Method for electrolytically forming tapered or contoured cavities

Claim 1

IN THE METHOD OF FORMING CAVITIES HAVING SHAPED SIDE WALLS AND THE LIKE IN A WORKPIECE CAPABLE OF BEING ELECTROCHEMICALLY ERODED WHEREIN THE CAVITY MOUTH IS OF APPRECIABLY GREATER DIMENSIONS THAN THE BASE, COMPRISING FORMING A PRELIMINARY GENERALLY STRAIGHT SIDED CAVITY IN THE WORKPIECE HAVING TRANSVERSE SHAPE AND DIMENSIONS CORRESPONDING TO BUT NOT GREATER THAN THOSE OF THE BASE OF THE FINISHED CAVITY, ADVANCING A FINISHING ELECTRODE INTO THE CAVITY A RELATIVELY HIGH FEED RATE OF AT LEAST ABOUT .100 INCH PER MINUTE, THE ELECTRODE HAVING ELECTRICALLY CONDUCTIVE SHAPING SIDE WALLS AND ELECTROLYTE PASSAGES THERETHROUGH, IMPRESSING A DIRECT CURRENT HAVING A VOLTAGE NOT GREATER THAN ABOUT 18 VOLTS BETWEEN THE WORKPIECE AND THE ELECTRODE IN A SENSE TO MAKE THE WORKPIECE ANODIC, FEEDING ELECTROLYTE THROUGH THE ELECTRODE PASSAGES UNDER A PRESSURE OF AT LEAST ABOUT 100 P.S.I. AT THE ENTRY TO THE ELECTRODE AND WITH A HIGH ELECTROLYTE VELOCITY SO AS TO FILL THE WORKPIECE CAVITY BEYOND THE WORKING TIP OF THE ELECTRODE AND TO ESCAPE FROM THE CAVITY BETWEEN THE CAVITY WALLS AND THE ELECTRODE SIDE WALLS, AND MAINTAINING A GAP SPACING BETWEEN THE ELECTRODE SIDE WALLS AND THE CAVITY WALLS OF NOT GREATER THAN ABOUT .015 INCH, WHEREBY THE CAVITY WALLS ARE ELECTROLYTICALLY ERODED TO A SHAPE COMPLEMENTAL TO THAT OF THE ELECTRODE AND GIVEN A SMOOTH FINISH.