This invention relates to an electrolytic combined processing machine which can process a workpiece with good surface roughness and good flatness in a state of less processing distortion.
Conventionally, when a workpiece is processed, electrolytic grinding, electrolytic combined polishing, electrolytic processing and the like have been carried out.
During electrolytic grinding, since the improvement in the processing efficiency is the aim, an electrolytic action is generated between a grinding wheel and a workpiece in a range of current density in which no passivation coating film is formed; that is a range of not less than a critical current density .rho. shown in FIG. 3, so as to perform processing with the grinding wheel while dissolving a large amount of the surface of the workpiece for a short period of time. However, the surface roughness of the workpiece is poor with only such processing, so that when it is intended to process the workpiece with good surface roughness, it is designed to apply machining processing onto the surface of the workpiece in the final step.
In addition, during electrolytic combined polishing, a series of cycles, in which a passivation coating film is formed on the surface of a workpiece by an electrolytic action while the passivation coating film is removed using a viscoelastic grinding wheel, are repeatedly executed, so as to process the surface of the workpiece. In this electrolytic combined polishing, it is preferable that each of the abrasive grains of the grinding wheel uniformly contacts with the surface of the workpiece with relatively small pressurizing force, so that a grinding wheel, which is capable of obtaining such a preferable contact state, and a grinding wheel in which abrasive grains are held by a viscoelastic material, is used.
Incidentally, the electrolytic processing is one in which only simple electrolysis is used to dissolve the surface of a workpiece to perform removing and processing.
However, such conventional processing methods have had problems as follows.
Namely, during conventional electrolytic grinding, it is necessary to apply the machining processing onto the surface of the workpiece in the final step as described above when the workpiece is processed with good surface roughness, and hence, when the workpiece is a brittle material, the machining processing thereof makes a cause for not only allowing much processing distortion to remain in the workpiece but also generating cracks on the surface of the workpiece in some cases. In such a manner, it is impossible to process the workpiece in a state of less processing distortion and with good surface roughness.
In addition, during conventional electrolytic combined polishing, the grinding wheel in which the abrasive grains are held by the viscoelastic material is used, however, in the case of such a grinding wheel, when undulations generated in pro-processing exist on the surface of the workpiece, the viscoelastic material which holds the abrasive grains performs elastic deformation along the undulations, so that it is impossible to grind and remove top portions of the undulations. Thus, the undulations remain as they are, or they are amplified to become large. As described above, the electrolytic combined polishing has no ability to correct the surface shape of the workpiece, and it is impossible to process the workpiece with good flatness.
On the other hand, in the conventional electrolytic processing, the action of only the simple electrolysis is used to merely dissolve and remove the surface of the workpiece, so that there is no ability to correct the surface shape of the workpiece, in which as compared with the processing using the grinding wheel, it is impossible to process the workpiece with good flatness.
Namely, when the processing is performed by means of electrolytic grinding and the electrolytic combined polishing as described above, in the prior art, the workpiece is subjected to wrapping processing, thereafter the workpiece after completion of the wrapping processing is subjected to etching, then the shape of the workpiece deteriorated by the etching is corrected by the first polishing finishing, and next the processing distortion of the workpiece is removed while increasing the surface roughness of the workpiece by the second polishing finishing, so that it takes time and labor to transport and set the workpiece after completion of the wrapping processing to a machine exclusively used for etching and the like, and hence it is impossible to process the workpiece with good efficiency.