roll being transferred to the sheet metal. The surface parameters of the rolls used are critical and must be closely controlled if the desired surface texture of the sheet metal is to be achieved.
It is known to texture the rolls by a process of blasting the roll surface with steel shot. The process is, however, difficult to control because of the wide range of variables involved, such as shot hardness, velocity and angle of impingement. In addition, it is now the trend to increase the life expectancy of the rolls by using very hard alloy combinations. Shot blast texturing of these hard rolls is very difficult.
It has previously been proposed to use the technology of electro-discharge machining (E.D.M.) to texture the surface of the rolls. This involves placing an electrode adjacent a roll to be textured and applying a pulse voltage across the gap, (usually though an electrolytic fluid) between the roll and electrode. A spark discharge will occur at the point where the electrode and roll are closest, the spark heating the surface of the roll and creating a minute crater therein. Repeated discharges at high frequency cause steady high-energy electrical discharges which produce many minute craters per second in the roll at various points on the roll surface, depending which point is closest to the electrode at the time, resulting in a uniform surface finish. E.D.M. is very controllable and is easily able to surface texture hard rolls.


SUMMARY OF THE INVENTION

It will be apparent that the positioning and shape of the electrode, as well as the number and strength of the electrical discharges, will have a critical effect on the surface texture of the roll.
In particular, if there occurs any uneveness in the relative attitudes of the electrode and workpiece, this will effect the overall shape of the machined surface of the workpiece. For example; if the electrode becomes tilted such that one end of the electrode is closer to the workpiece, than the other end, then discharge will occur much more at the closer end and the workpiece will become unevenly machined. This is undesirable (unless of course such an unevenly machined workpiece is the desired end result, but in this case an undesirable result would be produced if the electrode were parallel to the workpiece). It is therefore apparant that it would be advantageous to the relative orientations of the electrode and workpiece could be monitored to give an indication of the orientation at any time, so that steps could be taken if the electrode and workpiece become orientated undesirably relative to each other. Maintaining correct orientation is very important to ensure correct machining.
Preferably, a number of sensors are used to obtain different types of information regarding the electrical conditions in the gap between the electrode and workpiece. Preferably, spark sensors arranged at intervals along the gap are used to provide information of where along the gap electrical discharges are occuring, so as to give an indication of the relative orientation of the electrode and workpiece. Ajustment of the relative orientation may then be made in the light of this information.
Further, it is also preferred that sensors be arranged to provide information regarding the condition of the electrical discharges occurring along the gap as this will affect the actual m

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patent: 4471199 (1984-09-01), Michishita et al.
patent: 4527034 (1985-07-01), Inoue et al.
patent: 4608476 (1986-08-01), Shimizu

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